Analysis of the ex vivo and in vivo antiretroviral activity of gemcitabine

Unveiling the Connection: Viral Infections and Genes in dNTP Metabolism

Deoxynucleoside triphosphates (dNTPs) are crucial for the replication and maintenance of genomic information within cells. The balance of the dNTP pool involves several cellular enzymes, including dihydrofolate reductase (DHFR), ribonucleotide reductase (RNR), and SAM and HD domain-containing protein 1 (SAMHD1), among others. DHFR is vital for the de novo synthesis of purines and deoxythymidine monophosphate, which are necessary for DNA synthesis. SAMHD1, a ubiquitously expressed deoxynucleotide triphosphohydrolase, converts dNTPs into deoxynucleosides and inorganic triphosphates. This process counteracts the de novo dNTP synthesis primarily carried out by RNR and cellular deoxynucleoside kinases, which are most active during the S phase of the cell cycle. The intracellular levels of dNTPs can influence various viral infections. This review provides a concise summary of the interactions between different viruses and the genes involved in dNTP metabolism.

Antiviral effects of micafungin against pteropine orthoreovirus, an emerging zoonotic virus carried by bats

Bat-borne emerging zoonotic viruses cause major outbreaks, such as the Ebola virus, Nipah virus, and/or beta coronavirus. Pteropine orthoreovirus (PRV), whose spillover event occurred from fruits bats to humans, causes respiratory syndrome in humans widely in South East Asia. Repurposing approved drugs against PRV is an effective tool to confront future PRV pandemics. We screened 2,943 compounds in an FDA-approved drug library and identified eight hit compounds that reduce viral cytopathic effects on cultured Vero cells. Real-time quantitative PCR analysis revealed that six of eight hit compounds significantly inhibited PRV replication. Among them, micafungin used clinically as an antifungal drug, displayed a prominent antiviral effect on PRV. Secondly, the antiviral effects of micafungin on PRV infected human cell lines (HEK293T and A549), and their transcriptome changes by PRV infection were investigated, compared to four different bat-derived cell lines (FBKT1 (Ryukyu flying fox), DEMKT1 (Leschenault's rousette), BKT1 (Greater horseshoe bat), YUBFKT1 (Eastern bent-wing bats)). In two human cell lines, unlike bat cells that induce an IFN-γ response pathway, an endoplasmic reticulum stress response pathway was commonly activated. Additionally, micafungin inhibits viral release rather than suppressing PRV genome replication in human cells, although it was disturbed in Vero cells. The target of micafungin's action may vary depending on the animal species, but it must be useful for human purposes as a first choice of medical care.

Drug repurposing for the treatment of COVID-19: Pharmacological aspects and synthetic approaches

In December 2019, a new variant of SARS-CoV emerged, the so-called acute severe respiratory syndrome coronavirus 2 (SARS-CoV-2). This virus causes the new coronavirus disease (COVID-19) and has been plaguing the world owing to its unprecedented spread efficiency, which has resulted in a huge death toll. In this sense, the repositioning of approved drugs is the fastest way to an effective response to a pandemic outbreak of this scale. Considering these facts, in this review we provide a comprehensive and critical discussion on the chemical aspects surrounding the drugs currently being studied as candidates for COVID-19 therapy. We intend to provide the general chemical community with an overview on the synthetic/biosynthetic pathways related to such molecules, as well as their mechanisms of action against the evaluated viruses and some insights on the pharmacological interactions involved in each case. Overall, the review aims to present the chemical aspects of the main bioactive molecules being considered to be repositioned for effective treatment of COVID-19 in all phases, from the mildest to the most severe.

