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Strasfeld L, Chou S. Antiviral drug resistance: mechanisms and clinical implications. Infect Dis Clin North Am 2010; 24:413-37. [PMID: 20466277 DOI: 10.1016/j.idc.2010.01.001] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Antiviral drug resistance is an increasing concern in immunocompromised patient populations, where ongoing viral replication and prolonged drug exposure lead to the selection of resistant strains. Rapid diagnosis of resistance can be made by associating characteristic viral mutations with resistance to various drugs as determined by phenotypic assays. Management of drug resistance includes optimization of host factors and drug delivery, selection of alternative therapies based on knowledge of mechanisms of resistance, and the development of new antivirals. This article discusses drug resistance in herpesviruses and hepatitis B.
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Strasfeld L, Lee I, Tatarowicz W, Villano S, Chou S. Virologic Characterization of Multidrug‐Resistant Cytomegalovirus Infection in 2 Transplant Recipients Treated with Maribavir. J Infect Dis 2010; 202:104-8. [DOI: 10.1086/653122] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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Elyas R, Guerra LA, Pike J, DeCarli C, Betolli M, Bass J, Chou S, Sweeney B, Rubin S, Barrowman N, Moher D, Leonard M. Is staging beneficial for Fowler-Stephens orchiopexy? A systematic review. J Urol 2010; 183:2012-8. [PMID: 20303527 DOI: 10.1016/j.juro.2010.01.035] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2009] [Indexed: 10/19/2022]
Abstract
PURPOSE Fowler and Stephens showed that by dividing the spermatic vessels a high intra-abdominal testis could be placed in the scrotum. Testicular atrophy is a potential complication of this technique. We conducted a systematic review to determine whether single or 2-stage Fowler-Stephens orchiopexy results in better testicular viability. MATERIALS AND METHODS We searched electronic databases, clinical trial registries and gray literature. We included reports describing boys younger than 18 years with a primary outcome of "testicular viability and position." We performed a meta-analysis using random effects models. Heterogeneity was assessed using forest plot and I(2) statistic. RESULTS We identified 1,807 citations and included 61 articles. Single stage Fowler-Stephens orchiopexy was discussed in 9 articles, a 2-stage procedure in 36 and both approaches in 16. There were no randomized controlled trials, and most studies were cohort or case series. The pooled estimate of success rates was 80% for single stage Fowler-Stephens orchiopexy (95% CI 75 to 86) and 85% for 2-stage Fowler-Stephens orchiopexy (95% CI 81 to 90). The pooled odds ratio of single stage vs 2-stage Fowler-Stephens orchiopexy was 2.0 (95% CI 1.1 to 3.9) favoring the 2-stage procedure. There was no difference in the success rate between laparoscopic and open techniques in either single or 2-stage Fowler-Stephens orchiopexy. There was no evidence of asymmetry on the funnel plot. There were no complications reported with single stage, while ileus, hematoma and infection were the most common complications with 2-stage Fowler-Stephens orchiopexy. CONCLUSIONS Both techniques have a fairly high success rate but 2-stage Fowler-Stephens orchiopexy appears to carry a higher rate of success than the single stage approach (85% vs 80%, OR 2 in favor of 2-stage). Laparoscopic and open techniques had the same success rate. However, the level of evidence of the studies was low, and a study of a more robust design, such as a randomized controlled trial, should be performed.
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Iwasenko JM, Scott GM, Rawlinson WD, Keogh A, Mitchell D, Chou S. Successful valganciclovir treatment of post-transplant cytomegalovirus infection in the presence of UL97 mutation N597D. J Med Virol 2009; 81:507-10. [PMID: 19152402 PMCID: PMC2786239 DOI: 10.1002/jmv.21397] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Mutations in the human cytomegalovirus (CMV) UL97 protein kinase are the most common mechanism of ganciclovir (GCV) resistance in the clinical setting. A CMV strain with a previously unrecognized UL97 mutation N597D was identified in the blood of a heart transplant recipient who experienced a persistent CMV infection with high viral loads accompanying pain and fever while receiving valganciclovir (valGCV) therapy. The N597D mutation was transferred by mutagenesis to an antiviral sensitive CMV strain for analysis of antiviral susceptibility by standardized phenotypic assay. Recombinant phenotyping showed N597D conferred a less than twofold increase in GCV IC(50) compared to the sensitive control strain. Despite the presence of this mutation, valGCV eventually resolved the infection after 6 weeks of therapy. A subsequent CMV reactivation was also responsive to valganciclovir. This case illustrates the diversity of UL97 mutations in the codon segment 590-607 usually associated with GCV resistance, with some mutations producing minimal levels of resistance that do not preclude a therapeutic response to the drug. Accurate interpretation of genotypic test results ultimately requires experimental determination of the level of resistance conferred by newly discovered UL97 mutations.
