Nucleosides. 110. Synthesis and antiherpes virus activity of some 2'-fluoro-2'-deoxyarabinofuranosylpyrimidine nucleosides

Synthesis of 2'-fluoro-5-[11C]-methyl-1-beta-D-arabinofuranosyluracil ([11C]-FMAU): a potential nucleoside analog for in vivo study of cellular proliferation with PET

Rapid in vivo catabolism limits the use of currently available radiotracers used in tumor proliferation studies with PET. This is manifested by the need to develop complex mathematical models to interpret kinetic and metabolite data obtained from imaging studies with agents such as carbon-11 labeled thymidine. A potential carbon-11 labeled radiotracer for cellular proliferation, 2'-fluoro-5-([11C]-methyl)-1-beta-D-arabinofuranosyluracil (FMAU), has been prepared using a previously described method for preparation of [11C]methyl-thymidine where selective alkylation of a pyrimidyl dianion is accomplished with [11C]methyl iodide at the 5-position of the pyrimidine ring. FMAU shares many in vivo characteristics of thymidine, including cellular transport, phosphorylation by mammalian kinase, and incorporation into DNA. Most importantly, in vivo catabolism of FMAU is limited, potentially yielding simplified kinetic models for determination of cellular proliferation with positron emission tomography.

Use of 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil as a novel antiviral agent for hepatitis B virus and Epstein-Barr virus

A novel anti-hepatitis B virus (anti-HBV) agent, 2'-fluoro-5-methyl-beta-L-arabinofuranosyluracil (L-FMAU), was synthesized and found to be a potent anti-HBV and anti-Epstein-Barr virus agent. Its in vitro potency was evaluated in 2.2.15 and H1 cells for anti-HBV and anti-Epstein-Barr virus activities, respectively. In vitro cytotoxicity in MT2, CEM, 2.2.15, and H1 cells was also assessed, and the results indicated high antiviral selectivities of L-FMAU in these cells.

Cellular and molecular events leading to mitochondrial toxicity of 1-(2-deoxy-2-fluoro-1-beta-D-arabinofuranosyl)-5-iodouracil in human liver cells

We have explored the mechanism(s) related to FIAU-induced liver toxicity, particularly focusing on its effect on mitochondrial function in a human hepatoma cell line-HepG2. The potential role of FMAU and FAU, metabolites detected in FIAU-treated patients were also ascertained. FIAU and FMAU inhibited cell growth and were effectively phosphorylated. A substantial increase in lactic acid production in medium of cells incubated with 1-10 microM FIAU or FMAU was consistent with mitochondrial dysfunction. Slot blot analysis demonstrated that a two week exposure to 10 microM FIAU or FMAU was not associated with a decrease in total mitochondrial (mt) DNA content. However, FIAU and FMAU were incorporated into nuclear and mtDNA and relative values suggest that both compounds incorporate at a much higher rate into mtDNA. Electron micrographs of cells incubated with 10 microM FIAU or FMAU revealed the presence of enlarged mitochondria with higher cristae density and lipid vesicles. In conclusion, these data suggest that despite the lack of inhibition of mtDNA content, incorporation of FIAU and FMAU into mtDNA of HepG2 cells leads to marked mitochondrial dysfunction as evidenced by disturbance in cellular energy metabolism and detection of micro- and macrovesicular steatosis.

Novel nucleoside strategies for anti-HIV and anti-HSV therapy

This mini-review describes the structure-activity relationships of several series of new nucleoside analogues. It also points to the possibilities of finding new molecular modifications which could lead to antivirals with activity both against human immunodeficiency viruses (HIV) and herpesviruses.

