Relationship between the cellular accumulation and the cytotoxicity of S12363, a new vinca alkaloid derivative

Summary

S 12363, a new vinca alkaloid derivative, was considerably more cytotoxic to murine L1210 cells and five human tumor cell lines (HL60, HT-29, COLO 320DM, NCI-H460, and PANC-1) than was vincristine (VCR) or vinblastine (VLB). S 12363 bound to tubulin in crude extracts from brain or L1210 cells with an affinity similar to that of VLB and VCR (apparentK _d value: 1.1–1.6, 1.2–1.7, and 0.6–0.8 μM, respectively). After 1 h exposure, the accumulation of 20 nM [³H]-S 12363 by L1210 cells was 4-to 18-fold that of [³H]-VLB and [³H]-VCR, respectively. After the cells had been preloaded for 1 h with the labeled drugs and then incubated for 3 h in drug-free medium, 37%–55% of the [³H]-S 12363 was retained by the cells vs 36%–47% of the [³H]-VCR and <6% of the [³H]-VLB. Similar results were obtained for the five human cell lines tested. The accumulation factors (intracellular vs extracellular concentrations) found for [³H]-S 12363 (54- to 167-fold) were significantly higher than those observed for [³H]-VCR (5- to 14-fold) or [³H]-VLB (19- to 41-fold). >90% of the radioactivity extracted from L1210 cells that had been treated with [³H]-S 12363 was recovered as unmodified drug, demonstrating that [³H]-S 12363 was not metabolized by these cells. S 12362, which differs from S 12363 only in the absolute configuration of the asymmetric carbon atom of its α-aminophosphonic side chain, was 300 times less cytotoxie, bound to tubulin with a lower affinity (apparentK _d value, 4.9–9.6 μm), and was neither accumulated nor retained by the cells. Taken together, these results demonstrate that the potency of S 12363 is due at least in part to its cellular accumulation and retention.