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.     

Synthesis and antiviral activity of (E)-5-(2-bromovinyl)uracil and (E)-5-(2-bromovinyl)uridine

(E)-5-(2-Bromovinyl)uracil (BVU) and (E)-5-(2-bromovinyl)uridine (BVRU) were synthesized starting from 5-formyluracil via (E)-5-(2-carboxyvinyl)uracil or starting from 5-iodouridine via (E)-5-(2-carbomethoxyvinyl)uridine and (E)-5-(2-carboxyvinyl)uridine, respectively. Depending on the choice of the cell system, BVU and BVRU exhibited a marked activity against herpes simplex virus type 1 (HSV-1) in vitro. Although BVU and BVRU were less potent than the reference compound (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU), their antiviral activity spectrum was remarkably similar to that of BVDU. The latter findings suggest that BVU and BVRU are metabolically converted to BVDU or a phosphorylated product thereof. In vivo, BVU protected mice against a lethal disseminated HSV-1 infection.     

Carbocyclic 5-iodo-2'-deoxyuridine (C-IDU) and carbocyclic (E)-5-(2-bromovinyl)-2'-deoxyuridine (C-BVDU) as unique examples of chiral molecules where the two enantiomeric forms are biologically active: interaction of the (+)- and (-)-enantiomers of C-IDU and C-BVDU with the thymidine kinase of herpes simplex virus type 1

The (+)- and (-)-enantiomers of the carbocyclic analogues of (E)-5-(2-bromovinyl)-2'-deoxyuridine (C-BVDU) and 5-iodo-2'-deoxyuridine (C-IDU) were synthesized by separate routes. Both the (+)- and (-)-enantiomers of C-BVDU and C-IDU were markedly inhibitory to herpes simplex virus type 1 (HSV-1) replication. (+)-C-BVDU and (+)-C-IDU were as inhibitory to HSV-1 as the racemic (+/-)-C-BVDU and (+/-)-C-IDU, respectively, whereas the (-)-enantiomers were only 10-fold less active. Also, the (+)- and (-)-enantiomers of C-BVDU were equally inhibitory to the growth of murine mammary carcinoma cells transformed by the HSV-1 or HSV-2 thymidine kinase (TK) gene (designated FM3A TK-/HSV-1 TK+ and FM3A TK-/HSV-2 TK+). The (+)- and (-)-enantiomers of C-BVDU and the (+)- and (-)-enantiomers of C-IDU had a remarkably similar affinity for HSV-1 TK [Ki, 0.09 and 0.19 microM for (+)-C-BVDU and (+)-C-IDU and 0.16 and 0.19 microM for (-)-C-BVDU and (-)-C-IDU, respectively]. The inhibition of HSV-1 TK by BVDU, IDU, (+)-C-BVDU, and (+)-C-IDU was purely competitive with regard to the natural substrate (thymidine), whereas (-)-C-BVDU, (-)-C-IDU, (+/-)-C-BVDU, and (+/-)C-IDU showed a linear mixed-type inhibition of HSV-1 TK. C-BVDU and C-IDU are examples of chiral molecules of which both isomeric forms are markedly active at both the cellular and enzymatic level.     

Thymidylate synthase is the principal target enzyme for the cytostatic activity of (E)-5-(2-bromovinyl)-2'-deoxyuridine against murine mammary carcinoma (FM3A) cells transformed with the herpes simplex virus type 1 or type 2 thymidine kinase gene

