ChemGenex shares falter as FDA requests more data on new leukemia drug

By Dr. Ananya Mandal, MDMar 23 2010

ChemGenex Pharmaceuticals Ltd. Shares fell most in the last 16 years to AUD$0.44 following a concern raised by the US drug regulators – US FDA. The FDA requested on Monday for more uniform clinical test data before they review and consider approval of the company’s new leukemia drug.

In a voting session of outside advisors to the US FDA, 7-1 votes came in favor of more uniform testing of the new drug from Chemgenex called Omapro.

ChemGenex has been working with the FDA and will meet with the regulator on April 9 to review its strategy for having Omapro approved, the Geelong, Victoria-based company said in a statement today.

“I doubt it will be years, but I suspect it will be months before the test is reviewed and validated”, Adam Craig, ChemGenex’s chief medical officer, said after the meeting.

Omapro, also known as omacetaxine mepesuccinate is a latest development in blood cancer chemotherapy that is purported to be useful in patients who have a genetic mutation that makes them non responsive to standard drugs currently used like Gleevec and Tasigna. Earlier studies have shown that most blood cancer patients with chronic myeloid leukemia eventually become non-responsive to Gleevec. It is also seen that 15% of general population due to a specific genetic change called T315I are non responsive to Gleevec from beginning.

Chronic myeloid leukemia is a form of blood cancer in which a genetic mutation causes production of large numbers of white blood cells. These cells clog up all the vital organs and are mailgnant. This disease slowly progresses and is usually fatal without treatment. About 4,830 people were diagnosed with the disease in the U.S. last year, according to the National Cancer Institute.

Clinical trial data that ChemGenex submitted to the FDA was based on tests that may have mistakenly identified some patients as having the genetic variation, panel members and FDA staff said before the vote. Such misdiagnoses may cost patients the opportunity to be treated with more effective, less toxic therapies, they said.

“This is something that just represents fairly sloppy drug development,” said panel chairwoman Gail Eckhardt, head of medical oncology at the University of Colorado in Denver.

The new drug Omapro is reported to have had a “low” response rate in the study data submitted by ChemGenex, FDA staff said in a report last month. In the drug reports that were submitted to the FDA for approval only 15% of patients responded to this therapy. Another major flaw in the study reported by FDA staff was that most patients enrolled in the study were not tested for the specific genetic change T315I that causes Gleevec non-responsiveness.

Ellin Berman, an attending physician at Memorial Sloan- Kettering Cancer Center’s hematologic oncology division, was the only panel member to vote against requiring additional test data. Berman said she was “comfortable” that all patients in the trial were resistant to other leukemia treatments.

“Here we have a drug that works in a portion of these patients,” Berman said. “It’s a step forward.”