Dicerna Trying to Succeed Where Novartis Has Admitted Defeat

This week, newly public RNAi Therapeutics company Dicerna initiated its first phase I study of a Dicer-substrate-based RNAi Therapeutic.  DCR-MYC targets the well-known Myc oncogene utilizing a liposomal delivery formulation (EnCore) for targeting a variety of cancers, solid and hematological (à Myc and lymphoma) malignancies alike, but with a planned focus on primary liver cancer in future studies.

The cancer trial start coincides with Novartis’ bitter, brake-slamming exit from internal RNAi Therapeutics development, largely blaming lack of suitable delivery technologies.  In particular, in classic Big Pharma style, Novartis seems to have selected its 31 RNAi trigger picks under the 2005 Alnylam license not based on where delivery is most advanced, but based on where it wished to strengthen its disease franchises.  It is this putting the cart-in-front-the-horse attitude that is at the root of Big Pharma’s miserable failure with an emerging platform technology that has its own mind of where it wants to go first.

According to commentary by Alnylam, cancer appears to have been a focus of Novartis’ target selection.  With regard to delivery to cancers, I would agree with Novartis to the extent that it is not as far developed as for example for the liver.  A problem with it is the inter- and intra-cancer heterogeneity of the EPR effect that most current cancer delivery approaches rely on.  You therefore have to be quite careful as to which cancers you select.  The same heterogeneity applies to target receptor expression (e.g. LDL-receptor, folate receptor) and Tekmira will have its good, not necessarily publicized reasons for why it chose neuroendocrine (NET) and adrenocortical carcinoma (ACC) for its ongoing phase II trial with TKM-PLK1, preliminary results from which are expected this year.

I’ve had the pleasure of attending the European Symposium of Controlled Drug Delivery in the Netherlands this week and presentation after presentation showed that for most liposomal formulations, tumor penetration is a major issue.  The good news is that EPR is very real, but the field has come to a point where it needs to establish the rules for which cancers are amenable and which strategies (size, lipophilicity) can be employed to aid in tumor penetration.

Imaging studies presented at the conference and the recent (conditional) European marketing approval of the companion-diagnostic/folate receptor-targeted cancer drug pair by Endocyte (Vintafolide) strongly suggest that patients should be pre-selected based on whether they have cancers amenable to EPR.  For example, pre-treatment with a small dose of the drug co-formulated with a diagnostic contrast reagent would both visualize amenable tumors as well as have the side benefit of de-sensitizing the patient to hypersensitivity reactions that are typically observed for infused drugs during the first administration.

So while I remain uncertain about the specific prospects of DCR-MYC partly due to concerns around the target and partly due to the relative inexperience of Dicerna in liposomal delivery, RNAi Therapeutics will become a reality in the treatment of cancers.  Just don’t expect clumsy Big Pharma R&D to rise to the challenge.

Dicerna Ends Year on Positive Note

With the Notice of Allowance of a US patent application covering its basic Dicer-substrate RNAi trigger technology and a $5M milestone payment from Kyowa Hakko Kirin (KHK) due to the formal initiation of development work for a Dicer-substrate oncology candidate by its Japanese partner, Dicerna can look optimistically into the New Year. These events also symbolize some of the important shifts that have taken place over the last 3 years, namely the increasing choice between RNAi trigger technologies and the increasing importance of Asia in the industry.

Dicer-substrate patent

The patent that is about to formally issue covers methods related to knocking down genes in mammalian cells using certain 25-30 base-pair double-stranded RNAs that undergo Dicer processing before incorporation into the RISC gene silencing complex and target cleavage. While not gate-keeping for Dicer-substrates, the patent will give Dicerna considerable clout over this particular gene silencing approach and has an expiration of at least 2025 if not a year or two longer following patent term adjustments. It is interesting to speculate that the Allowance was also a trigger for the $5M milestone payment.

