Oligonucleotide Therapeutics Need to Embrace New Genomic Era in Cancer Medicine

With ASCO 2014 behind us, I am left with the impression that oligonucleotide therapeutics have failed to keep pace with important developments in cancer drug development.  Most importantly, cancer oligonucleotide therapeutics need to take advantage of the latest genomic tools and insights in cancer biology to select the patient populations most likely to respond treatment to both increase success rates and to save development dollars.  After all, this is what you would expect from a platform most suited to personalized medicine.

In some cases, drugs are being developed a priori with specific mutations in mind such as the selective EGFR-mutant inhibitors by Clovis Oncology and AstraZeneca which have caused quite a stir amongst clinicians and investors at ASCO.  In other cases, and this is something spearheaded by companies like Foundation Medicine and their pharmaceutical partners, comprehensive next-gen sequencing is employed as trials progress to identify often complex signatures that render a cancer susceptible to a treatment. 

And particularly relevant for delivery aspects, other companies such as Endocyte are using imaging diagnostics to identify those cancers that either express the right surface receptors for a ligand-targeted agent or those amenable to the EPR effect relevant for nanoparticle-based delivery.

Although I believe that Tekmira has also a delivery-related rationale in selecting adrenocortical carcinoma and neuroendocrine cancers for TKM-PLK1 based on their insights in liposomal delivery, the oligonucleotide field at large is failing to take advantage of delivery-related cancer selection strategies.

In terms of tumor response related to hitting the right targets and pathways, I would like to see the field embrace the personalized genetics approach.  Prospectively targeting KRAS mutant colorectal cancers with a PLK1-RNAi therapeutic would be one example.  Going one step further, a development strategy that looks at the genomic profiles of various cancers and then pull out the formulation with the right RNAi trigger or antisense oligo against critically activated pathways would play into the strength of the technology: every signature is ‘actionable’ as the technology leaves no target behind.

Especially for delivery approaches that can penetrate tumors well, innovative cancer development could unlock the considerable potential that oligonucleotide therapeutics have for oncology.  Beyond TKM-PLK1, the androgen receptor antisense compound by ISIS/AstraZeneca could be an important first test case for this concept in oligonucleotide therapeutics.

ASCO for RNAi Therapeutics in Line with Expectations, but Curious Nevertheless (Part II- Atu027)

With some delay, only mirroring the strange delay by the sponsor company, Silence Therapeutics, in disseminating the results, here are my thoughts on the Atu027 phase I results presented at this year's ASCO and some speculations on the potential corporate fate of Silence Therapeutics.  

For part I (ALN-VSP02 ASCO discussion) here.

AtuPLEX Delivery Tech Tolerated Up to Twice Dose Required for Endothelial Knockdown

In retrospect, the phase I Atu027 surprised to the upside, especially in that the relatively ‘unsophisticated’ (some would say simple = elegant) AtuPLEX formulation used was apparently well tolerated in humans at doses well above where we would expect target gene knockdown in endothelial cells, the target cell population of this RNAi delivery technology: the 0.18mg/kg in this study yielded plasma siRNA concentrations where noticeable knockdown was seen in preclinical monkey studies in endothelial cells, and 0.336mg/kg is the recommended dose for further studies.   

I should caution, however, that the PK data are strictly inferring endothelial cell knockdown in the lung (of monkeys) to knockdown in tumor endothelia.  Although the data indicate that AtuPLEX (unlike e.g. DACC for lung endothelia) has a fairly broad target spectrum of endothelia in various tissues, there are some slight differences.  

On the downside, this study in patients with advanced solid tumors failed to provide striking evidence that Atu027 has indeed anti-tumor efficacy.  Although not a primary goal of this dose-finding dose escalation study, with only a paucity of efficacy-related data collected in this trial (in stark contrast to Alnylam’s heroic efforts with ALN-VSP02), it would have been comforting to see more evidence of efficacy besides the two reported regressions of a lung and a liver met plus the ‘stable disease responses’ -which really mean little in the absence of a control group.  The biomarker data were certainly curious, but without disclosing the full dataset could have been as well a cherry-picking exercise.  On this note, I also would have liked for Silence Therapeutics to disclose the full PK dataset.  

Besides for the small patient numbers (33), an explanation for a possible failure to see anti-tumor efficacy could be the choice of target gene, PKN3 (downstream of PI3K), which is a new clinical molecular target in the oncology arena.  On the other hand, I am pleased to see others in the blogosphere point out that the choice of a higher-risk target may be more than compensated for by the differentiation value it brings.  So in this case, you not only have an RNAi mechanism of action, but also the drug target as two major value-adding differentiating factors (see the March of the Lemmings by Bruce Booth).  But if target choice eventually turned out to be a problem here, the Atu027 PK results represent an important de-risking for the AtuPLEX delivery platform.   

Financial worries to the fore 

I’m sure many will be happy that this trial has finally wrapped up (last patient dosing expected later this month).  However, this also means that the focus will now be on a much-feared financing; feared, because the last financings by Silence Therapeutics have been catastrophic to existing shareholders. It is a shame that Silence Therapeutics has failed to obtain any non-dilutive funding despite numerous opportunities.

