A Herpes Simplex Virus 1 DNA Polymerase Multidrug Resistance Mutation Identified in a Patient With Immunodeficiency and Confirmed by Gene Editing.

BACKGROUND: Herpes simplex virus 1 can cause severe infections in individuals who are immunocompromised. In these patients, emergence of drug resistance mutations causes difficulties in infection management. METHODS: Seventeen herpes simplex virus 1 isolates were obtained from orofacial/anogenital lesions in a patient with leaky severe combined immunodeficiency over 7 years, before and after stem cell transplantation. Spatial/temporal evolution of drug resistance was characterized genotypically-with Sanger and next-generation sequencing of viral thymidine kinase (TK) and DNA polymerase (DP)-and phenotypically. CRISPR/Cas9 was used to introduce the novel DP Q727R mutation, and dual infection-competition assays were performed to assess viral fitness. RESULTS: Isolates had identical genetic backgrounds, suggesting that orofacial/anogenital infections derived from the same virus lineage. Eleven isolates proved heterogeneous TK virus populations by next-generation sequencing, undetectable by Sanger sequencing. Thirteen isolates were acyclovir resistant due to TK mutations, and the Q727R isolate additionally exhibited foscarnet/adefovir resistance. Recombinant Q727R mutant virus showed multidrug resistance and increased fitness under antiviral pressure. CONCLUSIONS: Long-term follow-up of a patient with severe combined immunodeficiency revealed virus evolution and frequent reactivation of wild-type and TK mutant strains, mostly as heterogeneous populations. The DP Q727R resistance phenotype was confirmed with CRISPR/Cas9, a useful tool to validate novel drug resistance mutations.

Thymidine kinase and protein kinase in drug-resistant herpesviruses: Heads of a Lernaean Hydra.

Herpesviruses thymidine kinase (TK) and protein kinase (PK) allow the activation of nucleoside analogues used in anti-herpesvirus treatments. Mutations emerging in these two genes often lead to emergence of drug-resistant strains responsible for life-threatening diseases in immunocompromised populations. In this review, we analyze the binding of different nucleoside analogues to the TK active site of the three α-herpesviruses [Herpes Simplex Virus 1 and 2 (HSV-1 and HSV-2) and Varicella-Zoster Virus (VZV)] and present the impact of known mutations on the structure of the viral TKs. Furthermore, models of ß-herpesviruses [Human cytomegalovirus (HCMV) and human herpesvirus-6 (HHV-6)] PKs allow to link amino acid changes with resistance to ganciclovir and/or maribavir, an investigational chemotherapeutic used in patients with multidrug-resistant HCMV. Finally, we set the basis for the understanding of drug-resistance in γ-herpesviruses [Epstein-Barr virus (EBV) and Kaposi's sarcoma associated herpesvirus (KSHV)] TK and PK through the use of animal surrogate models.

ST-246 is a key antiviral to inhibit the viral F13L phospholipase, one of the essential proteins for orthopoxvirus wrapping.

OBJECTIVES: ST-246 is one of the key antivirals being developed to fight orthopoxvirus (OPV) infections. Its exact mode of action is not completely understood, but it has been reported to interfere with the wrapping of infectious virions, for which F13L (peripheral membrane protein) and B5R (type I glycoprotein) are required. Here we monitored the appearance of ST-246 resistance to identify its molecular target. METHODS: Vaccinia virus (VACV), cowpox virus (CPXV) and camelpox virus (CMLV) with reduced susceptibility to ST-246 were selected in cell culture and further characterized by antiviral assays and immunofluorescence. A panel of recombinant OPVs was engineered and a putative 3D model of F13L coupled with molecular docking was used to visualize drug-target interaction. The F13L gene of 65 CPXVs was sequenced to investigate F13L amino acid heterogeneity. RESULTS: Amino acid substitutions or insertions were found in the F13L gene of six drug-resistant OPVs and production of four F13L-recombinant viruses confirmed their role(s) in the occurrence of ST-246 resistance. F13L, but not B5R, knockout OPVs showed resistance to ST-246. ST-246 treatment of WT OPVs delocalized F13L- and B5R-encoded proteins and blocked virus wrapping. Putative modelling of F13L and ST-246 revealed a probable pocket into which ST-246 penetrates. None of the identified amino acid changes occurred naturally among newly sequenced or NCBI-derived OPV F13L sequences. CONCLUSIONS: Besides demonstrating that F13L is a direct target of ST-246, we also identified novel F13L residues involved in the interaction with ST-246. These findings are important for ST-246 use in the clinic and crucial for future drug-resistance surveillance programmes.

