Alkoxy propane prodrugs of foscarnet: effect of alkyl chain length on in vitro antiviral activity in cells infected with HIV-1, HSV-1 and HCMV

Synthesis, physicochemical properties and biological activities of novel alkylphosphocholines with foscarnet moiety

A series of alkylphosphocholines with foscarnet moiety was synthesized. The structure of these zwitterionic amphiphiles was modified in both polar and non-polar parts of surfactant molecule. Investigations of physicochemical properties are represented by the determination of critical micelle concentration, the surface tension value at the cmc and the surface area per surfactant head group utilising surface tension measurements. Hydrodynamic diameter of surfactant micelles was determined using the dynamic light scattering technique. Alkylphosphocholines exhibit significant cytotoxic, anticandidal (Candida albicans) and antiamoebal (Acanthamoeba spp. T4 genotype) activity. The relationship between the structure, physicochemical properties and biological activity of the tested compounds revealed that lipophilicity has a significant influence on biological activity of the investigated surfactants. More lipophilic alkylphosphocholines with octadecyl chains show cytotoxic activity against cancer cells which is higher than that of the compounds with shorter alkyl chains. The opposite situation was observed in case of anticandidal and antiamoebal activity of these surfactants. The most active compounds were found to have pentadecyl chains. The foscarnet analogue of miltefosine C15-PFA-C showed the highest anticandidal activity. The minimum value of anticandidal activity of this compound is 1,4 μM thus representing the highest anticandidal activity found within the group of alkylphosphocholines.

Acyclic nucleoside bisphosphonates: synthesis and properties of chiral 2-amino-4,6-bis[(phosphonomethoxy)alkoxy]pyrimidines

2-Amino-4,6-bis[(phosphonomethoxy)alkoxy]pyrimidines bearing two equal or different achiral or chiral phosphonoalkoxy chains have been prepared either by aromatic nucleophilic substitution of 2-amino-4,6-dichloropyrimidine or by alkylation of 4,6-dihydroxy-2-(methylsulfanyl)pyrimidine with appropriate phosphonate-bearing building block. Alkylation of 4,6-dihydroxy-2-(methylsulfanyl)pyrimidine proved to be the method of choice for efficient preparation of variety of bisphosphonates. The enantiomeric purity of selected compounds was determined by capillary electrophoresis. Antiviral activity of bisphosphonates is discussed.

Alkoxyalkyl esters of 9-(s)-(3-hydroxy-2-phosphonomethoxypropyl) adenine are potent and selective inhibitors of hepatitis B virus (HBV) replication in vitro and in HBV transgenic mice in vivo

Alkoxyalkyl esters of acyclic nucleoside phosphonates have previously been shown to have increased antiviral activity when they are administered orally in animal models of viral diseases, including lethal infections with vaccinia virus, cowpox virus, ectromelia virus, murine cytomegalovirus, and adenovirus. 9-(S)-(3-Hydroxy-2-phosphonomethoxypropyl)adenine [(S)-HPMPA] was previously shown to have activity against hepatitis B virus (HBV) in vitro. To assess the effect of alkoxyalkyl esterification of (S)-HPMPA, we prepared the hexadecyloxypropyl (HDP), 15-methyl-hexadecyloxypropyl (15M-HDP), and octadecyloxyethyl (ODE) esters and compared their activities with the activity of adefovir dipivoxil in vitro and in vivo. Alkoxyalkyl esters of (S)-HPMPA were 6 to 20 times more active than unmodified (S)-HPMPA on the basis of their 50% effective concentrations in 2.2.15 cells. The increased antiviral activity appeared to be due in part to the increased uptake and conversion of HDP-(S)-HPMPA to HPMPA diphosphate observed in HepG2 cells in vitro. HDP-(S)-HPMPA retained full activity against HBV mutants resistant to lamivudine (L180M, M204V), but cross-resistance to a mutant resistant to adefovir (N236T) was detected. HDP-(S)-HPMPA is orally bioavailable and provides excellent liver exposure to the drug. Oral treatment of HBV transgenic mice with HDP-(S)-HPMPA, 15M-HDP-(S)-HPMPA, and ODE-(S)-HPMPA for 14 days reduced liver HBV DNA levels by roughly 1.5 log units, a response equivalent to that of adefovir dipivoxil.

