Antiviral activity and intracellular metabolism of bis(tButylSATE) phosphotriester of beta-L-2',3'dideoxyadenosine, a potent inhibitor of HIV and HBV replication

The beta-L-nucleoside analogue beta-L-2',3'-dideoxy adenosine (beta-L-ddA) has been shown to exhibit limited antiviral activities. This was attributed to its rapid catabolism through cleavage of the glycosidic bond and poor phosphorylation to the nucleotide beta-L-2',3'-dideoxyadenosine-5'-mono phosphate (beta-L-ddAMP) (Placidi et al., 2000). However, the nucleotide beta-L-2',3'-dideoxyadenosine-5'-triphosphate (beta-L-ddATP) inhibited the activity of both HIV-1 reverse transcriptase (RT) and viral DNA polymerase isolated from woodchuck hepatitis virus-infected serum (a model of hepatitis B) with an inhibitory concentration (IC50) of 2.0 microM without inhibiting human DNA polymerases alpha, beta, or gamma up to a concentration of 100 microM. These results suggested that prodrugs of beta-L-ddAMP may bypass the poor metabolic activation of beta-L-ddA and lead to more potent and selective antiviral activity. Therefore, the mononucleoside phosphotriester derivative of beta-L-ddAMP incorporating the S-pivaloyl-2-thioethyl (tButylSATE) groups, beta-L-ddAMP-bis(tButylSATE) was synthesized. Beta-L-ddAMP-bis(tButylSATE) inhibited HIV replication in human peripheral blood mononuclear cells (PBMCs) and HBV replication in 2.2.15 cells with effective concentrations (EC50s) of 2 and 80 nM, respectively. Intracellular metabolism of beta-L-ddAMP-bis(tButylSATE) demonstrated that beta-L-ddATP was the predominant intracellular metabolite in PBMC and liver cells. The intracellular half-life of beta-L-ddATP was 5.4 and 9.2 h in HepG2 and PBMCs, respectively. The intracellular concentrations of beta-L-ddATP were maintained above the EC50 for the inhibition of HIV RT and hepatitis B virus (HBV) for as long as 24 h after removal of the drug.

S-Acyl-2-thioethyl aryl phosphotriester derivatives as mononucleotide prodrugs

The synthesis and biological activities of phosphotriester derivatives of 3'-azido-2',3'-dideoxythymidine (AZT) bearing a phenyl group or L-tyrosinyl residues are reported. The target compounds were obtained via either P(V) or P(III) chemistry from the appropriate aryl precursors. All the derivatives were evaluated for their in vitro anti-HIV activity, and they appeared to be potent inhibitors of HIV-1 replication in various cell culture experiments, with EC(50) values between the micro- and nanomolar range. Furthermore, compounds incorporating an amino- and/or acid-substituted tyrosinyl residue demonstrated significant anti-HIV effects in thymidine kinase-deficient (TK(-)) cells showing their ability to act as mononucleotide prodrugs. The proposed decomposition process of these mixed mononucleoside aryl phosphotriesters may involve esterase activation followed by phosphodiesterase hydrolysis.

Inhibition of the ras-dependent mitogenic pathway by phosphopeptide prodrugs with antiproliferative properties

Phosphopeptide prodrugs bearing two S-acyl-2-thioethyl (SATE) biolabile phosphate protections were developed. They are capable to inhibit the Shc/Grb2 interaction and MAP kinases (ERK1 and ERK2) phosphorylation in cellular assay. The S-acetyl-2-thioethyl (MeSATE) analogue showed an IC50 of 1 microM in the inhibition of the colony formation of tumor cell line NIH3T3/HER2.

