Second-Tier RNAi Therapeutics Companies Starting to Deliver Clinically

Alnylam has had a 3 year head-start on the competition with GalNAc RNAi Therapeutics, but now additional companies are populating the field with actual clinical data.  While the knockdowns appear robust and the chemistries well tolerated, therapeutic utility and the potential of liver toxicity from off-targeting will have to be demonstrated in upcoming longer-term studies.

Dicerna clinically validates new target for primary hyperoxaluria

Dicerna used to be the leader in applying RNAi Therapeutics to primary hyperoxaluria (PH), an orphan genetic condition caused by dangerously high levels of oxalate in the blood.  Oxalate crystallization and deposition may then poison first the kidneys and then various organs leading to premature death.  Unfortunately, as its old LNP technology proved to be impractical, Alnylam's directly competing program targeting glycolate oxidase (GO) assumed the lead.

When Dicerna then came up with a GalNAc-based follow-up candidate (DCR-PHXC), it also chose a new target: hepatic lactate dehydrogenase (LDHA), a target which may have be applicable also for forms of PH beyond the most frequently diagnosed PH1 and for which GO is a suitable target.  Cynics may suspect that the new target was not chosen because it is the better one, but in an effort to provide differentiation over more advanced competition.  To wit, first-mover advantage can be significant in the orphan drug arena.

Perhaps due to its long-standing, deep relationship with the PH community, Dicerna has been able to recruit patients more quickly than I had suspected (in light of Alnylam's parallel recruitment efforts) in its first-in-patient study.  First data from this study (PHYOX) were revealed last week.  To their relief, LDHA knockdown resulted in oxalate lowering in all 9 subjects (8 PH1, 1 PH2) tested.

Following a single-dose of either 1.5mg/kg or 3.0mg/kg, at least 30% reductions in urinary oxalate were seen and all or almost all subjects got to urinary oxalate levels at or below 1.1mmol/24hrs/1.73m2, a level predictive of end-stage-renal-disease freedom.

More detailed data will be presented later this year where we will get a better sense in how the results stack up with those of Alnylam.  Earlier this summer, Alnylam reported 64% mean urinary oxalate reductions relative to baseline before following more than one dose.  Another area of concern is that it appears that 3 out of the 9 injections resulted in injection site reactions (ISR).  To see ISRs is not surprising per se, but the frequency appears to be on the high end based on early experience and could be a competitive disadvantage.  Similarly, no word was said about liver enzymes.

Given that Dicerna has been rushing the PHYOX trial without so much as testing multi-dose regimens, I expect the regulatory agencies to demand at least 2 dosing schemes in the upcoming pivotal trials.  A nightmare scenario would see Dicerna being sent back to phase II to test the safety of multi-dosing, a fate that Regulus Therapeutics had suffered before in Europe.

Disclosure: Over the last few months, I have been largely playing the volatility of DRNA- both on the long and short side.  Looking ahead to the end of the year, I would be hesitant of taking a substantial long position due to a market cap approaching $1B with the potential of negative surprises both on safety and efficacy when more detailed PHYOX data will be presented.  On the other hand, a deal (such as on the IND-ready mystery candidate) could provide a catalyst to the upside at least in the short-term.

Arrowhead sees best HBsAg knockdowns so far with new GalNAc candidate

When similar to Dicerna Arrowhead had to retool its lead programs with the GalNAc technology, one question was whether they could achieve knockdowns as potent as with DPC delivery which employed explicit cell penetrating chemistries.  It was therefore cause for celebration when the company reported -2log HBV surface antigen (HBsAg) knockdowns at the World Gastroenterologists Summit, better than with ARC520 and ARC521 before (slides here).  Also, the knockdown was observed regardless of e-antigen status, but that was to be expected with the new sequence design.

Intriguingly, following 3 monthly injections, the knockdown curves still kept coming down, making it almost look like HBV can be beaten into submission by the knockdown effect alone and without the help of an immune boosting effect.

Unfortunately, only HBsAg results from the 100mg and 200mg monthly dosing cohorts were disclosed even though the company had dosed 9 other dosing and patient cohorts.  Based on cohorts 8-11, it appears that best results may in fact have been obtained with the 300mg monthly regimen which will probably be disclosed in the run-up to this year’s AASLD meeting.

Similar to Alnylam in 2014, after showing impressive RNAi target knockdowns in the clinic, the wait is now on to show that the knockdowns will translate into therapeutic benefits.  Given the speed of the company’s execution in general, I would expect pertinent data to emerge from the HBV program in late 2019/early 2020.

