"Because drugs act on specific enzyme conformations, knowledge of these conformations has significant implications in drug design. "Topoisomerase is like several enzymes in one because its various conformations are so different," Dr. Wang said. "Each one is a potential drug target." Many anticancer drugs, initially recognized for their ability to kill cells, have turned out to target topoisomerases, Dr. Wang said. Among these are doxorubicin (Adriamycin), etoposide, and mitoxantrone."