ISIS Pharmaceutical Reveals Dynamic PolyConjugate Efforts

When Arrowhead Research made a splash 1 ½ years ago at the Boston OTS meeting in late October 2012 with impressive subQ DPC knockdown efficacy in monkeys, there was a large number of meeting participants crowding the speaker after his presentation.  Although I sat a few rows away, the most eager questioner was an employee from ISIS Pharmaceuticals who managed to beat the Merck representative to the podium!

There were times when I believed that the interest of large companies in the technology of small companies boded well for partnership potential.  It has become clear to me, however, that while this may be true to some extent, the first instinct by the large guys is to get close to the innovators so that they can appropriate as much of the technology as possible without paying a dime.

While I have long shelved Merck into that category and DPCs will now be a research priority at Alnylam following their acquisition of Sirna/Merck, a now published patent application by ISIS Pharmaceuticals on melittin-based, GalNAc-targeted single-stranded antisense delivery (ssRNAi and conventional ASO) demonstrates that ISIS ticks no different.

With a priority date of WO 2014/089146 A1 of December 4, 2012, this poor employee and collaborating patent agent had to stitch together a patent application in just a month after returning home from the conference.  Unsurprisingly, the patent application lacks any actual experimental data to support the 'ínvention'.

I don’t want to be too cynical about this as this is how the industry and the patent system function.  It is an important lesson for small companies though that they should not get overly excited about interest they generate for their technology and they should only engage in deeper relationships once they have established that the larger party is not just trying to steal their technology by pretending to collaborate with them.

It is this unwillingness to share and attendant mistrust that in my experience impedes much business development that makes great sense on paper.  This ultimately delays timelines, leads to litigation, and makes the pie smaller for everybody.

And for the future of gene knockdown in the liver…if ~5mg per week may be possible for GalNAc-targeted gen 2.5 RNaseH ASOs, one can only wonder what a melittin-type escape mechanism would add to its potency, and safety. 

Comment on Seeking Alpha bear article on ISIS Pharmaceuticals

Last night, a detailed bear article on ISIS came out that shook the market in after-hours trading.  In summary, the thesis rests on the poor safety profile, especially immunogenicity of gen 2.0-based KYNAMRO (2’MOE gapmer) and that this is likely to translate to all other gen 2.0 drugs based on shared chemical composition and the (in my opinion idiotic) claim by the CEO of ISIS that KYNAMRO is a success and is representative for gen 2.0.  Talk about shooting yourself in the foot.

While I agree that the KYNAMRO data have raised legitimate questions around the safety of gen 2.0 phosphorothioate oligonucleotides, the bear article conveniently ignores the abundant clinical data that have emerged since for a number of other antisense drugs based on gen 2.0 chemistry.  These support the claim by ISIS that through improved screening, they are now able to better weed out the sequences that will likely prove immunogenic in the clinic. 

Importantly, in oligonucleotide therapeutics in general, while nucleic acid chemistry has a great influence on whether a molecule is immunogenic, it is the exact sequence composition that ultimately decides whether this is actually the case.

This is illustrated by the recent phase II clinical results for ApoCIII (no discontinuations noted), Factor XI, and GCGR.  Not only were robust gene knockdowns achieved, in sharp contrast to KYNAMRO, the company claimed that they were no flu-like symptoms, chills and other symptoms indicative of the immunostimulatory potential of oligonucleotides.  By contrast, about 1/3 in the KYNAMRO studies exhibited such events, with even higher numbers in the open-label extension phase.

Granted, given that these were 13-week studies, it is impossible to disprove the thesis that things are bound to get worse over the long-run.  However, no flu-like symptoms versus 1/3 of patients exhibiting flu-like symptoms in studies of comparable duration is a dramatic difference and allows one to extrapolate that the safety of the follow-on drugs will similarly be greatly superior to KYNAMRO over time.

While I had been tempted to let the Seeking Alpha article by Dr. Anonymous pass as raising legitimate concerns, the blatant failure to mention the more recent experience with gen 2.0 and the after-hours action last night makes this article suspect and outright useless given the lack of new information or insight.

Further Possibilities for Arrowhead Phase I Dose Extension

Last night’s speculations on the reason for the phase I dose extension of the HBV RNAi phase I trial by Arrowhead Research was actually positive: they are tackling the potency issue presented by the 2mg/kg dose. 