Along with the disclosure of the ASCO presentation, the company thus announced in an quite unusual move that ‘advanced discussions’ were under way to raise 4-5M UK pounds.  Judging from the previous fund-raisings, this may well double the share count.  Despite such a dilutive capital raise, the terms for which would more likely than not be dictated by the new investors, it would still be preferable over a Marina Bio-style cash crunch.  Actually, from where I sit in my armchair, a combination between the two ‘second-tier’ players Silence Therapeutics and Marina Biotech does not look that illogical as long as can find ways to further cut down on cash burn.  Note that some of Marina Biotech’s important business relationships are with European companies: Debiopharm, Girindus, Novosom tech and IP, usiRNA IP from Denmark etc etc.  

I'll be watching intently as to what the next move will be...

ASCO for RNAi Therapeutics in Line with Expectations, but Curious Nevertheless (Part I- ALN-VSP02)

Alnylam and, finally, Silence Therapeutics have by now disclosed the latest results from the phase I studies of their RNAi Therapeutics candidates, ALN-VSP02 and Atu027, for solid cancers at this year's ASCO.  As the studies have thus more or less come to a conclusion, one has to say that, although clearly nothing spectacularly positive came out of them, these two candidates warrant further evaluation and their safety and pharmacokinetic profiles augur well for the other candidates based on the same SNALP and AtuPLEX delivery platforms.  

With most of the results known, I will therefore focus my discussions of the RNAi Therapeutics ASCO 2012 on the new insights and include some comments on recent corporate maneuvers of the companies involved.

  

ALN-VSP02 Provides First Insights into SNALP Repeat Dosing (and yes, SNALP technology belongs to Tekmira and AlCana is an instrument of Alnylam)

The extension study with ALN-VSP02 that was the subject of Alnylam's ASCO poster presentation included 7 patients with cancers involving the liver that had been rolled over from the main study (results presented a year ago here) and provided more insights into the long-term safety/tolerability of SNALP delivery technology.  It was good to see that even very sick patients could be given 1^st generation SNALP formulations at dosages of 0.7mg/kg or more every other week for quite prolonged periods of time (up to 2 years).  As the phase I results with ALN-PCS02 indicate, such concentrations will allow for solid gene knockdowns in normal liver cells with some of the improved SNALP formulations. When I first got excited about SNALP delivery technology 6 years ago, one of the main risks that I saw was around repeat-dosing including antibody formation against the PEG component and other immune stimulations upon repeat dosing.  On that front at least, the ALN-VSP02 study, especially based on the PK data, was a clear pass. 

Certainly, there remains controversy around whether the precautionary transient pre-treatment with immunosuppressives (e.g. corticosteroids) that was applied here and may have aided in achieving these results is a realistic product feature of a RNAi Therapeutics.  As I have said before, personally I believe that for severe indications such as many cancers, this is mostly a minor practical inconvenience; it may, however, impede their adoption for less severe conditions in larger patient populations.

One new safety-related item worth mentioning is the reported effect of prolonged ALN-VSP02 administration on spleen size and Alnylam’s interpretation thereof.  As we know, the spleen is a non-essential organ in humans and the vast majority of us would not notice if we were without one.  Thus, the reduction in spleen size observed in this trial with prolonged treatment was not considered a severe adverse event or dose-limiting toxicity.  Spleen toxicity would not really be surprising for nanoparticle-formulated drugs such as ALN-VSP02 (and also phosphorothioate-based oligonucleotide therapeutics) as they are often observed in animal studies.  I therefore considered it possible that it could be a platform-based toxicity.  

Alnylam, however, put forward a more optimistic interpretation by claiming that it is more likely an on-target toxicity, meaning that knockdown of the proliferative gene KSP in the spleen was responsible for it.  Considering the biodistribution of SNALP and the recently highlighted data on SNALP and other LNP-mediated gene knockdown in immune cells that are enriched in lymphoid organs such as the spleen, this is certainly a plausible explanation as well and is further supported by the new monkey data presented at ASCO.  Adding to this confusion is the fact that ‘Alnylam’ has been developing 3^rd generation SNALP technology to ameliorate spleen toxicity.  So if the spleen shrinkage was no general effect, why bother with 3^rd generation?

Aside from these scientific developments, including a very nice complete response by RECIST in an endometrial cancer patient with multiple liver mets which had already started to respond during the main phase of the trial, my interest was equally piqued by the fact that the press release by Alnylam lacked any mention of the fact that ALN-VSP02 involves critical delivery technology by Tekmira and that key IP of a siRNA ingredient may also well belong to Tekmira, pending the outcome of an Interference proceeding in the US.  If you look for even more support for Tekmira’scontention that Alnylam has been aiming to marginalize the company, and as yet another of Alnylam's main rivals, Marina Biotech, looks like it is going out of business (my bet is that they will participate in some kind of consolidation to survive in another form), look no further.  The PR is only rivaled in silliness by the misleading one issued by Alnylam’s Canadian subsidiary, Alnylam Canada (AlCana), two weeks ago on the status of the Tekmira-Alnylam showdown in Canada (the misleading part being in quite obviously trying to suggest that the Canadian courts reversed all earlier decisions that went against AlCana, including handing over the allegedly stolen documents back to their rightful owners, Tekmira). 

