A path from synthesis to emergency use authorization of molnupiravir as a COVID-19 therapy

Coronaviruses are a group of enveloped viruses with non-segmented, single-stranded, and positive-sense RNA genomes. It belongs to the 'Coronaviridae family', responsible for various diseases, including the common cold, SARS, and MERS. The COVID-19 pandemic, which began in March 2020, has affected 209 countries, infected over a million people, and claimed over 50,000 lives. Significant efforts have been made by repurposing several approved drugs including antiviral, to combat the COVID-19 pandemic. Molnupiravir is found to be the first orally acting efficacious drug to treat COVID-19 cases. It was approved for medical use in the UK in November 2021 and other countries, including USFDA, which granted approval an emergency use authorization (EUA) for treating adults with mild to moderate COVID-19 patients. Considering the importance of molnupiravir, the present review deals with its various synthetic strategies, pharmacokinetics, bio-efficacy, toxicity, and safety profiles. The comprehensive information along with critical analysis will be very handy for a wide range of audience including medicinal chemists in the arena of antiviral drug discovery especially anti-viral drugs against any variant of COVID-19.

Molnupiravir versus favipiravir in at-risk outpatients with COVID-19: A randomized controlled trial in Thailand

OBJECTIVES

Evaluate and compare the efficacy and safety of molnupiravir and favipiravir in outpatients with mild to moderate COVID-19 and at risk of severe COVID-19.

METHODS

In an open-label, parallel-group, multicenter trial in Thailand, participants with moderate COVID-19 and at least one factor associated with severe COVID-19 were randomly assigned 1:1 to receive oral molnupiravir or oral favipiravir (standard of care). Phone calls for remote symptom assessment were made on Days 6, 15, and 29. Participants with worsening symptoms were instructed to return to the hospital. The primary endpoint was pulmonary involvement by Day 29, as evidenced by ≥2 of the following: dyspnea, oxygen saturation <92% or imaging.

RESULTS

Nine hundred seventy-seven participants (487 molnupiravir, 490 favipiravir) were enrolled from 8 July 2022 to 19 January 2023. 98% had received ≥1 dose of COVID-19 vaccine and 83% ≥3 doses. By Day 29, pulmonary involvement occurred in 0% (0/483) in molnupiravir arm versus 1% (5/482) in favipiravir arm (-1.0%; Newcombe 95.2% CI: -2.4% to -0.0%; P = 0.021); all-cause death in 0% (0/483) and <1% (1/482); COVID-19 related hospitalization in <1% (1/483) and 1% (3/482); treatment-related adverse event in 1% (5/483) and 1% (4/486); and serious adverse event in 1% (4/483) and 1% (4/486).

CONCLUSIONS

Favipiravir and molnupiravir had a similar efficacy and safety profile. Whether either of the two reduced the risk of complications during the omicron era in this population with a low risk of pulmonary involvement and a high vaccine coverage remains unclear. There were no differences in any of the safety endpoints.

THAI CLINICAL TRIALS REGISTRY ID

TCTR20230111009.

Effect of molnupiravir on SARS-CoV-2 evolution in immunocompromised patients: a retrospective observational study

INTRODUCTION

Continued SARS-CoV-2 infection among immunocompromised individuals is likely to play a role in generating genomic diversity and the emergence of novel variants. Antiviral treatments such as molnupiravir are used to mitigate severe COVID-19 outcomes, but the extended effects of these drugs on viral evolution in patients with chronic infections remain uncertain. This study investigates how molnupiravir affects SARS-CoV-2 evolution in immunocompromised patients with prolonged infections.

METHODS

The study included five immunocompromised patients treated with molnupiravir and four patients not treated with molnupiravir (two immunocompromised and two non-immunocompromised). We selected patients who had been infected by similar SARS-CoV-2 variants and with high-quality genomes across timepoints to allow comparison between groups. Throat and nasopharyngeal samples were collected in patients up to 44 days post treatment and were sequenced using tiled amplicon sequencing followed by variant calling. The UShER pipeline and University of California Santa Cruz genome viewer provided insights into the global context of variants. Treated and untreated patients were compared, and mutation profiles were visualised to understand the impact of molnupiravir on viral evolution.

FINDINGS

Patients treated with molnupiravir showed a large increase in low-to-mid-frequency variants in as little as 10 days after treatment, whereas no such change was observed in untreated patients. Some of these variants became fixed in the viral population, including non-synonymous mutations in the spike protein. The variants were distributed across the genome and included unique mutations not commonly found in global omicron genomes. Notably, G-to-A and C-to-T mutations dominated the mutational profile of treated patients, persisting up to 44 days post treatment.

INTERPRETATION

Molnupiravir treatment in immunocompromised patients led to the accumulation of a distinctive pattern of mutations beyond the recommended 5 days of treatment. Treated patients maintained persistent PCR positivity for the duration of monitoring, indicating clear potential for transmission and subsequent emergence of novel variants.

FUNDING

Australian Research Council.

Molnupiravir increases SARS-CoV-2 genome diversity and complexity: A case-control cohort study

Molnupiravir, an oral direct-acting antiviral effective in vitro against SARS-CoV-2, has been largely employed during the COVID-19 pandemic, since December 2021. After marketing and widespread usage, a progressive increase in SARS-CoV-2 lineages characterized by a higher transition/transversion ratio, a characteristic signature of molnupiravir action, appeared in the Global Initiative on Sharing All Influenza Data (GISAID) and International Nucleotide Sequence Database Collaboration (INSDC) databases. Here, we assessed the drug effects by SARS-CoV-2 whole-genome sequencing on 38 molnupiravir-treated persistently positive COVID-19 outpatients tested before and after treatment. Seventeen tixagevimab/cilgavimab-treated outpatients served as controls. Mutational analyses confirmed that SARS-CoV-2 exhibits an increased transition/transversion ratio seven days after initiation of molnupiravir. Moreover we observed an increased G->A ratio compared to controls, which was not related to apolipoprotein B mRNAediting enzyme, catalytic polypeptide-like (APOBEC) activity. In addition, we demonstrated for the first time an increased diversity and complexity of the viral quasispecies.

Safety of RNA-Dependent RNA Polymerase Inhibitors, Molnupiravir and VV116, for Oral Treatment of COVID-19: A Meta-Analysis

Background

The RNA-dependent RNA polymerase (RdRp) inhibitors, molnupiravir and VV116, have the potential to maximize clinical benefits in the oral treatment of COVID-19. Subjects who consume these drugs may experience an increased incidence of adverse events. This study aimed to evaluate the safety profile of molnupiravir and VV116.

Methods

A comprehensive search of scientific and medical databases, such as PubMed Central/Medline, Embase, Web of Science, and Cochrane Library, was conducted to find relevant articles in English from January 2020 to June 2023. Any kind of adverse events reported in the study were pooled and analyzed in the drug group versus the control group. Estimates of risk effects were summarized through the random effects model using Review Manager version 5.2, and sensitivity analysis was performed by Stata 17.0 software.

