by Luke Timmerman, Xconomy

An experimental drug from Aveo was able to at least partially shrink tumors for one-fourth of patients, and keep the cancer from spreading for a median of 11.8 months, in a mid-stage clinical trial including 272 patients with advanced kidney cancer. The drug had minimal side effects, with the most common ones being high blood pressure and hoarseness of voice, according to research presented today at the American Society of Clinical Oncology meeting in Orlando, FL.

The data is compelling enough that Aveo plans to initiate a pivotal clinical trial later this year, the company said in a statement. It will be the biggest test yet for tivozanib, also known as AV-951, an oral pill designed to very specifically block three different VEGF receptors—molecules on the surface of cells that allow formation of new blood vessels that nourish tumors. This drug is supposed to be a more selective blocker of VEGF than two currently marketed drugs that work in a similar way—Pfizer’s sunitinib (Sutent) and Bayer and Onyx Pharmaceuticals’ sorafenib (Nexavar). Researchers hope that more selective VEGF receptor blockers will become a new generation of more effective drugs, that also avoid blocking similar receptors on healthy cells—which can cause side effects.

If Aveo’s drug can make it through the last stage of clinical testing, it could reach a sizable group of patients and a lucrative potential market. About 54,000 new cases of kidney cancer were diagnosed in the U.S. last year, and 13,000 people died from the disease, according to the American Cancer Society. Pfizer’s sunitinib, first approved in January 2006, generated $850 million in sales in 2008. Bayer and Onyx’s sorafenib generated $678 million in sales the same year. Drugs that block VEGF receptors are also thought to have wide-ranging potential, because blood vessel formation plays an important role in many types of cancer.

“One of the reasons there’s so much interest in the clinical community is that the study of this drug will really test the hypothesis of whether more selective is better,” says Robert Motzer, a kidney cancer expert at Memorial Sloan-Kettering Cancer Center in New York. The results so far are encouraging, but more data will be needed to confirm the drug’s effectiveness, Motzer says.

This mid-stage trial required patients to take the Aveo drug once a day for three weeks, then take a week off, and repeat the cycle for 16 weeks, Aveo said in a statement. The company is still waiting to get data on how long patients lived while taking the drug—the gold standard measurement of success in cancer drug development.

The bigger test for the Aveo drug will come in a Phase III trial that would compare it head-to-head with one of the standard drugs from Pfizer and Bayer, Motzer says. Pfizer and GlaxoSmithKline also have other drugs in development (axitinib and pazopanib) made to be more selective blockers of VEGF receptors than the existing products. But the Aveo candidate appeared in animal tests to be the most precise inhibitor in the bunch, Motzer says.