Preclinical pharmacology and pharmacokinetics of the anti-hepatitis virus agent 2'-fluoro-5-ethyl-1-beta-D-arabinofuranosyluracil in mice and rats

The preclinical pharmacology and pharmacokinetics of 2'-fluoro-5-ethyl-1-beta-D-arabinofuranosyluracil (FEAU), a selective inhibitor of herpesvirus and hepatitis virus replication, were investigated in the mouse and rat. Following intravenous (i.v.) or oral (p.o.) administration, FEAU was cleared from the plasma primarily unchanged, with a terminal half-life of 58 to 80 min in the mouse and 63 to 78 min in the rat. The steady-state volumes of distribution times bioavailabilities of FEAU were approximately 2.1 and 3.4 times the total body water volumes after p.o. administration of 10 mg of drug per kg of body weight in mice and rats, respectively. A comparison of the area under the concentration-time curve after i.v. and p.o. FEAU administration indicated that the p.o. dose was completely absorbed in both species. When tritiated FEAU was used in mice, 35.0% of the i.v. dose and 33.5% of the p.o. dose were excreted in urine as unchanged FEAU, 8.1% (i.v. dose) and 9.2% (p.o. dose) were excreted as tritiated water, and 15.6% (i.v. dose) and 18.1% (p.o. dose) were excreted as unknown metabolite(s) in urine within 24 h of dosing. Only 1.24% (i.v. dose) and 2.6% (p.o. dose) of the total doses were found in urine as 3H2O when the FEAU dose was increased to 50 mg/kg. However, a higher percentage of the total dose (59.6% for the i.v. dose and 61.3% for the p.o. dose) was recovered within 24 h as intact FEAU in rat urine, less than 1.4% (i.v. dose) and 2.7% (p.o. dose) of the total dose were found to be 3H2O, and 5.6% (i.v. dose) and 6.7% (p.o. dose) of the total dose were excreted as known metabolite(s). The distribution ratios for total radioactivity in tissue relative to those in plasma were 0.5 to 1.3 in spleen, testes, muscle, and liver during the first hour after a 10-mg/kg dose in rats. Of the total FEAU radioactivity administered, only 1.38% was excreted in bile as unchanged FEAU. No FEAU glucuronide metabolite was detected. Tissue concentrations of 0.15 to 0.6 microM at 6 h after dosing are in the range of the effective antiviral concentration for FEAU. In conclusion, FEAU administered p.o. to mice and rats was well absorbed; FEAU was rapidly distributed into tissues and remained above in vitro antiviral concentrations for more than 6 h; in mice, [3H]FEAU showed metabolism-mediated tritium exchange with water; and in rats, FEAU was less extensively metabolized than in mice and clearance was primarily via renal processes, mainly in the form of unchanged FEAU.

Evaluation of 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-ethyluracil in a rabbit model of herpetic keratitis

The nucleoside analog 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5- ethyluracil (FEAU) was tested in a rabbit model of acute herpetic keratitis and its effectiveness compared with that of acyclovir (ACV). FEAU or ACV was applied topically 3 times daily, beginning 3 days post-HSV-1 inoculation and continued for a period of 7 days. FEAU at a concentration of 1% (w/v) or 3% ACV resulted in significant lessening of the severity of corneal lesions, conjunctivitis, iritis, and corneal clouding at 24 to 48 h after beginning chemotherapy. No toxic reaction was observed in any rabbit eyes treated with either FEAU or ACV. The duration of virus shedding into tear film and colonization of the trigeminal ganglia, however, were not reduced by either FEAU or ACV treatment begun 3 days post-inoculation. Fifty percent effective dose (ED50) of FEAU determinations performed on isolates from tear film and on the virus inoculum in secondary rabbit kidney cultures yielded a range of 4.6-7 microM, with two in vitro resistant isolates having ED50S of greater than or equal to 1500 microM of FEAU. Fifty percent cell growth inhibition for FEAU was 3000 microM at 72 h.

Structure-activity relationship between (E)-5-(2-bromovinyl)- and 5-vinyl-1-beta-D-arabinofuranosyluracil (BV-araU, V-araU) in inhibition of Epstein-Barr virus replication