In addition to further increase dose, it could also involve prolonging drug infusion times which we know, based on Alnylam’s GalNAc data, could optimize hepatocyte uptake by the GalNAc-targeted DPCs.

Regardless, you have got to question why extending beyond 2mg/kg had not been part of the original plan and why the study extension has not been publicly discussed, e.g. in the latest conference call.   

Extending the study to further potency is the most rose-colored scenario that one can draw.  The other scenario would have to do with safety concerns, possibly raised by regulators.  As I had discussed before, for DPC, especially the 2 molecule version, the tox-limiting element is the melittin-like peptide.  Melittin is derived from bee venom and although the MLP is not the identical sequence as melittin, there are theoretical concerns around allergic reactions.  In general, having peptides involved raises a new set of immune issues, especially when you require 2mg/kg of them.

Of note, one of the exclusion criteria for the phase IIa HongKong trial is excluding those with a history of allergy to bee venom, indicating that this has been an issue with regulators:

·         Has a history of allergy to bee venom or history of hypersensitivity reaction requiring an emergency visit to a physician or hospital and/or requirement for treatment with steroids and/or epinephrine.

So how about adding transient immune suppressant to the mix- e.g. an anti-histamine?  Nothing spectacular, a safety precaution, but once again highlighting the benefit of Arrowhead Research making advances with the single-molecule version, also for applications outside the liver (see today’s positive news around Endocyte and folate targeting for cancer as just one example of where such research could be directed at).

Potency matters, and wouldn’t it be ironic that as Tekmira is weaning itself off immune suppression (à dose-intensive TKM-EBOLA trial), on the back of developing more potent formulations, Arrowhead Research, not known as a public supporter of liposomal RNAi delivery, is adopting such?  

Arrowhead Research Breaks Up Dynamic PolyConjugates into Two

Arrowhead Research announced yesterday that it had received Notice of Allowance from the USPTO for a Dynamic PolyConjugate-related patent application (for systemic RNAi delivery).  Instead of it being your run-of-the-mill patent PR involving known technology that finally received patent protection, it was really about revealing Arrowhead’s fundamentally new approach towards DPC delivery (for my take on the original form of DPC, see here).

The patent, part of a series of patent filings that have come out recently, shows that under Roche’s ownership, the technology has morphed through a number of iterations from the original complex polyconjugate chemistry combining endosomolytic polymer, masking groups, RNAi trigger, PEG, and cell targeting ligand all in one molecule (schematic shows such molecule and presumed mechanism of delivery), into one where a RNAi trigger and the masked polymer, both targeted individually, are administered as separate agents. 

One problem with the original design has been that combining all the functional groups, including negatively charged RNAi triggers and positively charged polymers, into one molecule was not particularly easy.  The tendency to aggregate and poor yields made it a quite expensive and difficult-to-scale proposition.

Turns out that such complicated chemistry wasn’t needed after all.  As long as the RNAi trigger and the masked endosomolytic agent end up in the same place, it does not make much of a difference whether they are getting there as one molecule or separately.  In the example provided, namely for gene knockdown in hepatocytes, the RNAi trigger could be conjugated to either cholesterol or a cluster of galactose sugars, whereas the masked endosomolytic polymer was targeted to the hepatocytes by galactose.  Viewed differently, the polymer allowed the cholesterol-siRNA that apparently gets trapped in the endosomes when alone to be released into the cytoplasm.  Hence, the multi-fold increase in potency (Arrowhead Research says it’s 500-fold) over Alnylam’s original 50mg/kg cholesterol-siRNA report (Soutschek et al., 2004).

Another potential advantage of this separated approach is that it makes each component smaller, perhaps 'one day' enabling subQ dosing.  However, as mipomersen's FDA AdCom meeting briefing docs show, when it comes to subQ dosing, be careful what you wish for.

Manufacturing appears to have been one of the issues delaying the clinical translation of DPCs for quite some time (Arrowhead Research says they are ready to file an IND in Q2 2012 for Arc520 in HepB).  Toxicity, mainly due to premature unmasking in the blood instead of in the target cell endosome, seems to have been the other main reason.  Such premature unmasking also adversely affected circulation times, thereby rendering attempts to get beyond the liver, one of the original promises of DPCs, futile.  We will probably get word from the company soon what solutions it found for this challenge, but it seems that, based on the emerging patent literature (including non-human primate data; e.g. WO 2012/083185), masking the membrane penetrating peptide mellitin with endosomal protease-sensitive groups, is a promising approach.