Spectrum of activity and mechanisms of resistance of various nucleoside derivatives against gammaherpesviruses.

The susceptibilities of gammaherpesviruses, including Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpesvirus (KSHV), and animal rhadinoviruses, to various nucleoside analogs was investigated in this work. Besides examining the antiviral activities and modes of action of antivirals currently marketed for the treatment of alpha- and/or betaherpesvirus infections (including acyclovir, ganciclovir, penciclovir, foscarnet, and brivudin), we also investigated the structure-activity relationship of various 5-substituted uridine and cytidine molecules. The antiviral efficacy of nucleoside derivatives bearing substitutions at the 5 position was decreased if the bromovinyl was replaced by chlorovinyl. 1-ß-D-Arabinofuranosyl-(E)-5-(2-bromovinyl)uracil (BVaraU), a nucleoside with an arabinose configuration of the sugar ring, exhibited no inhibitory effect against rhadinoviruses but was active against EBV. On the other hand, the fluoroarabinose cytidine analog 2'-fluoro-5-iodo-aracytosine (FIAC) showed high selectivity indices against gammaherpesviruses that were comparable to those of brivudin. Additionally, we selected brivudin- and acyclovir-resistant rhadinoviruses in vitro and characterized them by phenotypic and genotypic (i.e., sequencing of the viral thymidine kinase, protein kinase, and DNA polymerase) analysis. Here, we reveal key amino acids in these enzymes that play an important role in substrate recognition. Our data on drug susceptibility profiles of the different animal gammaherpesvirus mutants highlighted cross-resistance patterns and indicated that pyrimidine nucleoside derivatives are phosphorylated by the viral thymidine kinase and purine nucleosides are preferentially activated by the gammaherpesvirus protein kinase.

KAY-2-41, a novel nucleoside analogue inhibitor of orthopoxviruses in vitro and in vivo.

The availability of adequate treatments for poxvirus infections would be valuable not only for human use but also for veterinary use. In the search for novel antiviral agents, a 1'-methyl-substituted 4'-thiothymidine nucleoside, designated KAY-2-41, emerged as an efficient inhibitor of poxviruses. In vitro, KAY-2-41 was active in the micromolar range against orthopoxviruses (OPVs) and against the parapoxvirus orf. The compound preserved its antiviral potency against OPVs resistant to the reference molecule cidofovir. KAY-2-41 had no noticeable toxicity on confluent monolayers, but a cytostatic effect was seen on growing cells. Genotyping of vaccinia virus (VACV), cowpox virus, and camelpox virus selected for resistance to KAY-2-41 revealed a nucleotide deletion(s) close to the ATP binding site or a nucleotide substitution close to the substrate binding site in the viral thymidine kinase (TK; J2R) gene. These mutations resulted in low levels of resistance to KAY-2-41 ranging from 2.7- to 6.0-fold and cross-resistance to 5-bromo-2'-deoxyuridine (5-BrdU) but not to cidofovir. The antiviral effect of KAY-2-41 relied, at least in part, on activation (phosphorylation) by the viral TK, as shown through enzymatic assays. The compound protected animals from disease and mortality after a lethal challenge with VACV, reduced viral loads in the serum, and abolished virus replication in tissues. In conclusion, KAY-2-41 is a promising nucleoside analogue for the treatment of poxvirus-induced diseases. Our findings warrant the evaluation of additional 1'-carbon-substituted 4'-thiothymidine derivatives as broad-spectrum antiviral agents, since this molecule also showed antiviral potency against herpes simplex virus 1 in earlier studies.