Drug screening identified gemcitabine inhibiting hepatitis E virus by inducing interferon-like response via activation of STAT1 phosphorylation

Exposure to hepatitis E virus (HEV) bears a high risk of developing chronic infection in immunocompromised patients, including organ transplant recipients and cancer patients. We aim to identify effective anti-HEV therapies through screening and repurposing safe-in-human broad-spectrum antiviral agents. In this study, a safe-in-human broad-spectrum antiviral drug library comprising of 94 agents was used. Upon screening, we identified gemcitabine, a widely used anti-cancer drug, as a potent inhibitor of HEV replication. The antiviral effect was confirmed in a range of cell culture models with genotype 1 and 3 HEV strains. As a cytidine analog, exogenous supplementation of pyrimidine nucleosides effectively reversed the antiviral activity of gemcitabine, but the level of pyrimidine nucleosides per se does not affect HEV replication. Surprisingly, similar to interferon-alpha (IFNα) treatment, gemcitabine activates STAT1 phosphorylation. This subsequently triggers activation of interferon-sensitive response element (ISRE) and transcription of interferon-stimulated genes (ISGs). Cytidine or uridine effectively inhibits gemcitabine-induced activation of ISRE and ISGs. As expected, JAK inhibitor 1 blocked IFNα, but not gemcitabine-induced STAT1 phosphorylation, ISRE/ISG activation, and anti-HEV activity. These effects of gemcitabine were completely lost in STAT1 knockout cells. In summary, gemcitabine potently inhibits HEV replication by triggering interferon-like response through STAT1 phosphorylation but independent of Janus kinases. This represents a non-canonical antiviral mechanism, which utilizes the innate defense machinery that is distinct from the classical interferon response. These results support repurposing gemcitabine for treating hepatitis E, especially for HEV-infected cancer patients, leading to dual anti-cancer and antiviral effects.

Disparate effects of cytotoxic chemotherapy on the antiviral activity of antiretroviral therapy: implications for treatments of HIV-infected cancer patients

BACKGROUND

Cancer is a leading cause of death in HIV-infected patients in the era of combination antiretroviral therapy (cART). Yet, there are no specific guidelines for the combined use of cART and chemotherapy in HIV-infected cancer patients. The cellular enzyme thymidylate synthase (TS) catalyses the conversion of dUMP to TMP, which is converted to TDP and ultimately to TTP, a building block in DNA synthesis. TS inhibitors are recommended in some cancers, particularly non-small cell lung cancer (NSCLC). Because TS inhibitors modulate intracellular concentrations of endogenous 2'-deoxynucleotides, we hypothesized that TS inhibitors could impact the anti-HIV activity of nucleoside analogue reverse transcriptase inhibitors (NRTIs).

METHODS

We evaluated gemcitabine and pemetrexed, two approved TS inhibitors, on the anti-HIV activities of NRTIs in infectivity assays using peripheral blood mononuclear cells (PBMCs) and in humanized mice.

RESULTS

Gemcitabine enhanced the anti-HIV activities of tenofovir, abacavir and emtricitabine (FTC) in PBMCs. In contrast, pemetrexed had no effect on tenofovir, enhanced abacavir and, unexpectedly, decreased FTC and lamivudine (3TC) activities. Pemetrexed inhibitory effects on FTC and 3TC may be due to lower concentrations of active metabolites (FTCtp and 3TCtp) relative to their competing endogenous nucleotide (dCTP), as shown by decreases in FTCtp/dCTP ratios. Gemcitabine enhanced tenofovir while pemetrexed abrogated FTC antiviral activity in humanized mice.

CONCLUSIONS

Chemotherapy with TS inhibitors can have opposing effects on cART, potentially impacting control of HIV and thereby development of viral resistance and size of the reservoir in HIV-infected cancer patients. Combinations of cART and chemotherapy should be carefully selected.

Short-Term Efficacy of Different First-Line Chemotherapy Regimens for Advanced Non-Small Cell Lung Cancer: A Network Meta-Analysis