Murine mammary carcinoma FM3A cells, deficient in cytosol thymidine (dThd) kinase (TK) activity and transformed by the herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2) TK gene (designated FM3A TK-/HSV-1 TK+ and FM3A TK-/HSV-2 TK+, respectively) proved extremely sensitive to the cytostatic action of the potent antiherpetic drugs (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and (E)-5-(2-iodovinyl)-2'-deoxyuridine (IVDU). The fact that FM3A TK-/HSV-2 TK+ cells were 5-fold more sensitive to the cytostatic action of BVDU and IVDU but incorporated [125I]IVDU to a 20-fold lower extent into their DNA than did FM3A TK-/HSV-1 TK+ cells led us to conclude that incorporation of these compounds into DNA of HSV TK gene-transformed cell lines is not directly related to their cytostatic action. In attempts to unravel the mechanism of the cytostatic effects of BVDU and IVDU on HSV TK gene-transformed FM3A cells, both compounds were submitted to an intensive biochemical study. Thymidylate synthase was identified as the principal target enzyme for the cytostatic action of BVDU and IVDU since (i) both compounds were far more inhibitory to 2(1)-deoxyuridine (dUrd) than to dThd incorporation into HSV TK gene-transformed FM3A cell DNA, (ii) the cytostatic action of BVDU and IVDU was more readily reversed by dThd than by dUrd, (iii) both compounds strongly inhibited the metabolic pathway leading to the incorporation of 2'-deoxycytidine (dCyd) into DNA thymidylate, (iv) BVDU and IVDU strongly inhibited tritium release from [5-3H]dCyd and [5-3H]dUrd in intact HSV TK gene-transformed FM3A cells, and (v) [125I]IVDU accumulated intracellularly as its 5'-monophosphate to concentration levels considerably higher than those required to inhibit partially purified thymidylate synthase. The inhibitory effects mentioned under (i) to (iv) were not observed with the parental FM3A/0 and FM3A/TK- cells; they were more pronounced for FM3A TK-/HSV-2 TK+ cells than for FM3A TK-/HSV-1 TK+ cells, which correlates with the differential cytostatic effects of BVDU and IVDU on these cells.     

Synthesis and antiviral properties of (E)-5-(2-bromovinyl)-2'-deoxycytidine-related compounds

Treatment of 3',5'-di-O-acetyl-(E)-5-(2-bromovinyl)-2'-deoxyuridine (2) with p-chlorophenyl phosphorodichloridate and 1,2,4-triazole gave 1-(3,5-di-O-acetyl-2-deoxy-beta-D-erythro-pentofuranosyl)-(E)-5-(2-br o movinyl)- 4-(1,2,4-triazol-1-yl)pyrimidin-2(1H)-one (3). Reaction of 3 with ammonia gave (E)-5-(2-bromovinyl)-2'-deoxycytidine (1), the overall yield from 2 being 60%. A similar 4-(1,2,4-triazol-1-yl) derivative (4) was obtained from 3',5'-di-O-acetyl-thymidine by the use of phosphoryl chloride as the condensing agent. Treatment of thymidine with trimethylsilyl chloride and then with phosphoryl chloride and 1,2,4-triazole gave upon workup 1-(2-deoxy-beta-D-erythro-pentofuranosyl)-5-methyl-4(1,2,4-triazol -1-yl) pyrimidin-2(1H)-one (5). (E)-5-(2-Bromovinyl)-2'-deoxyuridine (BVDU) when similarly treated gave the corresponding (E)-5-(2-bromovinyl) compound 7. A minor product formed in both cases was a 4-(1,2,4-triazol-1-yl) derivative in which the nucleoside 5'-hydroxyl group had been replaced by chlorine (6 and 8). Whereas compounds 4-6 and 8 did not exhibit a selective antiviral effect, compounds 1-3 and 7 proved almost as active as the reference compound BVDU. In particular, compound 7, the 4-triazolyl derivative of BVDU, would seem worth pursuing for its potential as an inhibitor of herpes simplex virus type 1 and varicella-zoster virus.     

Differential metabolism of (E)-5-(2-iodovinyl)-2'-deoxyuridine (IVDU) by equine herpesvirus type 1- and herpes simplex virus-infected cells

Thymidine kinase (TK) enzymes encoded by herpes simplex viruses types 1 and 2 (HSV-1, HSV-2), and equine herpesvirus type 1 (EHV-1) catalyze the phosphorylation of thymidine (dThd) and (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU). The replication of HSV-1 is sensitive to BVDU, but the replication of HSV-2 and EHV-1 is not. To investigate the differential sensitivity of the viruses to halogenated vinyldeoxyuridine drugs, the phosphorylation of 125I-labeled (E)-5-(2-iodovinyl)-2'-deoxyuridine (IVDU) was studied. Cytosol enzymes from cells infected by HSV-2 and EHV-1 phosphorylated [125I]IVDU to the monophosphate, IVDUMP, but did not convert IVDUMP to higher di- plus triphosphates (IVDUDP plus IVDUTP) forms. In contrast, enzymes from HSV-1-infected cells converted [125I]IVDU to radioactive IVDUMP and IVDUDP plus IVDUTP. Experiments with mixtures of EHV-1- and HSV-1-induced enzymes showed that the EHV-1 enzyme did not inhibit formation of the IVDUDP plus IVDUTP by the HSV-1 enzyme. With [125I]IVDU as substrate, the Km values for the EHV-1 and HSV-1 TKs were 1.82 and 0.34 microM, respectively, and the Ki (dThd) value for the EHV-1 TK was 0.35 microM. In vivo experiments showed that HSV-1-infected cells converted IVDU to the mono- and the di- plus triphosphate forms. In contrast, EHV-1-infected cells converted IVDU to the monophosphate to a lesser extent than did HSV-1-infected cells, and did not produce the di- plus triphosphates. Thus, inefficient phosphorylation of the monophosphates probably contributes to the insensitivity of EHV-1 replication to IVDU, as it does to the insensitivity of HSV-2 replication to this drug.     