Results

Fifteen studies involving 32,796 subjects were included. Eleven studies were placebo-controlled, and four were Paxlovid-controlled. Twelve studies reported adverse events for molnupiravir, and three studies described adverse events for VV116. The total odds ratio (OR) for adverse events in the RdRp inhibitor versus the placebo-controlled group was 1.01 (95% CI=0.84-1.22; I2=26%), P=0.88. The total OR for adverse events in the RdRp inhibitor versus the Paxlovid-controlled group was 0.32 (95% CI=0.16-0.65; I2=87%), P=0.002. Individual drug subgroup analysis in the placebo-controlled study showed that compared with the placebo group, a total OR for adverse events was 0.97 (95% CI, 0.85-1.10; I2=0%) in the molnupiravir group and 3.77 (95% CI=0.08-175.77; I2=85%) in the VV116 group.

Conclusion

The RdRp inhibitors molnupiravir and VV116 are safe for oral treatment of COVID-19. Further evidence is necessary that RdRp inhibitors have a higher safety profile than Paxlovid.

Comparison of effectiveness and safety of molnupiravir versus sotrovimab for COVID-19: A systematic review and meta-analysis

BACKGROUND AND AIM

This systematic review and meta-analysis aimed to compare the effectiveness and safety of molnupiravir and sotrovimab in the treatment of patients with coronavirus disease 2019 (COVID-19).

METHODS

Cochrane Library, Web of Science, PubMed, medRxiv, and Google Scholar were systematically searched to identify relevant evidence up to December 2023. The risk of bias was assessed using the risk of bias in nonrandomized studies of interventions tool. Data were analyzed using Comprehensive Meta-Analysis (CMA).

RESULTS

Our search identified and included 13 studies involving 16166 patients. The meta-analysis revealed a significant difference between the molnupiravir and sotrovimab groups in terms of the mortality rate (odds ratio [OR] = 2.07, 95% confidence interval [CI]: 1.16, 3.70). However, no significant difference was observed between the two groups in terms of hospitalization rate (OR = 0.71, 95% CI: 0.47, 1.06), death or hospitalization rate (OR = 1.51, 95% CI: 0.81, 2.83), and intensive care unit admission (OR = 0.59, 95% CI: 0.07, 4.84). In terms of safety, molnupiravir was associated with a higher incidence of adverse events (OR = 1.67, 95% CI: 1.21, 2.30).

CONCLUSION

The current findings indicate that sotrovimab may be more effective than molnupiravir in reducing the mortality rate in COVID-19 patients. However, no statistical difference was observed between the two treatments for other effectiveness outcomes. The certainty of evidence for these findings was rated as low or moderate. Further research is required to provide a better comparison of these interventions in treating COVID-19 patients.

Virology and safety profile of Molnupiravir at three different doses for treatment of SARS-CoV-2: a systematic review and meta-analysis

Molnupiravir is incorporated into the viral genome, thereby increasing errors, mismatching, and misdirecting the viral polymerase thereby, halting viral RNA replication of SARS-CoV-2. Following PRISMA guidelines, a thorough literature search was performed on electronic and medical databases from December 2022 till January 2023. Molnupiravir 800 mg showed significance in creating viral RNA error rate at Day 5 (WMD: 4.91; 95% CI; [1.19, 8.63] p = 0.01; I2  = 0%). Similarly, at 400 mg, Molnupiravir creates an RNA error rate (WMD: 2.27; 95% CI; 2.27 [0.50, 4.65] p = 0.02; I2  = 0%). Furthermore, exhibit a significant outcome for mean change in SARS-CoV-2 RNA viral load from baseline in nasopharyngeal sample at 800 mg Molnupiravir on Day 3 (WMD: -0.22; 95% CI; [-0.35, -0.08] p = 0.002; I2  = 0%), Day 5 (WMD: -0.32; 95% CI; [-0.53, -0.11] p = 0.003; I2  = 24%) and overall pooled analysis (WMD: -0.17; 95% CI; [-0.29, 0.33] p = 0.003; I2  = 32%). Moreover, Molnupiravir 400 mg significantly reduced the incidence of death compared to the placebo group (RR: 0.17; 95% CI; [0.07, 0.43] p = 0.0002; I2  = 0%). Molnupiravir effectively treats SARS-CoV-2 patients by eliminating the virus from the host.

A molnupiravir-associated mutational signature in global SARS-CoV-2 genomes

Molnupiravir, an antiviral medication widely used against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), acts by inducing mutations in the virus genome during replication. Most random mutations are likely to be deleterious to the virus and many will be lethal; thus, molnupiravir-induced elevated mutation rates reduce viral load1,2. However, if some patients treated with molnupiravir do not fully clear the SARS-CoV-2 infections, there could be the potential for onward transmission of molnupiravir-mutated viruses. Here we show that SARS-CoV-2 sequencing databases contain extensive evidence of molnupiravir mutagenesis. Using a systematic approach, we find that a specific class of long phylogenetic branches, distinguished by a high proportion of G-to-A and C-to-T mutations, are found almost exclusively in sequences from 2022, after the introduction of molnupiravir treatment, and in countries and age groups with widespread use of the drug. We identify a mutational spectrum, with preferred nucleotide contexts, from viruses in patients known to have been treated with molnupiravir and show that its signature matches that seen in these long branches, in some cases with onward transmission of molnupiravir-derived lineages. Finally, we analyse treatment records to confirm a direct association between these high G-to-A branches and the use of molnupiravir.

Molnupiravir in unvaccinated patients with COVID-19

Overview of: Jayk Bernal A, Gomes da Silva MM, Musungaie DB, et al Molnupiravir for oral treatment of COVID-19 in nonhospitalized patients. NEJM 2021;doi:10.1056/NEJMoa2116044 [Epub ahead of print 16 Dec 2021].

Molnupiravir for Oral Treatment of Covid-19 in Nonhospitalized Patients

BACKGROUND

New treatments are needed to reduce the risk of progression of coronavirus disease 2019 (Covid-19). Molnupiravir is an oral, small-molecule antiviral prodrug that is active against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

METHODS

We conducted a phase 3, double-blind, randomized, placebo-controlled trial to evaluate the efficacy and safety of treatment with molnupiravir started within 5 days after the onset of signs or symptoms in nonhospitalized, unvaccinated adults with mild-to-moderate, laboratory-confirmed Covid-19 and at least one risk factor for severe Covid-19 illness. Participants in the trial were randomly assigned to receive 800 mg of molnupiravir or placebo twice daily for 5 days. The primary efficacy end point was the incidence hospitalization or death at day 29; the incidence of adverse events was the primary safety end point. A planned interim analysis was performed when 50% of 1550 participants (target enrollment) had been followed through day 29.