But the real clincher of that PR was the following: despite of pointing out the elephant in the room, namely that the Canadian proceedings are part of a wider confrontation between Tekmira and Alnylam, Alnylam Canada hilariously and awkwardly at the same time failed to mention Alnylam at all- in the entire press release!  If they believed that this would make AlCana, a de facto academic lab financially supported and strategically instructed by Alnylam all along, any more independent of Alnylam, try again (note: a key element in the litigation is that Alnylam established an ‘independent’ company- AlCana- to gain insights into key Tekmira trade secrets and know-how thereby minimizing legal liability if caught).  More unintended humor was provided by stating that the Canadian case had been post-poned until resolution of the US case between the ‘corporate’ parties, implying that neither AlCana nor the courts consider AlCana to be a true, independent corporation.  Although I have not had the chance to read the primary court documents myself, the decision strongly suggests that the Canadian court took pity on the AlCana scientists and does not like to see them being thrown under the bus by their de facto employer, Alnylam.

In part 2, I will cover the latest data on Atu027 and share some thoughts on the confusing corporate strategies of that company.

ASCO 2012: Silence and Alnylam Provide Update on RNAi Therapeutics Candidates for Solid Cancer

It is this time of the year again when abstracts for the upcoming ASCO mega-cancer meeting are released (ASCO 2012 in Chicago, June 1-5).  Among the poster abstracts were phase I updates for Atu027 by Silence Therapeutics and ALN-VSP02 by Alnylam for advanced solid cancers and cancers with liver involvement, respectively.  Although the full details are yet to be presented at the meeting and the abstract date was in early February (this particularly means that critical data from the high-dose cohorts for Atu027 are missing), I will post here the abstracts as appetizers, each one followed by some brief comments. Highlights are mine.

 

Abstract No. e13597 by Silence Therapeutics

Antimetastatic activity of Atu027, a liposomal small interfering RNA formulation, targeting protein kinase N3 (PKN3): Final results of a phase I study in patients with advanced solid tumors.

Sub-category:
New Targets, New Technologies

Category:
Developmental Therapeutics - Experimental Therapeutics

Author(s): Dirk Strumberg, Beate Schultheis, W Meyer-Sabellek, C. Vank, F Gebhardt, A. Santel, O. Keil, K. Giese, J. Kaufmann, Joachim Drevs; University of Bochum, Marienhospital Herne, Department of Internal Medicine III, Herne, Germany; Silence Therapeutics AG, Berlin, Germany; Tumorzentrum UniFontis am Eduarduskrankenhaus, Köln, Germany

Background: Atu027 contains siRNA-lipoplexes, which elicits RNAi mediated suppression on PKN3 in vascular endothelial cells. In various xenograft mouse models, silencing of PKN3 expression and significant inhibition of invasive growth, lymph node and pulmonary metastasis formation was shown. Methods: Atu027 was applied to patients (pts) as a single 4h-infusion with subsequent follow-up for 3 wks. Thereafter pts were treated twice weekly for 4 weeks. In case of SD, pts were treated until PD. Dose escalation was associated with assessment of toxicity, pharmacokinetics (PK), and multiplex biomarker analyses in plasma from treated pts. Results: A total of 33 pts have received Atu027 of 11 dose levels (DL) up to 0.336 mg/kg. No pre-medication was required. No cytokine activation (TNF-α, IL-1β, IFN-γ, IL-6) was observed. In some subjects transient activation of the complement system (C3a, Bb, sC5b-9) was found, but without any clinical relevance. PK-data showed dose-dependent increase in plasma siRNA as well as lipid levels. Among various biomarkers tested, sVEGFR-1 plasma levels decreased significantly upon treatment. Across all dose levels, Atu027 was well-tolerated. Adverse events possibly related to Atu027 were fatigue grade G1 (6pts), hair loss G1 (2pts), sweating G1 (1pt), and abdominal pain G2 (1pt). G3 AEs not considered as DLTs were elevated lipase (2 pts, DL2+DL10) and diarrhea (1 pt, DL5). So far, no DLTs were seen in the last DL. Stable disease after 3 and 6 months was observed in 10 and 3 pts, respectively. Two pts with neuroendocrine cancer had disease stabilization for 9 and 12 months, respectively, including partial regression of pulmonary metastases in 1 pt. Another patient with breast cancer had regression of liver metastases.Conclusions: Atu027 is well-tolerated and anti-metastatic activity has been observed. Soluble VEGFR-1 might serve as a biomarker. So far, 0,336 mg/kg is the recommended dose for further phase II trials.

Comments: Importantly, dose escalation in this dose-finding study could proceed to the second highest planned dose level (0.336mg/kg), which at least based on the previously presented PK data should be well above the dose necessary (~0.25mg/kg) for obtaining solid target gene knockdown in endothelial cells.  As 0.336mg/kg was dose cohort 10 (up to 11 planned) and 33 patients have been dosed, this means that one cohort probably included 6 instead of 3 the subjects. I am curious to learn the reason for this in June and particularly will be looking for more insight on the complement activations which have been described to be ‘without any clinical relevance’.  Also of interest is that the soluble version of the VEGF-receptor 1 was found to decrease significantly upon treatment (maybe as an adaptation to an anti-angiogenic mechanism of Atu027?) leading the company to speculate that this could serve as a biomarker in future trials.  On the efficacy front, still nothing really conclusive can be said and there were no additional ‘hints’ of efficacy in the higher dose cohorts as one might have hoped.   Overall, however, I look forward to the updated and fleshed-out data in 2 weeks.

