Incorporation of 5-substituted pyrimidine nucleoside analogues into DNA of a thymidylate synthetase-deficient murine FM3A carcinoma cell line.

Various 5-substituted 2'-deoxyuridine (dUrd), 2'-deoxycytidine (dCyd), 1-beta-D-arabinofuranosyluracil (araU) and 1-beta-D-arabinofuranosylcytosine (araC) analogues have been investigated for their stimulatory effect on the growth of a thymidylate (dTMP) synthetase-deficient murine mammary carcinoma cell line (FM3A/TS-) that is auxotrophic for thymidine (dThd). Such stimulatory effect may be considered as indicative for the incorporation of the nucleoside analogue into host cell DNA. Based on this premise, several dUrd analogues were found to be incorporated into FM3A/TS- cell DNA (in decreasing order of incorporation): 5-bromo-dUrd greater than 5-chloro-dUrd greater than 5-(3-hydroxy-1-propynyl)-dUrd greater greater than 5-(1-pentynyl)-dUrd approximately 5-(1-propynyl)-dUrd approximately 5-iodo-dUrd greater than 5-(5-carboxy-1-hexenyl)-dUrd greater than 5-(3,3-dimethyl-1-butynyl)-dUrd greater than 5-ethyl-dUrd greater than 5-(5-chloro-1-pentynyl)-dUrd greater than 5-ethynyl-dUrd approximately 5 vinyl-dUrd greater than 5-phenylethynyl-dUrd greater than 5-(5-cyano-1-pentenyl)-dUrd greater than 5-(1-propenyl)-dUrd greater than 5-(1-hexynyl)-dUrd greater than 5-(5-hexyn-1-enyl)-dUrd. Among the 5-substituted dCyd analogues, 5-methyl-dCyd, 5-chloro-dCyd, 5-bromo-dCyd and 5-iodo-dCyd were also found to stimulate cell growth, and are therefore assumed to be incorporated into FM3A/TS- cell DNA. Since the stimulatory effects of these compounds on FM3A/TS- cell proliferation were suppressed in the presence of a Cyd deaminase inhibitor (tetrahydrouridine) or dCMP deaminase inhibitor (2'-deoxytetrahydrouridine), it is surmised that the dCyd analogues are first deaminated to the corresponding dUrd analogues before they are incorporated into DNA. None of the 5-substituted araU or araC analogues tested were able to sustain the growth of FM3A/TS- cells. It is postulated, therefore, that these araU or araC analogues are not incorporated to any appreciable extent into the DNA of FM3A/TS- cells, or, if they are incorporated, prevent cell growth. Thus, the dTMP synthetase-deficient FM3A/TS- cell line represents a unique system to distinguish those pyrimidine nucleoside analogues that are able to sustain cell growth and, therefore, assumed to be incorporated into the host cell DNA from those pyrimidine nucleoside analogues that are not.