RESULTS

A total of 1433 participants underwent randomization; 716 were assigned to receive molnupiravir and 717 to receive placebo. With the exception of an imbalance in sex, baseline characteristics were similar in the two groups. The superiority of molnupiravir was demonstrated at the interim analysis; the risk of hospitalization for any cause or death through day 29 was lower with molnupiravir (28 of 385 participants [7.3%]) than with placebo (53 of 377 [14.1%]) (difference, -6.8 percentage points; 95% confidence interval [CI], -11.3 to -2.4; P = 0.001). In the analysis of all participants who had undergone randomization, the percentage of participants who were hospitalized or died through day 29 was lower in the molnupiravir group than in the placebo group (6.8% [48 of 709] vs. 9.7% [68 of 699]; difference, -3.0 percentage points; 95% CI, -5.9 to -0.1). Results of subgroup analyses were largely consistent with these overall results; in some subgroups, such as patients with evidence of previous SARS-CoV-2 infection, those with low baseline viral load, and those with diabetes, the point estimate for the difference favored placebo. One death was reported in the molnupiravir group and 9 were reported in the placebo group through day 29. Adverse events were reported in 216 of 710 participants (30.4%) in the molnupiravir group and 231 of 701 (33.0%) in the placebo group.

CONCLUSIONS

Early treatment with molnupiravir reduced the risk of hospitalization or death in at-risk, unvaccinated adults with Covid-19. (Funded by Merck Sharp and Dohme; MOVe-OUT ClinicalTrials.gov number, NCT04575597.).

An updated practical guideline on use of molnupiravir and comparison with agents having emergency use authorization for treatment of COVID-19

BACKGROUND AND AIMS

Molnupiravir is a newer oral antiviral drug that has recently received emergency use authorization (EUA) in USA, UK and India. We aim to conduct an update on our previous systematic review to provide practical clinical guideline for using molnupiravir in patients with COVID-19.

METHODS

We systematically searched the electronic database of PubMed, MedRxiv and Google Scholar until January 5, 2022, using key MeSH keywords.

RESULTS

Final result of phase 3 study in 1433 non-hospitalized COVID-19 patients showed a significant reduction in composite risk of hospital admission or death (absolute risk difference, -3.0% [95% confidence interval {CI}, -5.9 to -0.1%]; 1-sided P = 0.02) although with a non-significant 31% relative risk reduction (RRR). RRR for death alone was 89% (95% CI, 14 to 99; P-value not reported). Number needed to treat to prevent 1 death or 1 hospitalization or death composite appears to be closely competitive to other agents having EUA in people with COVID-19. However, cost-wise molnupiravir is comparatively cheaper compared to all other agents.

CONCLUSION

Molnupiravir could be a useful agent in non-pregnant unvaccinated adults with COVID-19 who are at increased risk of severity including hospitalization. However, it is effective only when used within 5-days of onset of symptoms. A 5-days course seems to be safe without any obvious short-term side effects.

Remdesivir, Molnupiravir and Nirmatrelvir remain active against SARS-CoV-2 Omicron and other variants of concern

We assessed the in vitro antiviral activity of remdesivir and its parent nucleoside GS-441524, molnupiravir and its parent nucleoside EIDD-1931 and the viral protease inhibitor nirmatrelvir against the ancestral SARS-CoV2 strain and the five variants of concern including Omicron. VeroE6-GFP cells were pre-treated overnight with serial dilutions of the compounds before infection. The GFP signal was determined by high-content imaging on day 4 post-infection. All molecules have equipotent antiviral activity against the ancestral virus and the VOCs Alpha, Beta, Gamma, Delta and Omicron. These findings are in line with the observation that the target proteins of these antivirals (respectively the viral RNA dependent RNA polymerase and the viral main protease Mpro) are highly conserved.

•

The omicron SARS-CoV-2 variant remains susceptible for GS-441524, Remdesivir, EIDD-1931, Molnupiravir and Nirmatrelvir.

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The target genes of these antivirals are highly conserved between SARS-CoV-2 variants.

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Similarly, the alpha, beta, gamma and delta variants remain susceptible to these antivirals.

Human genetic risk of treatment with antiviral nucleoside analog drugs that induce lethal mutagenesis: The special case of molnupiravir

This review considers antiviral nucleoside analog drugs, including ribavirin, favipiravir, and molnupiravir, which induce genome error catastrophe in SARS-CoV or SARS-CoV-2 via lethal mutagenesis as a mode of action. In vitro data indicate that molnupiravir may be 100 times more potent as an antiviral agent than ribavirin or favipiravir. Molnupiravir has recently demonstrated efficacy in a phase 3 clinical trial. Because of its anticipated global use, its relative potency, and the reported in vitro "host" cell mutagenicity of its active principle, β-d-N4-hydroxycytidine, we have reviewed the development of molnupiravir and its genotoxicity safety evaluation, as well as the genotoxicity profiles of three congeners, that is, ribavirin, favipiravir, and 5-(2-chloroethyl)-2'-deoxyuridine. We consider the potential genetic risks of molnupiravir on the basis of all available information and focus on the need for additional human genotoxicity data and follow-up in patients treated with molnupiravir and similar drugs. Such human data are especially relevant for antiviral NAs that have the potential of permanently modifying the genomes of treated patients and/or causing human teratogenicity or embryotoxicity. We conclude that the results of preclinical genotoxicity studies and phase 1 human clinical safety, tolerability, and pharmacokinetics are critical components of drug safety assessments and sentinels of unanticipated adverse health effects. We provide our rationale for performing more thorough genotoxicity testing prior to and within phase 1 clinical trials, including human PIG-A and error corrected next generation sequencing (duplex sequencing) studies in DNA and mitochondrial DNA of patients treated with antiviral NAs that induce genome error catastrophe via lethal mutagenesis.

Molnupiravir: A new candidate for COVID-19 treatment

The novel coronavirus disease 2019 (COVID‐19) emerged in late December 2019 in china and has rapidly spread to many countries around the world. The effective pharmacotherapy can reduce the mortality of COVID‐19. Antiviral medications are the candidate therapies for the management of COVID‐19. Molnupiravir is an antiviral drug with anti‐RNA polymerase activity and currently is under investigation for the treatment of patients with COVID‐19. This review focuses on summarizing published literature for the mechanism of action, safety, efficacy, and clinical trials of molnupiravir in the treatment of COVID‐19 patients.

Vaccines, therapeutics, and diagnostics for covid-19: redesigning systems to improve pandemic response

Rohit Ramchandani and colleagues propose a framework to ensure essential public health tools are fairly distributed in future pandemics

Antiviral pills could change pandemic's course

[Figure: see text].

Molnupiravir in COVID-19: A systematic review of literature

BACKGROUND AND AIMS

Molnupiravir is a newer oral antiviral drug that has recently been tested in COVID-19. We aim to conduct a systematic review of literature to find out the efficacy and safety of molnupiravir in patients with COVID-19.

METHODS

We systematically searched the electronic database of PubMed, MedRxiv and Google Scholar from inception until October 15, 2021, using MeSH keywords. Ongoing trials of molnupiravir in COVID-19 were additionally searched from the ClinicalTrials.Gov and ctri.nic.in/Clinicaltrials. We retrieved all the available granular details of phase 1 to 3 studies of molnupiravir in COVID-19. Subsequently we reviewed the results narratively.

