Activation by thymidine kinase and potent antiherpetic activity of 2'-nor-2'-deoxyguanosine (2'NDG)

Genome-wide screens connect HD82 loss-of-function to purine analog resistance in African trypanosomes

Nucleoside analogs have been used extensively as anti-infective agents, particularly against viral infections, and have long been considered promising anti-parasitic agents. These pro-drugs are metabolized by host-cell, viral, or parasite enzymes prior to incorporation into DNA, thereby inhibiting DNA replication. Here, we report genes that sensitize African trypanosomes to nucleoside analogs, including the guanosine analog, ganciclovir. We applied ganciclovir selective pressure to a trypanosome genome-wide knockdown library, which yielded nucleoside mono- and diphosphate kinases as hits, validating the approach. The two most dominant hits to emerge, however, were Tb927.6.2800 and Tb927.6.2900, which both encode nuclear proteins; the latter of which is HD82, a SAMHD1-related protein and a putative dNTP triphosphohydrolase. We independently confirmed that HD82, which is conserved among the trypanosomatids, can sensitize Trypanosoma brucei to ganciclovir. Since ganciclovir activity depends upon phosphorylation by ectopically expressed viral thymidine kinase, we also tested the adenosine analog, ara-A, that may be fully phosphorylated by native T. brucei kinase(s). Both Tb927.6.2800 and HD82 knockdowns were resistant to this analog. Tb927.6.2800 knockdown increased sensitivity to hydroxyurea, while dNTP analysis indicated that HD82 is indeed a triphosphohydrolase with dATP as the preferred substrate. Our results provide insights into nucleoside/nucleotide metabolism and nucleoside analog metabolism and resistance in trypanosomatids. We suggest that the product of 6.2800 sensitizes cells to purine analogs through DNA repair, while HD82 does so by reducing the native purine pool.IMPORTANCEThere is substantial interest in developing nucleoside analogs as anti-parasitic agents. We used genome-scale genetic screening and discovered two proteins linked to purine analog resistance in African trypanosomes. Our screens also identified two nucleoside kinases required for pro-drug activation, further validating the approach. The top novel hit, HD82, is related to SAMHD1, a mammalian nuclear viral restriction factor. We validated HD82 and localized the protein to the trypanosome nucleus. HD82 appears to sensitize trypanosomes to nucleoside analogs by reducing native pools of nucleotides, providing insights into both nucleoside/nucleotide metabolism and nucleoside analog resistance in trypanosomatids.

Efficient selection of knocked-in pluripotent stem cells using a dual cassette cellular elimination system

Although recent advances in genome editing technology with homology-directed repair have enabled the insertion of various reporter genes into the genome of mammalian cells, the efficiency is still low due to the random insertion of donor vectors into the host genome. To efficiently select knocked-in cells without random insertion, we developed the "double-tk donor vector system," in which the expression units of the thymidine kinase of herpes simplex virus (HSV-tk) are placed on both outer sides of homology arms. This system is superior in enriching knocked-in human induced pluripotent stem cells (hiPSCs) than conventional donor vector systems with a single or no HSV-tk cassette. Using this system, we efficiently generated fluorescent reporter knockin hiPSCs targeting POU5F1 (OCT3/4), EEF1A1, H2BC21 (H2B clustered histone 21), ISL1, and MYH7 genes. These results indicate that the double-tk donor vector system enables efficient selection of knocked-in hiPSCs carrying reporter proteins.

Evidence supporting the use of therapeutic drug monitoring of ganciclovir in transplantation

PURPOSE OF REVIEW

This review describes current knowledge of ganciclovir (GCV) and valganciclovir (ValGCV) pharmacokinetic/pharmacodynamic characteristics, highlighting the likely contribution from host genetic factors to interpatient variability. The evidence and challenges surrounding optimization of drug dosing through therapeutic drug monitoring (TDM) are examined, with recommendations made.

RECENT FINDINGS

Pharmacokinetic studies of current dosing guidelines have shown high interindividual and intraindividual variability of GCV concentrations. This is sometimes associated with a slow decline in cytomegalovirus (CMV) viral load in some transplant recipients. A high incidence of GCV-associated myelosuppression has limited the use of this drug in the transplant setting. Patient groups identified to benefit from GCV TDM include pediatric patients, cystic fibrosis with lung transplantation, obese with kidney transplantation, and patients with fluctuating renal function or on hemodialysis. The emergence of refractory resistant CMV, particularly in immune compromised patients, highlights the importance of appropriate dosing of these antivirals. Host genetic factors need to be considered where recently, two host genes were shown to account for interpatient variation during ganciclovir therapy. Therapeutic Drug Monitoring has been shown to improve target antiviral-level attainment. The use of TDM may guide concentration-based dose adjustment, potentially improving virological and clinical outcomes. However, evidence supporting the use of TDM in clinical practice remains limited and further study is needed in the transplant cohort.