New oncology candidate formulated in KHK delivery tech

The press release on the $5M milestone noted that while the RNAi trigger of the candidate that is at the center of the $5M milestone payment is licensed from Dicerna (possibly targeting KLF5), the drug delivery tech would be KHK’s own. Based on comments made in early 2010 when Dicerna and KHK first announced their collaboration plus quite a few liposome-related patent apps by KHK, it is likely that the delivery tech relates to a cationic liposomal formulation. I would be a bit wary though about the novelty and strength of these liposomes since at least the patent apps merely claim cationic LNP formulations of chemical compositions that have been known for years in the art an manufacturing method that may be somewhat unique to KHK, but maybe too complex for industrial applicability. Moreover, the described approach lacked the scientific rigor that I would expect of a company that intends to enter clinical development soon.

Dicerna employs Tekmira SNALP delivery

Dicerna has also been saying to be developing delivery technologies, including LNPs and another (actively) targeted delivery system. Interestingly, in an analytical assay development paper that has just been published (Jiao et al., 2011), Dicerna employed Tekmira’s SNALP delivery technology. It is unclear whether the SNALPs were reproduced based on the literature or whether there has been some sort of collaboration between the two companies. However, since Tekmira has been investigating a variety of non-Alnylam RNAi trigger technologies, the latter hypothesis is not that farfetched. The Allowance should provide further impetus for the two companies to work together more closely.

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On the Importance of Semple-Wheeler

The Semple-Wheeler (S-W) patents can be considered essential intellectual property (IP) for those liposomal siRNA formulations currently in development that have shown clinical promise. Because Alnylam obtained significant control over Semple-Wheeler (S-W) through a license from Tekmira, this patent estate has been important to Alnylam in controlling access to Tekmira’s SNALP delivery technology and, equally important, keeping Tekmira close to its chest.

Today, I will provide a brief re-cap of S-W and explain why its strategic importance is rapidly waning as patent expiration dates draw close.

What Semple-Wheeler Covers

Most critically, S-W cover LNPs comprising

a) ionizable lipids (e.g. DLinDMA, MC3), a modified lipid that prevents particle aggregation (e.g. PEG-lipid) in addition to the nucleic acid cargo (e.g. siRNA; Semple US6858225); and/or

b) a cationic lipid, a non-cationic lipid, a PEG-lipid conjugate in addition to the nucleic acid (i.e. the chemistry of a SNALP liposome; Wheeler US6815432).

While, until S-W has been tested in court, there will always been some uncertainty as to the real scope of the claims, e.g. in light of such newfangled terms like ‘lipidoids’ or other classes of lipids that may not have been covered by the examples in the specification, such strategies would seem to stand on weak scientific grounds.

Ownership and Control over Semple-Wheeler

Originally, Old Tekmira had an exclusive license to S-W from the University of British Columbia (UBC). Realizing the importance of liposomal delivery for the first wave of value creation in systemic RNAi Therapeutics, Alnylam obtained exclusive rights to Tekmira’s exclusive rights to S-W in January 2007. By this, Old Tekmira’s ability to further monetize this patent estate became greatly limited, and, in the absence of other significant RNAi assets at that time (i.e. lack of Protiva IP, know-how, and trade secrets), was widely regarded as a de facto satellite company of Alnylam.

Fair enough- not only did Alnylam pay $8M in upfront for these rights and is on the hook for milestones and royalties, Old Tekmira was in turn granted RNAi trigger IP and the use of S-W for the selected targets. Interestingly, the latter has been brought into question by Alnylam by stating in their recent Response to Tekmira’s Amended Complaint that Tekmira actually does not have rights to S-W and that Alnylam had given Tekmira such notice:

‘23. Consistent with this pattern, Tekmira has failed to adequately disclose the limitations of its licenses to investors. Despite the clear terms of the license agreements and notice from Alnylam that it lacked licenses to the Semple & Wheeler patent series and Isis patents, Tekmira made representation to the contrary in its public filings with the SEC and in other documents provided to investors.’

It is unclear on what grounds Alnylam makes these claims. Does it claim that Tekmira apparently was never granted such rights, or does it simply mean that Alnylam considers the lawsuit brought by Tekmira as grounds for terminating these rights? In any case, the irony is not lost as it is Tekmira through which Alnylam gained access to S-W and it is for Tekmira to terminate Alnylam's rights if at all.