RESULTS

Two phase 1 double-blind, randomized, placebo-controlled (DBRPC) studies of molnupiravir showed that 1600 mg daily dose is safe and tolerable, without any serious adverse events up to 5.5 days. One phase 2 DBPRC study found significantly lower time to clearance (RNA negativity) with molnupiravir 800 mg twice daily compared to the placebo (log-rank p value = 0.013) in mild to moderate COVID-19. Interim report of one phase 3 DBRPC study in non-hospitalized COVID-19 found a significant reduction in the risk of hospital admission or death by 50% (p = 0.0012). However, no significant benefit was observed with molnupiravir in the later stage of moderate to severe COVID-19.

CONCLUSION

Molnupiravir is first oral antiviral drug to demonstrate a significant benefit in reducing hospitalization or death in mild COVID-19 and could be an important weapon in the battle against SARS-CoV-2. However, its role in moderate to severe COVID-19 is questionable and more studies are needed.

Developing a direct acting, orally available antiviral agent in a pandemic: the evolution of molnupiravir as a potential treatment for COVID-19

Despite the availability of vaccines, there remains an urgent need for antiviral drugs with potent activity against SARS-CoV-2, the cause of COVID-19. Millions of people are immune-suppressed and may not be able to mount a fully protective immune response after vaccination. There is also an increasingly critical need for a drug to cover emerging SARS-CoV-2 variants, against which existing vaccines may be less effective. Here, we describe the evolution of molnupiravir (EIDD-2801, MK-4482), a broad-spectrum antiviral agent originally designed for the treatment of Alphavirus infections, into a potential drug for the prevention and treatment of COVID-19. When the pandemic began, molnupiravir was in pre-clinical development for the treatment of seasonal influenza. As COVID-19 spread, the timeline for the development program was moved forward significantly, and focus shifted to treatment of coronavirus infections. Real time consultation with regulatory authorities aided in making the acceleration of the program possible.

F-aza-T-dCyd (NSC801845), a Novel Cytidine Analog, in Comparative Cell Culture and Xenograft Studies with the Clinical Candidates T-dCyd, F-T-dCyd, and Aza-T-dCyd

In this article, 5-aza-4'-thio-2'-β-fluoro-2'-deoxycytidine (F-aza-T-dCyd, NSC801845), a novel cytidine analog, is first disclosed and compared with T-dCyd, F-T-dCyd, and aza-T-dCyd in cell culture and mouse xenograft studies in HCT-116 human colon carcinoma, OVCAR3 human ovarian carcinoma, NCI-H23 human NSCLC carcinoma, HL-60 human leukemia, and the PDX BL0382 bladder carcinoma. In three of five xenograft lines (HCT-116, HL-60, and BL-0382), F-aza-T-dCyd was more efficacious than aza-T-dCyd. Comparable activity was observed for these two agents against the NCI-H23 and OVCAR3 xenografts. In the HCT-116 study, F-aza-T-dCyd [10 mg/kg intraperitoneal (i.p.), QDx5 for four cycles], produced complete regression of the tumors in all mice with a response that proved durable beyond postimplant day 150 (129 days after the last dose). Similarly, complete tumor regression was observed in the HL-60 leukemia xenograft when mice were dosed with F-aza-T-dCyd (10 mg/kg i.p., QDx5 for three cycles). In the PDX BL-0382 bladder study, both oral and i.p. dosing of F-aza-T-dCyd (8 mg/kg QDx5 for three cycles) produced regressions that showed tumor regrowth beginning 13 days after dosing. These findings indicate that further development of F-aza-T-dCyd (NSC801845) is warranted. GRAPHICAL ABSTRACT: http://mct.aacrjournals.org/content/molcanther/20/4/625/F1.large.jpg.

Ketamine and other glutamate receptor modulators for depression in bipolar disorder in adults

BACKGROUND

There is emerging evidence that glutamatergic system dysfunction might play an important role in the pathophysiology of bipolar depression. This review focuses on the use of glutamate receptor modulators for depression in bipolar disorder.

OBJECTIVES

1. To assess the effects of ketamine and other glutamate receptor modulators in alleviating the acute symptoms of depression in people with bipolar disorder.2. To review the acceptability of ketamine and other glutamate receptor modulators in people with bipolar disorder who are experiencing acute depression symptoms.

SEARCH METHODS

We searched the Cochrane Depression, Anxiety and Neurosis Review Group's Specialised Register (CCDANCTR, to 9 January 2015). This register includes relevant randomised controlled trials (RCTs) from: the Cochrane Library (all years), MEDLINE (1950 to date), EMBASE (1974 to date), and PsycINFO (1967 to date). We cross-checked reference lists of relevant papers and systematic reviews. We did not apply any restrictions to date, language or publication status.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing ketamine, memantine, or other glutamate receptor modulators with other active psychotropic drugs or saline placebo in adults with bipolar depression.

DATA COLLECTION AND ANALYSIS

At least two review authors independently selected studies for inclusion, assessed trial quality and extracted data. Primary outcomes for this review were response rate and adverse events. Secondary outcomes included remission rate, depression severity change scores, suicidality, cognition, quality of life, and dropout rate. We contacted study authors for additional information.

MAIN RESULTS

Five studies (329 participants) were included in this review. All included studies were placebo-controlled and two-armed, and the glutamate receptor modulators - ketamine (two trials), memantine (two trials), and cytidine (one trial) - were used as add-on drugs to mood stabilisers. The treatment period ranged from a single intravenous administration (all ketamine studies), to repeated administration for memantine and cytidine (8 to 12 weeks, and 12 weeks, respectively). Three of the studies took place in the USA, one in Taiwan, and in one, the location was unclear. The majority (70.5%) of participants were from Taiwan. All participants had a primary diagnosis of bipolar disorder, according to the DSM-IV or DSM-IV-TR, and were in a current depressive phase. The severity of depression was at least moderate in all but one study.Among all glutamate receptor modulators included in this review, only ketamine appeared to be more efficacious than placebo 24 hours after the infusion for the primary outcome, response rate (odds ratio (OR) 11.61, 95% confidence interval (CI) 1.25 to 107.74; P = 0.03; I² = 0%, 2 studies, 33 participants). This evidence was rated as low quality. The statistically significant difference disappeared at three days, but the mean estimate still favoured ketamine (OR 8.24, 95% CI 0.84 to 80.61; 2 studies, 33 participants; very low quality evidence). We found no difference in response between ketamine and placebo at one week (OR 4.00, 95% CI 0.33 to 48.66; P = 0.28, 1 study; 18 participants; very low quality evidence).There was no significant difference between memantine and placebo in response rate one week after treatment (OR 1.08, 95% CI 0.06 to 19.05; P = 0.96, 1 study, 29 participants), two weeks (OR 4.88, 95% CI 0.78 to 30.29; P = 0.09, 1 study, 29 participants), four weeks (OR 5.33, 95% CI 1.02 to 27.76; P = 0.05, 1 study, 29 participants), or at three months (OR, 1.66, 95% CI 0.69 to 4.03; P = 0.26, I² = 36%, 2 studies, 261 participants). These findings were based on very low quality evidence.There was no significant difference between cytidine and placebo in response rate at three months (OR, 1.13, 95% CI 0.30 to 4.24; P = 0.86, 1 study, 35 participants; very low quality evidence).For the secondary outcome of remission, no significant differences were found between ketamine and placebo, nor between memantine and placebo. For the secondary outcome of change scores from baseline on depression scales, ketamine was more effective than placebo at 24 hours (MD -11.81, 95% CI -20.01 to -3.61; P = 0.005, 2 studies, 32 participants) but not at one or two weeks after treatment. There was no difference between memantine and placebo for this outcome.We found no significant differences in terms of adverse events between placebo and ketamine, memantine, or cytidine. There were no differences between ketamine and placebo, memantine and placebo, or cytidine and placebo in total dropouts. No data were available on dropouts due to adverse effects for ketamine or cytidine; but no difference was found between memantine and placebo.