This study intends to compare short‐term efficacy of 12 chemotherapy regimens in treatment of advanced non‐small cell lung cancer (NSCLC) by a network meta‐analysis (NMA). PubMed, Cochrane Library, and Embase were searched from the inception of each database to June 2018. Randomized controlled trials (RCTs) of the 12 chemotherapy regimens for advanced NSCLC were included. Direct and indirect evidence were combined by NMA to evaluate the odds ratio and the surface under the cumulative ranking curves (SUCRA) of the 12 chemotherapy regimens. Nineteen RCTs that met our inclusion criteria were collected in this study. For partial response (PR), gemcitabine exhibited relatively poor efficacy compared with cisplatin + gemcitabine, carboplatin + gemcitabine, carboplatin + paclitaxel, paclitaxel + gemcitabine, and cisplatin + gemcitabine + vinorelbine. For overall response rate (ORR), gemcitabine had poorer efficacy than cisplatin + gemcitabine and paclitaxel + gemcitabine. For disease control rate (DCR), compared with carboplatin + gemcitabine and gemcitabine, paclitaxel + gemcitabine had a better efficacy. Gemcitabine had the lowest SUCRA values in terms of complete response, PR, ORR, stable disease, and DCR; whereas paclitaxel + gemcitabine ranked the highest in ORR, progressive disease, and DCR. The cluster analysis revealed that cisplatin + gemcitabine, paclitaxel + gemcitabine, and cisplatin + gemcitabine + vinorelbine had better short‐term efficacy for advanced NSCLC. Collectively, short‐term efficacy of multidrug combination chemotherapy regimens was superior to that of single‐drug chemotherapy regimens for advanced NSCLC. Cisplatin + gemcitabine, paclitaxel + gemcitabine, and cisplatin + gemcitabine + vinorelbine may have particularly prominent short‐term efficacy for advanced NSCLC.

Distinct dual antiviral mechanism that enhances hepatitis B virus mutagenesis and reduces viral DNA synthesis

Reverse transcriptase (RT) is an essential enzyme for the replication of retroviruses and hepadnaviruses. Current therapies do not eliminate the intracellular viral replication intermediate termed covalently closed circular (ccc) DNA, which has enhanced interest in hepatitis B virus (HBV) reverse transcription and cccDNA formation. The HBV cccDNA is generated as a plasmid-like episome in the host cell nucleus from the protein-linked relaxed circular (rc) DNA genome in incoming virions during HBV replication. The creation of the cccDNA via conversion from rcDNA remains not fully understood. Here, we sought to investigate whether viral mutagens can effect HBV replication. In particular, we investigated whether nucleoside analogs that act as viral mutagens with retroviruses could impact hepadnaviral DNA synthesis. We observed that a viral mutagen (e.g., 5-aza-2'-deoxycytidine, 5-aza-dC or 5-azacytidine, 5-aza-C) severely diminished the ability of a HBV vector to express a reporter gene following virus transfer and infection of target cells. As predicted, the treatment of 5-aza-dC or 5-aza-C elevated the HBV rcDNA mutation frequency, primarily by increasing the frequency of G-to-C transversion mutations. A reduction in rcDNA synthesis was also observed. Intriguingly, the cccDNA nick/gap region transcription was diminished by 5-aza-dC, but did not enhance viral mutagenesis. Taken together, our results demonstrate that viral mutagens can impact HBV reverse transcription, and propose a model in which viral mutagens can induce mutagenesis during rcDNA formation and diminish viral DNA synthesis during both rcDNA formation and the conversion of rcDNA to cccDNA.

Lethal mutagenesis of an RNA plant virus via lethal defection

Lethal mutagenesis is an antiviral therapy that relies on increasing the viral mutation rate with mutagenic nucleoside or base analogues. Currently, the molecular mechanisms that lead to virus extinction through enhanced mutagenesis are not fully understood. Increasing experimental evidence supports the lethal defection model of lethal mutagenesis of RNA viruses, where replication-competent-defectors drive infective virus towards extinction. Here, we address lethal mutagenesis in vivo using 5-fluorouracil (5-FU) during the establishment of tobacco mosaic virus (TMV) systemic infections in N. tabacum. The results show that 5-FU decreased the infectivity of TMV without affecting its viral load. Analysis of molecular clones spanning two genomic regions showed an increase of the FU-related base transitions A → G and U → C. Although the mutation frequency or the number of mutations per molecule did not increase, the complexity of the mutant spectra and the distribution of the mutations were altered. Overall, our results suggest that 5-FU antiviral effect on TMV is associated with the perturbation of the mutation-selection balance in the genomic region of the RNA-dependent RNA polymerase (RdRp). Our work supports the lethal defection model for lethal mutagenesis in vivo in a plant RNA virus and opens the way to study lethal mutagens in plant-virus systems.