For a discussion of the Atu027 results at last year’s ASCO meeting, click here.

Abstract No. 3062 by Alnylam Pharmaceuticals

Sub-category:
New Targets, New Technologies

Category:
Developmental Therapeutics - Experimental Therapeutics

Author(s): Maria Alsina, Josep Tabernero, Geoffrey Shapiro, Howard Burris, Jeffrey R. Infante, Glen J. Weiss, Andres Cervantes-Ruiperez, Mrinal M. Gounder, Luis Paz-Ares, Rick Falzone, Jamie Hill, Jeffrey Cehelsky, Akshay Vaishnaw, Jared Gollob, Patricia LoRusso; Molecular Therapeutics Research Unit, Vall d'Hebron University Hospital, Barcelona, Spain; Dana-Farber Cancer Institute, Boston, MA; Sarah Cannon Research Institute, Nashville, TN; Virginia G. Piper Cancer Center at Scottsdale Healthcare, Scottsdale, AZ; Department of Hematology and Medical Oncology, INCLIVA, University of Valencia, Valencia, Spain; Memorial Sloan-Kettering Cancer Center, New York, NY; University Hospital - Virgen del Rocio, Seville, Spain; Alnylam Pharmaceuticals, Cambridge, MA; Karmanos Cancer Institute, Detroit, MI

Background: ALN-VSP02 is an RNA interference (RNAi) therapeutic comprised of lipid nanoparticle-formulated small interfering RNAs targeting vascular endothelial growth factor (VEGF)-A and kinesin spindle protein (KSP). In a phase 1 trial, ALN-VSP02 administered as an iv infusion q2 wks was well-tolerated and showed evidence of anti-VEGF pharmacology and antitumor activity. Methods: Patients treated on the phase I trial with stable disease (SD) or better after 4 months (8 doses) were eligible to continue on an extension study until disease progression. Main objectives included continued evaluation of safety/tolerability and assessment of disease response. Results: Seven of 37 patients (18.9%) evaluable for response went onto the extension study, including 1 of 7 (14.2%) at 0.4 mg/kg, 2 of 5 (40%) at 0.7 mg/kg, and 4 of 11 (36.3%) at 1.0 mg/kg. All had progressed after one or more prior therapies. Tumor types included head and neck squamous cell carcinoma, angiosarcoma, endometrial cancer, renal cell carcinoma (RCC, N=2), and pancreatic neuroendocrine tumor (PNET, N=2). At the time of enrollment, 6 had SD and one (endometrial cancer with multiple liver metastases) had an unconfirmed partial response (PR). The average length of time on treatment (including phase I and extension studies) was 9.5 months (range 5-19). As of January 2012, 3 patients remain on study, including the endometrial cancer patient with an ongoing PR who has had >80% tumor regression after 19 months of treatment at 0.7 mg/kg and two patients with RCC and PNET with continued SD after nearly 1 year of treatment at 1.0 mg/kg. The other patients with RCC and PNET at 1.0 mg/kg with SD came off after 8.5 and 5.5 months, respectively, for adverse events that included fatigue or elevated alkaline phosphatase. A decrease in spleen volume, likely an on-target effect and not associated with any adverse events, occurred to a greater degree on the extension study than on the phase I trial and was most pronounced in patients receiving ≥ 12 doses. Conclusions: ALN-VSP02 has preliminary activity against endometrial cancer, RCC and PNET and a favorable safety profile that permits chronic dosing. Phase II trials are warranted in these and other VEGF-overexpressing tumors.

Comments: Final results for this study were presented at last year’s ASCO meeting (for a discussion click here). The new data relate to the open-label extension phase which is of particular interest as it relates to the longer-term safety and tolerability of ALN-VSP02, and possibly first-generation SNALP delivery technology in general.  It is too early to tell to what extent siRNA sequence and modification-dependent effects played a role, but the apparent spleen toxicity is consistent with what one might expect from such formulations. Although the spleen is not an essential organ and most of us will do just fine without one, this could become a dicey issue for a chronically dosed drug like ALN-PCS02 in a ‘lesser’ disease such as many types of hypercholesterolemia.  Overall, however, this is an encouraging start for the longer-term safety of SNALP delivery technology.  Based on the indications of efficacy, another more focused study may be warranted before a final determination as to the viability of ALN-VSP02 for the treatment of cancers with liver involvement.

Silence Therapeutics Reports at ASCO 2011 that Atu027 has Achieved Important Pharmacokinetic and Safety Endpoints

On Monday at ASCO 2011, Silence Therapeutics provided an extensive update on its ongoing phase I trial of Atu027 for the treatment of advanced solid tumors (additional background on Atu027 and the current study provided here and here). While there are a few signs already that the drug candidate may have some anti-tumor activity, the even more important message was that Atu027 has been remarkably safe and well tolerated, while reaching drug exposures in the ongoing dose escalation at which, based on the pre-clinical experience, bona fide RNAi knockdown of the targeted gene can be expected.

