Two Promising RNA Therapeutics to Face Off in Paris ATTR Amyloidosis Meeting

I’m en route a high-speed train to Paris to witness how RNA Therapeutics are starting to revolutionize the care of patients afflicted by ATTR amyloidosis.  Towards that end, the presentations on pivotal trials with Patisiran (APOLLO; RNAi) and Inotersen (NEURO-TTR; ASO) to an audience of key opinion leaders and patients at the inaugural European ATTR meeting will critically inform the adoption of these medicines.

Top-line data for these agents in the polyneuropathy-leaning form of the disease (FAP) have been disclosed previously (here and here).

This will only be the beginning though, with more potent, safe, and better tolerated follow-up RNA Therapeutics being developed and patient identification becoming more sophisticated.  Ultimately, I envision a world where, for the inherited version of the disease, patient identification based on genetics will be possible such that TTR lowering therapies can be initiated before organ damage through TTR deposition occur.

Patisiran seen leading

When Alnylam disclosed a month ago that intravenously infused Patisiran not only halted disease progression as had been reported for Ionis’ subQ Inotersen, but apparently improved symptoms compared to baseline, the stock shot up ~60% while Ionis stock dived ~15%. Furthermore, safety and tolerability looked solid with much less treatment discontinuations (7.4% vs 37.7%) and nominally less deaths observed in the Patisiran treatment arm versus placebo control (4.7% vs 7.8%). By contrast, Inotersen has been living under a safety shadow ever since deaths due to phosphorothioate ASO-dependent thrombocyte lowering wereseen in addition to renal toxicity.

Can Inotersen stage a comeback?

So even before Patisiran data were presented, the Big Pharma partner for Inotersen, GSK, dumped the drug (by not exercising the option).  Obviously, Ionis wants this to be seen as an act of Dumb Pharma throwing away highly valuable drugs under the directive of bean counters and smartly dressed corporate overhaulers (here: GSK leaving orphan drugs).  Nevertheless, it is difficult to believe that GSK gave rights to Inotersen back for free when it saw Inotersen competitive with Patisiran which easily accounts for roughly half of Alnylam’s  $11B market cap.

Still, while to many it is a foregone conclusion that today’s presentations won’t change much in the competitive dynamics between Patisiran and Inotersen, there are a few scenarios which could change it.

Firstly on efficacy, we still have to learn whether the disease improvement over baseline as reported for Patisiran by Alnylam is medically meaningful over the disease halt reported for Inotersen.  As such, it is possible that the (mean and median) mNIS+7 scores were barely negative (i.e. nominal improvement) as the phase II open-label extension trial results with Patisiran would have predicted.  And who knows, mNIS+7 values for Inotersen could actually be nominally negativ!

Somewhat complicating mNIS+7 matters is that the two companies are using slightly different scales, but I don’t expect this to have much impact on the discussion.

In addition to closing the gap on absolute efficacy, Inotersen could emerge as the winner in terms of treatment efficacy versus placebo.  Importantly, the placebo group in the Patisiran study received steroid treatment around the time of infusion since Patisiran treatment entails this to manage potentially dangerous reactions around the time of infusion and subsequent hours.  Although Patisiran clearly outperformed placebo, steroids, albeit given intermittently, should have some impact on perceived disease symptoms and I found it notable that while Inotersen was statistically better than placebo (no drug at all) at an intermediate time-point 9 months, Patisiran wasn’t yet at 8 months.

It’s therefore possible that Inotersen has the delta advantage over Inotersen which, of course, would influence how docs regard the inherent efficacy of Patisiran alone.

Finally, the placebo issue could also negate another apparent advantage of Patisiran over Inotersen: safety and tolerability. Notably, there was a ~40% SAE rate in both the Patisiran and placebo groups which are historically high for TTR amyloidosis clinical trials.  For example, an 18 month trial with TTR tetramer stabilizer Tafamidis had SAEs of less than 10%.  Is it therefore possible that steroid treatment accounts for the high SAE rate and that the overall SAE rate for Inotersen (to be disclosed) is much lower? 

 With the presentations being less than 8 hours away, we shall find out any time now as my train reaches the outskirts of Paris…