Checkpoints Drugs Promise to Unlock RNA Therapeutics Cancer Potential

If you are involved in cancer drug development, you are probably thinking of ways to exploit checkpoint inhibitors for your purposes.  Checkpoints are the mechanisms whereby cancer cells avoid being recognized by the immune system as foreign and the initial clinical results of inhibiting them, e.g. by targeting CTLA4 and PD-1/PD-L1, has caused immune-oncology as a whole to take the cancer drug development space by storm.

Suddenly, every scientist and their technician believe that by taking checkpoints out of the equation, their immune approach to cancer, which in many cases was marked by failure after failure in the past, will work. 

Take e.g. cancer vaccines and the idea of grinding up tumors and use the cell mash to train dendritic cells.  Sounds compelling to me, but I also know that I lost a bunch much money on the very same idea 10 or so years ago with nothing, but some early promising data from the clinical Wild East to support it. 

Others meanwhile believe that their technologies may enable immune-oncology by e.g. being able to modulate the tumor microenvironment so as to permit better access of the tumor killing cells.

RNA Therapeutics are no exception.  RNA Therapeutics, due to its endless targeting opportunities, has always been considered promising for oncology, but has struggled to show clear-cut success either due to drug delivery issues or due to the difficulties of predicting immune activities based on rodent studies.

Emblematic of this reversal of fortunes is the toll-like receptor (TLR) field of activating the innate immune system with oligonucleotide stimulants.  The idea here is to provide an environment that is more conducive to tumor cell killing and/or to directly impact tumor cell survival (e.g. interferon stimulation).  Art Krieg, of TLR9 (CpG) fame, but who has been erring as its lost son in the (blooming) deserts of RNAi, RNaseH antisense, splice modulation, and RNA activation, is apparently re-energized enough to go back to TLR Therapeutics and has started Checkmate Pharmaceuticals which will likely try and harness TLR agonists for cancer immunotherapy.

Nanoparticle delivery may also see a revival.  This is because they have a propensity, usually undesired, to be taken up by phagocytic cells, some of which may be effective in antigen presentation (e.g. dendritic cells).  I have thus noticed that a number of mRNA cancer vaccine approaches involve nanoparticle delivery with the aim of expressing tumor antigens in the training camps of the immune system, the lymph nodes.  

Nanoparticles may also be a way to knock down the gate-keepers in the tumor microenvironment which inhibit tumor infiltration by cytotoxic T (incl. CAR T-cells) and other helpful immune cells.  Since gate-keepers should be most useful when positioned at the entrance, this might actually take advantage of another limitation of many nanoparticle delivery technologies, namely getting stuck close to the vasculature instead of penetrating deep into the tumor.

Once deeper into the tumor, the struggle may not be over for cytotoxic T cells and tumor eating cells due to potentially immunosuppressive activities in the tumor microenvironment.  This is the new positioning for the phosphorothioate-based antisense molecule ISIS-STAT3 by Isis Pharmaceuticals and AstraZeneca for which, like for other phosphorothioate-based approaches, the demonstration of robust uptake and gene knockdown activity in tumor cells themselves is lacking, but functional uptake in cells of the tumor microenvironment has been reported.

Finally, RNA Therapeutics such as CRISPR genome editing or straightforward self-delivering RNAi (see recent license of MirImmune from RXi Pharmaceuticals) can be tools for the ex vivo preparation of T- and dendritic cells.  A self-delivering approach may be advantageous here as it may function in normal cell culture media and thus not confound cell signaling pathways in the maturation of these cells.

Investor, tread carefully

Overall, I’m convinced that there are synergistic potentials to be exploited and checkpoint inhibition may open the door to certain that have failed in the past.  Nevertheless, one should be mindful that most immune oncology drugs only work in a fraction (maybe 25%) of patients and the current hype around immune oncology guarantees that there will be many bad apples for investors to avoid.  Trust me, I've seen it when RNAi was indiscrimately hyped and abused for short-term financial gain in 2006-8.  Just because you can contrive a link to immune oncology or because a desperate Big Pharma does a deal, does not mean that all the biological problems will dissolve.  The bubble will burst after which mostly only well-financed quality plays will recover.

Disclosure: I am fishing for short opportunities in the immune oncology space as a hedge against a (hopefully temporary) correction to what seems to be an in a number of areas (e.g. gene therapies, immune oncology, one-drug orphan wonders such as Alexion etc) overheated biotech space.

