ASCO Abstracts on Atu027 and ALN-VSP02 Published!

It is 6 o’clock in the morning in my part of the world, have not slept all night, but am more awake now than I have been for a long time: The ASCO abstracts on Silence Therapeutics’ Atu027 (for advanced solid cancers) and Alnylam’s ALN-VSP02 (for cancers with liver involvement) have just been released and both surpassed my already optimistic expectations (copies of abstracts, see below).

For one, I fully expected to learn about additional warts with regards to the safety profile of the drug candidates, aspects that the companies may have chosen to ignore until now for obvious reasons. This, however, was not the case. Atu027 seems to be remarkably innocuous and well tolerated at doses where we can expect to see anti-tumor activity based on the pharmacological evidence. No dose-limiting toxicities (DLTs) and no cytokine inductions with this positively charged lipid-siRNA formulation! ALN-VSP02 also did very well in that only one additional DLT at the very high 1.5mg/kg dose (a case of hypokalemia, i.e. too little potassium) was disclosed that we had not heard of before. Together, Atu027 and ALN-VSP02 demonstrate that lipid-siRNA/nucleic acid formulations are clinically viable indeed.

On the efficacy front, Atu027 exceeded my expectations considerably. Keeping in mind that this has been a small phase I study (abstract relates to the first 21 patients and dose escalation still ongoing), the fact that one patient with highly advanced (an enrolment criteria) neuroendocrine cancer had disease stabilization for 9 months and another had a partial regression of pulmonary metastases sounds very encouraging already and would seem to justify a more targeted phase I study in this patient population, but considering that there was still another breast cancer patient that had regression of liver metastases (breast cancer patients die from such metastases, not the primary cancer) makes it even more impressive and almost more than just ‘anecdotal’ evidence of anti-tumor efficacy.

The clinical investigators of Alnylam’s ALN-VSP02 also had some new intriguing data to report with regard to efficacy: while only 1 of 12 patients up to 0.4mg/kg had stable disease for at least 2 months, 7 of 15 had stable disease for that time period if given more than 0.4mg/kg. This does not look like chance at all and maybe these mouse experiments tell us something about the potential of RNAi Therapeutics for cancers after all. The only clarification that I hope to get is whether some of that difference might be explained by a difference in baseline characteristics, especially in light of the fact that the enrolment criteria had been adjusted at 0.7mg/kg to limit the extent of liver metastases a trial participant could have.

With the abstracts released, all eyes are now on the data presentation at the actual Meeting in 2-3 weeks’ time. We should then learn of more details related to the data contained in today’s abstracts, and with the appetite thus wetted….updates from the more recent patients in the higher dose groups for Atu027 (every additional cohort is a significant plus) and the dose expansion phase of ALN-VSP02.

The sleep is finally over, lots more RNAi Therapeutics clinical data to come.

Atu027 (abstract 3057)

First-in-human phase I study of Atu027, a liposomal small interfering RNA formulation, targeting protein kinase N3 (PKN3) in patients with advanced solid tumors. Background: Atu027 is a novel RNAi therapeutic based on cationic lipoplexes containing chemically stabilized siRNAs, which targets PKN3 gene expression in the vascular endothelium. PKN3 acts as a downstream effector of PI3K-signaling pathway and is implicated in controlling cellular morphology and locomotion in endothelial and cancer cells. Preclinical data obtained in various cancer mouse models revealed target-specific, RNAi-mediated silencing of PKN3 expression and significant inhibition of tumor progression and metastasis formation. Methods: Patients (pts) (ECOG PS 0-2) received Atu027 as a single 4h-infusion with 3wks follow-up, and were thereafter treated twice weekly over another four week period. Upon SD, pts were given the opportunity to continue until PD. Dose escalation was accompanied by assessment of data related to toxicity and pharmacokinetics (PK). Results: The study design comprises 11 escalating doses. To date, 21 pts have received Atu027 of seven dose levels up to 0.120 mg/kg. Mean age = 62.4 years (range 29-81), 12 female, 9 male. No premedication 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. Preliminary PK-data showed dose-dependent increase in plasma siRNA as well as lipid levels. Across the dose levels tested, Atu027 was generally well-tolerated. Adverse events possibly related to Atu027 were fatigue grade (G)1 (4pts), hair loss G1 (2pts), sweating G1 (1pt), and abdominal pain G2 (1pt). G3 AEs not considered as DLTs were elevated lipase (1 pt, DL2) and diarrhea (1 pt, DL5). No dose limiting toxicities (DLTs) were seen so far. Stable disease after 3 months was observed in 6 pts. Two pts with neuroendocrine cancer had disease stabilization for 9 months, and partial regression of pulmonary metastases, respectively. Another patient with breast cancer had regression of liver metastases.Conclusions: Atu027 is well-tolerated and antitumor activity has been observed. Accrual is ongoing to determine the MTD of Atu027.