Strategic Importance of Semple-Wheeler in Light of Upcoming Patent Expirations

In biotechnology, patent infringement typically only becomes ground for lawsuits either when drugs/devices allegedly covered by such claims are about to be commercialized or as generics want to muscle their way onto the markets before the expiration of patents covering an innovator drug. Because of the so called Research Exemption, it is very difficult to enforce patent rights before any commercialization of related drugs, i.e. during the period that patented technologies are being used for drug development pre-commercialization.

Certain licensing and collaboration agreements may be considered to fall between the Research Exemption and the commercialization of drugs, as they may involve technologies covered by 3^rd party patents, even if these patents can be assumed to have expired by the time drugs are ready to be commercialized. In other words, the LCAs may be interpreted as a way of commercializing patents. Although such actions are less common, emotions are running high, so Alnylam may use S-W as pre-text for throwing a wrench into any significant LCA that Tekmira may strike. Old Tekmira e.g. once sued Protiva for allegedly licensing S-W to Merck, and one can only speculate to what extent Alnylam instructed Old Tekmira to do so.

The reason though why such actions are unusual is that chances of enforcing such patent rights are slim if the parties involved in an LCA word their agreement appropriately (e.g. by simply excluding the appearance, implicitly or explicitly, that the partner gains rights to S-W; performing work in countries where S-W is not in force etc etc). As such, Tekmira has substantial freedom to strike deals as long as SNALP-based drugs are not being commercialized before the expiration of the fundamental S-W patents…which should be around 2015-7:

Semple US6858225 (ionizable LNPs):

Date of patent: Feb 22, 20005

Filing date: June 29, 2001

Priority date: May 14, 1997 (claims priority to No. 08/856474)

Approximate term of patent: Feb 22, 2005- May 14, 2017

Wheeler US6815432 (SNALP chemistry):

Date of patent: Nov 9, 2004

Filing date: Feb 24, 2003

Priority date: June 7, 1995 (claims priority to No. 08/5981501; note that although this is just before the famous June 1995 cut-off date, because the patent application of ‘432 was filed after that date, patent terms are according to the new regime)

Approximate term of patent: Nov 9, 2004- June 7, 2015

Tekmira business development prospects

Two factors largely controlled by Alnylam have long held back Tekmira’s full business development potential. In addition to granting Alnylam exclusive rights to S-W, it was particularly Alnylam’s RNAi trigger gate-keeper claim that tied SNALP technology to Alnylam.

Until the expiration of S-W, only those companies with access to S-W (Tekmira, Alnylam, Roche, Takeda, and supposedly Novartis) could commercialize SNALP-based drugs until 2017. Because Tekmira has 8 target picks for which it can use S-W, Tekmira is able to offer an acquirer or product-specific co-development partner more than enough access to S-W until then. 6 years is not a long time in drug development, about the time it would take from initiation of phase I to approval if all goes smoothly. The ~2017 expiration of S-W therefore means that its strategic importance for the development of SNALP-based RNAi Therapeutics is waning rapidly. 2007-8 was a different story.

In this light, a gate-keeping position of Alnylam in RNAi triggers, based on the Tuschl and Kreutzer-Limmer patents would be the real rate-limiting factor, as the terms for these patents may last into 2021-2. However, the RNAi trigger landscape has changed significantly over the last 2-3 years as the importance of Kreutzer-Limmer is rapidly diminishing in Europe and is nowhere to be seen in the US, Tuschl I turns out to be of no relevance for therapeutic applications, and even the validity of Tuschl II is now being questioned. Even if T-II can survive the Utah challenge, as it covers only certain RNAi triggers with certain 3’ overhangs, it is not the type of gate-keeping IP that KL or T-I may have become with a bit of luck.

Consequently, with the strategic importance of S-W waning and access to RNAi triggers ceasing to be a limiting factor, Tekmira’s business development is almost entirely out of Alnylam’s control. If, as a result of the litigation, Alnylam lost all rights to Tekmira’s technology (certainly a plausible outcome if it comes to a trial*), the attraction of partnering with or acquiring Tekmira would increase even more.