The structure-activity relationship between (E)-5-(2-bromovinyl)- and 5-vinyl-1-beta-D-arabinofuranosyluracil (BV-araU and V-araU) in inhibition of Epstein-Barr virus (EBV) was evaluated. Both V-araU and BV-araU effectively inhibited EBV replication in virus-producer P3HR-1(LS) cells, as determined by DNA-DNA hybridization. The 50% effective doses (ED50) for viral DNA replication were 0.005 and 0.3 microM for V-araU and BV-araU, respectively. The in vitro therapeutic index was 4000 for V-araU and 1300 for BV-araU. Synthesis of EBV-induced polypeptides with molecular weights of 145,000 (145, 140, 130, and 110 kDa) was significantly inhibited by both drugs. Only V-araU inhibited the synthesis of 85-, 55-, and 32-kDa polypeptides by approx. 50%. Kinetic analysis of inhibition and reversibility of EBV DNA replication after removal of the drugs indicated that BV-araU has a more prolonged inhibitory effect than V-araU. These results indicate that the substitution of H by Br in the 5-vinyl group results in marked reduction in anti-EBV activity while prolonging the drug effect and diminishing cytotoxicity.

Incorporation and metabolism of 2'-fluoro-5-substituted arabinosyl pyrimidines and their selective inhibition of viral DNA synthesis in herpes simplex virus type 1 (HSV-1)-infected and mock-infected Vero cells

The incorporation and metabolism of 2'-fluoro-5-substituted arabinosyl pyrimidine analogs, and their selective inhibition of viral DNA synthesis in herpes simplex virus type 1 (HSV-1)-infected and mock-infected Vero cells were studied by HPLC and CsCl isopycnic density gradient analysis of isolated DNAs. The amounts of radiolabeled analogs incorporated as parent compound following 10 microM exposure for 4 h were 10-fold higher in HSV-1-infected vs mock-infected cells for 2'-fluoro-5-difluoromethyl-Ara-U (F2FMAU); 4.3-fold higher for 5-ethyl deoxyuridine (EdU); 2.6-fold higher for 2'-fluoro-5-methyl-Ara-U (FMAU) and 1.7-fold higher for dThd. For 2'-fluoro-5-ethyl-Ara-U (FEAU), 3.0 pmole of unchanged moiety was incorporated per 10(6) HSV-1-infected cells but no incorporation was detected in mock-infected cells. HPLC profiles showed that the percentages of radiolabeled analogs incorporated as parent compound in the DNA extracted from HSV-1-infected cells were 31.0% for F2FMAU, 99.6% for EdU, 83.5% for FEAU and 98.3% for FMAU; from mock-infected cells, they were 63.6% for F2FMAU, 96.7% for EdU, 97.3% for FMAU and no incorporation into DNA for FEAU was detected. CsCl density gradient analyses of isolated DNA showed that viral DNA synthesis was inhibited 98% by 10 microM FEAU, 92% by 10 microM F2FMAU, 90% by 2 microM FMAU and 80% by 50 microM EdU, whereas cellular DNA synthesis was inhibited by 53, 44, 61, 66 and 54%, respectively. We conclude that: (a) FEAU incorporation into host-cell DNA was not detectable but FEAU was selectively incorporated into HSV-infected cells; (b) FMAU and FEAU were metabolically stable; however, F2FMAU was extensively metabolized; (c) FEAU and F2FMAU were among the most selective inhibitors of HSV-1 DNA synthesis while allowing cellular DNA synthesis to continue.

A mammalian cell line designed to test the mutagenic activity of anti-herpes nucleosides

The herpes simplex virus (HSV) thymidine kinase (tk) gene was transfected into Chinese hamster ovary (CHO) 51-11 gly- cells to test its effect on the cytotoxic and mutagenic activity of anti-herpetic nucleoside analogues. Insertion of the viral tk was verified by Southern blot analysis, by sensitivity to acyclovir, and by elevated in vitro thymidine kinase (TK) activity. TK activity was increased by superinfection with a tk- virus and inhibited by antibody to viral TK. Acyclovir (ACV) was somewhat more cytotoxic in the 51-D3 cell line that expresses the viral TK than in the 51-11 parent line. Growth in ACV did not increase over background mutations at the hprt locus. FIAC (2'-fluoro-5-iodio-aracytosine) was slightly cytotoxic to the parent 51-11 line and the tk-containing clone 51-D3. FMAU (2'-fluoro-5-methyl-arauracil) had pronounced cytotoxicity in both cell lines: the 50% survival points were 1.0 microM for 51-11 cells and 0.2 microM for 51-D3. The clone 51-D3 was more sensitive than 51-11 to low concentrations of FIAU (2'-fluoro-5-iodo-arauracil), and when treated with FIAU 51-D3 had a mutation frequency to glycine independence 5 times greater than that of 51-11 cells. With both cell lines the mutation frequency at the hprt locus did not increase after growth in the presence of FIAC or FIAU. A 7-fold increase in mutation frequency at the hprt locus was detected after 51-D3 cells were grown with iododeoxyuridine. Trifluorothymidine was more toxic to 51-D3 than to 51-11 cells and increased the mutation frequency 2-fold. Cytosine-beta-D-arabinofuranoside showed no differential cytotoxicity on the two cell lines and did not increase the mutation frequency at the hprt locus.