AUTHORS' CONCLUSIONS

Reliable conclusions from this review are severely limited by the small amount of data usable for analysis. The body of evidence about glutamate receptor modulators in bipolar disorder is even smaller than that which is available for unipolar depression. Overall, we found limited evidence in favour of a single intravenous dose of ketamine (as add-on therapy to mood stabilisers) over placebo in terms of response rate up to 24 hours; ketamine did not show any better efficacy in terms of remission in bipolar depression. Even though ketamine has the potential to have a rapid and transient antidepressant effect, the efficacy of a single intravenous dose may be limited. Ketamine's psychotomimetic effects could compromise study blinding; this is a particular issue for this review as no included study used an active comparator, and so we cannot rule out the potential bias introduced by inadequate blinding procedures.We did not find conclusive evidence on adverse events with ketamine. To draw more robust conclusions, further RCTs (with adequate blinding) are needed to explore different modes of administration of ketamine and to study different methods of sustaining antidepressant response, such as repeated administrations. There was not enough evidence to draw meaningful conclusions for the remaining two glutamate receptor modulators (memantine and cytidine). This review is limited not only by completeness of evidence, but also by the low to very low quality of the available evidence.

A novel cytidine analog, RX-3117, shows potent efficacy in xenograft models, even in tumors that are resistant to gemcitabine

RX-3117 (fluorocyclopentenylcytosine) is a cytidine analog and this class of drugs, including gemcitabine, has been widely used for the treatment of various types of cancers. However, there is no oral formulation of gemcitabine and drug resistance to gemcitabine is common. In this study, the efficacy of orally-administered RX-3117 was examined in 9 different human tumor xenograft models (colon, non-small cell lung, small cell lung, pancreatic, renal and cervical), grown subcutaneously in athymic nude mice. In the Colo 205, H460, H69 and CaSki models, gemcitabine treatment resulted in 28%, 30%, 25% and 0% tumor growth inhibition (TGI), respectively, whereas oral treatment with RX-3117 induced 100%, 78%, 62% and 66% TGI, respectively. This indicates that RX-3117 may have the potential to be used for the treatment of tumors that do not respond to gemcitabine. RX-3117 was also evaluated in a single primary low-passage human pancreatic Tumorgraft™CTG-0298 (TGI 76%), which is relatively resistant to gemcitabine (TGI 38%) and has a favorable RX-3117-activating enzyme profile. These studies demonstrated the therapeutic potential and anticancer efficacy of RX-3117.

DNA methyltransferase inhibitors improve the effect of chemotherapeutic agents in SW48 and HT-29 colorectal cancer cells

DNA methylation is an epigenetic phenomenon known to play an important role in the development and progression of human cancer. Enzyme responsible for this process is DNA methyltransferase 1 (DNMT1) that maintains an altered methylation pattern by copying it from parent to daughter DNA strands after replication. Aberrant methylation of the promoter regions of genes critical for normal cellular functions is potentially reversible. Therefore, inactivation of DNMT1 seems to be a valuable target for the development of cancer therapies. Currently, the most popular DNMT inhibitors (DNMTi) are cytidine analogues like 5-azacytidine, 5-aza-2′-deoxycytidine (decitabine) and pyrimidin-2-one ribonucleoside (zebularine). In colorectal cancer, epigenetic modifications play an essential role at each step of carcinogenesis. Therefore, we have addressed the hypothesis that DNA methyltransferase inhibitors may potentiate inhibitory effects of classical chemotherapeutic agents, such as oxaliplatin and 5-fluorouracil (5-FU), commonly used in colorectal cancer therapy. Here, our report shows that DNMTi can have positive interactions with standard chemotherapeutics in colorectal cancer treatment. Using pharmacological models for the drug-drug interaction analysis, we have revealed that the combination of decitabine with 5-FU or oxaliplatin shows the most attractive interaction (synergism), whereas the effect of zebularine in combinations with chemotherapeutics is moderate and may be depended on genetic/epigenetic background of a cell line or secondary drug used in combination. Our results suggest that DNMTi administered in combination with standard chemotherapeutics might improve the treatment of patients with colorectal cancers.

Cyclopentenyl cytosine (CPEC): an overview of its in vitro and in vivo activity

The experimental cytotoxic drug cyclopentenyl cytosine (CPEC) is an analogue of cytidine. Besides its antiviral effect, its potential use in the treatment of cancer has become an important area of research. CPEC is activated by intracellular phosphorylation ultimately forming its metabolite CPEC-TP. CPEC-TP is a non competitive inhibitor of cytidine-5'-triphosphate synthetase (CTP-synthetase), an important enzyme in the formation of CTP. Studies have shown that cancer cells have a high CTP synthetase activity, thus making them interesting targets for chemotherapy. CPEC has been preclinically studied in different malignancy models. In vitro results on leukemia show activity in the nanomolar range on several cell lines. However in vivo results are conflicting and the findings vary from increase in life span over 100% to only limited effectiveness. Interesting results have been obtained in colorectal and neuroblastoma cells. In several neuroblastoma cell lines incubation with CPEC in combination with cytarabine or gemcitabine has resulted in increased cell death compared to incubation with with only one of the agents. CPEC has been studied in a phase I trial in patients with solid tumors. In five of 26 patients unexplained cardiotoxicity (extreme hypotension) occurred. The cardiotoxic effects could not be reproduced in animal models. However, precautions should be taken when using this drug in future clinical trials. Low dosage of CPEC seems necessary and intensive cardiac monitoring is advisable. In this manuscript, it is demonstrated that CPEC has an anti-cancer effect in several tumor models: CPEC might be a potentially useful drug in anticancer treatment.

