Unique cooperative binding interaction observed between a minor groove binding Pt antitumor agent and Hoechst dye 33258.

The trinuclear compound [{Pt(NH3)3}2mu-{trans-Pt(NH3)2(H2N(CH2)6NH2)}2(6+) (0,0,0/t,t,t) binds to DNA only through noncovalent hydrogen bonding and electrostatic interactions. The presence of this 6+ cation allows discrimination of binding modes for common DNA ligands: binding of minor-groove agents such as Hoechst 33258 is cooperative, and dye-DNA interaction is enhanced whereas intercalation as exemplified by ethidium bromide is competitively inhibited.