Silenseed Lifts Secrecy of First Clinical RNAi Slow-Release Formulation

Last week saw the first peer-reviewed publication of the LODER RNAi delivery system developed by Israeli biotech Silenseed (Khvalevsky et al. 2013).  Following a ~17-subject phase 0/I study in pancreatic cancer patients that was initiated in 2010 and a more recent phase I study with siG12D in ~100 patients with locally advanced, unresectable pancreatic cancer, LODER (Locally Drug EluteR) had become the first matrix-assisted slow-release RNAi Therapeutic formulation in clinical development.  Nevertheless, I have struggled to understand the basics of the technology largely based on the patent literature which is often ambiguous.

Slow-release RNAi Therapeutics

Slow-release RNAi formulations promise to minimize the need for and frequency of repeat drug administrations.  This is of particular value when systemic delivery options are limited and direct access to the diseased site difficult and/or dangerous to the patient.  Ocular applications are one such area as large molecule drugs are commonly administered by intravitreal needle injections which carry a cumulative risk of injury to the retina and other complications when given every month or two as is common today.  Other areas are wound healing applications (e.g. sites of broken bones) where you basically get the chance to apply the RNAi just once and pharmacology is only needed for a few months, or for diseases of the pancreas where surgical manipulations carry the risk of potentially life-threatening pancreatitis.

While RNAi activity in non-dividing tissues is remarkably extended- it now seems that with stabilizing RNAi trigger modifications and efficient delivery you should be able to achieve potent silencing in the liver for 2 to 3 months following a single administration- slow-release strategies are attractive if the goal is to go beyond that.

 

Slow-release strategies typically involve matrices with embedded RNAi triggers that dissolve over time thus releasing the RNAi payload.  A major challenge is to find matrices and formulations that are not only biocompatible and bioresorbable, but that do so gradually.  This is because for most matrices you initially get a great burst of activity with a relatively quick drop-off in drug release thereafter.

LODER technology

At the basis of LODER technology is the PLGA (polylactic glycolic acid) workhorse of the medical device industry.  Staying with simplicity, it appears as if the RNAi triggers are simply embedded in the ~1-by-4mm pellets in unmodified Tuschl RNAi trigger format.  As the PLGA dissolves, the RNAi triggers are liberated with about 55% released in the first week, followed by another 25% or so over the next 60 days. 

The release kinetics appear acceptable and it is good to see the RNAi trigger being protected from degradation while inside the matrix (albeit not totally unexpected).  What seems to be far from optimal, however, is the apparent reliance on intracellular delivery by naked, unmodified RNAi triggers alone.  It seems that a combination of the PLGA matrix with self-delivering RNAi triggers or other cellular delivery formulations is called for (shameless self-advertisement : I can always be had for consulting projects).

siG12D LODER

Nevertheless, the PNAS publication by Silenseed reports good evidence of gene silencing in mouse models, one involving luciferase gene silencing in a transgenic mouse with luciferase expression in the liver, others involving ectopic and orthopic pancreatic tumor masses.

Importantly, performing insightful analyses of the relationship between distance from the implanted pellet(s) and gene silencing, it was found that gene silencing was marked in a sphere up to 2mm away from a pellet.  In the pancreatic cancer models, this was accompanied by local necrosis as expected from the specific knockdown of mutant KRAS which is thought to drive the majority of pancreatic cancers.  

Given that silencing is so locally restricted, this makes me wonder how best to apply the technology in the clinic.  In the pancreatic cancer trials by Silenseed, resectable and non-resectable cancer settings have been tested, in single- and multi-dose regimens.  Intuitively, I could imagine that post-operative settings are attractive, where the pellets are deposited at the border between cancer and normal tissue following the excision of the bulk tumor to kill any remaining cancer cells much in the same way that radiation therapy is often indicated following breast cancer surgery.  In cases of non-resectable pancreatic cancer, it would seem that stuffing the pancreas with LODER pellets once and then hope for the best (maybe in combination with gemcitabine and the like) is the go-for strategy.

I am encouraged by this new way of applying RNAi Therapeutics, but also see a number of simple ways of how to improve upon this first generation LODER formulation.  This would further resolve potential IP issues that come with the use of a prototypical Tuschl-type RNAi trigger. 

