Another Second-Generation GalNAc-RNAi Rocked by Off-Target Concerns

With the approval of ONPATTRO and the current overall clinical picture, in particular the highly encouraging safety profile seen with PCSK9-targeting Inclisiran in well over a 1000 subjects (à The Medicines Company and Alnylam), the RNAi mechanism can be considered a clinically validated  new drug modality. 

Liver enzyme elevations, however, have been seen across a few clinical programs.  This includes ALN-AAT for alpha-1 antitrypsin-related liver disease, ALN-AT3 for hemophilia, and now also Givosiran (ALN-AS1).  The most likelyreason for these observations is that the minimization of off-targeting had been neglected for these ‘2^nd-generation GalNAc-RNAi triggers’, thereby raising the risk that the relatively high off-target noise (dozens of off-targets) can be detrimental to target cell health. 

To wit, the spectrum of off-target genes varies tremendously from RNAi trigger sequence to RNAi trigger sequence and affects biologically unrelated genes.  This makes it very hard to predict whether the off-target noise will have adverse effects or will be just irrelevant noise to the cell.  Not helping is the fact that lab animals due to their genome sequence differences cannot model the safety around off-targeting.  The hope is that perhaps organ explants or mice with humanized organs (e.g. humanized mouse livers) will be better predictors since the target cell is almost the same as in the clinical setting.

Marked liver enzyme elevation in Givosiran pivotal trial

This week, Alnylam provided an interim read-out from the ENVISION trial, the registrational study with GalNAc-siRNA Givosiran for acute hepatic porphyria (AHP).  AHP is a rare disease caused by defects in heme synthesis.  This results in the accumulation of toxic intermediates such as PBG and ALA which can cause a range of symptoms, including severe pain attacks.

The study envisioned an interim biomarker read-out in a first cohort of patients that had been treated for at least 3 months with study drug.  It had been agreed before with the FDA that if lowering of ALA could be found in this read-out, it might form the basis for an accelerated approval.

Unsurprisingly, urinary ALA levels were reported to be statistically significantly lower in patients treated with Givosiran compared to placebo- in-line with the phase I/II experience (p<0 .001="" span="" style="mso-spacerun: yes;"> 

Unfortunately, there were numerically more than twice as many Givosiran-treated sujects (5/23) that experienced a serious adverse event (SAE) than in the placebo group (2/20).  One of the Givosiran-treated subjects had to discontinue treatment due to liver enzyme levels above the pre-specified threshold (>8x upper limit of normal).  While no liver enzyme elevations had been reported in a similar number of patients in the earlier-stage studies, I wished the company could have talked more about the presence of other liver enzyme increases of less than 8x ULN to get a better sense of the magnitude of the problem and whether such incidence would be compatible with giving the drugs in a chronic fashion.

Having said that, with 5 SAEs in 23 subjects treated a little more than 3 months on average (on top of a case of drug-related anaphylaxis in the phase I/II open-label extension study), SAEs that might be drug-related, would already seem to invalidate Givosiran being used in those with the same genetic condition, but not necessarily with recurrent pain attacks.  This would have tremendously extended the market opportunity of Givosiran.   

In the same vein, with the present safety questions, an accelerated approval that would shave off a few months before the full dataset will be available in early 2019, can now be ruled out with high certainty.

To add insult to injury, Akcea reported earlier this week that a GalNAc-version of the competitive RNaseH antisense technology did not suffer from thrombocytopenia as unconjugated ASOs typically do, thus putting ASOs back in the race for liver targets.  Still, in the long-term and in particular with the more specific new GalNAc-RNAi trigger chemistries, RNAi should win for most liver targets, but for some targets where either RNAi has inherent difficulties achieving high potencies or in cases where off-targeting toxicity still strikes (albeit at a much lower rate), RNaseH ASOs may emerge victorious.

Disclosure: long ALNY, but have taken some off the table following these data and questions around cardiac issues with ONPATTRO; it is important now for Inclisiran to re-instill confidence in the safety of RNAi Therapeutics; short AKCA as I do not believe that their current TTR and triglyceride-lowering drugs TEGSEDI and WAYLIVRA, respectively, can be commercially successful drugs and its artificially bloated market cap is a result of the low float and short interest in this stock and not a reflection of the value that the market sees in Akcea.

Givosiran on Track for Accelerated Approval, but Anaphylaxis Event Rattles Investors

Alnylam last weekend provided an update on its early clinical experience with Givosiran in patients with acute intermittent porphyria (AIP), a severe ultra-orphan disease characterized by debilitating abdominal pain.  The results further demonstrate that the ALA 1 Synthase (ALAS1)-targeting GalNAc-siRNA conjugate has a profound impact on disease symptoms, an impact that, excitingly, appears to improve over time based on the open-label extension data.

