A Defining Month for Tekmira

As if Ebola has not showered Tekmira with enough attention, Tekmira will be front and center in the RNA Therapeutics industry in October.  It will be clinical results from two other drug candidates utilizing Tekmira’s RNAi delivery technology (TKM-PLK1 and ALN-TTR02) and pre-clinical data for TKM-HBV that will define Tekmira's trajectory as a 'normal' biotech company.  'Normal' as I have little idea how Ebola will change all this.

Accordingly, depending on the dataflow, Tekmira could finally be transformed into an established biotech company.  If there are serious disappointments, Tekmira risks being delegated to being 'the Ebola company'.

Event 1 (October 10-11): Do GI-NET patients respond to TKM-PLK1?

The first upcoming data event is the phase IIa update for TKM-PLK1 in gastrointestinal neuroendocrine tumor (GI-NET) and adrenocortical carcinoma (ACC) patients.  This one can be considered a bonus event for Tekmira as barely anybody has been paying attention to the potential of this first-generation SNALP-based product candidate.

 

Results from a  multi-dose escalating phase I study suggested a dose-dependent benefit with patients receiving 0.6mg/kg or more having an increased likelihood of showing ‘clinical benefit’ (stable disease or partial response) than those receiving less of the drug.  In particular, almost all (5/6) GI-NET and ACC patients in that trial with otherwise enrolled across a wide range of cancer types exhibited at least stable disease, with a partial response by RECIST and a 19.3% reduction in tumor size.

One aspect that I found particularly encouraging in these results was that TKM-PLK1 which involves a long-circulating form of SNALP achieved ‘several fold’ increased target tumor concentrations compared to an earlier, short-circulating SNALP product (ALN-VSP02 from Alnylam).   Unfortunately, the precise differences were not disclosed.

The factor that makes me most optimistic about a positive update (--> multiple tumor responses) at the upcoming 7^th Annual NET Conference in Nashville is that there is evidence that SNALP LNP delivery should work particularly well in the GI-NET and ACC settings.  Not only did GI-NET and ACC patients seem to perform well in the phase I study, there have historically been apparent biological effects of other nanoparticulate cancer RNAi Therapeutics in neuroendocrine tumor patients, including cases of extended stable disease with Atu027 by Silence Therapeutics.  

Moreover, the adrenal cortex, and possibly other endocrine structures, seems to be a preferred target organ (next to liver) for SNALP LNP delivery.

What makes me less excited about this program is that TKM-PLK1 is based on fairly old SNALP LNP delivery technology, and wouldn’t it be nice to see the potent PLK1 RNAi trigger being utilized in the latest delivery formulation.

Event 2 (October 13): Does ALN-TTR02 show a therapeutic benefit in TTR amyloidosis?

At the upcoming American Neurological Association’s 2014 Annual Meeting, Alnylam will present first data from its high-profile ALN-TTR02 product candidate that will look not just at target gene knockdown (expected to be in the 80% range), but also whether this translates into an apparent therapeutic benefit.

ALN-TTR02 is an RNAi Therapeutic for the treatment of the FAP form of TTR amyloidosis and uses Tekmira’s delivery technology.  As a result, Tekmira stands to financially benefit from it in the form of development milestone payments and royalties (in the low to mid single-digit percent of revenues) which may reach ~$50-100M annually for this $500M market cap company if analyst projections as to the FAP market prove correct.

The data to be presented comes from the open-label extension (OLE) of the relatively short phase II study.  In this OLE study, Alnylam will look every 6 months how patients are doing according to the mNIS+7 functional score which will then be compared to data gathered from a Natural History study of the disease. 

It is expected that 20 patients that had been rolled over from the phase II study will now have reached the first 6 month time-point.  The phase II study was too short (2 doses spaced apart 3-4 weeks) to reasonably expect an obvious therapeutic benefit from the knockdown of the disease-causing transthyretin gene.

It is important to remember that a failure to see a therapeutic improvement after 6 months with ALN-TTR02 does not necessarily reflect badly on SNALP LNP delivery technology as long as the knockdown remains in the 80% range and is well tolerated.  In that scenario, target risk and an insufficient period of knockdown may be responsible instead and this is where each RNAi Therapeutic has its unique development risk.

My prognosis is that first divergences from the Natural History will be seen if the preclinical experiences and those from other amyloidotic diseases such as AA amyoloidosis are any guide (~50% knockdown and beyond should lead to a benefit).  From a Tekmira technology point-of-view, I will pay close attention as to the safety and tolerability of longer-term dosing, which so far looks quite good.