In vitro and in vivo antiviral activity of 2'-fluorinated arabinosides of 5-(2-haloalkyl)uracil

5-(2-Fluoroethyl)-2'-deoxyuridine (FEDU), its 2'-fluoroarabinofuranosyl analog (FEFAU) and the 2'-fluoroarabinofuranosyl analog (CEFAU) of the potent anti-herpesvirus compound 5-(2-chloroethyl)-2'-deoxyuridine (CEDU) were evaluated for activity against herpes simplex virus type 1 (HSV-1) and HSV-2 in vitro and in vivo. FEDU, FEFAU and CEFAU proved to be potent and selective anti-herpesvirus agents in vitro. Their potency is evident from their low minimum inhibitory concentrations for HSV-1 and HSV-2, and their selectivity is attested by the marginal inhibition of cell proliferation at relatively high concentrations, and by the high concentrations at which DNA-, RNA- or protein synthesis in normal uninfected host cells is inhibited. Their activity spectrum is broader than that of CEDU: in addition to being highly effective against HSV-1 replication, these derivatives, in particular FEFAU, inhibit HSV-2 replication at concentrations comparable to acyclovir (ACV). In the systemic and cutaneous HSV-1 infection models in mice, FEDU, FEFAU and CEFAU were markedly less potent than CEDU in suppressing the development of lesions and in reducing the mortality rate. In HSV-2 infections in mice and in guinea pigs FEDU, FEFAU and CEFAU were virtually ineffective. CEDU, however, exerted a protective effect in these animal models, albeit at relatively high concentrations.

Chemotherapy of herpesvirus infections

The following paper is intended to review those nucleoside analogs currently licensed for the treatment of herpetic diseases. Potentially efficacious congeners also will be considered. The mechanism of action, preclinical and clinical efficacy, and the problems associated with the use of each nucleoside analog will be described.

Cell differentiation effects of 2'-fluoro-1-beta-D-arabinofuranosyl pyrimidines in HL-60 cells

A group of 2'-fluoro and 5-substituted arabinosyl pyrimidines and a group of base-substituted pseudoisocytidine analogs were evaluated for their capacity to induce differentiation in the human promyelocytic leukemia cell line, HL-60. These compounds were compared to 1-beta-D-arabinofuranosylcytosine (Ara-C) by monitoring: (1) inhibition of cell growth; (2) morphological maturation; (3) nitroblue tetrazolium (NBT) reduction; (4) expression of a myeloid differentiation antigen, Mo1; and (5) inhibition of colony formation. Exposure of logarithmically growing cells for 5 days to Ara-C, 2'-fluoro-Ara-C (FAC), 2'-fluoro-5-methyl-Ara-C (FMAC) and 2'-fluoro-5-ethyl-Ara-C (FEAC) resulted in cell growth inhibition at ED50 concentrations of 0.007, 0.11, 1.7 and 18 microM, and at cytostatic concentrations of 0.1, 0.5, 5.0 and 50 microM, respectively. These compounds induced granulocytic and monocytic maturation, reduction of NBT, increased expression of Mo1 antigen and a decrease or loss of both cell proliferation and colony formation in semisolid medium. There were few, if any, cell differentiation effects for the uracil nucleosides and pseudoisonucleosides tested. We found that Ara-C was the most cytotoxic of the compounds, and that when comparing absolute numbers of differentiated cells, i.e. percent of positive cells multiplied by the number of viable cells, FAC, FMAC and FEAC were superior to Ara-C inducing differentiation of HL-60 cells.

