Friday, November 28, 2014

BioMarin $700M Acquistion of Prosensa Comes Down to Attraction of RNA Therapeutics

Earlier this week, the scientist in me was shocked by the ~$700M acquisition of Prosensa by orphan disease company BioMarin for its Duchenne Muscular Dystrophy splice modulation candidate drisapersen.  My initial surprise was due to drisapersen being a drug that had not long ago gloriously failed a pivotal phase III trial, not least due to a questionable therapeutic index.  All this is not very surprising since drisapersen is based on antiquated oligonucleotide chemistry (2’-O-methyl phosphorothioate).

After a moment of reflection though, I have come to take a more positive view of the deal as it is actually a very bullish sign of the interest by the wider pharmaceutical industry in RNA Therapeutics.   This is because BioMarin is taking the gamble here that it will be able to argue its way to approval by pointing towards drisapersen having shown evidence that it can positively influence the splicing of the disease-causing gene, dystrophin.  So even if your clinical evidence of efficacy is anecdotal at best, it is difficult to argue with the notion that such evidence in combination with being able to positively impact the root cause of a disease is not an important step in treating an orphan disease of very high unmet medical need.

It should be clear to everybody that if drisapersen can get marketing approval, other exon 51 splice skippers with superior chemistries (many of which are pushing forward in development) will eventually replace it as best-in-class.  I would be surprised if BioMarin did not see it the same way, but similar to Roche acquiring Intermune for $8.3B for its IPF drug which had marginal efficacy in a severe disease of high unmet need, the rationale seems to be that being first-to-market in such pioneer indications will allow you to build a strong franchises in those areas.

It will be interesting to see whether this strategy pans out and BioMarin can get accelerated approval in 2015-6 based on some seemingly positive phase IIresults in combination with the dystrophin biomarker evidence.

Regardless, the $700M valuation and ~60% premium of the offer to its stock price is a powerful reminder that part of the reason what makes RNA Therapeutics so compelling is that it often allows you to drill down to the root cause of a disease.  From a commercial perspective this is particularly valuable in an environment favoring drugs for severe orphan diseases.

Monday, November 24, 2014

Tekmira with Multi-Trigger and Parallel Development Plans

As a veteran armchair RNAi Therapeutics strategist, I am frequently frustrated at the inflexibility of companies in the face of rapidly moving competitive and drug development environments.  The worst offenders are those with management and Boards that view their positions as entitlements and could not care less about the science and acknowledge the flaws of their technology.  

Often related to this, another common violation is a failure to cut your losses on an obviously failed development program at the cost of the platform, a strategy though that sometimes works if you can find a greater fool (the ~$700M acquisition of Prosensa by Biomarin yesterday falls into that category).  

Tekmira, too, has been at risk of suffering from such inflexibility in light of an industry-wide shift from nanoparticle-based to small conjugate-based delivery.  This does not mean that nanoparticle-based delivery will not have an important role to play in the future of RNA(i) Therapeutics, but that you have to realize your relative strengths in a highly competitive space.  In addition, Tekmira has been slow to realize the shifting regulatory and payor landscape making biomarker-focused orphan drug development in genetically defined patient populations highly attractive.

Having listened to the Tekmira Analyst Day last Friday, I was therefore quite pleased that not only is Tekmira catching up by beginning to realize that it is running a business and not a scientific think tank, it can even be considered to take on a strategic leadership role in at least two regards:

1)      the adoption of multi-payload candidates thereby addressing the i.v. nanoparticle versus single molecule subQ debate and leveraging key advantages of nanoparticle technology;

2)      running trials in parallel to quickly find out which delivery chemistry platform works best in humans.

1.       Multi-targeting: a key differentiator of nanoparticle-enabled RNA(i) Therapeutics

At the Analyst Day, Tekmira re-iterated that it will put a multivalent HBV formulation into the clinic that will contain three RNAi triggers.  In addition to ensuring that most patients thus become a match for the therapy, just as the two-trigger ARC520 by Arrowhead Research had been geared towards, Tekmira also wants multi-targeting to address viral resistance of the kind it observed in the woodchuck model of HBV.  