Silence Therapeutics to Validate Endothelial RNAi Knockdown in Man

This Monday, Silence Therapeutics held an investor evening in London.  To my surprise, interest in the company and technology was such that 80-100 largely analysts, investors, and fund managers crowded the elegant Victorian-style room at the Royal Institution.  In stark contrast to the quaint setting, the main message of the evening was that the company won’t play it conservatively when it comes to this cutting-edge medical technology and is about to test whether their lipoplex-based delivery technologies can knock down genes expressed in endothelial cells…in Man.

Whereas RNAi Therapeutics have more or less conquered the liver, opening up a whole host of indications to RNAi Therapeutics, despite the apparent accessibility of the vascular endothelial system to delivery and promising animal studies, it has proven a more difficult tissue to firmly establish gene-specific knockdowns.  Part of this technical problem is due to the fact that the vasculature, especially the capillaries which are of most functional importance, is tightly interwoven into the tissues that they supply.   This causes experimental difficulties of obtaining pure endothelial cell populations, a particular concern when genes are also expressed in the more abundant host tissue cells.  Moreover, unlike the liver, proteins (and RNA) expressed in the vasculature are not commonly found in the serum.  The latter is of particular importance in clinical studies where taking appropriate biopsies is either not technically feasible or would be deemed unethical.

Similar to how the clinical demonstration of target gene knockdown in the liver has turned around the fortunes of the likes of Alnylam and Tekmira, Silence Therapeutics also wishes to remove remaining doubts by conducting a second phase Ib/IIa study with lead candidate Atu027, this time not in pancreatic cancer (impossible to obtain adequate biopsies in advanced pancreatic cancer patients), but for head and neck cancer (anticipated regulatory submission in 2014).  Head and neck cancer is one of the few cancers for which the tissue is readily accessible.  And while they are at it, they also will take muscle biopsies to look for PKN3 target repression, and look at a whole slew of other assays, some serum-based, for their ability to assess gene expression in vascular endothelial cells.

In addition to the clinical efforts, I also expect the company to more strongly adopt non-human primates for their delivery studies.  When it comes to liver-directed RNAi, non-human primates have been accepted to be a highly predictive surrogate for performance in humans and one can expect the same to be true for endothelial gene knockdown.

The strategic changes are accompanied by continued corporatere-organization of which the most notable overall change may be the increased clinical focus.  This effort is spear-headed by Dr. Michael Khan who is trained in internal medicine and thus has a good feel for selecting interesting indications of unmet medical need and conducting the appropriate clinical studies.  On the scientific front, the most notable change is the departure of long-time CSO Dr. Klaus Giese (due to family reasons), succeeded by long-time comrade Dr Joerg Kaufmann.

In addition to picking up details like the ones above, such investor events are also an invaluable opportunity to gather insights into the investor base and other people associated with the company.  In that regard, the new CEO Ali Mortazavi has done an remarkable job not only at expanding the technical, clinical, and business development expertise of the company, but also at putting the company in a position to become a sustainable stand-alone biotech company which, if you have followed the fate of UK biotech, is not an easy task.  With Atu027 clinical efforts in high gear and Atu111 for acute lung injury likely to join the clinical pipeline in 2014, the coming period will not only test the organizational skills of management, but also their ability to react to share-price moving clinical events.  Expecting success, Silence Therapeutics is striving for a full listing on the LSE thereby opening up the company to an even larger investor base.        

To learn more about Silence Therapeutics and related events, please follow this link.

Silence Therapeutics First to Advance Systemic Cancer RNAi Therapeutics into Phase II

Among the first crop of systemic RNAi Therapeutics for cancer (see also CALAA01 by Arrowhead and ALN-VSP02 by Alnylam), Atu027 has become the first to officially enter phase II clinical development.  Following the completion of a bridging phase Ib study testing the safety of Atu027 in combination with chemotherapeutic gemcitabine for a treatment cycle of 28 days, Silence Therapeutics announced this week that safety and efficacy of the RNAi-chemo combo will now be more rigorously tested in an expanded phase II study for the treatment of pancreatic cancer.

