Nitrosoureas including BCNU, CCNU, methyl-CCNU and chlorozotocin are of clinical value in the treatment of a broad spectrum of neoplasms, including CNS diseases, leukemia, and Hodgkin's disease. Present evidence favors nucleic acids as one of the principal cell target sites. The detailed molecular mechanism of action of nitrosoureas is not understood which is preventing rational structure modification to enhance antitumor properties. In the next phase of our work the first objective is to synthesize and characterize by nmr 15N and 13C labelled E and Z 2-chloroethyldiazohydroxides which are implicated among the electrophiles generated from nitrosoureas and responsible for their anticancer action. Certain chiral nitrosoureas will be synthesized with a view to determining the fate of stereochemical integrity of the alkyl portion upon reaction with DNA. We will employ the specifically N18O labeled nitrosoureas we have synthesized for reaction with DNA to determine the mechanistic origin of the critical 2-hydroxyethylation lesion. Supercoiled PM2-DNA will be used in conjunction with T4 thymine photodimer repair endonuclease to determine if the antileukemic sulfoxide nitrosourea NSC 321528 which generates novel 1,2-oxathietanes functions by inducing photodimers following the [02s + 02a] cycloreversion. Additional analogues of the promising lead compound, the sulfur-mustard nitrosourea NSC 292684, of novel nitrosothioureas and disulfide-linked nitrosoureas designed to be preferentially activated by hypoxic tumors will be designed, synthesized and tested. In addition intercalator bound nitrosoureas will be prepared to improve their targeting towards DNA in the cell. Plans to introduce NSC 292648 into the clinic will be pursued.
