Tekmira Expands Biodefense Efforts to Cover Both Ebola and Marburg Virus

Following the successes with its Ebola biodefense program, Tekmira has started to present increasingly promising data for treating a related filovirus, the Marburg virus.  With 100% survival rates in non-human primate models and new RNAi triggers that should cover a broad spectrum of strains and possibly related viruses, the company is well positioned to also take away the Marburg indication from competitor Sarepta which in turn has become preoccupied with its exon-skipping drug candidate for DMD.  

For the Ebola program alone, the $100M market cap company estimates that the successful development of a drug under the so called Animal Rule could result in stockpiling orders from the US government worth about $100M annually.

From guinea pigs...

In a publication last month, Tekmira and their collaborators from the UTMB in Galveston, Texas, reported the successful treatment of guinea pigs infected with a number of different strains of the Marburg virus.  Because the development of treatments for rapidly mutating viruses and viruses with a multitude of divergent strains is hampered by sequence diversity, a broader strain coverage was achieved, like in Tekmira’s Ebola approach or in Arrowhead’s chronic HepB strategy (ARC520), through the concurrent use of two siRNAs in a single formulation.

Given that rodents have limited predictiveness for anti-filoviral efficacy in Man and given that the formulation was apparently a 1^st generation D-LinDMA-based SNALP, I was not all that excited about the publication due to the apparent early stage of development.

...to non-human primates

In a positive surprise therefore, the Chief Scientific Officer of the company, Ian MacLachlan, presented gold standard non-human primate data of SNALP RNAi Therapeutics for Marburg virus at the ongoing OligoDIA regulator-industry conference.  Accordingly, Tekmira’s newer LNP formulations (‘SNALP-G’) were shown to fully protect monkeys from death due to Marburg infection when given at 0.5mg/kg (=the magic safety threshold for SNALP).

As an important comparison, Sarepta last year reported ‘83% to 100%’ protection rates in comparable models when treatment was initiated up to 96 hours after infections with its newer PMOplus morpholino chemistry.   It is therefore of interest to test the impact of further delaying treatment with SNALPs.

As I have been following Tekmira’s biodefense program over the years, one development I noticed, especially in the era of budget cuts, was the apparent push by the Department of Defense for biomergency treatments that can address not just multiple strains of a virus, but multiple viruses all-in-one.  Intriguingly, one of the bullet points in Tekmira’s slide presentation on goals for the Marburg program (slide 36) talks about the ‘Design broad spectrum siRNA to target multiple MARV and Ebola’.  Does this mean that the ultimate prize here are stockpiling contracts for a single drug addressing both Marburg and Ebola?

Having a better ear for and adjusting to the needs of the DoD is also one reason why I believe Tekmira will continue to have the upper hand over competitor Sarepta with its DMD distractions and an investor base that could not care less about the Marburg program.  Although the targets were explicitly not disclosed, I wonder whether there are host factors one could target and which would be beneficial for various viral applications.  This would be an alternative to trying to come up with target sequences that are conserved across the viruses.

Finally, serving as yet another example of illustrating the value of biodefense contracts for platform technology companies, Tekmira disclosed plans that a first clinical trial with a lyophilized SNALP formulation, TKM-EBOLA, is planned for the first quarter of 2014. 

A First Clinical Step Towards Subcutaneously Administered RNAi Therapeutics

Today, Alnylam reported more detailed results from their phase I study of ALN-TTRsc for the treatment of the cardiomyopathy form of TTR amyloidosis (press release here, data presentation here).  As telegraphed by COO Barry Greene at the recent Morgan Stanley Healthcare Conference, 5mg/kg and more of the subcutaneously administered ALN-TTRsc were required to obtain a persistent knockdown of 80% (5mg/kg) and more (10mg/kg dose).  

As these doses fail the 2.5mg/kg challenge the company had set itself earlier, increased injection volumes and injection numbers are being evaluated.  A phase II trial with ALN-TTRsc is planned to start at the end of the year with a pivotal phase III study slated to start in 2014.

Small potency differences to monkey studies matter for ALN-TTRsc

As I had indicated earlier, the preclinical monkey studies with ALN-TTRsc (see slide 7) left open the possibility that with an 80% target knockdown, ALN-TTRsc can be sufficiently effective at 2.5mg/kg which corresponds to the magical injection volume of 1ml for safe and convenient subcutaneous administration.  However, the phase I human data are shifted by 1 dose cohort meaning that 5.0mg/kg were required for an approx. 80% sustained knockdown (see slide 11 where 2.5mg/kg clearly missed).

