Different mutations in the HHV-6 DNA polymerase gene accounting for resistance to foscarnet

BACKGROUND: Human herpesvirus 6 (HHV-6), which is closely related to human cytomegalovirus, is sensitive to foscarnet (PFA). Up to now, the resistance of HHV-6 to PFA has not been investigated. OBJECTIVES: The goal of the study was to isolate and characterize PFA-resistant HHV-6 mutants in order to determine the mechanisms of resistance to the drug. METHODS: PFA-resistant viruses, isolated in MT4 cell culture under increasing concentrations of PFA, were characterized phenotypically and genotypically. The mutations identified in the HHV-6 DNA polymerase gene were evaluated in a functional assay using recombinant mutated forms of the enzyme, and their effect on protein structure was analysed in a three-dimensional model derived from available structures of DNA polymerases. RESULTS: Two mutants were selected and were 8- and 15-fold more resistant to PFA than the wild-type strain. Four amino acid changes were detected in the HHV-6 DNA polymerase in association with PFA resistance: T435R, H507Y, C525S, located in the deltaC conserved domain, and F292S. Either alone or in combination, these substitutions significantly decreased the inhibitory effect of PFA at the level of the polymerase, as measured by the incorporation of radiolabelled nucleotides in a DNA elongation assay. In the three-dimensional model of HHV-6 DNA polymerase structure the four changes were not located within the putative catalytic site, but they might induce either a disturbance of local conformation or a restricted access of PFA to its target site. CONCLUSION: This first characterization of HHV-6 resistance to PFA highlights the role of distinct DNA polymerase gene mutations.     

Antiretroviral activity and pharmacokinetics in mice of oral bis(pivaloyloxymethyl)-9-(2-phosphonylmethoxyethyl)adenine, the bis(pivaloyloxymethyl) ester prodrug of 9-(2-phosphonylmethoxyethyl)adenine.

Lipophilic ester prodrugs of 9-(2-phosphonylmethoxyethyl)adenine (PMEA), i.e., bis(pivaloyloxymethyl)-PMEA [bis(POM)-PMEA] and diphenyl-PMEA, have been synthesized in an attempt to increase the oral bioavailability of this broad-spectrum antiviral agent. The antiretroviral efficacy was determined in severe combined immune deficiency (SCID) mice infected with Moloney murine sarcoma virus (MSV). They were treated twice daily for 5 days after infection. Oral treatment with bis(POM)-PMEA at a dose equivalent to 100 or 50 mg of PMEA per kg of body weight per day proved markedly effective in delaying MSV-induced tumor formation and death of the mice. Oral bis(POM)-PMEA afforded anti-MSV efficacy equal to that of subcutaneous PMEA given at equimolar doses. Oral treatment with PMEA or diphenyl-PMEA proved less efficient. Similarly, in mice infected with Friend leukemia virus (FLV), oral treatment with bis(POM)-PMEA at a dose equivalent to 100 or 50 mg of PMEA per kg per day effected a marked inhibition of FLV-induced splenomegaly (87 and 48% inhibition, respectively), the efficacy being equal to that of PMEA given subcutaneously at equivalent doses. Pharmacokinetic experiments with mice showed that the oral bioavailabilities of PMEA following oral gavage of bis(POM)-PMEA, diphenyl-PMEA, or PMEA (at a dose equivalent to 50 mg of PMEA per kg) were 53,3, and 16%, respectively. These data were calculated from the levels of free PMEA in plasma. Also, the recoveries of free PMEA in the urine upon oral administration of bis(POM)-PMEA, diphenyl-PMEA, or PMEA (at a dose equivalent to 25 mg of PMEA per kg) were 48, 4, and 7%, respectively. Oral bis(POM)-PMEA was not recovered from plasma, suggesting that it was readily cleaved to free PMEA. In contrast, diphenyl-PMEA was not efficiently cleaved to free PMEA, resulting in a rather low oral bioavailability of PMEA from this prodrug. Bis(POM)-PMEA appears to be an efficient oral prodrug of PMEA that deserves further clinical evaluation in human immunodeficiency virus-infected individuals.     

The Influenza Virus Polymerase Complex: An Update on Its Structure,Functions, and Significance for Antiviral Drug Design

Influenza viruses cause seasonal epidemics and pandemic outbreaks associated with significant morbidity and mortality, and a huge cost. Since resistance to the existing anti‐influenza drugs is rising, innovative inhibitors with a different mode of action are urgently needed. The influenza polymerase complex is widely recognized as a key drug target, given its critical role in virus replication and high degree of conservation among influenza A (of human or zoonotic origin) and B viruses. We here review the major progress that has been made in recent years in unravelling the structure and functions of this protein complex, enabling structure‐aided drug design toward the core regions of the PA endonuclease, PB1 polymerase, or cap‐binding PB2 subunit. Alternatively, inhibitors may target a protein–protein interaction site, a cellular factor involved in viral RNA synthesis, the viral RNA itself, or the nucleoprotein component of the viral ribonucleoprotein. The latest advances made for these diverse pharmacological targets have yielded agents in advanced (i.e., favipiravir and VX‐787) or early clinical testing, besides several experimental inhibitors in various stages of development, which are all covered here.     

