Monday, August 31, 2015

Cholesterol-lowering RNAi Therapeutic Shocks Monoclonal Antibody Establishment

Not too long ago, RNAi Therapeutic got dumped by Big Pharma in a big way not least because of the monoclonal/recombinant protein pedigree and corresponding bias among the top dogs of these organizations.  This was most obvious with Roche and Merck when changes in their overall R&D organizations led to the loss of their last internal RNAi champions.

How times have changed. Yesterday, The Medicines Company (who have now become a natural acquisition target) and Alnylam presented data (press release here, data here) strongly suggesting that an RNAi Therapeutic will push aside the temporally more advanced monoclonal antibody competition to become the best-in-class agent in the potentially top pharmaceutical category over probably the next two decades: the inhibition of PCSK9 for the prevention of cardiovascular morbidity and mortality.

The data in support of this claim were presented yesterday at the 2015 ESC congress in London that in retrospect was apparently named in honor of the delivery technology underlying ALN-PCSsc, a so-called Enhanced Stabilization Chemistry-based RNAi conjugate.

Treatment adherence

Importantly, the single-dose part of the study showed that starting with a dose of 300mg of ALN-PCS, PCSK9 levels were flat-lined to ~25% of normal levels for at least 4-5 months and haven’t started to perk up yet by the data cut-off date for this presentation.  It is to be expected that the knockdown will be even more pronounced with repeat dosing as supported by the initial repeat-administration data (2/3 doses) showing mean PCSK9 reductions to ~15% of normal.

Since in the PCSK9 category, it is PCSK9 that is driving LDLc lowering, the ultimate aim of this therapeutic approach, similar kinetics were seen in terms of LDLc levels in the blood with reductions (and safety/tolerability profiles) comparable to that seen with the recently approved monoclonal antibodies PRALUENT (by Regeneron/Sanofi) and REPATHA (by Amgen), ~55-60%.

In the case of the monoclonal antibodies, dose administrations every two weeks is really what it takes to consistently suppress PCSK9/LDLc because their inhibitory ability is directly correlated to their amount in the blood which declines rather precipitously after drug administration.  In the case of RNAi, however, you only need minute amounts to clamp down gene expression and at least for the liver, it appears that quarterly/semi-annual dosing schedules are realistic (it also depends on target and how much it needs to be repressed; e.g. with CC5 you may need much more target gene knockdown than 58-90%).

Sticking a needle into you just 2 or 4 times a year instead of 26 times, of course, has great advantages when it comes to treatment adherence. Keeping patients on drugs is a major issue for such life-long therapies especially since the disease is not felt acutely.  This point was made repeatedly by cardiovascular disease thought leader Dr. Kastelein on the companies’conference call.  By being able to co-ordinate drug administration with routine doctor visits, it would be possible to achieve very high compliance rates thereby preventing intermittent LDL cholesterol spikes that are believed to be particularly harmful.

In other words, assuming cardiovascular outcomes to be almost entirely driven by LDLc lowering, ALN-PCSsc would/should be best-in-class in the PCSK9 category.  There are numerous examples such as Eylea in the wet AMD space where injection frequency is the main competitive driving force among competing agents (here VEGF inhibitors) that exemplify how being a best-in-class follower can be very profitable.  Let the monoclonals build the PCSK9 market for ALN-PCSsc to then take it.


Last but not least, the ultimate value from being different will come from the results of the cardiovascular outcomes (and actually overall survival) studies that will really unleash the wide adoption of the PCSK9 class.  Due to their similarities, there is every reason to believe that the results from the monoclonal antibodies will cluster tightly.  By contrast, for better or worse, the outcome studies from ALN-PCSsc should be notably different and given that an RNAi agent mimics the compelling human genetics behind the PCSK9 story (extreme LDLc lowering in PCSK9-mutant individuals without other apparent untowards effects such as elevated liver triglycerides etc) much more closely, I like my chances here.  

We all know about the intricate feedback mechanisms of lipid biology so that binding a player merely in the serum as the monoclonals do as opposed to removing it from both inside and outside the cell could have unanticipated consequences.  Albeit early, the preliminary data from ALN-PCSsc support that in that the percent LDLc knockdown is the same whether in the presence or absence of high-dose statins whereas that of the monoclonal antibodies becomes muted.

Having said that, expect the monoclonal antibody establishment to play the 'RNAi is different from monoclonal antibody card' lest ALN-PCS piggy-backs on the MAb CVOT results expected to come out starting in 2017.

Back to my self-imposed exile, but I couldn't resist on commenting on what could be a perfect Oligonucleotide Therapeutics storm that is building. Next up is (maybe) ARC-520 for HBV.  And yes, I'm long MDCO as if that's not obvious.

Tuesday, June 23, 2015

The RNAi Therapeutics Blog is Taking a Break

When it feels that everything has been said, it may be time to be silent for a while.

This point has come for me and the RNAi Therapeutics blog and I look forward to take part in the conversation with renewed energy and ideas.  Until then, you can follow the 'light' version of this blog on Twitter @RNAiAnalyst. 

Thursday, June 11, 2015

There is No Doubt: Splice Modulator Drug for Spinal Muscular Atrophy Works

The fairy-tale story of the splice modulation for spinal muscular atrophy (SMA) continues.  This morning, Isis Pharmaceuticals provided an update on the phase II study of ISIS-SMNRx in type I SMA infants.  The data built on already highly promising data as of last September, showing that a doubling (~9 to ~18 months) of the median ‘event-free survival’ compared to the Natural History has now been reached with numbers still increasing as more than half the infants remain event-free.

Only one out of 12 infants still on study suffered an event (permanent ventilation) over the last 9 months.  This one in 108 month event rate compares to 6 events in ~200 months in the prior phase of the study, suggesting that if babies can be diagnosed and treated early enough so that they are covered during a critical period of development (e.g. maturation of the neuromuscular synapse) chances are that they will enjoy a very significant treatment benefit from ISIS-SMNRx.

This is thus consistent with the biomarker data showing that ISIS-SMNRx increases the missing functional full-length SMN protein by 2-3 times essentially turning a type I SMA infant (usually 2 copies of SMN2) with an 80% chance of dying or going on permanent ventilation by 18 months into a much milder form of the disease where patients have 4 or more copies of SMN2 and have an almost normal life expectancy (note: those with 3 copies, usually type II SMA, live into teens/early adulthood). 

While as a parent, I would almost do anything for my child to get access to the drug and I do understand there to be calls for immediate (à once diagnosed, the window of treatment opportunity may be quite narrow) regulatory action, the first consequence of today’s data should be getting SMA on mandatory genetic panels for newborn screening.  Only then will there be maximal benefit once the ongoing blinded phase III study reads out in late 2016/early 2017.

Wednesday, June 10, 2015

Alnylam Slams Dicerna with Trade Secret Complaint

How times have changed.  Four years ago, Alnylam found itself on the receiving end of a trade secret lawsuit regarding the delivery technology du jour, SNALP LNP then, in which it ended up paying near-bankrupt Tekmira ~$70M to settle the allegations.  As I opined back then, Alnylam seemingly used almost any means to get access to the know-how to make SNALP LNP delivery work in primates in an effort to rid itself of the reliance on Tekmira, the inventors.

At that time, all Alnylam's CEO had to say on the topic of honoring trade secrets: 'you pay for it, you own it'.

Tonight, Alnylam claims to be the victim of similar trade secret misappropriations surrounding RNAi delivery technology.  In this case, Alnylam alleges (see Complaint) that Dicerna had hired ex-Merck RNAi scientists to gain access to critical GalNAc trade secrets invented at Merck after Merck sold their RNAi assets to Alnylam and laid off related employees.

An interesting aside of this is that it appears, contrary to representations by Alnylam, that the GalNAc-ESC technology were invented at Merck, not in-house at Alnylam.

