Monoclonal antibodies to antitumor Vinca alkaloids: thermodynamics and kinetics.

Spleen cells from a mouse and a rat immunized with vinblastine coupled to bovine serum albumin were fused in two independent experiments with P3 X 63-Ag8 (non-secreting variant) mouse myeloma cells. Three mouse X mouse (Vinca 1-3) and two rat X mouse (Vinca 4 and 5) hybrids were selected for production of Vinca alkaloid binding monoclonal antibodies. Each antibody had characteristic cross-reactivities with alkaloids structurally related to vinblastine: Vinca 1 reacted preferentially with deacetylated alkaloids (deacetyl vinblastine and vindesine) and Vinca 2 had a higher affinity for vinblastine and vincristine. Vinca 3-5 recognized equally vinblastine, vincristine and vindesine but differed with respect to their affinities for other analogues. No significant cross-reactivity of the monomeric alkaloids vindoline or catharanthine was observed with any antibody, and dimeric alkaloids modified in the catharanthine moiety had reduced immunoreactivity. Mouse monoclonal antibodies (Vinca 1 and 3) showed moderate affinity (2.2 X 10(-7) and 5.8 X 10(-9) M) for their respective best ligands and fast kinetics (dissociation rate constants greater than 3 X 10(-3) sec-1). Vinca 4 and 5, derived from the rat X mouse hybrids, had much higher affinities (1.5 X 10(-11) and 1.1 X 10(-11) M) and slower kinetics (dissociation rate constants: 2.4 X 10(-5) and 7.2 X 10(-6) sec-1). The major difference between these two antibodies was that Vinca 4 binds and releases the antigen more rapidly than Vinca 5 does. Somatic hybridization techniques thus generated monoclonal antibodies recognizing a given class of low mol. wt antigens with variable specificity, affinity and kinetic behavior, allowing the selection of reagents most appropriate for particular immunochemical applications.