Press release by Silence Therapeutics: here.

ALN-VSP02 (abstract 3025)

Phase I dose-escalation study of ALN-VSP02, a novel RNAi therapeutic for solid tumors with liver involvement.

Background: ALN-VSP02 is a RNA interference (RNAi) therapeutic comprised of lipid nanoparticle-formulated small interfering RNAs (siRNAs) targeting the expression of vascular endothelial growth factor (VEGF)-A and kinesin spindle protein (KSP). Methods: A multi-center, open label, phase I dose-escalation trial of ALN-VSP02 administered as a 15-minute iv infusion q2 wks was initiated in patients (pts) with advanced solid tumors and at least one measurable liver lesion. Main objectives included evaluation of safety/tolerability and assessment of PK/PD. Results: Thirty-one pts were enrolled across 7 dose levels (0.1-1.5 mg/kg); median age 57 yrs, all with multiple prior therapies. A total of 140 doses were administered, mean of 4.5 (range 1-17). Treatment was generally well-tolerated, with no dose-dependent trends in clinical or laboratory adverse events. One on-study death (liver failure in a pt with near complete replacement of the liver by tumor) deemed possibly related to treatment occurred at 0.7 mg/kg. Low-grade acute infusion reactions occurred in 10% of pts and were managed with slowing of infusion. Dose-limiting toxicities at doses >0.7 mg/kg included 1 episode each of reversible grade 3 thrombocytopenia (1.25 mg/kg) and hypokalemia (1.5 mg/kg). Plasma PK showed dose-proportional AUC and Cmax. Post-treatment biopsies from 10 pts (7 liver and 3 extrahepatic tumors) showed pharmacologically relevant concentrations (0.3-142 ng/g tissue) of both siRNAs. Molecular evidence of RNAi-mediated VEGF mRNA cleavage was shown in liver (n=2 at 0.4 mg/kg) and in an extrahepatic tumor (ovarian cancer at 1.25 mg/kg) through use of the 5’ RACE assay on tumor biopsies. Additional evidence for an anti-VEGF effect with ALN-VSP02 included a decrease in Ktrans of at least 40% by DCE-MRI in 56% of evaluable pts. Among 27 pts evaluable for response, 8.3% (1 of 12) at doses ≤ 0.4 mg/kg had stable disease (SD) for at least 2 mo compared to 46.6% (7/15) with SD (n=6) or PR (n=1, endometrial cancer with liver metastases) at doses ≥ 0.7 mg/kg. Conclusions: ALN-VSP02 is well-tolerated and has antitumor activity. Pharmacodynamic data are consistent with an anti-VEGF effect, and 1.25 mg/kg q2wks is the recommended phase II dose.

Press release by Alnylam: here.

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.

The Settlement That Wasn’t

Shareholders of Alnylam Pharmaceuticals may be forgiven for heaving a sigh of relief when news broke of a Settlement between Alnylam and Max Planck on the one hand and the Whitehead Institute and the University of Massachusetts (UMass) on the other hand which seemed to resolve the Tuschl II ownership issue and finally put an end to the lengthy and costly Tuschl Litigation (follow filings and commentary here).

At the heart of the dispute was Alnylam’s fear that Merck could gain access to the siRNA 3’ overhang feature if UMass got its way and certain data concerning such overhangs were left in the US Tuschl I patent application. UMass found itself to be in a particularly tough spot since whether it gave in to Alnylam’s demands or not, somebody, Alnylam or Merck, would be quite unhappy with them. So when Alnylam announced that it had ‘reach[ed] settlement in litigation regarding Tuschl patents’ and noted that Alnylam granted as part of the settlement UMass the right to sublicense the U.S. Tuschl II patent family to Merck (emphasis mine), it seemed like Alnylam, UMass, and Merck achieved the impossible and untied the Gordian Knot that Tuschl II had become.

Exhibits (Exh. 10-2 and 10-3) filed as part of Alnylam’s quarterly securities filings, however, strongly suggest that the settlement effectively solved nothing and only delayed/slightly shifted the problem. Importantly, there is no evidence that Merck agreed to or conceded anything with this settlement. In fact, the filings indicate that Merck was not part at all of the settlement negotiations as it had yet to see its details. The Merck reference is only a reference that UMass will present Merck with the option to utilize Tuschl II in the US. The only reason why Merck would remotely see any value in this is if Alnylam succeeded in stripping away the 3’ overhang claims from Tuschl I.

But even then, I very much doubt that Merck would be agreeable. One insight into its current thinking about Tuschl II comes from a recent opposition that Merck filed against that patent estate in Europe. On April 4 2011, that is after the news of the Tuschl Settlement, it and others (including Pfizer and Silence Therapeutics) appealed a recent decision by the EPO to uphold Tuschl II. In Europe, it will be the objectives of Merck and UMass, still responsible for Tuschl I patent prosecution there, to eventually get a broader Tuschl I issued and/or invalidate Tuschl II. Personally, I’m wondering whether the EPO will eventually raise the same double patenting issue the USPTO raised.

