Alnylam’s Second-Generation GalNAc Data Impress

Earlier this week at the American Society of Hematology meeting in San Francisco, Alnylam presented first multi-dose knockdown data in humans for its second-generation GalNAc-siRNA conjugate technology (ESC-GalNAc).  Accordingly, an almost 60% knockdown was seen in the first (and so far only) patient dosed at 0.045 mg microgram per kilogram ESC-GalNAc siRNA with the knockdown yet having to reach its nadir.  Moreover, further knockdown benefits are likely to accrue with dosing beyond 3 times weekly as was the case in this study.

At these low doses, no remarkable adverse events were reported, including injection site reactions or increases in liver enzymes which were seen with first-generation GalNAc-siRNAs in humans at much higher doses.

Though the data from this phase I study of ALN-AT3 in hemophilia patients is still early and there will be gene target-dependent differences in knockdown potency, they do support Alnylam’s claim that second generation GalNAc is indeed considerably, as much as 50x more potent than first-generation GalNAcs.  Only last week I had speculated that it may be more appropriate to estimate 2^nd gen GalNAc to be ‘only' 5x more potent than 1^st gen GalNAcs.

I was wrong.

In non-human primates, ALN-AT3 had an ED90 of 0.5mg/kg with weekly dosing.  Based on the phase I data thus far, I expect the corresponding ED90 dose in humans to be a ~ weekly 0.075mcg/kg 0.075mg/kg for a ~7-fold improvement in potency in humans versus non-human primates, a relative potency improvement that is not seen for first-generation GalNAcs.  Add to this the inherent 5x improved intra-species potency of second- versus first-gen GalNAc (Nair et al 2014), it is indeed possible that ESC-GalNAc enjoy an up to 50x improved potency advantage.

In other words, it should be possible to now achieve highly potent knockdown with a once-monthly dosing regime and sub-1 ml subcutaneous injection volumes. 

The value of this for the ALN-AT3 program, which harnesses a unique mechanism in an otherwise crowded hemophilia field which in general is moving towards less frequent dosing/infusion regimens and less immunogenic molecules, remains to be seen.  The slow enrolment pace of the phase I trial, ~5 hemophilia patients enrolled in 6 months, gives cause for commercial concern.     

The competition

While the improved potency is great for Alnylam, the gene knockdown competition is unlikely to yield the liver to Alnylam.  Highly potent knockdowns are possible with other platforms by Arrowhead, ISIS, Tekmira, and possibly Dicerna, too. Beyond route of administration [subQ for Alnylam GalNAc, ISIS (GalNAc-) ASOs, Arrowhead’s single molecule DPCs, and Dicerna GalNAc versus intravenous for Arrowhead’s 2-molecule DPCs and Tekmira’s SNALP LNPs], differentiation will come from safety/tolerability and dosing frequencies.

The next datapoints in this regard will come from the R&D Day by Dicerna early next week (Dicer-substrate GalNAcs) and the 4mg/kg phase I data from the immensely exciting anti-miR122 program by Regulus Therapeutics (employing GalNAc-antisense chemistry) in January 2015.

Alnylam Second-Generation GalNAc Chemistry ~5x More Potent

The GalNAc-RNAi trigger strategy pioneered by Alnylam and Arrowhead Research has opened up new opportunities for RNAi Therapeutics, partly due to the fact that they may be administered subcutaneously (note: for Arrowhead that means the single molecule DPC which is not yet in clinical development).  Although the first such product candidate, ALN-TTRsc, looks like it could be a decent drug for a severe disease such as TTR amyloidosis, there is room for improvement both in terms of efficacy (--> injection volumes) and tolerability/safety (liver enzyme elevations, skin reactions).

It is therefore no surprise that Alnylam keeps stressing the fact that it has improved upon ALN-TTRsc, now referring to the original GalNAc chemistry as ‘standard chemistry’ (STC) and the improved version as ‘enhanced stabilization chemistry’ (ESC).  By inter- and extrapolating data from various model systems and for various target genes, the company has come up with the notion that ESC ‘has the potential’ to be around 50x more potent than STC (IR departments know that investors will be blind to qualifiers like ‘has the potential’).

I love it when maths meets biology.

These numbers games, of course, make little pharmacological sense, mostly due to the fact that the same delivery chemistry can result in disparate knockdown efficacies just due to sequence and target gene differences.  In addition, concluding anything about a dose response from a ~25% knockdown in a single-dose, single dose level phase I study (--> ALN-AT3) is impossible.  In RNAi, a 25% knockdown can be achieved with homeopathic drug levels and does not inform at which drug concentrations more robust >50% knockdowns will be observed.