Disclosure: similar to Dicerna, I have been recently playing the volatility of ARWR stock, getting long as it had been consolidating around the $14 level, then selling and going short into last week’s 50% spike to a $2B market cap.  With the puts I then sold ($21 and $20 September strikes), I have a ~10% cushion should the stock zoom past $21 by the September options expiration and my max gain is ~13%.  This is intended as a short-term trade

New Arrowhead Data Shows RNAi Ratting Out HBV

When Arrowhead suffered its DPC fiasco a year ago, it got a chance to re-prioritize its pipeline.  It therefore caught my attention that despite the significant theory risk that still persisted, it chose HBV as one of its lead indications.

To wit, knocking down HBV genes promised to re-awaken the host immune system thought to be exhausted in chronic HBV patients.  The HBV surface antigen (HBsAg) had been regarded to be the main culprit for this exhaustion, although other gene products are now thought to play a role, too.

Previous update suggested long road ahead

When Arrowhead left off, clinical data had shown robust HBV gene suppression (~1-2log range) when the RNAi trigger target sites were present (in treatment-naïve e-antigen positive patients).  Curiously, in e-antigen negative patients where many HBV transcripts lack the ARC-520 target sites, a modest, protracted anti-HBV response could be observed.

Unfortunately, data presented this spring at EASL suggested that long, if not chronic RNAi dosing might be necessary since viral rebounds were seen in all but one subject once ARC-520 dosing had been stopped after half a year of treatment.

Chronic dosing, if indeed it can be shown to lead to a reduction of cirrhosis, liver cancer, and death, is conceivable with a subcutaneously administered RNAi agent.  The road, however, to proving such value and broad adoption in the clinic would be harder and longer compared to demonstrating host control of the virus after a finite treatment period.

New update shows host gaining upper hand

Based on the latest data presented yesterday at HepDART, including ~8 months of additional follow-up in the same patients, this may not be the case anymore.  This is because in 50% of the subjects (in 2 out of 3 e-positive and 2 out of 5 e-negative) given ARC-520 along with polymerase inhibitor entecavir, there have been sustained anti-viral responses after the initial rebound. 

In all cases, HBsAg continued trending down until the last time-point reported, and in 3 of these 4 subjects HBsAg was approaching the limit of detection.   Intriguingly, this was accompanied by a modest spike in liver enzymes, consistent with the host immune system regaining the ability to spot and remove infected hepatocytes. 

Of note, the HBsAg declines are more robust (5.0, 3.1, 2.0, and 0.6) and faster than would be expected based on entecavir treatment alone (~0.5log per year).

Since the enzyme elevations generally followed on the heels of the viral rebound, it is possible that treatment cessation and getting HBV to come out of hiding is actually beneficial.  Nevertheless, in the one subject (patient 01-7985) where there was no viral rebound, ALT values still rose.  

Experimenting with treatment schedules will therefore be an important component of future HBV trials.

In the meantime, we can look forward to an update on the same subjects after another few months. Could it possibly be that we are witnessing  the first HBsAg clearances and host control of HBV brought about by RNAi?

HBsAg Rules at International Liver Congress

Now that the HBV world has gathered extensive clinical experience with interferons and polymerase inhibitors (NUCs) and with the resolve to finally find a cure for a serious disease afflicting hundreds of millions worldwide, the hepatitis B surface antigen (HBsAg) has become recognized as the key determinant for treatment outcome.  This is being confirmed by trial after trial investigating combining the actions of both NUCs and interferons, either one after the other or together at once.

Some of these studies were presented at the International Liver Congress last week in Vienna (ILC2015).  Emerging from them are actionable HBsAg rules which can predict fairly well whether a patient will eventually seroconvert to (or at least lose) HBsAg.  No matter the excitement around CRISPR technologies, HBsAg seroconversion remains the gold standard outcome in HBV treatment in the foreseeable future.

These rules can be divided into pre- and post-IFN treatment onset.

In the pre-IFN setting, it is those patients that have below ~500 IU/ml serum HBsAg as a result of NUC treatment that will most likely respond to interferon treatment/immune stimulation with s-antigen seroconversion (see earlier blog entry).  Since NUCs alone hardly do anything to promote s-antigen seroconversion despite its dramatic lowering of viral HBV titers, it appears to be their slow impact on HBsAg levels ( 0.1 log per year HBsAg reduction) that has the synergistic effect with interferon: with HBsAg lowering you take off the foot on the immune brake, with interferon you step on the immmune gas pedal.

As such, HBsAg knockdown by RNA(i) Therapeutics would seem to do the same for interferons as NUCs do, only in a more rapid and potent manner.  Of course, both could be used concurrently as a run-in to IFN treatment.