  

                Event 3 (October 15): Coming out for TKM-HBV

Possibly the dataset with the most impact on Tekmira is the revelation of the company’s RNAi candidate for HBV infection.  Based on data revealed earlier this year by Alnylam which showed a SNALP LNP-based RNAi compound to have multi-log viral knockdown and 2 log HBsAg knockdown in the challenging chimpanzee model with moderate amounts of drug, TKM-HBV is set to become most-potent and therefore hopefully best-in-class among the knockdown approaches by Arrowhead Research (ARC520, first-mover), ISIS/GSK, and Alnylam.

To facilitate cross-comparisons, Tekmira may wish to directly compare its candidate with Arrowhead’s ARC520 for which the structural identity is known.

One aspect that I will be paying particular attention to is whether the data support dosing without transient immune suppression.  This is because I am concerned that such a regimen, especially if it involved steroid use, would not be acceptable in the HBV setting. As you may remember, the company attempted to get away without immune suppression with TKM-EBOLA in a trial in healthy volunteers, but at moderate-to-high dose levels immune stimulations were seen prompting the FDA to put that program on Clinical Hold for the volunteer population. 

Having said that, TKM-Ebola is now being used in much more fragile patients actually infected with Ebola, and anecdotally even the most stringent dosing regimens such as 7x daily appear to be tolerated here, presumably without pre-medication.

As per the last quarterly conference call, Tekmira management seemed confident that TKM-HBV would not require pre-medication.  Since such immune stimulation is thought to be highly sequence-dependent, I do not fully understand their confidence, but maybe a little bit of immune stimulation is not that bad in the Ebola setting after all.

An IND for TKM-HBV is planned by the end of the year with first dosing starting in early 2015.

Buckle up for an exciting month with Tekmira, and if all that weren’t enough, it unfortunately looks like we are still in the early innings with Ebola as being ahead of the curve is a concept foreign to the governing authorities.

Disclosure: long Tekmira.

Regado Biosciences Should Trade Up Over 30% within 3-5 Months

Sometimes Wall Street just needs a bit help to see all the free money around it.  The current share price of Regado Biosciences is one example of that.

As discussed in an earlier blog entry, aptamer company Regado Biosciences recently was forced to permanently hold development of their only asset to speak of, the antithrombotic Revolixys kit, aka REG1.  As a result of that, the company disclosed yesterday that it would wind down all activities associated with this program and conduct a strategic review of the company’s future which the company says ‘could maximize returns for Regado shareholders in the near future’.  

At the end of that re-organization period, projected to be at the end of 2014, the company should have $50-55M in cash and no liabilities to speak of.  The company has 34 million shares outstanding, and given its spectacular 90% drop in valuation over 6 months, there is little risk that this will be diluted much from the exercise of options and warrants.

In other words, the company will have $1.47-1.62 cash per share and is currently trading at $1.17 per share.  That is, the shares are trading at a 20-28% discount to the cash it will have when it can start over its biotech adventure with a clean slate (meaning the shares would have to rise 26-38% to equal cash on hand). 

This 26-38% upside is my base case that I am confident that RGDO will achieve over the next 3-5 months with relatively little risk- just as the result of investors realizing that the discount does not make any sense.  The upside should be much more if management and the Board could find a new biotech asset that can generate some excitement. 

The major risk to this free money scenario would be that class action lawsuits by disgruntled shareholders (who, of course, knew all about the risks involved in biotech investing) will cost the company a significant amount of cash, but in this instance it should be relatively easy to thwart off the ambulance chasers given all that had been known about Revolixys kit, including the rare acute immune reactions seen in phase II.

(Following paragraph added on Sep26, 2014)  A lesser risk (because that only happens once in a blue moon in biotech) to the numbers would be in case the company actually decided to return its cash to shareholders and close up shop.  Under that scenario, the Series F Convertible Preferred Stock Holders would claim and thereby take off $10M from the cash balance.  

You would not believe it, but with the valuations of small biotech companies being quite depressed right now, it is a buyers’ market again for numerous assets.  Given that in similar situations (lead drug has failed, pipeline otherwise weak), biotech companies like Celsion and Oncothyreon have recently opted for RNA Therapeutics assets, and not least because Regado Biosciences is already an RNA Therapeutics company, chances are that the asset will be an RNA Therapeutics one.