Given the severe nature of the disease, with intermittent acute pain by some referred to as being ‘incompatible with life’ and chronic pain in between attacks, the attack rate results and their remarkable correlation with ALA/PBG biomarker changes point towards smooth sailing towards accelerated approval of Givosiran in early 2019.  Accordingly, the ongoing registrational ENVISION phase III study has now recruited its 30^th patient, setting up for a biomarker read-out in the second half of this year which would form the basis of an IND submission.

Despite the solid efficacy results, biomarker and attack rate reductions down about 10x and 4x, respectively, the EASL update wasn’t all positive.  To begin, increasing the dose to 5mg/kg did not support the sustained ~70% ALAS1 mRNA and ~90% ALA/PBG lowering seen with 2.5mg/kg monthly dosing when given quarterly.  Such sustained reduction in neurotoxic ALA/PBG appear necessary for Givosiran disease-modifying efficacy.  Since there is no real competition for Givosiran on the horizon, this is a minor issue that will likely be addressed by next-generation AIP compounds by Alnylam.

More important, however, was the revelation of the first case of GalNAc RNAi-triggered anaphylaxis in the open-label extension (OLE) part of the study.  Within hours of a subcutaneous injection, a patient suffered anaphylaxis which, fortunately, was not fatal, but sufficient for the patient to drop out of the study.  Of note, there was no evidence of pre-existing anti-drug antibodies and this patient had a history of allergy.

The overall implications of this adverse events for Alnylam and the RNAi industry remain to be seen.  This was the first case of anaphylaxis among close to 3000 subjects dosed across various GalNAc-RNAi trigger studies by Alnylam, Arrowhead, and Dicerna.  This includes the hundreds of subjects exposed to PCSK9-lowering Inclisiran.  

At worst, anaphylaxis is a rare, unpredictable event to GalNAc-RNAi triggers in general which would have most impact of using this technology for less severe, large non-orphan indications.  More likely, however, anaphylaxis is a risk of specific compounds in this class and only seen in patients with a pre-disposition to allergy as in this instance.  

Both Alnylam and Arrowhead traded down 5% on the news, likely reflecting investor caution in light of the new data.   With Alnylam now trading over 35% below its recent all-time high and strong Patisiran and Givosiran approvals on the near-term horizon, Alnylam has now become my number one position.  Any such sustained weakness in share price makes it vulnerable to a hostile takeover attempt in this hot biotech M&A environment.

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.

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.

Alnylam’s Venture into Preeclampsia Exudes Confidence about Safety of RNAi Therapeutics

Last week, Alnylam disclosed yet another one of their development candidates (press release here, slide presentation here), this time ALN-AGT for the treatment of preeclampsia.  While most previously disclosed candidates address severe orphan diseases of high unmet medical needs such as TTR amyloidosis and complement-related diseases, some candidates such as ALN-PCSsc for hypercholesterolemia already have the potential to go after larger patient populations with less severe diseases.

With the preeclampsia indication, Alnylam has gone one step further, not in the sense that preeclampsia was not a very serious condition, but because pregnancy-related drug development is a largely shunned arena as the safety stakes are particularly high here.  Alnylam’s decision to go after this indication therefore must mean that the company has high confidence that RNAi Therapeutics, at least their particular breed in the form of GalNAc-siRNAs, should be very safe and succeed where small molecules have failed before.

Preeclampsia and current management

Preeclampsia affects about half a million pregnancies annually in the developed world and is a leading cause of pregnancy-related death (16% of maternal mortalities), frequently the result of stroke or end-organ damage such as in the liver and kidneys.  Because the disease can be the death sentence for a previously young, healthy woman (and her child), preeclampsia is a much dreaded condition where better diagnostics (esp. those that predict which preeclampsia cases will progress catastrophically) and new drugs are urgently needed.

Preeclampsia is characterized by high blood pressure (>140/90 mm Hg), frequently accompanied by protein in the blood (proteinuria).  It is a disease of the vasculature (Silence Therapeutics- listen up!) and while the causes are not fully understood, overexpression of VEGF/angiogenesis inhibitor sFLT may be a key early event in the disease.  It is probably the combination of vascular abnormalities and high blood pressure that ultimately can kill a woman.

The only cure for preeclampsia is delivery of the placenta.  Unfortunately, this may be much too early for the baby or mean delivery as early as 25 weeks of gestation with all the attendant infant mortality and developmental deficiencies. 