Heterogeneity and evolution of thymidine kinase and DNA polymerase mutants of herpes simplex virus type 1: implications for antiviral therapy.

BACKGROUND: Infections caused by acyclovir-resistant isolates of herpes simplex virus (HSV) after hematopoietic stem cell transplantation (HSCT) are an emerging concern. An understanding of the evolutionary aspects of HSV infection is crucial to the design of effective therapeutic and control strategies. METHODS: Eight sequential HSV-1 isolates were recovered from an HSCT patient who suffered from recurrent herpetic gingivostomatitis and was treated alternatively with acyclovir, ganciclovir, and foscavir. The diverse spectra and temporal changes of HSV drug resistance were determined phenotypically (drug-resistance profiling) and genotypically (sequencing of the viral thymidine kinase and DNA polymerase genes). RESULTS: Analysis of 60 clones recovered from the different isolates demonstrated that most of these isolates were heterogeneous mixtures of variants, indicating the simultaneous infection with different drug-resistant viruses. The phenotype/genotype of several clones associated with resistance to acyclovir and/or foscavir were identified. Two novel mutations (E798K and I922T) in the viral DNA polymerase could be linked to drug resistance. CONCLUSIONS: The heterogeneity within the viral populations and the temporal changes of drug-resistant viruses found in this HSCT recipient were remarkable, showing a rapid evolution of HSV-1. Drug-resistance surveillance is highly recommended among immunocompromised patients to manage the clinical syndrome and to avoid the emergence of multidrug-resistant isolates.

Reduced tumorigenicity and pathogenicity of cervical carcinoma SiHa cells selected for resistance to cidofovir.

BACKGROUND: Insights into the mechanisms associated with chemotherapy-resistance are important for implementation of therapeutic strategies and for unraveling the mode of action of chemotherapeutics. Although cidofovir (CDV) has proven efficacious in the treatment of human papillomavirus (HPV)-induced proliferation, no studies concerning the development of resistance to CDV in HPV-positive tumor cells have been performed yet. METHODS: From the cervical carcinoma SiHa cells (SiHaparental), which are HPV-16 positive, cidofovir-resistant cells (SiHaCDV) were selected, and differential gene expression profiles were analyzed by means of microarrays. We examined in vitro phenotyping of resistant cells compared to parental cells as well as tumorigenicity and pathogenicity in a mouse-xenograft model. RESULTS: SiHaCDV had a resistant phenotype and a reduced growth both in vitro and in vivo. A markedly diminished inflammatory response (as measured by production of host- and tumor-derived cytokines and number of neutrophils and macrophages in spleen) was induced by SiHaCDV than by SiHaparental in the xenograft model. Gene expression profiling identified several genes with differential expression upon acquisition of CDV-resistance and pointed to a diminished induction of inflammatory response in SiHaCDV compared to SiHaparental. CONCLUSIONS: Our results indicate that acquisition of resistance to cidofovir in SiHa cells is linked to reduced pathogenicity. The present study contributes to our understanding on the antiproliferative effects of CDV and on the mechanisms involved, the inflammatory response playing a central role.

Mutations conferring resistance to viral DNA polymerase inhibitors in camelpox virus give different drug-susceptibility profiles in vaccinia virus.