Apparently, Alnylam is seeing it the same way and probably has received the same criticism from other sources.  It has now provided on two recent occasions much more informative datasets on the relative potencies of STC versus ESC.

At the Cantonese Nucleic Acids Forum (CNAF) in Guangzhou, China, in early November, Dr. Manoharan revealed that if you turn the STC of ALN-TTRsc into an ESC, the gain is a 5x in potency.  Consistent with this 5x notion is the Nair et al. paper that published 2 days ago in JACS where the same exercise for an siRNA sequence against the murine transthyretin gene resulted in the same 5x improved potency.

Of importance to the RNAi community, the enhanced metabolic stability was achieved by the use of phosphorothioate bonds at the 5’ ends of both the guide and passenger strands, while the 3’ ends are protected in both generations by phosphorothioates in the overhang (guide strand) and the GalNAc ligand (passenger strand), respectively.  I would not necessarily have predicted that phosphorothioates were tolerated at the guide 5’ end and this could be all the material difference there is between STC and ESC.

All eyes are now on the ALN-AT3 phase I data presentation at the upcoming ASH meeting next Monday (abstract here).  To wit, in part A of that study, Alnylam reported a ~25% mean peak knockdown for the 0.03mg/kg starting dose in healthy volunteers earlier this year (single dose).  Although there was no dose response data and they had failed to reach the maximum allowable AT3 knockdown of 40%, part A was deemed a success with the study proceeding into part B in hemophilia patients for further dose escalation and repeat dosing.  First data from that part is to be revealed.  

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'.

What to Expect from RNAi Therapeutics in 2013

2012 was the most exciting year in the ~12-year history of RNAi Therapeutics- both from a scientific and financial perspective.  Left for dead by most, unambiguous gene knockdown results in Man have allowed the technology to regain much-needed respectability.  With the start of 2013, the industry is looking to build on these successes with additional clinical trial results, interesting new therapeutic candidates and product-specific and platform-related deals, particularly in the area of delivery.  With appetite for innovation increasing in a low interest rate economy and with the orphan drug tsunami, 2013 could be a quite rewarding year for the discerning investor.

Clinical results to look out for

Clinical results in 2013 that will continue to shape perceptions of the technology include phase II study results for ALN-TTR02 in TTR-FAP by Alnylam, phase I results from its GalNAc conjugate version ALN-TTRsc, and phase I results from a number of other programs, foremost from oncology drug candidate TKM-PLK1 by Tekmira, ALN-AT3 for hemophilia by Alnylam, and finally RXI-109 for dermal scarring by RXi Pharmaceuticals.  

For ALN-TTR02, it will be important to confirm the impressive knockdown results from the phase I study, but over longer periods of time and with still acceptable safety.  ALN-TTRsc will be an important proof-of-concept for the subcutaneous delivery of RNAi Therapeutics and should provide a good idea of what to expect for ALN-AT3 which is based on the same GalNAc siRNA conjugate technology.  The success or lack thereof of Alnylam’s GalNAc technology will also affect the perception of Arrowhead’s DPC technology as either a competing or necessary subQ alternative to GalNAcs.

Tekmira’s TKM-PLK1 has not gotten much credit so far.  This, however, could change with the presentation of the full phase I results, possibly at this year’s ASCO.  I consider PLK1 as the single most attractive target for cancer RNAi and I am bullish that the molecular analyses will show molecular, if not clinical efficacy at this early stage.  And while TKM-PLK1 could overcome the safety-efficacy hurdle for some indications, the importance of PLK1 as a target demands that Tekmira will continuously work on improved follow-on versions.

Finally, RXi’s second phase into RNAi for skin applications.  I also consider dermal scarring as an interesting differentiated, because cosmeceutical RNAi product opportunity.  

Cool pipeline additions

As detailed in my last blog entry, there are two exciting infectious disease drug candidates for which clinical development will ramp up in 2013: Arrowhead’s ARC520 aiming to achieve for HBV what has recently been achieved in HCV (dramatically increased cure rates and less suffering from the side effects of interferons), and Calimmune’s ddRNAi-based HIV drug candidate aiming to keep the virus out of immune cells.

It looks like we will have to wait for clinical efficacy results from these programs for a while (2014-2015), either due to the nature of the cell competition approach involved in the HIV program or because of the use of healthy volunteers.  I believe the latter is what Arrowhead has guided for ARC520, but from an investor perspective this would be highly unforunate as this would delay the demonstration of gene knockdown with the DPC platform.  And from a medical perspective, I am struggling to see what the value or necessity of a volunteer trial would be.  