Intraocular Properties of An Alkoxyalkyl Derivative of Cyclic 9-(S)-(3-Hydroxyl-2-Phosphonomehoxypropyl) Adenine, An Intravitreally Injectable Anti-HCMV Drug in Rabbit and Guinea Pig

PURPOSE

The aim of this study was to investigate intraocular properties and determine the highest nontoxic dose of hexadecyloxypropyl-cyclic-HPMPA (HDP-cHPMPA), a novel, potent, intravitreally injectable, slow-releasing crystalline drug for long-acting treatment of cytomegalovirus (CMV) retinitis.

METHODS

Various concentrations of HDP-cHPMPA were first studied in vitro in a human foreskin fibroblast (HFF) cell line infected with human cytomegalovirus (HCMV) to determine the EC50. In vivo, 9 pigmented rabbits and 3 doses (55, 100, and 550 microg/eye) were tested in triplicate in 1 eye of each animal. The eyes were monitored with slit lamp, tonopen, indirect ophthalmoscopy, electroretinography (ERG), and histology. A confirmation toxicity study with the dose equivalent to the highest nontoxic dose in rabbit was performed in 9 guinea pig eyes (a second species) to study the potential adverse effect on intraocular pressure (IOP).

RESULTS

In vitro testing in HFF cells showed an EC50 against HCMV of 0.02 microM, which is 75- and 60-fold greater than that of ganciclovir and cidofovir, respectively. All eyes injected with 550 microg/eye and 1 eye injected with 100 microg/eye of HDP-cHPMPA showed toxicity clinically (e.g., vitreous cells, disc edema, and retinal inflammation) as well as histologically (e.g., inflammatory cells in iris, vitreous, and retinal layers with disorganization). None of the eyes injected with 55 microg/eye of HDP-cHPMPA showed toxicity clinically (including ERG) and histologically. The equivalent dose (9.2 microg/eye) in the guinea pig eyes did not show toxicity either, including IOP evaluation (P > 0.05 at all time points after injection).

CONCLUSIONS

Intravitreal injection of the highest nontoxic dose of 55 microg/eye of HDP-cHPMPA in rabbit eyes yields a calculated intravitreal concentration of 65 microM, which is 3250-fold greater than the EC50 against HCMV (0.02 microM). Also, it does not cause hypotony in rabbit and guinea pig eyes and has a vitreous residence time of over 4 months.

Synthesis and antiviral evaluation of alkoxyalkyl esters of acyclic purine and pyrimidine nucleoside phosphonates against HIV-1 in vitro

Alkoxyalkyl esters of cidofovir, an acyclic nucleoside phosphonate, have been shown to have antiviral activities several orders of magnitude greater than unmodified cidofovir against cytomegalovirus, herpes simplex virus, vaccinia, cowpox, ectromelia and adenoviruses in vitro. Hexadecyloxypropyl-cidofovir is orally bioavailable and active in lethal animal models of vaccinia, cowpox, ectromelia and cytomegalovirus. To see if this strategy is also applicable to other acyclic nucleoside phosphonates, we have converted several phosophonomethoxyethyl purines and pyrimidines to their hexadecyloxypropyl, octadecyloxyethyl and oleyloxyethyl esters and compared their activity against HIV-1 with the activity of the respective unmodified acyclic nucleoside phosphonates. The hexadecyloxypropyl esters of phosphonomethoxyethyl-adenine, phosphonomethoxyethyl-2,6-diaminopurine and phosphonomethoxyethyl-N(6)-cyclopropyl-diaminopurine were 3-5 orders of magnitude more active against HIV-1 in vitro than the parent nucleotides. The EC(50) values for these compounds were in the 10-20 pM range with selective indexes of 1,250 to >4,000. The acyclic pyrimidine phosphonates were generally inactive against HIV-1 in vitro. Phosphonomethoxyethyl-cytosine and phosphonomethoxyethyl-5-fluorocytosine were inactive against HIV-1. Surprisingly, hexadecyloxypropyl-phosphonomethoxyethyl-5-fluorocytosine was active against HIV-1 with a submicromolar EC(50) and a selective index of 174. Esterification of acyclic nucleoside phosphonates with alkoxyalkyl moieties may represent a general approach for increasing antiviral activity and selectivity of this class of antivirals.