Maybe Marina Biotech would be an interesting shop to visit, given that it has a lot of different technologies on offer, has a history of giving away their assets for cheap, and since Marina could use some cash.  Another target might be the RNAi assets of Novartis.

Disclosure: I had been long RGDO at sub $1, but went longer still today after management provided more clarity last night on the Revolixys close-down costs.  It certainly beats the 0.2% interest you might get these days in a savings account. But remember: do your own due diligence before investing.

TKM-EBOLA Making RNAi History

Today, Tekmira disclosed that an acceptable regulatory pathway has been found with US and Canadian regulators to use its RNAi Therapeutic against Ebola infection, TKM-EBOLA, in the current outbreak.  In fact, the company added that 'TKM-Ebola, has been administered to patients on an emergency basis and the repeat infusions have been well-tolerated'.

While not going into specifics, it is more or less a confirmation that Dr Sacra who was said to have received multiple courses of a treatment was indeed treated with TKM-EBOLA (he seems to have pulled through).  Further substantiating that suspicion was a comment by a relative that subsequent administrations of the experimental drug were better tolerated:

'He also tolerated the research drug well – better than he had the previous doses he was given.”'

This is consistent with infusion reactions of many intravenously administered drugs being a particular problem during the first administration only.

Then there was another report that a number of suspected, early cases had been evacuated from Western Africa to the US with the intention of giving them experimental treatments.  This, in fact, would be the ideal setting for using TKM-EBOLA, or for that matter most other experimental treatments against Ebola.  It should be remembered that while in the preclinical monkey studies, the efficacy of TKM-EBOLA started to wane if treatment was delayed for more than 3 days following infection of the animal, this experimental setting is more akin to a needle stick accident in the lab given the large amount of virus involved in the innoculum.

By contrast, in the current outbreak in Western Africa, not every contact obviously leads to a successful transmission of the virus, a reflection of the fact that the starting viral population will be much less compared to the experimental setting.  This means that it would take the virus more than 3 days to overwhelm the capacity of TKM-EBOLA and the immune system to stall the infection in its tracks.  Hopefully, Tekmira is conducting analogous innoculum-window-of-opportunity studies in monkeys to get a better sense of how much treatment can be delayed when infectious doses are quite low.

With this in mind, I am more or less convinced that RNAi Therapeutics is saving patient lives for the first time.  I personally would risk an anaphylactic shock in a closely supervised clinical setting any day over the prospect of not getting specific treatment when infected with Ebola. #RNAiHistory

ProQR Therapeutics- an RNA Therapeutics IPO to Be Enjoyed Responsibly

This week, a new RNA Therapeutics company went public: mRNA repair company ProQR Therapeutics.  This Dutch company from genetics hotbed Leiden sets out to cure severe diseases that are caused by small mutations by repairing the mutations at the messenger RNA level.  First on the list is a treatment for Cystic Fibrosis caused by the 508 deletion.

If Only Science Were Always That Way

The repair is thought to be mediated by the provision of at least two synthetic RNA oligonucleotides (CF4 and CF6 in the image above), a long, modified one (~30nt) with complementarity to the area around the mutation, and a shorter (~10nt), 5’ and 3’-phosphorylated, but otherwise unmodified one of the desired sequence.  Add this to living cells, and hocus-pocus, mutant mRNA is converted into good mRNA.

What makes the publication by Zamecnik et al. from 2004 on which PRO-010 for Cystic Fibrosis is based so amazing, is that by just wishing to repair an RNA and without knowledge of an mRNA repair pathway (note: I’ve considered myself an RNA molecular biologist for close to 10 years, but never came across even the notion of such a mechanism), they obtained the desired results wanted.  Unfortunately, this is not how science works—never. 

In fact, even they considered themselves somewhat lucky, as they had initially thought that the repair first required a third oligonucleotide which by acting via RNaseH mechanism would cleave the target mRNA so that it becomes more amenable to repair ligation reactions.  But when they tried it, it did not make a difference (I would have expected a knockdown), so they stuck with the 2 oligo approach.  Equally amusing was the fact that the phosphorylations were just added for good luck, without any investigation on whether they were useful or necessary.  But as they say, never change a winning team.

Molecular Mechanism Supported Only by Tricky PCR

Most bothersome to me was the fact that the claimed mRNA repair could only be supported after trying out a bunch of PCR amplification reactions, with some reactions suggesting that something might have occurred to the target mRNA. 