SUMMARY

Further studies examining novel biomarkers are needed to guide target concentrations in prophylaxis and treatment. The use of TDM in transplant recipients is likely to improve the clinical efficacy of current antivirals and optimize outcomes in transplant recipients.

NUDT15 polymorphism influences the metabolism and therapeutic effects of acyclovir and ganciclovir

Nucleobase and nucleoside analogs (NNA) are widely used as anti-viral and anti-cancer agents, and NNA phosphorylation is essential for the activity of this class of drugs. Recently, diphosphatase NUDT15 was linked to thiopurine metabolism with NUDT15 polymorphism associated with drug toxicity in patients. Profiling NNA drugs, we identify acyclovir (ACV) and ganciclovir (GCV) as two new NNAs metabolized by NUDT15. NUDT15 hydrolyzes ACV and GCV triphosphate metabolites, reducing their effects against cytomegalovirus (CMV) in vitro. Loss of NUDT15 potentiates cytotoxicity of ACV and GCV in host cells. In hematopoietic stem cell transplant patients, the risk of CMV viremia following ACV prophylaxis is associated with NUDT15 genotype (P = 0.015). Donor NUDT15 deficiency is linked to graft failure in patients receiving CMV-seropositive stem cells (P = 0.047). In conclusion, NUDT15 is an important metabolizing enzyme for ACV and GCV, and NUDT15 variation contributes to inter-patient variability in their therapeutic effects.

Solution structure and functional investigation of human guanylate kinase reveals allosteric networking and a crucial role for the enzyme in cancer

Human guanylate kinase (hGMPK) is the only known enzyme responsible for cellular GDP production, making it essential for cellular viability and proliferation. Moreover, hGMPK has been assigned a critical role in metabolic activation of antiviral and antineoplastic nucleoside-analog prodrugs. Given that hGMPK is indispensable for producing the nucleotide building blocks of DNA, RNA, and cGMP and that cancer cells possess elevated GTP levels, it is surprising that a detailed structural and functional characterization of hGMPK is lacking. Here, we present the first high-resolution structure of hGMPK in the apo form, determined with NMR spectroscopy. The structure revealed that hGMPK consists of three distinct regions designated as the LID, GMP-binding (GMP-BD), and CORE domains and is in an open configuration that is nucleotide binding-competent. We also demonstrate that nonsynonymous single-nucleotide variants (nsSNVs) of the hGMPK CORE domain distant from the nucleotide-binding site of this domain modulate enzymatic activity without significantly affecting hGMPK's structure. Finally, we show that knocking down the hGMPK gene in lung adenocarcinoma cell lines decreases cellular viability, proliferation, and clonogenic potential while not altering the proliferation of immortalized, noncancerous human peripheral airway cells. Taken together, our results provide an important step toward establishing hGMPK as a potential biomolecular target, from both an orthosteric (ligand-binding sites) and allosteric (location of CORE domain-located nsSNVs) standpoint.

1H, 13C and 15N resonance assignment of human guanylate kinase

Human guanylate kinase (hGMPK) is a critical enzyme that, in addition to phosphorylating its physiological substrate (d)GMP, catalyzes the second phosphorylation step in the conversion of anti-viral and anti-cancer nucleoside analogs to their corresponding active nucleoside analog triphosphates. Until now, a high-resolution structure of hGMPK is unavailable and thus, we studied free hGMPK by NMR and assigned the chemical shift resonances of backbone and side chain ¹H, ¹³C, and ¹⁵N nuclei as a first step towards the enzyme's structural and mechanistic analysis with atomic resolution.

Ganciclovir

Ganciclovir is synthetic nucleoside analog of guanine closely related to acyclovir but has greater activity against cytomegalovirus. This comprehensive profile on ganciclovir starts with a description of the drug: nomenclature, formulae, chemical structure, elemental composition, and appearance. The uses and application of the drug are explained. The methods that were used for the preparation of ganciclovir are described and their respective schemes are outlined. The methods which were used for the physical characterization of the dug are: ionization constant, solubility, X-ray powder diffraction pattern, crystal structure, melting point, and differential scanning calorimetry. The chapter contains the spectra of the drug: ultraviolet spectrum, vibrational spectrum, nuclear magnetic resonance spectra, and the mass spectrum. The compendial methods of analysis of ganciclovir include the United States Pharmacopeia methods. Other methods of analysis that were reported in the literature include: high-performance liquid chromatography alone or with mass spectrometry, electrophoresis, spectrophotometry, voltammetry, chemiluminescence, and radioimmunoassay. Biological investigation on the drug includes: pharmacokinetics, metabolism, bioavailability, and biological analysis. Reviews on the methods used for preparation or for analysis of the drug are provided. The stability of the drug in various media and storage conditions is reported. More than 240 references are listed at the end of the chapter.