* As I am writing this, Alnylam has just filed a $150M shelf registration with the SEC. This typically happens in anticipation of selling stock to the public. The timing of this shelf registration is unusual though, because Alnylam has over $300M in cash/cash equivalents, meaning that with the current and anticipated burn, it should not have a need for raising funds any time soon- under normal circumstances. Given my assessment of the strength of Tekmira’s case and the existential risk to Alnylam’s business, it would not surprise me if Alnylam’s lawyers are advising the company to settle the case. A $150M capital raise may be in the right range to allow for Alnylam to survive and remain an independent company.

A hostile takeover attempt as an alternative explanation? On paper, this would probably make most sense for Alnylam, but I don’t think so.

Marina Biotech Continues to Drive Sector Consolidation, Acquires Novosom’s Liposomal Delivery IP

Marina Biotech, formerly known as mdRNA, continues to snap up assets in the oligonucleotide therapeutics and diagnostics space, this time acquiring the liposomal delivery IP from Novosom, a privately held drug delivery company based in Germany. This comes only a week after shareholders approved mdRNA’s merger with tkRNAi company Cequent Pharmaceuticals to form Marina Biotech. It will be curious to see whether Marina’s strategy of challenging Alnylam's industry-leading position by taking advantage of the depressed market for oligonucleotide therapeutics will succeed in luring Big Pharma and pay off for shareholders. The investment this time: $5M in newly issued stock.

Similar to Silence Therapeutics, Marina acts on the premise that in order to capture those lucrative partnerships, being able to provide a choice of delivery technologies, plus some claims in RNAi triggers, too, is key. This, of course, is in contrast to Tekmira’s so far quite successful strategy of doing one thing very well, meaning clinically maturing and expanding the applicability of its industry-leading SNALP delivery technology and avoid some of the deal frenzy and dilution of effort.

By the looks of it, Novosom has to be considered one of the more bona fide delivery companies. Similar to Tekmira’s SNALP, Novosom’s SMARTICLES can change their surface electrical charge and therefore reconcile (serum and storage) stability with endosomal release functionality. Unlike SNALPs, however, these liposomes also contain anionic lipids, in addition to cationic and neutral lipids, and do not employ PEG stabilizers. This stability can be attributed to the negative charge of SMARTICLES at phyisiologic pH which ought to avoid various interactions with host factors and resulting toxicities often associated with positively charged lipids. However, as the pH acidifies upon endosomal uptake of these particles, they become positively charged and competent for membrane disruption and cytoplasmic release. For similar reasons, ionizable SNALPs as practiced by Tekmira not only employ PEGylation, but are also essentially uncharged at physiologic pH.

In terms of IP, from the looks of it, Novosom has assembled a respectable IP estate with various fairly broad patents granted also in the important US market. This should provide Marina with considerable options to leverage its other liposomal assets, trp-cage targeting technology and amino acid-derived lipids, that I have felt lacked robust patent protection when used in liposomal formulations similar in composition to Tekmira’s SNALPs.

Theory and IP, of course, are only part of the equation. In terms of actual data, the literature bears out the tolerability of these liposomes. In terms of in vivo knockdown efficacy, I haven’t really seen much for liposomal delivery of siRNA in the peer-reviewed literature. There was, however, a paper on the liposomal delivery of a CD40 antisense oligo (under license from ISIS) in a rodent inflammatory disease model and that supported specific CD40 knockdown and disease amelioration while the unformulated antisense oligo appeared to be inactive. In general, based on the literature and also Novosom’s website, their technology seems to be in the late rodent stage and yet to be validated in larger mammals including non-human primates and Man.

There should, however, be an open IND for the delivery of a DNAi compound (no mis-spelling) by PRONAI which makes use of Novosom’s technology. However, it appears that PRONAI’s funding situation may have delayed actual dosing.

Novosom also entered into at least 2 collaborations with RNAi companies. One with (now defunct) DNA-directed RNAi company Nucleonics for treating hepatitis viral infections, and one with Boehringer-Ingelheim for the validation of drug targets in the liver and lung. Again, because Novosom is a private company I can only speculate whether the lipids used by Nucleonics in their soon aborted phase I study stemmed from the Novosom collaboration. Similarly, the status of the Boehringer-Ingelheim collaboration is unclear to me. Who knows, but maybe Boehringer-Ingelheim is actively looking for (liposomal) delivery and triggers for the development of RNAi Therapeutics, which raises another point: although the press release did not specify this, but selling what looks like the entire IP estate would appear to be tantamount to selling the entire company, existing partnerships and programs included.

