Interactions of 1-[(S)-3-Hydroxy-2-(phosphonomethoxy)propyl]cytosine (Cidofovir) Diphosphate with DNA Polymerases α, δ and ε*

GS-9191 is a novel topical prodrug of the nucleotide analog 9-(2-phosphonylmethoxyethyl)guanine with antiproliferative activity and possible utility in the treatment of human papillomavirus lesions

GS-9191 is a novel double prodrug of the nucleotide analog 9-(2-phosphonylmethoxyethyl)guanine (PMEG) designed as a topical agent to permeate skin and be metabolized to the active nucleoside triphosphate analog in the epithelial layer. The prodrug was shown to be metabolized intracellularly to 9-(2-phosphonylmethoxyethyl)-N(6)-cyclopropyl-2,6,diaminopurine (cPrPMEDAP) and subsequently deaminated to PMEG. The active form, PMEG diphosphate, was shown to be a potent inhibitor of DNA polymerase alpha and beta while showing weaker activity against mitochondrial DNA polymerase gamma (50% enzyme inhibition observed at 2.5, 1.6, and 59.4 microM, respectively). GS-9191 was markedly more potent than PMEG or cPrPMEDAP in a series of human papillomavirus (HPV)-positive cell lines, with effective concentrations to inhibit 50% cell growth (EC(50)) as low as 0.03, 207, and 284 nM, respectively. In contrast, GS-9191 was generally less potent in non-HPV-infected cells and primary cells (EC(50)s between 1 and 15 nM). DNA synthesis was inhibited by GS-9191 within 24 h of treatment; cells were observed to be arrested in S phase by 48 h and to subsequently undergo apoptosis (between 3 and 7 days). In an animal model (cottontail rabbit papillomavirus), topical GS-9191 was shown to decrease the size of papillomas in a dose-related manner. At the highest dose (0.1%), cures were evident at the end of 5 weeks, and lesions did not recur in a 30-day follow-up period. These data suggest that GS-9191 may have utility in the treatment of HPV-induced lesions.

Synthesis of acyclic nucleoside phosphonates

Acyclic nucleoside phosphonates (ANPs) are important biologically active nucleotide analogs. They contain an isopolar phosphonomethyl function linked to the hydroxyl group of an acyclic side-chain via an undegradable ether group. Though their most important activity is antiviral, some exhibit cytostatic or antiprotozoic effects. The three most important groups of ANP are presented here as synthetic procedures for a large laboratory scale. Synthesis follows three principles: (1) introduction of a protected phosphonomethyl group to the hydroxyl on an appropriate alkyl side-chain of an acyclic nucleoside, (2) alkylation of the heterocyclic base by a synthon with all characteristic features of the future phoshonate-bearing side-chain, or (3) transformation of a reactive group at the heterocyclic base. The last step in all these cases is removal of the phosphonate esters. Preparation methods are described in detail for PMEA, PMEG, PMEDAP and its N(6)-cyclopropyl derivative, (R)-PMPA, and (S)-HPMPA, as well as all intermediates and synthons.

The substrate activity of (S)-9-[3-hydroxy-(2-phosphonomethoxy)propyl]adenine diphosphate toward DNA polymerases alpha, delta and epsilon

In this study, we examined the substrate potency of (S)-9-[3-hydroxy-(2-phosphonomethoxy)propyl]- adenine diphosphate (HPMPApp) toward DNA polymerases alpha, delta and epsilon. The efficiency of HPMPApp incorporation decreased in the order pol epsilon >pol delta =pol alpha and was from 5.4- to 23-fold lower than that of dATP. Depending on which template-primer was used, the HPMPAppKm value was 3.3- and 8.3- (pol alpha), 3- and 0.82- (pol delta) or 2-fold (pol epsilon) higher than dATPKm. The ability of HPMPA to accumulate in DNA decreased in the order pol epsilon >pol alpha >pol delta. The difference between the elongation rate of DNA with and without one HPMPA molecule at 3' termini was about 1.1-2.3 fold. The 3'-5'-exonuclease activity of pol delta and epsilon can excise HPMPA from DNA. These observations indicate that interaction of HPMPApp with pol alpha, delta and epsilon may contribute to its cellular toxicity and explain its antiviral activity against polyomavirus.