5-IODO-2'-DEOXY-L-URIDINE AND (E)-5-(2-BROMOVINYL)-2'-DEOXY-L-URIDINE- SELECTIVE PHOSPHORYLATION BY HERPES-SIMPLEX VIRUS TYPE-1 THYMIDINE KINASE, ANTIHERPETIC ACTIVITY, AND CYTOTOXICITY STUDIES

5-lodo-2'-deoxy-L-uridine (L-IdU) and (E)-5-(2-bromovinyl)-2'-deoxy-L- uridine (L-BVdU) have been prepared and found to inhibit herpes simple x virus type 1 (HSV-1) thymidine kinase (TK) with activities comparabl e to those of their analogs with the natural D-sugar configuration. Th e mechanism of inhibition is purely competitive for L-IdU (K-i = 0.24 mu M) and mixed-type for L-BVdU (K-i = 0.13 mu M). High performance li quid chromatographic analysis of the reaction products demonstrated th at the viral enzyme phosphorylates both L-enantiomers to their corresp onding monophosphates with efficiency comparable to that for D-enantio mers. Neither L-enantiomer inhibits the human cytosolic TK. In contras t to their D-enantiomers, L-IdU and L-BVdU have no effect on human thy midylate synthase, either in HeLa cells or in TK-deficient HeLa cells transformed with the HSV-1 TK gene. Both L-enantiomers (i) have no eff ect on HeLa cell growth, (ii) are 1000-fold less cytotoxic toward TK-d eficient HeLa cells transformed with the HSV-1 TK gene than are their D-enantiomers, (iii) in contrast to their D-enantiomers, are fully res istant to hydrolysis by nucleoside phosphorylase, and, (iv) in spite o f their much lower cytotoxicity, most probably due to the very low aff inity of L-BVdU monophosphate and L-IdU monophosphate for thymidylate synthase, are only 1 or 2 orders of magnitude less potent than their D -enantiomers in inhibiting viral growth, with potency comparable to th at of acyclovir.