But back to the fundamental question: Consolidating into a one-stop-shop, almost an ‘anti-Alnylam’, a la Marina and Silence versus technological deep-dive a la Tekmira- which strategy will create more shareholder value? The next 3 months should provide for some of the answers.

Please let your voice be heard and vote on the right.

Bristol-Myers Squibb Deal Further Positions Tekmira as RNAi Therapeutics Delivery Hub

Yesterday, Tekmira added Bristol-Myers Squibb to an already impressive line-up of RNAi Therapeutics delivery partners that further include Alnylam Pharmaceuticals, Roche, Merck, and Takeda. The new research collaboration specifically aims at developing SNALP RNAi for delivery beyond the liver. It follows a previously undisclosed target validation collaboration between BMS and former Protiva (now merged into New Tekmira), and is yet another vote of confidence for the clinical viability of SNALP RNAi delivery.

SNALP RNAi delivery is well validated for gene knockdown in the liver, including in non-human primates. Just this week, Alnylam published in the scientific journal PNAS the lowering of PCSK9, a cardiovascular disease target, in rodent and monkey liver using SNALP liposomes. For clarification purposes since there has been much confusion on the issue of SNALPs and lipidoids, while the particular SNALP formulation used in the publication contained lipidoids, lipidoids are just one of the various other lipids that could be used with SNALP technology. Moreover, Tekmira has non-exclusive access to lipidoids from the MIT via Alnylam in case they wanted to incorporate them into their own SNALPs.

Investing in SNALP delivery outside the liver (Tekmira expects to receive $450k from BMS for the second half of 2008) should therefore expand the therapeutic potential of this technology and directly aid the development of a broad and balanced Tekmira RNAi Therapeutics pipeline. Strategically, it should also provide Tekmira with a potential future development partner and access to disease know-how and gene targets.

Cancer is the most obvious non-liver target given what we know from the passive targeting of SNALP/liposomal particles to solid cancer tissues. Further validation for the concept of using liposomal RNAi delivery for cancer comes from plasmid delivery data from Tekmira itself and various liposomal RNAi publications by others. Some of that research made use of active tumor targeting, and it is not far-fetched that the research collaboration will also consider such active targeting strategies. These may also hold promise for indications outside solid cancer such as hematological malignancies, blood vessel-related disorders (e.g. cardiovascular/metabolic disorders), and immunological diseases.

Cancer and metabolic/cardiovascular disease would also make sense as the two focus areas of BMS research and development. While the scope of the Tekmira-BMS collaboration may indicate that the returns of investing in SNALP delivery to the liver are diminishing with first INDs expected to be filed within the next 12 months, it may also be interpreted as accommodating Alnylam or even point towards a follow-on deal with Alnylam which may not want to further dilute the perceived value of what it has granted its previous platform licensing partners.

Cancer on the other hand is a genetically highly diverse set of diseases, and with SNALP and RNAi, Big Pharma must feel like kids in a candy store with more than enough targets and unmet needs for everybody to pick from. One note of caution though is that while SNALP RNAi has demonstrated potent activity in pre-clinical models of liver cancer, much less is known about its actual knockdown activity in other cancer types. It will therefore be important to confirm the clinical feasibility of SNALP RNAi for cancer through conference presentations and scientific publications.

BMS’ decision, of course, has also to be seen as part of the rush by Big Pharma to transform themselves into developers of innovative biotech drugs. Offers by Roche and BMS itself for Genentech and Imclone, respectively, are just two recent high-profile examples. The deal also demonstrates BMS’ increasing commitment towards the RNAi platform. Only last year, BMS entered into an antisense collaboration with ISIS Pharmaceuticals for PCSK9 knockdown in cardiovascular disease. Interestingly, this was largely based on BMS’ successful validation of PCSK9 as a cardiovascular target using RNAi (and as we now know most likely SNALP-enabled as part of the BMS-Protiva target validation collaboration), data of which was presented at last year’s OTS meeting in Berlin. When asked why BMS decided on antisense, not RNAi in light of the impressive RNAi data presented, the response was that ISIS’ mipomersen represented clinical proof-of-concept that antisense could knock down genes in human liver. It now seems that like other pharmaceutical companies, positive experience with RNAi as a target validation tool has translated into embracing it as a therapeutic platform in its own right.