From that perspective, the intravenously administered TKM-HBV is preferable to single molecule approaches by Alnylam and ISIS Pharmaceuticals which are both administered subcutaneously.
Tekmira does not limit multivalent RNA Therapeutics to viral applications such as in their HBV and Ebola programs, it will also apply the concept outside that space such as in its hypertriglyceridemia program where it is considering dual-targeting formulations with ApoCIII, ANGPTL3, and DGAT2 as candidate targets.  

Equally or even more intriguing, in the Q&A session it was hinted that other therapeutic strategies that the company is considering may not merely involve multiple payloads of the same type, but even payloads from different categories such as an mRNA and an RNAi trigger.  Obviously, such combinations could open up entirely new therapeutic strategies (e.g. mRNA-RNAi combos for alpha-1 antitrypsin), or maximize potency (e.g. RNAi trigger-RNaseH ASO for HBV).

Scientifically, I see no reason why single molecule technologies such as GalNAc-siRNAs should not be amenable to certain (but not all, e.g. mRNA) multivalent approaches.  Culturally, however, multi-valency takes away from the single molecule simplicity that the pharmaceutical industry apparently loves, ideally in pill form.  From a regulatory point of view, it seems to be the case that nanoparticle-encapsulated RNAi products are seen as just one drug no matter how many RNAi triggers it contains, and it remains to be seen what the regulatory thinking would be when combining multiple single RNAi triggers (I can imagine Alnylam trying to combine their HBV mRNA-targeting GalNAc-siRNA with its PD-L1 GalNAc-siRNA).

In some ways, ARC520 (which is not a nanoparticle) strongly indicates that multi-targeting is not an insurmountable challenge for the non-nanoparticle approaches, so that regulatory advantage may not exist in the future. 

Nevertheless, my prediction is that multi-targeting will be mostly practiced in the nanoparticle and not the conjugate sector of RNAi Therapeutics and nanoparticle-based companies ought to consider multi-targeting almost a Must when there is direct conjugate delivery competition.

Although Tekmira is the most visible RNAi company for multi-targeting, it should be added that multi-targeting has been the motto for US-China-based Sirnaomics from the get-go in 2007.

2.       Testing Multiple Delivery Technologies in Parallel

The RNAi Therapeutics field is both blessed and plagued by the rapid progress in refining particular delivery platforms.  Tekmira has already arrived at the 4th generation of SNALP LNPs while Alnylam is now talking about GalNAcs with standard and enhanced chemistries.  With a multitude of preclinically validated alternatives, it is often difficult to determine which one should be prioritized for human development. 

This can lead to protracted development timelines when a first formulation yields unsatisfactory results in the clinic and the payload has to be re-formulated into a new delivery chemistry.  Especially in competitive environments this can be fatal.  And even if you were somewhat satisfied with the initial results, chances are that you left a lot of money on the table by not finding out about the performance of other formulations in humans.

Needless to say, having multiple candidates for a target is not a unique challenge in the pharmaceutical industry and if money were not an issue, we would see a lot more parallel development programs.  However, RNAi and related delivery is unique as the investment can be amortized across the platform.  

Moreover, in practical terms, RNAi offers a number of opportunities to directly and accurately measure target engagement and thereby assess the impact of changing the formulation.  This is one of the reasons why the early RNAi programs targeting genes in the liver involve targets which can be found in the blood.  For other modalities (e.g. microRNA inhibition in the RNA Therapeutics field), what you measure in your blood sample or other biopsies may differ significantly from what is actually going on in the body.

For these reasons, namely to speed up time-to-market in a competitive market and to inform which delivery formulations should be used with other LNP-enabled candidates, Tekmira announced that it is about to put two formulations of TKM-HBV in the clinic that will only differ in their delivery chemistry while using the identical (3) RNAi triggers.

Tekmira investors are not seeing double: the company is becoming a modern drug developer.

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.
By Dirk Haussecker. All rights reserved.

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