How I treat resistant cytomegalovirus infection in hematopoietic cell transplantation recipients

Cytomegalovirus (CMV) infection is a significant complication in hematopoietic cell transplantation (HCT) recipients. Four antiviral drugs are used for preventing or treating CMV: ganciclovir, valganciclovir, foscarnet, and cidofovir. With prolonged and repeated use of these drugs, CMV can become resistant to standard therapy, resulting in increased morbidity and mortality, especially in HCT recipients. Antiviral drug resistance should be suspected when CMV viremia (DNAemia or antigenemia) fails to improve or continue to increase after 2 weeks of appropriately dosed and delivered antiviral therapy. CMV resistance is diagnosed by detecting specific genetic mutations. UL97 mutations confer resistance to ganciclovir and valganciclovir, and a UL54 mutation confers multidrug resistance. Risk factors for resistance include prolonged or previous anti-CMV drug exposure or inadequate dosing, absorption, or bioavailability. Host risk factors include type of HCT and degree of immunosuppression. Depending on the genotyping results, multiple strategies can be adopted to treat resistant CMV infections, albeit no randomized clinical trials exist so far, after reducing immunosuppression (if possible): ganciclovir dose escalation, ganciclovir and foscarnet combination, and adjunct therapy such as CMV-specific cytotoxic T-lymphocyte infusions. Novel therapies such as maribavir, brincidofovir, and letermovir should be further studied for treatment of resistant CMV.

Effects of Penciclovir and Famciclovir in a Murine Model of Encephalitis Induced by Intranasal Inoculation of Herpes Simplex Virus Type 1

Mice inoculated intranasally with a potentially lethal dose of HSV-1 (strain SC16) were used to evaluate the efficacy of penciclovir (PCV) and its oral form, famciclovir (FCV) in the treatment of acute herpes encephalitis. In a comparative experiment, orally administered PCV was less effective than ganciclovir (GCV) in reducing mortality of infected mice, but was of similar effectivenss to acyclovir (ACV), Late deaths from ongoing infections were observed following cessation of treatment with both ACV and FCV. Delaying the onset of treatment by more than 1 day post infection markedly reduced the ability of orally administered ACV, PCV, and FCV to prevent death. Treatment from day 1 with FCV administered ad libitum in the drinking water resulted in rapid clearance of infectious virus from all parts of the brain, but latent virus was detected by Southern blot hybridization in the peripheral and central nervous system of survivors 1 month post infection. In untreated mice, infectious virus was also detected in the epithelium of the turbinate bones and in the lungs from 1 day after intranasal inoculation, and acute inflammatory changes were seen in the lungs. FCV was more effective in clearing virus from the lungs than from the turbinate bones in these mice. These data, concerning the importance of virus replication in the respiratory tract with regard to subsequent encephalitis, are considered to be a novel aspect of this study.

Antiviral Drugs

Viruses are major pathogenic agents causing a variety of serious diseases in humans, other animals, and plants.

Drugs that combat viral infections are called antiviral drugs. There are no effective antiviral drugs for many viral infections. However, there are several drugs for influenza, a couple of drugs for herpesviruses, and some new antiviral drugs for treatment of HIV and hepatitis C infections.

The arsenal of antivirals is complex. As of March 2014, it consists of approximately 50 drugs approved by the FDA, approximately half of which are directed against HIV. Antiviral drug creation strategies are focused on two different approaches: targeting the viruses themselves or targeting host cell factors.

Direct virus-targeting antiviral drugs include attachment inhibitors, entry inhibitors, uncoating inhibitors, protease inhibitors, polymerase inhibitors, nucleoside and nucleotide reverse transcriptase inhibitors, nonnucleoside reverse-transcriptase inhibitors, and integrase inhibitors.

Protease inhibitors (darunavir, atazanavir, and ritonavir), viral DNA polymerase inhibitors (acyclovir, valacyclovir, valganciclovir, and tenofovir), and an integrase inhibitor (raltegravir) are included in the list of Top 200 Drugs by sales for the 2010s.

Pharmacokinetic considerations in the use of antivirals in neonates

INTRODUCTION

Neonatal patients, because of the inability of their immune system to properly respond to microbial challenge, are highly susceptible to viral infections. Immunoglobulins, monoclonal antibody and antiviral drugs are used for prophylaxis and treatment of viral diseases in neonates. Neonates and, especially, preterm infants differ in drug absorption, distribution, metabolism and excretion from adults and older children.

AREAS COVERED

This review will evaluate deficiencies of neonatal immune responses to microbial challenge that predispose newborns to viral infections, clinical manifestations and the treatment of viral diseases in neonates. We focus on published studies describing antiviral drug pharmacokinetics in neonates and make recommendations on the dosing of these drugs, allowing achievement of maximal clinical benefits in neonates.

EXPERT OPINION

While some efforts were undertaken to study pharmacokinetics and pharmacodynamics of antiviral drugs, much more needs to be done. Current data indicate that the pharmacokinetics of antiviral drugs may vary significantly depending on gestational age, maturation processes of drug-metabolizing enzymes and renal clearance. Specifics of pharmacokinetics of antiviral drugs need to be taken into consideration when they are prescribed to neonates and infants.

Clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir in children with cytomegalovirus infection

INTRODUCTION

Among infants and immunocompromised children cytomegalovirus (CMV) is associated with significant morbidity and mortality.

AREAS COVERED

This review describes the clinical pharmacokinetics and pharmacodynamics of ganciclovir and valganciclovir for the treatment and prevention of CMV infection in children.

EXPERT OPINION

A 24-h ganciclovir area under the concentration versus time curve (AUC₀₋₂₄) of 40 - 60 μg h/ml decreased the risk of CMV infection for adults undergoing CMV prophylaxis. For adults undergoing treatment for active CMV disease, a target AUC₀₋₁₂ of 40 - 60 μg h/ml has been suggested. The applicability of these targets to children remains uncertain; however, with the most sophisticated dosing regimens developed to date only 21% of patients are predicted to reach these targets. Moving forward, identification of optimal pediatric ganciclovir and valganciclovir dosing regimens may involve the use of an externally validated pediatric population pharmacokinetic model for empirical dosing, an optimal sampling strategy for collecting a minimal number of blood samples for each patient and Bayesian updating of the dosing regimen based on an individual patient's pharmacokinetic profile.

Enzymes to die for: exploiting nucleotide metabolizing enzymes for cancer gene therapy

Suicide gene therapy is an attractive strategy to selectively destroy cancer cells while minimizing unnecessary toxicity to normal cells. Since this idea was first introduced more than two decades ago, numerous studies have been conducted and significant developments have been made to further its application for mainstream cancer therapy. Major limitations of the suicide gene therapy strategy that have hindered its clinical application include inefficient directed delivery to cancer cells and the poor prodrug activation capacity of suicide enzymes. This review is focused on efforts that have been and are currently being pursued to improve the activity of individual suicide enzymes towards their respective prodrugs with particular attention to the application of nucleotide metabolizing enzymes in suicide cancer gene therapy. A number of protein engineering strategies have been employed and our discussion here will center on the use of mutagenesis approaches to create and evaluate nucleotide metabolizing enzymes with enhanced prodrug activation capacity and increased thermostability. Several of these studies have yielded clinically important enzyme variants that are relevant for cancer gene therapy applications because their utilization can serve to maximize cancer cell killing while minimizing the prodrug dose, thereby limiting undesirable side effects.

Acyclonucleosides: Part 2. diseco-Nucleosides

This chapter is the second of a sequence of three chapters that appears in successive volumes of this series dealing with the chemistry of acyclonucleosides. The first chapter appeared in the previous volume [97AHC391] and dealt with seco-nucleosides (one bond disconnection). This chapter deals with diseco-nucleosides (two bond disconnections). The final chapter of this series will deal with tri-, tetra-, and pentaseco-nucleosides, as well as contain an appendix of the literature that appeared after the three chapters were prepared.

Synthesis and antimicrobial evaluation of guanylsulfonamides

A series of guanylsulfonamides, 2-amino-9-[2-substituted-4-(4-substituted piperidin-1-sulfonyl)phenyl]-1,9-dihydropurin-6-ones, was synthesized by adopting reductive aminoformylation of 2-amino-5-nitro-6-[4-(piperidin-1-sulfonyl)phenylamino]-3H-pyrimidin- 4-one and subsequent intramolecular ring condensation as key steps. All the guanylsulfonamides were assayed for their in vitro antibacterial activities against Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, and Streptococcus faecalis, and their antifungal activities against Aspergillus flavus, Aspergillus niger, and Candida albicans. Of the guanylsulfonamides, 13e and 13f displayed better antibacterial activities than that of Norfloxacin against the bacterial strains S. aureus and S. faecalis except 13f against S. faecalis, which exhibited the activity similar to that of Norfloxacin. Against the fungal strains A. flavus and A. niger, 13g and 13h showed similar activities to that of Griseoflavin-16 except 13h against A. niger, which displayed a profound drop in the activity compared to that of Griseoflavin-16. The remarkable inhibition of the growth of the bacterial and fungal strains makes these substances promising microbial agents.

Tricyclic nucleoside analogues as antiherpes agents

Tricyclic (T) guanine analogues are a class of compounds in which the N1 and N(2) atoms of the guanine system are linked by etheno bridge to form the 3,9-dihydro-9-oxo-5H-imidazo[1,2-a]purine system. Almost 70 tricyclic derivatives of guanine-type potent antiherpetic agents acyclovir (ACV), ganciclovir (GCV) and 9-{[cis-1',2'-bis(hydroxymethyl)cycloprop-1'-yl]methyl}guanine were synthesized and evaluated for activity against viruses of the herpes family. Here, we review the most successful compounds in terms of their antiviral activity and physico-chemical properties. These features are modulated by the kind and position of additional substituents present in the appended third ring of aglycone. The best antiherpetic activity-fluorescence combinations as well as activity of compounds in comparison to parent congeners are summarized. The data presented indicate that compounds of the 6-(4-RPh) family are of particular importance because of their advantageous antiviral potency, increased lipophilicity and good or moderate fluorescence properties.