Although large randomized trials are lacking (because they would be difficult to justify), it is widely accepted that lowering blood pressure with antihypertensives lowers the risk of stroke and end-organ damage and thereby can help buy valuable extra weeks for the fetus to further mature. 

How RNAi can help

The management of high blood pressure is typically a multi-drug approach.  This means that for a given patient multiple antihypertensives are attempted sequentially or in combination until the desired control is achieved.

The drug cabinet for pregnancy-related hypertension, however, empties rapidly to a few somewhat trusted ones such as hydralazine and labetalol due to the suspected or known side effects (to the fetus) of most of them.   This includes otherwise widely prescribed antihypertensives which tackle high blood pressure along the renin-angiotensin-aldosterone system (e.g. ACE inhibitors). 

The toxicity here is due to the small molecules entering fetal circulation and consequently interfering with blood pressure regulation in the fetus thereby causing often fatal cardiac and renal defects as well as a general failure to thrive.

By contrast, an RNAi therapeutic would allow you to target the angiotensin pathway in the mother only.  The target of ALN-AGT, angiotensinogen, for example is expressed in the liver and both angiotensinogen as well as a GalNAc-siRNA would be restricted to the circulation of the mother.   Given the biodistribution of oligonucleotide therapeutics, I could also imagine RNAi Therapeutics to go after targets in the kidney with the same benefit of being limited to the mother.

ALN-AGT good for both (rat) mom and baby

In data presented last week at High Blood Pressure Research 2014, GalNAc-enabled ALN-AGT was shown to inhibit angiotensinogen of the mother by 90% in rodent models of preeclampsia.  Importantly, this was accompanied by a 20mm Hg reduction of mean arterial pressure, in addition to a reduction in proteinuria.

Such a 20mm reduction is clinically meaningful, given that reducing blood pressure from 160 and 140mm Hg can be the difference of highly likely stroke to no stroke.

Interestingly, not only did the maternal manifestations of the disease improve, the placental blood supply and architecture was improved, too, resulting in considerable benefits to the fetus as seen by increased birth weights and normalized brain:liver weight ratios.  

Safety and future development path

The data provided little discussion of the potential drawbacks and safety concerns around ALN-AGT.  One concern would be hypotension (lowering blood pressure too much) and related to this the reversibility and/or half-life of ALN-AGT.  Given that RNAi Therapeutics targeting genes expressed in the liver are typically active for weeks, close attention needs to be paid to hypotensive potential.

 

Encouragingly, the rat data indicate that the effect of ALN-AGT on blood pressure is more pronounced when blood pressure is high and medication is indicated (delta of 20mm Hg) compared to when it is normal (delta of 5mm Hg).  Another parameter that would be useful to consider in this context would be the dose/knockdown-blood pressure relationship and intrapatient/intra-rat variability.  E.g. would increasing the knockdown from 90% to 95% have a dramatic effect on blood pressure lowering or would it make little difference?

It will be safety that will guide the future clinical development path of ALN-AGT.  I can imagine Alnylam to first address women with a high likelihood of developing the devastating consequences of preeclampsia, perhaps with the help of a companion diagnostic.  Alternatively, it is not farfetched to think that ALN-AGT will first be used on top of other antihypertensives when they alone are not able to sufficiently control blood pressure.

Albeit little-loved by the pharmaceutical industry, once having been validated by proper clinical development in pregnant women, a drug like ALN-AGT would be poised to immediately become a mainstay in this indication.  From there, ALN-AGT could take on the rest of the $30-40B antihypertensive market.

Wild speculation

A drug like ALN-AGT is unlikely to be commercialized by Alnylam, both in the focused, likely hospital-based preeclampsia setting and in the wider antihypertensive market.  For preeclampsia, it would seem like a good addition to the portfolio of The Medicines Company, Alnylam’s partner for ALN-PCS in hypercholesterolemia.  

It is my suspicion that Alnylam rues the day it gave away ALN-PCS when times were hard. I don't believe Wall Street is anywhere close to grasping the potential of ALN-PCS to become a well-differentiated best-in-class in what is predicted to be a very large market.   And since Alnylam is known for its zeal to exploit all the RNAi value there is, with licensing and collaboration partners (usually referred to as 'friends') regularly turning into fierce 'competitors', it could be just a matter of time before Alnylam will claw back control over ALN-PCS.  ALN-AGT looks like the perfect trade-in. 

