WASHINGTON - Phase II clinical results show Sugen Inc.'s lead drug, SU101, a small-molecule inhibitor of platelet derived growth factor (PDGF) receptor activity, relieved the pain associated with advanced hormone-refractory prostate cancer and caused tumor regression.
The study, conducted in 44 men with hormone refractory prostate cancer, offers a proof of principle that the South San Francisco-based company intends to test in a pivotal trial to begin sometime in 1999.
Kevin Kwok, director of corporate affairs and business development for Sugen, said the company is "very enthused about moving forward."
SU101 works by blocking the signaling of the PDGF receptor. Certain brain, prostate, ovarian and non-small-cell lung cancers are believed to be driven in by the activity of the PDGF receptor.
The company tested a weekly infusion of SU101 in hormone-refractory prostate cancer patients. Of the 21 patients evaluable for bone pain, nine reported meaningful reductions of pain with SU101.
Researchers also measured blood concentrations of prostate-specific antigen (PSA), which usually increase as the disease progresses. Of the 38 patients evaluable for stable or reduced PSA responses, four had a reduction in PSA response (ranging from 25 to 100 percent decrease in PSA level), while nine saw their PSA levels stabilize.
Of the 19 patients who received bone scans, two experienced tumor regression and three had their tumors stabilize.
Side effects of the drug included fatigue and gastrointestinal problems. Study participants reported somewhat more fatigue, hypertension and confusion with the medication than in previous studies of the drug.
"These patients were older, which may have contributed to the increase in side effects," Kwok said. "But, overall, this drug's activity makes it much more tolerable than many cancer therapies."
Because SU101 works to stymie a tumor cell's growth rather than out and out killing the cell, Sugen is planning to study the drug in a Phase I/II trial in hormone-refractory prostate cancer in combination with mitoxantrone, the most recently approved cytotoxic drug for prostate cancer.
Kwok said any Phase III trial in prostate cancer will likely use SU101 in combination with another agent rather than as a monotherapy.
Sugen has SU101 in a Phase III clinical trial to treat relapsed glioblastoma, an aggressive brain tumor. The company also is testing the drug in combination with the chemotherapeutic agent BCNU (carmustine) for newly diagnosed glioblastoma patients, and is evaluating the product in Phase II trials in ovarian and non-small-cell lung cancer.
"We are really working to turn cancer into a manageable chronic disease," Kwok said.
Sugen's stock (NASDAQ:SUGN) closed Friday at $15, down $0.25. n