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 Moves to Increased Dosing Frequency as Knockdown Duration Shortens

The ALN-TTR02 phase II results have finally been announced.  The results are consistent with the view that ALN-TTR02 is a strong candidate for becoming RNAi’s first marketed drug.  Having said that, the knockdown efficacy results came short of what one could have expected based on the phase I and non-human primate results and explain why the company has amended the protocol to test increased dosing frequencies.

Non-human primate studies show cumulative dosing

Alnylam had long telegraphed the results for the phase II studies.  They stated that we should expect the clinical results to be essentially the same as what they are seeing with the drug in non-human primates.  I understand that non-human primates are an immensely insightful model system in RNAi Therapeutics development.  Still, making such strong suggestions just weeks before clinical data release seemed a bit odd in that it risked stealing its own thunder.

Anyhow, the non-human primate studies showed the peak and the terminal knockdown (terminal knockdown defined as the knockdown just before repeat dosing) increased with each additional dose administration.  Whereas the peak/terminal knockdown in cycle 1 was ~85%/47% at 0.3mg/kg, they were ~90%/58% in cycle 2 and so on.  This is what Alnylam refers to as with ‘cumulative’ efficacy.

Unfortunately, this was only partially repeated in humans.

Knockdown not as sustained with repeat dosing

The ALN-TTR02 phase II study represented the first opportunity to rigorously test gene knockdown of a SNALP-delivered RNAi Therapeutic following repeat dosing.  Whereas the phase I study in healthy volunteers was a one-dose study, this phase II study was a 2-dose repeat-administration trial in European patients with TTR amyloidosis (FAP form).  In both studies, target gene knockdown could easily be determined by measuring TTR levels in the blood.

In my analysis of the data, I will stick with slide 10 of Alnylam’s slide set which seems to provide the clearest overview of the data.  At the critical 0.3mg/kg dose level, the peak knockdown either remained +/- the same (~80à80% for once-every-4-weeks) or showed evidence of cumulative activity (~80à88% for once-every-3-weeks) when comparing the first with the second dose administration.  While this looks quite good, albeit somewhat less than what was observed in the phase I study, slide 5), the downside surprise comes with the terminal knockdown values.  Here, the knockdown for cycle one (day 28; n=6) was around 75% with tight error bars, but dropped to 60% for cycle two (day 56; n=5) with much more considerable inter-patient variability.  The same was observed for the 0.15mg/kg dose level with ~53% and ~45% reductions after cycle one and two, respectively.

I have no idea where Alnylam is getting the 93% knockdown from that is so prominently mentioned in the press release.  Are they referring to a single patient that achieved such knockdown?    

Once-every-3-weeks to stay on top of competition

You can safely assume that reduced knockdown duration and the fact that the critical phosphorothioate antisense competitor by ISIS/GSK has a ~70% knockdown have driven Alnylam’s decision to amend the ongoing phase II study by including once-every-3-week regimens.

Data for the first such cohort was provided.  As noted above, once-every-3-weeks showed evidence of cumulative peak knockdown activity thus staying on top of the antisense competition.  It is a shame though that the data provided coincidentally ended on day 35, only a week before the important repeat terminal knockdown point.  It is thus not possible to tell whether diminished terminal knockdown is also an issue for the once-every-3-week regimen.

Safety findings largely related to route of administration  

Safety findings were only reported at the 0.3mg/kg level (4 events in 9 patients).  The infusion-related reaction and the 'nuisance' side effect of fever/chills are known for SNALP delivery, but do not appear to be prohibitive.   Unfortunately, there was a serious adverse event due to a misplacing of the infusion needle.  New to me is the finding of polyuria (peeing a lot). 

Based on this profile, Alnylam will try to lower the amount of immune suppression given with the drug.  Immune suppression is given as a precaution to avoid hypersensitivity reactions seen with SNALP-enabled TKM-ApoB.  It seems to me that in introducing the once-every-3-week regimen, Alnylam wants to dial up the product profile by lessening the burden of the immune suppression.

The future of ALN-TTR02

Given the high unmet medical need for FAP patients, ALN-TTR02 should remain on track of making it to the market provided reduced TTR levels indeed translate into a clinical benefit (a low risk at 80% knockdowns).  Some additional warts, however, have been added to the product profile and my main interest as to the future data will be how efficacy and safety is maintained not after just two, but after 3, 4, 5 doses and so on.  

It would also be good to find an explanation for the diminished knockdown duration (e.g. some neutralizing antibodies or a peculiarity of TTR gene regulation?).  Tekmira, the delivery partner which should receive a $5M milestone on the initiation of ALN-TTR02 phase III studies at the end of this year, would be an important ally in answering this question.  This could therefore be an important test of whether the two companies can put aside past differences.