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Gill RB, Frederick SL, Hartline CB, Chou S, Prichard MN. Conserved retinoblastoma protein-binding motif in human cytomegalovirus UL97 kinase minimally impacts viral replication but affects susceptibility to maribavir. Virol J 2009; 6:9. [PMID: 19159461 PMCID: PMC2636770 DOI: 10.1186/1743-422x-6-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2008] [Accepted: 01/21/2009] [Indexed: 11/10/2022] Open
Abstract
The UL97 kinase has been shown to phosphorylate and inactivate the retinoblastoma protein (Rb) and has three consensus Rb-binding motifs that might contribute to this activity. Recombinant viruses containing mutations in the Rb-binding motifs generally replicated well in human foreskin fibroblasts with only a slight delay in replication kinetics. Their susceptibility to the specific UL97 kinase inhibitor, maribavir, was also examined. Mutation of the amino terminal motif, which is involved in the inactivation of Rb, also renders the virus hypersensitive to the drug and suggests that the motif may play a role in its mechanism of action.
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Chou S. Cytomegalovirus UL97 mutations in the era of ganciclovir and maribavir. Rev Med Virol 2008; 18:233-46. [PMID: 18383425 DOI: 10.1002/rmv.574] [Citation(s) in RCA: 135] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Mutations in the human CMV UL97 kinase gene are a major mechanism of viral resistance to two anti-CMV drugs, ganciclovir (GCV) and maribavir (MBV). GCV, the most widely used and established therapy for CMV, is a substrate for the UL97 kinase. Well-characterised GCV-resistance mutations at UL97 codons 460, 520 and 590-607 impair the phosphorylation of GCV that is necessary for its antiviral activity, presumably by altering substrate recognition. In contrast, MBV is an inhibitor of the UL97 kinase and is the first new CMV therapy to reach later stage clinical trials in many years. No MBV-resistant CMV isolates have yet been detected in clinical trials, but after culture propagation under drug, UL97 mutations that confer moderate to high-level MBV resistance have been identified at codons 353, 397, 409 and 411. These mutations are located upstream of the GCV-resistance mutations and are close to the ATP-binding and catalytic domains common to all kinases, consistent with MBV acting as a small molecule ATP-competitive kinase inhibitor. So far, no UL97 mutations are known to confer resistance to both GCV and MBV.
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Shapira MY, Resnick IB, Chou S, Neumann AU, Lurain NS, Stamminger T, Caplan O, Saleh N, Efferth T, Marschall M, Wolf DG. Artesunate as a potent antiviral agent in a patient with late drug-resistant cytomegalovirus infection after hematopoietic stem cell transplantation. Clin Infect Dis 2008; 46:1455-7. [PMID: 18419454 DOI: 10.1086/587106] [Citation(s) in RCA: 122] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
This is the first report of treatment of cytomegalovirus infection with artesunate, for a stem cell transplant recipient with a newly identified foscarnet-resistant and ganciclovir-resistant DNA polymerase L776M mutation. Artesunate treatment resulted in a 1.7-2.1-log reduction in viral load by treatment day 7, with a viral half-life of 0.9-1.9 days, indicating a highly effective block in viral replication.
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Chou S, Marousek G, Li S, Weinberg A. Contrasting drug resistance phenotypes resulting from cytomegalovirus DNA polymerase mutations at the same exonuclease locus. J Clin Virol 2008; 43:107-9. [PMID: 18502683 DOI: 10.1016/j.jcv.2008.04.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2008] [Accepted: 04/11/2008] [Indexed: 10/22/2022]
Abstract
BACKGROUND Diverse mutations in the cytomegalovirus (CMV) DNA polymerase (pol) gene confer resistance to one or more of the antiviral drugs ganciclovir, foscarnet or cidofovir. The levels of resistance conferred by specific mutations are variable, ranging from insignificant resistance to triple-drug resistance. OBJECTIVES Three pol mutations, I521T, P522A and P522L, detected in patients who received antiviral therapy for CMV infection, were studied by recombinant phenotyping to characterize their associated drug resistance. STUDY DESIGN The individual mutations were transferred by homologous recombination into a reference CMV strain modified with a reporter gene and the drug concentrations required to reduce the reporter signal by 50% (IC50) were determined. RESULTS The mutations I521T and P522A each conferred 3- to 4-fold increases in IC50 to both ganciclovir and cidofovir, while mutation P522L conferred no significant resistance to either drug. None of these mutations conferred foscarnet resistance. CONCLUSIONS The resistance phenotypes of mutations I521T and P522A are as predicted from the known mutation P522S, but divergent results with P522L indicate that different amino acid substitutions at the same position may not have the same effect on drug resistance. New mutations must be individually validated for proper interpretation of genotypic resistance testing.
