Pharmacological properties of a new alpha-aminophosphonic acid derivative of vinblastine.

S 12363 is a new vinca alkaloid derivative obtained by grafting an optically active alpha-aminophosphonate at the C23 position of O4-deacetyl vinblastine. This compound was as potent as Vincristine (VCR), and less potent than Vinblastine (VLB), in inhibiting in vitro tubulin polymerization. However, S 12363 was found to be 7 to 553 and 12 to 74-fold more cytotoxic than VCR and VLB, respectively, when tested on a panel of 2 murine and 6 human tumor cell lines using the Microculture Tetrazolium Assay. S 12362, which differs only by the configuration of the asymmetric carbon atom of the side chain, was 18 to 59-fold less cytotoxic. At equitoxic doses, all these compounds induced a "G2 + M" phase accumulation of L1210 cells, suggesting a similar mechanism of action. S 12363, administered i.p. or i.v., was at least as active as reference compounds on two murine transplantable tumors (P388 leukemia and B16 melanoma) while the optimal dosage was 20-fold lower: 0.15-0.20 mg/kg versus 2-5 mg/kg, respectively. S 12362 was practically inactive at 1-3 mg/kg. The hematological toxicity of S 12363 (0.1 mg/kg) was similar to that of VLB (4 mg/kg). The exceptionally high potency of S 12363 did not appear to be due to a better interaction with tubulin, its intracellular target, but rather to some properties conferred by the alpha-aminophosphonic acid, such as a facilitated uptake and/or a better cellular retention.