Uptake studies with Aplidin, a marine depsipeptide under clinical development Free

1564

Aplidin (plitidepsin) is a promising novel agent, currently in phase II trials for the treatment of acute leukemia. Phase I studies show that Aplidin does not have significant marrow toxicity at the MTD. In order to understand the relative selectivity for leukemia and lymphoma cells, and the synergy we have demonstrated with cytarabine (Banerjee D, et al. Blood. 207b: 4496, 2004), we have initiated studies of its transport in leukemia and lymphoma cell lines as well as in blasts from leukemia patients. In SKI-DLBCL cells, a large B-cell lymphoma cell line, C¹⁴ Aplidin uptake is rapid, and peaks @ 15-30 minutes, followed by a rapid decrease in intracellular levels by 60 minutes. Concomitant exposure to Cytarabine increased Aplidin uptake by 20%, providing a possible explanation for the cytotoxic synergy observed. Uptake was ATP dependent, as a one hr exposure in glucose-free medium containing sodium azide and 2-deoxyglucose markedly reduced drug uptake, that was reversed by addition of MgATP. A previous study in Jurkat cells indicated that Aplidin was incorporated into lipid rafts, where it aggregated with death receptors, ligands and down stream molecules, triggering cell death processes (Gajate C and Mollinedo F, JBC 280: 11641-11647, 2005). Using methyl -B- cyclodextrin, a compound that disrupts lipid rafts by extracting cholesterol, we found that Aplidin uptake was inhibited in Jurkat cells, but not in HL-60, K562, and CEM-CCRF cells, indicating that the mechanism of cytotoxicity of Aplidin may differ depending on the cell type. Based on these and previous studies indicating that Aplidin decreases cellular ATP content (Humeniuk et al., submitted), we hypothesize that Aplidin toxicity in most leukemia and lymphoma cells is due to a pharmacodynamic effect at the mitochondrial level.