  

The ALN-TTR02 Phase II Results...Abstract Today, Presentation Tomorrow

The abstracts for the Peripheral Nerve Society Meeting in France have been published.  The abstract on ALN-TTR02 does not reveal the results, but I post them anyway as a warm-up for tomorrow.  You can notice though that there is a relative shift towards the once-every-3-week regimen and the dose escalation started at the same point as the phase I study did (0.01mg/kg).  Check back for more tomorrow.

INTERIM RESULTS FROM PHASE II TRIAL OF ALN-TTR02, A NOVEL RNAi THERAPEUTIC FOR THE TREATMENT OF FAMILIAL AMYLOIDOTIC POLYNEUROPATHY

Adams D1, Coelho T 2, Suhr O3, Conceicao I4, Waddington-Cruz M5, Schmidt H 6, Campistol J7, Pouget J8, Buades J9, Falzone R10, Harrop J10, De Frutos R10, But- ler J10, Cehelsky J10, Nochur S10, Vaishnaw A10, Gollob J10. 1Centre Paris-Sud, APHP, Hopital de Bicetre, INSERM U788, Service de Neurologie, and Centre de Reference des Neuropathies Amyloides Familiales Le Kremlin-Bicetre, France; 2Unidade Clinica de Paramiloidose, Hospital de Santo Antonio, Porto, Portugal; 3Department of Public Health and Clinical Medicine, Umea University, Umea, Sweden; 4Centro Hospitalar Lisboa Norte-Hospital de Santa Maria, Lisbon, Por- tugal; 5Hospital Universitario Clementino Fraga Filho, Rio de Janeiro,Brazil; 6TheUniversityHospitalofM¨unster,M¨unster, Germany; 7Hospital Clinic, Barcelona, Spain; 8Centre de Ref- erencedesMaladiesNaueromusculairesetdelaSLA,Hopital de la Timone, Marseille, France; 9Hospital Son Llatzer, Palma de Mallorca, Spain; 10) Alnylam Pharmaceuticals, Cambridge, MA, USA.

Familial amyloidotic polyneuropathy (FAP) is a fatal, autosomal dominant, multi-system disease caused by abnormal tissue deposition of mutant and wild-type transthyretin (TTR). Almost all circulating TTR is synthesized by hepatocytes, and in FAP this liver-derived TTR is responsible for amyloid accumulation in the main target organs, including peripheral nerves, gastrointestinal tract and heart. Treatment approaches have focused on reduction of amyloidogenic TTR monomer either through elimination of hepatic production of mutant TTR (liver transplantation) or stabilization of the TTR tetramer (tafamidis). While both of these approaches have been shown to slow neuropathy progression in a limited subset of FAP patients with the V30M mutation and early disease, there remains a significant unmet need for new therapies that can impact FAP patients with different TTR mutations across a broader range of disease severity. ALN-TTR02 is a systemically administered lipid nanoparticle (LNP) formulation of a small interfering RNA (siRNA) targeting wild-type and all mutant forms of TTR. This formulation predominantly delivers the siRNA to the liver, thereby inhibiting synthesis of TTR at the primary site of production. In non-human primates, repetitive dosing with ALN-TTR02 every 3–4 weeks at doses up to 0.3 mg/kg resulted in an average relative TTR suppression of up to 90% with no tachyphylaxis of the pharmacodynamic effect. In a randomized, placebo-controlled, Phase I dose-escalation trial in healthy volunteers, a single intravenous infusion of ALN-TTR02 administered over 60 minutes was shown to be safe and well-tolerated, and potently suppressed serum TTR levels by 82-94% at doses of 0.15–0.5 mg/kg. TTR reduction of up to 67% was observed out to 28 days post- dose, suggesting that sustained TTR knockdown could be achieved with a monthly dosing schedule. Based on these promising results, a multi-national Phase II trial of ALN-TTR02 in FAP patients was initiated in mid-2012 to evaluate the safety/tolerability and pharmacodynamic effect of multiple doses of ALN-TTR02. Patients receive two doses of ALN- TTR02 administered every 3–4 weeks at dose levels ranging from 0.01 to 0.3 mg/kg, with a total anticipated enrollment of approximately 27 patients. In this presentation, we will provide an update on the results of this ongoing clinical trial.

