[I-125 I-127]IODOHOECHST-33342 - SYNTHESIS, DNA-BINDING, AND BIODISTRIBUTION/

An iodinated analog of the DNA-minor-groove-binding agent Hoechst 3334 2 has been synthesized and evaluated for DNA binding and tumor targeti ng. The bis-benzimidazole ring system of the title compound was constr ucted from the piperazinyl terminus via a Pinner-type cyclization foll owed by oxidative cyclization of the diamine Schiff base. To synthesiz e radioiodoHoechst 33342, (trimethylstannyl)Hoechst 33342 was prepared by the same strategy and subjected to mild radioiodedestannylation in the presence of lactoperoxidase. After purification by HPLC, the radi ochemical was separated in carrier-free form with >85% radiochemical y ield and >99% chemical and radiochemical purity. Fluorescence spectrom etric analysis of the binding of iodoHoechst 33342 calf thymus DNA gav e an equilibrium association constant (K-a) of 2.57 x 10(7) M(-1) comp arable to the K-a value of Hoechst 33342. Fluorescence microscopy of v iable V79 cells demonstrated that the iodinated dye stained the nuclei with avidity similar to that of the noniodinated dye. The biodistribu tion of [I-125]-iodoHoechst 33342 in LS174T tumor-bearing athymic mice 4 h postadministration showed a tumor uptake of 3-4% injected dose pe r gram (ID/g), tumor/blood ratio of 6-8, and tumor/nontumor ratios abo ve unity for most organs. A low thyroid uptake (similar to 2% ID/g) in dicated that the radiochemical did not deiodinate and was stable in vi vo.