MOLECULAR AND CELLULAR PHARMACOLOGY OF NOVEL PHOTOACTIVE PSORALEN ANDCOUMARIN CONJUGATES OF PYRROLE-CONTAINING AND IMIDAZOLE-CONTAINING ANALOGS OF NETROPSIN

The molecular and cellular pharmacology of novel sequence-directed pho toactive agents, in which either psoralen or coumarin is conjugated to minor groove-binding AT-selective pyrrole-, or more GC-selective imid azole-containing analogues of netropsin, is described. The compounds w ere relatively non-toxic in the dark and showed marked photoinduced cy totoxicities when irradiated at 366 nm UV. The psoralen-containing pyr role (1) and imidazole (2) compounds gave the largest photoinduced eff ect, were more active than 8-methoxypsoralen (8-MP) itself by 333-and 22-fold, respectively, and were more potent than the corresponding cou marin-containing analogues 3 and 4. Following irradiation, 1 and 2 wer e >300- and >10-fold more efficient at producing interstrand cross-lin ks in naked DNA, respectively, than 8-MP. 1 was at least 10-fold more efficient at producing cross-links in cells than 2, reflecting the dif ference in their IC50 values. No cross-links were observed with the co umarin analogues, but these compounds were more potent than 8-MP. AT a nd GC sequence recognition was confirmed by DNA footprinting, and site s of covalent modification mapped by a polymerase stop assay. All comp ounds produced blocks at thymine base sites following irradiation. 1 w as more efficient than 8-MP and produced a different pattern of covale nt modification, whereas 2 was more selective than either 1 or 8-MP. A H-1-NMR study on a 1:1 complex of 2 with the hexamer (5'-dA(1)T(2)G(3 )C(4)A(5)T(6)-3')(2) indicated that the imidazole carboxamide moieties of 2 reside in the minor groove of the sequence 5'-GCAT-3' of the hex amer with the C-terminus located on the 3'-TA site, and the psoralen g roup intercalated between the 5'-A(1)T(2)-3' base pairs.