The Complaint makes it clear that Alnylam feels threatened by the technologically very direct competition.  In a way, Dicerna’s new strategy was to become Alnylam's clone.  What could be worse, given the differences in the RNAi trigger lengths (~19bp Tuschl-type siRNAs by Alnylam; 25/27 and longer Dicer-substrate versions by Dicerna) and the apparent importance of stability/degradation in GalNAc technology, there is the distinct possibility that Dicerna’s version, everything else being equal, would outperform (or underperform) Alnylam’s.

In light of recent apparently rapid progress at Dicerna on GalNAc technology and the timing of events, the idea that Dicerna may have benefited from the GalNAc know-how of ex-Merck scientists does not seem far-fetched.  

It is unclear to me, however, whether you can expect expert oligonucleotide chemists to suddenly forget everything about their former job. 

Alnylam obviously takes care of that problem by enforcing harsh non-compete and pay-for-silence practices against their former employees, meaning that if you are an RNAi scientist that job at Alnylam will be your last RNAi job in the industry, period. 

Looking forward, I predict that the outcome of the case will hinge less on the physical documents that were alleged to have been ‘misappropriated’, but on whether or not the ex-Merck scientists could have re-invented GalNAc-ESC based on their skills and publicly available information (including from Alnylam) at the time.  If so, then Alnylam only has Merck to blame that it does not force their employees to leave their profession when they lay them off.

Regardless, the GalNAc-ESC genie is out of the bottle.

Thursday, June 4, 2015

What to Watch for in RG-101 Post Regulus Therapeutics Executive Departures

As you will probably know already, Regulus Therapeutics surprised us this week with the sudden departures of both their CEO and CSO.  These two individuals also happened to be the insiders selling major positions in the stock earlier this year just days ahead of critical data to be released on their lead clinical candidate, RG-101 for the treatment of HCV ('Reading the tea leaves on Regulus insider sales').

While this would be a good reason for what looks like a sacking of the company’s two key executives (especially since the exodus came as a pair), for investors the all-important question is whether it is also related to bad news that we do not know about yet.  Most importantly, does this also have anything to do with the failure to report the viral resistance analysis which had been promised to us for the EASL meeting in April?

It is this analysis that will determine whether the miR-122 inhibitor can facilitate 4-week treatment regimens which must be the goal for this asset.  This is because RG-101 is the only serious long-acting agent out there in the HCV drug development arena and 4 weeks of oral, short-acting antivirals do not seem capable of getting rid of the virus. 

If there was no resistance to RG-101, based on the available data RG-101 given on week 4 would add ~6 weeks to deep viral suppression to the treatment regimen, in a way resembling a 10-week oral regimen which have much higher odds of viral clearance.  If viral resistance (and not waning drug levels as I am assuming) played a role in the rebounds seen in the single-dose study, then this would not necessarily be the case.  I say ‘not necessarily’ because even then, the risk of developing viral resistance to RG-101 should be much lower when given in combination with other agents as is the plan.

Take-home: I remain cautious (but not short any more) prepared to take advantage of another bout of panic selling that could come with the release of the resistance analysis.  The quality of the new leadership to lead the exciting microRNA platform will also indicate whether Regulus can finally live up to its original promise.  Long-term, whether precipitated by the insider sales or not, the changes should be good as morale at the company from what I can tell had been low.

PS: in more positive news, Regulus Therapeutics today reported that a first-in-man study with their second most advanced microRNA Therapeutic, RG-012 for the kidney-related orphan disease Alport Syndrome, has begun dosing.

Wednesday, May 27, 2015

RXi Pharmaceuticals Could Be Much More Than Skin Wound Healing

RXi Pharmaceuticals today commenced a secondary offering setting it on course to raise ~$10M, enough to finance the company for another year while expanding its pipeline and technology.  It could thus mark a new chapter in the life of this company which had shoe-boxed itself into a single-product (RXI-109 for dermal wound healing) company following a toxic 2012 financing that gave Tang Capital Partners de facto control over the company (pro tip: when you see the likes of Tang or Deerfield getting involved, it usually is not to the benefit of common stock holders). 

The news this morning that the preferred stock overhang (àTang Capital Partners) had finally been cleared, then paved the way towards the financing (amount and pricing to be determined).  

With RXI-109 winding its way through phase II studies, it became clear that RXi had to open itself up to new opportunities enabled by its promising self-delivering RNAi platform.  The financing will initially allow RXi to develop RXI-109 also for ocular (retinal and corneal) scarring-related indications such as wet AMD and cataract surgery.  First eye-related clinical trials with self-delivering RNAi triggers are expected to commence later this year.

The eye is an interesting application of sd-RNAi technology not only for the lucrative eye disease market (both genetic and age-related of considerable unmet medical need), but also because they seem to be able to penetrate throughout the eye (see image) whereas in the skin, distribution currently is limited to areas close to the injection site barring new delivery breakthroughs (patches, creams and the like).  In addition to cholesterol, it may also be interesting to test other ligands such as Vitamin A and E for enhanced uptake into certain ocular cell types.

Lots of unexplored potential

Beyond the skin and eye, self-delivering RNAi strategies hold considerable promise for other tissue targets, both by direct/local and systemic delivery.  In terms of local delivery, I would be highly interested in the biodistribution of intrathecally administered sd-RNAi triggers in non-human primates.  This is because of their long phosphorothioated single-strand overhang and thus similarity to phosphorothioate antisense oligonucleotides which are starting to show amazing results in the clinic for CNS applications (watch out for update on the infant ISIS-SMNRx study by Isis Pharmaceuticals).

In terms of systemic delivery, sd-RNAi chemistry and structure may synergize well with conjugate-RNAi approaches, both in their simple (--> Alnylam GalNAc-type) and more refined form (--> Arrowhead DPC-type).  Even without further modification, RXi-type self-delivering RNAi has shown surprising knockdown efficacy in models of pre-eclampsia as shown by respected UMass scientists Melissa Moore and Anastasia Khvorova (formerly of RXi Pharmaceuticals).  

If RXi can get the backing from serious biotech investors and eventually a new management fit to lead a modern biotechnology company, the current $16M market valuation (for RXI-109 in the clinic for dermal scarring and soon in the eye; self-delivering platform potential; stake in MirImmune) of the company could make it an irresistible investment opportunity.  If management, however, continues to dig in their heels and refuses to listen to outside advice chances are that the financial death spiral will continue. 
Suspicious shorting into financing

It used to be common biotech practice that investors-in-the-know were allowed to short into financing resting assured that the offering will allow them to cover at a lower share price.  It is therefore remarkable that in the days and weeks before the financing, the short interest has sky-rocketed from virtually none to around 10% of the float and possibly much more by now due to the delays in reporting short interest.

Saturday, May 16, 2015

Aptamer-Targeted RNAi Trigger Delivery

In honor of 25 years of aptamers, or better the SELEX process which underlies the discovery of aptamers, I thought it might be a good time to revisit aptamers for the delivery of RNAi Therapeutics.

Aptamers are nucleic acids that have been selected to preferentially recognize a target, usually a protein, via their 3-dimensional structure in analogy to how monoclonal antibodies recognize their targets.  Aptamers are showing most promise in therapeutic development for the targeting of extracellular proteins in the eye for applications like wet AMD and diabetic macular edema (see Fovista from Ophthotech). 

Its success for systemic applications has been much more modest, however, with short circulation times and unexpected adverse events in a recent phase III study (likely due to the PEG portion of the aptamer drug) largely accounting for it.

Aptamers have also been considered as cell-targeting agents for RNAi Therapeutics.  Early reports suggested efficacy in HIV and cancer models.  Skepticism around the on-target mechanism in these examples was considerable though largely due to questions around how they were supposed to escape the endosomes.