Dicerna Should Focus on Conjugate Delivery

Barely 3 months a public company, Dicerna has yet to emerge as a distinct RNAi Therapeutics player similar to the likes of Alnylam (à subQ GalNAc), Arrowhead Research (receptor-targeted DPCs), and Tekmira (àhigh potency liposomal RNAi).  Without leveraging the potential advantages of its Dicer-substrate RNAi triggers on which it had been founded, Dicerna will be remembered by the market as not much more than an IP workaround play.

Currently, Dicerna is utilizing liposomal delivery for its lead programs in cancer and orphan disease primary hyperoxaluria 1 (PH1), a highly versatile approach, but a niche that might be better left to Tekmira.  At least for the greater good of RNAi Therapeutics investment dollars.

Instead, Dicerna should compete more directly with both Alnylam and Arrowhead in conjugate delivery.  This is because Dicer substrates allow for the liberation of the active small interfering RNA from the conjugated ligand and/or polymer backbone by Dicer directly chewing off the conjugate.  By contrast, for conjugates like current GalNAc-siRNAs or DPCs, removal of the ligand/backbone has to be accomplished via more complex or difficult-to-work-with linker chemistries including protease-sensitive linkers or disulfides.  Such removal is usually necessary to allow for efficient incorporation into the RNAi effector complex RISC. 

In fact, it may be this chemical attachment challenge that has delayed Arrowhead’s single-molecule DPCs which I am so keen seeing progress into the clinic.

Of course, similar to adopting liposomal delivery, becoming expert in conjugate delivery probably won’t happen overnight and requires the hiring of appropriate talent.  Competition for such talent ought to be fierce with both Arrowhead and and particularly hometown rival Alnylam well cashed up and even antisense company ISIS entering the field.

We have now well crossed the point that RNAi Therapeutics is ready to churn out drugs.  If each of the players were to focus on its core strengths, it would ensure that the reach of the technology will grow in a most efficient manner.  

Alnylam GalNAc Improvements Incremental, but Likely Enough to Beat PCSK9 Antibodies

Over the last week, Alnylam presented pre-clinical data for their new development candidates for the treatment of hypercholesterolemia (ALN-PCSsc) and liver disease related to forms of alpha-1 antitrypsin deficiency (ALN-AAT).  These candidates are based on second-generation GalNAc-conjugate chemistry that the company is now dubbing ESC (Enhanced Stabilization Chemistry).  They involve the increased use of chemical nucleic acid modifications for stability with attendant improvements in knockdown potency and duration over first-generation GalNAc conjugates such as ALN-TTRsc.  ALN-TTRsc is the lead GalNAc candidate and currently in phase II development.

Borderline first-generation GalNAcs

In a phase I study of ALN-TTRsc, potent knockdowns were achieved with about:

-60% knockdown at 2.5mg/kg;

-80% knockdown at 5.0mg/kg (ED80), and

-90% knockdown at 10.0mg/kg.

At the risk of insulting medical geneticists for oversimplifying, assume that an RNAi technology that can safely achieve an 80% target gene knockdown provides for a solid platform.  In the case where a subcutaneous route of administration is desired and/or necessary, this should ideally also fit into a 1ml injection volume which in the case of GalNAc conjugates would correspond to a 2.5mg/kg dose.

There is some controversy around acceptable injection volumes and as often is the case, increased standards are applied to RNAi Therapeutics.  I say this because drugs and drug candidates such as expected mega-blockbuster PCSK9 antibody from Amgen, AMG-145, has been administered at 2ml volumes.  In fact, to achieve once-every-4-week dosing, 6ml (3x2ml) have been administered (see Giugliano et al. 2012).

In light of this, ALN-TTRsc has failed the 1ml test, but 80% are certainly possible with this first-generation GalNAc chemistry.  There is therefore room, and in some cases a competitive need (àcompetition with more potent delivery technologies such as Tekmira’s SNALP LNPs and Arrowhead’s single molecule DPCs) for improvements in GalNAc conjugation technology.    

Second-generation data could indicate progress

In agreement with this, Alnylam is now advertising the ESC second-generation GalNAc and has presented critical non-human primate data for their new development candidates ALN-PCSsc and ALN-AAT.  Non-human primate data are ‘critical’ because the RNAi knockdown observed in monkeys typically closely predicts what will be seen in humans based on the experiences with ALN-PCS (SNALP), ALN-TTR (SNALP), and ALN-TTRsc. 

In interpreting the newly presented data, it should be noted that in the case of ALN-TTRsc, an 80% knockdown was already observed at 2.5mg/kg (and 5mg/kg) in non-human primates, but that this shifted to 5mg/kg in humans.  Numerically a relatively small difference, in practical terms an important one.   