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Chou S, Marousek GI, Van Wechel LC, Li S, Weinberg A. Growth and drug resistance phenotypes resulting from cytomegalovirus DNA polymerase region III mutations observed in clinical specimens. Antimicrob Agents Chemother 2007; 51:4160-2. [PMID: 17709468 PMCID: PMC2151462 DOI: 10.1128/aac.00736-07] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recombinant phenotyping of cytomegalovirus (CMV) pol region III mutations from clinical specimens showed that T813S and G841A each conferred foscarnet resistance and approximately threefold increased ganciclovir resistance; adding the UL97 mutation C592G increased ganciclovir resistance to approximately sixfold. Bacterial artificial chromosome CMV clones containing pol mutation L845P were nonviable unless repaired with the wild-type sequence.
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Hertel L, Chou S, Mocarski ES. Viral and cell cycle-regulated kinases in cytomegalovirus-induced pseudomitosis and replication. PLoS Pathog 2007; 3:e6. [PMID: 17206862 PMCID: PMC1764433 DOI: 10.1371/journal.ppat.0030006] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2006] [Accepted: 11/13/2006] [Indexed: 12/26/2022] Open
Abstract
A process of pseudomitosis occurs during human cytomegalovirus infection that appears similar to cellular mitosis but involves the formation of multiple spindle poles, abnormal condensation, and mislocalization of chromosomal DNA. The relationship of this process to viral replication and cell cycle regulation during infection has been poorly understood. Pseudomitosis consistently peaks at late times of infection in all viral strains examined but at overall highest frequencies (30% to 35% of cells) using one common laboratory strain variant (AD169varATCC). Cyclin-dependent kinase 1 (Cdk1) plays a crucial role in pseudomitosis, mirroring its role in conventional mitosis. Dominant negative Cdk1 inhibits and wild-type Cdk1 stimulates this process; however, viral yields remain the same regardless of pseudomitosis levels. Broad inhibition of cell cycle−regulated kinases (Cdk1/Cdk2/Cdk5/Cdk9) with indirubin-3′-monoxime substantially decreases viral yields and synergizes with the viral UL97 kinase inhibitor, maribavir. Thus, Cdk1 is necessary and sufficient to drive pseudomitosis, whereas a combination of viral and cell cycle−regulated kinases is important during viral replication. The human herpesvirus cytomegalovirus, which infects most people worldwide, orchestrates a stimulatory effect on cell growth and division, creating an environment that appears similar to many cancer-causing viruses that may be important in viral disease. In previous work, we discovered that viral infection stimulates cells to proceed to an abnormal state mimicking cell division or mitosis but blocks the formation of daughter cells. Here the abnormal state (pseudomitosis) is shown to depend on viral events that drive high levels of the cellular enzyme cyclin-dependent kinase 1 (Cdk1), normally associated with progression through cell division. Although Cdk1 by itself exerts no detectable influence on viral replication levels, host cell cyclin-dependent kinases play an overlapping role with the virus-encoded protein kinase (UL97) in viral replication. Specific inhibitors of these host and viral kinases are used to demonstrate that Cdk1 is necessary and sufficient to drive pseudomitosis; however, viral as well as cell cycle−regulated kinases are important for efficient viral replication.
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Tonelli M, Hemmelgarn B, Gill JS, Chou S, Culleton B, Klarenbach S, Manns B, Wiebe N, Gourishankar S. Patient and allograft survival of Indo Asian and East Asian dialysis patients treated in Canada. Kidney Int 2007; 72:499-504. [PMID: 17554253 DOI: 10.1038/sj.ki.5002367] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Kidney failure is relatively common among Canadians of Asian origin. However, little is known about the health outcomes after initiation of renal replacement therapy in this population. Our study evaluates differences in the likelihood of renal transplantation and graft loss among Asian and white patients. We studied 21 523 adults of East Asian, Indo Asian or white ethnicity who had initiated dialysis in Canada from 1990-2000. Subjects were followed until death, loss to follow-up or end of study (2004). The proportion of the eligible subjects who were East Asian, Indo Asian, or white was 6, 3, and 91%, respectively. Compared to white patients, East Asian and Indo Asian patients were significantly less likely to receive a renal transplant after adjusting for potential confounding factors. This disparity is greater for transplants from living donors as compared to those from deceased donors. The adjusted death censored graft loss in transplant recipients was not significantly different between ethnic groups. The adjusted risk of death following transplantation, however, was significantly lower in Indo Asian than in white patients. Our findings show that in a Canadian population, patients of East Asian or Indo Asian origin had lower rates of renal transplantation than white patients, especially for living donor transplantation. These findings warrant further study, especially given the good graft outcomes in these individuals.