If you are confused about the press release prefers which talks about an 87.5% 'mean' (n=3) knockdown ‘at nadir’ for the 5.0mg/kg dose, it is more appropriate for this indication to refer to the average knockdown level over time which was more like 80-82% (slide 11).  

Nevertheless, oozing with optimism, Alnylam set itself an even higher bar for ALN-TTRsc for future studies with a sustained target knockdown of 90%.  Such a level of knockdown was only achieved in this study at the very high dose of 10mg/kg.  Indicative that 10mg/kg is not a desirable dose, the company amended its study to evaluate 7.5mg/kg given as two 1.5ml injections in addition to 5.0mg/kg and 7.5mg/kg every 2 weeks to determine whether less frequent dosing is feasible.

Personally, I believe 5.0mg/kg twice a week would be a more promising dosing schedule as with higher doses there should be diminishing returns due to receptor saturation.

Safety OK, but questions raised

The reported safety profile did not yield apparent nasty surprises.  This is obviously very good in a phase I study of a new chemistry.  However, it has also become obvious that injection site reactions could become an issue.  Unlike ISIS Pharmaceuticals which has declared such reactions to be a cosmetic problem in the past, injection site reactions have to be closely watched as they could indicate systemic immune issues.

Despite the small numbers, the injection site reactions appear to be dose-related with 3 out of 3 subjects at the 10mg/kg exhibiting them during the 5 weeks of the study.

 

These observations are also relevant to the competitive DPC delivery technology by Arrowhead Research because both involve galactose conjugations.  In the case of the intravenous version of DPC, the galactose has been added to the endosomolytic peptide, while a cholesterol is added to the RNAi trigger administered separately. 

Initially, I had thought IP issues could have prompted Arrowhead to put the galactose on the ‘less precious’ peptides.  However, an alternative explanation could be that galactose conjugated to nucleic acid might be more prone to immune stimulations.  Due to the apparent dose-relatedness of the reactions, it will be important that future subQ candidates (both Alnylam's GalNAc and Arrowhead's subQ DPC which have galactose and the RNAi trigger on the same molecule) have therapeutic knockdown potencies at 2.5mg/kg and below.  

A very perplexing observation, albeit not discussed at all, is the fact that elevated immune cytokine levels were reported in the placebo cohort, but none in the ALN-TTRsc cohorts (see slide 15 of the presentation).  I really don’t know what to make of this. 

Summary

Despite some of the blemishes above, the results are a decent start for subcutaneously administered RNAi Therapeutics for liver-expressed gene expression.  In addition to the safety profile, this thus renders also the last argument for phosphorothioate-based RNaseH antisense technology in such indications obsolete, namely the ‘patient-friendly’ route of administration.  Patients with TTR amyloidosis and their relatives can now look forward to two attractive RNAi options, and I expect there to be continued RNAi improvements for this indication.

For those interested in Tekmira, the results are positive in the sense that they increase the value of ALN-TTR02 given the modest potency of ALN-TTRsc, and support SNALP to be the clinically validated gold standard in RNAi delivery.  For those interested in Arrowhead Research, the results are positive as they underline the value of more potent subQ RNAi delivery technologies and because they lower the safety risk around the galactose chemistry.

Alnylam Comments Suggest SubQ Tech Failed to Achieve Efficacy Goal

At today’s Morgan Stanley Healthcare Conference, the President and COO of Alnylam, Barry Greene, told the audience to assume that it took a dose of 5 to 10mg/kg of ALN-TTRsc to achieve the 80% knockdown that had been reported in July.  This suggests that ALN-TTRsc has failed to meet the stated goal of limiting the subcutaneous injection volume to 1ml or less as this is predicted to correspond to a dose of 2.5mg/kg.

If it holds up, this would have a number of important implications.  Firstly, it would affect the profile of ALN-TTRsc itself.  I don’t believe it to be necessarily terminal in a disease like the FAC form of TTR amyloidosis for which ALN-TTRsc is being developed.  Nevertheless, squeezing 2 or even 4ml into the subcutaneous space, or alternatively administering multiple 1ml shots in one sitting, could put some needle-phobic patients off, especially as TTR amyloidosis is set to become a competitive marketplace.