Specific targeted antiviral therapy for hepatitis C

Since the discovery of the hepatitis C virus (HCV) as the major cause of non-A, non-B hepatitis in 1989, the search for specific targeted antiviral therapy for HCV (STAT-C) has been underway. Recently, major advances in the understanding of HCV biology and the development of an in vitro system of HCV replication have contributed to the selection of multiple candidate drugs for the treatment of hepatitis C. In 2006, five such candidate drugs have entered phase II clinical trials in patients chronically infected with hepatitis C, including small molecule inhibitors of the HCV NS3 serine protease and NS5B RNA-dependent RNA polymerase. This review focuses on hepatitis C protease and polymerase inhibitors that have progressed to phase II clinical development, foreshadowing the era of STAT-Cs.

Treatment combining X-irradiation and a ribonucleoside anticancer drug, TAS106, effectively suppresses the growth of tumor cells transplanted in mice

PURPOSE

To examine the in vivo antitumor efficacy of X-irradiation combined with administration of a ribonucleoside anticancer drug, 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (TAS106, ECyd), to tumor cell-transplanted mice.

METHODS AND MATERIALS

Colon26 murine rectum adenocarcinoma cells and MKN45 human gastric adenocarcinoma cells were inoculated into the footpad in BALB/c mice and severe combined immunodeficient mice, respectively. They were treated with a relatively low dose of X-irradiation (2 Gy) and low amounts of TAS106 (0.1 mg/kg and 0.5 mg/kg). The tumor growth was monitored by measuring the tumor volume from Day 5 to Day 16 for Colon26 and from Day 7 to Day 20 for MKN45. Histologic analyses for proliferative and apoptotic cells in the tumors were performed using Ki-67 immunohistochemical and terminal deoxynucleotidyl transferase-mediated nick end labeling staining. The expression of survivin, a key molecule related to tumor survival, was assessed by quantitative polymerase chain reaction and immunohistochemical analysis.

RESULTS

When X-irradiation and TAS106 treatment were combined, significant inhibition of tumor growth was observed in both types of tumors compared with mice treated with X-irradiation or TAS106 alone. Marked inhibition of tumor growth was observed in half of the mice that received the combined treatment three times at 2-day intervals. Parallel to these phenomena, the suppression of survivin expression and appearance of Ki-67-negative and apoptotic cells were observed.

CONCLUSIONS

X-irradiation and TAS106 effectively suppress tumor growth in mice. The inhibition of survivin expression by TAS106 is thought to mainly contribute to the suppression of the tumor growth.

Angiostatic activity of DNA methyltransferase inhibitors

Inhibitors of DNA methyltransferases (DNMT) and histone deacetylases can reactivate epigenetically silenced tumor suppressor genes and thereby decrease tumor cell growth. Little, however, is known on the effects of these compounds in endothelial cell biology and tumor angiogenesis. Here, we show that the DNMT inhibitors 5-aza-2'-deoxycytidine and zebularine markedly decrease vessel formation in different tumor models. We show that DNMT inhibitors are antiproliferative for tumor-conditioned endothelial cells, without affecting endothelial cell apoptosis and migration. Furthermore, these compounds inhibit angiogenesis in vitro and in vivo as shown by inhibition of endothelial cells sprouting in a three-dimensional gel and inhibition of microvessel formation in the chorioallantoic membrane, respectively. 5-Aza-2'-deoxycytidine, as well as the histone deacetylase inhibitor trichostatin A, reactivates the growth-inhibiting genes TSP1, JUNB, and IGFBP3, which are suppressed in tumor-conditioned endothelial cells. Despite enhanced DNMT activity and increased overall genomic methylation levels in tumor-conditioned endothelial cells, silencing of these genes seemed not to be regulated by direct promoter hypermethylation. For IGFBP3, gene expression in endothelial cells correlated with histone H3 acetylation patterns. In conclusion, our data show that DNMT inhibitors have angiostatic activity in addition to their inhibitory effects on tumor cells. This dual action of these compounds makes them promising anticancer therapeutics.

Review: recent clinical trials in epigenetic therapy

Epigenetic factors such as DNA methylation and histone deacetylation are known to contribute to the malignant transformation of cells by silencing critical genes. Drugs that inhibit DNA methyltransferases or histone deacetylases were shown to have the potential to reactivate silenced genes and induce differentiation or apoptosis of malignant cells. The most intensively studied class of such agents is DNA methyltransferase inhibitors, including 5-azacytidine (azacitidine) and 5-aza-2'-deoxycytidine (decitabine). In 2004, azacitidine was approved for the treatment of myelodysplastic syndrome on the basis of phase II and III studies that showed a response rate (complete and partial responses) of 15%. Azacitidine is also being evaluated in clinical trials for other malignant diseases. Decitabine has response rates of 17-49% in myelodysplastic syndrome in multiple phase II and III studies and also activity in acute and chronic myelogenous leukemia. Histone deacetylase inhibitors belong to another class of epigenetic modifying agents that include depsipeptide, butyrate derivatives, suberoylanilide hydroxamic acid and valproic acid. No agent in this class has been studied in a phase III trial, but several agents have been or are being studied in phase II trials. Further research is needed to determine the appropriate patient selection and dosing schedules.

Mechanism of inhibition of DNA methyltransferases by cytidine analogs in cancer therapy

Hypermethylation of tumor suppressor genes caused by aberrant activity of DNA methyltransferases is an important mechanism that contributes to cancer. The reaction mechanism of DNA methyltransferases, which includes formation of a covalent intermediate between the enzyme and the target base, is the basis of the success of several anti-cancer drugs that are targeted against DNA methylation. These include 5-fluoro-2'-deoxycytidine, 5-aza-2'-deoxycytidine (Decitabine) and 2-H pyrimidinone-1-beta-D(2'-deoxyriboside) (Zebularine). This review provides an insight to how the chemistry of DNA methylation is involved in the performance of these drugs targeted against it.

New nucleoside analogs in the treatment of solid tumors

Physiologic deoxynucleotides are required for an error-proof DNA replication, repair and synthesis. Any inaccuracy in this process results in a block in DNA synthesis until the error is corrected. If the cell enzymes are unable to correct the error, a signal for apoptosis is generated. This mechanism is the main target for anticancer nucleoside analogs. They also interact with the metabolism of physiological nucleosides, and consequently, have a large number of intracellular targets to induce cytotoxicity. In addition, it is now reported that some analogs may interfere directly with RNA synthesis. A great deal of synthesized nucleoside analogs provide the opportunity to understand the structure-based differences in their metabolism and mechanisms of action as well as to identify the specific intracellular targets and diseases, in which each of these newer nucleoside analogs acts most efficiently. This paper summarizes developments in the area of new nucleoside analogs undergoing clinical evaluation for the treatment of solid tumors, namely tezacitabine, troxacitabine, DMDC, CNDAC, ECyD, clofarabine, and decitabine.