As anybody who’s ever work with PCR knows, a lot of strange products are generated during most PCR reactions, either in tiny amounts or less tiny amounts (the infamous PCR artefacts that make lab meetings a fun event).  A related problem is that no conclusions can be drawn from end-point PCRs as used in that seminal paper regarding the amount of these products.  This would have answered the question of whether the phenotypic changes that were reported could be explained by the x % of wild-type CFTR mRNA being generated.

At the minimum, the generation of wildtype CFTR mRNA should have been shown through a hybridization method, not PCR.

Biology’s Best-Kept Secret

As you might imagine, the ability to repair mRNAs with simple oligonucleotides would generate a lot of interest, the type of interest for example that the discovery of RNAi received.   In the case of RNAi, the seminal findings by Tuschl and colleagues that RNAi gene silencing worked in mammalian cells were instantly followed by an explosion of publications harnessing this technology.  Strangely, however, according to GoogleScholar, only 9 papers have cited the mRNA repair publication by Zamecnik et al.  This is explained by most scientists just shaking their heads on reading the publication and then move on, with the more gullible ones failing to reproduce the results.

Laughing All the Way to the Bank

I know that as a scientist I have to be open-minded, but as described above my BS-recognition system, is lighting up bright red.  I  am therefore upset that such science was able to raise $90M in the IPO, valuing ProQR Therapeutics at 300 million dollar- US, not Zimbabwean ones!  On the one hand, I should be glad that financial interest in orphan diseases and RNA Therapeutics is so big right now that this was even possible.  And if you invest according to relative valuations, you will probably do quite well in RNA Therapeutics (Regulus e.g. is worth around the same $300M).  On the other hand, I am always afraid about backlashes from the failures of such companies.  It is therefore important to remember that the qualities of RNA technologies differ vastly in quality from company to company.

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. 

RXi Provides Disappointing Clinical Update for Scarring Drug

At the Rodman & Renshaw investor conference today, the CEO of RXiPharmaceuticals dropped a little bombshell in the form of a disappointing clinical update on their lead clinical candidate, RXI-109 for the treatment or prevention of dermal scarring.  In that interim look for efficacy, RXI-109 and placebo were not really distinguishable in scar severity sending the stock down 30-40% in the middle of today’s trading session.

1301 study design

The 1301 study is the first of three phase IIa studies evaluating 109 in a number of different scar settings.  In this case, RXI-109 was administered following scar revision surgery on the lower abdomen.  Part of the same scar received either 3 injections of the self-delivering RNAi compound, another part placebo solution.  Half of the subjects (50% of the study/16 subjects have enrolled as of today), received 109 on days 1, 8, and 15 following surgery (cohort 1), the other half received injections on days 14, 21, and 28 following surgery, the latter apparently inspired by clinical design trends observed for competitor antisense drug from Pfizer/Excaliard.

I find that blindly adjusting your clinical design based on such competitive intelligence is a worrisome sign of lack of confidence.

1301 study results

The first interim look for efficacy took place at 1 month post-surgery.  Results were based on the blinded visual assessment of scar severity on a scale from 1 (good fine-line scar) to 10 (worst scar imaginable). 

Unfortunately, the close to 50% knockdown of target CTGF observed in a similar 3-dose phase I study, did not translate to an obvious improvement in scar severity: for the immediate treatment group, the VAS score was 2.0 for both the 109 and the placebo side of the scar; for the delayed treatment group, the VAS score was slightly better in the 109 side (2.0) than on the placebo side (2.5) even reaching statistical significance.

Before you get excited and buy into the biological rationalizations by the CEO for why it makes sense that delayed, but not immediate would exhibit such a benefit, note that a VAS difference of 0.5 on a scale from 1 to 10 would appear to be clinically meaningless despite the statistical significance.  Moreover, looking at the VAS scores across the board, it seems that the placebo side in the delayed treatment cohort is a statistical outlier as it should not have performed any different than the placebo cohort in the immediate treatment group.    

On the other hand, given that the scars have not had time to fully develop and the VAS scores were still so low, it is possible that real differences will emerge at later time-points such as month 3 when the next interim look will take place and it may thus be premature to declare the study or drug for that matter a failure.

