Highly selective cytostatic activity of (E)-5-(2-bromovinyl)-2'-deoxyuridine derivatives for murine mammary carcinoma (FM3A) cells transformed with the herpes simplex virus type 1 thymidine kinase gene
(E)-5-(2-Bromovinyl)-2'-deoxyuridine (BVDU) and various structurally related analogues thereof, i.e., (E)-5-(2-iodovinyl)-2'-deoxyuridine (IVDU) and (E)-5-(2-bromovinyl)-2'-deoxycytidine (BVDC), and the carbocyclic analogues of BVDU, IVDU, and BVDC, were evaluated for their inhibitory effects on the growth of murine mammary carcinoma FM3A cells, deficient in thymidine kinase (TK) activity but transformed with the herpes simplex virus type 1 (HSV-1) TK gene (designated FM3A/TK-/HSV-1 TK+). BVDU and its congeners were much more inhibitory to the growth of FM3A/TK-/HSV-1 TK+ than to the growth of the wild type (FM3A/0) cells. For BVDU, for example, the 50% inhibitory dose for the FM3A/TK-/HSV-1 TK+ cells was 0.5 ng/ml, as compared to 11 micrograms/ml for the FM3A/0 cells. Evidently, BVDU and its congeners required phosphorylation by the HSV-1 TK to exert their cytostatic action. In attempts to evaluate further the mechanism of this cytostatic action, BVDU, IVDU, and their carbocyclic analogues were evaluated for their inhibitory effects on thymidylate synthetase (TS) and their incorporation into DNA. TS was identified as one, but not the sole, target in the cytostatic activity of BVDU and its derivatives. With [125I]IVDU and its carbocyclic analogue C-[125I]IVDU, clear evidence was obtained for the incorporation of these radiolabeled analogues into DNA of the FM3A/TK-/HSV-1 TK+ cell line and a TS-deficient mutant thereof, FM3A/TK-/HSV-1 TK+/TS-. No incorporation was detected with [125I]IVDU or C-[125I]IVDU into DNA of FM3A/0 and FM3A/TS- cells. To what extent the incorporation of [125I]IVDU and C-[125I]IVDU contributed to their cytostatic action against FM3A/TK-/HSV-1 TK+ cells remains the subject of further study.