A second study published in the same journal suggests that troponin I, a protein found in human cartilage, may, like angiostatin, choke the blood supply to tumors. "It makes sense that cartilage contains an agent stopping the formation of blood vessels, since no blood vessels actually pass through cartilage," says Gorman. "The idea of cartilage as a potential cancer fighter has been around for some time, but it could yet turn out to be a fiction -- if there were natural products capable of defeating cancer, the chances are cancer would not have been with us for millennia."
Cancer scientists now know how the drug angiostatin deprives tumors of their blood supply, but that won't quiet the doubters. Research published Tuesday in the Proceedings of the National Academy of Sciences shows that the drug blocks the construction capability of ATP synthase, the enzyme that builds a tumor's blood-vessel infrastructure. The question that remains is at what cost. "The human body is constantly using ATP synthase to build new blood vessels, and you have to wonder about the side effects of a drug that potentially stops that activity," says TIME medical correspondent Christine Gorman. "The new finding is one more piece of the scientific puzzle, but we still don't know that it will have any application for patients."