Quantitative determination of antiviral nucleoside analog in DNA

A technique for the analysis of the amount of an antiviral nucleoside analog incorporated into DNA, utilizing enzymatic digestion of DNA, followed by high-performance liquid chromatography is described. The cells or tissue samples were treated with perchloric acid to inactivate the nucleases, then digested with pronase in the presence of EDTA. DNA was purified by CsCl centrifugation followed by Sephadex chromatography and treatment with deoxyribonuclease 1 and venom phosphodiesterase. The deoxyribonucleoside monophosphates and the monophosphate of the nucleoside analog liberated from DNA were separated and quantitated by HPLC analysis and measurement of radioactivity. This assay is more sensitive, specific, and precise than the determination of DNA density shift. It is also applicable for nucleoside analogs which do not change the density of DNA either because of their structure or their very small degree of incorporation.

Enzymology and pathogenicity in mice of a herpes simplex virus type 1 mutant resistant to 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodocytosine

The deoxypyrimidine nucleoside analog 2'-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodocytosine (FIAC) is a potent and selective inhibitor of herpes simplex virus type 1 in vitro (C. Lopez, K. A. Watanabe, and J. J. Fox, Antimicrob. Agents Chemother. 17:803-806, 1980). Isopycnographic analysis demonstrated that 1 microM FIAC inhibited herpes simplex virus DNA replication by more than 95% but inhibited cellular DNA replication by only 32%. Mutant herpes simplex virus type 1 selected resistant to FIAC displayed linked resistance to other nucleoside analogs, including arabinosylthymine and acyclovir. Lysates derived from Vero cells infected with FIAC-resistant virus showed markedly lower levels of thymidine kinase activity and were unable to phosphorylate selectively arabinosylthymine or FIAC, in contrast to lysates from cells infected with wild-type herpes simplex virus type 1. Finally, drug-resistant virus displayed a 6,000-fold decrease in pathogenicity when inoculated intraperitoneally into genetically susceptible A/J mice. These results indicate that resistance to deoxypyrimidine nucleoside analogs is due, at least in part, to alterations in viral thymidine kinase and is accompanied by decreased pathogenicity in vivo.

Mutagenic potential of anti-herpes agents

A number of anti-herpes agents which are either licensed for clinical use (acyclovir) or subject of clinical studies (bromovinyldeoxyuridine, fluoroiodoaracytidine, dihydroxypropoxymethylguanine) or under preclinical investigation (i.e., fluoroiodoarauridine), fluoromethylarauridine, dihydroxybutylguanine, bromovinyldeoxycytidine, bromovinylarauridine and carbocyclic bromovinyldeoxyuridine) were evaluated for their ability to induce sister chromatid exchange (SCE), an indicator of mutagenesis. SCE was scored on metaphase chromosomes of human lymphocytes which had been exposed to 5-bromo-2'-deoxyuridine and varying concentrations of the test compounds. The antiviral assays were based on the inhibition of the cytopathogenicity of herpes simplex virus for human diploid fibroblasts. Most compounds, i.e. acyclovir, bromovinyldeoxyuridine or carbocyclic bromovinyldeoxyuridine, did either not induce SCE or only so at concentrations far above their minimum antiviral concentrations. However, fluoroiodoaracytidine and dihydroxypropoxymethylguanine were found to affect the SCE rate at a concentration (greater than or equal to 4.5 micrograms/ml) that is readily achievable in blood following intravenous injection.

Activity of 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodouracil against simian varicella virus infections in African green monkeys

The fluorinated pyrimidines 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) and 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-methyluracil (FMAU) are highly effective inhibitors of herpesvirus infections in vitro and in vivo. This report is concerned with an evaluation of their activities in African green monkeys (Cercopithecus aethiops) infected with simian varicella virus, a herpesvirus closely related to human varicella-zoster virus. Oral or intravenous administration of FIAU at 50 mg/kg per day as divided doses beginning 48 h after virus inoculation prevented the development of evidences of clinical infection. Oral treatment with FIAU at 30 mg/kg per day deferred as late as 7 days after virus inoculation modified the course of the disease. When treatment was started 48 h after virus inoculation, daily doses of FIAU as small as 1 mg/kg inhibited development of infections; daily doses of 0.2 mg/kg were ineffective. At the latter dose FMAU prevented development of clinical disease, suggesting that it was more active than FIAU. No signs of FIAU toxicity were observed, with the single exception of an early but transitory elevation in aspartate aminotransferase activity in serum.

