Monday, November 17, 2014

Study Provides Insights into Masked RNAi Trigger Approach by Solstice Biologics

In early 2013, Solstice Biologics was the first most notable RNAi platform start-up after the industry had gone through the 2008-2011 RNAi Valley of Death.  The idea was to develop new single molecule RNAi triggers that would have better pharmacologic attributes than the highly negatively charged small double-stranded RNAs, as well as increased stability and reduced immunogenicity.

Today, a publication by the Dowdy group (Meade et al 2014), the academic birthplace of the technology, was published in Nature Biotechnology revealing for the first time more detailed insights into the fundamental approach.

Accordingly, the charge and stability issues have been addressed by esterifying the sugar-phosphate backbone with a biocleavable thioester, turning the phosphate diester into a triester.  Despite some steric constraints due to the nature of the double helix, the majority of phosphates could thus be triesterified thereby creating a more or less neutral RNAi trigger molecule: siRNNs (small interfering ribonucleic neutrals).

Once in the cytoplasm of the target cell, the triesterified RNAi triggers get converted by the ubiquitously expressed thioesterases into canonical charged RNAi triggers which only then become competent for utilization by the RNAi machinery.

Importantly, the molecules could be synthesized by methods closely related to standard phosphoramidite-based synthesis using modified phosphoramidites as the building blocks.  To this end, the Dowdy group and Solstice have created a library of modified phosphoramidites, including those amenable to the conjugation to cell-targeting ligands and endosomal release functionalities.

The study validated the high stability and reduced immunogenicity of the siRNNs and showed their increased binding affinity to plasma proteins such as albumins.  The latter is predicted to facilitate improved pharmacokinetics.  

Unfortunately, the in vivo validation stopped at the stage of using GalNAcs as the targeting ligand, because this attribute is predicted to be an advantage for particularly the delivery outside the liver where we might not find receptors with high uptake capacity similar to ASGPR on hepatocytes.

Another favorable attribute of the charge-neutral siRNNs, but which remains to be demonstrated, is improved tissue penetration.   Finally, it is possible that siRNNs have an advantage in overcoming cell membranes as well which is consistent with the apparent improved potency of GalNAc-siRNNs over standard siRNA-GalNAc conjugates (40 vs 55% knockdown in an experiment).

In many ways, siRNNs remind me of the self-delivering RNAi trigger approach first pioneered by Dharmacon and later adopted by RXi Pharmaceuticals.  However, there are at least two important differences: 1) self-delivering RNAi triggers still contain negative charge; and 2) self-delivering RNAi triggers should be structurally more flexible due to the shortened double-stranded region (~12 base-pairs vs 19 base-pairs) which, however, comes at the expense of impaired potency.

I greatly welcome this publication as it represents a fundamentally differentiated approach to RNAi Therapeutics drug development and it will be exciting to see where the Dowdy group and Solstice Biologics will take this versatile platform for RNAi and potentially beyond.

Dicerna Admits Defeat, Licenses LNP Tech from Tekmira

Show me the non-human primate data.  Robust evidence of gene knockdown in monkeys is a key requirement to gain confidence in a company’s liposomal delivery claims.  Dicerna has never done that and yet been able to pull off an IPO and make claims about clinical development timelines without actually being in possession of a realistic delivery technology.

In retrospect, it is not surprising that they eventually had to come hat in hand to the liposomal delivery powerhouse, aka Tekmira- after claiming that its liposomal delivery technology (EnCore) was superior to Tekmira’s…  After all, Dicerna is under pressure to get its first proper development candidate in the clinic for Primary Hyperoxaluria Type I (PH1), especially after Alnylam had publicly announcedtheir intention to go after PH1, too.

According to the agreement announced today, Dicerna will use Tekmira’s 3rd generation LNP technology and manufacturing to get DCR-PH1 into the clinic sometime in 2015.  In return, Tekmira will get $2.5M upfront, $22M in potential development milestones and single-digit royalties- in other words, nothing to write home about other than the satisfaction that they were proven right scientifically.

You may interject that Dicerna already has a clinical program using EnCore technology, DCR-MYC for cancer.  Unfortunately, there are many ways to curing cancer in mice and I am yet to be convinced that they have been primarily the result of RNAi mechanism of action.

In summary, a moral victory for Tekmira, a deal that made sense for Dicerna and which could and should have happened a long time ago.  In a final twist of irony, Dicerna has given Tekmira a back-handed compliment in issuing another press release today where it announces that future development programs will be based on Dicerna’s conjugate delivery technology.