I also fell into the camp of doubters (and still have some reservations), but have adjusted my view to a more productive one after it became clear that IF you had highly productive endosomal uptake like ASGPR/GalNAc and a highly stabilized RNAi trigger, gene silencing is possible even without explicit endosomal release chemistry.

Time to try the next iteration: Aptamer-DPCs

As there may not be another ASGPR-type receptor in the body and to compensate for lower drug exposure compared to the liver, in the quest to make aptamer-delivered RNAi Therapeutics more robust, the new learnings of RNAi trigger stability are probably best applied within the context of DPC delivery technology by Arrowhead Research.

Accordingly, the perhaps 10x lower uptake in say PSMA-expressing prostate cancer cells will be compensated by adding the RNAi trigger-aptamer complex (as one or separately) to a masked endosomal release polymer.  In case that the target cell receptor is only abundant, but does not support productive endosomal uptake, another aptamer may target a second co-receptor on the same cell (akin to some bispecific antibodies, co-receptors in viral cell uptake).

Following endosomal uptake, the masking groups come off, endosomal permeability increased so that the RNAi trigger may escape into the cytoplasm.  In certain configurations, a Dicer substract-type RNAi trigger structure may simplify design and increase stability.

Tuesday, May 12, 2015

Dicerna Keeps Searching for Its Identity

Dicerna Pharmaceuticals recent move from Watertown to Cambridge is symbolic for its continued search for a place in the RNAi Therapeutics landscape.  Following some setbacks in its cancer and home-brew LNP efforts, the company now pins its hope on that it can compete head-on with Alnylam in the development of GalNAc-RNAi trigger conjugates for gene knockdown in the liver.

Oncology on hold

Like others in the field, confidence in its cancer program (DCR-MYC in phase I/II studies for solid cancers and HCC) seems to be low.  In the absence of clear-cut early development-stage cancer responses and confirmation of bona fide tumor-wide gene knockdown, cancer drug development remains a hit-and-usually-miss for the Oligonucleotide Therapeutics industry.

As a result, Dicerna seems to view their own mouse data with skepticism just as I myself have yet to see data supporting tumor penetration and bona fide knockdown in well-controlled studies.  The company has to be credited that it is now setting the bar for DCR-MYC quite high when clinical data from higher-dose cohorts is expected to emerge around year-end.  If DCR-MYC does not make the cut, Dicerna will likely cut its losses in cancer drug development and LNP research in general.

DCR-PH1 close call

Dicerna management was also surprisingly frank about their hesitations about the technical success of their most interesting current program, namely DCR-PH1 for the treatment of hyperoxaluria type I. 
After reviewing the latest non-human primate studies, it now appears that at least an 85% mRNA knockdown of the HAO-1 target gene will be required to see the key oxalate biomarkers ‘move’, and over 90% for more robust movement.  Based on rodent data, the company had thought that 75% might be sufficient.

In NHP studies of DCR-PH1, an 84% average peak knockdown was seen following a single dose of 0.3mg/kg of a Tekmira SNALP LNP formulation with 68% knockdown remaining at week 4.  0.3mg/kg seems to be the current well-tolerated upper dose of Tekmira’s LNP formulations and almost identical (protein) knockdowns were observed with 0.3mg/kg of Tekmira LNP-formulated ALN-TTR02. 

In clinical 3-weekly multi-dose studies of ALN-TTR02, this translated into sustained 80-85% target gene knockdowns.  This means that Dicerna now relies on the safety of DCR-PH1 to allow for doses of around 0.5mg/kg.  Not impossible, but probably a close call given the history of SNALP LNP and further exposes DCR-PH1 to competitive threats.

GalNAcs coming

Given the stage of their internal cancer and LNP efforts, Dicerna is now pinning its hopes on taking on Alnylam with GalNAc-RNAi trigger.  This is where Dicerna is currently investing most of its R&D efforts in.

It has now disclosed non-human primate data from those efforts, with 5 consecutive daily doses of 2.5mg/kg GalNAc-Dicer substrates resulting in ~70% knockdown of HAO-1 2-3 weeks after this loading dose.  Given the larger molecular size of the extended Dicer-substrates versus Tuschl-type siRNAs, this corresponds on a molar basis to ~1.5mg/kg of Alnylam’s GalNAc-siRNAs.  

This is somewhat less than what Alnylam presented for their PH1 program at OTS 2014 (ED80s in rodents of ~2.5mg/kg weekly) and Dicerna's GalNAcs would seem to require some further refinements to be competitive.

But in this case, they will end up with something that has little pharmacological distinction, is 3-4 years behind Alnylam, which in turn is not shy to put legal/IP pressure on its competition.

In my opinion, Dicerna management and Board need to put in quality time to find their true identity.

Disclosure: I am short DRNA as a relative valuation short for my ARWR long position. DRNA has a slightly larger market cap than ARWR, but ARWR has a distinguished, more mature DPC pipeline with ARC-520 and ARC-AAT two attractive candidates in the clinic whereas DRNA has nothing in the clinic it apparently has confidence in.  It's possible that both stocks are grossly undervalued, but relative valuation is one of my main RNAi investment methods and this is why I'm applying it here. Nothing personal.

Sunday, May 3, 2015

Arrowhead Publishes SubQ Delivery Technology to Go Beyond the Liver

In late 2012, Arrowhead Research shocked the Oligonucleotide Therapeutics world when it presented spectacularly potent and prolonged gene knockdown data in non-human primates using a subcutaneously administered single-molecule Dynamic Polymer Conjugate (DPC) formulation.  This arguably represented the most elegant delivery technology at the time.  Moreover, also due to its small, but not too small size (10-20nm) and slight negative charge, it provided us with a glimpse into the future of systemic RNAi delivery for regulating genes beyond the liver.

It certainly got my full attention and made me invest almost 100% of my stock portfolio back then.

Unfortunately, despite the validation in non-human primates which suggested clinical readiness would not be far off, the subQ DPC technology has seemingly struggled to reach clinical/commercial maturity. Not only Arrowhead’s lead development candidate, ARC520 for HBV, but also its second development candidate, ARC-AAT for AAT-related liver disease, was still based on the intravenously administered two molecule DPC version.  Although the reasons for the delays were never really disclosed, a few comments here and there made it seem very likely that chemistry and manufacturing issues were behind the delay.

Back to the Future

Last week, Arrowhead Research finally published a paper showing that single molecule DPC is still alive and kicking (Rozema et al.2015) and is progressing towards clinical application.  In essence, the new single-molecule subQ DPC prototype comprises of a membrane-active polymer which has been masked from premature cytotoxic interactions by pegylation and cell-targeting ligands that are added via protease-sensitive bonds; as before, the highly modified/stabilized RNAi triggers are appended by disulfide chemistry. 

The DPC is made in a 4-step process followed by a purification step to remove unwanted side-products and reactants.  The latter step is apparently important when going into primates.

The new old DPCs are thus distinguished from the intravenous version not only in that it combines the RNAi trigger and endolysosomal release polymer in a single molecule, but most importantly by the nature of its triggered release mechanism.  Whereas in the former DPC generations triggered release was dependent on changes in pH such as they occur when a DPC is endosomally taken up, they are now responsive to the presence of certain proteases in lysosomes

pH-dependent formulations apparently suffered from instabilities both in the body and during storage.  This was adequate for targeting genes in the liver because of the ready access of macromolecules in the circulation to this organ following intravenous administration, but not when the DPC first has to reach the circulation from the subcutaneous space and when less well accessible target organs are the ultimate destination.

Accordingly, non-liver single-molecule DPCs of the latest publication had impressive circulation half-times of the intact, protected molecule of 11 hours.  Similarly, such DPCs are stable for at least a year both in solution and when lyophilized. 

