Most existing cancer treatments and drugs are poisons, designed to attack and hopefully kill cancer cells, or at least slow their growth. But most of these treatments attack not just cancer cells, but healthy cells, too. Thus, people taking the drugs too often suffer horrible side effects on top of whatever havoc the cancer itself is already wreaking. They become thin and weak. They lose their hair and their color.
But now, the next revolution in cancer therapy may have arrived.
It’s called “molecularly targeted therapy.” The treatment consists of drugs designed at the molecular level of the cell to specifically attack and kill only the cancer cells of a specific type of cancer. And they are tailor-made to recognize specific molecules unique to specific cancers.
The model drug leading the way is Glivec, also known as STI571. It is active against a relatively rare form of leukemia — chronic myeloid leukemia, or CML — characterized by excessive overproduction of white blood cells. Approximately 7,000 Americans are diagnosed with CML each year.
Doctors are extremely hopeful that the drug could provide a model for similar drugs to treat cancers affecting many thousands more people. This year, alone, some 1.3 million Americans will be diagnosed with cancer.
“This is as important as it gets. A cancer-specific target, a drug specifically designed for the target, the most effective agent ever,”says Paul A. Bunn Jr., president-elect of the American Society of Clinical Oncology. “Read my lips, this is real, not mice.”
Designer Drugs
Dr. Brian Druker, director of the Leukemia Program at the Oregon Health Sciences University in Portland, is the main researcher on the drug, which is being developed by Novartis Pharmaceuticals.
“If we understand the critical abnormalities that drive a cancer, we can target the cancer with an effective and non-toxic therapy,” Druker says. “We need to identify the critical abnormalities in each and every cancer so drugs like STI571 can be developed for each cancer.”
The current issue of the New England Journal of Medicine has two studies led by Druker on the clinical benefits of STI571 in treating leukemia. The study results were released now.
Dr. Lou Fehrenbacher, a hematology/oncology specialist at Kaiser Permanente Medical Center in Vallejo, Calif., said in an e-mail to ABCNEWS: “The major importance of this drug is the nature of its discovery [it is a logically engineered creation]. … The enzyme was isolated, reproduced, and then a drug to inhibit it was engineered.”
These molecular “designer” drugs are created working backward from a known abnormal molecule specific to a certain type of cancer. Once the molecule is identified, a drug can be designed that interferes with that molecule. So, these drugs, by design, have a very limited spectrum of use.
“This drug … will not have broad applicability in a wide variety of tumors,” says Dr. Grover Bagby Jr., director of the Oregon Cancer Institute at OHSU, “precisely because it is targeted to a specific small set of molecules.”
FDA Planning Fast Track Treatment In addition to CML, Druker discovered in 1993 that STI571 also worked against a rare gastrointestinal cancer — gastrointestinal stromal tumor, or GIST. It is effective due to an enzyme unique to GIST that is related to the original target enzyme in CML.
A case study that appears in the current issue of the New England Journal of Medicine on the clinical outcome of one GIST patient in Finland treated with STI571 showed a significant reduction in the size of the patient’s tumor.
Additional findings from larger clinical trials of STI571 for GIST will be presented at the American Society of Clinical Oncology meeting in May.
Glivec is getting a priority review by the Food and Drug Administration for treatment of CML as a result of its positive clinical findings and will be available to patients within the next few months.
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