Cidofovir or (S)-HPMPC is one of the three antiviral drugs that might be used for the treatment of orthopoxvirus infections. (S)-HPMPC and its 2,6-diaminopurine counterpart, (S)-HPMPDAP, have been described to select, in vitro, for drug resistance mutations in the viral DNA polymerase (E9L) gene of vaccinia virus (VACV). Here, to extend our knowledge of drug resistance development among orthopoxviruses, we selected, in vitro, camelpox viruses (CMLV) resistant to (S)-HPMPDAP and identified a single amino acid change, T831I, and a double mutation, A314V+A684V, within E9L. The production of recombinant CMLV and VACV carrying these amino acid substitutions (T831I, A314V, or A314V+A684V) demonstrated clearly their involvement in conferring reduced sensitivity to viral DNA polymerase inhibitors, including (S)-HPMPDAP. Both CMLV and VACV harboring the A314V change showed comparable drug-susceptibility profiles to various antivirals and similar impairments in viral growth. In contrast, the single change T831I and the double change A314V+A684V in VACV were responsible for increased levels of drug resistance and for cross-resistance to viral DNA polymerase antivirals that were not observed with their CMLV counterparts. Each amino acid change accounted for an attenuated phenotype of VACV in vivo. Modeling of E9L suggested that the T→I change at position 831 might abolish hydrogen bonds between E9L and the DNA backbone and have a direct impact on the incorporation of the acyclic nucleoside phosphonates. Our findings demonstrate that drug-resistance development in two related orthopoxvirus species may impact drug-susceptibility profiles and viral fitness differently.

Crystal structure of poxvirus thymidylate kinase: an unexpected dimerization has implications for antiviral therapy.

Unlike most DNA viruses, poxviruses replicate in the cytoplasm of host cells. They encode enzymes needed for genome replication and transcription, including their own thymidine and thymidylate kinases. Some herpes viruses encode only 1 enzyme catalyzing both reactions, a peculiarity used for prodrug activation to obtain maximum specificity. We have solved the crystal structures of vaccinia virus thymidylate kinase bound to TDP or brivudin monophosphate. Although the viral and human enzymes have similar sequences (42% identity), they differ in their homodimeric association and active-site geometry. The vaccinia TMP kinase dimer arrangement is orthogonal and not antiparallel as in human enzyme. This different monomer orientation is related to the presence of a canal connecting the edge of the dimer interface to the TMP base binding pocket. Consequently, the pox enzyme accommodates nucleotides with bulkier bases, like brivudin monophosphate and dGMP; these are efficiently phosphorylated and stabilize the enzyme. The brivudin monophosphate-bound structure explains the structural basis for this specificity, opening the way to the rational development of specific antipox agents that may also be suitable for poxvirus TMP kinase gene-based chemotherapy of cancer.

Phosphorylation of dGMP analogs by vaccinia virus TMP kinase and human GMP kinase.

Vaccinia virus thymidylate kinase, although similar in sequence to human TMP kinase, has broader substrate specificity and phosphorylates (E)-5-(2-bromovinyl)-dUMP and dGMP. Modified guanines such as glyoxal-dG, 8-oxo-dG, O(6)-methyl-dG, N(2)-ethyl-dG and N(7)-methyl-dG were found present in cancer cell DNA. Alkylated and oxidized dGMP analogs were examined as potential substrates for vaccinia TMP kinase and also for human TMP and GMP kinases. Molecular models obtained from structure-based docking rationalized the enzymatic data. All tested nucleotides are found surprisingly substrates of vaccinia TMP kinase and also of human GMP kinase. Interestingly, O(6)-methyl-dGMP is the only analog specific for the vaccinia enzyme. Thus, O(6)-Me-dGMP could be useful for designing new compounds of medical interest either in antipoxvirus therapy or in experimental combined gene/chemotherapy of cancer. These results also provide new insights regarding dGMP analog reaction with human GMP kinase and their slow recycling by salvage pathway nucleotide kinases.

Enantioselectivity of human AMP, dTMP and UMP-CMP kinases.