The extra-hepatic potential thus facilitated by increased stability now needs to be demonstrated by finding suitable targeting ligands and I’m sure Arrowhead has been busy working on that.  It should be noted that for target tissues where high concentrations comparable to the liver are unlikely to be achieved following systemic delivery, the extra kick that comes from an explicit release chemistry could provide a critical advantage over competing approaches.  These include simple conjugates of the GalNAc-type and probably also self-delivering RNAi trigger chemistries which incorporate ‘milder’ release chemistries (like lipid tails).

Knockdown lasting for weeks and months

The most impressive demonstration of the single molecule DPC performance in the Rozema paper came from the primate studies.  Here, a single administration of 0.5mg/kg 2’-O-methyl/F-modified RNAi trigger led to a highly potent knockdown (peak knockdown >95%) of liver expressed Factor VII with >80% knockdown of 2 and 4 months following subcutaneous and intravenous administration, respectively.

Following the 2012 delays and some uncertainties around what was really new and old in the recent publication, I am somewhat hesitant to declare that subQ DPC is now fully de-risked and ready-to-go.  In that regard, it would be helpful to learn more about the tox profile of the new molecules and related to that which polymers will be eventually used (e.g. 2-molecule with melittin-like peptide, a polyacrylate in the publication).

Nevertheless, since Arrowhead has said that the new 2015 development candidate may be from the subQ line of DPCs (or if not going after a extra-hepatic target) one would think that the most important challenges have now been overcome.

Wednesday, April 29, 2015

HBsAg Rules at International Liver Congress

Now that the HBV world has gathered extensive clinical experience with interferons and polymerase inhibitors (NUCs) and with the resolve to finally find a cure for a serious disease afflicting hundreds of millions worldwide, the hepatitis B surface antigen (HBsAg) has become recognized as the key determinant for treatment outcome.  This is being confirmed by trial after trial investigating combining the actions of both NUCs and interferons, either one after the other or together at once.

Some of these studies were presented at the International Liver Congress last week in Vienna (ILC2015).  Emerging from them are actionable HBsAg rules which can predict fairly well whether a patient will eventually seroconvert to (or at least lose) HBsAg.  No matter the excitement around CRISPR technologies, HBsAg seroconversion remains the gold standard outcome in HBV treatment in the foreseeable future.

These rules can be divided into pre- and post-IFN treatment onset.

In the pre-IFN setting, it is those patients that have below ~500 IU/ml serum HBsAg as a result of NUC treatment that will most likely respond to interferon treatment/immune stimulation with s-antigen seroconversion (see earlier blog entry).  Since NUCs alone hardly do anything to promote s-antigen seroconversion despite its dramatic lowering of viral HBV titers, it appears to be their slow impact on HBsAg levels ( 0.1 log per year HBsAg reduction) that has the synergistic effect with interferon: with HBsAg lowering you take off the foot on the immune brake, with interferon you step on the immmune gas pedal.

As such, HBsAg knockdown by RNA(i) Therapeutics would seem to do the same for interferons as NUCs do, only in a more rapid and potent manner.  Of course, both could be used concurrently as a run-in to IFN treatment.

However, once on IFNs (post-IFN onset), it is the relative HBsAg decline that has high positive predictive value in prognosticating who will seroconvert.  Of note, the HBsAg decline comes before any adaptive immunity can be detected.  This supports that HBsAg decline in itself contributes to seroconversion rather than it being a mere correlation.  In that setting, it is a 1 log decline in HBsAg the first few weeks after IFN treatment onset that separates the winners from the losers. 

It is uncertain to me, however, whether 1 log is a precondition to s-antigen seroconversion as the non-responders do not even come close to that (maybe 0.3log).  It is therefore possible that anything that pushes HBsAg below say -0.3-0.5log could have a dramatic effect on s-antigen seroconversion rates.

An RNAi Therapeutic for HBV used simultaneously with IFNs may therefore aim at helping IFNs to get to the  0.5-1log reduction threshold, and rapidly at that.

Ergo, there are now a number of obvious strategies that one can apply regarding the use of RNAi Therapeutics in HBV with various knockdown goals, both absolute and relative.  The exact strategy would depend on how the RNA agent is combined with polymerase inhibition/NUCs or immune stimulation. 

While a number of other HBV targets were reported at the conference such as core assembly and entry inhibitors, HBsAg (and HBV mRNA knockdown in general) lowering remains the most distinguished and the mechanism predicted to be most synergistic to existing treatment approaches.  As combination treatment is strongly predicted to be the future of HBV, HBsAg lowering should become a pillar of those treatment regimes.

Disclosure: long ARWR, looking for lower entry in TKMR.

Monday, April 27, 2015

Regulus Therapeutics RG-101 Continues to Have Potential in HCV Treatment Landscape

Having attended the International Liver Congress last week in Vienna, Austria, it has become clear to me that HCV is not going away soon.  Even in the US where progress towards its ‘eradication’ may be considered most advanced with about 1/5 of the known patient population treated last year alone (~250k), it will be an uphill battle to identify, treat, and pay for the millions more infected. Worse still, it is not enough to simply cure the existing pool of HCV patients, but also stop the cycle of re-infection (largely the result of injection drug use).

Treatment cost is one challenge and the current drug rationing approach leads to the counterproductive warehousing phenomenon where current medical intervention is focused on the patients with more advanced liver disease.  This is not only the hardest-to-treat population, but also allows the liver health of the previously less sick patients to deteriorate.  This obviously makes little sense also from a pharmaco-economical perspective when getting rid of HCV early on has now been shown over and over again to dramatically reduce HCV-related cirrhosis and liver cancer.

Another problem is the fractured treatment landscape that exists for the various patient populations (split up according to fibrosis/cirrhosis stage, genotype, co-morbidities, the rapidly growing concerns around drug-drug interactions, available/accessible meds etc) making it difficult for even the learned gastroenterologist to keep up with the latest developments and putting HCV treatment practically out-of-reach for the general practicioner.  

12-24 weeks remains the standard drug treatment duration with docs worrying about shorter treatment regimens being sub-optimal.  A triple regimen by Gilead after 4 weeks of treatment merely achieved a 27% SVR12 which in the DAA world is practically synonymous with a cure.  The best shot at shortening treatment duration may therefore come from Achillion with 6 week of DAAs achieving high cure rates in 'easy' patient populations.

While interferon is on the way out, it could make an at least transient comeback for the hard-to-treat genotype 3 where, in addition to cirrhosis, cure rates with the all-oral DAAs low (60-80%).

To sum it up, the liver community has expressed multiple times at ILC2015 that a short-acting pangenotypic regimen is an important goal in the development of new medications for HCV.   And if they paid attention at the oral late-breaker on Saturday, RG-101 is poised to play a critical role in filling this unmet treatment goal due to its long duration of antiviral activity following administration, regardless of genotype.

RG-101 update: more relapses, but thesis intact

The clinical investigators of Regulus Therapeutics presented a 20 week update on the phase I study in genotype 1, 3, and 4 patients with good to moderate liver health.  28 patients received study drug RG-101, 4 placebo.

At the primary endpoint on week 8 (reported in earlyFebruary), slightly more than half (15/28) of patients treated with RG-101 were below the level of quantitation (BLOQ).  According to the company, most of them were not only BLOQ, but undetectable (by sensitive PCR) at that.  This is a remarkable feat given that the GalNAc-conjugated phosphorothioate antisense molecule had been only given once.

According to the latest update, half of those patients eventually relapsed (7-8 depending on whether you count the patient that was lost to follow-up), most of them shortly after week 8.  Although the relapsers are slightly disappointing as in the short-acting DAA world undetectable virus for 8 (or better 12, SVR12) weeks following cessation of treatment is more or less equivalent to a full-blown cure.

