The new drug, made by Bristol-Myers Squibb (BMY), put 86 percent of patients who tried it into remission — meaning signs of their cancer disappeared, the researchers said.
Although this was only a Phase I trial meant to show the drug was safe, the effects were dramatic, the doctors told a meeting in San Diego of the American Society of Hematology (search).
"Certainly it is wonderful. It will save lives," said Dr. Alan Kinniburgh, senior vice president of research for The Leukemia and Lymphoma Society, which helped sponsor the study.
Rumors of the new drug's success have been leaking for months because cancer experts are so excited by the results. Oncologists hope the approach may work in many other cancers, too.
The new drug is being tested in patients with chronic myeloid leukemia, which affects about 4,400 Americans a year and 10,000 people around the world.
The drug is known by its experimental name BMS-354825. During the trial, also financed by Bristol-Myers, 31 of 36 patients with advanced CML who had not been helped by Gleevec had a complete hematologic response, meaning their bodies stopped producing leukemia cells.
This translates to an 86 percent remission rate, said Dr. Charles Sawyers, a Howard Hughes Medical Institute investigator at the University of California Los Angeles who is helping test the drug.
Gleevec, made by Swiss drug company Novartis, targets an enzyme called BCR-ABL that leukemia cells use to proliferate. It attaches to the cancerous cells and stops them from growing and spreading.
TARGETED CANCER PILL
Sold in Europe under the name Glivec, it was the first "targeted" cancer drug. It made headlines when it was approved in 2001 because never before had a simple pill shown such dramatic effects in cancer.
Later Sunday Novartis will report on its new compound AMN107, dubbed "super Glivec," also designed to overcome the weaknesses in Gleevec.
Gleevec, or imatinib, is Novartis's second-biggest product, with sales in the first nine months of this year of $1.1 billion.
But in a few patients, perhaps 12 percent, the cancer cells mutate just enough to slip out of Gleevec's grip. The cancer comes back.
So some of the researchers who worked on Gleevec teamed with Bristol-Myers Squibb to develop the new pill, which is less picky about how it grabs onto a cancer cell to deactivate it.
The Bristol-Myers drug affects a different enzyme called SRC, pronounced "sark."
"It is definitely not Gleevec," Sawyers said in a telephone interview. "It's not Gleevec 2. It has a completely different chemical structure."
Sawyers said he and colleagues worried that there could be unforeseen side-effects in patients, as no one had ever tested a SRC inhibitor in people. But so far it seems safe, he said.
There are more than 17 known mutations in leukemia cells that allow the cancer to evade Gleevec's effects, but most of them seem to be susceptible to BMS-354825, Sawyers said.
One mutation, known as T315I, resists both Gleevec and the Bristol drug. "That mutation will likely require a different drug, and researchers are working on that now," said Sawyers.
Kinniburgh said it is likely that the new pills will be used in combination, like old-fashioned chemotherapy.
"I know of no cancer where one single drug has ever cured the cancer," he said.