Identifying drug-resistant tumors.

Drug resistance is the leading reason why cancer chemotherapy fails. Simply put, if a cancer cell is drug resistant, it won't succumb to therapy," according to Steven D'Ambrosio, director of the Division of Radiobiology at Ohio State University's Comprehensive Cancer Center.

He and a team of researchers have developed a way to measure the ability of particular cancer cells to repair the damage done to DNA by a category of commonly utilized anti-cancer drugs that are known as alkylating agents, including nitrosourea and cisplatinin. They are used to treat leukemias, lymphomas, and cancers of the lung, breast, and prostate.

Alkylating agents work by inducing changes in DNA molecules that lead to the death of the cancer cell. Similar damage also is caused by exposure to radiation and toxic chemicals in the environment. "If this damage were to, go unchecked in the course of day-to-day life, it would be very detrimental to the individual." As a result, healthy cells have developed a repair protein to mend it.

Cancer cells often call upon that same protein to repair the otherwise fatal damage inflicted by alkylating agents. For patients, the result follows a typical course: At first, the tumor regresses and...