Design, synthesis, and evaluation of mitomycin-tethered phosphorothioate oligodeoxynucleotides.

Abstract

Mitomycin C (1) is the prototypical bioreductive alkylating agent. Studies have shown that mitomycin C and its derivatives selectively alkylate guanine residues within di- and trinucleotide DNA sequences. This investigation sought to improve the selective DNA bonding properties of the mitomycins by coupling them with antisense oligodeoxynucleotides. Two procedures were developed that allowed the attachment of a phosphorothioate oligodeoxynucleotide containing a hexylamino spacer at the 5' terminus with a C(10)-activated mitomycin. In the first procedure, decarbamoylation of 1 (NaOCH3/ benzene) afforded 10-decarbamoylmitomycin C (10), which was treated with either dimethyl sulfate or methylthiochloroformate and base to yield 10-decarbamoylporfiromycin (11) and N(1a)-[(methylthio)-carbonyl]-10-decarbamoylmitomycin C (12), respectively. Activation of the C(10) site in 11 and 12 with 1,1'-carbonyldiimidazole or with 1,1'-thiocarbonyldiimidazole provided the N(1a)-substituted mitomycin 10-decarbamoyl-10-O-carbonylimidazoles (5, 7) and 10-decarbamoyl-10-O-thiocarbonylimidazoles (6, 8), respectively. Compounds 5-8 were reacted with glycine methyl ester hydrochloride (17) and base in both methylene chloride and aqueous buffered solutions to determine the ease and efficiency in which these C(10)-activated mitomycin derivatives coupled to amines. It was found that 5-8 all reacted with 17 in methylene chloride to give the coupled products 18-21 but that improved amine coupling yields in water were observed for the 10-decarbamoyl-10-O-thiocarbonylimidazoles 6 and 8 as compared with the 10-decarbamoyl-10-O-carbonylimidazoles 5 and 7. This finding led to the coupling of the phosphorothioate oligodeoxynucleotide, H2N(CH2)6-P(S)(OH)-GGCCCCGTG-GTGGCTCCAT (22) to 8. Compound 22 complemented a 19-base sequence in the translation initiation region of the human A-raf-1 gene. Use of excess 8 (28 equiv) with 22 gave only a 36% yield of the coupled product 23, which proved difficult to separate from 22. In the second procedure, phosphorothioate oligodexynucleotides that contained a hexylamino spacer at the 5'termini were coupled to 10-des(carbamoyloxy)-10-isothiocyanatoporfiromycin (9). Compound 9 was prepared in four steps from 11. Mesylation (methanesulfonyl chloride/pyridine) of 11 gave the C(10) mesylate 13, which was then treated with NaN3 (dimethylformamide, 90 degrees C) to give 10-des(carbamoyloxy)-10-azidoporfiromycin (14). Catalytic reduction (PtO2, H2) of 14 in pyridine afforded C(10) amine 15. Treatment of 15 with di-2-pyridyl thionocarbonate provided the desired 10-des(carbamoyloxy)-10-isothiocyanatoporfiromycin (9). Compound 9 readily coupled with 17 and base in both methylene chloride and aqueous buffered solutions to give 25. Use of the 5'hexylaminophosphorothioate oligodeoxynucleotides 32-35 in place of 17 gave the conjugated adducts 28-31, respectively, in a 12% to near-quantitative yield. The products were purified by semipreparative HPLC. Antisense agents 28-31 were designed to target a 30-base-long region from the coding region of the human FGFR1 gene. One adduct, 29, reduced the number of FGFR1 receptors in human aortic smooth cells for bFGF on the cell surface, which suggested down-regulation of FGFR1 gene expression. Further, 29 inhibited cultured human aortic smooth muscle cell proliferation and was less cytotoxic than porfiromycin (2). The biological assay data suggest that the phosphorothioate oligodexynucleotide porfiromycin conjugates may be more target selective and less toxic than either mitomycin or porfiromycin and thus be promising therapeutic agents.