Comparative activities of lipid esters of cidofovir and cyclic cidofovir against replication of herpesviruses in vitro

Cidofovir (CDV) is an effective therapy for certain human cytomegalovirus (HCMV) infections in immunocompromised patients that are resistant to other antiviral drugs, but the compound is not active orally. To improve oral bioavailability, a series of lipid analogs of CDV and cyclic CDV (cCDV), including hexadecyloxypropyl-CDV and -cCDV and octadecyloxyethyl-CDV and -cCDV, were synthesized and found to have multiple-log-unit enhanced activity against HCMV in vitro. On the basis of the activity observed with these analogs, additional lipid esters were synthesized and evaluated for their activity against herpes simplex virus (HSV) types 1 and 2, human cytomegalovirus, murine cytomegalovirus, varicella-zoster virus (VZV), Epstein-Barr virus (EBV), human herpesvirus 6 (HHV-6), and HHV-8. Using several different in vitro assays, concentrations of drug as low as 0.001 microM reduced herpesvirus replication by 50% (EC50) with the CDV analogs, whereas the cCDV compounds were generally less active. In most of the assays performed, the EC50 values of the lipid esters were at least 100-fold lower than the EC50 values for unmodified CDV or cCDV. The lipid analogs were also active against isolates that were resistant to CDV, ganciclovir, or foscarnet. These results indicate that the lipid ester analogs are considerably more active than CDV itself against HSV, VZV, CMV, EBV, HHV-6, and HHV-8 in vitro, suggesting that they may have potential for the treatment of infections caused by a variety of herpesviruses.

Comparison of the antiviral activities of alkoxyalkyl and alkyl esters of cidofovir against human and murine cytomegalovirus replication in vitro

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.

Synthesis and Evaluation of Novel Prodrugs of Foscarnet and Dideoxycytidine with a Universal Carrier Compound Comprising a Chemiluminescent and a Photochromic Conjugate

To facilitate intracellular delivery of hydrophilic drugs, a general lipophilic carrier molecule was designed and synthesized. The carrier comprised a chemiluminescent-photochromic conjugate that potentiates diffusion across cell membranes to enhance intracellular uptake of the drug. The designed mechanism involves activation of the chemiluminescent moiety by intracellular oxygen free radicals and intermolecular energy transfer of the excited state energy to the photochromic moiety to result in release of the drug to allow the desired pharmacological effect to occur. Prodrugs of foscarnet and dideoxycytidine with several carriers caused suppression of a human immunodeficiency virus infection in human cultured macrophages that was up to five times more effective than the drug alone. Successful in vivo efficacy testing of prodrug has been accomplished by demonstrating the suppression of a retroviral infection of Friend leukemia virus in mice. Acute toxicity studies of the carrier indicated that it was nontoxic.

Relationship between 3'-azido-3'-deoxythymidine resistance and primer unblocking activity in foscarnet-resistant mutants of human immunodeficiency virus type 1 reverse transcriptase

Phosphonoformate (foscarnet) is a pyrophosphate (PP(i)) analogue and a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), acting through the PP(i) binding site on the enzyme. HIV-1 RT can unblock a chain-terminated DNA primer by phosphorolytic transfer of the terminal residue to an acceptor substrate (PP(i) or a nucleotide such as ATP) which also interacts with the PP(i) binding site. Primer-unblocking activity is increased in mutants of HIV-1 that are resistant to the chain-terminating nucleoside inhibitor 3'-azido-3'-deoxythymidine (AZT). We have compared the primer-unblocking activity for HIV-1 RT containing various foscarnet resistance mutations (K65R, W88G, W88S, E89K, S117T, Q161L, M164I, and the double mutant Q161L/H208Y) alone or in combination with AZT resistance mutations. The level of primer-unblocking activity varied over a 150-fold range for these enzymes and was inversely correlated with foscarnet resistance and directly correlated with AZT resistance. Based on published crystal structures of HIV-1 RT, many of the foscarnet resistance mutations affect residues that do not make direct contact with the catalytic residues of RT, the incoming deoxynucleoside triphosphate (dNTP), or the primer-template. These mutations may confer foscarnet resistance and reduce primer unblocking by indirectly decreasing the binding and retention of foscarnet, PP(i), and ATP. Alternatively, the binding position or orientation of PP(i), ATP, or the primer-template may be changed in the mutant enzyme complex so that molecular interactions required for the unblocking reaction are impaired while dNTP binding and incorporation are not.