Of course, the prognostic rules for a long-acting agent like RG-101 with a slower onset of antiviral knockdown ought to be different.  The notion that the viral rebounds were simply due to waning drug levels in the liver (and not due to viral escape mutations!), was supported by the biomarker analysis in the healthy volunteer part of the phase I study, also presented at ILC2015, where the trough in viral knockdown (~day 28) more or less coincided with maximal total cholesterol lowering as a predicted by miR-122 biology.

Of note, there was no apparent benefit of increasing the dose from 2 to 4mg/kg which was consistent with preclinical evidence that showed a declining liver/kidney drug ratio at 4mg/kg and maximal cholesterol lowering at 2mg/kg in humans.  This indicates that ASGPR receptor binding becomes saturated when too much GalNAc antisense is given at once.  The increased drug liver concentration at higher concentrations observed in earlier preclinical studies probably indicate uptake in non-productive compartments of the liver, including Kupffer and sinusoidal endothelial cells.
The hope is that with a second dose of RG-101 28 days after the first shot, maximal viral suppression can be maintained for at least another 4 weeks to stave off any viral comeback as seen in the single-dose study.  This is supported by both the healthy volunteer part of the study and the chimeric PXB mouse experiments presented which showed that such a second dose not only maintained drug potency, but in fact led to a step-up in efficacy.  I am therefore optimistic that with 2 doses of RG-101 monotherapy alone ~50% cure rates can be achieved in patient populations similar to that in the phase I study.

This, however, is not even the goal.  The ultimate goal would be to establish a simple pan-genotypic 4-week treatment regimen.  Accordingly, the combination of RG-101 with a DAA(s) (sandwich regimen) can be expected to result in a very, very deep viral knockdown by week 4.  At this point, a second shot of RG-101 would be administered to give the immune system another 6 weeks or so to finish off the virus.  I believe a very realistic scenario, and depending on which patient populations you are looking at a very compelling alternative to current HCV medications and those in development. 

PS: Open questions

Unfortunately, given that cholesterol lowering was still close to maximal at week 8, it would have been comforting to show a mutation analysis from the clinical study to confirm that viral relapse was not explained by the virus successfully developing resistance against RG-101.  This is such an obvious question that one wonders why Regulus did not present the data (yet). 

Another question mark around the current data set is why Regulus is not disclosing the differential effect of RG-101 on good and bad cholesterol and instead is reporting total cholesterol lowering.  The study investigator said that they are still analyzing the data from the multi-dose healthy volunteer study  (months after completing dosing???) and are planning to publish those.  I am mildly optimistic that this could unexpectedly bring to the fore the cardiovascular potential of miR-122 targeting, although in this case (à mostly chronic treatments) the liver cancer concern around miR-122 inhibition may be more valid than it is for the 2-shot HCV treatment goal. 

Thursday, April 23, 2015

Absolute HBsAg Levels, Not Percent Decline May Be Goal of HBV RNAi

I just walked into an early morning session at the International Liver Congress in Vienna and may have learned the most important nugget of information regarding RNAi treatment for HBV.

During the discussion in the ‘Banishing B’ session, Dr. Joerg Petersen referred to clinical analyses to be presented this Saturday showing that patients who achieve HBsAg levels of less than 500, or even better 200 IU/ml and then are given an interferon have a much better chance of eventually losing HBsAg, i.e. being functionally cured, than those that do not.

Dr. Petersen has been involved in clinical studies combining nukes and an interferon, and data presented at last year’s American Liver meeting (AASLD) showed that 9% treated with the combination for 1 year lost HBsAg in the year following combination therapy compared to just 2.8% receiving interferon alone.

Note that currently only interferons are thought to give you a chance of functionally curing HBV by medication and that HBsAg seroconversion attributed to interferon treatment may occur in the years after cessation of interferon therapy.  It will therefore be important to see whether this increase in seroconversion with combination treatment continues to hold up in subsequent years. The nukes are ‘only’ thought to protect the liver from the ongoing damage from HBV replication and may have to be given indefinitely.

I am not sure whether the new insight comes from a fresh clinical study or are the result of a more detailed subgroup analysis of the previous study.  Regardless, it hammers home a message that can be heard again and again, even more so in Vienna this year than at the London meeting last year: it is all about HBsAg lowering.

Implications for HBV RNAi

The implications of the new analysis for RNAi approaches for the treatment of HBV is obvious: use RNAi to get HBsAg below the threshold. In other words, it may be less about getting a magical 1log knockdown, but more about getting patients below 500IU/ml. 

For this, Dr. Petersen recommended using 2 nukes so that the tiny and very slow HBsAg declines observed on nukes continue ( < 0.1 log per year). With RNAi agents, you would likely achieve this goal for a patient with an HBsAg at baseline of 1000IU/ml within a month, even with a single 2mg/kg dose of ARC520 from Arrowhead Research as reported last year. 

The absolute knockdown potency of an RNAi agent would determine which fraction of the HBV population fall within this sweet spot. With a 1log knockdown e.g. you could start RNAi with patients with as much as 5000IU/ml.

For the clinical development of RNAi agents for HBV, the first step will be to determine the HBsAg decline on a background of nukes (just what Arrowhead is doing right now).  For pivotal trials, an immunostimulatory agent such as an interferon should be added to the nukeà RNAi/nuke treatment regimen to finish off the virus.

Stay tuned to learn about the fold benefit of HBV cures in patients falling below the 500IU/ml threshold, and the 3-4mg/kg single-dose results for ARC520 from Arrowhead Research to be reported later this quarter (note to Arrowhead PR department: next Monday may be a good time to do so).

Wednesday, April 22, 2015

First RNAi Therapeutic Nearing Finish Line

ALN-TTR02 for the treatment of TTR amyloidosis is the most advanced RNAi Therapeutic in clinical development and has been carrying the torch for the field as whole. Expectations are therefore high and a stumble in this program as a result of the therapeutic hypothesis underlying the program not panning out would likely trigger a temporary*, but steep sector-wide sell-off.  

* it should be clear, however, that with the current ability to robustly knock down genes in the liver, RNAi Therapeutics will result in a number of successful treatments.

It therefore came as a relief yesterday when Alnylam presented (press release here, data slides here) 12-month data from an open-label extension phase II study of ALN-TTR02 in the polyneuropathy form of the disease (FAP) showing

a)      continued robust gene knockdowns for more than a year (88-80% reductions peak/trough in 3-week cycle);

b)      disease stabilization (if not improvement) when the Natural History of the disease would have predicted marked deterioration (predicted mNIS+7 at 12 months of +18 in Natural History vs ~-2.5 on ALN-TTR02).

Furthermore, the safety of this liposomal formulation enabled by Tekmira seemed more than sufficient for a disease as severe as FAP TTR amyloidosis (5-15 year survival following diagnosis) with the most significant adverse events being related to the intravenous route of administration meaning that ALN-TTR02 should be given under trained medical surveillance.

There are some questions that remain open, some of which should be answered by the ongoing phase III APOLLO study which should complete sometime in 2016 (with an 18 month primary endpoint).

Firstly, it will be important to show disease stabilization to be strictly related to ALN-TTR02.  In the phase II study, most patients (20 of 27) were on tetramer stabilizers which have previously shown to result in very modest (tafamidis) to moderate (diflusinal) therapeutic benefits.  While neither tafamidis nor diflusinal have shown disease stabilization after 12 months, the concern remains that they could have contributed to the apparent therapeutic benefit seen in the phase II study.

To my surprise, the 7 patients not taking tetramer stabilizers on top of ALN-TTR02 seemed to do even better, at least numerically than those taking them (-6.5+/-9.2 vs -1.1+/2.5).  Although the number was quite small, the fact that this is the opposite result from what one might have expected, it is possible that a slight placebo effect may have played a role in this open-label study: those for which ALN-TTR02 was the only medical intervention might have had a greater ALN-TTR02-driven placebo effect.