Role of the incorporation of (E)-5-(2-iodovinyl)-2'-deoxyuridine and its carbocyclic analogue into DNA of herpes simplex virus type 1-infected cells in the antiviral effects of these compounds

The carbocyclic analogue of (E)-5-(2-iodovinyl)-2'-deoxyuridine (C-IVDU) is, like its parent compound (E)-5-(2-iodovinyl)-2'-deoxyuridine (IVDU), a potent and selective inhibitor of herpes simplex virus type 1 (HSV-1). There is a close correlation between the inhibition of viral DNA synthesis and the antiviral activity of both IVDU and C-IVDU. IVDU and C-IVDU inhibit viral DNA synthesis at 0.2 and 0.5 microM, respectively, and interfere with cellular DNA synthesis at concentrations that are 10- to 40-fold in excess of their antivirally effective doses. At concentrations affording a similar antiviral effect, C-[125I]IVDU is incorporated into viral and cellular DNA of HSV-1-infected Vero cells to a 7- to 10-fold lesser extent than IVDU. [125I]IVDU but not C-[125I]IVDU leads to breakage of both DNA strands when incorporated into HSV-1 DNA.     

Synthesis and antiviral properties of (Z)-5-(2-bromovinyl)-2'-deoxyuridine

(Z)-5-(2-Bromovinyl)uracil was obtained by photoisomerization of the E. isomer. Similarly, (E)-5-(2-bromovinyl)-2'-deoxyuridine gave the required Z isomer. (Z)-5-(2-Bromovinyl)-2'-deoxyuridine is much less active against herpes simplex virus type 1 (HSV-1) and somewhat less active against herpes simplex virus type 2 than is the E isomer. Both isomers show similar activity against vaccinia virus. Therefore, the highly potent and selective activity of (E)-5-(2-bromovinyl)-2'-deoxyuridine against HSV-1 is due to its E configuration.     

5-(Haloalkyl)-2'-deoxyuridines: a novel type of potent antiviral nucleoside analogue

Syntheses of 5-(2-haloethyl)-2'-deoxyuridines, 5-(3-chloropropyl)-2'-deoxyuridines, and 5-(2-chloroethyl)-2'-deoxycytidine are described. The antiviral activities of these compounds were determined in cell culture against herpes simplex virus types 1 and 2. All compounds were shown to possess significant and selective antiviral activity. The most potent derivative, 5-(2-chloroethyl)-2'-deoxyuridine (CEDU), inhibited HSV-1 at concentrations below 0.1 microgram/mL. It exerted measurable inhibitory effects on cell proliferation only at concentrations higher than 100 micrograms/mL. In vivo CEDU reduced the mortality rate of HSV-1-infected mice at concentrations lower than 5 mg/kg per day when given intraperitoneally and orally. Thus, it proved to be more effective in this in vivo model than the reference compounds (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and 9-[(2-hydroxyethoxy)methyl]guanine (ACV).     

Synthesis and antiviral activity of the enantiomeric forms of carba-5-iodo-2'-deoxyuridine and carba-(E)-5-(2-bromovinyl)-2'-deoxyuridine

Both enantiomers of the carbocyclic analogues of 5-iodo-2'-deoxyuridine (14 and ent-14) and of (E)-5-(2-bromo-vinyl)-2'-deoxyuridine (16 and ent-16) were synthesized by using (+)- or (-)-endo-norborn-5-en-2-yl acetate or butyrate, respectively, as starting materials. Against herpes simplex virus type 1 (+)-C-BVDU (16) was only slightly less active than BVDU itself, whereas (-)-C-BVDU (ent-16) proved to be 10-400-fold less effective, depending on the strain investigated. Against HSV-2 both (+)- and (-)-C-BVDU as well as (+)- and (-)-C-IDU showed minor activity. All carbocyclic analogues were inactive against TK-HSV-1 strains, pointing to the prerequisite of phosphorylation (activation) by the viral thymidine kinase (TK).     

