FDA Approves Important New Leukemia Drug
Offers Further Proof of Principle for Molecular Targeting in Cancer Treatment
The U.S. Food and Drug Administration (FDA) announced today its approval of the drug Gleevec as an oral treatment for chronic myelogenous leukemia (CML).
The announcement, issued at a press conference in Washington, also marks the approval of the first drug that directly turns off the signal of a protein known to cause a cancer. Other molecular-targeting drugs previously approved by the FDA interfere with proteins associated with other cancers, but not with proteins that directly cause the disease.
Gleevec, also known as STI571, was discovered and developed by Novartis Oncology in collaboration with its colleagues in academia.
CML is a disease in which too many white blood cells are made in the bone marrow, the spongy tissue inside the large bones in the body. Most of the 4,500 Americans diagnosed with CML each year are middle-aged or older, although the cancer can occur in children. In the first stages of CML, most people do not have any symptoms of cancer, and the disease progresses slowly.
Bone marrow transplantation in the initial chronic phase of the disease is the only known cure for CML. However, many patients are not young or healthy enough to tolerate transplantation or do not have a suitable marrow donor, and the procedure can cause serious side effects or death.
Treatment with the drug interferon alfa may produce remission, restoring a normal blood count in up to 70 percent of patients with chronic phase CML. If interferon alfa is ineffective or patients stop responding to the drug, the prognosis is generally bleak.
Gleevec has produced higher remission rates in three short-duration, early phase clinical trials. In the results of one clinical trial, reported in April in the New England Journal of Medicine, Gleevec restored normal blood counts in 53 out of 54 interferon-resistant CML patients, a response rate rarely seen in cancer with a single agent. Fifty-one of these patients were still doing well after a year on the medicine, and most reported few minor side effects.
In March 2001, the FDA granted an expedited review of Gleevec based on these clinical trials. Today, after only two months of review--one of the fastest reviews ever for a cancer drug --the FDA approved Gleevec.
Richard Klausner, M.D., director of the National Cancer Institute, said that he shared in the excitement of people with CML, but he also mentioned several caveats. He said many research questions remain to be answered, such as how long Gleevec will control CML. Does the drug actually cure CML patients? Or, does it delay the onset of more advanced forms of the cancer?
Klausner said NCI, in a cooperative research and development agreement (CRADA) with Novartis Oncology, is now investigating these issues in ongoing clinical trials involving people with CML. Several clinical trials are also testing the possible effectiveness of Gleevec in other cancers including glioma, soft tissue sarcoma, and a rare kind of gastrointestinal cancer called gastrointestinal stromal tumor (GIST).
Despite the caveats, Klausner said Gleevec serves as a bellwether for other molecular-targeting cancer drugs. He said an intensive effort is now under way in academia and industry to identify unique, cancer-causing proteins in other tumors.
"For the first time, cancer researchers now have the necessary tools to probe the molecular anatomy of tumor cells in search of cancer-causing proteins," said Klausner. "Gleevec offers proof that molecular targeting works in treating cancer, provided that the target is correctly chosen. The challenge now is to find these targets."