In the first stage of human testing, which involved 23 people with terminal cancer, the tumors of one-quarter of the patients shrank by half or more.
Studies with similar drugs have proved disappointing — prompting no dramatic tumor shrinkage in early tests, as hoped. Scientists say the latest results will likely revive flagging enthusiasm for the approach.
The findings were presented Wednesday at a cancer therapy meeting in Frankfurt.
"Any activity in this situation is very promising since everything else has failed, but we did not expect to see such a high number of responses in a range of cancers," said the study's leader, Dr. Eric Raymond, head of the early drug testing unit at the Gustave-Roussy Institute in Villejuif, France.
The drug, which does not yet have a name, is a newcomer to the field of anti-angiogenics — drugs designed to damage tumors by attacking the network of blood vessels that feed them.
Although it has been a major focus of research over the last decade, anti-angiogenesis has not so far lived up to its early research promise.
Such drugs have shown only slight benefit, indicating they might sometimes slow or even stop some tumor growth, at least temporarily. None of them prompted the kind of dramatic tumor shrinkage or disappearance that doctors look for, even in the first stages of human testing, which are largely intended to see if medicines are safe.
"Initially, we thought that this drug would be an agiostatic agent that stabilizes tumors, rather than an agiotoxic agent that actively shrinks tumors," Raymond said. "We were happily surprised ... it seems that the drug is killing the blood vessels into tumors, regardless of the tumor type."
Tumors shrank by more than 50 percent in six of the 23 patients. The cancer stabilized in another five people.
"There is hardly a single drug that had more than 5 percent regression rate (in early human trials). Although this is not proven as a drug, this is fascinating," said Dr. Jaap Verweij, head of experimental chemotherapy and pharmacology at Erasmus University in Rotterdam, the Netherlands.
Experts said they believe part of the reason why the new drug seems so much more powerful than others is that it attacks from three directions instead of just one.
As well as blocking a protein involved in blood vessel growth called vascular endothelial growth factor, the new drug also interferes with two other blood vessel growth factors — basic fibroblast growth factor and platelet-derived growth factor. Some scientists suspect those enzymes might do more than just support blood vessel growth.
The drug is being developed by Sugen, a subsidiary of the U.S. pharmaceutical company Pharmcia.
"The intriguing observations of so many individual tumor responses is surprising and tantalizing," said Dr. William Li of the nonprofit Angiogenesis Foundation in Cambridge, Massachusetts. "One possible reason is that those three growth factors may also serve as survival factors for cancer cells, as well as for angiogenesis. Hence, (the drug) may serve as a double-barreled assault against both tumor blood vessels and tumor cells."
The early promise of the drug illustrates the new thinking in cancer therapy, according to Dr. Michael Caligiuri, chairman of cancer research at Ohio State University.
Scientists are amassing a wealth of knowledge about the way that cancer works at the molecular level from the first scrap of rogue DNA in a cell nucleus that starts the process to the devastating assault of metastatic cancer.
The next decade will see a shift of emphasis from conventional treatment toward targeting the cellular and molecular abnormalities at the heart of cancer.
Another advance in that direction was reported Wednesday in a study of mice that found a recently developed targeted leukemia drug — Gleevec — could boost the effectiveness of standard chemotherapy in many types of cancer by enabling more of the medication to get inside tumors.
By Emma Ross