Potentiation of methylglyoxal-bis-guanylhydrazone by alpha-difluoromethylornithine in rat prostate cancer.

The polyamines, putrescine, spermidine, and spermine, are fundamentally related to both normal and neoplastic cell proliferation. The prostate gland and prostatic tumors in man and rodents contain large amounts of polyamines. This suggests that inhibition of polyamine biosynthetic enzymes, ornithine decarboxylase (ODC) and S-adenosyl-methionine decarboxylase (SAMDC) may retard the growth of prostatic cancer. Since alpha-difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG) are irreversible and competitive inhibitors of ODC and SAMDC, respectively, they were tested as single agents and in combination on a transplantable rapidly growing and hormone-resistant G subline of the Dunning R-3327 rat prostatic adenocarcinoma. Groups of rats bearing tumors were treated with various regimens of DFMO, MGBG, and DFMO plus MGBG, daily for 21 days. Analysis of differences in tumor growth between treatment groups and controls showed DFMO had no antitumor effect but was well tolerated, MGBG retarded growth rate significantly but resulted in drug deaths in over 50% of the animals, and the combination of DFMO and MGBG resulted in rapid decline in tumor growth rates after 5 to 9 days of treatment with reduced toxicity. At 21 days, or death, 38 of 60 (63%) rats had no viable tumor on histologic study, whereas tumor was present in each of the animals in the other groups. Alpha-difluoromethylornithine increased the intracellular uptake of MGBG and potentiated the antigrowth activity of MGBG on a hormone refractory rat prostatic tumor with less toxicity than MGBG alone.

Antigrowth effect of some inhibitors of polyamine synthesis on transplantable prostate cancer.

Inhibitors of polyamine synthesis were tested for therapeutic effectiveness on transplantable prostate cancer. Inhibition of either ornithine decarboxylase or S-adenosyl-L-methionine decarboxylase (AMDC) by alpha-difluormethylornithine (DFMO) or methylglyoxal-bis[guanylhydrazone] (MGBG), respectively, was associated with significant antitumor effect. The combination of DFMO with MGBG was not only more effective but no more toxic than MGBG alone. Combination of MGBG with 9-B-D-arabinofuranosyladenine, an indirect effector of SAMDC, failed to increase therapeutic effectiveness of MGBG.

Comparisons of liver transfer RNA methyltransferase and adenosylmethionine decarboxylase activities of male and female rats.

The activities of liver transfer RNA (tRNA) methyltransferases from control or ovariectomized female rats were found to be higher than those of control or castrated males. Administration of testosterone to ovariectomized females caused activity to decrease to the level of the males. Conversely, administration of estrogen to castrated males resulted in liver enzyme levels similar to those of the females. When the substrates for in vitro methylation were either mixed heterologous tRNA's from Escherichia coli or mixed homologous methyl-deficient tRNA from livers of ethionine-treated rats, the difference in activity between males and females was about 35%. When amino acid-specific tRNA's from E. coli were used as substrates, the ratios of activity of enzymes from females to that of males were: tRNANfMet 1.5; tRNAMetMet 1.1; tRNASer3 1.85; tRNAPhe 1.1; and tRNATyr 1.25, indicating that there are qualitative as well as quantitative differences in the liver tRNA methyltransferases of the two sexes. The adenosylmethionine decarboxylase activity of female rat liver preparations was approximately double that found for males. Testosterone, given to ovariectomized females, lowered the activity of this enzyme to about the same level as that of males. It is not clear whether the observed sex-related differences in activity of several adenosylmethionine-utilizing liver enzymes represent isolated phenomena or are indicative of a sex-related difference in the rate of liver adenosylmethionine turnover.