The bridging study became necessary since in the initialphase I study, the safety of Atu027 was assessed in isolation only.   The press release by the company now suggests that the bridging study testing 0.253mg/kg of Atu027 along with 1000mg/m2 gemcitabine was uneventful since no expansion of cohorts was deemed necessary.  Such an expansion would have become necessary if a dose-limiting toxicity had been observed.   Accordingly, the results are in line with the phase I studies where a dose limiting toxicity was only observed at the 0.336mg/kg dose of this AtuRNAi-lipoplex formulation.

Given that Atu027 is not thought to have a strong effect in terms of directly killing cancer cells, but instead is expected to inhibit metastatic spread, the company believes that it will be clinically most useful in combination with an antineoplastic agent such as gemcitabine in pancreatic cancer.  The choice of pancreatic cancer was probably driven by the high unmet medical need in this indication and it is possible that additional combinations will be explored for a range of other cancers.  Such an expansion of the Atu027 franchise will have to be balanced by the advancement of other RNAi Therapeutic candidates with more straightforward mechanisms of actions to put the company on a more balanced financial footing.

* In addition to the systemically delivered Atu027, two other RNAi Therapeutics for cancer have entered phase II development.  These are the implanted RNAi trigger-eluting siG12D LODER from Silenseed, also for pancreatic cancer, and ex vivo ddRNAi-GMCSF gene therapy combo bi-shRNAfurin by Gradalis for a variety of cancers.

Small RNAs with First Clinical Impact

Small RNAs are about to make their clinical debut. This week, Asuragen, a leading microRNA diagnostics and therapeutics company, announced that it is about to launch the first microRNA-based diagnostic test for the differentiation between chronic pancreatitis and pancreatic ductal adenocarcinoma (PDAC). PDAC is the most prevalent pancreatic cancer type and known for its late clinical presentation and poor prognosis. Because chronic pancreatitis that has a roughly comparable incidence and presents with often similar symptoms such as abdominal pain, digestive problems, and biliary obstruction resulting in mis-diagnosis rates of up to 25%, diagnostics that help to differentiate between them are invaluable for ensuring optimal treatment.

The test will be made available on May 2, 2008, from Asuragen’s own CLIA-certified test laboratory. It is a PCR-based test of apparently a single microRNA that is specific for pancreatic cancer cells and was originally identified as part of a collaboration between Asuragen and a clinical group from a hospital in Bochum, Germany [Szafranska et al. MicroRNA expression alterations are linked to tumorigenesis and non-neoplastic processes in pancreatic ductal adenocarcinoma. Oncogene 26:4442-52 (2007)].

Other tests by Asuragen, but also notably Rosetta Genomics and Exiqon in the field, are about to enter the market in the coming months. Like the present one, they are PCR-based diagnostics of one or a few microRNAs. Despite the 25% mis-diagnosis rate, it seems that the need to obtain biopsies from the pancreas is not trivial and may therefore limit the use of this particular test. Tests which may diagnose a cancer based on microRNAs isolated from blood samples, and are currently under development, should have wider applicability, although this may be at a rather late stage of cancer.

Asuragen is a private company and it has been therefore more difficult for me to follow their progress. The fact that they beat the publicly held Rosetta Genomics and Exiqon in bringing the first microRNA diagnostic to market is likely based on their heritage of having been spun-out from the RNA research reagents company Ambion (now an Applied Biosystems subsidiary), therefore giving them prime access to very relevant technologies and know-how. The fact that they operate a CLIA-certified laboratory, of course, may be another significant efficiency giving them an advantage over its competitors. Ultimately, however, it would appear that the commercial success will depend on their ability to make the test widely available through larger diagnostics distribution partners. Alternatively, microRNA diagnostics that are tied to certain drugs, such as Rosetta’s squamous versus non-squamous non-small cell lung cancer (NSCLC) Dx that ensures that Genentech’s Avastin is not used for squamous NSCLC, could benefit from the marketing reach of large therapeutics partners.

At any rate, the fact small RNAs are about to have a real clinical impact less than a decade after their widespread occurrence in biology was first recognized, is to be celebrated and indicates that their small size and stability, and their biological involvement in disease makes them a very promising class for molecular diagnostics.