ALN-PCSsc achieved 80% PCSK9 target gene knockdowns at 2mg/kg in a weekly multi-dose study in non-human primates.  This resulted in a highly competitive 60% LDLc lowering in the absence of statins.  Similarly impressive in light of the monoclonal antibody competition was that 80% PCSK9 knockdown and 50-60% LDLc reductions were achieved and sustained for over 3 months (!) when a single dose of 10mg/kg (2x2ml) was given.  Compare this to 57% LDLc lowering with AMG145 in a once-every-4 week regimen in the MENDEL-2 phase III study of AMG145:

-ALN-PCSsc (RNAi): 50-60% LDLc reduction, 2x2ml subcutaneous, once-every-3-months

-AMG145 (monoclonal antibody): 57% LDLc reduction, 3x2ml subcutaneous, once-every-4-weeks (phase III MENDEL-2 monotherapy study)

(Yes, I do keep an eye on cash-rich, sub-$2B market cap The Medicines Company, Alnylam’s licensee for ALN-PCSsc for this reason).

Before I get carried away with all the advantages of the RNAi platform over monoclonal antibodies for even extracellular targets such as PCSK9, in terms of GalNAc improvements, these knockdown results are very much in line with what was seen for TTR in non-human primates. 

The same applies for ALN-AAT where a single dose of 3mg/kg translated into a 60% knockdown which, based on TTR and PCSK9, will likely translate into a weekly multi-dose ED80 of 2.0-2.5mg/kg in non-human primates.

However, with the caveat of different half-lives for different target genes, the durability of the PCSK9 knockdown is quite impressive and more than what is typically seen with e.g. SNALP LNPs which have historically utilized minimally modified RNAi triggers.  Such triggers may be turned over more rapidly in liver cells.

Similarly, the RNAi trigger sequence in the TTR development candidate is an extraordinarily potent one with low single-digit picomolar EC50 potency in tissue culture.  It is therefore possible that equivalent animal potencies have now been achieved with less potent sequences meaning that the underlying delivery technology has improved.

It’s been fascinating to watch the various delivery platforms, and indeed RNaseH antisense, compete over the years and pushing each other to new heights.  In this context, I am anxiously waiting for Arrowhead’s presentation at next week’s TIDES meeting with the intriguing title:  “Next Generation Dynamic Polyconjugates for siRNA Delivery in vivo,”

Market commentary: I remain mostly on the sidelines.  Years ago, these scientific data would have made me jump head-first into the market with me buying all I could in the opening minutes.  These days, however, I view them as ensuring the long-term value of RNAi stocks, but fail to see how they will support share prices in the current, growth-to-value rotating trading environment for more than a trading week or so.  I am therefore speculating on a capitulation event before some of the important clinical data read-outs roll in.  

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'.

Is Alnylam Foolishly Betting the Farm on GalNAcs?

It is remarkable that Alnylam seems to be embracing GalNAc subcutaneous delivery for all pipeline candidates, but for perhaps ALN-TTR02, that are most important to its 5x15^TM development and commercialization strategy: ALN-TTRsc (TTR amyloidosis), ALN-AT3 (hemophilia), and ALN-AS1 (acute intermittent porphyria).  Considering that gene knockdown has not been demonstrated in Man with GalNAc conjugates, and potency could be a critical issue determining whether this really is a subQ approach, this apparent high-risk strategy is uncharacteristic of a company with the laudable attitude of raising capital when the company does not need it.   

ALN-TTRsc: The Missing Clinical Trial

One possible reflection of the fact that management does not really feel as confident about the strategy as it may seem, is the missing entry of the ALN-TTRsc phase I clinical trial on clinicialtrials.gov (and other registries I looked at).

I like to look at clinical trial registries, esp. clinicaltrials.gov, also for the reason that information contained therein often provide interesting clues into otherwise undisclosed safety and efficacy issues.  For example, is it a single and/or multiple dose, what are the dosing ranges, etc. 

With ALN-TTRsc, I do not expect safety to be necessarily the dose limiting factor.  Rather, it may well be the ability to show robust efficacy with an injection volume of 1ml or less, the magic upper limit for subQ approaches.  It turns out that adequate efficacy was seen in non-human primates only starting at 2.5mg/kg which apparently corresponds to the 1ml volume in humans.  Moreover, the dose-response curve is relatively shallow making it difficult to extrapolate predicted doses from preclinical models into humans (being off by a factor of 2 in the ED50 could already prove disastrous).