Now that makes actually sense for a Dicer-substrate-based company.  Expect Alnylam to increase its saber-rattling vis-a-vis Dicerna.

Disclosure: Long Dicerna, no position in Tekmira

Friday, November 14, 2014

Injection Site Reactions and Liver Toxicity Emerge as Major Issues for GalNAc-siRNA Technology

Alnylam this morning reported top-line results from a phase II study of their first clinical candidate based on the GalNAc-siRNA conjugate delivery technology, ALN-TTRsc for TTR amyloidosis.  Accordingly, average knockdowns of ~85% were seen in the 5mg/kg dose group, thus confirming the robust potency at around the dose that the company plans to take forward in later-stage studies.

Such potency, however, came at the apparent expense of relatively frequent injection site reactions (23% of patients), with an additional skin reaction seen outside the area of injection.  Moreover, there was a trend towards elevated liver enzymes, a marker of liver toxicity, including one that was adjudicated a serious adverse event (SAE; ~4x ULN deemed mild severity).

The efficacy data do not come as a surprise given that they were largely in line with that seen in the phase I study a year ago, which included the same dose group (5mg/kg) at the same dosing schedule (first 5x daily, then weekly for 5 weeks).  In both cases average TTR reductions  of ~85% were seen, with the difference being that this study involved 23 subjects at this dose (plus 3 subjects at 7.5mg/kg which was not further pursued for undisclosed reasons) while the phase I study involved only 3 comparable subjects.

The efficacy is thus in line with the intravenous ALN-TTR02 which utilizes Tekmira’s liposomal delivery technology and which so far has been very well tolerated.  Critics (aka LNP haters), however, are keen to point out the use of (transient) immune suppression.  The efficacy of ALN-TTRsc is superior to the antisense compound by ISIS and GSK which has shown 70% target gene knockdown in a short 4-week phase I study.  Assuming maximal knockdown efficacy has not been reached at this time-point, ISIS-TTRRx is likely to max out between 75 and 80%.

Similar to potency, the injection site reactions were not really a surprise given that in the phase I study this was the most common side effect.  What is new is that there was a skin reaction that occurred outside the area of injection possibly indicating systemic immune activation.

The liver enzyme elevations, however, were certainly new.  This could be related to histologic observations of granulations in the cytoplasm of hepatocytes, likely reflecting storage sites of the fairly stable modified RNAi triggers.

My hope and expectation is that particularly the injection site reactions, but also liver enzyme elevations will lessen with the lower doses enabled by the more effective second generation ESC GalNAc chemistry.  Still, for ALN-TTRsc the safety profile looks adequate for an indication like FAC (familial amyloidotic cardiomyopathy), but 23 is still a small number to be sure.  

Lastly, if I had to choose between ALN-TTRsc, ISIS-TTRRx, and ALN-TTR02, I would go with ALN-TTR02 with the best apparent risk:reward, regardless of whether it's an intravenous procedure or not.   

Disclosure: Long ISIS Pharmaceuticals, no positions in Tekmira and Alnylam.

Monday, November 10, 2014

Co-delivering Antisense and RNAi for Cancer

The upcoming phase I top-line data for ISIS-STAT3Rx in liver cancer (HCC) to be presented at the upcoming EORTC-NCI-AACR triple meeting in Barcelona (Nov 18-21) will be an important test of the potential utility of RNAseH antisense oligonucleotides (ASOs) incorporating high-affinity chemistry in oncology.  

Based on the body language by ISIS Pharmaceuticals* and last week's $7.5M milestone payment from partner AstraZeneca for progress on ISIS-STAT3Rx (aka AZD9150) , I am tempted to speculate on more than just ‘encouraging’ results.  On the other hand, Regulus Therapeutics partner Sanofi at the Canton Nucleic Acid Forum (CNAF) also last week, noted the need for formulating antisense oligonucleotides to get their anti-miR21 oncology candidate into liver cancer tissue. It is likely that they will be using liposomes for that (--> Tekmira?).

* I was surprised that at the CNAF in Guangzhou, China, Brett Monia from ISIS mentioned STAT3Rx and cancer right after gene silencing in the liver as the next interesting application for ASOs- that is ahead of even the exciting CNS opportunity.

The discrepancy in body language may be explained by just cultural differences (conservative, blasé Big Pharma versus risk-taking, enthusiastic biotech); it may also be a reflection of different requirements for effective tissue concentrations with RNaseH versus anti-microRNA modalities or different target requirements.  Whatever the reason, the Sanofi comments clearly support the notion that getting naked, even phosphorothioated oligonucleotides into cancer tissues is not as robust as with other tissues such as the liver and kidney.