Middle East Respiratory Syndrome and Severe Acute Respiratory Syndrome: Current Therapeutic Options and Potential Targets for Novel Therapies

No specific antivirals are currently available for two emerging infectious diseases, Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS). A literature search was performed covering pathogenesis, clinical features and therapeutics, clinically developed drugs for repurposing and novel drug targets. This review presents current knowledge on the epidemiology, pathogenesis and clinical features of the SARS and MERS coronaviruses. The rationale for and outcomes with treatments used for SARS and MERS is discussed. The main focus of the review is on drug development and the potential that drugs approved for other indications provide for repurposing. The drugs we discuss belong to a wide range of different drug classes, such as cancer therapeutics, antipsychotics, and antimalarials. In addition to their activity against MERS and SARS coronaviruses, many of these approved drugs have broad-spectrum potential and have already been in clinical use for treating other viral infections. A wealth of knowledge is available for these drugs. However, the information in this review is not meant to guide clinical decisions, and any therapeutic described here should only be used in context of a clinical trial. Potential targets for novel antivirals and antibodies are discussed as well as lessons learned from treatment development for other RNA viruses. The article concludes with a discussion of the gaps in our knowledge and areas for future research on emerging coronaviruses.

Characterization of permeability, stability and anti-HIV-1 activity of decitabine and gemcitabine divalerate prodrugs

BACKGROUND

Over 25 drugs have been approved for the treatment of HIV-1 replication. All but one of these drugs is delivered as an oral medication. Previous studies have demonstrated that two drugs, decitabine and gemcitabine, have potent anti-HIV-1 activities and can work together in synergy to reduce HIV-1 infectivity via lethal mutagenesis. For their current indications, decitabine and gemcitabine are delivered intravenously.

METHODS

As an initial step towards the clinical translation of these drugs for the treatment of HIV-1 infection, we synthesized decitabine and gemcitabine prodrugs in order to increase drug permeability, which has generally been shown to correlate with increased bioavailability in vivo. In the present study we investigated the permeability, stability and anti-HIV-1 activity of decitabine and gemcitabine prodrugs and selected the divalerate esters of each as candidates for further investigation.

RESULTS

Our results provide the first demonstration of divalerate prodrugs of decitabine and gemcitabine that are readily permeable, stable and possess anti-HIV-1 activity.

CONCLUSIONS

These observations predict improved oral availability of decitabine and gemcitabine, and warrant further study of their ability to reduce HIV-1 infectivity in vivo.

Novel inhibitors of human immunodeficiency virus type 2 infectivity

Human immunodeficiency virus type 2 (HIV-2) infects about two million people worldwide. HIV-2 has fewer treatment options than HIV-1, yet may evolve drug resistance more quickly. We have analysed several novel drugs for anti-HIV-2 activity. It was observed that 5-azacytidine, clofarabine, gemcitabine and resveratrol have potent anti-HIV-2 activity. The EC50 values for 5-azacytidine, clofarabine and resveratrol were found to be significantly lower with HIV-2 than with HIV-1. A time-of-addition assay was used to analyse the ability of these drugs to interfere with HIV-2 replication. Reverse transcription was the likely target for antiretroviral activity. Taken together, several novel drugs have been discovered to have activity against HIV-2. Based upon their known activities, these drugs may elicit enhanced HIV-2 mutagenesis and therefore be useful for inducing HIV-2 lethal mutagenesis. In addition, the data are consistent with HIV-2 reverse transcriptase being more sensitive than HIV-1 reverse transcriptase to dNTP pool alterations.

Targeting host nucleotide biosynthesis with resveratrol inhibits emtricitabine-resistant HIV-1

OBJECTIVE

The M184V mutation in the HIV-1 reverse transcriptase gene is frequent (>50%) in patients, both in resource-rich and resource-limited countries, conferring high-level resistance (>100-fold) to the cytosine analog reverse transcriptase inhibitors lamivudine and emtricitabine. The reverse transcriptase enzyme of M184V HIV-1 mutants has reduced processivity, resulting in reduced viral replication, particularly at low deoxynucleotide (dNTP) levels. We hypothesized that lowering intracellular dNTPs with resveratrol, a dietary supplement, could interfere with replication of M184V HIV-1 mutants.