In cancer drug development in particular, the name of the game in phase I trials is to test how much drug can be given without causing severe, dose-limiting toxicities. Often, in studies like this one, patients of highly varied, late-stage cancers are enrolled and too few of them are treated at the high dose levels. In that regard, the trial progress can be called quite satisfactory in that no dose-limiting toxicities were reported and the SAEs judged as unrelated to study drug. The most commonly reported side-effect was minor grade 1 fatigue. It is possible that this is drug-related, although many cancer patients suffer from fatigue for many reasons. Also of note, and as indicated in the abstract, the observed complement activations were transient and not clinically significant.

Making the safety findings even more meaningful, the measured pharmacokinetic data indicate that the drug was safe at concentrations in the blood where RNAi knockdown can be expected based on the preclinical studies in rodents and monkeys and the known knockdown potency of the RNAi trigger in tissue culture cells.

There were also preliminary signs of anti-tumor efficacy. 9 of the 24 patients had stable disease one week after receiving the last of 9 doses 2 months after study initiation, 6 of which remained stable until the end of the study (3 months after initiation). Moreover, there were two cases where tumor masses were notably reduced. Particularly notable was the case of the individual with the neuroendocrine cancer where a 2-3cm tumor mass disappeared following the re-peat administration of Atu027 (see also my earlier blog on the abstract). However, none of these apparent responses could be scored as responses by stringent RECIST criteria. It is possible that this is because other masses present in those patients did not respond. Also, stable disease did not appear to be dose-related, which may not be surprising given that most of the 24 patients enrolled so far were not given pharmacologically relevant dosages.

Outlook

Considering the safety profile so far, i.e. the absence of dose-limiting and other dose-proportional toxicities, I am hopeful that even higher dosages will be tolerated. Silence Therapeutics may even want to seek an extension of the study should the remaining 3 dose cohorts remain uneventful in terms of safety. As for Alnylam’s ALN-VSP02, the future development plan, especially a narrower patient selection and combination treatments, remain unclear and will be best explored in collaboration with a larger partner so that Atu027 can test and reach its full potential in a timely manner. Further investments seem more than justified and the main risk may be in the drug target.

Alnylam Presents ALN-VSP02 Liver Cancer Data at ASCO 2011

Widely expected, Alnylam presented over the weekend detailed safety and preliminary efficacy data from its multi-dose, dose-escalation phase I trial of ALN-VSP02 in 41 patients of advanced solid tumors with liver involvement. ALN-VSP02 is a SNALP formulation containing 2 siRNAs, one targeting VEGF (anti-angiogenic mechanism), the other kinesin spindle protein (KSP; anti-proliferative).

The data suggest that ALN-VSP02 has an adequate safety profile for such a cancer application at dosages where gene knockdown can be expected with such formulations in normal liver cells. While not geared towards showing efficacy, there are preliminary signs of efficacy with one case of clear tumor response and a dose-dependent increase in the number of stable patients.

Safety profile bodes well for SNALP delivery platform

Probably as, or even more important than studying the safety of ALN-VSP02, this study was the most rigorous test yet for the SNALP delivery platform. The detailed safety data show that while there were some minor toxicities at the lower dosages, innate immune-related toxicities such as chills and rigor become an issue at doses of 1mg/kg and higher, although none of these events were of high severity (grade 3) where they would be considered dose-limiting. There were also two cases of dose-limiting grade 3 thrombocytopenias at the 1.25mg/kg. Overall, this profile justified a recommended dose of 1mg/kg every 2 weeks for future studies.

Importantly, this study strongly suggests that SNALP delivery is amenable to repeat-administration with no apparent changes in the pharmacology upon re-administration. The ability to repeat-administer had been one of the question marks when SNALP delivery was in its infancy and this was the first such clinical experience.

While this safety profile is adequate for most cancer applications and other applications for severe diseases such as Ebola viral infections, the record suggests that for less severe indications, especially when chronic application is required, improvements in the potency and tolerability of SNALP delivery are necessary. Of course, based on Tekmira’s proprietary insights, considerable improvements in the therapeutic index have been achieved since ALN-VSP02 was locked down. In this light, the 1mg/kg mark determined here is very encouraging. Nevertheless, we still have to await clinical data with the newer formulations, starting with ALN-PCS later this year to fully justify such optimism.

Signs of preliminary efficacy

Although not the primary objective of such a study, Alnylam made significant efforts to study whether ALN-VSP02 works as designed and whether there are any signs of anti-tumor efficacy. In this regard, the highlight of the study is probably a patient with primary endometrial cancer and multiple liver metastases that showed a partial, but very considerable 70% tumor response and that has been on study drug for now more than a year. Moreover, among evaluable patients, only 1 in 13 given a dose up to 0.4mg/kg had stable disease for 2 months compared to 12 in 24 dosed with larger amounts of study drug (caveat: base-line criteria may not be fully comparable as the patient recruitment criteria were slightly adjusted during dose escalation).

