Prostate cancer patients are lobbying the FDA for approval of Abbot’s oral anti-cancer drug Xinlay (atrasentan), but the FDA is not impressed with the drug.

Abbott Laboratories Inc. did not provide clear evidence of effectiveness for Xinlay, U.S. Food and Drug Administration staff said in a preliminary report on Monday.

Studies of Xinlay also raised “serious cardiovascular safety issues,” the FDA staff said in a report posted on the FDA’s Web site.

In the only trial sufficient to evaluate for approval, Xinlay “does not demonstrate any clear evidence of clinical efficacy” in prostate cancer that has failed to respond to standard hormone therapy, the FDA staff report said.

Abbott, in a separate summary on the FDA Web site, said “the weight of evidence suggests that (Xinlay) provides measurable clinical benefit with a manageable safety profile.”

A panel of experts from outside the FDA is scheduled to decide Tuesday whether to recommend Xinlay for approval. The committee will consider the FDA staff comments, as well as arguments from Abbott.

The FDA will make the final decision later, but the agency usually follows the recommendations from the advisory panels.

Some industry analysts have predicted annual sales for Xinlay could reach $2 billion if the drug wins approval.

But J.P. Morgan analyst Michael Weinstein said there were “low odds” the panel would support Xinlay or that the FDA would approve the drug in the near term.

The FDA staff reviews “reveal a clear bias against approval, absent new trial data,” Weinstein said in a research note.

Xinlay is an oral, once-a-day drug that targets a protein called endothelin receptor A, which is believed to help cancer cells spread. The drug’s generic name is atrasentan.

Two studies of Xinlay failed to show the drug slowed progression of advanced prostate cancer. Abbott, however, said pooled data from the trials demonstrated Xinlay delayed the disease’s spread and reduced pain from the disease’s spread to the bone.

Findings based on pooled data were presented at the annual American Society of Clinical Oncology (ASCO) conference in May 2005. A team from Johns Hopkins said patients with advanced prostate cancer who received Xinlay experienced less disease progression and less pain than patients receiving placebo.

In a meta-analysis of one dose-level, 10 mg, of the two earlier trials, Michael Carducci M.D. and his team found “statistically significant evidence for benefit from Xinlay.” Compared with patients receiving placebo, patients treated with atrasentan 10 mg were 14% less likely to experience disease progression, had an 18% less likelihood of experiencing bone pain, had a 22% less chance of experiencing PSA progression, and were 46% less likely to experience bone alkaline phosphatase progression (a forerunner of symptomatic advanced prostate cancer).

“The relative probability of remaining progression-free was 10% greater at 3 months and 22% greater at 6 months for patients treated with atrasentan 10 mg compared with those treated with placebo, where the probability of remaining progression-free on placebo was 49% and 27% at 3 and 6 months respectively,” Varducci’s study says.

“Bone pain … ultimately ends up crippling men (with prostate cancer) in their last days of life. We feel strongly there is a benefit with Xinlay for these men,” Abbott spokeswoman Jennifer Smoter said.

The FDA staff said the “pooled” studies could not be combined to draw conclusions about effectiveness because they used different designs, patients and definitions of disease progression.

In the larger study, more patients treated with Xinlay experienced congestive heart failure, irregular heart beats, heart attacks and chest pain than others who got a placebo, the FDA staff said.

Abbott said the problems were infrequent. Patients at risk for heart failure could be monitored or the complication, which can be treated with medication, the company said.

This report includes information from Reuters, psa-rising.com, and FDA.