oxamflatin and Lymphoma

P-glycoprotein (P-gp) can induce multidrug resistance (MDR) through the ATP-dependent efflux of chemotherapeutic agents. We have previously shown that P-gp can inhibit nondrug apoptotic stimuli by suppressing the activation of caspases. To determine if this additional activity is functionally linked to ATP hydrolysis, we expressed wild-type and ATPase-mutant P-gp and showed that cells expressing mutant P-gp could not efflux chemotherapeutic drugs but remained relatively resistant to apoptosis. CEM lymphoma cells expressing mutant P-gp treated with vincristine showed a decrease in the fraction of cells with apoptotic morphology, cytochrome c release from the mitochondria and suppression of caspase activation, yet still accumulated in mitosis and showed a loss of clonogenic potential. The loss of clonogenicity in vincristine-treated cells expressing mutant P-gp was associated with accumulation of cells in mitosis and the presence of multinucleated cells consistent with mitotic catastrophe. The antiapoptotic effect of mutant P-gp was not affected by antibodies that inhibit the efflux function of the protein. These data are consistent with a dual activity model for P-gp-induced MDR involving both ATPase-dependent drug efflux and ATPase-independent inhibition of apoptosis. The structure-function analyses described herein provide novel insight into the mechanisms of action of P-gp in mediating MDR.

Topics: Adenosine Triphosphatases; Adenosine Triphosphate; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; Apoptosis; ATP Binding Cassette Transporter, Subfamily B, Member 1; Caspases; Cell Line; Cell Line, Tumor; Cell Membrane; Cell Nucleus; Cell Survival; Cytochromes c; DNA Mutational Analysis; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Enzyme Activation; Green Fluorescent Proteins; Humans; Hydrolysis; Hydroxamic Acids; Idarubicin; Lymphoma; Mitosis; Mutation; Retroviridae; Structure-Activity Relationship; Time Factors; Vincristine