The one-million-dollar question weighing on the minds of Alnylam investors will be whether yesterday’s development heralds the next Alnylam platform alliance deal. In the past, partners tended to come to Tekmira as Alnylam sub-licensees. Although details of the deal are lacking, due to otherwise too many potential conflicts-of-interests and the importance of Alnylam to Tekmira, it is unlikely that BMS will turn out to be a Merck-like star in the Alnylam-Tekmira constellation. Given that Tekmira has inherited a number of additional technology feasibility partnerships with Big Pharma and biotech from Protiva, further such deals are likely to materialize with Tekmira functioning as one of Alnylam's baits.

An interesting aspect in this context is that the corresponding author of this week’s paper, Kevin Fitzgerald, came to Alnylam (leader of the oncology and cardiovascular/metabolic disease group) from BMS. At BMS, he had been part of the target validation group, very likely the same group that had been involved in the BMS-Protiva collaboration. Obviously, RNAi has not disappointed him, but beyond that, is this part of a larger puzzle?

Now that Tekmira has RNAi delivery partnerships with Alnylam, Roche, Merck, Takeda, and BMS, and more to come, the 100-employee strong Tekmira is slowly emerging as the RNAi Therapeutics delivery hub. This also starts to pay off financially with essentially no appreciable decrease in cash reserves over the last quarter. It will also be interesting whether Tekmira will pursue interests beyond liposomal RNAi delivery. Combining various delivery technologies into one operation, whether as an independent company or not, would have a number of synergies as many of the same questions need to be addressed with the different technologies.

Tekmira and Protiva Reunification Forms Leading RNAi Therapeutics Delivery Company

[Corrections/clarifications following Tekmira conference call: Apparently, the new company has also exercised an InterfeRx pick for the ApoB program. In addition, the PLK-1 option by Alnylam is for a 50:50 development and commercialisation arrangement to be exercised any time before start of phase II trials.]

Over the past weekend, as the RNAi world was congregating in nearby Whistler, something very unusual happened in Vancouver, BC. For the sake of RNAi Therapeutics, personal ambition has been set aside and an equitable and very cleverly crafted outcome was found. The outcome relates to a fight for one of the leading systemic RNAi delivery platforms that has cost the Tekmira and Protiva literally almost as much in legal and other related expenses and management time as was spent on technology development. It has also put their many partners, currently Alnylam, Regulus, Merck, Roche, and others, with at least four more pharmaceutical parties evaluating the technology, in a difficult situation and created many inefficiencies.

With more than $35M in cash (Tekmira: ~$20M; Protiva: ~$15M; Roche and Alnylam equity investments: $10M; minus fees, minus severance pay), leading liposomal siRNA delivery IP and science, numerous and lucrative partnership activities, lawsuits out of the way, plus 7 InterfeRx licenses from Alnylam, the new Tekmira will emerge as the first strong public RNAi Therapeutics delivery-focused company. The $10M equity investments for $2.4 a share, $5M each by the Roche Venture Fund and Alnylam, values the combined company at over $100M, almost 3x the current price, with 48% owned by former Tekmira, 44% by formerly privately held Protiva, and 4% by Alnylam and Roche each. It is moreover more than likely that this sets the stage for further partnership arrangements, some of them potentially similar to the one involved in the exercise of the first target pick under the InterfeRx license.

Through this reunion, Tekmira has now also selected its long-awaited first target under InterfeRx. The target is polo-like kinase 1 which Protiva had been developing for the treatment of liver cancer and metastatic colorectal cancer. Perhaps related to the fact that one of Alnylam’s lead development programs is also aimed at liver cancer, Alnylam has retained the right to obtain this program prior to the start of phase II trials. The other development program in Protiva’s portfolio is/was ApoB 100, for which no InterfeRx pick was exercised. This is consistent with the observation from probably half a dozen RNAi studies on ApoB knockdown that I have heard from which have reported sequence-specific fatty liver phenotypes in pre-clinical models.