However, once on IFNs (post-IFN onset), it is the relative HBsAg decline that has high positive predictive value in prognosticating who will seroconvert.  Of note, the HBsAg decline comes before any adaptive immunity can be detected.  This supports that HBsAg decline in itself contributes to seroconversion rather than it being a mere correlation.  In that setting, it is a 1 log decline in HBsAg the first few weeks after IFN treatment onset that separates the winners from the losers. 

It is uncertain to me, however, whether 1 log is a precondition to s-antigen seroconversion as the non-responders do not even come close to that (maybe 0.3log).  It is therefore possible that anything that pushes HBsAg below say -0.3-0.5log could have a dramatic effect on s-antigen seroconversion rates.

An RNAi Therapeutic for HBV used simultaneously with IFNs may therefore aim at helping IFNs to get to the  0.5-1log reduction threshold, and rapidly at that.

Ergo, there are now a number of obvious strategies that one can apply regarding the use of RNAi Therapeutics in HBV with various knockdown goals, both absolute and relative.  The exact strategy would depend on how the RNA agent is combined with polymerase inhibition/NUCs or immune stimulation. 

While a number of other HBV targets were reported at the conference such as core assembly and entry inhibitors, HBsAg (and HBV mRNA knockdown in general) lowering remains the most distinguished and the mechanism predicted to be most synergistic to existing treatment approaches.  As combination treatment is strongly predicted to be the future of HBV, HBsAg lowering should become a pillar of those treatment regimes.

Disclosure: long ARWR, looking for lower entry in TKMR.

Absolute HBsAg Levels, Not Percent Decline May Be Goal of HBV RNAi

I just walked into an early morning session at the International Liver Congress in Vienna and may have learned the most important nugget of information regarding RNAi treatment for HBV.

During the discussion in the ‘Banishing B’ session, Dr. Joerg Petersen referred to clinical analyses to be presented this Saturday showing that patients who achieve HBsAg levels of less than 500, or even better 200 IU/ml and then are given an interferon have a much better chance of eventually losing HBsAg, i.e. being functionally cured, than those that do not.

Dr. Petersen has been involved in clinical studies combining nukes and an interferon, and data presented at last year’s American Liver meeting (AASLD) showed that 9% treated with the combination for 1 year lost HBsAg in the year following combination therapy compared to just 2.8% receiving interferon alone.

Note that currently only interferons are thought to give you a chance of functionally curing HBV by medication and that HBsAg seroconversion attributed to interferon treatment may occur in the years after cessation of interferon therapy.  It will therefore be important to see whether this increase in seroconversion with combination treatment continues to hold up in subsequent years. The nukes are ‘only’ thought to protect the liver from the ongoing damage from HBV replication and may have to be given indefinitely.

I am not sure whether the new insight comes from a fresh clinical study or are the result of a more detailed subgroup analysis of the previous study.  Regardless, it hammers home a message that can be heard again and again, even more so in Vienna this year than at the London meeting last year: it is all about HBsAg lowering.

Implications for HBV RNAi

The implications of the new analysis for RNAi approaches for the treatment of HBV is obvious: use RNAi to get HBsAg below the threshold. In other words, it may be less about getting a magical 1log knockdown, but more about getting patients below 500IU/ml. 

For this, Dr. Petersen recommended using 2 nukes so that the tiny and very slow HBsAg declines observed on nukes continue ( < 0.1 log per year). With RNAi agents, you would likely achieve this goal for a patient with an HBsAg at baseline of 1000IU/ml within a month, even with a single 2mg/kg dose of ARC520 from Arrowhead Research as reported last year. 

The absolute knockdown potency of an RNAi agent would determine which fraction of the HBV population fall within this sweet spot. With a 1log knockdown e.g. you could start RNAi with patients with as much as 5000IU/ml.

For the clinical development of RNAi agents for HBV, the first step will be to determine the HBsAg decline on a background of nukes (just what Arrowhead is doing right now).  For pivotal trials, an immunostimulatory agent such as an interferon should be added to the nukeà RNAi/nuke treatment regimen to finish off the virus.

Stay tuned to learn about the fold benefit of HBV cures in patients falling below the 500IU/ml threshold, and the 3-4mg/kg single-dose results for ARC520 from Arrowhead Research to be reported later this quarter (note to Arrowhead PR department: next Monday may be a good time to do so).

ARC520 for Chronic HepB: The Immune System…It’s Reactivating!

Usually, immune stimulation which manifest itself as flu-like symptoms and the like is something that you do not want to see with an RNAi Therapeutic.  Having said that, there are settings in which you want to see immune stimulations.  This is also the case for the treatment of chronic HBV with a HBsAg knockdown approach. 