Is the omission to list ALN-TTRsc on clinicaltrials.gov an attempt at hiding that the dose escalation schedule indicates that 2.5mg/kg is an optimistic guess? Of course, the secrecy could also be for competitive reasons in light of its race with the competing antisense approach by GSK-ISIS.  But for a company that so far has listed every clinical trial, including ALN-TTR01 and ALN-TTR02 all of which have been conducted exclusively outside the US, there will be a reason for it and doubts about GalNAc potency is a plausible one.

GalNAc Steals Spotlight from DPCs

Recently, Arrowhead scientists presented impressive subQ hepatic knockdown data with the DPC polyconjugate platform.  While the response to the presentation at the Oligonucleotide Society Meeting in Boston last year was tremendous, possibly the most enthusiastic one among all the presentations (and one of the reasons why I am bullish that there is wider industry demand for DPCs), Arrowhead has been getting no love from the financial markets, thus putting it at a disadvantage in any licensing negotiations.  One factor for that might be GalNAcs which take away in the typical investor’s mind the uniqueness about it being a subQ RNAi delivery approach.  So if Alnylam eventually realizes that it needs an alternative, it might get access to it on more affordable terms.  The phase I ALN-TTRsc results expected mid-year could be the critical event in that dynamic: poor results would benefit Arrowhead Research.

GalNAc Plus

Of course, the confidence in GalNAcs may rest in the knowledge that ALN-TTRsc is actually the pipeline candidate with the weakest potency, and if IT shows efficacy, it will be a stroll for all the others.  These apparently have proven to be more potent in preclinical studies.  

I consider this a possibility, but am not fully convinced that these conjugates can really be called GalNAc-siRNA conjugates.  This is because the TTR siRNA is a particularly potent one already and I am wondering how you would achieve a 10x increase in potency from ALN-TTRsc to ALN-PCSsc with stabilizing nucleic acid chemistry alone.  Moreover, it is a small miracle already that a simple siRNA with a targeting ligand can achieve ED50s in the low mg/kg, because the related cytoplasmic release would likely rely on spontaneous endosome rupture (miracle probably explained by the high volume ASGPR receptor-mediated trafficking).

Consequently, my feeling is that the GalNAc Plus conjugates involve additional functional moieties beyond stabilizing chemistries such as 2'-o-methyl and 2'-F…such as endosomolytic activities.  In a 2009 patent application by Manoharan et al. (WO 2009/126933) such endosomal release activities, melittin included, were indeed contemplated in the context of GalNAc-siRNAs.  In fact, the claims would cover GalNAc-targeted DPCs such as the one described in the Mirus/Arrowhead in the 2007 PNAS paper (Mirus cientists Publish Elegant Paper on Targeted siRNA Delivery to Hepatocytes).

The patent application, somewhat of an attempt at an early land-grap being devoid of any actual experimental data, is not very remarkable really as it is obvious to somebody skilled in the art that in order to significantly enhance GalNAc-siRNAs such functionalities will be highly desirable, so a lot of it would come down again to chemistry and figuring out which exact compositions are functional and safe.

In my mind, it is fair game to pursue promising (delivery) technologies, especially under the Research Exemption in the US.  However, as the Tekmira-Alnylam relationship has shown, it is foolish for two companies to collaborate on delivery when both are working on GalNAc conjugates internally.  At best, the technology is useless and the whole thing will be forgotten.  At worst, the technology is valuable and both parties will try to control it and not pay the other party their dues.   

Overall, I think that betting the farm on GalNAcs is taking on more risk than warranted considering the advancements and validation achieved with SNALP technology.  Also, if Alnylam considered the subcutaneous approach to be that much more attractive than intravenous, you would think DPCs are the logical fall-back, if not more desirable than simple GalNAcs.  But maybe GalNAc Plus and DPCs are not all that dissimilar and we are on the same page after all.


Note added in proof (March 27, 2013): the ALN-TTRsc clinicaltrials.gov entry has now appeared.  As expected, however, no insights were provided into the dosing range. Only interesting tidbit: the volume of the placebo injection will be matched to that of ALN-TTRsc.  Injection volumes will be critical.

Alnylam Sets Record With $125M Secondary Offering

The $125M stock offering just announced by Alnylam may well be the largest secondary offering in the history of RNAi Therapeutics.  Adding the two VC fundraisings by Gradalis and Solstice earlier this month, it brings the total investment in RNAi Therapeutics by private investors to $167M this January alone!  Compare this to the wide perception a little more than a year ago that RNAi Therapeutics was destined to die and the approx. $21, 57, 40, and 122M raised in 2009-2012 respectively (uptick obviously in 2012).

