Thioproline: an inhibitor of chemical carcinogenesis

Experimental DBA/1 mice were implanted with methylcholanthrene impregnated filterpaper disks. The disks were removed six weeks after implantation and median induction of fibrosarcomas occurred in 114.5 +/- 6 days. Two weeks pretreatment with thioproline, a reverse transformation drug, followed by maintenance throughout the duration of the experiment (27 weeks) reduced the tumor incidence to 60% that of controls. Pretreatment with thioproline and drug administration continued only through the six weeks post-implantation period failed to alter tumor incidence.