Deals and Big Pharma

In addition to clinical trial results, RNAi Therapeutics investors will be getting up each morning to check the internet for whether a deal has been announced.  Alnylam’s ALN-PCSK9 is the most imminent partnering candidate and will be an indicator of the mere differentiation value of RNAi Therapeutics.  While clinically more advanced monoclonal antibody-based programs for the industry’s most desired target, PCSK9, exist, should monoclonal antibody stumble as a class, RNAi Therapeutics and ALN-PCS could suddenly have the market for itself.  Considering the multi-billion $$$ potential of PCSK9, a gamble worth taking for a Big Pharma in my opinion.

Similarly to ALN-PCS in the hypercholesterolemia market, the size and complexity of the clinical program that would be required to turn ARC520 into a major HBV drug well exceeds Arrowhead capacities, and this could mean that we will see an early licensing deal around that asset, too.  While proof-of-concept clinical knockdown data would greatly increase the partnering value of ARC520, from a financial perspective (--> di-lu-tion!) early partnering may be prudent if no alternative non-dilutive capital alternative presented itself.

As delivery is gating for all of the above RNAi Therapeutics product opportunities, delivery naturally should be the subject of a few more platform-type relationships.  Tekmira’s SNALP technology for addressing diseases of the liver, lung, and cancer tops the list for a meaningful partnership (>$10M upfront), and also Arrowhead’s DPCs for liver-targeted gene knockdown ought to see some interest.  

Delivery-related deals should also reveal which Big Pharma company is still committed to the RNAi Therapeutics platform.  For the efforts at Takeda, Merck, and Novartis (the three most significant ones in terms of investment to-date), it could be a make-or-break year.  I cannot imagine that these groups are allowed to exist in their current forms for much longer before they get anything into the clinic.  For this, they probably need to swallow their own pride and accept that expert outside help is necessary for their delivery needs (rather than attempting home-brew versions).  Given the recent clinical and late preclinical results for SNALPs and DPCs, chances that they will finally do something have certainly increased.

A Happy New Year everybody.

Detailed Genetic Modeling Triggers Change in Hemophilia RNAi Target Gene Selection: ALN-APC Out, ALN-AT3 In

This week, Alnylam presented data for its hemophilia program which aims at providing particularly those patients that have developed antibodies ('inhibitors') against the recombinant factor VIII and IX standard-of-care with a treatment alternative.  After ALN-TTR for TTR amyloidosis, this is the second of the two programs the company wants to focus its internal development resources on.  The presentation, however, showed that the timelines have been delayed due to a change in target gene selection.  So with an IND planned for this program in 2013, it thus appears that the original 5x15^TM, which stated that the company wanted to move 5 clinical candidates into late-stage development by 2015, is more and more turning into a ‘1 out of 5’- if all goes well.  What a difference 18 months can make!

Sarcasm aside, the reason for the change in target gene selection is due to modeling the impact of various degrees of gene knockdown on the desired biological outcome: a 50% knockdown of antithrombin (AT) goes much further in terms of thrombin generation (the biomarker used in the study) than a 50% knockdown of the target gene in ALN-APC, protein C.

The type of detailed genetic analysis behind this realization is actually a very important one that companies should think more about when selecting RNAi target genes.  All too often, target gene selection is based on classical black-and-white gene knockout genetics which can be misleading.  Indeed, the VEGF component in ALN-VSP02 may be one of those. 

In the presentation, Alnylam further emphasized that ALN-AT3 utilizes a conjugate-siRNA approach amenable to subcutaneous administration.  Although the hemophilia community is very familiar with the intravenous route of drug administration, the company essentially claims that this is ‘a highly preferred mode of administration in the setting of hemophilia’.  

Really?  In any case, adopting GalNac-siRNA conjugation as an alternative to the gold-standard SNALP delivery would also make strategic sense for Alnylam.  Alnylam has become overly dependent on Tekmira’s technology to the extent that it apparently/allegedly felt compelled to mis-appropriate the technology which is subject to a high-profile ongoing litigation.  Not a good position to be in when the supplier (and owner) of that technology could pull the plug any day.  

On the other hand, the scientific evidence, particularly the shallow dose response in non-human primates which suggest that antisense-type large amounts of drug would be needed (3-10mg/kg), suggest that just maybe GalNac conjugation is not ready yet for prime time.   .