This very positive business development goes hand in hand with the recent presentations of much improved SNALP and SNALP-like formulations pushing the IC50s down to the 0.1mg/kg range, particularly important since the therapeutic index is by far the most pressing issue with liposomal RNAi delivery. Methods enabling the delivery of liposomes into the endosomes of target cells, with subsequent safe, yet efficient escape of the siRNA cargo into the cytoplasm, will be critical. I am sure the scientific group led by Ian MacLachlan will be best qualified to find such solutions.

This is also the time to congratulate the managements of the parties to a deal that until now almost seemed impossible given the complicated entanglements and heated exchanges in the past. One can only hope that this sets an example for RNAi Therapeutics to hold off on the legal battles until real products come close to reality.

Disclosure: The author currently owns Tekmira stock.

A Framework for Progressing RNAi Therapeutics into the Clinic

This week was quite busy for the RNAi Therapeutics space with important corporate developments for CytRx/RXi (succesful spin-out/IPO), Nastech/mdRNA (announcements of patents filings and scientific advisory board), Silence Therapeutics (extension of AstraZeneca collaboration to Atuplex delivery), and Arrowhead Research/Calando (filing of first cancer IND). I hope to provide a wrap-up soon, but as I am contemplating the further developments in delivering RNAi to the liver, I would like to use the clinical development of liposomal RNAi as a case example of how one might think about development timelines for RNAi Therapeutics in general. While this discussion focuses on SNALP/liposomal-siRNAs just because it is an area that I am following more closely than others, it can easily be translated to for example to PEIs and delivery to the lung, or for that matter AAV/lentivirus and delivery to the brain.

RNAi Therapeutics are thought to speed up drug development, because once a target is identified, finding an appropriate siRNA should be a straight-forward process. However, it is clear that right now developing ways to get the RNAi triggers into the cells is the rate-limiting factor, meaning that the benefits of rapid drug development won’t necessarily all be realized for a good fraction of the first crop of RNAi Therapeutics. In order to assure that the next batch may more readily move through development, it will therefore be important to establish a number of predictable delivery technologies for the different target tissues. Once such a delivery system has been identified for a given tissue, virtually any gene of interest could be targeted in a manner that reduces development risk mainly to target risk (should be quite low given the virtually unlimited target space of RNAi) and safety profile of the particular RNAi trigger (particularly due to the less predictable off-targeting effect).

The question for Alnylam now is whether to choose liver cancer or hypercholesterolemia as the indication for their first SNALP/lipidoid-RNAi IND. Assuming that they feel quite confident with the gene targets and that they intend to use the same delivery formulation since the target tissue is fairly similar (normal versus tumour liver tissue), why choose one over the other? As we know, safety and finding a SNALP/lipidoid formulation with a good therapeutic index is as much of a concern as is efficacy. One could argue that starting with liver cancer may be a less risky business decision since the length of dosing and nature of the disease should be more forgiving in terms of the tolerated safety profile. By contrast, to derive a cardiovascular benefit through cholesterol lowering requires long-term chronic treatment which is why tolerability is so important for this indication. On the other hand, the PCSK9 program would provide a host of information as to the efficacy of this novel delivery system. Circulating PCSK9 levels could be readily measured and this information be used to adjust dosing strategies not only for the late-stage development of this particular program, but also all the other programs, including liver cancer, making use of the same delivery system.

I can imagine that the decision won’t be an easy one to make, but with improvements in the therapeutic index of SNALP-RNAi, the PCSK9 program becomes relatively more attractive. If successful, it should be possible to realize the anticipated advantages of RNAi Therapeutics in terms of increased development speed. Although true for drug development in general, from a technology and business development point-of-view it is therefore particularly important for the field of RNAi Therapeutics that its early clinical candidates, using unproven delivery systems, target genes where proof-of-concept can be established at an early stage.

