Indanocine, a microtubule-binding indanone and a selective inducer of apoptosis in multidrug-resistant cancer cells

Background: Certain antimitotic drugs have antitumor activities that appare ntly result from interactions with nontubulin components involved in cell g rowth and/or apoptotic cell death. Indanocine is a synthetic indanone that has been identified by the National Cancer Institute's Developmental Therap eutics Program as having antiproliferative activity. In this study, we char acterized the activity of this new antimitotic drug toward malignant cells. Methods: We tested antiproliferative activity with an MTT [i.e., 3-(4,5-di methylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay, mitochondrial damage and cell cycle perturbations with flow cytometry, caspase-3 activati on with fluorometry, alterations of the cytoskeletal components with immuno fluorescence, and antimicrotubule activity with a tubulin polymerization: a ssay. Results/Conclusions: Indanocine is a cytostatic and cytotoxic indanon e that blocks tubulin polymerization but, unlike other antimitotic agents, induces apoptotic cell death in stationary-phase multidrug-resistant cancer cells at concentrations that do not impair the viability of normal nonprol iferating cells. Of the seven multidrug-resistant cell lines tested, three (i.e.,MCF-7/ADR, MES-SA/DX5, and HL-60/ADR) were more sensitive to growth i nhibition by indanocine than were their corresponding parental cells. Confl uent multidrug-resistant cells (MCF-7/ADR), but not drug-sensitive cancer c ells (MCF-7) or normal peripheral blood lymphocytes, underwent apoptotic ce ll death 8-24 hours after exposure to indanocine, as measured by sequential changes in mitochondrial membrane potential, caspase activity, and DNA fra gmentation. Indanocine interacts with tubulin at the :colchicine-binding si te, potently inhibits tubulin polymerization in vitro, and disrupts the mit otic apparatus in dividing cells, Implications: The sensitivity of stationa ry multidrug-resistant cancer cells to indanocine suggests that indanocine and related indanones be considered as lead compounds for the development o f chemotherapeutic strategies for drug-resistant malignancies.