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Recently, there has been renewed interest in finding orally active drugs against smallpox. Cidofovir (CDV) given by parenteral injection has been shown to protect against lethal poxvirus infection. We have been interested in the synthesis and evaluation of orally active derivatives of CDV. Previous studies showed that the CDV and cyclic cidofovir (cCDV) analogs 1-Ohexa-decyloxypropyl-CDV (HDP-CDV) and 1-O-hexadecyloxypropyl-cCDV (HDP-cCDV), show Ͼ100-fold increases in antiviral activity versus the unmodified nucleosides against cells infected with orthopoxviruses, cowpox, and vaccinia virus. In contrast to CDV, HDP-CDV is orally bioavailable and has been reported to be orally active in lethal cowpox virus infection in mice. To assess the metabolic basis for the increased antiviral activity of HDP-CDV in vitro, we studied the cellular uptake and anabolic metabolism of 14 C-labeled CDV, cCDV, and their alkoxyalkanol esters HDP-CDV and HDP-cCDV. HDP-CDV and HDP-cCDV were taken up rapidly by MRC-5 human lung fibroblasts in vitro, but uptake of CDV and cCDV was much slower. Analysis of cellular metabolites showed that levels of cidofovir diphosphate (CDV-DP), the active antiviral compound, were Ͼ100 times greater with HDP-CDV than levels observed with CDV. When cells were exposed to HDP-CDV, the intracellular half-life of CDV-DP was 10 days versus 2.7 days reported when cells are exposed to CDV. HDP-CDV seems to circumvent poor cellular uptake by rapid association with cellular membrane phospholipids, whereas CDV uptake proceeds via the slow process of fluid endocytosis.

The acyclic nucleoside phosphonate cidofovir (CDV) and its closely related analogue (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)-adenine ([S]-HPMPA) have been reported to have activity against many adenovirus (AdV) serotypes. A new series of orally active ether lipid-ester prodrugs of CDV and of (S)-HPMPA that have slight differences in the structure of their lipid esters were evaluated, in tissue-culture cells, for activity against 5 AdV serotypes. The results indicated that, against several AdV serotypes, the most active compounds were 15-2500-fold more active than the unmodified parent compounds and should be evaluated further for their potential to treat AdV infections in humans.

9-(S)-(3-Hydroxy-2-phosphonomethoxypropyl)adenine [(S)-HPMPA] was one of the first acyclic nucleoside phosphonates described and has been reported to have good antiviral activity against most double-stranded DNA viruses, including the herpes group viruses and the orthopoxviruses. However, (S)-HPMPA is not orally bioavailable and has not been developed for clinical use. We have prepared orally bioavailable lipid esters of (S)-HPMPA and report their synthesis and antiviral evaluation against cytomegalovirus and orthopoxviruses. These esters were evaluated in vitro in cells infected with human cytomegalovirus (HCMV), murine cytomegalovirus (MCMV), vaccinia (VV), and cowpox viruses (CV). The most active compound, oleyloxyethyl-(S)-HPMPA, was found to have EC50 value of 0.003 microM against HCMV vs 1.4 microM for unmodified HPMPA. In cells infected with VV and CV, octadecyloxyethyl-(S)-HPMPA had EC50 values of 0.01-0.02 microM versus 2.7-4.0 microM for unmodified HPMPA. When compared with the alkoxyalkyl esters of cidofovir, the corresponding alkoxyalkyl esters of (S)-HPMPA were equally active against HCMV and MCMV but were 15-20-fold more active against VV and CV in vitro. The alkoxyalkyl esters of (S)-HPMPA are promising new compounds worthy of further investigation for treatment of infections caused by herpes viruses and orthopoxviruses.