Antiretroviral Efficacy and Pharmacokinetics of Oral Bis(isopropyloxycarbonyloxymethyl)9-(2-Phosphonylmethoxypropyl)adenine in Mice

To overcome the low oral bioavailability of the highly potent and selective antiretroviral agent (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA), a new lipophilic ester derivative, i.e., the bis(isopropyloxycarbonyloxymethyl)-ester [bis(POC)-PMPA], was prepared. The usefulness of bis(POC)-PMPA as an oral prodrug for PMPA was investigated in the intestinal mucosa Caco-2 cell monolayer model. The total transport of bis(POC)-PMPA was 2.7%, whereas it was less than 0.1% for PMPA. Bis(POC)-PMPA was considerably metabolized inside the epithelial cells, since the majority of the compound was recovered after transport in the form of the monoester metabolite [mono(POC)-PMPA]. In contrast, bis(POC)-PMPA was relatively resistant to degradation at the luminal side of the Caco-2 cells. Pharmacokinetic studies with mice showed that the oral bioavailability of bis(POC)-PMPA (calculated from the curves of the concentration of free PMPA in plasma) was 20%. Neither bis(POC)-PMPA nor mono(POC)-PMPA could be recovered in plasma, suggesting the efficient release of the active drug PMPA after oral administration of bis(POC)-PMPA. Severe combined immunodeficient (SCID) mice infected with Moloney murine sarcoma virus (MSV) and treated orally with bis(POC)-PMPA for 5 or 10 days (dosages, 50, 100, or 200 mg of PMPA equivalent per kg of body weight per day) showed a significant delay in MSV-induced tumor appearance and tumor-associated death. The antiviral efficacy of oral bis(POC)-PMPA was related to the dosage and treatment period and was not significantly different from that of subcutaneous PMPA given at an equivalent dose. The favorable pharmacokinetic profile, marked antiviral efficacy, and low toxicity make bis(POC)-PMPA an attractive oral prodrug of PMPA that should be further pursued in clinical studies with patients infected with human immunodeficiency virus or hepatitis B virus.     

Differential antiherpesvirus and antiretrovirus effects of the (S) and (R) enantiomers of acyclic nucleoside phosphonates: potent and selective in vitro and in vivo antiretrovirus activities of (R)-9-(2-phosphonomethoxypropyl)-2,6-diaminopurine.

The (S)- and (R)-enantiomers of acyclic purine nucleoside phosphonate analogs (i.e., 3-hydroxy-2-phosphonomethoxypropyl [HPMP] derivatives, 3-fluoro-2-phosphonomethoxypropyl [FPMP] derivatives, and 2-phosphonomethoxypropyl [PMP] derivatives of adenine [A], 2-aminopurine, 2,6-diaminopurine [DAP], and guanine [G]) have been synthesized and evaluated for antiviral activity. As a rule, the HPMP derivatives proved effective against DNA viruses but not RNA viruses or retroviruses. In particular, (S)-HPMPA, (S)-HPMPDAP, and (R)- and (S)-HPMPG were exquisitely inhibitory to herpes simplex virus type 1 (50% effective concentrations, 0.63, 0.22, 0.10, and 0.66 microM, respectively). The FPMP and PMP derivatives showed marked inhibitory activities against retroviruses but not DNA viruses. The (S)-enantiomer of FPMPA and the (R)-enantiomer of PMPA were approximately 30- to 100-fold more effective against human immunodeficiency virus and Moloney murine sarcoma virus (MSV) than their enantiomeric counterparts. In contrast, both (S)- and (R)-enantiomers of the DAP and G derivatives proved equally effective against retroviruses, except for (R)-PMPDAP, which was 15- to 40-fold more inhibitory than (S)-PMPDAP. (R)-PMPDAP emerged as the most potent and selective inhibitor of MSV-induced transformation of murine C3H/3T3 cells and human immunodeficiency virus-induced cytopathicity in MT-4 and CEM cells (50% effective concentration, approximately 0.1 to 0.6 microM). When administered intraperitoneally at a single dose as low as 2 mg/kg, (R)-PMPDAP efficiently decreased MSV-induced tumor formation in newborn NMRI mice and significantly increased the survival time of MSV-infected mice. In addition, upon oral administration to MSV-infected mice, (R)-PMPDAP showed marked antiretroviral efficacy.     