L-nucleoside analogues such as lamivudine are active for treating viral infections. Like D-nucleosides, the biological activity of the L-enantiomers requires their stepwise phosphorylation by cellular or viral kinases to give the triphosphate. The enantioselectivity of NMP kinases has not been thoroughly studied, unlike that of deoxyribonucleoside kinases. We have therefore investigated the capacity of L-enantiomers of some natural (d)NMP to act as substrates for the recombinant forms of human uridylate-cytidylate kinase, thymidylate kinase and adenylate kinases 1 and 2. Both cytosolic and mitochondrial adenylate kinases were strictly enantioselective, as they phosphorylated only D-(d)AMP. L-dTMP was a substrate for thymidylate kinase, but with an efficiency 150-fold less than D-dTMP. Both L-dUMP and L-(d)CMP were phosphorylated by UMP-CMP kinase although much less efficiently than their natural counterparts. The stereopreference was conserved with the 2'-azido derivatives of dUMP and dUMP while, unexpectedly, the 2'-azido-D-dCMP was a 4-fold better substrate for UMP-CMP kinase than was CMP. Docking simulations showed that the small differences in the binding of D-(d)NMP to their respective kinases could account for the differences in interactions of the L-isomers with the enzymes. This in vitro information was then used to develop the in vivo activation pathway for L-dT.

Nucleotide binding to human UMP-CMP kinase using fluorescent derivatives -- a screening based on affinity for the UMP-CMP binding site.

Methylanthraniloyl derivatives of ATP and CDP were used in vitro as fluorescent probes for the donor-binding and acceptor-binding sites of human UMP-CMP kinase, a nucleoside salvage pathway kinase. Like all NMP kinases, UMP-CMP kinase binds the phosphodonor, usually ATP, and the NMP at different binding sites. The reaction results from an in-line phosphotransfer from the donor to the acceptor. The probe for the donor site was displaced by the bisubstrate analogs of the Ap5X series (where X = U, dT, A, G), indicating the broad specificity of the acceptor site. Both CMP and dCMP were competitors for the acceptor site probe. To find antimetabolites for antivirus and anticancer therapies, we have developed a method of screening acyclic phosphonate analogs that is based on the affinity of the acceptor-binding site of the human UMP-CMP kinase. Several uracil vinylphosphonate derivatives had affinities for human UMP-CMP kinase similar to those of dUMP and dCMP and better than that of cidofovir, an acyclic nucleoside phosphonate with a broad spectrum of antiviral activities. The uracil derivatives were inhibitors rather than substrates of human UMP-CMP kinase. Also, the 5-halogen-substituted analogs inhibited the human TMP kinase less efficiently. The broad specificity of the enzyme acceptor-binding site is in agreement with a large substrate-binding pocket, as shown by the 2.1 A crystal structure.

Looking for new pyrimidine acyclic nucleotide analogues designed for phosphorylation by human UMP-CMP kinase.

Human UMP-CMP kinase is involved in the phosphorylation of nucleic acid precursors and also in the activation of antiviral analogues including cidofovir, an acyclic phosphonate compound that mimicks dCMP and shows a broad antiviral spectrum. The binding of ligands to the enzyme was here investigated using a fluorescent probe and a competitive titration assay. At the acceptor site, the enzyme was found to accommodate any base, purine and pyrimidine, including thymidine. A method for screening analogues based on their affinity for the UMP binding site was developed. The affinities of uracil vinylphosphonate derivatives modified in the 5 position were found similar to (d)UMP and (d)CMP and improved when compared to cidofovir.

Cross-metathesis mediated synthesis of new acyclic nucleoside phosphonates.

With the commercial availability of well-defined ruthenium metathesis catalysts which combine high stability and broad functional group compatibility, olefin metathesis is now routinely integrated in various syntheses. We will report here the overwhelming power and scope of cross-metathesis in the area of new acyclic nucleoside phosphonates. Scope and limitations of this approach, and especially the E/Z stereocontrol, are discussed on selected examples from our drug discovery group.

Alkyne-azide click chemistry mediated carbanucleosides synthesis.

