ATHENS, Ga., Oct. 3 (UPI) — Smaller, less toxic amounts of chemotherapy medicine given frequently slowed tumor growth in a study of mice with human prostate cancer, U.S. researchers say.

Study co-author Robert D. Arnold, an assistant professor in the University of Georgia College of Pharmacy, said the mice suffered fewer side effects compared with traditional cancer treatment relying on heavy doses that can cause hair and bone loss.

Chemotherapy given repeatedly in small portions — metronomic dosing — is not new, but dosing appears to alter the cellular activity of the drug topotecan, Arnold said.

The finding, published in the journal Cancer Biology and Therapy, suggests metronomic dosing of topotecan can reduce prostate cancer growth at drug concentrations far below those that can be toxic to healthy cells in the body.

Topotecan given to patients in large, traditional doses kills cancer cells by deactivating proteins in enzymes necessary for cell growth, Arnold said. By contrast, metronomic dosing of topotecan prevents new blood vessels-which are necessary for growth from forming in the tumor.

Arnold and colleagues discovered topotecan did not change the amount of blood vessels formed (which feed tumor growth), but significantly decreased tumor size and altered genes critical for controlling cell growth.