Background: The study of new substances capable of counteracting tumor development has focused, in recent years, on several of the steps in a cell's initiation of the process of apoptosis. One of the crucial events is the activation of p53, leading to a cell cycle G1/S block or to programmed cell death.
Methods: We report here a parallel flow cytometric method for semiquantitative detection of p53 protein and apoptosis (percent of apoptotic cells) in a pre-B leukemic cell line (NALM-6) exposed to various antitumor agents (2.35 microg/ml etoposide; 0.175 microg/ml FCE296; 0.4 microg/ml FCE624; and 1.5 microg/ml L-PAM).
Results: All of the substances proved to be capable of inducing an increase of p53 after 16 or 24 h of incubation. In all experiments with antitumor agents we also found an onset of apoptosis after 24 h of incubation with the substance, as determined by the annexin V flow cytometric assay and by DNA fragmentation.
Conclusions: This technique, based on flow cytometric data of both p53 intracellular content and percentage of apoptotic cells, is suitable to determine the amount of antitumor agent needed to induce p53, and thus to dose the drug in relation to the sensitivity of a defined tumor as well as choose the more efficacious drug, depending on cell responsiveness. The study of antitumor substances that induce apoptosis, bypassing p53, could also be evaluated by this method, in view of the development of substances for the treatment of p53-mutated tumors.