Secondly, such doses would not bode well for Alnylam’s GalNac delivery platform on which the company has pinned its future.  For example, one of the big draws of the hemophilia drug candidate ALN-AT3 which is about to enter clinical development was supposed to be its subcutaneous, instead of intravenous route of administration. However, as I speculated last week (Alnylam's GalNAcs as Cholesterol-siRNA 2.0), I believe ‘GalNac-siRNAs’ have advanced somewhat since ALN-TTRsc with the addition of lipophilic moieties such as cholesterol and the jury could therefore still be out regarding the capabilities of the GalNac delivery platform.

And finally, a weak potency of ALN-TTRsc would further increase the value of competing delivery technologies, especially SNALP (Tekmira) and the subcutaneous version of DPCs (Arrowhead Research). In fact, if the full results that are to be presented in about a week at the American Heart Failure Meeting confirm the 5-10mg/kg doses, it would explain why Alnylam chose not to have ALN-TTRsc compete with and potentially replace SNALP-based ALN-TTR02. Instead, the intravenous ALN-TTR02 will likely be applied to the earlier onset, more rapidly progressing form of TTR amyloidosis (FAP), whereas the subcutaneous ALN-TTRsc will be used for the more slowly progressing, later onset form of the disease (FAC).

BiogenIdec Obtains Exclusive Rights to Most Attractive Application of ISIS Technology

It is official.  With BiogenIdec obtaining 6 years of exclusive rights to ISIS’ antisense technology (ASO) for the evaluation of potential drug targets in the CNS and the treatment of neurological disease with ASOs, ISIS has essentially given up on the homerun potential that single-stranded antisense technology could have had in this therapeutic area.  Instead, the company continues to cap its upside and distract its attention by partnering with multiple companies in various disease areas.  What is more, in the one area where it likes to retain most ownership, targeting genes expressed in the liver for cardiovascular disease, it is likely to be eclipsed by best-in-class solutions from RNAi Therapeutics.

Deal Recognizes Unparalleled Druggability of Oligonucleotide Therapeutics

Neurological disease is arguably the most attractive application of antisense technology because of the surprisingly deep tissue penetration of the CNS following local delivery and the multitude of severe diseases of very high unmet medical need such as SMA, Huntingon’s, myotonic dystrophy and ALS.  These diseases are often genetically well-defined and thus ideal targets for the entire repertoire of antisense functionalities (gene knockdown in- and outside of the nucleus, boosting and redirecting gene expression through splice modulation).  Indeed, the fact that BiogenIdec commits so much attention to Antisense Therapeutics speaks volumes to the great competitive advantage of Oligonucleotide Therapeutics: the vastly superior drug target space versus small molecules and monoclonal antibodies, including the ability to go after the root cause of diseases.

Compared to RNAi Therapeutics, I view the deep tissue penetration following local administration of phosphorothioate-based oligos as the key competitive advantage.  This is especially the case when the target cells have a broad distribution in the CNS.  For more localized target areas, virally delivered DNA-directed RNAi Therapeutics should be competitive.

  

Flawed Business Model Based On Old Times

If you follow biotechnology, you will know that keeping commercialization rights to successful drugs rather than wholesale partnering and collecting royalties here and there is the ultimate path to shareholder value creation.

ISIS’ aversion to commercializing drugs itself can be traced back to the experience of its CEO, Dr. Stan Crooke, at Big Pharma GSK.  In his mind, it is the commercialization focus and large sales forces of Big Pharma that have been killing innovation and is wasting capital. 

The flaw in this reasoning is that times have changed and the specialty/orphan drug business model, the sweet spot of Oligonucleotide Therapeutics at that, has become a huge success in the industry.  Witness the likes of Aegerion and Alexion, but also Alnylam where retaining essentially the full rights to the TTR amyloidosis franchise alone is valued by the market at close to the entire market cap of ISIS with its dozens of clinical programs.  Accordingly, the ISIS TTR program that has been licensed to GSK is an also-ran in the valuations of ISIS Pharmaceuticals.