Inhibitors of DNA methylation in the treatment of hematological malignancies and MDS

DNA methylation abnormalities have recently emerged as one of the most frequent molecular changes in hematopoietic neoplasms. Since methylation and transcriptional status are inversely correlated, the hypermethylation of genes involved in cell-cycle control and apoptosis could have a pathogenetic role in the development of cancer. In particular, high-risk myelodysplastic syndromes (MDS) and secondary leukemias show a high prevalence of tumor suppressor gene hypermethylation. The progression of chronic myeloproliferative diseases and of myelodysplastic syndromes, as well as that of lymphoproliferative diseases, is associated with an increased methylation rate, pointing to a role for hypermethylation of critical promoter regions in the transformation to more aggressive phenotypes. In the same line, a significantly worse prognosis has been shown for patients with hypermethylation of several genes compared to that of patients with unmethylated genes. For these reasons, the use of irreversible DNA methyltransferase inhibitors, such as 5-azacytidine and Decitabine, appears to be a promising option for the treatment of MDS and acute myeloid leukemia. In clinical trials, Azacytidine results in a significantly higher response rate, improved quality of life, reduced risk of leukemic transformation, and improved survival compared to supportive care. Similarly, Decitabine showed favorable results, promising response rates, a good nonhematologic toxicity profile, and a trend for better survival compared to intensive chemotherapy, particularly in older patients. The synergistic effect of histone deacetylase inhibitors, including phenylbutyrate (PB), in reactivating silenced genes encouraged clinical studies on the combination of PB and demethylating agents in hematological diseases, characterized by p15 silencing. The sequential administration of a "first generation" demethylating agent and HDAC inhibitors gave preliminary evidence of a reduced methylation of target genes, as also described with Decitabine. Clinical trials are still ongoing, and preliminary data indicate for the first time that the natural history of MDS may be changed by a non-intensive treatment, characterized by an outstanding toxicity profile.

A role for DNA mismatch repair in sensing and responding to fluoropyrimidine damage

The phenomenon of damage tolerance, whereby cells incur DNA lesions that are nonlethal, largely ignored, but highly mutagenic, appears to play a key role in carcinogenesis. Typically, these lesions are generated by alkylation of DNA or incorporation of base analogues. This tolerance is usually a result of the loss of specific DNA repair processes, most often DNA mismatch repair (MMR). The availability of genetically matched MMR-deficient and -corrected cell systems allows dissection of the consequences of this unrepaired damage in carcinogenesis as well as the elucidation of cell cycle checkpoint responses and cell death consequences. Recent data indicate that MMR plays an important role in detecting damage caused by fluorinated pyrimidines (FPs) and represents a repair system that is probably not the primary system for detecting damage caused by these agents, but may be an important system for correcting key mutagenic lesions that could initiate carcinogenesis. In fact, clinical studies have shown that there is no benefit of FP-based adjuvant chemotherapy in colon cancer patients exhibiting microsatellite instability, a hallmark of MMR deficiency. MMR-mediated damage tolerance and futile cycle repair processes are discussed, as well as possible strategies using FPs to exploit these systems for improved anticancer therapy.

Comparative evaluation of L-Fd4C and related nucleoside analogs as promising antiviral agents

As documented in the recent literature, there are more than 50 million people infected with HIV worldwide to date since the emergence of HIV and AIDS in the Western world in 1981. More importantly, about 7000 people die of AIDS daily with 2.5 and 2.6 millions total deaths in 1998 and 1999, respectively. On the other hand, human hepatitis B virus (HBV) is the leading cause of chronic hepatitis in the world. According to WHO executive summary, over 350 millions (approximately 5% of the world s population) people are chronically infected with HBV. There are about 1 million chronic HBV carriers in the United States. Although safe and effective vaccination for HBV is available for developing countries, there is still no effective treatment for the millions of chronically infected individuals. Consequently, long term infection with chronic HBV could lead to cirrhosis, and hepatocellular carcinoma. In light of these facts, it is evident that the discovery and development of novel antiviral agents for the treatment of HIV and HBV is an extremely important undertaking.The interest in L-nucleosides was spurred in recent years by the findings that L-nucleosides are generally endowed with lower host toxicity while maintaining good antiviral activity in comparison to their respective D-nucleosides. The recent FDA approval of Lamivudine [L-BCH 189 (3TC)] for the treatment of HIV and HBV further supports these notions. Since the discovery of Lamivudine, a large number of 2 ,3 -dideoxy (dd)- and 2 ,3 -didehydro-2 ,3 -dideoxy (D4)-L-nucleoside analogs have been synthesized and evaluated in hopes of identifying even better antiviral agents. As a result, 2 ,3 -Dideoxy-2 ,3 -didehydro-beta-L-fluorocytidine (beta-L-Fd4C) was found to be a promising new lead. The first synthesis and antiviral activity assessment of L-Fd4C were reported by Lin and Cheng et al. in 1996. Recent disclosures from several laboratories clearly demonstrated that L-Fd4C was the most potent anti-HBV agent reported to date (vs. 3TC, L-FddC, L-FMAU, etc.). In fact, L-Fd4C proved to be at least 10 times more potent than Lamivudine on HBV DNA synthesis in the hepatoma cell line HepG2 2.2.15. Compared with L-Fd4C, D-Fd4C showed similar anti-HIV activity yet reduced anti-HBV activity. 2 F-L-Fd4C exhibited excellent acid stability but reduced antiviral activity and cytotoxicity. Although L-Fd4C is converted intracellularly by cytoplasmic deoxycytidine kinase to its mono-, di- and triphosphate metabolites,43 the newly prepared bis(SATE)-L-Fd4CMP proved to be more potent against HBV yet less cytotoxic than L-Fd4C itself. The chemically synthesized L-Fd4CTP was found to be a poor substrate for human polymerase gamma. A recent report from Zhu and Cheng et al. indicated that L-Fd4C had no inhibitory effect on mitochondrial DNA synthesis at concentrations up to 10 microM. An in vivo study involving HBV-infected ducks showed that longer administration of L-Fd4C induced a sustained suppression of viremia (>95%) and of viral DNA synthesis in the liver. The same study also demonstrated that L-Fd4C is more potent than 3TC in vivo. In summary, on the basis of the data presented in this chapter, it is evident that L-Fd4C is endowed with exceptional anti-HBV activity (both in vitro and in vivo) as well as an acceptable toxicity profile, thus rendering it a very promising development candidate.