Preventing Heart Disease with RNAi Therapeutics

High blood cholesterol, a major risk factor for heart disease, already is an enormous public health problem that is likely to worsen given current lifestyle and demographic trends. Fittingly, statins, a class of small molecules that inhibit cholesterol synthesis and therefore have a wide range of effects that together lower the risk of developing heart disease, are probably the best-selling drugs on the market today. However, many patients still do not achieve their cholesterol goals and there is significant demand for new innovative treatment options.

An RNAi Therapeutic alternative, due to the ability to target almost any gene, is particularly interesting because of well validated targets, but which have proven refractory to targeting by the existing drug classes. These genes are not directly involved in cholesterol synthesis and targeting them should be synergistic with statins. Currently the most interesting gene targets are ApoB100 and PCSK9. ApoB100 is the sole protein component of “bad” LDL cholesterol and is produced in the liver. Notably, targeting ApoB100 by RNAi in the using cholesterol-conjugated siRNAs in 2004 by Alnylam scientists was also the first demonstration of gene silencing following systemic administration of siRNAs. This study not only showed considerable reductions of ApoB mRNA and protein, but also the hoped for decrease in blood LDL cholesterol. I should add that clinical data from phase I and II trials conducted by ISIS Pharmaceuticals using antisense oligo technology further document the promise of ApoB100 as a target for hypercholesterolemia. It will be interesting to follow their further clinical progress, but I expect siRNAs to do even better, because of increased specificity and potency thus allowing for lower amounts of nucleic acids to be administered.

Two years later after the demonstration of systemic RNAi in mice, Alnylam scientists then reported even enhanced ApoB-100 silencing and improved lipid profiles in monkeys, this time using liposomal formulations originally developed by Protiva Biotherapeutics. These and similar liposomal formulations have proven to be very efficient for liver gene knockdown in general and are now being pursued by a number of companies in preparations for the first systemic RNAi clinical trials. Unfortunately, however, their promise has also led to legal haggling as to who owns the IP behind this delivery technology. Companies involved in this dispute involve Protiva, Inex Pharmaceuticals, and Sirna Therapeutics/Merck and I hope that legal issues will not do further damage to the development of this promising delivery technology. No matter who owns the commercial rights to the technology, Protiva scientists have to be credited with this major achievement.

Interestingly, despite their publication record on ApoB100, Alnylam decided to target PCSK9 for the treatment of hypercholesterolemia. Although I cannot exclude that this move is partly due to a deal with one of their collaborators in siRNA delivery, PCSK9 has a lot riding for it. In fact, they are pursuing this program in collaboration with scientists from UT Southwestern Medical Center that arguably are world-leading in the genetics of hypercholesterolemia. PCSK9 itself is a protease that degrades LDL-receptors (LDL-R). LDL uptake by the liver is important for clearing LDL in circulation and it is expected that increasing LDL-R levels by suppressing their inhibitors should lower LDL cholesterol. Indeed, data presented at this year’s Keystone Meeting support this thesis. However, it should be kept in mind that many drug development projects fail, not because the drug fails to reach its target, but because of side-effects. Side-effects are a particularly important consideration for drugs that have to be taken chronically as is often the case for hypercholesterolemia. So one of the major questions here is whether long-term downregulation of PCSK9 can have adverse consequences. Here, the genetics of PCSK9 are compelling: Naturally occurring mutations in the human population that increase PCSK9 activity have been shown to increase LDL and lead to hypercholesterolemia, while those that inactivate it lower LDL dramatically- without any obvious detrimental consequences! Of course, compensation mechanisms cannot be excluded, but this is probably as good as you can get with choosing a target based on human genetics.

In summary, due to the availability of excellent “non-druggable” targets and the ability to knockdown genes in the liver with current delivery technologies, RNAi Therapeutics are a promising strategy for treating hypercholesterolemia. Alnylam is expected to initiate phase I studies in the second half of this year, and I would not be surprised to see further studies being initiated in the near future by Protiva or Inex (mere speculation here though). The major obstacle for these trials that I see are side-effects due to the liposomal formulations, and my advice would be to carefully characterise them in animal models before committing to phase I instead of simply bowing to investor expectations.