ANTIBODIES AGAINST (1R,2R)-CYCLOHEXANEDIAMINEPLATINUM(II)-DNA ADDUCT RECOGNIZE THE CONFORMATIONAL DIFFERENCES OF ISOMERIC ANALOGS OF CYCLOHEXANEDIAMINE

Antibodies reactive to (1R,2R)-cyclohexanediamineplatinum(II)-DNA ((1R,2R)-cyclohexanediamine: 1R,2R-dach) adducts were elicited by immunization of rabbit with calf thymus DNA modified by Pt(1R,2R-dach)Cl2 at a ratio of bound platinum per nucleotide ( D N)b) of 0.0335. In an enzyme-linked immunosorbent assay (ELISA), the binding of specific antibodies to Pt(1R,2R-dach)-DNA adduct (60 μl of 1.235 · 10-7 M Pt in each wells) on the assay plate was competitively inhibited by Pt(1R,2R-dach)-DNA adduct ( D N)b = 0.0653) in the solution. Almost equal inhibition was observed with Pt(1S,2S-dach)-DNA (( D N)b = 0.0412), an optical isomer of 1R,2R-dach. Pt(1R,2S-dach)-DNA (( D N)b = 0.0371) and Pt(1R,3S-dach)-DNA (( D N)b = 0.0281) in which the cyclohexane ring is stereochemically perpendicular to the platinum chelate plane, also inhibited antibody binding, but these adducts gave only incomplete inhibition at higher Pt-DNA adduct concentrations. Although Pt(1R,2R-dach)-d(GpG) and Pt(1R,2R-dach)(NH3)2 inhibited antibody binding, the affinity of the antibody for Pt(1R,2R-dach)(NH3)2 was lower than with Pt(1R,2R-dach)-DNA, and the inhibition behavior of Pt(1R,2R-dach)-d(GpG) was biphasic, i.e., at the lower concentration the inhibition curve was consistent with that of Pt(1R,2R-dach)-DNA, but at the higher concentration it shifted to that of Pt(1R,2R-dach)(NH3)2. The affinity of the antibody for cis-DDP was markedly lower than with Pt(1R,2R-dach)(NH3)2. These facts suggest that the antibodies may bind to the substituents (the platinum and its surroundings) of the various Pt complexes rather than the DNA structure altered by platinum binding. © 1990.