The 1‐year Renal Biopsy Index: a scoring system to drive biopsy indication at 1‐year post‐kidney transplantation

Surveillance biopsies after renal transplantation remain debatable. To drive the decision of such intervention, we propose a predictive score of abnormal histology at 1‐year post‐transplantation, named 1‐year Renal Biopsy Index (1‐RBI). We studied 466 kidney recipients from the DIVAT cohort alive with a functioning graft and a surveillance biopsy at 1‐year post‐transplantation. Patients displaying abnormal histology (49%) (borderline, acute rejection, interstitial fibrosis and tubular atrophy [IFTA] grade 2 or 3, glomerulonephritis) were compared to the normal or subnormal (IFTA grade 1) histology group. Obtained from a lasso penalized logistic regression, the 1‐RBI was composed of recipient gender, serum creatinine at 3, 6, and 12 month post‐transplantation and anticlass II immunization at transplantation (internal validation: AUC = 0.71, 95% CI [0.53–0.83]; external validation: AUC = 0.62, 95% CI [0.58–0.66]). While we could not determinate a threshold able to identify patients at high chance of normal or subnormal histology, we estimated and validated a discriminating threshold capable of identifying a subgroup of 15% of the patients with a risk of abnormal histology higher than 80%. The 1‐RBI is computable online at www.divat.fr . The 1‐RBI could be a useful tool to standardize 1‐year biopsy proposal and may for instance help to indicate one in case of high risk of abnormal histology.     

Viral Evolution and Immunology of SARS-CoV-2 in a Persistent Infection after Treatment with Rituximab

Background. Prolonged shedding of SARS-CoV-2 in immunocompromised patients has been described. Furthermore, an accumulation of mutations of the SARS-CoV-2 genome in these patients has been observed. Methods. We describe the viral evolution, immunologic response and clinical course of a patient with a lymphoma in complete remission who had received therapy with rituximab and remained SARS-CoV-2 RT-qPCR positive for 161 days. Results. The patient remained hospitalised for 10 days, after which he fully recovered and remained asymptomatic. A progressive increase in Ct-value, coinciding with a progressive rise in lymphocyte count, was seen from day 137 onward. Culture of a nasopharyngeal swab on day 67 showed growth of SARS-CoV-2. Whole genome sequencing (WGS) demonstrated that the virus belonged to the wildtype SARS-CoV-2 clade 20B/GR, but rapidly accumulated a high number of mutations as well as deletions in the N-terminal domain of its spike protein. Conclusion. SARS-CoV-2 persistence in immunocompromised individuals has important clinical implications, but halting immunosuppressive therapy might result in a favourable clinical course. The long-term shedding of viable virus necessitates customized infection prevention measures in these individuals. The observed accelerated accumulation of mutations of the SARS-CoV-2 genome in these patients might facilitate the origin of new VOCs that might subsequently spread in the general community.     

Polyomavirus BK Genome Comparison Shows High Genetic Diversity in Kidney Transplant Recipients Three Months after Transplantation

BK polyomavirus (BKPyV) is a human DNA virus generally divided into twelve subgroups based on the genetic diversity of Viral Protein 1 (VP1). BKPyV can cause polyomavirus-associated nephropathy (PVAN) after kidney transplantation. Detection of BKPyV DNA in blood (viremia) is a source of concern and increase in plasma viral load is associated with a higher risk of developing PVAN. In this work, we looked for possible associations of specific BKPyV genetic features with higher plasma viral load in kidney transplant patients. We analyzed BKPyV complete genome in three-month samples from kidney recipients who developed viremia during their follow-up period. BKPyV sequences were obtained by next-generation sequencing and were de novo assembled using the new BKAnaLite pipeline. Based on the data from 72 patients, we identified 24 viral groups with unique amino acid sequences: three in the VP1 subgroup IVc2, six in Ib1, ten in Ib2, one in Ia, and four in II. In none of the groups did the mean plasma viral load reach a statistically significant difference from the overall mean observed at three months after transplantation. Further investigation is needed to better understand the link between the newly described BKPyV genetic variants and pathogenicity in kidney transplant recipients.     

Recovery of humoral immunity is critical for successful antiviral therapy in disseminated mouse adenovirus type 1 infection

Severe adenovirus infections in transplant recipients undergoing immunosuppressive therapy are of increasing concern. Controversy exists on the contribution of antiviral therapy and the host immune response to recovery from these infections. Here, we established a systemic mouse adenovirus type 1 (MAV-1) infection in cyclophosphamide (CyP)-treated BALB/c mice. CyP was administered at 100 mg per kg of body weight every other day for 2, 3, or 4 weeks, thereby inducing general but reversible leukopenia, with a major suppression of the B-cell numbers and functionality that was more pronounced than that seen with T cells. The outcome of MAV-1 infection was dependent on the duration of CyP therapy, as the mice with the most severe immunosuppression were the most vulnerable to MAV-1-induced hemorrhagic enteritis and mortality. The protective effect of concomitant antiviral therapy with cidofovir depended on the level of immunosuppression. The combination of cidofovir treatment with the withdrawal of immunosuppression was the most successful regimen for increasing survival rates. Survival was clearly correlated with the clearance of virus and increased titers of MAV-1-specific antibodies in sera. In addition, the passive transfer of MAV-1-specific immunoglobulin G into MAV-1-infected SCID BALB/c mice caused a marked delay in mortality, the extent of the delay being dependent on the titer of MAV-1-specific antibodies. Based on the critical role of the humoral immune response in the early defense against disseminated adenovirus infection, the concomitant use of adenovirus-specific immunoglobulins and antiviral therapy should be considered for transplant patients at risk for severe adenovirus infections.