An efficient synthesis of acyclic N7- and N9-adenine nucleosides via alkylation with secondary carbon electrophiles to introduce versatile functional groups at the C-1 position of acyclic moiety

The introduction of versatile functional groups, allyl and ester, at the C-1 position of the acyclic chain in acyclic adenine nucleosides was achieved for the first time directly by alkylation of adenine and N6-potected adenine. Thus, the C-1'-substituted N9-adenine acyclic nucleoside, adenine-9-yl-pent-4-enoic acid ethyl ester (11), was prepared by direct alkylation of adenine with 2-bromopent-4-enoic acid ethyl ester (6), while the corresponding N7-regioisomer, 2-[6-(dimethylaminomethyleneamino)-purin-7-yl]-pent-4-enoic acid ethyl ester (10), was obtained in one step by the coupling of N, N-dimethyl-N'- (9H-purin-6-yl)-formamidine (9) with 2-bromopent-4-enoic acid ethyl ester (6). The functional groups, ester and allyl, were converted to the desired hydroxymethyl and hydroxyethyl groups, and subsequently to phosphonomethyl derivatives and corresponding pyrophosphorylphosphonates.

Synthesis of 9-[1-(substituted)-3-(phosphonomethoxy)propyl]adenine derivatives as possible antiviral agents

Acyclic N9 adenine nucleosides substituted at C-1' position were prepared by the Mitsunobu reaction of 1-tert-butyldimethylsilyl-4-pivaloylbutan-1,2,4-triol (5) with adenine. Pivaloyl hydroxyl was modified to the phosphonomethoxy derivatives, and the tert-butyldimethylsilyl hydroxyl was converted to methoxy, azido, amino, fluoro, and c-hydroxyethyl and was eliminated to give vinyl. The resulting phosphonic acids were converted to prodrugs also.

Synthesis of 9-[1-(substituted)-2-(phosphonomethoxy)ethyl]adenine derivatives as possible antiviral agents

Various C-1'-substituted acyclic N9 adenine nucleosides were prepared from 9-[(1-hydroxymethyl)(3-monomethoxytrityloxy)propyl]-N6-monomethoxytrityladenine. The hydroxymethyl was modified to the phosphonomethoxy derivative, and the 3-monomethoxytrityloxy was converted to hydroxyl, methoxy, azido, and amino. Other substituents, such as ethyl and ea-hydroxyethyl were also prepared. The resulting phosphonomethoxy derivatives were converted to prodrugs.

The role of a HSV thymidine kinase stimulating substance, scopadulciol, in improving the efficacy of cancer gene therapy

BACKGROUND

The most extensively investigated strategy of suicide gene therapy for treatment of cancer is the transfer of the herpes simplex virus thymidine kinase (HSV-TK) gene followed by administration of antiviral prodrugs such as acyclovir (ACV) and ganciclovir (GCV). The choice of the agent that can stimulate HSV-TK enzymatic activity is one of the determinants of the usefulness of this strategy. Previously, we found that a diterpenoid, scopadulciol (SDC), produced a significant increase in the active metabolite of ACV. This suggests that SDC may play a role in the HSV-TK/prodrug administration system.

METHODS

The anticancer effect of SDC was evaluated in HSV-TK-expressing (TK+) cancer cells and nude mice bearing TK+ tumors. In vitro and in vivo enzyme assays were performed using TK+ cells and tumors. The phosphorylation of ACV monophosphate (ACV-MP) was measured in TK- cell lysates. The pharmacokinetics of prodrugs was evaluated by calculating area-under-the-concentration-time-curve values.

RESULTS

SDC stimulated HSV-TK activity in TK+ cells and tumors, and increased GCV-TP levels, while no effect of SDC was observed on the phosphorylation of ACV-MP to ACV-TP by cellular kinases. The SDC/prodrug combination altered the pharmacokinetics of the prodrugs. In accord with these findings, SDC enhanced significantly the cell-killing activity of prodrugs. The bystander effect was also significantly augmented by the combined treatment of ACV/GCV and SDC.

CONCLUSIONS

SDC was shown to be effective in the HSV-TK/prodrug administration system and improved the efficiency of the bystander effect of ACV and GCV. The findings will be considerably valuable with respect to the use of GCV in lower doses and less toxic ACV. This novel strategy of drug combination could provide benefit to HSV-TK/prodrug gene therapy.

