Exelixis, Inc. Suspends Enrollment Of New Patients In XL999 Phase II Clinical Trial Program

Exelixis, Inc. today announced that it has suspended enrollment of new patients in the XL999 clinical trial program until further data have been collected and analyzed. The company currently anticipates that it will incur a delay in the clinical program for XL999 of between two weeks and three months. Exelixis suspended enrollment after a preliminary review of patient data relating to cardiovascular adverse events for the month of October. Through the end of September, 117 patients had been dosed with XL999, of whom 12 (10.3%) experienced serious adverse cardiovascular events. However, 4 of the 14 patients enrolled during October also experienced such events, which raised a concern with the company's internal safety monitoring committee. The company therefore decided to suspend enrollment of new patients pending further review of the data. Because 115 of the 131 subjects enrolled in the XL999 clinical program to date have received repeated doses of XL999 (every week or every other week) ranging from 2 doses (2 weeks) to 53 doses (approximately 2 years) with no reported cardiac toxicities, the company has elected to allow patients already enrolled to continue to receive XL999.

"The apparent increase in the frequency of cardiovascular events during October concerns us," said George A. Scangos, PhD, president and chief executive officer of Exelixis. "These are recent observations, and we are in the process of collecting and analyzing all of the relevant primary data. Our primary responsibility is the safety of the patients in the trial, and so we are suspending the enrollment of new patients until we have had a chance to analyze the data. Since all but one of the events occurred on first administration of XL999, we are continuing to treat those patients presently enrolled in the trial. We will of course keep you informed as we go forward analyzing the data."

WHAT is XL-999?
XL999 is a potent inhibitor of key receptor tyrosine kinases [receptors on the cell surface that transmit signals to the nucleus such as to grow] implicated in the development and maintenance of tumor vasculature and in the proliferation of some tumor cells. It inhibits the FGFR, VEGFR and PDGFR RTKs and also is a potent inhibitor of FLT3, an important driver of leukemia cell proliferation in some patients with acute myelogenous leukemia (AML). Those receptors are all growth oriented telling the cell to grow, put out new vessels to feed the tumor and to divide.

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