Apparently realizing the problems with this business model, the company has been making contortions trying to accommodate what must be hefty investor criticism with business development gimmicks such as ‘preferred partnerships’ and keeping drugs longer before licensing.  The BiogenIdec relationship obviously violates the latter principle.

With most other companies, I would not be as harsh when it comes to a $100M plus X biodollars deal. But for a $3.5B market cap company and the reasons stated above, it is difficult to find even a financial rationale for capping the value in the most attractive disease area for its technology.

Alnylam’s GalNAcs As Cholesterol-siRNA 2.0

That Alnylam bets its future on GalNAc-siRNAs is remarkable and indicates that the company feels the technology is clinically viable.  Accordingly, the preclinical animal data leaves open the possibility that the required volume of an effective dose of ALN-TTRsc, the first GalNAc-based clinical candidate, can be administered in a volume of 1ml or less, the stated goal of the company (results to be presented at HFSA, Sep22-25).  

While I view ALN-TTRsc as a cliffhanger in terms of commercial viability, not just because of the volume issue but also in light of the likely more effective SNALP option in the form of ALN-TTR02, the potency of GalNAc-based ALN-AT3 for hemophilia looks quite adequate.

Alnylam’s claim that a simple ligand-siRNA conjugate was able to mediate gene silencing in vivo required a rethinking of RNAi delivery by many since similar efforts involving especially aptamer-siRNA conjugates have been ‘viewed with skepticism’ to put it nicely.

Did Alnylam mislead the competition?

If you are a student and your funding body just spent $3000 to send you to a conference to learn about your subject, you might be forgiven if you came away with the notion that simple siRNA-conjuates such as Alnylam’s GalNAc-siRNAs can be effective (see e.g. slide 16 of the presentation by John Maraganore at the OTS last year).  The trick apparently is that with a magic ligand-receptor pair such as GalNAc-ASGPR all you need is to conjugate an RNAi trigger chemically modified for stability.  

Of course, the imaginary student here is only collateral damage as the real target audience of a presentation by Alnylam is its investors, potential partners, and competition.

As such, it may not surprise that according to patent application US2012/0136042A1, a simple GalNAc-siRNA conjugate has no activity on its own.  

Instead, silencing activity critically depends on the molecule also having a cholesterol (=lipophilic group) attached to it.  Since Alnylam had worked on such cholesterol-siRNA conjugates before (Soutschek et al. 2004), what now appears to be the actual GalNAc-siRNA structure can be viewed as an evolution of the cholesterol-siRNA which showed knockdown activity only at doses of 50mg/kg and higher.

DPCs by Arrowhead Research Take another Step

The 10-20 fold gains in potency with the addition of the GalNAc ligand shows how comparatively inefficient ApoE/LDL-based uptake systems are for liver-directed RNAi delivery.  The reason why SNALP is still more effective than GalNAc-siRNA is because cholesterol-siRNAs do an even poorer job when it comes to the next rate-limiting step in delivery: endosomal release.

With Arrowhead’s Dynamic Polyconjugates (DPCs) for liver-directed knockdown, you combine the best of both worlds: effective attachment to hepatocytes via multivalent GalNAc-ASGPR interactions and effective endosomal release through endosomolytic polymers/peptides.  

In fact, because of the potent chemistries used for the latter step, the endosomolytic agent has to be masked which initially made me a bit wary about the safety of DPCs (note: clinical safety data for ARC520 are about to be released, probably in October, and the preclinical safety performance looks good so far). 

According to Arrowhead’s research, this combination allows for more than 500-fold potency gains compared to cholesterol-siRNAs (Wong et al. 2012).  

Because the ratio of siRNA to endosomal-release peptide has to be held constant in the clinical studies of ARC520 which is based on the 2-molecule DPC version, you will not see these improvements in potency translated into clinical practice.  This is not all that critical anyway since ARC520 is administered intravenously and cholesterol-siRNAs should not be toxic even at elevated dosages.  Still, while I’m excited about ARC520 for all the stated reasons (see the HBV Knockdown Blog), for the sake of Arrowhead’s platform, I really would like to see the elegant single-molecule DPCs enter development.  This should not take much longer given the advanced data presented at OTS 2012.

But hey, maybe they have already advanced into development, but they are just being referred to as 'GalNAc-siRNA'.