Co-delivering Antisense and RNAi for Cancer

The upcoming phase I top-line data for ISIS-STAT3Rx in liver cancer (HCC) to be presented at the upcoming EORTC-NCI-AACR triple meeting in Barcelona (Nov 18-21) will be an important test of the potential utility of RNAseH antisense oligonucleotides (ASOs) incorporating high-affinity chemistry in oncology.  

Based on the body language by ISIS Pharmaceuticals* and last week's $7.5M milestone payment from partner AstraZeneca for progress on ISIS-STAT3Rx (aka AZD9150) , I am tempted to speculate on more than just ‘encouraging’ results.  On the other hand, Regulus Therapeutics partner Sanofi at the Canton Nucleic Acid Forum (CNAF) also last week, noted the need for formulating antisense oligonucleotides to get their anti-miR21 oncology candidate into liver cancer tissue. It is likely that they will be using liposomes for that (--> Tekmira?).

* I was surprised that at the CNAF in Guangzhou, China, Brett Monia from ISIS mentioned STAT3Rx and cancer right after gene silencing in the liver as the next interesting application for ASOs- that is ahead of even the exciting CNS opportunity.

The discrepancy in body language may be explained by just cultural differences (conservative, blasé Big Pharma versus risk-taking, enthusiastic biotech); it may also be a reflection of different requirements for effective tissue concentrations with RNaseH versus anti-microRNA modalities or different target requirements.  Whatever the reason, the Sanofi comments clearly support the notion that getting naked, even phosphorothioated oligonucleotides into cancer tissues is not as robust as with other tissues such as the liver and kidney.

I am therefore pleased that it is a Big Pharma, the last place where I had expected that from, that is connecting the dots and is considering delivery formulations, even the supposedly ‘toxic’ LNPs.  The concept is that the nanoparticle would facilitate a higher tumor concentration of the oligonucleotide, and once in the tumor interstitial space, cellular delivery may be facilitated via two routes.  Firstly, it may be traditional liposome-dependent cell uptake and cytosolic release.  Alternatively, those LNPs that get stuck in the interstitial space would spill the phosphorothioate oligo which may then diffuse further and get into the target cell by self-delivery. 

The same concept, of course, applies not only to phosphorothioate ASOs, but also to self-delivering RNAi triggers (+/- conjugation).

But why stop there? I propose that for cancer delivery, one should strongly consider and co-formulate RNAi triggers and ASOs into a shared nanoparticle.  They could target either the same gene, or they could target different genes thus taking into account the desire for a multi-pronged attack on cancer   (-> resistance).  In that scenario you would benefit from the superior gene silencing efficacy of RNAi triggers in those cells that they were able to reach, but then extent your reach with the help of the more agile, penetrative single-stranded antisense molecules. 

As such, PS-ASOs have an advantage in addressing intra-tumor heterogeneity of the EPR effect which is a well-recognized problem of nanoparticle delivery for cancer.

Another benefit of combining RNAi triggers with RNaseH ASOs is that you could achieve additive gene silencing activity when going after a shared target.  For example, if the RNaseH ASO and the RNAi trigger had both say a 70% knockdown activity on their own in the nucleus and cytoplasm, respectively, the combined activity would likely be ~90% which genetically could make a huge difference.

There is also a potency benefit, although more minor, when going after different targets because at least in RNAi, the best you can hope for when combining RNAi triggers against different targets is that they do not interfere/compete with each other.

With solid cancer data from both Tekmira (RNAi) and ISIS/AZ out over the coming weeks, we will soon get a sense of whether the field has moved forward in oncology and what the next steps ought to be.

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.

Tekmira Setting New Standards in mRNA Therapeutics…and They Have Only Started

Tekmira today presented impressive data on pre-clinical messenger RNA (mRNA) delivery to the liver and solid cancers (PR here, slide deck here).   The data presented at the AsiaTides in Tokyo greatly exceeded those reported in the literature, including a 4 log increase in potency of liver gene expression compared to the seminal paper by Kariko et al.paper (2008). 

Importantly, the formulation process and chemistry were optimized for mRNA delivery thus generating electron-dense ~80nm particles and easily surpassing >90% encapsulation efficiencies that are thought to be required to pass regulatory CMC muster.