Inhibition of adenylyl cyclase by acyclic nucleoside phosphonate antiviral agents

Acyclic derivatives of adenine, known as highly effective nucleotide analogs with broad spectrum antiviral activity, were evaluated for potential cross-reactivity with adenylyl cyclases, a family of membrane-bound enzymes that share putative topologies at their catalytic sites with oligonucleotide polymerases and reverse transcriptases. A series of derivatives of 9-(2-phosphonylmethoxyethyl)adenine (PMEA) inhibited a preparation of adenylyl cyclase derived from rat brain with IC(50) values that ranged from 66 microM (PMEA) to 175 nM for its diphosphate derivative (PMEApp) and mimics of it. PMEApp mimics included PMEAp(NH)p, PMEAp(CH(2))p, PMEAp(CX(2))p (X = fluorine, chlorine, or bromine), PMEAp(CHX)pp, and PMEAp(C(OH)CH(3)pp. The data suggest that inhibition of adenylyl cyclases may contribute to the therapeutic action of some of these or similar compounds or constitute part of their side effects in therapeutic settings.

Synthesis and anti-retroviral activity of O,O'-bis(3'-azido-2',3'-dideoxythymidin-5'-yl) phosphoramidate derivatives

A simple and efficient protocol for the preparation of various symmetrical dinucleoside phosphoramidates derived from AZT, is presented. It consists of the phosphonylation of AZT with phosphonic acid in the presence of DCC to produce the symmetrical H-phosphonate diester, followed by its oxidative conversion to various phosphoramidate analogues. The synthesized compounds were evaluated for their anti-HIV activity in different cell cultures.

Synthesis of the tBuSATE pronucleotide of AZT by two different synthetic approaches

A large scale synthesis of the tBuSATE pronucleotide of AZT was required for in vivo studies. A comparative synthesis of this derivative by phosphoramidite and monophosphate approaches is reported.

Synthesis, anti-HIV activity and stability studies of 3'-azido-2',3'-dideoxythymidine 5'-fluorophosphate

The synthesis, in vitro anti-HIV activity, and stability studies of AZT 5'-fluorophosphate (F-AZTMP) are reported. The present results demonstrate that such compound is a bioprecursor of its parent 5'-mononucleotide (AZTMP) but its biotransformation does not allow its selective intracellular delivery. Moreover, several attempts were carried out in order to improve the biological activity of this compound by the use of a SATE prodrug strategy.

Synthesis and anti-HIV activity of some S-acyl-2-thioethyl (SATE) phosphoramidate derivatives of 3'-azido-2',3'-dideoxythymidine

The synthesis and in vitro anti-HIV activity of tBuSATE phosphoramidate derivatives of AZT incorporating several methyl-esterified alpha-amino acids are reported. The biological evaluation strongly supports the hypothesis that such compounds exert their anti-HIV effects via intracellular delivery of the corresponding 5'-mononucleotide.

Anti-HIV pronucleotides: SATE versus phenyl as a protecting group of AZT phosphoramidate derivatives

We comparatively studied the decomposition pathways in CEM cell extract of several PHENYL phosphoramidate diesters of AZT. A correlation between anti-HIV activities in TK- cell lines and pharmacokinetic data has been observed. This study would help to design corresponding SATE phosphoramidate diesters which revealed potent anti-HIV properties.

Prodrugs of Ara-CMP and Ara-AMP with a S-acyl-2-thioethyl (SATE) biolabile phosphate protecting group: synthesis and biological evaluation

The bis(S-pivaloyl-2-thioethyl) phosphotriesters of Ara-C and Ara-A were synthesized as potential bioreversible mononucleotide prodrugs. Some N- and O-acylated derivatives were also prepared with the aim to modify the lipophilicity of the title pronucleotides. Compounds were tested for their antitumor/antiviral activity against a variety of tumor cells and viruses.

New series of mixed pronucleotides. Synthesis and anti-HIV activities of mononucleoside phenyl SATE phosphotriesters

The synthesis and anti-HIV activities of phenyl S-pivaloyl-2-thioethyl (tBuSATE) phosphotriesters of AZT and d4T are reported. These compounds show similar activity compared to bis(tBuSATE) phosphotriesters and appear to be able to deliver the corresponding 5'-mononucleotides inside the cells.

ddC- and 3TC-bis(SATE) monophosphate prodrugs overcome cellular resistance mechanisms to HIV-1 associated with cytidine kinase deficiency

A 2',3'-dideoxycytidine (ddC)-resistant T-lymphoid cell line (MOLT-4/8rddC250), in which deoxycytidine kinase (dCK) gene-expression was decreased when compared with parental cells, has been selected. Cytotoxic and antiretroviral activity of ddC and 3TC was significantly lower in MOLT-4/8rddC250-than in parental MOLT-4/8 cells. ddC- and 3TC-bis(SATE)phosphotriesters completely overcame cellular resistance mechanisms and showed comparable both cytotoxic and antiretroviral activity in parental and ddC-resistant cells.