In terms of mechanism of action, 5’ RACE RNAi cleavage results and a reduction in tumor blood flow and leakiness as measured by DCE-MRI support an anti-angiogenic mechanism of action due to VEGF knockdown, but overall the mechanism of action data fell slightly short of my expectations, although technical challenges in taking such biopsies and analyzing them may account for that. In particular, no data supporting a knockdown of KSP was reported. 5’ RACE cleavage assays apparently suffered from technical challenges, and the analysis of mitotic spreads was not mentioned at all.

Study validates SNALP siRNA delivery to liver

When I reviewed last year ALN-VSP02, I was a bit confused about Alnylam’s choice of a short-circulating C14-PEG-lipid instead of a longer-circulating C18-PEG-lipid. I even thought that there might be a mistake in Alnylam’s cartoons of the formulations, but my question remained unanswered. Having listened to the recent ThinkEquity presentation by Tekmira’s CEO Mark Murray, it is clear to me that this was not a typo: Tekmira’s solid cancer candidate TKM-PLK1 is a longer-circulating formulation, and as we know, Tekmira is getting more and more interested in competing with ALN-VSP02 in liver cancer.

Why does C14 vs C18 matter? In short, C14-PEG-lipids are most suited for gene knockdown in normal liver cells, not liver cancer cells. Normal hepatocytes largely derive their blood supply from the portal vein, whereas most liver cancers primarily tap into the arterial blood supply. For this reason, even when addressing tumors in the liver, a more stable formulation would have been desirable. This also applies to tumors outside the liver (note: the vast majority of patients in Alnylam’s phase I study had such turmors).

Therefore, when Alnylam reports siRNA concentrations in the liver biopsies that were often well above concentrations associated with potent knockdown of genes expressed in the liver in pre-clinical studies, it is mainly a validation that the DLinDMA C14 formulations successfully deliver siRNAs to the liver.

Why did Alnylam choose C14? This may be more of a rhetorical questions and if you follow the Tekmira litigation you will understand why. In other words, my suspicion is that if Alnylam were to develop another liver cancer candidate, it would indeed choose a longer-circulating formulation.

In conclusion, the ALN-VSP02 phase I study nicely adds to the accumulating evidence that up to 1mg/kg of SNALP-siRNA is readily feasible which predicts a comfortable therapeutic index for the liver-targeted SNALP pipeline. ALN-VSP02 will likely have to be studied in more targeted patient population and together with other therapeutic modalities before its real potential becomes clear. It won’t be an easy stroll, but the data show that there are a few reasons to be optimistic.

PS: Silence Therapeutics also presented today at ASCO an update on Atu027 for advanced solid cancers. The press release can be found here. I am currently traveling and will provide further commentary when I get a chance.

RNAi Therapeutics at ASCO 2011- A Preview

This year’s ASCO meeting will feature two important RNAi Therapeutics clinical studies: Silence Therapeutics’ Atu027 for advanced solid cancers, and Alnylam’s ALN-VSP02 for cancers with liver involvement. The data presentations kick off the most important period of clinical newsflow in the history of RNAi Therapeutics. Over the next couple of months, first clinical data from the best crop yet of systemic RNAi Therapeutics candidates will be announced for indications ranging from cancer, TTR amyloidosis, and hypercholesterolemia. The importance of the data is amplified by the fact that these candidates employ delivery systems for which additional candidates are already in the clinical queue.

ASCO will be first about the safety of ALN-VSP02 and Atu027 and their underlying delivery systems. In this regard, the phase I studies may be considered successes if the reported or anticipated maximally tolerated dose levels are well into the range where based on the preclinical data anti-tumor efficacy would be expected. Second, it will be important to see evidence that these drugs act via their predicted mechanisms of action. Needless to say, data hinting at preliminary efficacy would be a definite bonus.

Atu027: Will dose escalation continue to pierce through the predicted efficacious dose?

Atu027 targets PKN3, a gene scientists at Silence Therapeutics first discovered to be involved in cancer-related processes downstream of the more widely recognized PI3K pathway (more on the background of Atu027 here). Although the precise mechanism remains somewhat unclear and could be relatively complex, as so often is the case in biology, various lines of evidence point towards an important role of PKN3 in the metastatic spread of tumor cells.

The phase I study of Atu027 to be presented at ASCO is an open-label, multi-dose dose escalation trial in patients with advanced solid tumors. Enrolment started at the end of 2009 at the low dose of 0.001mg/kg. This low starting dose was a consequence of this being the first human experience with the Atuplex delivery system and the known potential of cationic lipoplexes to stimulate various immune responses.

The trial experience, however, suggests that this is not an insurmountable challenge, and in fact, the safety profile of Atu027 so far has been very encouraging. As of the last update (Silence Therapeutics financial update conference call in April 2011), 24 patients had been enrolled in 8 dose cohorts. The only noted safety issue was a transient activation of the alternative complement pathway, something which was not surprising for this positively charged formulation, but which the company characterized as not being clinically meaningful. Accordingly, after more than 170 dose administrations, no dose limiting toxicities had been reported. The company also remarked that, unlike competing technologies, Atu027 does not make use of pre-medications in order to hedge against potential, or expected, immune stimulations, obviously pointing the finger at ALN-VSP02 (see discussion below). Indeed, in a foundational paper on Atu027 (Aleku et al. 2008 in Cancer Research), the company demonstrated pretty convincingly the absence of cytokine responses.