Synthesis and biological activity of 5-(2,2-difluorocyclopropyl)-2'-deoxyuridine deoxyuridine diastereomers.

The synthesis of the two diastereomers (9 and 10) of 5-(2,2-difluorocyclopropyl)-2'-deoxyuridine are described. Their antiviral and cytotoxic activities were determined, in comparison with (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and 5-fluoro-2'-deoxyuridine (FDU), respectively. 5-[(1R)-2,2-Difluorocyclopropyl]-2'-deoxyuridine (10) was the most active antiviral agent against HSV-1 (IC50 = 5 micrograms/ml) relative to BVDU (IC50 = 0.082 micrograms/ml), and cytotoxic agent in the CCRF-CEM (IC50 = 230 microM) screen relative to FDU (IC50 = 4.7 x 10(-3) microM). The 5-[(1S)-2,2-difluorocyclopropyl] diastereomer was inactive in both screens. Partition coefficients (P) and affinity for the mouse erythrocyte nucleoside transporter (Ki) were not determinants of antiviral or cytotoxic activities. However, the (1R)-diastereomer (10) was more resistant to glycosidic bond cleavage by thymidine phosphorylase than the (1S)-diastereomer (9).     

Evaluation of (E)-5-(2-bromovinyl)- and 5-vinyl-1-beta-D-arabinofuranosyluracil (BrVaraU, VaraU) in the treatment of experimental herpes simplex virus type 1 keratitis in rabbits: comparison with (E)-5-(2-bromovinyl)-2'-deoxyuridine (BrVUdR)

The 5-substituted 1-beta-D-arabinofuranosyl (araU) analogues, (E)-5-(2-bromovinyl)-araU (BrVaraU) and 5-vinyl-araU (VaraU), which can be considered as structural analogues of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BrVUdR), are potent and selective inhibitors of herpes simplex virus type 1 (HSV-1) replication in vitro. BrVaraU and VaraU have been compared with BrVUdR for their therapeutic effect on acute HSV-1 keratitis in rabbits. Both araU derivatives applied as 0.1% eyedrops suppressed the development of keratitis as monitored by the reduced number of herpes efflorescences. The healing effect of BrVaraU and VaraU was less pronounced than that of 0.1% BrVUdR eyedrops, the difference between BrVUdR and VaraU being statistically significant at the 10th day of treatment. As a further indication of the healing effect the number of cornea with opacities seen after cessation of drug treatment were 3.3, 7.4, 27.6 and 46.9% for the BrVUdR-BrVaraU-, VaraU- and placebo-treated eyes, respectively.     

Differential binding affinities of sugar-modified derivatives of (E)-5-(2-bromovinyl)-2'-deoxyuridine for herpes simplex virus-induced and human cellular deoxythymidine kinases

The affinity of a large number of sugar-modified derivatives of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) was determined towards deoxythymidine (dThd) kinases (TK) of various origin, i.e. human cytosol and mitochondrial TK, as well as herpes simplex virus (HSV) type 1 and type 2 TK. Substitution at the 3'- and 5'-position had differential effects on the interaction of BVDU with TK from different sources. The binding affinity of the nucleoside analogs for these different TKs was also influenced by the nature of the 5-substituent (2-bromovinyl vs 2- chlorovinyl ). The 5'-azido and 5'-amino derivatives of BVDU showed affinity for HSV-1 TK only and may, therefore, be useful to differentiate HSV-1 TK from all other TKs . There was no stringent correlation between the antiviral effects of the compounds and their binding constants for viral TK, suggesting that phosphorylation by viral TK is an essential but not sufficient factor in determining the antiviral activity of these analogs.     

Genotoxic Properties of (E)-5-(2-Bromovinyl)-2'-deoxyuridine (BVDU)