Chemical library screen for novel inhibitors of Kaposi's sarcoma-associated herpesvirus processive DNA synthesis

Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma and certain lymphoproliferative disorders. The role of KSHV lytic replication has been implicated in the tumor pathogenesis. A highly specific molecular complex formed by the KSHV DNA polymerase (POL8) and processivity factor (PF8) is indispensable for lytic viral DNA synthesis and may serve as an excellent molecular anti-KSHV target. The majority of conventional nucleoside-based anti-herpetic DNA synthesis inhibitors require intracellular phosphorylation/activation before they can exert inhibitory activity as competitive substrates for viral DNA polymerases. Novel and more potent inhibitors of KSHV DNA synthesis may be discovered through POL8/PF8-targeted high throughput screening (HTS) of small molecule chemical libraries. We developed a microplate-based KSHV POL8/PF8-mediated DNA synthesis inhibition assay suitable for HTS and screened the NCI Diversity Set that comprised 1992 synthetic compounds. Twenty-eight compounds exhibited greater than 50% inhibition. The inhibitory activity was confirmed for 25 of the 26 hit compounds available for further testing, with the 50% inhibitory concentrations ranging from 0.12+/-0.07 microM (mean+/-S.D.) to 10.83+/-4.19 microM. Eighteen of the confirmed active compounds efficiently blocked KSHV processive DNA synthesis in vitro. One of the hit compounds, NSC 373989, a pyrimidoquinoline analog, was shown to dose-dependently reduce the levels of KSHV virion production and KSHV DNA in lytically induced KSHV-infected BCBL-1 cells, suggesting that the compound blocked lytic KSHV DNA synthesis. HTS for KSHV POL8/PF8 inhibitors is feasible and may lead to discovery of novel non-nucleoside KSHV DNA synthesis inhibitors.

Evaluation of scopadulciol-related molecules for their stimulatory effect on the cytotoxicity of acyclovir and ganciclovir against Herpes simplex virus type 1 thymidine kinase gene-transfected HeLa cells

Herpes simplex virus type 1 thymidine kinase (HSV TK) is involved in both antiherpetic therapy and cancer gene therapy with acyclovir (ACV) and ganciclovir (GCV). Enhanced sensitivity to these drugs is advantageous in their clinical use. In the present study, scopadulciol (SDC) and its related compounds were evaluated for their stimulatory effect on the cytotoxicity of ACV and GCV by determination of selective toxicities against HSV TK-expressing HeLa cells. Although SDC remarkably potenciated the cytotoxicity of ACV and GCV, the other tested compounds showed only weak selectivity, except for compound 34.

Emerging biological therapies for pancreatic carcinoma

AIMS

The incidence of pancreatic carcinoma remains approximately equal to its mortality, with the vast majority of patients having advanced disease at presentation. This review is an update of the promising novel approaches involving biological therapy that may be used in conjunction with new chemotherapeutic agents in the near future.

METHODS

A literature review was performed using the National Library of Medicine's Pubmed database, combined with recently published data from the AGA and ASCO conferences.

RESULTS

Rapid progress is being made in gene and molecular technology potentially enabling us to inhibit pancreatic carcinogenesis and to reduce disease progression. Different targets include signal transduction inhibitors, gene therapy, genetic prodrug activation therapy, antisense therapy, immunotherapy, matrix metalloproteinase and cyclo-oxygenase-2 inhibition and hormonal manipulation.

CONCLUSION

A variety of biological agents are currently undergoing clinical trials, targeting different areas of the pancreas'neoplastic process. .

Biosynthetic ganciclovir triphosphate: its isolation and characterization from ganciclovir-treated herpes simplex thymidine kinase-transduced murine cells

A method is described for the preparation of ganciclovir triphosphate (GCV-TP) using murine colon cancer cells (MC38) transduced with the herpes simplex virus-thymidine kinase (MC38/HSV-tk). Murine cells transduced with viral-tk contain required viral and host enzymes needed for complete cellular synthesis of this potent antiviral metabolite. Dose response studies showed optimal intracellular levels of GCV-TP occurred after exposure of MC38/HSV-tk cells to 300 microM ganciclovir for 24 h producing 7.5 nmol GCV-TP/10(6) cells. This reflects cellular accumulation of GCV-TP to levels 25-fold greater than the medium concentration of parent drug. A simple isolation scheme included methanolic extraction and anion-exchange chromatography to recover the target triphosphate. Mass spectral analysis and selective enzyme degradation provided structural confirmation of the purified product. Biological activity of the purified GCV-TP was demonstrated by competitive inhibition experiments using human DNA polymerase alpha and HSV DNA polymerase that showed substantially greater sensitivity for the viral polymerase in agreement with previous reports. The GCV-TP obtained was further used to enzymatically prepare GCV mono- and diphosphate in high yield. This method provides an easily scalable means of preparing milligram amounts of the triphosphates of pharmacologically active acyclic nucleosides like ganciclovir.

Molecular technology and pancreatic cancer

BACKGROUND

Pancreatic cancer is the fifth leading cause of cancer death in the Western world. Despite improvement in operative mortality rates, little impact has been made on overall 5-year survival. This review discusses the molecular changes peculiar to pancreatic cancer and how the use of molecular technology might affect detection, screening, diagnosis and treatment of the disease.

METHODS

A literature review was performed using the National Library of Medicine's Pubmed database; this was combined with ongoing work within the Queen Elizabeth Hospital, Birmingham.