Alkylglycerol prodrugs of phosphonoformate are potent in vitro inhibitors of nucleoside-resistant human immunodeficiency virus type 1 and select for resistance mutations that suppress zidovudine resistance

Phosphonoformate (foscarnet; PFA) is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT), but its use for the treatment of HIV-1 infection is limited by toxicity and the lack of an orally bioavailable formulation. Alkylglycerol-conjugated prodrugs of PFA (1-O-octadecyl-sn-glycero-3-PFA [B-PFA]) having sn-2 substituents of hydrogen (deoxybatyl-PFA [DB-PFA]), methyl (MB-PFA), or ethyl (EB-PFA) are more-potent inhibitors of wild-type HIV-1 in vitro than unmodified PFA and are orally bioavailable in mice. We have evaluated the activities of these compounds against a panel of nucleoside-resistant HIV-1 variants and have characterized the resistant variants that emerge following in vitro selection with the prodrugs. Except for an HIV-1 variant encoding the K65R mutation in RT that exhibited 3.3- to 8.2-fold resistance, the nucleoside-resistant viruses included in the panel were sensitive to the PFA prodrugs (<3-fold increase in 50% inhibitory concentration), including multinucleoside-resistant variants encoding the Q151M complex of mutations or the T69S[SA] insert. Viruses resistant to the PFA prodrugs (>10-fold) were selected in vitro after 15 or more serial passages of HIV-1 in MT-2 cells in escalating prodrug concentrations. Mutations detected in the resistant viruses were S117T, F160Y, and L214F (DB-PFA); M164I and L214F (MB-PFA); and W88G and L214F (EB-PFA). The S117T, F160Y, and M164I mutations have not been previously identified. Generation of recombinant viruses encoding the single and double mutations confirmed their roles in prodrug resistance, including 214F, which generally increased the level of resistance. When introduced into a zidovudine (AZT)-resistant background (67N 70R 215F 219Q), the W88G, S117T, F160Y, and M164I mutations reversed AZT resistance. This suppression of AZT resistance is consistent with the effects of other foscarnet resistance mutations that reduce ATP-dependent removal of AZT monophosphate from terminated template primers. The favorable activity and resistance profiles of these PFA prodrugs warrant their further evaluation as clinical candidates.

In vitro and in vivo activity of 1-O-hexadecylpropanediol-3-phospho-ganciclovir and 1-O-hexadecylpropanediol-3-phospho-penciclovir in cytomegalovirus and herpes simplex virus infections

Human cytomegalovirus (HCMV) and herpes simplex virus (HSV) can cause a wide variety of clinical manifestations in man. Ganciclovir (GCV) is effective against HCMV infection when administered by the intravenous route and may be used orally in large doses for prophylaxis of HCMV infections in organ transplantation patients and in AIDS patients. In previous studies with acyclovir (ACV), we found that covalent attachment of an alkyl glycerol phosphate moiety greatly increased oral bioavailability and increased antiviral activity against hepatitis B virus. Adducts of ACV with alkyl propanediol phosphate were more active than the alkyl glycerol phosphate analogue in vitro in 2.2.15 cells, which constitutively produce hepatitis B virus. To see if this strategy would work for two other poorly absorbed nucleoside analogues, we synthesized 1-O-hexadecylpropanediol-3-phospho-GCV (HDP-P-GCV) and 1-O-hexadecyl-propanediol-3-phospho-penciclovir (HDP-P-PCV), and evaluated the in vitro antiviral activity, selectivity and oral antiviral activity of both compounds versus GCV or PCV in mice infected with HSV-1 or HDP-P-GCV versus murine cytomegalovirus (MCMV). HDP-P-GCV is orally active in both MCMV and HSV-1 infection in mice with antiviral activity equivalent to (HSV-1) or greater than oral GCV (MCMV). Oral HDP-P-PCV was more active than PCV orally versus intranasal HSV-1 infection in mice.