Activities of 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine and its metabolites against herpes simplex virus types 1 and 2 in cell culture and in mice infected intracerebrally with herpes simplex virus type 2

As measured by plaque and yield reduction assays, several metabolites of 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine (FIAC) were highly active against herpes simplex virus types 1 and 2. These metabolites included the 2'-deoxy-2'-fluoroarabinosyl derivatives of 5-iodouracil (FIAU), cytosine (FAC), uracil (FAU), and thymine (FMAU). In mice inoculated intracerebrally with herpes simplex virus type 2, the relative order of potency of these compounds and licensed antiviral drugs was as follows: FMAU much greater than FIAC approximately equal to FIAU greater than acyclovir approximately equal to vidarabine much greater than FAC approximately equal to FAU. One of the main metabolites of FMAU, 2'-fluoro-5-hydroxymethyl-arabinosyluracil, was essentially inactive in vivo. FIAC-, FIAU-, FMAU-, FAC-, and FAU-resistant herpes simplex virus variants prepared in cell culture were found to be (i) devoid of viral thymidine kinase, (ii) cross-resistant to one another and resistant to drugs requiring viral thymidine kinase for activation, and (iii) sensitive to vidarabine or phosphonoformate. These results indicate that FIAC, FIAU, and FMAU require the virally encoded thymidine kinase for activation and suggest that the antiviral activity of FAU and FAC in cell cultures is also mediated by this enzyme. The interaction of the fluoroarabinosyl pyrimidine nucleosides with herpes simplex virus thymidine kinase in a cell-free system is also described.

Drug resistance patterns of herpes simplex virus isolates from patients treated with acyclovir

A decrease in the in vitro sensitivity to acyclovir (ACV) was observed in successive isolates of herpes simplex virus type 1 from three immunocompromised patients during intravenous therapy with this drug. The ACV-resistant isolate from patient 1 was cross-resistant to dihydroxypropoxymethylguanine and bromovinyldeoxyuridine, but still susceptible to three fluoro-substituted pyrimidines, 2'-fluoro-5-iodo-1-beta-D-arabinofuranosylcytosine (FIAC), 2'-fluoro-5-iodo-1-beta-D-arabinofuranosyluracil (FIAU), and 2'-fluoro-5-iodo-1-beta-D-arabinofuranosylthymine (FMAU). The thymidine kinase (TK) from the resistant isolate showed a 50-fold or greater reduction in affinity for thymidine, FIAU, FMAU, and ACV, but the total enzyme activity was similar to that of the sensitive isolate. The ACV-resistant isolate from patient 2 was also resistant to dihydroxypropoxymethylguanine, bromovinyldeoxyuridine, and the fluoro-substituted compounds; TK activity for this isolate was less than 1% of the patient's pretherapy isolate. An isolate obtained during a subsequent recurrence in patient 2 was susceptible to ACV and the other TK-dependent agents. The ACV-resistant isolate from patient 3 was partially resistant to FIAC and FIAU but still susceptible to FMAU; the viral TK had a 10-fold-lower affinity for ACV, FIAU, and FMAU than did the sensitive pretherapy isolate, while the level of TK activity detected was reduced to 6%. In none of the isolates studied was a change in sensitivity to phosphonoformic acid observed. Compared with the corresponding pretherapy ACV-sensitive isolates, there was a 30-fold decrease in neurovirulence for mice of the two drug-resistant isolates with diminished levels of thymidine-phosphorylating activity and no change in virulence for the third isolate. These findings indicate that mixed patterns of drug-resistance to TK-dependent antiviral compounds can occur in clinical isolates, resulting from changes in either the amount or the affinity of viral TK activity.

