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FDA reviewers raise questions about two cancer drugs prior to advisory committee meeting

Monday, February 08 2010 | Comments

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What's This? Ahead of a Food and Drug Administration advisory panel meeting, FDA staff members have raised concerns about two hematological cancer drugs, one of which is being investigated as a treatment for lymphoma and the other as a treatment for leukemia.

The FDA reviewers questioned the efficacy data for Cell Therapeutics Inc.'s pixantrone, an experimental drug for relapsed or refractory aggressive non-Hodgkin's lymphoma. They also said the drug, which Cell Therapeutics is planning to market under the brand name Pixuvri, has several notable side effects.

The staff said their questions are related to Cell Therapeutics' main study for pixantrone. In briefing documents posted on the FDA's Web site, the reviewers said their issues included "the reliability of [efficacy] conclusions" from the Phase III study and "[s]ubstantial hematologic and cardiac toxicity." In addition, they noted that the pixantrone trial had fewer than half of the expected number of patients.

Further, the reviewers mentioned data that they believe are indicative of pixantrone being toxic to the heart. However, they said "no conclusions can be drawn concerning its toxicity relative to other anthracyclines/anthracenediones."

In a separate document prepared for the panel, Cell Therapeutics said its data demonstrated that pixantrone worked better than comparator drugs and had "manageable toxicities."

A final decision on the approval of pixantrone is due by April 23.

In related news, regulatory staff questioned a study involving ChemGenex Pharmaceuticals Ltd.'s experimental drug Omapro (omacetaxine mepesuccinate), which is being considered as a treatment for chronic myeloid leukemia in patients who have developed the Bcr-Abl T315I mutation and have not responded to prior treatment with Novartis AG's Gleevec (imatinib mesylate).

In briefing materials on the FDA's site, staff members said they were concerned about the low response rate in the Omapro efficacy study, as well as the lower-than-expected number of enrolled patients. ChemGenex submitted efficacy data for 66 patients, whereas the planned enrollment was 100 patients. The reviewers noted that additional patients were enrolled after the data cutoff for the 66 patients that were included in the New Drug Application submitted for the drug.

Also, Omapro is intended for patients who have a specific genetic mutation, but the FDA staff remarked that "there is no commercially available assay for the detection of this mutation." Further, the reviewers mentioned that 35 percent of the study patients had no confirmation of Bcr-Abl T315I mutation status at enrollment, even though that was a criterion for study entry.

In a separate briefing document, ChemGenex stated that Omapro showed "an acceptable benefit-to-risk ratio in heavily pretreated patients who have a poor prognosis and no proven treatment options," and that the drug has a "manageable safety profile" in this population.

The FDA's Oncologic Drugs Advisory Committee is scheduled to discuss both pixantrone and Omapro on Feb. 10.

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