[Combined efficacy of polyamine antimetabolites and cis-diamminedichloroplatinum]

The combined antitumor effects of the polyamine antimetabolites, alpha-difluoro methylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG), with CDDP were studied using human gastric cancer cells xenotransplanted into nude mice. DFMO (1000 mg/kg in two divided doses) and MGBG (50 mg/kg) were given IP for six consecutive days from the time when the xenotransplanted tumor weighted about 100 mg, and CDDP (3.0 mg/kg) was given IP every other day from the same time. Animals treated with DFMO plus MGBG with or without CDDP as well as with CDDP only displayed suppressed tumor growth, compared to untreated mice. In mice treated with these three drugs, however, tumor growth was rather rapid compared to those treated with CDDP only, although tumoral CDDP levels in animals given DFMO, MGBG and CDDP were higher than those given CDDP only. When DFMO, MGBG and CDDP or DFMO and MGBG were administered, tumoral spermidine and spermine levels decreased markedly. On the other hand, tumor DNA biosynthesis in the CDDP only group dropped markedly 24 hours after the termination of therapy. These results suggest that an alteration in the DNA structure caused by polyamine deficiency may prevent cross-link formation in DNA by CDDP.