Exelixis Zeroes in on Lead Drug, Sees Activity in the Bones of Prostate Cancer Patients

6/6/11Follow @xconomy

Exelixis gambled a little more than a year ago, deciding to go “all-in” on its lead drug candidate for cancer after many investors lost interest in its strategy of building a broad pipeline with lots of different drugs.

It was risky thing to do in a business where most drugs fail in clinical trials, but it raised about $180 million on early data to support this idea back in March, and now more and more public data is rolling in to buttress the argument.

The South San Francisco-based biotech company (NASDAQ: EXEL) has shown off results over the past several days from a trial that enrolled 490 patients with nine different tumor types, to see where cabozantinib (XL184) might work best. The latest batch of data for this drug, from 171 patients with prostate cancer, is being presented to doctors today at the American Society of Clinical Oncology (ASCO) meeting in Chicago.

Exelixis has taken an unusual tack in the prostate cancer drug business, where drugs are primarily judged on whether they can help men live longer. In this early trial, Exelixis has focused on how its drug was able to partially or completely wipe out bone lesions for about three-quarters (82 of 108) patients whose prostate cancer had spread to the bones. Prostate cancer is notorious for migrating into bones and essentially splintering them from the inside out, causing intense pain and helping send many patients into a death spiral. About 30,000 men in the U.S. die of prostate cancer each year, and while promising advances have been made recently by Dendreon’s sipuleucel-T (Provenge) and Johnson & Johnson’s abiraterone (Zytiga), neither drug has primarily focused on an ability to preserve bones.

“For the first time, we have enough patients on the drug, long enough, to say ‘Wow, cabo resolves bone scans for almost 80 percent of patients, and you can see clinical benefit,’ ” says Exelixis CEO Mike Morrissey. “We have a lot of support from investigators, especially in prostate cancer. When metastatic prostate cancer goes to the bone, it drives pain, complications, fractures, spinal cord compression, anemia. Everything combined really puts the patient in a bad place. We have investigators who doing this for several decades who have never seen this level of activity in the bone. They are incredibly enthusiastic.”

Mike Morrissey

The drug, pronounced “CAH-bo” like the resort town in Baja California, is a daily pill designed to specifically block two biological targets thought to help cancer grow and spread—MET and VEGFR2. These targets are implicated in a number of forms of cancer, and since Exelixis didn’t know the best possible use for sure, it designed the trial to enroll patients with nine different tumor types, see how the drug performed in a few patients from each group. Then it enrolled many more patients with malignancies that appeared most susceptible to the new drug.

Based on this study, prostate and ovarian cancer have emerged as the two settings in which Exelixis has seen the most interesting results, Morrissey says. Small-cell lung cancer, pancreatic cancer, stomach cancer provided less convincing evidence, Exelixis said.

In the group of prostate cancer patients, researchers found that if they took the Exelixis drug and it got rid of their bone lesions, it helped improve their overall clinical outlook compared to those who didn’t see an improvement in bone lesions. Researchers, at six months of follow up, found patients who had improved bone scans were much more likely to … Next Page »

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