Alkoxyalkyl esters of cidofovir (CDV) have substantially greater antiviral activity and selectivity than unmodified CDV against herpesviruses and orthopoxviruses in vitro. Enhancement of antiviral activity was also noted when cyclic CDV was esterified with alkoxyalkanols. In vitro antiviral activity of the most active analogs against human cytomegalovirus (HCMV) and orthopoxviruses was increased relative to CDV up to 1,000-or 200-fold, respectively. Alkyl chain length and linker structure are important potential modifiers of antiviral activity and selectivity. In this study, we synthesized a series of alkoxyalkyl esters of CDV or cyclic CDV with alkyl chains from 8 to 24 atoms and having linker moieties of glycerol, propanediol, and ethanediol. We also synthesized alkyl esters of CDV which lack the linker to determine if the alkoxyalkyl linker moiety is required for activity. The new compounds were evaluated in vitro against HCMV and murine CMV (MCMV). CDV or cyclic CDV analogs both with and without linker moieties were highly active against HCMV and MCMV, and their activities were strongly dependent on chain length. The most active compounds had 20 atoms esterified to the phosphonate of CDV. Both alkoxypropyl and alkyl esters of CDV provided enhanced antiviral activities against CMV in vitro. Thus, the oxypropyl linker moiety is not required for enhanced activity. CDV analogs having alkyl ethers linked to glycerol or ethanediol linker groups also demonstrated increased activity against CMV.Cidofovir (CDV), an acyclic phosphonate analog of dCMP, is an antiviral agent that is active against all double-stranded DNA viruses including herpes simplex, cytomegalovirus (CMV), orthopoxviruses, adenovirus, Epstein-Barr virus, polyomavirus, and papillomavirus (9). CDV is not orally active but is effective when administered intravenously for CMV retinitis in patients with AIDS (8,19). Esterification of CDV with certain alkoxyalkanols dramatically increases the antiviral activity and selectivity of CDV in vitro (2, 11, 13, 15) and confers oral bioavailability (4,5,6,14,20). Hexadecyloxypropyl-CDV (HDP-CDV) and various other alkoxyalkyl CDV esters are orally active in three lethal challenge models of poxvirus disease (5, 20) and in animal models of CMV disease (4, 14).The alkyl chain length of these CDV analogs is related to solubility and the ability of the compounds to associate with biomembranes. To examine the effect of structure on antiviral activity and selectivity of alkoxyalkanol-CDV analogs against CMV, we synthesized a family of alkoxypropylCDVs and -cyclic CDVs (cCDVs) varying in overall chain length from 8 to 24 atoms. The nature of the linker group is also important because it may strongly affect the rate of cellular metabolic conversion to CDV. We synthesized several representative analogs having propanediol, ethandiol, or glycerol linkers to assess the effect of the linker structure. Finally, we also synthesized and evaluated a series of alkylCDVs lacking the linker.The various CDV and cCDV analogs were tested...

A new series of ether lipid esters of cidofovir (CDV) were evaluated against vaccinia and cowpox viruses. Activity was dependent on number of atoms in the alkyl or alkoxyalkyl chain, the linker moiety, and the presence of a double bond in the alkoxyalkyl chains linked to the phosphonate moiety of CDV.The threat of an intentional or unintentional spread of poxvirus infections to a vulnerable population has led to increased efforts to find safe, rapidly deployable treatments against such infections. Although vaccination is now being offered to some healthcare workers and other "first responders," there are valid concerns about potential vaccine risks (3, 9). Vaccination is not recommended for those with eczema and other exfoliative skin disorders or those with immunodeficiencies or for pregnant women. Therefore, the use of antiviral therapy in the event of a poxvirus outbreak or in the treatment of vaccination complications against smallpox virus (4) points to the continued need to examine available antiviral therapies as well as to develop new and more efficient treatment.Cidofovir (CDV) and cyclic CDV (cCDV) have been shown to be potent inhibitors of poxvirus replication in vitro (1,7,8,13) and in animal model studies (5, 10, 12); however, these compounds are inactive when given orally.Previous in vitro studies have shown that multiple-log increases in antiviral activity against orthopoxvirus replication (8), as well as enhanced inhibition of cytomegalovirus and herpesvirus replication by these esters (2), were observed with hexadecyloxypropyl (HDP) and octadecyloxyethyl (ODE) derivatives of CDV and cCDV (HDP-CDV, HDP-cCDV, ODE-CDV, and ODE-cCDV) compared to the results seen with the parent compounds. HDP-CDV, ODE-CDV, and oleyloxypropyl-CDV (OLP-CDV) have oral bioavailabilities of 88 to 93% in mice (6) and have oral activity against vaccinia virus (VV) and cowpox virus (CV) infections in mice (11).In this study, the unmodified acyclic nucleoside phosphonates CDV and cCDV (along with a new series of analogs synthesized by esterification of these compounds with an alkyl chain with or without the propoxy-or ethoxy-linker moieties) were evaluated (using methodologies described previously) (7) for activity (plaque reduction assay) against VV and CV and for cytotoxicity (neutral red uptake assay) in human foreskin fibroblast (HFF) cells. To determine efficacy, briefly, HFF cells seeded in 6-well plates 2 days prior to use were infected with either VV or CV by the addition of 20 to 30 PFU per well. After a 1-h incubation period, various concentrations of drug were added to triplicate wells and plates were incubated at 37°C for 3 days. Toxicity was evaluated using HFF cells seeded in 96-well plates incubated with various concentrations of drug for 7 days at 37°C. After incubation, cell monolayers were stained with a 0.01% solution of neutral red. The compounds were synthesized as reported previously (8).As presented in Table 1, the most active ether lipid esters of CDV were OLE-CDV, ODBG-CDV, TDP-CDV, OLP-CDV, and ODP-...

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