PD 114595 is a Benzothiopyrano-indazole cpd. Cl-958, PD 121373, and PD 114595 belong to a new class of DNA complexers, substituted 2H-[1]benzothiopyrano[4,3,2-cd] indazoles, and are being further developed as antitumor drugs based on their curative properties against murine solid tumor models. The biochemical effects of these drugs on L1210 leukemia cells and their interaction with DNA were studied and compared to clinically used intercalators. The benzothiopyranoindazoles bound to DNA with a relatively high affinity, having intrinsic association constants of between 3 and 4 x 10(5) M-1.