ARC520 is the lead candidate in this effort and yesterday the sponsor, Arrowhead Research, presented very exciting data in a chronically infected chimpanzee that had been treated with the RNAi agent.  The data are not only exciting because they presumably represent the fastest reduction of the HBsAg antigen ever seen in a real infection (note: only the chimpanzee is thought to reflect human HBV infection), no, what is even more exciting is that the data are consistent with a HBsAg-specific T-cell immune response.  

As the success of an HBsAg knockdown approach for the treatment of chronic HBV hinges on the hypothesis that by knocking down HBsAg it might be possible for the body to re-activate an adaptive immune response against the virus, the data in my mind are the biggest de-risking event in the development of ARC520.

The data

At the 2013 Liver Meeting of the AASLD in Washington DC, Arrowhead Research presented more detailed data on the chimpanzee that had been treated with ARC520.  Before that we had known that two doses of ARC520 (one of 2.0mg/kg and one of 3.0mg/kg) spaced 14 days apart was able to knock down HBsAg by ~80%, HBeAg by over 90%, and serum HBV DNA by 1-2logs.  The important knockdown here is that of HBsAg, an otherwise ‘undruggable’ target.  Reverse transcriptase inhibitors such as entecavir are not able to meaningfully reduce HBsAg.

The discrepancy of the degrees of HBsAg and HBeAg/HBV DNA knockdowns is likely explained by the prolonged half-life of HBsAg.  Repeat dosing for an extended period of time should lead to even further reductions in HBsAg.  Moreover, the treated chimpanzee was an unusually tough challenge, because old (HBV for over 35 years alone), heavy and with extremely high viremia (>10exp10 genomes per ml). 

Importantly, as predicted by the HBsAg knockdown-immune reactivation hypothesis, there was an apparent T cell-mediated anti-HBsAg immune response shortly after peak HBsAg knockdown levels were reached.  The peak HBsAG knockdown occurred somewhere between ~days 25 and 38 and there was a flare-up in liver enzymes around day 43.   

 

A liver-enzyme flare-up would be expected when anti-HBsAg cytotoxic T-cells start to attack HBV-infected hepatocytes.  Consistent with it being due to a T-cell response, markers of T cell activation, most notably interferon gamma, were also up-regulated around the time of the flare-up.  Interestingly, liver enzyme levels did not fully revert back to normal, but remained somewhat elevated compared to base-line suggesting that the RNAi knockdown kicked into gear a more persistent immune response.

Such delayed dynamics are consistent with what is seen following successful treatment with interferons.  In the ~5-10% of cases where interferons are able to achieve the gold standard HBsAg elimination (in the presence or absence of HBsAg seroconversion), the elimination usually occurs after the ~52 week course of interferon, in many cases years afterwards.

Of course, the present chimpanzee data do not show an elimination of HBsAg.  While I do not exclude the possibility that Arrowhead Research will come back in another 3 months or so to report that the immune system has finally overcome HBsAg, I prefer to keep expectations for such an event low and instead consider the present data as a nice starting point that indeed ARC520 is able rekindle the desired immune response after only two doses over 14 days.

Why it is unlikely to be a non-specific immune response

It is very important here to emphasize that what we are seeing here was not due to a non-specific innate immune response triggered by an immunostimulatory RNAi agent.  Similarly, some RNAi delivery strategies run the risk of causing direct damage to hepatocytes which would also manifest itself by increases in liver enzymes.

The most convincing argument to me is in the timing of the flare-up and cytokine elevations.  While non-specific responses usually occur in the hours and days immediately following RNAi administration, in this case, they occurred 3-5 weeks after the second dose.

Consistent with a ‘clean’ safety profile of ARC520, no such liver enzyme and cytokine elevations were seen in the phase I volunteer study for which Arrowhead reported initial safety data a month ago (2mg/kg highest dose in that study).  Nevertheless, as those data only focused on the safety in the first few days following drug administration for the above reasons and the 30-day follow-up still remains to be reported, one formally cannot exclude the possibility that the unique DPC chemistry is associated with liver damage and the like only weeks after drug administration.  I consider this quite unlikely though.

Going along with this theme, I expect the phase IIa study which will involve infected patients in Hong Kong and is scheduled to initiate enrollment in early 2014 to be ARC520 on top of an RT inhibitor such as entecavir.  As RT inhibitors stabilize the liver of HepB patients and in light of the phase I data, any flare-ups that would be seen in that single-dose study would presumably be the result of HBsAg-specific immune reactivation.  

Lots of exciting catalysts ahead over the next 6 months and who knows, due to intrapatient variability, maybe there will be a cure or two in the phase IIa study already.  

PS: For more background on RNAi knockdown for HBV and ARC520, please visit my cureHBV companion blog.