In terms of efficacy, it is relevant that the study has now entered dose ranges where based on the preclinical pharmacology in non-human primates and rodents, knockdown and anti-cancer efficacies can be expected. Considering the apparently benign safety profile, this in itself is highly promising and I look forward to seeing the investigators continue to dose escalate and wrap up the study this fall.

There have been 6 patients that remained stable 3 months after their enrolment in the trial. There is also one anecdotal report of tumor regression:

As can be seen on the CT on the left, a ~2 centimeter metastatic lesion in the lung of a cohort 6 patient disappeared one week after receiving 8 infusions of Atu027 (left/right panel: before/after). It is worth bearing in mind though that this trial design may not best capture the utility of Atu027 as its primary benefit may be not only in inhibiting or reversing primary tumor masses, but in preventing their metastatic spread.

Overall, this study appears to be on a very promising trajectory and I look forward to a more thorough discussion of the updated data at ASCO.

ALN-VSP02: Clearer picture of the safety profile and mechanistic data

Unlike Atu027, the SNALP-formulated ALN-VSP02 targets tumor cells, taking advantage of the Enhanced Permeability and Retention (EPR) effect of nanoparticle delivery to solid tumors. It is also of particular interest that this drug candidate targets two validated cancer genes simultaneously: kinesin-spindle protein (KSP) to inhibit cell division and VEGF for anti-angiogenesis. In principle, I like this dual targeting quite a bit, also as it blazes the regulatory trail for other multi-targeted siRNA therapeutics not only in cancer indications (more on the background of ALN-VSP02 here).

The multi-dose phase I study of ALN-VSP02 has enrolled over 40 patients and escalated up to the solid dose of 1.5mg/kg. Three acute infusion reactions were noted, but these were readily managed by adjusting the infusion rate and did not preclude future dosing. There were, however, two dose-limiting toxicities. One was a death, the other a grade 3 thrombocytopenia. The thrombocytopenia occurred at the relatively high dose of 1.25mg/kg so this should not be overly concerning. The other was a death at the 0.7mg/kg dose. As I had discussed in a previous blog entry, it is difficult to tell what precipitated this death. However, as it was possible that this was related to the drug and the extent of the metastatic tumor burden in the liver, subsequent enrollment criteria were adjusted to limit the extent of liver cancer.

The trial already shed light on one important aspect of the SNALP delivery platform (developed by Tekmira): the feasibility of repeat-administration. Before this study, it was unknown whether repeat-administration would affect pharmacology and safety through adaptive immune responses. This for example was a particular issue for first-generation monoclonal antibodies, and, to some degree, still is. It is therefore a great relief that the pharmacokinetics of ALN-VSP02 are apparently unchanged following repeat-administration. It is little things like this, or the ability to manufacture at large quantities, that will decide whether a delivery platform will ultimately be successful.

In terms of efficacy, the company reported at last year’s ASCO that the blood perfusions of liver tumors were significantly reduced in a majority of patients treated with ALN-VSP02. This would be consistent with an anti-angiogenic effect as a result of VEGF knockdown. Given, however, that this was not a dose-proportional effect, it is probably premature to conclude that this was due to on-target activity.

This is one of the reasons why I don’t really like the choice of VEGF as one of the target genes. Cytokines are known to have the potential to affect angiogenesis, sometimes inhibiting, sometimes promoting it. The origin of ALN-VSP02 fell in a time when Alnylam’s target selection was less developed than it is today. It also fell in a time when immune stimulation was blissfully ignored by many if not most players in the field and tensions with Protiva/Tekmira were quite high. Tekmira had long recognized that almost as important as delivering the siRNA to the right place is the need to carefully characterize and mitigating liposomal nucleic acid-triggered cytokine responses, and are to be considered experts in this area.

In the absence of a peer-reviewed publication on ALN-VSP02, I have looked through the related patent literature and conference and company presentations, but could not find an immunological evaluation of ALN-VSP02 as it has become industry-standard today. And as Silence Therapeutics has been hinting at, it is also notable that the study protocol of ALN-VSP02 involves concurrent treatment with steroids, H1 and H2 blockers, and acetaminophen. To be clear, such drugs of often used to manage potential infusion reactions which are observed with many systemically administered chemotherapeutics and monoclonal antibodies, but it makes me wonder a bit.

I’m just putting this out for everybody to form their own opinions, and maybe for Alnylam to address some of these issues in future presentations. I would also stress that in SNALP delivery, it is not about whether cytokine responses are induced or not, it is about characterizing and mitigating/abolishing them.

It is therefore all the more important for Alnylam to provide more evidence that the main mechanism of action of ALN-VSP02 is via RNAi target cleavage. In this regard, important data were presented earlier this year when Alnylam showed in a carefully controlled experiment that ALN-VSP02 triggered bona fide RNAi cleavage in liver cells obtained from biopsies. Moreover, in similar biopsy analyses, the company showed drug levels in the liver that are consistent with RNAi knockdown activities based on the extensive preclinical experience with SNALP delivery.