Other more complicated explanations based on TTR lowering affecting the PK/PD relationship of tetramer stabilizers are also possible if this phenomenon is for real.

Fortunately, the blinded phase III APOLLO study will compare ALN-TTR02 to patients taking no tetramer stabilizers to treat their FAP.  Finally, it would be of interest to look at the effect of ALN-TTR02 on the spleen in the APOLLO study as spleen toxicity due to lipid stability might be the most important safety parameter with chronic dosing.    

In summary, yesterday’s 12-month data removed important overhangs over the RNAi sector and we are on track for the first commercial RNAi drug in 2017. Seeing is believing.

Sunday, April 19, 2015

Checkpoints Drugs Promise to Unlock RNA Therapeutics Cancer Potential

If you are involved in cancer drug development, you are probably thinking of ways to exploit checkpoint inhibitors for your purposes.  Checkpoints are the mechanisms whereby cancer cells avoid being recognized by the immune system as foreign and the initial clinical results of inhibiting them, e.g. by targeting CTLA4 and PD-1/PD-L1, has caused immune-oncology as a whole to take the cancer drug development space by storm.

Suddenly, every scientist and their technician believe that by taking checkpoints out of the equation, their immune approach to cancer, which in many cases was marked by failure after failure in the past, will work. 

Take e.g. cancer vaccines and the idea of grinding up tumors and use the cell mash to train dendritic cells.  Sounds compelling to me, but I also know that I lost a bunch much money on the very same idea 10 or so years ago with nothing, but some early promising data from the clinical Wild East to support it. 

Others meanwhile believe that their technologies may enable immune-oncology by e.g. being able to modulate the tumor microenvironment so as to permit better access of the tumor killing cells.

RNA Therapeutics are no exception.  RNA Therapeutics, due to its endless targeting opportunities, has always been considered promising for oncology, but has struggled to show clear-cut success either due to drug delivery issues or due to the difficulties of predicting immune activities based on rodent studies.

Emblematic of this reversal of fortunes is the toll-like receptor (TLR) field of activating the innate immune system with oligonucleotide stimulants.  The idea here is to provide an environment that is more conducive to tumor cell killing and/or to directly impact tumor cell survival (e.g. interferon stimulation).  Art Krieg, of TLR9 (CpG) fame, but who has been erring as its lost son in the (blooming) deserts of RNAi, RNaseH antisense, splice modulation, and RNA activation, is apparently re-energized enough to go back to TLR Therapeutics and has started Checkmate Pharmaceuticals which will likely try and harness TLR agonists for cancer immunotherapy.

Nanoparticle delivery may also see a revival.  This is because they have a propensity, usually undesired, to be taken up by phagocytic cells, some of which may be effective in antigen presentation (e.g. dendritic cells).  I have thus noticed that a number of mRNA cancer vaccine approaches involve nanoparticle delivery with the aim of expressing tumor antigens in the training camps of the immune system, the lymph nodes.  

Nanoparticles may also be a way to knock down the gate-keepers in the tumor microenvironment which inhibit tumor infiltration by cytotoxic T (incl. CAR T-cells) and other helpful immune cells.  Since gate-keepers should be most useful when positioned at the entrance, this might actually take advantage of another limitation of many nanoparticle delivery technologies, namely getting stuck close to the vasculature instead of penetrating deep into the tumor.

Once deeper into the tumor, the struggle may not be over for cytotoxic T cells and tumor eating cells due to potentially immunosuppressive activities in the tumor microenvironment.  This is the new positioning for the phosphorothioate-based antisense molecule ISIS-STAT3 by Isis Pharmaceuticals and AstraZeneca for which, like for other phosphorothioate-based approaches, the demonstration of robust uptake and gene knockdown activity in tumor cells themselves is lacking, but functional uptake in cells of the tumor microenvironment has been reported.

Finally, RNA Therapeutics such as CRISPR genome editing or straightforward self-delivering RNAi (see recent license of MirImmune from RXi Pharmaceuticals) can be tools for the ex vivo preparation of T- and dendritic cells.  A self-delivering approach may be advantageous here as it may function in normal cell culture media and thus not confound cell signaling pathways in the maturation of these cells.

Investor, tread carefully

Overall, I’m convinced that there are synergistic potentials to be exploited and checkpoint inhibition may open the door to certain that have failed in the past.  Nevertheless, one should be mindful that most immune oncology drugs only work in a fraction (maybe 25%) of patients and the current hype around immune oncology guarantees that there will be many bad apples for investors to avoid.  Trust me, I've seen it when RNAi was indiscrimately hyped and abused for short-term financial gain in 2006-8.  Just because you can contrive a link to immune oncology or because a desperate Big Pharma does a deal, does not mean that all the biological problems will dissolve.  The bubble will burst after which mostly only well-financed quality plays will recover.

Disclosure: I am fishing for short opportunities in the immune oncology space as a hedge against a (hopefully temporary) correction to what seems to be an in a number of areas (e.g. gene therapies, immune oncology, one-drug orphan wonders such as Alexion etc) overheated biotech space.

Wednesday, April 8, 2015

AstraZeneca Selects MicroRNA Development Candidate, Blazes Innovative Trail

When it is screaming into your face that your business model has failed you and the young competition is running circles around you, only then you might be compelled to change. 

This certainly is true for Big Pharma which have lost sight that their business is to make a buck while increasing the health of their customers instead of wasting time and energy on challenges like turning a twice-a-pill into a once daily therapy.  In its quest to optimize their business processes, it has thus thrown out of the window revolutionary, innovative technologies that just would not fit into those loved models.

Case in point, Merck writing off their multi-billion dollar investment in RNAi Therapeutics and selling it to Alnylam for $175 in largely equity and some cash. Alnylam then turned around and made at least a 10x return on the RNAi trigger stabilization chemistry by Merck in little more than a year.

This is a rough estimation of how much the Merck RNAi assets have approximately contributed to increasing Alnylam’s market cap.

AstraZeneca leading the way for Big Pharma in RNA Therapeutics

Not long ago, AstraZeneca was widely vilified for being the worst of the worst in terms of R&D productivity.  Their labs just would not produce new compounds that mattered to patients.

After a corporate shake-up, things certainly have changed on the innovation front.  AstraZeneca has fully emerged as a real risk-taker when it paid Moderna $240M in upfront monies alone for access to a comparatively early-stage mRNA Therapeutics platform in 2013. 

Before that, however, it already got active in the RNA Therapeutics in a less visible manner, notably with a much smaller, but possibly more profitable deal with microRNA Therapeutics platform company Regulus Therapeutics.

In the 2012 deal, AstraZeneca made a $25M equity investment in addition to a token $3M cash hand-out in the then privately-held Regulus Therapeutics.  In exchange, AstraZeneca received 3 microRNA target picks in the cardiovascular, metabolic, and/or oncology areas.

The best part of the deal for AstraZeneca (and the reason why I took money off the table today at what I considered an outsized reaction) was that it only has to pay $2.5M per target/candidate pick and Regulus Therapeutics has to pay for part of the work involved in generating the candidate at that.  There would, of course, be the milestones and royalties, but they should also be modest, in-line with the $2.5M payment due now. 

Oh, those were the good old times of abusive (because they could) Big Pharma biotech business development deal right on par with the steal that The Medicines Company got from Alnylam with regard to the PCSK9 target.

But still, you have got to credit AstraZeneca that unlike its brethren they not only sealed the deal, but actually advanced one of the first clinical candidates involving a fundamentally new molecular target class.  It will be interesting whether they will do the same in mRNA Therapeutics.

