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So Isis (NASDAQ:ISIS) and its partner Sanofi (NYSE:SNY) have received FDA approval for mipomersen (branded as Kynamro). Late last year, the European Medicines Agency turned them down, which has people wondering about the drug's future. But here they are, albeit with a warning on the label about liver toxicity.

Mipomersen is designed to lower the Apo-B lipoprotein in people with the most severe (homozygous) form of familial hypercholesterolemia. That's a small patient population, but they're definitely in need of help. The really significant thing about this approval, in my mind, is that it's a pure antisense therapy, and it comes about 20 years after there was supposed to be a world-changing flood of them. (Isis did get one through the process back in 1996, fomivirsen, but it's never had much of an impact.) It was a standing joke back in the late 1980s and early 1990s that everyone had heard from a headhunter recruiting for one antisense company or another.

I don't think that mipomersen will ever reach the heights that Isis thought it might a few years ago; the liver tox problems will see that it's only used in life-threatening situations. (I note that one time when I wrote about the drug, fans of ISIS showed up rolling their eyes at the mistaken notion that liver tox could ever be a problem.) But I'm divided between congratulating them on finally getting something onto the market, and wondering about how difficult it's been to get there. As far as I know, the liver tox seen in this case is largely (completely?) thought to be due to the mechanism of action on lipid handling in the liver itself.

So how about the other antisense compounds in the clinic? As of that 2010 link above, we had trabedersen, for TGF-beta2, which is actively being tried against pancreatic cancer. Alicaforsen, for Crohn's et al., has shown disappointing efficacy in Crohn's, but is still alive for ulcerative colitis. Aganirsen, for various vascular conditions in the eye, is still in development, with more funding having arrived recently. Oblimersen has shown some effects in the clinic, but CLL is a crowded area and its current status is unclear, at least to me. And custirsen is in Phase III, with mixed results in Phase II trials.

Actually, that lineup looks a lot like drug development in the rest of the industry, to be honest. Some stuff looks OK and is moving along, some not so OK, and some has wiped out. It's important to realize that even if liver tox is not some general feature of the mipomersen-generation antisense compounds, that we still have efficacy failures. The indications where we can really laser right in on a key target do not make a long list. Many of those are orphans, too. In contrast, the list of giant-unmet-medical-need indications where we can laser right in on a key target is, I think, waiting for something -- anything -- to be written on it.

Disclosure: None.

Source: Mipomersen Approved, Bonus Antisense Roundup Included