Tumors giving liver run for its money

What had caught my eye when Tekmira presented firstmRNA delivery data at the Tuebingen mRNA conference in October 2013 and which was further substantiated in the present presentation, in terms of absolute gene expression, their mRNA delivery seems to perform as well if not better in liver cancer and non-liver cancer models compared to in normal hepatocytes.  This could be due to a less RNA degradative environment in tumors versus the liver of which an important function is detoxification.  This is supported by the fact that the duration of mRNA expression in tumors greatly exceeded that in the liver (a gene with a short protein half-life was used).

This made me think of the recent oncology spin-out (Onkaido)by mRNA Therapeutics company Moderna, the darling of mRNA Therapeutics which has raised around half a billion dollars in partnership money (AstraZeneca, Alexion, DoD) and fund raisings over the last 18 months alone.  The spin-out and internal focus on genetically defined orphan diseases may mean that Moderna would like somebody else to fund Onkaido, for example as part of a joint venture.  Remember, for most Big Pharma companies, RNA Therapeutics are first and foremost interesting for oncology as it allows them to go after the targets that their scientists have been dreaming about for so long yet were not able to drug.

Given that most of the de-risking in oncology drug development occurs late in clinical development, it is debatable whether Tekmira, already with a lead candidate in oncology (TKM-PLK1) should focus their in-house mRNA development attention towards oncology initially and whether this might not be better done as part of a spin-out/joint venture (Onkaido and/or Big Pharma).

For the liver, mRNA expression was detected in essentially every hepatocyte.  This supports the use of SNALP-mRNAs not only for the use of the liver as a factory for protein production, but also for diseases with defects in single genes expressed in the liver, including those genes that act only in the cell that they were expressed in (cell autonomous).  Compared to oncology, such indications would also allow for earlier clinical de-risking and together with orphan status mean that they better match the profile of a (still) sub $500M market cap company.

More upside

Given that Tekmira has only been working on mRNA Therapeutics for a year plus (1-year stability data were presented) and since simple off-the-shelf mRNA chemistry was used, one can only dream which diseases could be addressed and where the company could go with this, including developing their own mRNA Therapeutics instead of viewing it as a simple monetization opportunity. 

Tekmira mRNA developments that I am looking out for include advances in mRNA delivery to the lung epithelium.  Tekmira has been, and according to the presentation is still actively working on inhaled LNPs, and it would be logical if they adapted that effort towards mRNA delivery.  Expressing CFTR in lung epithelia for the treatment of cystic fibrosis (CF) would be an obvious target here that could rally a lot of support from various stakeholders (important for companies like Tekmira).  Gene therapy involving the inhalation/instillation of DNA to the lung has failed, in large part due to the difficulty of getting the DNA from the cytoplasm across the nuclear membrane into the nucleus.  Just like in RNAi, mRNAs only need to get into the cytoplasm, a much simpler task.  Moreover, in CF you should not need to get the mRNA into every cell.

A final opportunity for Tekmira is the co-formulation of mRNAs and siRNAs into a single LNP.  Imagine an oncology drug targeting both cancer drivers such as PLK1 and overexpressing tumor suppressors.

Oyasuminasai.

Disclosure: long TKMR.

Cancer RNAi Therapeutics Moving On

As RNAi Therapeutics targeting genes expressed in the liver, especially for orphan indications, have captured much of the recent interest in the technology, it is time to once again pay closer attention to RNAi Therapeutics in the oncology space.

Atu027 and TKM-PLK1 Moving into Phase II

Silence Therapeutics have just announced that they got the green light from the German regulators to test Atu027 in combination with small molecule gemcitabine in pancreatic cancer.  Following a short phase Ib to establish the safety of the combination (note: the original phase I was a monotherapy trial), the plan is to rapidly move into phase II which will aim at establishing proof of concept for efficacy.  Depending on the funding situation, it is possible that the company will expand Atu027 into other indications in phase II, possibly in collaboration with private investigators in the UK.

Clearly, the strength of Atu027 is its safety profile so far, one that has surpassed my own expectation for this positively charged lipoplex formulation.  The clinical attraction meanwhile is that Atu027 aims at a quite novel anti-cancer mechanistic approach by inhibiting metastatic spread by fortifying the vascular endothelia. 