Thanks to the SNALP-enabled clinical trial results over the last year and the orphan drug tsunami to which RNAi technology, as a genetic one, lends itself particularly well, a few companies have dug their way out to take a deep breath of fresh capital.  

[Update January 16, 2013: Apparently due to strong investor demand, Alnylam announced on Jan15 that it sold 8 million shares at $20.13. Overalottment option of up to 1.2M also fully exercised. Net amount raised: $173M]

Business As Usual?

First of all, Alnylam did the right thing to raise capital when the share price is strong and investor confidence high.  The clinical results have surprised most to the upside, and who knows, the next results may be interpreted as not so exciting, the economy may throw a wrench in the works, etc.  And following the settlement with Tekmira which cost Alnylam $65M immediately and $10M in likely, near-term milestones plus the legal fees, its cash reserves have dwindled faster than the company may have liked ($225M year-end cash).

So as a company rapidly expanding its clinical pipeline to take advantage of the proven ability to knock down genes in the liver, the $125M will most likely be used to satisfy its large, recurring appetite for capital.  Even orphan drug development can get expensive when you adopt quite a few of them.  Thus, the $125M plus/minus to be raised will be good for a year’s worth of operating expenses.  Accordingly, Alnylam did its last offering a year ago.

Keeping a nice cash cushion is one of the smarter things that Alnylam has always done and stands in contrast to other companies’ hand-to-mouth existence, ultimately sustaining painful dilutions and making themselves vulnerable in the marketplace in general (I spare you giving you a rundown of the names).

A Shopping Spree?

Of course, the more fun thing would be to watch Alnylam go on a shopping spree.  While this may seem unwise assuming no other revenue to compensate for operating cash burn, Alnylam has been hitting on all cylinders in 2012 when it came to monetizing IP and marketing rights.  With ALN-PCS02 and ROW rights for Alnylam’s other 5x15^TM programs, you would think that the track record will be maintained in 2013.

While some RNAi assets have gone up in value, most notably the valuations of Tekmira (~$70M market cap, $50M of which in cash) and Silence Therapeutics, with an ~$150M market cap (about $5M of which in cash), there is still quite a bit to be bought with even much less than $125M.

While it is still blowing my mind that Alnylam did not buy Tekmira 5 years ago, Tekmira, for various reasons, will not be on Alnylam’s shopping list if there was one. 

Considering that Alnylam is fully focused on the liver and has recently repeatedly stated that it considers RNAi delivery beyond the liver to be years away from clinical development, according to this logic there really only remains Arrowhead’s DPC technology which has sufficient maturity to fulfill Alnylam’s pipeline needs.  Indeed, the situation between the two companies is somewhat reminiscent to the one between Alnylam and Tekmira about 7 years ago:

Alnylam (GalNAc-siRNA) and Arrowhead (DPCs) compete with each other for subcutaneous delivery of RNAi triggers to the liver, yet Alnylam is looking under Arrowhead’s hood via its collaboration signed a year ago (SNALP-lipidoid analogy). 

If DPC proved to be safe and well tolerated, it would put Alnylam in a vulnerable position e.g. if Arrowhead, also in collaboration with a larger partner or following an acquisition, were to develop competing, best-in-class RNAi Therapeutics.  Does Merck ring a bell?  The situation may be amplified, if GalNAc-siRNAs were to struggle with potency as is the case for ALN-TTRsc with its projected 2.5mg/kg that will just squeeze into the magic 1ml injection volume.   Finally, gaining access to a more potent subQ technology may pay for itself in this case by increasing the value of the assets Alnylam is seeking to partner, including PCSK9.

Will they ever learn?

Arrowhead and Alnylam Vying for Subcutaneous RNAi Delivery Success

The use of the intravenous route of administration for the currently leading systemic RNAi delivery technology, Tekmira’s SNALP technology, has been noted to be a drawback of the technology, especially for non-severe diseases and in therapeutic areas historically dominated by oral medicines (e.g. the cholesterol-lowering market).  As a result, the arrival of two delivery approaches that promise to allow for subcutaneous administration has been welcomed: Arrowhead’s Dynamic Polyconjugates (DPCs) and Alnylam GalNAc-siRNA conjugates which have shown data suggesting their clinical use for gene knockdown in the liver (at least initially; DPC with potential to go beyond the liver).  

A day ahead of Alnylam’s Roundtable on conjugate delivery, I thought it would be a good time to get into the mood and compare the two competing technologies.

Basic Chemistries

GalNAc-siRNAs consist of siRNAs to which a cluster of three N-acetylgalactosamine residues have been appended.  It is these GalNAcs that are recognized by the ASGPR receptor protein that is abundantly presented on hepatocytes.  The choice of three over just one or two GalNAcs is due to the synergistic binding of multiple GalNAcs to the receptor.