I am therefore pleased that it is a Big Pharma, the last place where I had expected that from, that is connecting the dots and is considering delivery formulations, even the supposedly ‘toxic’ LNPs.  The concept is that the nanoparticle would facilitate a higher tumor concentration of the oligonucleotide, and once in the tumor interstitial space, cellular delivery may be facilitated via two routes.  Firstly, it may be traditional liposome-dependent cell uptake and cytosolic release.  Alternatively, those LNPs that get stuck in the interstitial space would spill the phosphorothioate oligo which may then diffuse further and get into the target cell by self-delivery. 

The same concept, of course, applies not only to phosphorothioate ASOs, but also to self-delivering RNAi triggers (+/- conjugation).

But why stop there? I propose that for cancer delivery, one should strongly consider and co-formulate RNAi triggers and ASOs into a shared nanoparticle.  They could target either the same gene, or they could target different genes thus taking into account the desire for a multi-pronged attack on cancer   (-> resistance).  In that scenario you would benefit from the superior gene silencing efficacy of RNAi triggers in those cells that they were able to reach, but then extent your reach with the help of the more agile, penetrative single-stranded antisense molecules. 

As such, PS-ASOs have an advantage in addressing intra-tumor heterogeneity of the EPR effect which is a well-recognized problem of nanoparticle delivery for cancer.

Another benefit of combining RNAi triggers with RNaseH ASOs is that you could achieve additive gene silencing activity when going after a shared target.  For example, if the RNaseH ASO and the RNAi trigger had both say a 70% knockdown activity on their own in the nucleus and cytoplasm, respectively, the combined activity would likely be ~90% which genetically could make a huge difference.

There is also a potency benefit, although more minor, when going after different targets because at least in RNAi, the best you can hope for when combining RNAi triggers against different targets is that they do not interfere/compete with each other.

With solid cancer data from both Tekmira (RNAi) and ISIS/AZ out over the coming weeks, we will soon get a sense of whether the field has moved forward in oncology and what the next steps ought to be.

Tuesday, November 4, 2014

Ocular Applications Back in the Focus of Oligonucleotide Therapeutics

Following yesterday's disclosure that yet another one of GSK’s target picks for clinical development under their antisense options agreement with ISIS Pharmaceuticals is an ocular one, I thought it worth highlighting that ocular applications are regaining traction in oligonucleotide therapeutics in general.  This follows a temporary lull in the area due to setbacks with older generations of the technologies and funding issues for the industry.

Aptamers still in the lead

It may surprise you, but the eye is the one area in oligonucleotide therapeutics where aptamers, nucleic acids binding protein targets based on their shape not sequence (similar to antibodies), are most advanced.  Despite of the fact that the first approved aptamer, Macugen, is considered a great disappointment as it lost out to the monoclonal antibody competition in the VEGF market for wet AMD and DME, there are at least two new development candidates that are poised to become blockbusters in the same market: Fovista by Ophthotech targeting PDGF which has shown unprecedented activity in a phase II study in combination with anti-VEGF antibody Lucentis, and an earlier-stage, but potentially superior VEGF/PDGF bispecific aptamer approach by privately held SomaLogic.

It is now thought that the Macugen failure was due to it not targeting the relevant VEGF isoforms.  In other words, it was a failure of target selection/biological insight, not a failure of the technology.  Aptamers should work well for trapping extracellular proteins for ocular applications, because unlike their often rapid elimination following systemic administration, they can be maintained at elevated concentrations in the eye for sustained periods of time.  Their limitation, however, is in the number of targets available to them, similar to monoclonal antibodies.  Nevertheless, it should be kept in mind that with even just 2 or 3 commercial successes in a therapeutic area, a platform technology can be considered tremendously valuable there.

Gene-regulatory oligos catching up

Although ocular drug development has also been popular in both the antisense and especially RNAi fields, previous technology generations were inadequate to effect robust gene modulation, especially target gene knockdown.  This holds true for 1st (à Vitravene) and 2nd generation (cRaf inhibitor by iCo Therapeutics) antisense and the ‘naked’ RNAi trigger folly of the early days of RNAi Therapeutics (à Acuity Pharmaceuticals, Sylentis, Quark, and Sirna/Allergan to name just some of the worst offenders of sound science).