Antitumor activity and pharmacokinetics of TAS-106, 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine

We examined the effects of dosage schedule on antitumor activity in vitro and in vivo to determine the optimal administration schedule for a new nucleoside antimetabolite 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, TAS-106). The cytotoxicity of TAS-106 in vitro against human tumors was evaluated at three drug exposure periods. TAS-106 exhibited fairly potent cytotoxicity even with 4 h exposure, and nearly equivalent and sufficiently potent cytotoxicity with 24 and 72 h exposures. These results suggest that long-term exposure to TAS-106 will not be required to achieve maximal cytotoxicity. The antitumor activity of TAS-106 in vivo was compared in nude rat models bearing human tumors on three administration schedules, once weekly, 3 times weekly, and 5 times weekly for 2 or 4 consecutive weeks. TAS-106 showed strong antitumor activity without serious toxicity on all three schedules, but the antitumor activity showed no obvious schedule-dependency in these models. When tumor-bearing nude rats were given a single i.v. dose of [(3)H]TAS-106, tumor tissue radioactivity tended to remain high for longer periods of time as compared to the radioactivity in various normal tissues. Furthermore, when the metabolism of TAS-106 in the tumor was examined, it was found that TAS-106 nucleotides (including the active metabolite, the triphosphate of TAS-106) were retained at high concentrations for prolonged periods. These pharmacodynamic features of TAS-106 may explain the strong antitumor activity without serious toxicity, observed on intermittent administration schedules, in nude rat models with human tumors. We therefore consider TAS-106 to be a promising compound which merits further investigation in patients with solid tumors.

Cyclopentenyl cytosine inhibits cytidine triphosphate synthetase in paediatric acute non-lymphocytic leukaemia: a promising target for chemotherapy

Cytidine triphosphate (CTP) synthetase is a key enzyme in the anabolic pathways of cytosine and uracil ribonucleotide metabolism. The enzyme catalyses the conversion of uridine triphosphate (UTP) into CTP, and has a high activity in various malignancies, which has led to the development of inhibitors of CTP synthetase for therapeutic purposes. We studied both CTP synthetase activity and ribonucleotide concentrations in leukaemic cells of 12 children suffering from acute non-lymphocytic leukaemia (ANLL), and performed incubation experiments with cyclopentenyl cytosine (CPEC), a nucleoside analogue that is capable of inhibiting CTP synthetase. The CTP synthetase activity in ANLL cells (5.1+/-2.3 nmol CTP/mg/h) was significantly higher compared with granulocytes of healthy controls (0.6+/-0.4 nmol CTP/mg/h, P=0.0002), but was not different from the CTP synthetase activity in non-malignant CD34+ bone marrow cells (5. 6+/-2.4 nmol CTP/mg/h). Major shifts were observed in the various ribonucleotide concentrations in ANLL cells compared with granulocytes: the absolute amount of ribonucleotides was increased with a substantial rise of the CTP (2.4 versus 0.4 pmol/microg protein, P=0.0007) and UTP (8.7 versus 1.6 pmol/microg protein, P=0. 0007) concentrations in ANLL cells compared with granulocytes. Treatment of ANLL cells in vitro with CPEC induced a major depletion (77% with 2.5 microM of CPEC) in the concentration of CTP, whilst the concentrations of the other ribonucleotides remained unchanged. Therefore, the high activity of CTP synthetase in acute non-lymphocytic leukaemic cells can be inhibited by CPEC, which provides a key to a new approach for the treatment of ANLL.

Long term prevention of allergic lung inflammation in a mouse model of asthma by CpG oligodeoxynucleotides

Asthma is an inflammatory disease of the airways that is induced by Th2 cytokines and inhibited by Th1 cytokines. Despite a steady increase in the incidence, morbidity, and mortality from asthma, no current treatment can reduce or prevent asthma for a prolonged period. We examined the ability of unmethylated CpG oligodeoxynucleotides (ODN), which are potent inducers of Th1 cytokines, to prevent the inflammatory and physiological manifestations of asthma in mice sensitized to ragweed allergen. Administration of CpG ODN 48 h before allergen challenge increased the ratio of IFN-gamma to IL-4 secreting cells, diminished allergen-induced eosinophil recruitment, and decreased the number of ragweed allergen-specific IgE-producing cells. These effects of CpG ODN were sustained for at least 6 wk after its administration. Furthermore, there was a vigorous Th1 memory response to the recall Ag, inhibition of peribronchial and perivascular lung inflammation, and inhibition of bronchial hyperresponsiveness 6 wk after administration of CpG ODN. Administration of CpG ODN in IFN-gamma -/- mice failed to inhibit eosinophil recruitment, indicating a critical role of IFN-gamma in mediating these effects. This is the first report of a treatment that inhibits allergic lung inflammation in presensitized animals for a prolonged period and thus has relevance to the development of an effective long term treatment for asthma.

Studies on the antitumor activity and biochemical actions of cyclopentenyl cytosine against human colon carcinoma HT-29 in vitro and in vivo

Cyclopentenyl cytosine (CPEC) is cytotoxic to several tumor cell lines. CPEC inhibits CTP synthesis resulting in depletion of cytidylate pools. The aim of this study was to examine CPEC's cytotoxic and antitumor activity in vitro and in vivo against human colon carcinoma HT-29, and to relate its action on CTP synthesis. CPEC exhibits potent cytotoxicity in vitro to HT-29 cells with an LC50 (concentration that is lethal to the survival of 50% cell colonies) of 2.4 microM and 0.46 microM following 2 h and 24 h exposure, respectively. Incubation of cells with CPEC for 2 h resulted in a dose-dependent decrease in cytidylate pools. The in vivo antitumor activity of CPEC in athymic mice transplanted subcutaneously (s.c.) with 3 million HT-29 cells was examined. Antitumor activity of CPEC was elucidated in early-staged tumor, wherein CPEC (1.5 mg/kg, QD x 9 or 3 mg/kg, QOD x 9) was administered intraperitoneally (i.p.) 24 h after tumor implantation and it resulted in a significant reduction in tumor weight to 48% of control. The effect of CPEC on established solid tumors in vivo was examined in athymic mice transplanted s.c. 14 days earlier with HT-29 cells and treated i.p. with 1.5 mg/kg CPEC, QD x 5 for 4 courses, with a 10 day-interval between courses. This treatment resulted in a significant reduction in tumor weight (72%) in the treated group. HPLC analysis of HT-29 tumor obtained from mice after treatment with CPEC showed a depletion of the CTP concentration reaching a nadir at 8 h. In conclusion, the present studies demonstrate potent antitumor activity of CPEC against freshly transplanted and established human colon carcinoma which can be corroborated with the drug's biochemical actions.

Prevention of simian immunodeficiency virus, SIVsm, or HIV-2 infection in cynomolgus monkeys by pre- and postexposure administration of BEA-005

OBJECTIVE

To study the possibilities and limitations of postexposure treatment to prevent the establishment of infection after accidental exposure to HIV.

DESIGN AND METHODS

The effect of 2,3'-dideoxy-3'-hydroxymethyl cytidine (B1 A-005) was investigated on acute simian immunodeficiency virus (SIV) and HIV-2 infections in macaques in pre- and postexposure treatment experiments.

RESULTS

Postexposure treatment with BLA-005 (3 x 10 mg/kg) for as short as 3 days prevented infection with SIVsm after intravenous or rectal inoculation. Infection with HIV-2 could also be blocked by postexposure BFA-005 treatment.

CONCLUSION

This study shows that therapeutic intervention can block early systemic and mucosal infections with SIV and HIV-2. Further evaluation is ongoing.