Problems in the development of analogs of anticancer drugs

Undoubtedly the progress of cancer chemotherapy is supported by the development of new anticancer drugs. In Japan, there is a tendency to develop anticancer drugs by both chemical modification of the known anticancer drugs (analogues) and finding new structures. However, we have to be cautious to develop analogues of the known anticancer drugs. Before we consider to put these drugs into the clinical trials, several points must be clarified: that is, the new compounds would have any merit or superior points compared to the mother compounds. Especially, we should observe whether or not the new compounds possess any reduction of major toxicities of the mother compounds, how about the situation of cross resistance, anticancer efficacies and particularly the results of toxicology studies. We have limited cancer patients for testing new drugs, and also from ethical view, some easy consideration for developing analogues having minor differences from the mother compounds, must be abandoned.