DPCs also comprise of siRNA conjugates, but involve an additional endosomolytic agent to facilitate siRNA release from the endosomes.  The two components can be mixed together so that the drug can be given as a single formulation.  This, however, also requires that both siRNA and endosomolytic agent end up in the same place.  For hepatocytes, this is achieved by conjugating the siRNA to a cholesterol moiety and the endosomolytic agent to GalNAc.  

The reason why two different targeting agents are employed are two-fold: reduced competition for the uptake receptor, and not requiring triantennal GalNAcs such as in Alnylam's case which seems to involve a quite costly chemistry. The reason why GalNAcs on the endosomolytic agent in DPCs are not so expensive is because as a polymer (a peptide in the latest versions) multiple mono-GalNAcs can be conjugated distributively and still achieve the same synergistic binding effect.

Potency and Safety

The Holy Grail in RNAi subcutaneous delivery appears to be to get formulations potent enough so that the desired level of knockdown can be achieved with volumes of 1ml or less: you can squeeze only that much liquid under your skin through a thin needle.

The first of Alnylam’s GalNAcs, ALN-TTRsc, achieves a 80% target gene knockdown (ED80) following repeat administration in preclinical animal studies.  This is below the (based on OTS 2012) 3mg/kg barrier that apparently would allow for 1ml or less volumes in humans.  What surprised me to see at the OTS meeting in late October was that the GalNAc potencies, both in rodents and non-human primates, varied quite a bit between the programs.  The TTR formulation actually had the poorest potency among the programs.  This surprised me even more so given that ALN-TTR01 and ALN-TTR02 (both SNALP programs) contained highly potent RNAi triggers.  In the case of PCSK9, ED50 of less than 0.1mg/kg were obtained.

It is possible that the differences are not just due to the natural sequence-specific differences in RNAi potency, but a result of advances in chemistry.  In particular, optimizing siRNA-conjugates for tissue/endosomal stability rather than serum stability as is often practiced in RNAi Therapeutics is critical.  Importantly, this consideration also applies to DPC technology.      

DPCs should be more potent than isolated GalNAc siRNAs.  This is because you are adding an endosomal release agent to the liver-targeted siRNA (e.g. GalNAc-siRNA) conjugate and unfacilitated release of nucleic acid out of endosomes is believed to be highly inefficient.

Arrowhead has reported various impressive potencies such as 99% knockdowns at sub-1mg/kg siRNA doses.  This to me is strong evidence of the superior potency of DPCs over GalNAc-siRNAs.  Moreover, it seems that DPCs may inherently require less frequent dosing compared to GalNAc-siRNAs for which Alnylam aims at weekly or twice monthly dosing.

What is unclear, however, is the amount and resulting safety and volume implications of the endosomal release agent.  In particular, the most impressive knockdown data seemed to involve saturating amounts of endosomal release agent (~6mg/kg).  The first-generation endosomal release agent, PBAVE, suffered from relatively high toxicity, partly as a result of premature unmasking in the blood.  It makes sense that the newer, ‘more natural’ peptide-based endosomolytic release agents are safer.  By contrast, assuming that the GalNAc sugar itself is harmless, I am not too concerned about the safety of Alnylam’s GalNAc conjugates.

In terms of potency, advantage Arrowhead, in terms of safety, advantage Alnylam.

Strategic Considerations

The challenge for Arrowhead will be to make the case of the benefit of increased complexity over GalNAc-siRNAs. Would the prospect of a 3- or 5-fold increase in potency e.g. be enough justification for the investment?  I say ‘prospect’ because Alnylam could obtain knockdown proof-of-concept data at least a year before Arrowhead, especially since Arrowhead is planning to conduct the first study with DPC (ARC-520 for HepB) in healthy volunteers and thus won’t be able to measure viral target knockdown.

In addition to potency, DPC has the important advantage that it may be a more widely applicable RNAi delivery platform.  This alone may tempt others to put some money down on the technology to see where it can go.

Although GalNAc-siRNAs and DPCs are currently clearly competing, there is also scope for them to synergize, especially in the area of oligonucleotide chemistry.  Curiously, Alnylam did seek access to DPCs earlier this year, supposedly for its evaluation in one of its 5x15^TM programs.  Learning about DPC siRNA chemistry may be of at least equal, if not considerably more value to Alnylam.

Which of the two delivery technologies do you prefer for target gene knockdown in the liver?  Take the survey on the top right-hand corner.