RXi needs a plan B and investors patience

In light of the disappointing trial update, it may not be a coincidence that Geert Cauwenbergh today took the opportunity to talk more about their other, preclinical pipeline candidates in the dermatology and ophthalmology space in much more detail than had been the case.   

I am less excited about the prospect of RXi expanding their dermatology footprint given the relatively modest gene knockdowns observed, limited tissue penetration from the site of injeciton, and the cosmeceutical nature of their current line-up (acne, depigmentation etc).  By contrast, I am much more excited about  the prospect and value of self-delivering RNAi triggers in the ophthalmology space given the great unmet medical needs there and the highly encouraging tissue penetration/biodistribution data for self-delivering RNAi in that organ.

There will be more to talk about that in the future.  As stock market investors, however, one has got to wonder whether management is aware of that value and knows how to best exploit it (pro tip: VEGF is a no-no for RNAi in the eye).  Even more concerning is the fact that the majority shareholder (Tang Capital) still holds close to half of the company and is in the process of unloading it thereby putting constant pressure on the stock. And with only $10M in the bank, you know what the trip to the Rodman & Renshaw conference was all about.

So no more than a small starter position for me despite the steep sell-off today.

Regado Shock Raises Questions for Oligonucleotide Therapeutics Field

Ave biotech investor, morituri te salutant.

Last week, aptamer company Regado Biosciences imploded in a spectacular fashion after it had to permanently terminate a large pivotal phase III trial of its lead therapeutic program, REG1.   It followed notification that an unacceptable rate of serious anaphylactic adverse events had occurred.

Aptamers are oligonucleotides that recognize their protein targets based on their 3-dimensional shape, instead of sequence complementarity as is the case with most other oligo-based mechanisms of action.  

Because REG1 involves oligonucleotides and pegylation chemistry, the event warrants the close attention of the wider oligonucleotide therapeutics field.  This blog tries to summarize what is known about REG1 and the adverse events and aims to pinpoint potential safety landmines as well as suggest strategies to circumvent them for the benefit of ongoing and future oligonucleotide drug candidates.

REG1 a 2-component system for the tight regulation of hemostasis

The bane of anticoagulant drug development is that too much of it and/or inhibiting clotting at the wrong drug targets can lead to great morbidity and death due to uncontrolled bleeding.  REG1 aims to address this catch 22 by providing an oligonucleotide-based aptamer that binds and therefore inhibits a key regulator of the clotting cascade, Factor IXa, but with the twist that the inhibition can in turn be turned off at will by administering an antisense oligonucleotide that has sequence complementary to that of the aptamer.  This disrupts the 3-dimensional shape of the aptamer thus abrogating its ability to bind Factor IXa.

The aptamer (pegnivacogin) itself consists of a heavily modified 31mer oligonucleotide with lots of 2’-O-methyl and 2’-O-fluoro residues (~10kDa molecular weight).  However, the bulk of the drug is made of a 40kDa polyethyleneglycol (PEG) moiety appended to the 5’ end of the oligonucleotide.  

The antisense oligonucleotide functioning as the antidote meanwhile is an unassuming 15mer 2’-O-methylated RNA, hardly something that would catch the eye of an oligonucleotide toxicologist.

The reason why the aptamer had been modified with PEG was to extend its circulation half-life.  What otherwise would likely be a half-life of a few minutes for a simple 2'-O-methyl/fluoro oligonucleotide, obviously of little use for the intended regulation of blood clotting, could thereby be extended to over 24 hours when administered intravenously (à REG1) or an even more impressive ~1 week when injected subcutaneously (àREG2).

Serious allergic events in REGULATE PCI study

The REGULATE-PCI study that has just been terminated aimed to enroll approximately 13000 (!) subjects undergoing percutaneous (through the skin) coronary interventions (PCI) to unclog arteries around the heart.  Because things tend to clot around devices introduced into the human body and in the presence of physical stresses such as clot disruptions, such procedures have to be performed with the concurrent use of anti-clotting agents (anticoagulants).

The study was terminated when after about one quarter of the target enrolment (~3200), an imbalance in what the company described as ‘serious allergic adverse events’ in its press release was noted by the body tasked with ensuring the safety of clinical trial participants (DSMB).

Unfortunately, I was not able to retrieve a replay of the conference call held by the company to discuss the trial termination to gather more information on the nature of the adverse events.