Hitherto unknown 1,4-disubstituted-[1,2,3]-triazolo-4',4'-dihydroxymethyl-3'-deoxy carbanucleosides were synthesized based on a "click approach." Various alkynes were introduced on a key azido intermediate by the "click" 1,3-dipolar Huisgen cycloaddition. Their antiviral activities and cellular toxicities were evaluated on vaccinia virus. None of the synthesized compounds exhibited a significant antiviral activity.

Resistance to the nucleotide analogue cidofovir in HPV(+) cells: a multifactorial process involving UMP/CMP kinase 1.

Human papillomavirus (HPV) is responsible for cervical cancer, and its role in head and neck carcinoma has been reported. No drug is approved for the treatment of HPV-related diseases but cidofovir (CDV) exhibits selective antiproliferative activity. In this study, we analyzed the effects of CDV-resistance (CDVR) in two HPV(+) (SiHaCDV and HeLaCDV) and one HPV(-) (HaCaTCDV) tumor cell lines. Quantification of CDV metabolites and analysis of the sensitivity profile to chemotherapeutics was performed. Transporters expression related to multidrug-resistance (MRP2, P-gp, BCRP) was also investigated. Alterations of CDV metabolism in SiHaCDV and HeLaCDV, but not in HaCaTCDV, emerged via impairment of UMP/CMPK1 activity. Mutations (P64T and R134M) as well as down-regulation of UMP/CMPK1 expression were observed in SiHaCDV and HeLaCDV, respectively. Altered transporters expression in SiHaCDV and/or HeLaCDV, but not in HaCaTCDV, was also noted. Taken together, these results indicate that CDVR in HPV(+) tumor cells is a multifactorial process.

Substrate specificity of vaccinia virus thymidylate kinase.

Anti-poxvirus therapies are currently limited to cidofovir [(S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine], but drug-resistant strains have already been characterized. In the aim of finding a new target, the thymidylate (TMP) kinase from vaccinia virus, the prototype of Orthopoxvirus, has been overexpressed in Escherichia coli after cloning the gene (A48R). Specific inhibitors and alternative substrates of pox TMP kinase should contribute to virus replication inhibition. Biochemical characterization of the enzyme revealed distinct catalytic features when compared to its human counterpart. Sharing 42% identity with human TMP kinase, the vaccinia virus enzyme was assumed to adopt the common fold of nucleoside monophosphate kinases. The enzyme was purified to homogeneity and behaves as a homodimer, like all known TMP kinases. Initial velocity studies showed that the Km for ATP-Mg2+ and dTMP were 0.15 mm and 20 microM, respectively. Vaccinia virus TMP kinase was found to phosphorylate dTMP, dUMP and also dGMP from any purine and pyrimidine nucleoside triphosphate. 5-Halogenated dUMP such as 5-iodo-2'-deoxyuridine 5'-monophosphate (5I-dUMP) and 5-bromo-2'-deoxyuridine 5'-monophosphate (5Br-dUMP) were also efficient alternative substrates. Using thymidine-5'-(4-N'-methylanthraniloyl-aminobutyl)phosphoramidate as a fluorescent probe of the dTMP binding site, we detected an ADP-induced conformational change enhancing the binding affinity of dTMP and analogues. Several thymidine and dTMP derivatives were found to bind the enzyme with micromolar affinities. The present study provides the basis for the design of specific inhibitors or substrates for poxvirus TMP kinase.

Cidofovir selectivity is based on the different response of normal and cancer cells to DNA damage.