Synthesis of new PMEA diphosphate mimics

We synthesized and characterized new diphosphate mimics of the acyclic nucleoside phosphonate PMEA [Adefovir, 9-(2-phosphonylmethoxyethyl)adenine].

The S-acyl-2-thioethyl pronucleotide approach applied to acyclovir: part I. Synthesis and in vitro anti-hepatitis B virus activity of bis(S-acyl-2-thioethyl)phosphotriester derivatives of acyclovir

The synthesis and in vitro anti-hepatitis B virus (HBV) activity of two mononucleoside phosphotriester derivatives of acyclovir incorporating S-acyl-2-thioethyl (SATE) groups are reported. In contrast to the parent nucleoside, the described phosphotriesters emerged as potent and selective inhibitors of HBV replication in HepG2.2.15 cells. This result can be attributed to the unique cellular metabolism of the SATE pronucleotides giving rise to the delivery to acyclovir 5'-monophosphate inside the infected cells. Moreover, the in vitro anti-HBV activities of one of these bis(SATE)phosphotriesters and of (-)-beta-L-2',3'-dideoxy-3'-thiacytidine (lamivudine, 3TC) were compared alone and in combination. Analysis of the combination data indicates that 3TC and the studied SATE pronucleotide of acyclovir exhibited strong synergistic interactions. The present study provides an example where the use of a pronucleotide approach extends the antiviral spectrum of a nucleoside analogue. Given the potency of SATE pronucleotides of acyclovir against HBV in HepG2.2.15 cells, further studies including animal experiments seem warranted to evaluate the potential of these compounds as anti-HBV agents.

The SATE pronucleotide approach applied to acyclovir: part II. Effects of bis(SATE)phosphotriester derivatives of acyclovir on duck hepatitis B virus replication in vitro and in vivo

The in vitro and in vivo antiviral activities of two mononucleoside phosphotriester derivatives of acyclovir (ACV) incorporating S-acyl-2-thioethyl (SATE) groups are reported using the duck model of hepatitis B (DHBV). In primary duck hepatocyte cultures, the described phosphotriesters significantly inhibited the replication of DHBV at submicromolar concentrations. They were found to be more potent than the parent nucleoside. This result was in agreement with our data concerning the anti-HBV activity of these pronucleotides in HepG2.2.15 cells (previous paper). In vivo, the studied SATE pronucleotide was also found to be more efficient than ACV in infected ducklings upon short-term oral therapy, while intraperitoneal treatment showed high anti-DHBV activity with both ACV and its SATE pronucleotide in this animal model. These findings demonstrate the potential of SATE pronucleotides of ACV as anti-HBV agents.

Rational design of a new series of mixed anti-HIV pronucleotides

MonoSATE aryl phosphotriesters of AZT are able to deliver intracellularly the corresponding 5'-mononucleotide. This process requires activation by an esterase followed by a phosphodiesterase. This finding opens the way to the design of new pronucleotide series.

Anti-HIV pronucleotides: decomposition pathways and correlation with biological activities

The purpose of the present study was to compare the decomposition pathways in CEM cell extracts of various phenyl phosphoramidate derivatives of AZT. In addition, the structures of their metabolites were identified. Correlations with their anti-HIV activities in a thymidine kinase deficient (TK-) CEM cell line have been established with a rationale of designing phosphoramidate pronucleotides capable of delivering intracellularly their respective 5'-nucleoside monophosphate derivatives.