(E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) is a 5-substituted2'-deoxyuridine antiviral compound that inhibits thymidylatesynthetase. The selectivity of BVDU for virus-infected cellshas been attributed to phosphorylation of BVDU by a virus-inducedthymidine kinase. Since the closely related compounds 5-bromo-2'-deoxyuridineand 5-iodo-2'-deoxyuridine are in vitro and in vivo mutagens,BVDU was tested for genotoxic activity in bacterial and mammaliancell mutation assays as well as in assays measuring DNA damage/repairand clastogenic activity. Mutation assays with BVDU at concentrationsranging from 10 to 5000 µg/plate using Salmonella typhimuriumstrains TA1535, TA1537, TA1538, TA98, and TA100 were negative,both with and without S9 activation. BVDU was also negativein the in vitro rat hepatocyte unscheduled DNA synthesis assayat concentrations of 750 and 1000 µg/ml. In contrast,BVDU was positive in the L5178Y TK^± mouse lymphoma mutationassay without S9 activation at five concentrations ranging from500 to 2000 µg/ml. A Chinese hamster ovary cell (CHO)/hypoxanthineguanine phosphoribosyl transferase gene mutation assay conductedwithout S9 over similar concentrations was negative. However,micronucleus induction by BVDU was detected with out S9 activationat concentrations between 500 and 1750 µg/ml using bothCHO and L5178Y cells. These results indicate that BVDU is apotential human clastogen.     

Synthesis of (E)-5-(3,3,3-trifluoro-1-propenyl)-2'-deoxyuridine and related analogues: potent and unusually selective antiviral activity of (E)-5-(3,3,3-trifluoro-1-propenyl)-2'-deoxyuridine against herpes simplex virus type 1

Syntheses of (E)-5-(3,3,3-trifluoro-1-propenyl)-2'-deoxyuridine (TFPe-dUrd) (1), 5-(3,3,3-trifluoro-1-propyl)-2'-deoxyuridine (11), 5-(3,3,3-trifluoro-1-methoxy-1-propyl)-2'-deoxyuridine (8), and 5-(3,3,3-trifluoro-1-hydroxy-1-propyl)-2'-deoxyuridine (10) from 5-chloromercuri-2'-deoxyuridine are described. The antiviral activity of TFPe-dUrd was determined in cell culture against herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2 (HSV-2), and vaccinia virus and compared concurrently with 5-(1-propenyl)-2'-deoxyuridine, 5-(2-bromovinyl)-2'-deoxyuridine, 5-iodo-2'-deoxyuridine, and 5-(trifluoromethyl)-2'-deoxyuridine. TFPe-dUrd demonstrated a potent and unusually selective activity against HSV-1, with a 2-log reduction in virus yield at 0.03 micrograms/mL (0.09 microM); L-1210 cell growth was inhibited by 50% only at 290 micrograms/mL. Isopycnic centrifugation of 32P-labeled DNA indicated that if 0.5 or 2 microM TFPe-dUrd was present for 0-6 h postinfection, viral DNA synthesis was reduced by ca. 50 and 85%, respectively; concomitantly, a new DNA band appeared at lower density than normal cellular or viral DNA.     

Comparative inhibition of DNA polymerases from varicella zoster virus (TK+ and TK-) strains by (E)-5-(2-bromovinyl)-2'-deoxyuridine 5'-triphosphate

The inhibitory effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) 5'-triphosphate on varicella zoster virus (VZV) DNA polymerase was studied using the parent strain (TK+-VZV) and the mutant strain (TK--VZV). The mutant strain was deficient in thymidine kinase (TK)-inducing activity and resistant to BVDU. In the absence of BVDU, TK--VZV and TK+-VZV induced an equivalent level of viral DNA polymerase activity in human embryo fibroblasts. In the presence of 5 microM BVDU, TK--VZV still induced viral DNA polymerase activity, whereas TK+-VZV failed to do so. BVDU 5'-triphosphate (BVDUTP) was considerably more inhibitory to the TK+- and TK--VZV DNA polymerases than to the cellular DNA polymerases. There were no significant differences in the affinity for dTTP as substrate and the sensitivity to BVDUTP as inhibitor between the TK+- and TK--VZV DNA polymerases. The Km value for dTTP and the Ki value for BVDUTP of the VZV DNA polymerases were 1.43 microM and 0.55 microM, respectively. The inhibitory effect of BVDUTP to VZV DNA polymerase was competitive with respect to the natural substrate.     