Quark RNAi Therapeutics Drug Candidate for Diabetic Macular Edema Effective, but Changing Competitive Landscape Weighs

A lot has changed in the treatment of diabetic macular edema (DME) since Quark sub-licensed its AtuRNAi compound to Pfizer in 2006. Most notably, the monoclonal antibodies against VEGF, Lucentis and the cheaper derivative Avastin, are replacing laser photocoagulation as the standard of care in this condition that adversely impacts the vision of up to 10% of those living with diabetes.

Quark last week reported 12-month data from the phase II study of PF-04523655 run by Pfizer (DEGAS) enrolling 184 patients with DME. The data suggest that the drug was on track of meeting its primary end-point which would have been superior improvements in mean visual acuity at 24 months compared to laser treatment: a 5.8 letter improvement for ‘655 at the highest dose (3mg) compared to 2.4 for laser (p= 0.08). Pfizer, the company that ran the trial, however, decided to terminate the study at this midway point as it deemed that the study objectives could no longer be met.

This is likely at least partly due to the new competition from the Roche/Novartis drug Lucentis that showed 24-month improvements of 12.5 letters versus 2.6 letters for sham control in a pivotal phase III study (RISE). Nevertheless, the efficacy of ‘655 looks much better if one considers that taking into account the 12 month completers only, the improvement was a very promising 9.1 letters for ‘655 versus 3.2 letters for laser. Moreover, the ‘655 data were reported to be dose responsive whereas the Lucentis data were not. Importantly, no serious adverse events were reported, although additional details remain to be reported at an upcoming conference.

Based on this dataset, it seems to me that ‘655 was efficacious, but unlikely to match the Lucentis data with the doses studied even when allowing for more patients to complete the study. Given the encouraging data, Quark decided to run a phase IIb study on its own dime, hoping that with higher doses the efficacy of Lucentis can be matched or even surpassed. This would confirm that the safety profile in DEGAS was satisfactory. In return, Quark would receive increased milestones and royalties should the drug eventually be approved.

Overall, the data are good news for RNAi Therapeutics in ocular indications in general. 3mg siRNA translate into almost a whopping 100mg per kilogram of human eye that were apparently well tolerated in this study (note, however, that the cost of goods for monoclonal antibodies would still be higher even at the current 0.3-0.5mg/injection). This paves the way for improved RNAi Therapeutics candidates with larger therapeutic indexes due to enhanced uptake and at the minimum the same frequency of administration as Lucentis (monthly). Some RNAi approaches, such as attempted by RXi Pharmaceuticals and Eyegate, may even dispense of the need for needle injections altogether. This would be a major differentiating factor.

Moreover, even with comparable single-drug efficacy, safety, and route of administration, ‘655 may be a viable alternative or complement to Lucentis as its mechanism of action is anticipated to be anti-apoptotic (stabilizing the blood-retina-barrier) instead of anti-angiogenic (preventing abnormal blood vessel formation). However, as indicated in my somewhat less optimistic blog entry last week, this is yet to be convincingly proven given the possibility that ‘655 may have at least partly worked through a non-RNAi mechanism. Demonstrating synergistic action in some animal models would go a long way in showing this.

For investors of Silence Therapeutics, I consider this better-than-expected data as they keep the drug alive and demonstrate the safety of the AtuRNAi design. How the new terms between Quark and Pfizer will affect Silence’s financial stake in the program and whether the present result will trigger any immediate payments, remains to be seen.

Update from March 18 Quark registration statement: In the parallel study of '655 in wet AMD, an interim analysis has shown improvements in mean visual acuity over 3 month period, but at 4 months, the primary endpoint, no numerical benefit over Lucentis was seen in any of the doses. The trial will be continued with full data expected in the second half of 2011.

ALN-RSV01 Update: The Drug is Safe- and Efficacious?

Alnylam provided this Monday an update on their phase II study results of ALN-RSV01 in lung transplant patients naturally infected with respiratory syncytial virus (RSV). RSV infection in lung transplant patients is linked to irreversible damage of the lung, decrease in quality of life, and sometimes even death. With no proven drug for the treatment of RSV, this remains an area of high unmet clinical need.

The 90 day data follow results announced in June that showed the drug to be well tolerated and adds to the growing evidence of safety obtained with this drug in various phase I and II studies. While safety was the primary objective, based on the initial 30 day data report no conclusions could be drawn on the efficacy of the drug as measured by either reduction of RSV titers or symptom scores due to differences in baseline characteristics between the drug-treated (N=16) and placebo control-treated populations (N=8).