In vitro anti-HIV-1 activity of sn-2-substituted 1-O-octadecyl-sn-glycero-3-phosphonoformate analogues and synergy with zidovudine

Monoalkyl ether lipid analogues of foscarnet (phosphonoformate, PFA) exhibit substantially greater in vitro antiviral activity than unmodified PFA against human immunodeficiency virus type 1 (HIV-1). Our previous studies indicate that the length of the alkyl chain must be 14-22 carbons for optimal antiviral activity. To further evaluate the structure-activity relationship, we prepared 1-O-octadecyl-sn-glycerol analogues of PFA with various substitutions at the sn-2 position of glycerol and determined the effect of structure on in vitro antiviral activity and selectivity against HIV-1 in MT-2 and CD4-expressing HeLa cells (HT4-6C). We also studied combinations of zidovudine with PFA, 1-O-octadecyl-2-O-methyl-sn-glycero-3-PFA, or 1-O-octadecyl-sn-glycero-3-PFA and calculated their combination index values against HIV-1 in HT4-6C cells. Alkyl substitutions of one to four carbons at the sn-2 position of glycerol showed optimal antiviral activity. Both alkyl ether lipid analogues were strongly synergistic with zidovudine over a wide range of drug ratios and concentrations. 1-O-octadecyl-sn-glycerol analogues of PFA have selective antiviral properties and warrant further evaluation as potential antiretroviral drugs.

Synthesis and antiviral evaluation of 1-O-hexadecylpropanediol-3-P-acyclovir: efficacy against HSV-1 infection in mice

We synthesized, 1-O-hexadecylpropanediol-3-P-acyclovir, an orally bioavailable lipid prodrug of acyclovir and evaluated it for in vitro and in vivo activity against herpes simplex virus infections. Although 1-O-hexadecylpropanediol-3-P- acyclovir was less active in vitro than acyclovir, on a molar basis it was 2.4 times more active orally in preventing mortality from acute HSV-1 infection in mice. In vitro, 1-O-hexadecylpropanediol-3-P-acyclovir was also more active than acyclovir in a thymidine kinase negative mutant strain of HSV-1 (DM21) and had somewhat higher activity in cytomegalovirus infection in vitro due to it's ability to bypass thymidine kinase.

Neoglycolipid conjugates of foscarnet with enhanced antiviral activity in cells infected with human cytomegalovirus and herpes simplex virus type 1

The synthesis of a series of neoglycolipid conjugates of foscarnet as potential drug targeting forms or lipophilic prodrugs of foscarnet is described. The compounds were obtained from suitably protected neoglycolipids, in which the lipid chain consisted of 12 to 20 carbon atoms, by ethoxycarbonylphosphonylation at the 6-hydroxyl or 4-hydroxyl group followed by deprotection. The in vitro antiviral activity of the compounds was determined in human foetal lung cells infected with human cytomegalovirus (HCMV) or herpes simplex virus type 1 (HSV-1). Compounds in which the lipid chain consisted of 14 to 20 carbon atoms showed pronounced antiviral activity against HCMV and HSV-1, the highest activity being shown by trans-9-octadecen-1-yl 6-O-carboxyphosphonyl-alpha-D-glucopyranoside against HCMV (approximately 50 times that of foscarnet) and by eicosyl 6-O-carboxyphosphonyl-beta-D-galactopyranoside against HSV-1 (approximately 15 times that of foscarnet). Cytotoxicity was determined by assessing the capability of mitochondrial enzymes to metabolise MTT and gave TC50 values for the compounds that were 30 to 350 times higher than their IC50 values against HCMV and 5 to 15 times higher than their IC50 values against HSV-1. Foscarnet was not liberated on incubation of n-tetradecyl 6-O-carboxyphosphonyl-alpha-D-glucopyranoside with rat liver or intestine homogenate, neither could the neoglycolipid conjugate nor foscarnet be detected in rat plasma following oral administration. Further metabolic and pharmacokinetic studies are required in order to determine whether neoglycolipid conjugates of foscarnet can find a use as drug targeting forms of foscarnet.