Deoxyribosyl exchange reactions leading to the in vivo generation and regeneration of the antiviral agents (E)-5-(2-bromovinyl)-2'-deoxyuridine, 5-ethyl-2'-deoxyuridine and 5-(2-chloroethyl)-2'-deoxyuridine

In the rat, the highly potent anti-herpes drug (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVdUrd) is rapidly converted to its base (E)-5-(2-bromovinyl)uracil (BVUra) through the action of pyrimidine nucleoside phosphorylases. However, BVdUrd can be regenerated or even generated de novo from BVUra by a pentosyl transfer reaction upon the administration of 2'-deoxythymidine (dThd), 2'-deoxyuridine (dUrd) or 5-ethyl-2'-deoxyuridine (EtdUrd). The antiherpetic drugs EtdUrd and 5-(2-chloroethyl)-2'-deoxyuridine (ClEtdUrd) can also be regenerated or generated de novo from their respective bases 5-ethyluracil (EtUra) and 5-(2-chloroethyl)uracil (ClEtUra), by a pentosyl transfer mediated by the administration of dThd or dUrd as deoxyribosyl donor. The generation or regeneration of BVdUrd, EtdUrd and ClEtdUrd from their bases (BVUra, EtUra and ClEtUra, respectively) is readily achieved because the latter have long half-lifes. Thus, the active anti-herpes drugs can be (re)generated repeatedly after a single administration of these nucleosides or their bases, followed by repeated administrations of dUrd.     

Antiherpes activity of (E)-5-(2-bromovinyl)- and 5-vinyl-1-beta-D-arabinofuranosyluracil and some other 5-substituted uracil arabinosyl nucleosides in two different cell lines

Of a series of 5-substituted 1-beta-D-arabinofuranosyluracil (5-X-araU) analogues, (E)-5-(2-bromovinyl)-araU(BrVaraU) and 5-vinyl-araU (VaraU) were the most potent inhibitors of plaque formation by two herpes simplex virus type 1 (HSV-1) strains in human embryonic lung fibroblast (HELF) cell cultures. They were not only more active than 5-methyl-araU (MaraU, araT) and 5-ethyl-araU (EaraU), but even more than 1000 times more potent than the 5-fluoro, 5-iodo, 5-formyl and 5-trifluoromethyl (FaraU, IaraU, faraU, CF3araU) analogues. BrVaraU and VaraU were superior to 9-(2-hydroxyethoxymethyl)guanine (Acyclovir, ACV) and comparable in potency with 2'-fluoro-5-iodoaracytosine (FIAC) and 2'-fluoro-5-methylarauracil (FMAU). Their anti-HSV-1 potency was surpassed only by (E)-5-(2-bromovinyl)-2'-deoxyuridine (BrVUdR). Surprisingly, in a HSV-1 plaque inhibition assay in African green monkey kidney (Vero) cells, BrVaraU and VaraU were nearly 100 times active or even inactive. In contrast, the antiherpes activity of ACV, FIAC, FMAU and BrVUdR differed only marginally in the two cell lines. The following order of (decreasing) activity against HSV-2 in HELF cells was found: FIAC = FMAU greater than MaraU (araT) greater than ACV greater than VaraU greater than BrVUdR greater than CF3araU greater than IaraU greater than FaraU = Eara U greater than BrVaraU greater than araU greater than faraU. When deoxyribose is replaced by arabinose in 5-X-UdR analogues, a slight increase in anti-HSV-1-77 activity was observed for the 5-vinyl or 5-ethyl substituent, whereas the other 5-X-araU nucleosides were two to more than 100 times less active than their deoxyribosyl counterparts. However, the sugar exchange led to a strong reduction in anti-HSV-2 activity regardless of the 5-substituent.     

Phosphorolysis of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and other 5-substituted-2'-deoxyuridines by purified human thymidine phosphorylase and intact blood platelets

Various 5-substituted-2'-deoxyuriclines (dUrd), inclucling 5-ethyl-,5-propyl-, 5-trifluoromethyl-, 5-hydroxymethyl-, 5-formyl-, 5-vinyl-, (E)-5-(2-chlorovinyl)-, (E)-5-(2-bromovinyl)-, 5-fluoro-. 5-chloro-. 5-bromo-. 5-iodo-, 5-cyano-, 5-thiocyano-, 5-nitro- and 5-amino-dUrd. were shown to be effective substrates for the thymidine (dThd) phosphorylase isolated from human blood platelets. Some of dUrd analogs, i.e. the highly potent and selective antiherpes agent (E)-5-(2-bromovinyl)-dUrd. were degraded more rapidly than the natural substrates, dUrd and dThd. All dUrd analogs were also readily catabolised by intact human blood platelets. The potent inhibitors of thymicline phosphorylase, 6-amino-thymine and 6-amino-5-bromo-uracil, strongly inhibited the phosphorolysis of (E)-5-(2-bromovinyl)-dUrd by both purified enzyme and intact platelets.