BACKGROUND: Cidofovir (CDV) proved efficacious in treatment of human papillomaviruses (HPVs) hyperplasias. Antiproliferative effects of CDV have been associated with apoptosis induction, S-phase accumulation, and increased levels of tumor suppressor proteins. However, the molecular mechanisms for the selectivity and antitumor activity of CDV against HPV-transformed cells remain unexplained. METHODS: We evaluated CDV drug metabolism and incorporation into cellular DNA, in addition to whole genome gene expression profiling by means of microarrays in two HPV(+) cervical carcinoma cells, HPV- immortalized keratinocytes, and normal keratinocytes. RESULTS: Determination of the metabolism and drug incorporation of CDV into genomic DNA demonstrated a higher rate of drug incorporation in HPV(+) tumor cells and immortalized keratinocytes compared to normal keratinocytes. Gene expression profiling clearly showed distinct and specific drug effects in the cell types investigated. Although an effect on inflammatory response was seen in all cell types, different pathways were identified in normal keratinocytes compared to immortalized keratinocytes and HPV(+) tumor cells. Notably, Rho GTPase pathways, LXR/RXR pathways, and acute phase response signaling were exclusively activated in immortalized cells. CDV exposed normal keratinocytes displayed activated cell cycle regulation upon DNA damage signaling to allow DNA repair via homologous recombination, resulting in genomic stability and survival. Although CDV induced cell cycle arrest in HPV- immortalized cells, DNA repair was not activated in these cells. In contrast, HPV(+) cells lacked cell cycle regulation, leading to genomic instability and eventually apoptosis. CONCLUSIONS: Taken together, our data provide novel insights into the mechanism of action of CDV and its selectivity for HPV-transformed cells. The proposed mechanism suggests that this selectivity is based on the inability of HPV(+) cells to respond to DNA damage, rather than on a direct anti-HPV effect. Since cell cycle control is deregulated by the viral oncoproteins E6 and E7 in HPV(+) cells, these cells are more susceptible to DNA damage than normal keratinocytes. Our findings underline the therapeutic potential of CDV for HPV-associated malignancies as well as other neoplasias.

Cidofovir treatment improves the pathology caused by the growth of human papillomavirus-positive cervical carcinoma xenografts in athymic nude mice.

Cidofovir has shown antiproliferative effects against human papillomavirus (HPV)-positive cells and successfully suppressed the growth of HPV-positive xenografts in athymic nude mice. The present study evaluated the effect of cidofovir on several disease parameters in this animal model. Intratumoral administration of cidofovir resulted in a beneficial effect on body weight gain, a reduction in splenomegaly, a partial restoration of tryptophan catabolism, and diminished the inflammatory state induced by the xenografts. Administration of cidofovir to tumor-free animals did not have a direct effect on these parameters. Beyond suppressing tumor growth, intratumoral treatment with cidofovir ameliorated the pathology associated with HPV-tumor growth.

Novel antiviral C5-substituted pyrimidine acyclic nucleoside phosphonates selected as human thymidylate kinase substrates.

Acyclic nucleoside phosphonates (ANPs) are at the cornerstone of DNA virus and retrovirus therapies. They reach their target, the viral DNA polymerase, after two phosphorylation steps catalyzed by cellular kinases. New pyrimidine ANPs have been synthesized with unsaturated acyclic side chains (prop-2-enyl-, but-2-enyl-, pent-2-enyl-) and different substituents at the C5 position of the uracil nucleobase. Several derivatives in the but-2-enyl- series 9d and 9e, with (E) but not with (Z) configuration, were efficient substrates for human thymidine monophosphate (TMP) kinase, but not for uridine monophosphate-cytosine monophosphate (UMP-CMP) kinase, which is in contrast to cidofovir. Human TMP kinase was successfully crystallized in a complex with phosphorylated (E)-thymidine-but-2-enyl phosphonate 9e and ADP. The bis-pivaloyloxymethyl (POM) esters of (E)-9d and (E)-9e were synthesized and shown to exert activity against herpes virus in vitro (IC(50) = 3 µM) and against varicella zoster virus in vitro (IC(50) = 0.19 µM), in contrast to the corresponding inactive (Z) derivatives. Thus, their antiviral activity correlates with their ability to act as thymidylate kinase substrates.