The reason why antisense and RNAi are both staging a comeback in ophthalmology is due to the use of higher affinity chemistries (e.g. cET by ISIS) and self-delivering RNAi triggers, both in the form of (partially) double-stranded (e.g. sd-rxRNAs by RXi Pharmaceuticals) and single-stranded RNAi triggers (à ISIS Pharmaceuticals).  The increased stability and lipophilicity combined with small molecular size should allow such an RNAi approach to efficiently penetrate the vitreous of the eye following needle injection and reach deep into the retina and other ocular structures.  Similarly, what used to be a mediocre 40% knockdown for ASOs could now be a genetically much more useful 70-80% knockdown with gen2.5 RNaseH.

It is too early to tell whether RNaseH gen2.5, ssRNAi, or sdrxRNAs will win out in the end.  At least in terms of timing, it will be as much a matter of investing in the technologies as it is about their potential.  In particular, I am disappointed by the failure of RXi Pharmaceuticals to recognize the need to further develop their sd-rxRNA chemistry.

So keep your eyes peeled as clinical results from the new wave of gene-modulating Oligo Therapeutics will start to emerge in 2016 and beyond.  It is possible that QPI-1007 by Quark Pharma for ocular neuroprotection for NAION may be earlier than that, although the chemical nature of this ‘2nd generation’ non-AtuRNAi trigger remains unclear to me and therefore might be, or might not be a 'self-delivering' RNAi trigger.  If not this one, the upcoming clinical development of CTGF-targeting RXI-109 for retinal scarring by RXi Pharmaceuticals should be an interesting one to follow.

Wednesday, October 22, 2014

Anti-MiR122 Therapeutic Stuns HCV World with Single-Dose Efficacy Results

This morning, Regulus Therapeutics greeted us with amazing results from a phase I study of RG-101, an anti-microRNA 122 oligo for the treatment of HCV infection.  The results show that in the exploratory HCV-infected patient subgroup, a single dose of 2mg/kg of RG-101 resulted in a mean viral load reduction of 4.1log on day 29.  All responded with viral declines, with 6 and 3 of the 14 patients with viral levels below the level of quantitation on days 29 and 57, respectively.   

These results even exceed my own wildest imaginations (as discussed here yesterday) and I’m amazed how much this virus, in all patients, seems to have come to rely on this host-derived microRNA for replication and/or genome stabilization.

It is not clear whether increasing the dose to 4mg/kg, the pre-planned upper dose in the HCV-infected cohort for which dosing is ongoing will bring any additional benefit given that the biomarker data (host genes targeted by miR-122) from the healthy volunteers showed a plateau already at 2mg/kg, indicating the power of this GalNAc chemistry approach.  My guess is that the main benefit from a higher dose would be a decrease in response variability.

Interestingly, IL-28 status, frequently a predictor of treatment success, did not influence the results, nor did HCV genotype seem to have an impact (small numbers).  This further supports that RG-101 could fill some of the more attractive opportunities in the current HCV market.   

Regarding safety, mild and transient injection site reactions seemed most significant with no serious adverse events in the entire study, including the healthy volunteer cohorts (up to 8mg/kg).  This is also consistent with data for Alnylam’sALN-TTRsc which uses a similar GalNAc chemistry and where multiple doses up to 10mg/kg had been tolerated, with injection site reactions, especially at 10mg/kg, being the main safety finding.   

So what’s it all worth?  The results position RG-101 to facilitate a 4-week HCV dosing regimen (compared to typically 8-12 weeks currently), potentially in combination with a single direct-acting antiviral such as Olysio by Johnson&Johnson.  One or two injections maximum.  Great compliance, potentially pan-genotypic, ideal for the busy practicing physician who does not have the time nor inclination to know the ins and outs of each DAA.

In dollar terms, I’d like to think that with this drug profile, this overlooked compound and company are worth as much as what Merck recently paid for HCV drug developer Idenix: $3.85B. The market valuation of Regulus before the news: $300M.  Needlessly to say that I'm long the stock.

PS: GSK once had rights to a precursor compound of RG-101 which it did not exercise.  Importantly, at the time, Regulus’ anti-miR122 compound was not GalNAc-enabled.  This would have necessitated much more frequent dosing and higher dosages and resulted in less potent and more protracted viral declines, i.e. something that would not have been competitive in the current HCV marketplace.  But as often the case with Big Pharma and cutting-edge technology, today’s data clearly shows them wrong.  It has to be said though that GSK more or less got out of HCV which also would have explained GSK’s decision RE anti-miR122.

PPS: Congrats to Peter Sarnow and Catherine Jopling who in 2005 made the mind-boggling discovery that HCV relies on a microRNA for its replication.  I hope they will be handsomely rewarded for it.