The main problem with solving the Tuschl situation is that when Alnylam sold its licenses to various Big Pharma companies, they must have been under the impression that Merck had either only limited or no rights at all to Tuschl II. After all, at least some of that half a billion dollar plus was for the strategic value that Tuschl II would give them. This is why Alnylam adds that the Tuschl II sublicense to Merck, or rather the offer of such a sublicense, is subject to certain 3^rd party obligations, pretty much meaning that Novartis will not easily give up on the exclusivity of its 31 target picks. Rest assured, Merck, having invested more than anybody else in RNAi Therapeutics, will never agree to such terms.

Something about the Settlement seemed odd to me, and I’m sure to others as well. It is, however, clear to me now that peace between Merck and Alnylam has not broken out yet.

Confidence in SNALP Safety Building

Alnylam Pharmaceuticals disclosed in their Q1 2011 results that it will expand the dose escalation of the phase I study of ALN-TTR01 in TTR amyloidosis, increasing the target dose in that study from 0.4mg/kg to now 1mg/kg. This puts the company in a good position to demonstrate, unambiguously, that systemically administered SNALPs can knock down genes in the human liver. This dose expansion is an important indication that, as we learn more about the clinical performance of SNALP delivery, confidence in its safety is growing.

Given yesterday's news, the phase I study being conducted in Europe should have almost fully enrolled its first 24 patients up to 0.4mg/kg. Regulatory applications for this study were filed in late 2009/early 2010, yet it took over half a year for the first patient to be dosed in July 2010. At that time, Alnylam revealed the 0.4mg/kg target dose. This was somewhat confusing and made me even speculate that TTR01 may involve a ‘generation 1.5’ formulation as it had been Alnylam’s stated goal to demonstrate proof-of-concept of gene knockdown with this study. 0.4mg/kg, depending on the gene, is about where you’d expect to start seeing efficacy with the initial SNALP formulations, so stopping at 0.4mg/kg would have been slicing it quite thinly. Indeed, the ED50 (dose of 50% drug efficacy) for ALN-TTR01 in non-human primates is around 0.4mg/kg.

In retrospect, the original conservative dose escalation schedule might have been due to safety concerns surrounding SNALP delivery. Around the time of the regulatory submissions, Alnylam knew of one death in their liver cancer trial with ALN-VSP02 (also using SNALP delivery) which occurred some time after a patient with extensive liver mets from pancreatic neuroendocrine cancer received a second infusion of 0.7mg/kg SNALP. Dose-limiting toxicities were not observed in that trial until then up to 0.4mg/kg. Although patients in that trial are quite fragile and autopsy revealed that the patient may have in fact died as a result of too much drug efficacy (extensive necrosis of the liver mets), it was a potentially drug-related severe adverse event nevertheless. ALN-VSP02 was subsequently escalated to the robust dose of 1.5mg/kg, with 1.25mg/kg being my predicted maximally-tolerated dose.

Shortly thereafter, in January 2010, Tekmira stopped early their phase I hypercholesterolemia trial for TKM-ApoB after one trial participant at the 0.6mg/kg dose level became hypotensive and suffered from general flu-like symptoms after receiving a SNALP formulation. Because the necessary safety/tolerability profile for a hypercholesterolemia drug differs from that of a cancer drug, Tekmira did the right thing and stopped the trial and take advantage of the technology progress in the SNALP delivery field with the aim of re-entering clinical development with a formulation with presumably improved potency and robust long-term safety. Just as for ALN-VSP02, 0.4mg/kg was the dose level up to which no significant adverse event was observed with TKM-ApoB.

Since no good deed goes unpunished in the competitive area of siRNA delivery, these events were quickly made out to prove that ‘SNALP delivery is toxic’ adding to the SNALP confusion caused by Alnylam's lipidoid line of work. Regulators may not be as emotional, but it is understandable that they and Alnylam took a cautious approach in selecting their initial doses. They were, however, clever enough to design an adaptive trial that would allow for further dose escalation depending on the safety findings up to the 0.4mg/kg level.

The enrollment of the anticipated additional 8 patients should therefore be a very good sign that the safety profile so far has been highly satisfactory, setting the scene for convincingly demonstrating TTR knockdown in the liver as measured by plasma protein levels. Alnylam plans to present top-line data from the completed study in the third quarter, hopefully building on good ASCO data on SNALP-based ALN-VSP02.

There has been some debate around whether the clinical development of SNALP technology was started pre-maturely. Yes, you can try and aim for perfection (that may be what Merck and Roche are waiting for), but by taking the necessary clinical precautions, Alnylam and Tekmira were able, in a timely manner, to gather much clinical data on the SNALP delivery platform that is really starting to pay off now as their synergistic value becomes obvious. Important months for RNAi Therapeutics are ahead of us.