Antiviral activity of 2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl-5-iodocytosine against human cytomegalovirus in human skin fibroblasts

2'-Deoxy-2'-fluoro-beta-D-arabinofuranosyl-5-iodocytosine (FIAC) was shown to be a selective anti-human cytomegalovirus agent in vitro with a 50% antiviral effective dose of 0.6 microM (J. M. Colacino and C. Lopez, Antimicrob. Agents Chemother. 26:505-508, 1983) and a 50% cell growth inhibitory dose of 8 microM. Antiviral activity was more readily reversed with 10-fold excess thymidine, whereby the 50% effective dose was increased to 11.3 microM. FIAC-induced cytotoxicity was more readily reversed with 10-fold excess of deoxycytidine, whereby the 50% inhibitory dose was increased to greater than 100 microM. Thymidine was unable to reverse completely the antiviral activity of FIAC. Although, the extent of phosphorylation of thymidine, deoxycytidine, and deoxyuridine was 6-, 4-, and 4-fold greater, respectively, in human cytomegalovirus-infected cell lysates than in uninfected cell lysates, the extent of phosphorylation of FIAC was only 1.3-fold greater in human cytomegalovirus-infected cell lysates than in uninfected cell lysates. By comparison, the extent of FIAC phosphorylation was 500 times greater in herpes simplex virus type 1-infected cells than in uninfected cell lysates. Methotrexate was 400 times more effective against human cytomegalovirus replication than it was against herpes simplex virus type 1 replication, indicating that thymidylate synthetase may be important for human cytomegalovirus replication. However, 10 microM FIAC did not inhibit thymidylate synthetase activity in uninfected or virus-infected cells as determined by their metabolism of [6-3H]deoxyuridine in the presence or absence of drug. FIAC at 1 microM suppresses and FIAC at 10 microM completely inhibits human cytomegalovirus DNA replication as indicated by Southern blot analysis. This inhibition was reversible. FIAC incorporation into the DNA of human cytomegalovirus strain AD169-infected cells was stimulated relative to that in nondividing, uninfected cells.

Selective in vitro and in vivo activities of 5-(2-haloalkyl)pyrimidine nucleoside analogs, particularly 5-(2-chloroethyl)-2'-deoxyuridine, against herpes simplex virus

5-(2-Chloroethyl)-2'-deoxyuridine (CEDU), 5-(3-chloropropyl)-2'-deoxyuridine (CPDU), and 5-(2-chloroethyl)-2'-deoxycytidine (CEDC) were evaluated for activity against herpes simplex virus type 1 (HSV-1) and HSV-2 in vitro. Their MICs for HSV-1 in primary rabbit kidney cell cultures were 0.15, 0.20, and 0.60 micrograms/ml, respectively; their MICs for HSV-2 were about 10-fold higher. When tested in parallel, the reference compounds 5-ethyl-2'-deoxyuridine, 5-iodo-2'-deoxyuridine, acyclovir, and (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) gave MICs of 0.20, 0.18, 0.04, and 0.015 micrograms/ml, respectively. The antiviral indexes of CEDU, CPDU, and CEDC, as determined by the ratio of the minimum toxic dose for the normal host cell to the minimum inhibitory dose for HSV-1, were about 2,000, 100, and greater than or equal to 400, respectively. The three 5-(2-haloalkyl)pyrimidine derivatives were further evaluated for their antiviral effects in vivo. In hairless mice, CEDU suppressed the development of cutaneous HSV-1 lesions, and associated mortality, when applied topically at a concentration as low as 0.1%. For the treatment of systemic HSV-1 infection in Naval Medical Research Institute mice, a single oral dose per day of 5 mg of CEDU per kg achieved a significant reduction in the mortality rate. Against HSV-1 encephalitis, CEDU exerted a significant protective effect at a dosage of 50 mg/kg per day when administered intraperitoneally. CEDU was effective against systemic HSV-1 infection and HSV-1 encephalitis in mice at a 5- to 15-fold-lower dose than either BVDU or acyclovir. When given orally, CPDU and CEDC were considerably less active than CEDU against systemic HSV-1 infection.