DESIGN AND METHODS

Evaluation of the activity of resveratrol on infection of primary peripheral blood lymphocytes by wild-type and M184V mutant HIV-1. We assayed both molecular clones and primary isolates of HIV-1, containing M184V alone and in combination with other reverse transcriptase mutations. Viral infection was quantified by p24 ELISA and by quantitative real-time PCR analysis. Cell viability was measured by colorimetric 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays.

RESULTS

In virus-infectivity assays, resveratrol did not inhibit replication of wild-type NL4-3 (resveratrol EC50 > 10 μmol/l), but it inhibited NL4-3 184V mutant (resveratrol EC50 = 5.8 μmol/l). These results were confirmed by real-time PCR analysis of early and late products of reverse transcription. Resveratrol inhibited molecular clones and primary isolates carrying M184V, alone or in combination with other reverse transcriptase mutations (resveratrol EC50 values ranging from 2.5 to 7.7 μmol/l).

CONCLUSIONS

Resveratrol inhibits HIV-1 strains carrying the M184V mutation in reverse transcriptase. We propose resveratrol as a potential adjuvant in HIV-1 therapy, particularly in resource-limited settings, to help control emtricitabine-resistant M184V HIV-1 mutants.

Targeting of the purine biosynthesis host cell pathway enhances the activity of tenofovir against sensitive and drug-resistant HIV-1

BACKGROUND

Targeting host-cell pathways to increase the potency of nucleoside/nucleotide analog reverse transcriptase inhibitors (NRTIs) is an important strategy for clinical investigation. Resveratrol is a natural product that inhibits cellular ribonucleotide reductase, prolonging the S phase of the cell cycle and preferentially lowering dATP levels.

METHODS

We performed in vitro evaluation of resveratrol on the antiviral activity of adenosine analog tenofovir (TFV) against sensitive and drug-resistant human immunodeficiency virus type 1 (HIV-1), from subtypes B and C, in primary cells.

RESULTS

Resveratrol enhanced the antiviral activity of TFV by up to 10-fold and restored susceptibility of TFV-resistant viruses. Resveratrol prevented wild-type HIV-1 from developing phenotypic resistance to TFV. Notably, resveratrol enhanced TFV activity against sensitive and resistant HIV-1 from both subtypes B and C.

CONCLUSIONS

Prolonged wide-scale use of thymidine analogs in the setting of viral failure has limited the efficacy of second-line NRTI-based regimens in Africa. Moreover, the extensive use of ddI and d4T has led to high frequencies of the K65R mutation, further compromising TFV efficacy. In light of increasing resistance to commonly used NRTIs in global HIV treatment programs, targeting nucleoside biosynthesis with resveratrol, or derivatives with improved bioavailabilities, is a potential strategy to maintain, enhance, and restore susceptibility of commonly used NRTIs.

Advances in the development of nucleoside and nucleotide analogues for cancer and viral diseases

Nucleoside analogues have been in clinical use for almost 50 years and have become cornerstones of treatment for patients with cancer or viral infections. The approval of several additional drugs over the past decade demonstrates that this family still possesses strong potential. Here, we review new nucleoside analogues and associated compounds that are currently in preclinical or clinical development for the treatment of cancer and viral infections, and that aim to provide increased response rates and reduced side effects. We also highlight the different approaches used in the development of these drugs and the potential of personalized therapy.

Advances in the development of nucleoside and nucleotide analogues for cancer and viral diseases

Nucleoside analogues have been in clinical use for almost 50 years and have become cornerstones of treatment for patients with cancer or viral infections. The approval of several additional drugs over the past decade demonstrates that this family still possesses strong potential. Here, we review new nucleoside analogues and associated compounds that are currently in preclinical or clinical development for the treatment of cancer and viral infections, and that aim to provide increased response rates and reduced side effects. We also highlight the different approaches used in the development of these drugs and the potential of personalized therapy.