Improved uptake and retention of lipophilic prodrug to improve treatment of HIV

Dideoxynucleosides currently in use for anti-HIV therapy have been found to be inefficient in passing through the blood-brain barrier to enter and maintain therapeutic drug levels in brain, a very significant reservoir of HIV. The low bioavailability of these drugs combined with the bone marrow toxicity of AZT (3'-azido, 3'-deoxythymidine, Zidovudine), resulting in anemia and leukopenia, pancreatitis with ddI (2',3'-dideoxyinosine, Didanosine) and painful peripheral neuropathy in case of ddC (2',3-dideoxycytosine, Zalcitabine) are the limiting factors in their use. In addition, the emergence of strains of HIV resistant to AZT, the most commonly used drug, further restricts its use. Thus the control of AIDS and its complications, needs special therapeutic approaches to combat the disease. In order to overcome these limitations, AZT and ddI have been synthesized as ester-linked ceramide- and phosphatidylcholine-linked prodrugs possessing therapeutic attributes lacking in the parent compounds. There is greater uptake and longer retention of these prodrugs in NIH/3T3 cells in vitro. Pretreatment with our prodrugs blocked infection of these cells by Moloney murine leukemia virus (M-MuLV) for an extended period, which the parent drugs failed to do. When human CD4+ HeLa cells were continuously exposed to the AZT prodrug, subsequent infection of these cells by HIV was blocked. Similar results were obtained with NIH/3T3 cells exposed to M-MuLV. AE(6)C, a prodrug of AZT linked to ceramide via a cleavable ester bond and a six carbon linker, was less toxic to both mouse and human bone marrow progenitor cells than free AZT. Most significantly, the prodrugs concentration was greater and the retention longer, in well known sanctuaries for HIV, such as the brain, testes and thymus.

Alkylthioglycerol prodrugs of foscarnet: synthesis, oral bioavailability and structure-activity studies in human cytomegalovirus-, herpes simplex virus type 1- and human immunodeficiency virus type 1-infected cells

In a previous study, we reported that 1-O-octadecyl-sn-glycero-3-foscarnet (ODG-PFA) was 40 to 93 times more potent than free foscarnet (PFA) in human cytomegalovirus (HCMV)-, herpes simplex virus type 1 (HSV-1)- and human immunodeficiency virus type 1 (HIV-1)-infected cells. To evaluate the effect of substituting a 1-S-alkyl thioether for a 1-O-alkyl ether, we synthesized a series of PFA conjugates of 1-S-alkyl-sn-thioglycerols with varied 1-S-alkyl chain lengths. To establish structure-activity relationships we measured the in vitro antiviral activity of liposomal formulations of the drugs in cells infected with HCMV, HSV-1 or HIV-1. The optimum 1-S-alkyl chain length in the series was 16 to 18 carbon atoms. We compared the antiviral activity of 16- and 18-carbon alkyl thioglycerol versus alkylglycerol prodrugs and did not observe any significant differences in their antiviral activities. The series' most active member, 1-S-octadecyl-sn-glycero-3-foscarnet (ODSG-PFA) was 56-, eight- and 45-fold more active than PFA in HCMV-, HSV-1- and HIV-1-infected cells in vitro. The oral absorption of PFA and 1-S-octadecyl-sn-thioglycero-3-PFA was compared in mice by measuring plasma levels of 14C after oral administration of radiolabelled compounds. The peak plasma level of 14C was sevenfold higher following administration of [14C]ODSG-PFA than following an equimolar dose of [14C]PFA. Area-under-the-curve was 23-fold greater for ODSG-PFA than for PFA. Like previously reported alkyloxyether-lipid PFA conjugates, alkylthioether conjugates provided enhanced antiviral activity and oral bioavailability. However, S-ether conjugates may be metabolized differently than O-ether conjugates. More detailed in vivo pharmacokinetic evaluation of the alkyl-thioether-PFA conjugates is required.

Synthesis and antiviral activity of 1-O-octadecyl-2-O-alkyl-sn-glycero-3-foscarnet conjugates in human cytomegalovirus-infected cells

A series of new lipid prodrugs with the general structure, 1-O-octadecyl-2-X-sn-glycero-3-PFA were synthesized and evaluated for antiviral activity in HCMV-infected human lung fibroblasts (X is -H, -OH or an O-alkyl group of increasing chain length) in order to study structure-activity relationships of PFA lipid prodrugs. The EC50 values for the 2-O-octyl, 2-O-butyl, 2-H, 2-OH, 2-O-methyl and 2-O-ethyl substituted analogs were 1.96, 0.36, 1.0, 0.7, 0.53 and 0.18 microM respectively versus 40 microM for PFA, representing increases in antiviral activity of 20-220 fold. We also synthesized the enantiomer of ODG-PFA, 3-O-octadecyl-sn-glycero-1-PFA, and found that the antiviral activity of both enantiomers as well as the racemate were not significantly different, with EC50 values in the range of 0.67-0.71 microM.