The 90 day data confirmed the safety of the drug that was administered 3 times daily via inhalation. The longer time period also allowed for monitoring lung function. Remarkably, while lung function was significantly impaired in about one third of both the drug and control populations at the start of the study, most likely as a result of the RSV infection, at 90 days after drug treatment only 14% of the ALN-RSV01 patients experienced an FEV1 value 20% below baseline compared to 38% in the placebo group. While this did not reach statistical significance in this small study, when another related measure of lung health was considered, namely the incidence of new or progressive BOS (bronchiolitis obliterans syndrome), ALN-RSV01 did significantly better than control (1 in 15 patients for ALN-RSV01 versus 4 in 8 patients of placebo).

Taken together, the drug was shown to do no harm and there is intriguing evidence for clinically relevant efficacy of the drug in a randomized, double-blind trial, albeit somewhat tainted by the baseline differences. The difficulty of running such a trial is illustrated by the fact that 13 institutions around the world were involved and I cannot see a regulatory body requiring a 200 person lung transplant trial when there are only about 2000 lung transplants a year and only a fraction of those actually becomes infected with RSV. The results are certainly better than the standard of care today, ribavirin, which has unproven efficacy at least in this setting and is well known to be toxic. Transplant surgeons certainly would love to have another treatment option, even if only supported by such data. Therefore, is there a case for Alnylam and their co-development partners to talk to the FDA about approving ALN-RSV01 in this orphan patient population (compassionate use argument), maybe after further follow-up confirm the positive trend in improving lung function which has to be the ultimate measure of treatment success?

It would be ironic for the FDA e.g. to deny such a request due to the difficulty in interpreting the RSV biomarker results while the medically relevant outcome, lung function, showed positive results. Normally, the agency rejects drugs that although the biomarkers were positive (e.g. blood sugar and cholesterol), more direct clinical outcomes were not.

Needless to say, such an outcome would be unexpected, but it does not cost much to ask. In any case, for the wider application of RNAi Therapeutics in lung disease it is comforting to see that the inhalation of unmodified siRNAs even in this fragile population was so well tolerated and it will be interesting to see how the RSV program, sometimes criticized for its seemingly labyrinthine course, will unfold.

Pfizer and Quark Progress RNAi Therapeutic for Diabetic Macular Edema into Phase II

Quark Pharmaceuticals today announced that development partner Pfizer has initiated dosing of the first patient in a phase II trial of the RNAi Therapeutic candidate PF-4523655/RTP801i-14) for diabetic macular edema (DME). The start of the phase II trials is a vote of confidence in RNAi Therapeutics for eye diseases by a major pharmaceutical company with a considerable eye care franchise and growing ambitions in RNAi Therapeutics.

The 160-person safety and efficacy trial follows phase I/II studies conducted by Quark that showed the drug to be safe and well tolerated in patients with wet age-related macular degeneration (wet AMD). Similar to DME which affects about 10% of type I and II diabetics, wet AMD is caused by the growth of leaky blood vessels in the back of the eye leading to blurred vision, and in some cases blindness. For this reason, it is not uncommon that a given compound is being tested for both indications.

The reason that Pfizer has chosen DME instead of wet AMD as the indication for this trial may be related to the fact that the wet AMD RNAi Therapeutics space has become crowded with Opko Health and Sirna Therapeutics/Merck having wet AMD RNAi Therapeutics in phase III and II studies, respectively. Opko Health also has a phase II study for DME using the same compound. It may also be related to the recent controversy caused by a Nature paper that showed that dsRNA-triggered immune responses alone may be anti-angiogenic in a mouse model for wet AMD and that this may have led to mis-interpretations of data from related pre-clinical RNAi Therapeutics studies.

However, PF-4523655 is unlike Sirna’s and Opko’s compounds in that it is intended to prevent abnormal blood vessel growth and leakage in a VEGF-independent manner. It is also a 19bp blunt-ended compound and therefore unlikely to trigger non-specific TLR3 responses (21bp seems to be the cut-off where you have to take TLR3 signaling into account). I trust that the former Coley Pharmaceutical’s folks with their deep understanding of TLR biology and that are now running the RNAi Therapeutics show at Pfizer will have closely looked at the issue.

Quark received an undisclosed amount for the initiation of the trials, Silence Therapeutics which had originally licensed the AtuRNAi technology to Quark collected $1.9M, and Alnylam from which a technology license was subsequently obtained on Pfizer’s insistence another undisclosed amount. Clearly, with today's allowance of Silence Therapeutics’ 10/633630 patent in the US which specifically claims AtuRNAi molecules of 18 or 19 base-pairs the IP battles are about to begin, and will be addressed in a follow-up blog entry. In any case, it is an interesting coincidence that the initiation of the phase II studies and the patent allowance occurred on the same day.

Independent of all these patent issues, I look forward to the results of this compound which has the makings of a safe and differentiated RNAi Therapeutic for DME.