It is, however, logical to assume that the serious allergic events are the same that had already been noted in the phase II RADAR trial.  Specifically, 3 of the ~500 subjects that received REG1 had allergic reactions ‘shortly’ after infusion of the pegnivacogin aptamer, 2 of which were considered ‘serious’ and in fact led to a stopping of the phase II trial after it was deemed that the study already had enough statistical power.  The affected patients were successfully managed with antihistamines and steroids (Povsic et al. 2013).

Immune reactions not foreign to Oligonucleotide Therapeutics

Immune stimulation, of course, is also the main safety risk of Oligonucleotide Therapeutics as a class.  We are all familiar with injection site reactions, alternative complement activations and attendant cytokine elevations, antibody generation to phosphorothioated oligonucleotides etc.  Some of them, e.g. TKM-Ebola most recently, have led to Clinical Holds or the discontinuation of drug candidates.  On the other hand, thousands of subjects have been given oligonucleotide therapeutics, some for years, with apparently acceptable safety profiles.

So is the oligonucleotide component of pegnivacogin the culprit for the ‘serious’ allergic reactions?

After reviewing the data, the safety issue is unlikely due to the aptamer itself.  A naked, in this case 2’-O-methylated, 2’-fluoro oligonucleotide alone is expected to be very safe, at least in terms of acute toxicity.  This conclusion can be drawn for example from the administration of naked, non-phosphorothioated oligonucleotides, including the systemic programs of Quark Pharmaceuticals. 

On the other hand, the reason for the apparent safety of unformulated oligonucleotides could be simply because such an oligonucleotide is rapidly excreted into urine and therefore has little chance to be toxic.  This is, however, unlikely since the allergic reactions were reported to occur shortly after drug administration, at a time when there would still be considerable concentrations of naked oligonucleotides left in circulation, therefore allowing for such a comparison.

It is interesting that only REG1 has been terminated so far, but not REG2.  Although this shoe could yet drop due to an abundance of caution, it suggests that the serious allergic events are dependent on the intravenous route of administration, a route of administration that is more generally plagued by immune-related ‘infusion reactions’ from small molecules to large biologics.

...enter Omontys...

This brings me to the topic of Omontys, aka peginesatide.  Omontys, of course, is a pegylated peptide that had to be withdrawn from the market 18 months ago following similar (rare) allergic events, including fatalities due to anaphylactic shock.  

Like pegnivacogin, the pegylation in Omontys had a molecular weight of 40kDa.

Like pegnivacogin, there were both intravenous and subcutaneous versions of peginesatide, but only the intravenous version was associated with the severe allergies that occurred shortly after drug administration.  

Like pegnivacogin, the allergies only occurred during the first administration of peginesatide (note: for pegnivacogin there is just 1 administration).

So taken together with the well-known hypersensitivity often seen in response to PEG, the evidence strongly points towards PEG as the culprit, not the oligonucleotide.

Pegylation widely used in RNAi Therapeutics

This unfortunately does not entirely exonerate oligonucleotide therapeutics.  The reason is that pegylation is a widely used tool in the biotech industry, and within Oligonucleotide Therapeutics, RNAi Therapeutics has made ample use of it and promises to support advances in delivery, especially beyond the liver. 

This raises the question of whether such problematic compounds can be spotted earlier.  If not, or if the decision is to continue development, can simple allergy tests identify the subjects that should not get the drug, or would anti-histamine and/or steroid pre-treatment be practical and acceptable?  Or is it even just a manufacturing/quality control issue or a matter of the molecular weight of PEG? I’m sure some of these questions sound familiar to the readers of this blog, and I expect that the field will learn over time if and when to use these and other strategies. 

As both fearlessness and fear can be fatal to drug development and investment returns, it is worth reminding ourselves here that numerous pegylated drugs have been approved and are being commercialized.  Also, there are various degrees of allergic events, some more serious than others.  

Finally, as a former Affymax (and Lehman Brothers in case you wanted to know) investor who lost a few feathers, I and Affymax just were incredibly unlucky.  It is my contention that Omontys would be widely used today if it had not been for the conservative market entry strategy by Omontys-distributor Fresenius Medical Care which involved the close monitoring of the first commercial Omontys patients which picked up the very rare events.  

Also, why simple strategies such as the use of anti-histamines or just going with the subcutaneous version were not attempted to salvage Omontys remains a mystery to me.  Blame it on the damaged goods theory.

  

For the sake of Regado investors and medicine, let’s hope that the parallels end here and Regado won’t follow in the footsteps of Affymax to bankruptcy and class action lawyers.