Nearly two months ago, we spoke here of the surprising use of arsenic trioxide (Trisenox) in treating various cancers. Trisenox, approved in the US in 2000 for treatment of acute promyelocytic leukemia (APL), is also being investigated for other hematologic malignancies.

Now, the 23 Jul issue of Business Week reports on a company making second-generation arsenicals that are believed to have less toxicity since the arsenic is linked to organic functional groups:

But the arsenic that Ziopharm uses in its Darinaparsin (ZIO-101) is organic, which reduces most toxic side effects, [Ziopharm CEO Dr Jonathan] Lewis says. "We are testing its use in treating myeloma and other blood cancers." ZIO-101 and another drug aimed at sarcoma, ZIO-201, are both in Phase 2 clinical trials.

"ZIO-101 is the first of a new class of arsenicals that are potentially safer and more effective for cancer treatment," says Chrystyna Bedrij of Griffin Securities, who rates the stock, now at 4.90, a buy, with a year's target of 20. On July 9, Ziopharm announced "positive interim data" from the ZIO-201 trials. Vinny Jindal of ThinkEquity Partners, also with a buy, notes that an oral form of ZIO-101 got FDA approval for human clinical testing.

Just to clarify the enthusiasm of the business folks, only ZIO-101 is an arsenical drug; ZIO-201 is a proprietary formulation of isophosphoramide mustard (IPM), an alkylating agent and the active metabolite of ifosfamide.

ZIO-101 is officially known as S-dimethylarsino-glutathione. However, I'm hard-pressed to find published data explaining why this organic form would exhibit lower systemic toxicity than the inorganic arsenic trioxide. There's very little in PubMed and Ziopharm's website refers primarily to meeting presentations (although they kindly reproduce PDFs of each poster presentation.)

Anyway, my main reason for bringing this to your attention is to point out that not only is arsenic an increasingly accepted drug, but its promise has led at least one company to bring second-generation arsenicals to clinical trials.