Tuesday, October 21, 2014

Predicting the Outcome of Regulus HCV microRNA Therapeutics Study

Regulus Therapeutics is on track to reveal phase I results of its anti-HCV compound by the end of the year according to a presentation at last week's OTS.  Although the phase I study is largely a healthy volunteer dose-escalating safety study, it does involve a cohort of HCV patients to assess the viral knockdown kinetics following a single dose of anti-miR122 RG-101. 

MicroRNA-122 is a small RNA host factor that had been identified to play an important role in HCV replication.  As a therapeutic target it promises a low risk of viral resistance, pan-genotypic activity, and entirely novel mechanism of action making it suitable for combination therapy.

Based on the experience with an LNA-based competitor compound by Santaris/Roche (Janssen et al. NEJM 2013), I predict a 2 to 3 log viral knockdown, with a 3 log viral knockdown setting the scene for RG-101 as a single shot in a 4-week treatment regimen in combination with other oral direct-acting antiviral agents (DAAs).  If viral reductions were on the low end of my expectations, it may require 2 or 3 doses within 4 weeks for GalNAc, cET-enhanced RG-101 to facilitate such a short treatment period which is considered a necessary attribute of future treatment regimens in an increasingly competitive market.

Miravirsen comparison

Earlier studies by Regulus competitor Santaris/Roche largely form the basis for my predictions.  In particular, a phase II study of 5 weekly doses of miravirsen at 3, 5, and 7mg/kg yielded 1.2log (3mg/kg) and ~3log (5 and 7mg/kg) viral knockdowns.  Miravirsen is an LNA-based antisense compound whereas RG-101 involves the analogous high-affinity cET chemistry.  Conservatively, miravirsen has a slight (1-3x) potency advantage over RG-101 without the GalNAc conjugation when considering non-human primate and clinical AldoA and cholesterol results which reflect anti-miR122 activity.

However, the GalNAc conjugate in RG-101 is giving it a great 10-30x boost in potency, meaning that overall RG-101 should be 3-30x more potent than miravirsen.  It is because of this and considering that RG-101 is given at 2 and 4mg/kg in the phase I trial in HCV patients, that I arrive at a predicted 2-3 log HCV reduction in the phase I study.  This also makes the conservative assumption that 3log viral reductions is all that an anti-miR122 treatment strategy may achieve based on the apparent plateauing of miravirsen at 5mg/kg.  The 3 log prediction would require that a single shot of RG-101 can already achieve super-therapeutic tissue levels of the oligo.  This, however, cannot be assumed given that for non-ligand-targeted phosphorothioate antisense technology at least this would normally require a multi-dose loading schedule.

But isn’t RG-101 late to the HCV game?

It’s long been thought that it’s game over for RG-101 given the dynamics in the HCV markets.  In particular, the already approved and soon-to-be-approved all-oral DAAs which typically achieve cures in >90% of patients in 8-12 weeks in well-supervised clinical trial settings, would make newer agents like RG-101 seem outdated.  On the other hand, especially given cost pressures (~$100K per average treatment and ~4 million infected in the US alone), the uptake of the new treatments has been relatively slow with only 1-2% treated thus far (according to some of the analyst reports that I have read).  And even then, the sales have been spectacular: Sovaldi e.g. is on track to become the most successful drug launch ever being on track for more than $10 billion in sales in its first launch year!!!

It is the cost pressures (pricing per pill, not per cure) and improved adherence that make a shortened 4-week treatment period so desirable.  A single or two subcutaneous injections in the doctor’s office during routine check-ups where blood is taken anyway should add to compliance.  Holding the subcutaneous route of administration of RG-101 against the drug is therefore wrong in my opinion and the ‘all-oral’ notion, a misnomer really, has only been so attractive because the former subcutaneous standard of care, interferon, was so unpopular not because of the needle injections, but because of its side effects.

So place your bets.  I believe RG-101 has value and will not only be superior to the Santaris/Roche drug, but has pretty much caught up with it in development terms given that miravirsen has only been tested with a DAA (telaprevir) that is already long outdated.  As to the necessary Big Pharma/Biotech licensee, Johnson&Johnson tops my list.

Disclosure: Long RGLS as an RNA Therapeutics stock waiting to be re-discovered with an increasingly broad and clinical-stage pipeline and good financials.  The RG-101 results should only be the trigger for the re-discovery of this ~$300M market cap company.   
By Dirk Haussecker. All rights reserved.

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