Overall, ALN-VSP02 looks like a decent candidate and it is clear already that RNAi is operative. The trial organizers have also done extremely well in escalating the study up to 1.5mg/kg and milking the study for data, all the while protecting the safety of trial participants. I therefore look forward to learning more about the mechanism of ALN-VSP02 in Man such as cytological analyses demonstrating spindle abnormalities as would be expected from a KSP knockdown. Of course, any type of tumor response and regression would be a major plus.

ALN-VSP02 Interim Safety and Early Signs of Activity Supporting Continuation of Trial

[This entry has been updated on May 21, 2010]

At precisely 6pm tonight, ASCO released the much-awaited abstracts for presentations at the upcoming cancer meeting. This included one on the interim analysis of Alnylam’s ALN-VSP02for the treatment of liver cancers (my review with Tobias Wolfram on VSP02) targeting both VEGF (antiangiogenic) and KSP (anti-proliferative) and delivered by first-generation SNALP technology*. Importantly, the drug showed an encouraging safety profile with no cases of flu-like hypersensitivity reactions up to the highest dose tested so far (0.7mg/kg, dose-escalation ongoing) and signs of hepatotoxicity up to 0.4mg/kg, the two most important expected potential toxicities for SNALP delivery-based drugs.

There was one death possibly related to the study drug in a patient with a pancreatic neuroendocrine tumor (most others had colorectal cancers) at the 0.7mg/kg dose level. This patient died of hepatic failure after receiving the 2^nd of the 4 bi-weekly 15-minute infusions. While liver patients do often die from hepatic failure and patients in the trial probably have a relatively short 1-2 year life expectancy which means that deaths are to be expected in such a trial just by chance, because of the temporal association of the treatment with the death, a contribution of the drug cannot be excluded. A general hepatotoxicity of the drug or delivery technology, however, is unlikely because, unlike flu-like reactions to liposomal siRNAs, hepatotoxicities should be more uniform, at least in 'average' persons, but were otherwise absent in the 0.4mg/kg cohort as well as in the two other patients dosed at 0.7mg/kg. Similarly, except for a minor grade 2 infusion reaction that responded to slowing of the infusion, there were otherwise no significant adverse events, quite remarkable for such a cancer trial, which supports that the death was an isolated case of which the exact cause remains to be fully determined.

Interestingly, in the deceased patient there was extensive tumor necrosis following drug treatment and this was correlated with decreased blood flow as measured by DCE-MRI, consistent with successful VEGF inhibition. Although it cannot be excluded at this point, it is probably too early to say whether the death may have even had to do with too rapid tumor necrosis due to VEGF and/or KSP inhibition by affecting already impaired liver function in liver cancer patients. Altogether, blood flow was measured in 8 of the 12 patients treated as of December 2009 with 80% of the tumors showing a remarkable >40% decline [in blood flow].

Eyes are now on the more detailed data presentation at the ASCO meeting in June that will include further safety, tolerability and also pharmacodynamic data, possibly at even higher dose levels**. More information on the exact distribution of the declines in blood flow and the neuroendocrine patient history will be of particular interest.

* Second generation SNALP formulation have potencies that are about 10-50 increased compared to the one used in the present trial that had a predicted 50% knockdown potency at around 1mg/kg. This means that at therapeutically relevant doses for future SNALP-based drugs of around 0.05-0.2mg/kg, no significant toxicities have been observed so far in both Tekmira's SNALP-ApoB and Alnylam's ALN-VSP02 trials.

Putting the ALN-VSP02 Adverse Event into Context (update May 21, 2010)

It has come to my attention that there is considerable angst, especially among investors, about the one death in the trial. While every such case is unfortunate and has to be studied in detail whether it is linked to treatment with the investigational drug, let me emphasize that the reason why liver metastases are specifically treated for most cancers, including in this trial, is because they turn out to be rate-limiting for many of these late-stage patients. As such, more deaths are to be expected in this trial, also and especially due to liver failure. One caveat, however, is that the patient died after the 2nd infusion, that is between 2-4 weeks after dosing had been initiated and one of the enrollment criteria for the trial was a life expectancy of >12 weeks, so a contribution of the drug is likely.

A good indication about the seriousness of these adverse events as it relates to drug safety and risk:benefit is how regulators react to such reports that by the way have to be made in a timely manner, meaning that if there had been more such reports they must not have been deemed sufficient to stop the trial. Related to this, it will be important to learn whether the regulators allowed further dose escalation or whether the patients that have been recruited since the December 2009 abstract deadline were treated largely at the 0.4 and 0.7mg/kg dosages to further study the drug safety around these dose levels, although the company did say in their press release that the maximum tolerated dose has not been 'reached' yet [update: the company has since confirmed that dose escalation has continued since December 2009, meaning that at the very least there should now be data for the 1.0mg/kg cohort if not higher which reflects favorably on the safety profile thus far].

It is surprising that Alnylam did not comment generally much about the detailed data in the press release about the abstract. It is possible that they consider doing so at this point as being of little value since much more comprehensive and informative data will be presented soon at the ASCO.

In the meantime, unlike drugs developed maybe for restless legs syndrome or ED, deaths are a frequent occurrence of cancer drug development and investors have to live with that without assuming the worst.