Idenix Pharma: Guilty By Association

NEW YORK (TheStreet) -- Thursday, Idenix Pharmaceuticals (IDIX) presented investors with a detailed update on IDX-184 and the earlier-stage IDX-19368, two hepatitis C drug candidates that were placed on clinical hold by the FDA last month.

Idenix' new investor slide deck, also filed as an SEC Form 8-K, offers lots of detail about the compounds' status and highlights management's admirably open-minded communication style. Unfortunately, I'm not convinced the company's woes will be easily fixed.

IDX-184 has had no safety issues to date. Nonetheless, structural similarities between Idenix's IDX-184 and Bristol-Myers Squibb's (BMY) BMS-094 were sufficient to warrant concern. Clinical development of the latter drug, which Bristol-Myers acquired in the $2.5 billion takeover of Inhibitex, has been discontinued because of severe cardiovascular toxicity.

The FDA's clinical hold -- effectively a "stop work" order triggered by unexpected safety issues -- suggests that regulators are also concerned about the safety of IDX-184. In order to get the clinical hold lifted and continue development, Idenix must now convince the FDA that IDX-184 doesn't put patients' lives at unnecessary risk. (At least one patient in the Bristol-Myers study died.)

Let's start with the good news by diving into some chemistry. IDX-184 and BMS-094 are both nucleotide polymerase inhibitors and, structurally speaking, 2′-methylguanosine (2′-MeG) triphosphates. When BMS-094 breaks down in the body, it produces 1-naphthol, a toxic metabolite possibly responsible for the drug's side effects. However, metabolism of IDX-184 does not produce 1-naphthol. Furthermore, while Bristol-Myers' compound showed evidence of mitochondrial toxicity in cell line studies at relatively low concentrations, IDX-184 has a wide margin of cellular level safety.

My first instinct was to recommend buying Idenix shares, which have plunged 40% since the FDA news. The company has three drug candidates in development for a disease that bulls expect will offer multiple players a mega-blockbuster opportunity. (I'm more skeptical than most about the commercial opportunity in hepatitis C, but there's no denying that it's a very attractive market for a company of Idenix' size.)

Management has also approached challenging conversations armed with details rather than deferrals. This commendable behavior doesn't make the company's problems any easier, but it does reduce worries about credibility. Finally, the prospects for several hepatitis C competitors have either blown-up or faded in recent months.

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