GLUTAMIC-ACID AND TRYPTOPHAN DO NOT PREVENT VINBLASTINE-INDUCED APOPTOSIS IN A HUMAN LYMPHOMA CELL-LINE

The amino acids glutamic acid and tryptophan reportedly reverse the antitumour effect of the cancer chemotherapeutic drug vinblastine. Recent studies have shown that a large part of vinblastine's antitumour effect is due to induction of apoptosis. In this morphological and DNA gel electrophoretic study, we have looked for inhibition of vinblastine-induced apoptosis by glutamic acid and tryptophan and, for comparison, have examined their effect on apoptosis induced by another cytotoxic drug, etoposide. Inhibition tests were also performed using the protein synthesis inhibitor, cycloheximide, and the protein kinase C activator, phorbol ester (PDBu). Apoptosis induced by vinblastine and etoposide was not prevented by cycloheximide but was abrogated to some extent by PDBu. Glutamic acid and tryptophan had no effect on the level of apoptosis produced by either vinblastine or etoposide. The reason for the reported reversal of antitumour effect of vinblastine by glutamic acid and tryptophan remains unclear.