Metabolic studies on the possible mode of action of isoniazid tumorigenicity

Summary Data on tumorigenicity and mutagenicity of INH show that INH is tumorigenic in mice but not in rats. The metabolic studies on the two species denote that rats are rapid inactivators whereas mice are slow inactivators of INH. Rats are also resistant to the immediate inhibitory effect of INH on DNA biosynthesis. Using Ames test it was observed that INH is mutagenic to salmonella typhimurium strains TA 100 and 1535 and this effect is abolished in presence of 59 mixture. In vivo and in vitro studies on INH interaction with macromolecules reveal that there is a greater interaction with RNA than with DNA and the site of interaction is the cytidine and deoxycytidine, respectively. A preliminary study is undertaken to see if healed TB cases have a higher risk for cancer. It is found that cancer incidence in this group is higher as compared to noncancer patients.