Anti-miR103/107 antagonism for improving liver health in diabetes

Initially, the focus  of the partnership had been on what looked like a very promising HDL-augmentation strategy by inhibiting miR33 in the liver, but this candidate has apparently taken a backseat in favor of the insulin-sensitizing strategy by inhibiting miR103/107.

It had been known that in type II diabetes, there is an inverse correlation between insulin sensitivity and miR103/107 expression.  Supporting a causal involvement, inhibiting miR103/107 in mouse models of diabetes with (unconjugated) antisense oligonucleotides increased not only insulin sensitivity, but also had positive effects on a couple of other diabetes-related parameters not only in the liver (e.g. triglyceride levels), but also body fat (adipocyte size/differentiation).

One puzzling aspect, somewhat akin to Regulus’ Alport’s program (--> miR-21), in exploiting anti-miR103/107 for pharmacological intervention is that it was initially uncertain what the target cells ought to be: adipocytes and/or hepatocytes?  A role for miR103/107 expression in adipocytes was particularly supported by the observation that its steady-state level there is higher than in the liver and the fact that single-strand phosphorothioate oligonucleotides also distribute to body fat.

However, with the adoption of GalNAc conjugation technology where most of the oligonucleotides now accumulate in hepatocytes it seems that AstraZeneca and Regulus have come to the conclusion that it is the liver that once again is calling the shots here as it usually does in diabetes.  You can deduce this from the fact that a GalNAc version was selected as the clinical candidate (AZD4076) slated to enter the clinic later this year.

Taking advantage of the observation that anti-miR103/107 has positive effects on liver triglyceride levels, the clinical development of AZD4076 will at least initially be geared towards treating non-alcoholic steatohepatitis (NASH) in diabetes patients.

Tuesday, April 7, 2015

Time is running out for Benitec

Benitec announced today that almost 1 ½ years after filing an IND for its DNA-directed RNAi HCV candidate, it has now obtained liver biopsy data from first 3 of the 4 patients dosed so far.  Needless to say, the analysis was a resounding success confirming that the right AAV vector coding for the shRNAs against HCV was administered to the trial subjects.

Given that no details were provided on the methods, I assume that the evidence is based on PCR analysis which pretty much picks up almost any activity.

TT-034 also shined on safety with ‘no treatment-related serious adverse effects (SAEs) in any of the four patients dosed’.

To wit, the motivation behind the gene therapy ddRNAi HCV trial is to provide a one-shot cure from HCV infection.  The company, however, said that ‘the amount of shRNA produced will not result in reduction of hepatitis C viral load’.  

So while this statement almost makes it sound like they did not look for antiviral efficacy, but that there might well have been, we can safely assume that they did (standard blood test to look for HCV; plus RNA analysis from biopsies) and failed to see such.  

It is also curious that no results from PCR-based target mRNA cleavage assays were disclosed which, while still PCR, requires a certain amount of RNAi robustness to detect with confidence and would have been used to further tout trial success. 

At this point, Benitec has almost completed the first 2 of 5 planned dose cohorts.  According to my notes, the top dose is about 25x higher than dose group 2.  To get from no change in viral titer to undetectable while increasing dose by 25x seems quite optimistic to me.  And even if this highly unlikely scenario materialized, at this pace, it will be sometime in 2023-4 when it would even be considered for approval.

So please, Benitec, if you cannot see a knockdown at the next higher dose cohort, give it a rest.   

Friday, April 3, 2015

Hereditary Angioedema: A High-Value RNA Therapeutics Target Confirmed by Antibody Trial

This week, Dyax released early, but arguably impressive data from a phase Ib trial of monoclonal antibody DX-2930 for the prophylaxis of Hereditary Angioedema (HAE), a rare disease (incidence of 1 in 10-50k births) with a rapidly evolving and growing market.  The results confirm that plasma kallikrein and, by extension, its precursor prekallikrein (PKK), are highly effective and safe targets for the treatment of HAE.

Due to the expression of kallikrein and other pathway components in the liver, HAE therefore shapes up as yet another high-value indication after PCSK9/cardiovascular disease and CC5/complement disorders PNH and aHUS (à Soliris) where RNA Therapeutics will be directly pitted against monoclonal antibodies to answer the following pharmasophical question: 

What would you prefer? Turn off the gene underlying a disease with a defined, synthetic molecule harnessing an endogenous biological mechanism, or mop up the disease-mediating gene product (protein) with a gemisch of cell-derived proteins?

You may know my preference already, and indeed, a phase I study of ISIS-PKKRx by Isis Pharmaceuticals targeting PKK has just been completed and showed a 80-90% gene knockdown at 300-400mg weekly subcutaneous injections.

Disease pathway: promoters and inhibitors

HAE is caused by the genetic absence or insufficient activity of C1 esterase inhibitor (C1-INH).  This predisposes to regular, often weekly to monthly episodes of tissue swelling which when abdominal can cause severe pain and when affecting the throat is life-threatening.

Although C1-INH is involved in a few intersecting pathways such as coagulation and complement, the results by Dyax confirm the growing evidence that in the end it is all about plasma kallikrein and subsequent vasoactive bradykinin generation.  The preclinical evidence includes an elegant study by Isis Pharmaceuticals (Bhattacharjee et al 2013) where the power of RNA Therapeutics was harnessed to knockdown a number of players in the coagulation and kinin-kallikrein pathways to show that only inhibition of members of the kinin-kallikrein pathway (e.g. PKK and factor 12) could reverse the symptoms caused by C1-INH deficiency.

Importantly, human genetics show that PKK deficiency is without apparent medical adverse consequence, thus making it a drug developer’s dream.

Therefore, although HAE is caused by a protein deficiency, a therapeutic knockdown approach is conceivable due to the presence of promoters and inhibitors in the pathway of disease. This is thus similar to antithrombin and hemophilia for which Alnylam is currently advancing a promising RNAi Therapeutics clinical candidate (ALN-AT3).

Poor pharmacokinetics of approved drugs leaves large unmet need

There are a handful of drugs approved for HAE.  Most of these are approved only for the mitigation of an acute HAE attack.  They have shown modest efficacy with kallikrein inhibitor Ecallantide/KALBITOR (a small protein by Dyax) and C1-INH protein replacement therapeutic CINRYZE (by Shire) approximately halving the severity of an attack or attack frequency, respectively. 

In addition to some potentially severe side effects like anaphylaxis (KALBITOR) and infusion reactions (CINRYZE), it is the poor pharmacokinetics necessitating frequent administration that render them impractical for prophylactic use.

For example, CINRYZE, the only agent approved for prophylactic use, has to be intravenously infused twice a week (and some investors/companies moan when Tekmira's RNAi LNP products have to be infused every 3-4 weeks), and still attack rates were reduced by only about a half.  This supports that despite frequent i.v. infusions, C1-INH levels cannot be kept above the needed threshold for long enough.

Given that once set in motion, the swelling cascade is probably difficult to stop cold, it is, however, chronic prophyxis that has the prospect of bringing most benefit to patients, in addition to filling the coffers of biotech companies and their investors (prophylactic CINRYZE: $300k per year).

DX2930 shaping up to be first satisfactory treatment

In light of the above, it is apparent that new drugs for HAE should have both increased potency and be sufficiently convenient for chronic prophylactic use.  In terms of dosing frequency, this means at a minimum once-a-quarter intravenous infusions, weekly subcutaneous injections, or daily oral pills.

As a subcutaneously administered antibody, DX-2930, of course, almost naturally satisfies the dosing frequency requirement.  Moreover, when 2 doses were given 14 days apart, the attack frequency for the 300 and 400mg cohorts dropped by ~10x from baseline during the time when plasma concentrations of the antibody were deemed above the threshold needed to keep the kinin-kallikrein pathway in check (~6 weeks after 2nd dose).  13/15 patients (87%) were thus attack free from days 8-50 compared to only 3/11 (27%) in the placebo group.