RESULTS

Over the past 20 years great strides have been made in our understanding of the molecular basis of disease. Advances in molecular biology are now reshaping how diseases are screened for, diagnosed, investigated and treated. In recent years collaboration between clinicians and basic scientists has revealed a unique pattern of genetic and molecular events in pancreatic cancer. This review discusses how these advances may impact on patients with this disease.

CONCLUSION

The past decade has seen some improvement in outlook for patients with pancreatic cancer, but the 'molecular age' promises to deliver even better results.

Novel non-operative treatment and treatment strategies in pancreatic cancer

Patients with advanced pancreatic cancer have traditionally been treated with palliative care only. The last decade has seen significant improvements in the surgical treatment of this disease but until the late 1990s there was no effective non-surgical treatment for these tumours. The introduction of gemcitabine has given clinicians treating patients with pancreatic cancer a new option. The published randomised data of gemcitabine in patients with pancreatic cancer has shown both a small survival advantage and significant improvements in quality of life indicators in these patients. These data have stimulated a resurgence of interest in pancreatic tumours and several studies have been or are currently investigating novel treatments or treatment strategies. The explosion in the molecular knowledge of cancer has led to the development of several 'molecular designer drugs' that have been tested in pancreatic cancer. The furthest advanced of these is a matrix metalloproteinase (MMP) inhibitor called marimastat. The first randomised data using this new class of agents is increasing and suggests that marimastat may have a role in the future treatment of patients with pancreatic cancer. Other agents such as gastrimmune, are about to enter Phase III studies and several other molecular treatment strategies are progressing from the in vitro stage towards the clinical arena. Each of these treatments and treatment regimens are discussed along with their current progress.

Antiviral activity of ganciclovir elaidic acid ester against herpesviruses

A fatty acid derivative of ganciclovir (GCV), elaidic acid ganciclovir (E-GCV), has been evaluated for its inhibitory activity against laboratory and clinical strains of herpes simplex type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV) and human cytomegalovirus (HCMV) in human embryonic lung fibroblasts. GCV, cidofovir, acyclovir (ACV), brivudin (BVDU) and foscarnet (PFA) were included as reference compounds. The viruses studied were wild-type, thymidine kinase-deficient (TK(-)) and PFA-resistant (PFA(r)) HSV strains. The IC(50) values obtained for E-GCV were 5- to 30-fold lower than those observed for GCV, the IC(50) value of E-GCV for HSV-1 strain KOS being 0.07 nM. A similarly increased activity of E-GCV (as compared to GCV) was noted for TK(-) and PFA(r) HSV-1 or HSV-2 strains. However, E-GCV did not exhibit superior activity over GCV to VZV or HCMV in vitro. The antiviral efficacy of E-GCV was also evaluated in vivo against intracerebral HSV-2 infection in NMRI mice. Animals were treated intraperitoneally or perorally with E-GCV, GCV or placebo once daily for 10 days, starting the day of infection. E-GCV compared to GCV at equimolar doses, proved markedly more efficacious than GCV in terms of reduction of mortality rate and delay of mean time of death. The elaidic acid ester of GCV should therefore be considered as a novel approach towards the treatment of HSV infections.

A Simple Solution to the Age Old Problem of Regioselective Functionalization of Guanine: First Practical Synthesis of Acyclic N(9)- and/or N(7)-Guanine Nucleosides Starting from N(2),N(9)-Diacetylguanine

Regioselective alkylation of guanine, a long-lasting challenge, has been overcome by understanding the role of acids as catalyst in the coupling reaction of DAG (10) with OBDDA (11). The acid-catalyzed and noncatalyzed reactions of 10 with OBDDA which mainly give N(7) and N(9) isomers, respectively, appear to follow different mechanisms. The practical utility of the noncatalyzed reaction, which gives almost quantitative yields of N(9) derivatives, is demonstrated by synthesizing acylovir/gancyclovir in high yields.

Acyclic oligonucleotide analogues

Acyclic analogues of oligothymidylate and oligoadenylate and their alternating copolymers were synthesized to study their thermal melting, their stability against snake venom phosphodiesterase and their primer/template properties using the Klenow fragment of the Escherichia coli DNA polymerase I enzyme. Acyclic dodecaadenylate (GlyA)12 hybridized to dodecathymidylate p(dT)12, and the complex presented a sharp melting with a Tm at 24 degrees C. This association was confirmed by circular dichroism curves which were similar to those of the natural oligonucleotide duplexes in A-conformation. (GlyA)12 proved very stable against snake venom phosphodiesterase hydrolysis. The reaction rate was more than 10,000 times slower than that of p(dT)12. (GlyA)12 served as a primer for the Klenow DNA polymerase. When (GlyA)12 was complexed with the poly(dT) template, the enzyme polymerized dATP but the reaction was much slower than with the (GlyT)12 primer. Molecular modelling of atactic (GlyA)12.(dT)12 of the A-conformation indicates that this conformation is energetically possible.