The challenge with Atu027, however, is that the gene target, PKN3, remains a relative black box.  This not only demands a certain leap of faith in mechanistic terms, but also complicates the clinical development as biomarkers and other tools are not readily available.

This is quite different from TKM-PLK1, the cancer RNAi Therapeutics by Tekmira.  Polo-like kinase 1 is a hot target, but specificity/safety issues have so far dogged drug development efforts with small molecules, most notably represented by Boehringer-Ingelheim.  By contrast, the SNALP RNAi delivery approach promises to be more cancer tissue targeted and consequently should avoid some of the dose-limiting toxicity observed so far, especially the hematologic ones.

TKM-PLK1 has flown a bit under the radar and the phase I update late last year did not capture much attention.  This is probably because the response rate did not seem too much to get excited about.  However, as Ian MacLachlan, the CSO of Tekmira, pointed out at the AsiaTides meeting last week, it was a small dose-escalating phase I trial (20-30 patients) in advanced solid cancer patients and only four patients actually received TKM-PLK1 for two or more cycles (6 infusions over 2 months) at 0.6 mg/kg or above, dose and durations you would think would be required for advanced cancer patients to get a chance to respond in the first place. Notably, two out of those four showed signs of efficacy: one partial response and one with stable disease after more than 6 months on study drug.

In light of that, the phase I profile of TKM-PLK1 supports my view that it could be the foundation for an exciting PLK1-related cancer franchise for Tekmira and I look forward to seeing the full results presented at the upcoming AACR meeting.  My attention will be particularly focused at any direct measures of target knockdown.  Beyond that, with the company’s healthy financial situation, I look forward to a rich phase II strategy involving a number of solid cancers and innovative study designs such as patient selection based on genetic criteria.  As good as Tekmira's science is, they now also need to be as proactive and innovative on the clinical front.

ALN-VSP02 and CALAA01 Falling Behind

As TKM-PLK1 and Atu027 are moving into phase II, fellow early movers in oncology RNAi ALN-VSP02 and CALAA01 are falling behind. 

The next step for ALN-VSP02 will be a phase I in hepatocellular carcinoma (‘real’ liver cancer) in China under a license by Alnylam to Ascletis.  As noted by Patrick Lu of Sirnaomics at AsiaTides though, it would be a mistake to believe that the Chinese regulatory environment is any less demanding than in the West.  Au contraire, it seems that much more paperwork is required to file an RNAi-realted IND as the authorities there are keen on building their expertise in this new technology.  Expect a delay of at least 6 months from IND application to the green light to go ahead, after all the paperwork has been submitted.  For Tekmira watchers, I expect the $5M milestone thus in 2014, not in 2013.

While ALN-VSP02 still has a pulse, despite of the fact that it lacks the long circulation thought to be necessary for cancer uptake (note: delivery to liver cancer is a very different animal from delivery to normal liver; TKM-PLK1 is a long circulating SNALP), RIP CALAA-01 by Arrowhead Research.  Having said that, the value of CALAA-01 to Arrowhead Research has not been lost entirely as the company has filed for a patent covering a low/high dose strategy of minimizing immune stimulation.  

As the recent high-profile pulling from the market of a pegylated peptide (Omontys by Affymax) due to hypersensitivity, even anaphylactic reactions demonstrate (and also the infusion reactions reported by Alnylam in their SNALP RNAi Therapeutics trials), administration-related hypersensitivity reactions are an issue for the entire drug development arena.  In order to rescue the value of a number of blockbuster franchises, I expect that changing administration schedules could be one area attracting increased attention.  A patent here could have unexpected value.   

A New Crop of Cancer RNAi Therapeutics

Behind TKM-PLK1 and Atu027, a new crop of cancer RNAi Therapeutics is emerging.   Dicerna has signaled that it will finally move into clinical development (Q1 2014) with a liposomal Dicer-substrate formulation with a focus on liver cancer.  Of note, the liposomal formulation process is quite distinct from that of SNALP involving sequential core and envelope formation steps, potentially amenable to ligand-directed targeted delivery.

Another program worth following is another one for liver cancer, the subject of a collaboration of Korean company Bioneer andSanofi-Aventis.  The attraction of that program is that the nanoparticle here, SAMiRNA, comprises a single molecule, even to the extent that the RNAi trigger and delivery components can be manufactured on a single column.  Although I’m opposed to the fundamental notion that the ease of route of administration and the manufacturing process should drive drug development, don’t underestimate the attraction of meeting idealistic product profile when it comes to partnering with Big Pharma.    

