Cytotoxicity and cellular uptake of pyrimidine nucleosides for imaging herpes simplex type-1 thymidine kinase (HSV-1 TK) expression in mammalian cells

ABSTRACT The Epstein-Barr virus (EBV) thymidine kinase (TK) was expressed in mammalian 143B TK− cells to investigate its substrate specificity. The herpes simplex virus type 1 (HSV-1) TK was similarly expressed for comparison. Both viral TKs conferred a TK+ phenotype on 143B TK− cells. The nucleoside analog ganciclovir (GCV) did not affect the growth of 143B EBV TK or 143B TK− cells but effectively killed 143B HSV-1 TK cells. Furthermore, lysates of 143B EBV TK cells could not phosphorylate GCV, which was confirmed by high-performance liquid chromatography. EBV TK, HSV-1 TK, and EBV TK N−, a truncated EBV TK missing 243 N-terminal amino acids, were purified as fusion proteins expressed in bacteria, and all had TK activity. In addition, EBV TK was observed to have a thymidylate kinase activity but could not phosphorylate GCV, acyclovir, or 2′-deoxycytidine. In competition assays, only nucleoside analogs of thymidine significantly inhibited thymidine phosphorylation by EBV TK, with the following rank order: 5-bromodeoxyuridine > zidovudine > stavudine > sorivudine. These results demonstrate that EBV TK substrate specificity is narrower than those of alphaherpesvirus TKs and that thymidine analogs may be the most suitable nucleoside antivirals to target the enzyme. Clinical implications for gammaherpesviruses are discussed.

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Antiviral activity of the 3′;-amino derivative of (E)-5-(2-bromovinyl)-2′;-deoxyuridine

Biochemical Journal ◽

10.1042/bj2110439 ◽

1983 ◽

Vol 211 (2) ◽

pp. 439-445 ◽

Cited By ~ 11

Author(s):

E De Clercq ◽

J Descamps ◽

J Balzarini ◽

T Fukui ◽

H S Allaudeen

Keyword(s):

Herpes Simplex Virus ◽

Herpes Simplex ◽

Thymidine Kinase ◽

Dna Polymerase ◽

Dna Polymerases ◽

Amino Derivative ◽

Dna Polymerase Alpha ◽

Simplex Virus ◽

Hsv 1

3′-NH2-BV-dUrd, the 3′-amino derivative of (E)-5-(2-bromovinyl)-2′-deoxyuridine, was found to be a potent and selective inhibitor of herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV) replication. 3′-NH2-BV-dUrd was about 4-12 times less potent but equally selective in its anti-herpes activity as BV-dUrd. Akin to BV-dUrd, 3′-NH2-BV-dUrd was much less inhibitory to herpes simplex virus type 2 than type 1. It was totally inactive against a thymidine kinase-deficient mutant of HSV-1. The 5′-triphosphate of 3′-NH2-BV-dUrd (3′-NH2-BV-dUTP) was evaluated for its inhibitory effects on purified herpes viral and cellular DNA polymerases. Among the DNA polymerases tested, HSV-1 DNA polymerase and DNA polymerase alpha were the most sensitive to inhibition by 3′-NH2-BV-dUTP (Ki values 0.13 and 0.10 microM, respectively). The Km/Ki ratio for DNA polymerase alpha was 47, as compared with 4.6 for HSV-1 DNA polymerase. Thus, the selectivity of 3′-NH2-BV-dUrd as an anti-herpes agent cannot be ascribed to a discriminative effect of its 5′-triphosphate at the DNA polymerase level. This selectivity most probably resides at the thymidine kinase level. 3′;-NH2-BV-dUrd would be phosphorylated preferentially by the HSV-1-induced thymidine kinase (Ki 1.9 microM, as compared with greater than 200 microM for the cellular thymidine kinase), and this preferential phosphorylation would confine the further action of the compound to the virus-infected cell.

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