Dimethylaminoparthenolide and gemcitabine: a survival study using a genetically engineered mouse model of pancreatic cancer

BACKGROUND

Pancreatic cancer remains one of the deadliest cancers due to lack of early detection and absence of effective treatments. Gemcitabine, the current standard-of-care chemotherapy for pancreatic cancer, has limited clinical benefit. Treatment of pancreatic cancer cells with gemcitabine has been shown to induce the activity of the transcription factor nuclear factor-kappaB (NF-κB) which regulates the expression of genes involved in the inflammatory response and tumorigenesis. It has therefore been proposed that gemcitabine-induced NF-κB activation may result in chemoresistance. We hypothesize that NF-κB suppression by the novel inhibitor dimethylaminoparthenolide (DMAPT) may enhance the effect of gemcitabine in pancreatic cancer.

METHODS

The efficacy of DMAPT and gemcitabine was evaluated in a chemoprevention trial using the mutant Kras and p53-expressing LSL-KrasG12D/+; LSL-Trp53R172H; Pdx-1-Cre mouse model of pancreatic cancer. Mice were randomized to treatment groups (placebo, DMAPT [40 mg/kg/day], gemcitabine [50 mg/kg twice weekly], and the combination DMAPT/gemcitabine). Treatment was continued until mice showed signs of ill health at which time they were sacrificed. Plasma cytokine levels were determined using a Bio-Plex immunoassay. Statistical tests used included log-rank test, ANOVA with Dunnett's post-test, Student's t-test, and Fisher exact test.

RESULTS

Gemcitabine or the combination DMAPT/gemcitabine significantly increased median survival and decreased the incidence and multiplicity of pancreatic adenocarcinomas. The DMAPT/gemcitabine combination also significantly decreased tumor size and the incidence of metastasis to the liver. No significant differences in the percentages of normal pancreatic ducts or premalignant pancreatic lesions were observed between the treatment groups. Pancreata in which no tumors formed were analyzed to determine the extent of pre-neoplasia; mostly normal ducts or low grade pancreatic lesions were observed, suggesting prevention of higher grade lesions in these animals. While gemcitabine treatment increased the levels of the inflammatory cytokines interleukin 1α (IL-1α), IL-1β, and IL-17 in mouse plasma, DMAPT and DMAPT/gemcitabine reduced the levels of the inflammatory cytokines IL-12p40, monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein-1 beta (MIP-1β), eotaxin, and tumor necrosis factor-alpha (TNF-α), all of which are NF-κB target genes.

CONCLUSION

In summary, these findings provide preclinical evidence supporting further evaluation of agents such as DMAPT and gemcitabine for the prevention and treatment of pancreatic cancer.

Back to the future: revisiting HIV-1 lethal mutagenesis

The concept of eliminating HIV-1 infectivity by elevating the viral mutation rate was first proposed over a decade ago, even though the general concept had been conceived earlier for RNA viruses. Lethal mutagenesis was originally viewed as a novel chemotherapeutic approach for treating HIV-1 infection in which use of a viral mutagen would over multiple rounds of replication lead to the lethal accumulation of mutations, rendering the virus population noninfectious - known as the slow mutation accumulation model. There have been limitations in obtaining good efficacy data with drug leads, leaving some doubt on clinical translation. More recent studies of the apolipoprotein B mRNA editing complex 3 (APOBEC3) proteins as well as new progress in the use of nucleoside analogs for inducing lethal mutagenesis have helped to refocus attention on rapid induction of HIV-1 lethal mutagenesis in a single or limited number of replication cycles leading to a rapid mutation accumulation model.