Synthesis and antiviral evaluation of SATE-foscarnet prodrugs and new foscarnet-AZT conjugates

The synthesis of a range of di- and triester derivatives of phosphonoformate (PFA; foscarnet) as potential lipophilic, membrane-soluble prodrugs is described. In addition to normal alkyl esters in the carboxylate and phosphonate residues of PFA, the bioreversible S-(pivaloyl)thioethyl (t-butyl-SATE) group was introduced in an attempt to deliver PFA after bioactivation inside the cells. Furthermore, PFA-AZT conjugates were prepared in order to develop combinational drugs. The key synthetic step was in all cases the formation of the P-C bond to build up the different PFA esters. In contrast to the diester derivatives, the triesters of PFA showed high hydrolytic instability during chromatographic purification. The compounds were evaluated in vitro for their ability to inhibit viruses in several tissue culture systems. All PFA alkyl di- and triesters proved poorly active or inactive against human immunodeficiency virus (HIV) and inactive against hepatitis B virus. In contrast, the PFA-AZT conjugates exhibited significant anti-HIV activity. However, this activity was nearly completely lost in thymidine kinase-deficient cells, suggesting a fast unselective chemical hydrolysis of the conjugates to yield the nucleoside analogue AZT in the cell culture medium. Furthermore, no synergistic effect of PFA and AZT was observed.

Decomposition pathways and in vitro HIV inhibitory effects of isoddA pronucleotides: toward a rational approach for intracellular delivery of nucleoside 5'-monophosphates

The decomposition pathways and kinetics in various biological media and the in vitro anti-HIV-1 and anti-HIV-2 activities of four derivatives of the 5'-mononucleotide of isoddA incorporating carboxylate esterase-labile transient phosphate protecting groups are reported and compared: namely, two mononucleoside aryl phosphoramidate derivatives 1a,b and two mononucleoside phosphotriester derivatives incorporating two S-acyl-2-thioethyl groups 2a,b. All four compounds show better antiviral activity, compared to the parent nucleoside analog isoddA. The results highlight that both types of compounds act as pronucleotides, i.e. they exert their antiviral effect via intracellular delivery of the 5'-mononucleotide of isoddA. The results may give insights for the design of new more efficient pronucleotides.

New insights regarding the potential of the pronucleotide approach in antiviral chemotherapy

The rationale for a pronucleotide approach based on the use of phosphotriesters which incorporate enzyme-mediated bio-labile protection is discussed in detail. Among the studied bio-labile phosphate protecting groups, the S-acyl-2-thioethyl (SATE) groups appeared the most promising as exemplified in cell culture systems in the case of the pronucleotides of 3'-azido-3'-deoxythymidine, 2',3'-didehydro-3'-deoxythymidine, 2',3'-dideoxyadenosine and acyclovir In vivo implementations of such bis(SATE) pronucleotides have been planned for future animal studies.

Anti-human immunodeficiency virus type 1 activities of dideoxynucleoside phosphotriester derivatives in primary monocytes/macrophages

Mononucleoside phosphotriester derivatives of dideoxynucleosides, following intracellular enzymatic activation, are likely to liberate their parent 5'-nucleoside monophosphate. Prodrugs of 3'-azido-2',3'-dideoxythymidine (AZT), 2',3'-didehydro-2',3'- dideoxythymidine (d4T), 2',3'-dideoxyinosine (ddl) and 2',3'-dideoxyadenosine (ddA) were evaluated for their anti-HIV1 activities in monocyte-derived macrophages, cells which are known to have low levels of nucleoside kinases. Prodrugs were found to be much more active, or just as active, as the corresponding dideoxynucleoside. Furthermore, their selectivity index was enhanced by a factor of 2 to 200.

Mononucleoside phosphotriester derivatives with S-acyl-2-thioethyl bioreversible phosphate-protecting groups: intracellular delivery of 3'-azido-2',3'-dideoxythymidine 5'-monophosphate

The synthesis, in vitro anti-HIV-1 activity, and decomposition pathways of several mononucleoside phosphotriester derivatives of 3'-azido-2',3'-dideoxythymidine (AZT) incorporating a new kind of carboxylate esterase-labile transient phosphate-protecting group, namely, S-acyl-2-thioethyl, are reported. All the described compounds showed marked antiviral activity in thymidine kinase-deficient CEM cells in which AZT was virtually inactive. The results strongly support the hypothesis that such pronucleotides exert their biological effects via intracellular delivery of the 5'-mononucleotide of AZT. This point was corroborated by decomposition studies in cell extracts and culture medium.