Thiazolidine-4-carboxylic acid, a selective drug against human cancers
Cancer is not one single disease entity but a collective of more than 100 neoplastic disorders, distinguished by the tissues and cell types from which they originate. Hence, it is a priori unlikely tha t chemotherapeutic drugs with comprehensive anticancer spectra can be developed. Drugs with selective toxicity for neoplastic diseases require for their development the recognition of vitally impor tan t biochemical differences between cancer cells and their normal counterparts as points of departure into drug design. The paucity of such informat ion has led to the int roduct ion of some drugs which are generally cytotoxic. Another shortcoming of cancer chemotherapy development is the use of fast growing experimental animal cancers as screening systems of which it is open to doub t tha t they represent valid test systems of neoplastic disease of man. One general characteristic of neoplastic cells is their insensitivity to contact inhibi t ion: growth of normal cells is controlled by contact with other cells while neoplastic cells are not inhibited by such contacts and invade healthy tissues. Gosalvez [1] has studied a series of compounds for action on the cell-membrane regulatory mechanism and has tested in vitro for the restorat ion of contact inhibi t ion in cultures of tumor cells. He obtained such "reverse transforma t ion" , i.e., a return of tumor cells to normal membrane function in vitro with t hiazolidine-4-car boxylic acid, T4C (Fig. 1). The compound is a reaction product of cysteine with formaldehyde and has been known since 1936 [2].