Gemcitabine is active against clinical multiresistant Staphylococcus aureus strains and is synergistic with gentamicin

This study provides insight into the antibacterial activity of the cytotoxic nucleoside analogue gemcitabine against clinical multiresistant Staphylococcus aureus strains. Classical methods were used for determination of the minimum inhibitory concentration (MIC) and synergy in vitro, and polymerase chain reaction (PCR) products were sequenced to search for mutations in nucleoside kinase genes in resistant strains. Gemcitabine and its derivative CP-4126 were effective against meticillin-susceptible S. aureus (MSSA), meticillin-resistant S. aureus (MRSA) and glycopeptide-intermediate S. aureus (GISA) isolates, with MICs ranging between 0.06 mg/L and 4.22 mg/L. Bactericidal activity was shown in time-kill studies as well as synergy with gentamicin. Mutations in the nucleoside kinase gene SadAK were observed in resistant strains, indicating a role for this enzyme in gemcitabine activity. Nucleoside analogues have antimicrobial activity and these results could be used for further identification and development of new antibiotics.

Activity of a novel combined antiretroviral therapy of gemcitabine and decitabine in a mouse model for HIV-1

The emergence of drug resistance threatens to limit the use of current anti-HIV-1 drugs and highlights the need to expand the number of treatment options available for HIV-1-infected individuals. Our previous studies demonstrated that two clinically approved drugs, decitabine and gemcitabine, potently inhibited HIV-1 replication in cell culture through a mechanism that is distinct from the mechanisms for the drugs currently used to treat HIV-1 infection. We further demonstrated that gemcitabine inhibited replication of a related retrovirus, murine leukemia virus (MuLV), in vivo using the MuLV-based LP-BM5/murine AIDS (MAIDS) mouse model at doses that were not toxic. Since decitabine and gemcitabine inhibited MuLV and HIV-1 replication with similar potency in cell culture, the current study examined the efficacy and toxicity of the drug combination using the MAIDS model. The data demonstrate that the drug combination inhibited disease progression, as detected by histopathology, viral loads, and spleen weights, at doses lower than those that would be required if the drugs were used individually. The combination of decitabine and gemcitabine exerted antiviral activity at doses that were not toxic. These findings indicate that the combination of decitabine and gemcitabine shows potent antiretroviral activity at nontoxic doses and should be further investigated for clinical relevance.

Mutagen-mediated enhancement of HIV-1 replication in persistently infected cells

Lethal mutagenesis, a new antiviral strategy to extinguish virus through elevated mutation rates, was explored in H61-D cells an HIV-1 persistently infected lymphoid cell line. Three mutagenic agents: 5-hydroxy-2(')-deoxycytidine (5-OHdC), 5-fluorouracil (5-FU) and 2,2(')-difluoro-2(')-deoxycytidine (gemcitabine) were used. After 54 passages, treatments with 5-FU and gemcitabine reduced virus infectivity, p24 and RT activity. Treatment with the pyrimidine analog 5-OHdC resulted in increases of p24 production, RT activity and infectivity. Rise in viral replication by 5-OHdC during HIV-1 persistence is in contrast with its inhibitory effect in acute infections. Viral replication enhancement by 5-OHdC was associated with an increase in intracellular HIV-1 RNA mutations. Mechanisms of HIV-1 replication enhancement by 5-OHdC are unknown but some potential factors are discussed. Increase of HIV-1 replication by 5-OHdC cautions against the use, without previous analyses, of mutagenic nucleoside analogs for AIDS treatment.

Discovery of drugs that possess activity against feline leukemia virus

Feline leukemia virus (FeLV) is a gammaretrovirus that is a significant cause of neoplastic-related disorders affecting cats worldwide. Treatment options for FeLV are limited, associated with serious side effects, and can be cost-prohibitive. The development of drugs used to treat a related retrovirus, human immunodeficiency virus type 1 (HIV-1), has been rapid, leading to the approval of five drug classes. Although structural differences affect the susceptibility of gammaretroviruses to anti-HIV drugs, the similarities in mechanism of replication suggest that some anti-HIV-1 drugs may also inhibit FeLV. This study demonstrates the anti-FeLV activity of four drugs approved by the US FDA (Food and Drug Administration) at non-toxic concentrations. Of these, tenofovir and raltegravir are anti-HIV-1 drugs, while decitabine and gemcitabine are approved to treat myelodysplastic syndromes and pancreatic cancer, respectively, but also have anti-HIV-1 activity in cell culture. Our results indicate that these drugs may be useful for FeLV treatment and should be investigated for mechanism of action and suitability for veterinary use.