Merck Paper Reveals Interest in GalNAc-targeted RNAi Therapeutics

Merck’s efforts have to be considered to be the strongest in RNAi Therapeutics among Big Pharma.  Its RNAi Therapeutics strategy so far, however, has consisted largely of trying to replicate the most promising technologies in-house. 

The latest publication by Merck RNAi scientists on the expression pattern of the asialoglycoprotein receptor (ASGPR1; Shi et al. 2013) confirms this as ASGPR is the target receptor of the two most advanced SNALP alternatives for gene silencing in the liver: the trail-blazing DPCs by Arrowhead Research (first use of GalNAc-targeted RNAi Therapeutics in Rozema et al.2007) and more recently the GalNAc-targeted siRNA conjugates by Alnylam (what these really seem to be will be covered in an upcoming blog...so stay tuned!).

Surveying ASGPR expression levels

When developing ligand-targeted therapeutics, it is important that the corresponding receptor is present on the target cell population.  Especially when targeting cancer, it can be difficult to find receptors that are not only present in large quantities, but also throughout the cell population.  

In the case of liver cancer (hepatocellular carcinoma/HCC), this question has occupied the RNAi field ever since the finding that SNALPs work really well for knockdown in normal liver due to uptake mediated by the LDL-receptor.  But is this mechanism also present on cells in liver cancer, a cancer of high unmet need where RNAi Therapeutics could have the biggest impact in oncology near- to midterm?

 

The Merck scientists set out to answer essentially the same question, but instead of interrogating LDL-receptor expression, they wanted to know about ASGPR expression on HCC cells.  Using tissue microarrays, they were able to test an impressively large set of 100s of tissues, including healthy human livers, liver cancer biopsies, and biopsies for other hepatic diseases such as viral hepatitis, chronic active hepatitis and cirrhosis.

Despite some apparent limitations with the tissue microarrays (e.g. normal liver samples were often marked as false negatives despite the known very high ASGPR expression level), the results seem to confirm that liver cancers in general have a tendency towards lower ASGPR expression and that inter-sample heterogeneity is comparatively large (some liver cancer samples had much more ASGPR expression than normal liver).  

This suggests that just as in the case in breast cancer where treatment decisions are often based on receptor expression levels, ASGPR-targeted liver cancer RNAi Therapeutics should also be combined with a companion diagnostics for ASGPR. 

For those curious about the status of ASGPR expression in chronic HBV since Arrowhead’s exciting ARC520 program for this indication involves a GalNAc-targeted melittin-like peptide, relax: livers infected with HBV express ASGPR just as well as normal livers.

Home-brew versus licensing

Based on the literature and conference presentations, it is reasonable to assume that Merck is well behind Arrowhead, and even Alnylam in developing GalNAc-targeted RNAi Therapeutics.  This begs the question, as it has in the case of SNALP, why does Merck not take a license or even acquire the original?

Of course, it always takes two for a deal, but given the financial capabilities of a Merck, if it wanted access, it could get it.

The likely explanation is that Merck's strategy in replicating technologies in-house is to first identify target technologies by validating them and then to develop viable IP workaround solutions.  In fact, in the apparent absence of a broad gate-keeping patent estate around GalNAc-targeted therapeutics, ASGPR has been a recognized drug target receptors well back into the 90's, there should be relatively little restrictions on the use of GalNAc per se.

Instead, a competitive advantage is largely gained through specific know-how like how to best link the GalNAc ligand to the oligonucleotide payload and synthesize the molecules cost effectively. The latter issue came to my attention recently when access to 'proprietary process for manufacturing GalNAc conjugates' from Alnylam was mentioned as the top corporate highlight in the quarterly update provided by Regulus Therapeutics.

For the aficionados, the triantennary GalNAcs as practiced by Alnylam are much more costly to synthesize than single GalNAcs as in the case of the liver-targeted DPC versions (where high affinity through multivalency is achieved by having multiple single GalNAcs along the DPC).

This situation is not unlike other areas in the drug development industry.  Take for example antibodies where, despite the various patent battles, there have been a number of commercially viable platforms based on specific libraries or optimization methods.  Nevertheless, despite this apparent freedom-to-operate, the way by which Big Pharma ended up gaining access to monoclonal antibodies was not by way of successfully developing them in-house, but by acquiring them.

I don't expect this to be any different in RNAi Therapeutics.