The efforts above are a reminder that cancer could be an even bigger commercial opportunity for RNAi Therapeutics than liver-related indications.  The genome-wide targeting opportunity with RNAi Therapeutics has not been lost.  The pharmaceutical industry is watching.

Register for the GTC RNAi Research and Therapeutics meeting in San Francisco today (June 20-21).  Get a free RNAi Therapeutics blog T-shirt and 20% discount on registration by entering discount code 'RNABLG13'.

AstraZeneca Shows Continued Commitment Towards RNAi Therapeutics through Partnership with Silence Therapeutics

One week after announcing the grant of a US patent covering RNAi triggers with enhanced guide strand loading, Silence Therapeutics today announced the one-year extension of its R&D collaboration with AstraZeneca for the ‘identification and optimization’ of five siRNAs targeting genes involved in cancer and respiratory disease. This relationship dates back to 2007 when AstraZeneca paid Silence a 7.5M pounds Sterling technology access fee plus the usual potential for future fees and milestones. After similarly extending and expanding relationships earlier this year with AstraZeneca and Dainippon Sumitomo in RNAi delivery, Silence Therapeutics has met important partnership goals earning it time to now prove to the investor and pharma worlds that its merger with Intradigm also brought with it technological synergies.

The way I read the AstraZeneca extensions is that Silence Therapeutics was certainly able to convince AstraZeneca that it is a RNAi Therapeutics company with scientific credibility, but that AstraZeneca still needed extra time before it could fully commit to Silence Therapeutics. It is interesting to speculate that AstraZeneca was a major force behind the Silence Therapeutics-Intradigm merger, as Intradigm had filed for a number of patents covering siRNA sequences against cancer-related as well as inflammatory targets also useful for respiratory diseases. Some of these have actually started to issue and may come in handy for this siRNA-specific collaboration [update: the company informed me that the Intradigm RNAi triggers would not be part of this collaboration, and re-confirmed that the RNAi trigger and delivery collaborations are separate. Sounds to me like they are holding back, possibly hoping to monetize some of these assets on even better terms to another potential licensee or as part of a larger collaboration with AZ eventually].

As to the targets, I could imagine that, based on the unmet need and AstraZeneca’s interests, RSV infection, asthma, COPD, and solid cancers esp. primary liver cancer are among them. Of note, mdRNA announced earlier this year an early collaborative effort with AstraZeneca China for studying that company's liposomal delivery technology for liver cancer, and today’s press release mentioned that AstraZeneca's Chinese R&D branch was part of the Silence collaboration, too. Since Silence Therapeutics appears to be keen to emphasize that the siRNA and delivery collaborations are separate- scientifically not necessarily the most sensible approach, but a deficiency that may open up the prospect of a more lucrative arrangement in the future- it is certainly an interesting thought if Silence’s siRNAs were to be formulated in mdRNA’s liposomes. Of course, it is more likely that mdRNA and Silence compete with each other for AstraZeneca China’s favor in liver cancer, but still...

As I said, it would eventually make a lot of sense to consolidate the two efforts, siRNA and delivery, into one larger collaboration. Based on Silence’s own data, I am fairly encouraged that its lipoplex-siRNA formulations could be generally useful for knocking down genes in the vascular endothelia, which not only would be of obvious relevance for cancer, but also lung disease which often involves vascular escape and infiltration of the lung by inflammatory cells. An alternative approach to siRNA delivery to the lung is, of course, by inhalation, desirable e.g. for RSV infection involving lung epithelial cells, although Silence hasn’t reported much progress in that regard. It remains to be seen what Intradigm's technology can add to that.

Ultimately, I consider today’s extension a major de-risking event for the near-term health of Silence Therapeutics. While much remains to be done, the stock at 5.5 pence and a market cap of little over $20M is simply too cheap, if not an insult to RNAi Therapeutics in general. It is especially encouraging that AstraZeneca shows continued interest in RNAi Therapeutics, a company that I honestly had at the bottom fifth of Big Pharma companies willing to embrace cutting-edge platform technologies to once again efficiently develop drugs that make a difference. Unless their goal is to buy back all their shares and eventually liquidate operations or become consumer healthcare companies selling diapers and skin lotions, realistically, it is their only way forward.