Attack frequencies for the 30mg and 100mg cohorts were not reported.  This probably means that these were not successful and support the notion that whether an attack can occur or not is a rather sharp threshold effect.  Also consistent with this was the fact that the 300mg cohort numerically performed better than the 400mg cohort in this small sample size. 

[correction] Attack frequencies for the 30 and 100mg cohorts were also dramatically reduced from days 8-50 although these doses had been predicted by Dyax to yield suboptimal plasma antibody levels, possibly raising questions about the patient population chosen.

Nevertheless, DX-2930 appears overall very promising and has further validated kallikrein/PKK as targets, but larger patient numbers are required to determine the more precise efficacy benefit over existing drugs, the dose response relationshipo, and, of course, safety.

RNA Therapeutics closing in

In addition to 2nd generation RNaseH antisense compound ISIS-PKKRx, I expect a number of additional RNA Therapeutics candidates to join the HAE fray due to the attractive economics of the market and the anticipated high rate of development success.  The latter is largely a function of the validated nature of the kinin-kallikrein pathway.

Although the DX-2930 study validates kallikrein, it should be cautioned that RNA Therapeutics cannot actually target kallikrein directly, but merely its precursor, PKK, as kallikrein is generated from PKK by enzymatic processing.  This means that the therapeutic threshold in terms of percent inhibition will be shifted either to the left or right depending on the enzymology of PKK processing.

In summary, HAE and the kinin-kallikrein pathway should be one to put on your RNA Therapeutics radar, also because it may offer new avenues towards important large markets such as diabetic macular edema and inflammatory bowel diseases.

Friday, March 27, 2015

FDA Hard-Pressed to Approve Biomarin, But Not Sarepta Drug

When Biomarin late last year bought Prosensa for its experimental exon skipper drisapersen for the treatment of Duchenne Muscular Dystrophy (for $680M plus potential milestones), it exuded confidence about the likelihood of getting approval for the 2’-O-methyl phosphorothioate antisense molecule.  This, despite of the fact that drisapersen failed in a pivotal phase III trial of 186 patients which prompted the old partner GSK to dump the drug and walk away.

Tenuous early evidence for drisapersen in earlier trials

The confidence is largely based on some supposedly successful earlier trials, especially a multi-center, randomized, blinded 53-patient phase II study which had seen improvements in the 6 minute walk distance (6MWD) at week 25, the primary endpoint of the study (Voit et al. 2014).  

This, however was statistically significant only the case in the subgroup of patients that received drisapersen continuously (à treatment in 10 out of 10 weeks with 6mg/kg), but not in patients which were treated identically, except for the small difference in skipping the last week in a 10-week treatment cycle.

At week 49, the difference with placebo failed to reach statistical significance and Prosensa had to resort to pooling both subgroups to claim victory for that time point. Similarly, drisapersen failed in obtaining statistically significant outcomes for other muscle function endpoints.

Since the mechanism of action for the DMD exon skipping candidates is to change splicing of the mutated dystrophin transcript to a form in which the reading frame is restored with recovery of partial activity, it is important to understand the relationship between drug treatment and dystrophin production.

Here, too, the evidence was less than robust.  For example, even when applying the sensitive immunofluorescence technique, no increase or even a decrease in dystrophin was seen in almost half of treated subjects.  With the less sensitive Western blot, an increase in dystrophin was seen in only a third of treated subjects (0 for placebo).

Therefore, given the failed phase III trial and the less than robust earlier evidence in favor of the drug, I struggle to understand Biomarin’s confidence in obtaining approval in 2016.   

The importance of dystrophin as a surrogate endpoint

Part of the difficulty of obtaining statistically significant results for muscle function endpoints is most likely due to the small patient size (orphan disease affecting ~1 in 3500 male births) and the consequent need to pool boys at various stages of the disease together in a given trial.  It would thus not be surprising if say obtaining 10% levels of normal or Becker-type dystrophin will translate into very meaningful clinical benefit in some, but not other boys.

This will be an even more challenging problem for the DMD subgroups that are not amenable to exon 51-based exon skipping which is targeted by drisapersen.  Probably insurmountable for first-generation chemistries like drisapersen.

Accordingly, in both the drisapersen and the competitive PMO-based eteplirsen trials, it has not been possible to correlate dystrophin production with functional outcomes.

For that reason, I strongly support the importance of establishing reliable, quantitative methods to measure dystrophin in clinical trials (there was an FDA workshop related to this last week).  Dystrophin-dependent markers may also be acceptable if they can be measured by means that do not involve taking painful muscle biopsies.  For example, serum-based microRNAs as developed by Rosetta Genomics and Marina Biotech would be of interest here.

Eteplirsen before drisapersen

I thus find it difficult to grasp the notion of rejecting the current crop of exon skippers like drisapersen or eteplirsen should they be found to produce functional dystrophin with few side effects.  After all, it is the loss of dystrophin function that causes Duchenne Muscular Dystrophy and one has to wonder how generating additional dystrophin cannot be beneficial to patients, especially since the principle behind drisapersen and eteplirsen is strongly supported by human genetic evidence (à Becker’s Muscular Dystrophy).

In this world, it has got to be eteplirsen that should be first in line for regulatory approval.  This is because there is overwhelming evidence (e.g. Heemskerk et al., 2009; Sarepta's Barclays presentation March 12, 2015) that the PMO-based drug is much more potent than drisapersen which, let’s face it, is based on stone-age antisense chemistry (2’-O-methyl phosphorothioate).  Such chemistry is characterized by minimal efficacy and dose-limiting toxicities, especially renal in the case of drisapersen.

In a paper comparing 2’-O-methyl to PMO chemistry for DMD exon skipping conducted by researchers close to eteplirsen, it was found that at same doses in mice, PMO chemistry is moderately to vastly more potent than 2’-O-methyl phosphorothioate antisense compounds of a size comparable to drisapersen.  The extent of the difference depended on whether the human or mouse dystrophin were targeted and the target sequence.   Unsurprisingly given the acrimonious competition between the two parties, Sarepta has also picked up on this and continued along these lines by showing that in addition to chemistry, eteplirsen has the edge over drisapersen in terms of the targeted sequence:

Sure, there is the theoretical caveat that PMO and 2’-O-methyl scale differently from mice to humans and that what is the most potent target sequence for one chemistry does not necessarily have to be the most potent one for the other.  Intuitively, however, the differences are too big for these factors to compensate the preclinical evidence.  Also, keep in mind that in the clinic, eteplirsen is being given at 5 to almost 10-fold increased doses than drisapersen and, on top of that, is much safer and better tolerated than drisapersen.

Because of this and the competition, it is not surprising and disingenuous when Biomarin would now suddenly like to de-emphasize the importance of dystrophin as a surrogate biomarker (see last week's workshop).

Dear regulatory agency, if you approve drisapersen, you cannot deny eteplirsen.  Sure, drisapersen has been tested in more patients than eteplirsen and Sarepta has conducted a clinical trial in the worst possible manner and probably ‘embellished’/overstated some of their results, including the dystrophin evidence.  However, given that eteplirsen almost certainly generates more dystrophin than drisapersen, the highly favorable side effect profile of eteplirsen (also in comparison to drisapersen), and in light of the 6MWD issue that applies to both drug candidates, the question is whether the bureaucratic application of rules should trump scientific evidence and patient interests.

Disclosure: I am long SRPT based on the notion that Biomarin, with its orphan disease savvy, will turn out to be the biggest supporter of eteplirsen getting approval this time around.  Additionally, the agency is partly responsible for the long duration of the ongoing eteplirsen trial (close to 4 years soon) and the repeated taking of muscle biopsies, and after all this taking away hope from patients and their close ones is difficult to fathom.
By Dirk Haussecker. All rights reserved.

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