Pharmacologic and toxicologic evaluation of thioproline: a proposed nontoxic inducer of reverse transformation.

: The ability of thioproline to act as a nontoxic inducer of reverse transformation was examined. Thioproline was unable to effect reproducibly morphologic changes characteristic of the reversed transformed state of HeLa, WI-38VA13, C1300 neuroblastoma, and CHO-K1 cell lines. Reversal of transformed cells with dibutyryl cyclic AMP was, however, readily demonstrated in both the CHO-K1 and C1300 cell lines. Thioproline produced severe, life-threatening CNS toxicity in both mice and rats at levels far below those previously reported to be without any toxic effects. We conclude that not only is thioproline incapable of producing a reversal of the transformed state in HeLa and other cell lines in vitro, it is also a compound that must be described as a strongly CNS toxic agent.