Hepatic purine and pyrimidine metabolism: implications for antiviral chemotherapy of viral hepatitis

The use of nucleoside analogues as antiviral agents is expanding. For most nucleoside analogues, intracellular phosphorylation is the major prerequisite for activity. Antiviral activity may be limited by poor uptake, absence of appropriate activating enzymes, catabolism, and competition from endogenous nucleotides. Appreciation of these factors, which are species-, tissue- and cell-specific is important in the understanding of the pharmacology and toxicology of nucleoside analogues. The use of nucleoside analogues against the agents of viral hepatitis is inherently problematic for many reasons including active hepatic nucleoside catabolism, probable absence of virus-specific activating enzymes, competition from endogenous nucleotides synthesised de novo or derived from RNA turnover, and factors related to mitochondrial toxicity. Despite these drawbacks, some nucleoside analogues have been found efficacious against hepatitis B virus and it is likely that as knowledge of their mechanism of action accumulates, their efficacy can be improved both by rational drug design and by use in combination with other drugs, including interferon.

Synthesis, antiviral activity and enzymatic phosphorylation of 9-phosphonopentenyl derivatives of guanine

(E)-9-(5-Phosphonopent-4-enyl)guanine and (E)-9-[3-(hydroxymethyl)-5- phosphonopent-4-enyl]guanine which bear a vinyl phosphonate moiety as a mimic of the phosphate group were synthesized. Their activities against human immunodeficiency virus type-1 (HIV-1), herpes simplex virus type-1 (HSV-1) and human cytomegalovirus (HCMV) were evaluated in vitro in parallel with those of 9-(5-phosphonopentyl)guanine and 9-(5,5-difluoro-5- phosphonopentyl)guanine. Both vinyl phosphonates exhibited anti-HIV-1 and anti-HCMV activities, whereas the methyl- and difluoromethyl phosphonate analogues were inactive. The selectivity index, calculated as the ratio of the toxicity for the host cells (50% reduction in cell viability or in [methyl-3H]thymidine incorporation) to the 50% inhibitory concentration for HIV-1 replication, was the highest for (E)-9-[3-(hydroxymethyl)-5-phosphonopent-4-enyl]guanine. The acyclonucleotide analogues were also studied as substrates of guanylate kinase, an enzyme believed to play a critical role in the conversion of acyclic phosphate and phosphonate derivatives of guanine to their antivirally active diphosphate derivatives. (E)-9-(5-Phosphonopent-4- enyl)guanine and (E)-9-[3-(hydroxymethyl)-5-phosphonopent-4-enyl]guanine were good substrates of guanylate kinase, being phosphorylated with efficiencies of 14 and 36% of that determined for GMP, respectively. These results contrast with the poor efficiency found for 9-(5-phosphonopentyl)guanine (0.3%) and the lack of phosphorylation of 9-(5,5-difluoro-5-phosphonopentyl)guanine by guanylate kinase (Navé et al. (1992) Arch. Biochem. Biophys. 295, 253-257). The role of the vinyl phosphonate group in the expression of the anti-HIV-1 activity of the phosphonopentenyl derivatives of guanine is discussed.

Stereochemical Aspects of the anti-HCMV Activity of Cytidine Nucleoside Analogues

The remarkable selectivity of the β-L enantiomers of 2′,3′-dideoxycytidine analogues against the viral polymerases of HIV and HBV has stimulated our interest in targeting β-L enantiomers of anti-HCMV cytidine analogues. Indeed, Ara-C, FIAC and DMDC are cytidine analogues with β-D configuration that show significant potency as anti-HCMV agents but lack selectivity. β-L enantiomers have therefore been synthesized and evaluated together with four other nucleoside analogues, and the β-L. enantiomers were found not to be inhibitory to HCMV replication. However, the three α-L isomers, α-L-Ara-C, α-L-Xylo-C and α-L-FMAU, emerged with activity against HCMV and have provided new approaches for the treatment of viral diseases with nucleoside analogues possessing the unusual L-configuration.

Retroviral transfer of HSV1-TK gene into human lung cancer cell line

We used a recombinant retrovirus as one of the potential vectors for human gene therapy to transfer a drug sensitivity gene into human lung cancer cells. The gene encoding the thymidine kinase (TK) of herpes simplex virus type 1 (HSV1) was used as the drug sensitivity gene. The antiherpes drugs acyclovir (ACV) and ganciclovir (GCV) were chosen to test the HSV1-TK activity transferred into the human lung cancer cell lines. The rationale for this approach was that ACV and GCV are nucleoside analogs specifically converted by HSV1-TK to a toxic form capable of inhibiting DNA synthesis or disrupting cellular DNA replication. The results obtained from our experiments demonstrate that the retroviral vector-mediated HSV1-TK gene transfer leads to ACV- and GCV-dependent cytotoxicity in human lung cancer cell lines, including both small-cell carcinoma and non-small-cell carcinoma. Although the gene transfer of HSV1-TK gene into tumor cells would be one model for gene therapy to control lung cancer, further investigations are necessary for the proper choice of the therapeutic gene and vector targeting such as tumor cell specific delivery of the gene or tumor cell specific expression of the transduced gene.