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.  

The Ebola Clinical Trial a Real ‘Haertetest’ for SNALP LNP Delivery

In German, a Haertetest is a test that challenges the performance of something under the most exacting conditions.  

It is therefore an apt description for the Ebola clinical trial now underway which is testing the safety and tolerability of SNALP LNP delivery following multiple consecutive daily administrations.  This compares to once-weekly and once-a-monthly regimens tested so far.  If SNALP LNP comes out positive from this, it would provide great comfort around the safety and tolerability of the industry’s most potent delivery technology for gene knockdown in the liver, in addition to paving the way towards more biodefense applications.

Teething problems with 1^st gen SNALP LNP

In January 2010, Tekmira reported clinical results from the phase I study of TKM-ApoB, the first clinical candidate employing SNALP LNP technology.  This trial was terminated prematurely due to immune stimulations observed at 0.6mg/kg, a dose at which only minimal target knockdown was observed at that.

This event triggered a healthy amount of soul searching and meant that subsequent SNALP LNP trials had to employ transient immune suppression.  A number of important practical lessons were learned from this.  

Firstly, it showed that the preclinical immune stimulation tests had been inadequate and this prompted the development and adoption of a more predictive test to better screen out candidates that are immunostimulatory before they enter humans.  Secondly, the phase I results were consistent with the notion that the DLinDMA lipid itself (and not just the RNAi trigger), the basis for the 1^st gen SNALP formulations, was immunostimulatory and that new lipids were needed.  And lastly, it highlighted the need to develop more potent SNALP formulations, including new lipids.

Research rises to the challenge

Three years following these events, all three challenges have been successfully addressed.  Today, the potency of SNALP LNP has increased ~30 fold from 1^st gen to 3^rd gen formulations (based on measuring gene knockdown in the liver), with the 2^nd gen MC3-based SNALP generation already with a confirmed 10-fold improvement in clinical potency based on phase I and II results of ALN-TTR02.

Tekmira not shy to ask the tough questions

Despite the progress, detractors of the technology like to point out that (transient) immune suppressions has still been employed in subsequent clinical trials.  With the recent initiation of the phase I study of TKM-Ebola by Tekmira, this has changed however.  Not only that, transient immune suppression has been dropped even as administration intensity is ratcheted up to 5-7 daily administrations. This compares to once-a-month and once-a-week dosing schedules anticipated for SNALP LNP applications involving gene knockdown in the liver and solid cancers, respectively.

The reason why TKM-Ebola necessitates daily administrations is due to the rapid progression of the otherwise fatal Ebola virus.  Therefore, in order to get it approved under the Animal Rule, Tekmira needs to demonstrate the safety and tolerability of SNALP LNP in human volunteers under conditions where they are able to rescue monkeys from succumbing to otherwise fatal infections.  

Moreover, while 0.2mg/kg already provided good protection in the monkey studies (2/3 survival), it was the 0.5mg/kg dose that complete protections were achieved.  0.5mg/kg also happens to be the ‘magic’ dose for SNALP LNPs following which idiosyncratic immune stimulations and other side effects may be expected.

The reason why I am pretty sure that TKM-EBOLA, despite the daily administrations and up to 0.5mg/kg dose, should not involve immune suppression is because it would be incompatible in a viral infection.  There is also no evidence that such pre-treatments are planned in the clinicaltrials.gov entry nor when Tekmira reported the monkey results.  The same considerations apply to the HBV candidate by Tekmira for which an IND is expected by year-end.

Should Tekmira come out of this trial unscathed, it would further de-risk the entire SNALP LNP platform and solidify its position as the most potent oligonucleotide therapeutics technology for gene knockdown in the liver, for hemorrhagic fever applications, and possibly oncology.

Where some see risk, others see opportunity.    

Clinical Experience with RNAi Therapeutics Suggests Class to be Remarkably Safe

One of the biggest concerns in developing an entirely new class of drugs is whether they will be well tolerated. At the height of the TLR scare, it almost seemed that just looking at an siRNA would cause you anaphylactic shock. Nevertheless, after several hundreds of patients have been dosed with probably around 1000 siRNA administrations for diseases affecting the eye, lung, skin, blood cells, liver, solid tumors, and kidney, RNAi Therapeutics have shown a very promising safety profile.

When RNAi Therapeutics candidates have been abandoned, it was mostly not because of safety issues, but for factors such as lack of efficacy, doubts about the mechanism of action of observed therapeutic effects, or changes in the commercial attractiveness of compounds (e.g. wet AMD candidates by Allergan/Merck and Opko). In one case, Tekmira’s ApoB SNALP for hypercholesterolemia, the decision to voluntarily abandon this first-generation ApoB candidate after one patient experienced mild flu-like symptoms, may well have had to do with the fact that much more potent LNPs had already been developed by then and there was thus no point to tempt fate and further dose escalate.

It is not surprising that side-effects related to the innate immune stimulatory potential of nucleic acids were the most frequently cited safety issue in clinical trials. In the case of nanoparticles, complement activation seems to be another area where attention needs to be paid. However, even when formulated with lipids, the currently most potent systemic delivery agents but which are known for their potential to amplify immune responses, patient lives have not been needlessly put at risk and the potencies of both Silence’s cationic lipoplexes and Tekmira’s (neutral) LNPs, especially in light of the significantly improved potencies of 2^nd generation LNPs, may be well within the therapeutic windows for a number of indications.

The most demanding test for the safety of RNAi Therapeutics are the ongoing cancer trials where the ability to dose escalate is the name of the game. Here, all 4 nanoparticle-formulated candidates by Calando, Silence, and Alnylam, seem to be still dose-escalating after having reached dosages of between 0.1 and 1.25mg/kg, dosages where anti-cancer efficacies may be expected based on animal models.

With this type of record, RNAi Therapeutics does not have to hide behind the more established classes of drugs. Even protein-based therapeutics which are highly sought after by Big Pharma and investors these days (well, all is relative) have to deal with a number of immune-related issues, both direct responses of the immune system to their introduction (anaphylaxis, antibody formation) as well as target-based toxicities as most of these drugs work by suppressing the immune system. And similar to protein-based therapeutics, and maybe even more so because they are likely to resemble each other more than protein-based therapeutics resemble each other, with experience the rate of attrition of RNAi Therapeutics due to safety should only decrease over time.