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Chou S, Wechel LCV, Marousek GI. Cytomegalovirus UL97 kinase mutations that confer maribavir resistance. J Infect Dis 2007; 196:91-4. [PMID: 17538888 DOI: 10.1086/518514] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2006] [Accepted: 01/29/2007] [Indexed: 11/03/2022] Open
Abstract
The cytomegalovirus (CMV) UL97 kinase inhibitor maribavir (MBV) is undergoing clinical antiviral trials. Two clinical CMV isolates serially passaged in cell culture under MBV showed >20-fold increases in MBV resistance after the development of the UL97 mutation V353A in one of the isolates and of T409M in the other. Marker transfer studies confirmed that the V353A and T409M mutations conferred ~15-fold and ~80-fold increases, respectively, in MBV resistance without significantly affecting ganciclovir susceptibility. The 3 UL97 mutations now known to confer MBV resistance are located upstream of UL97 mutations linked to ganciclovir resistance, closer to kinase domains that are associated with adenosine triphosphate binding and phosphotransfer.
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Marfori JE, Exner MM, Marousek GI, Chou S, Drew WL. Development of new cytomegalovirus UL97 and DNA polymerase mutations conferring drug resistance after valganciclovir therapy in allogeneic stem cell recipients. J Clin Virol 2007; 38:120-5. [PMID: 17157554 DOI: 10.1016/j.jcv.2006.11.005] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2006] [Revised: 11/07/2006] [Accepted: 11/11/2006] [Indexed: 11/25/2022]
Abstract
BACKGROUND We report on two allogeneic stem cell transplant recipients who developed cytomegalovirus disease associated with new viral mutations that conferred antiviral drug resistance. METHODS Blood specimens obtained during symptomatic disease were analyzed for mutations in the CMV UL97 and DNA polymerase genes and new mutations were assessed by recombinant phenotyping. RESULTS Rising cytomegalovirus (CMV) antigenemia occurred after 4-5 months of preemptive valganciclovir therapy, followed by symptomatic CMV disease including fatal pneumonia in one case. In one case, a new viral UL97 mutation (deletion of codons 601-603) was found which conferred 15-fold increased ganciclovir resistance. In the other case, a known UL97 resistance mutation M460V and a new DNA polymerase (pol) mutation D413A were found. D413A conferred ganciclovir and cidofovir resistance. CONCLUSIONS Known and newly discovered drug resistance mutations arising during preemptive therapy may complicate post-transplant CMV disease in stem cell recipients. Improved recombinant phenotyping methods enable the rapid quantitation of the resistance conferred by newly identified UL97 and pol mutations.
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Chou S, Marousek GI. Maribavir antagonizes the antiviral action of ganciclovir on human cytomegalovirus. Antimicrob Agents Chemother 2006; 50:3470-2. [PMID: 17005835 PMCID: PMC1610080 DOI: 10.1128/aac.00577-06] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The cytomegalovirus (CMV) UL97 kinase inhibitor maribavir antagonized the anti-CMV effect of ganciclovir, increasing the ganciclovir 50% inhibitory concentration against a sensitive strain by up to 13-fold. Antiviral activities of foscarnet and cidofovir were unaffected by maribavir.
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Scott GM, Weinberg A, Rawlinson WD, Chou S. Multidrug resistance conferred by novel DNA polymerase mutations in human cytomegalovirus isolates. Antimicrob Agents Chemother 2006; 51:89-94. [PMID: 17043128 PMCID: PMC1797699 DOI: 10.1128/aac.00633-06] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The emergence of antiviral-resistant cytomegalovirus (CMV) strains is a continuing clinical problem, with increased numbers of immunocompromised patients given longer-duration antiviral prophylaxis. Two previously unrecognized CMV DNA polymerase mutations (N408K and A834P) identified separately and together in at-risk lung and kidney transplant recipients and a third mutation (L737M) identified in a liver transplant recipient were characterized by marker transfer to antiviral-sensitive laboratory strains AD169 and Towne. Subsequent phenotypic analyses of recombinant strains demonstrated the ability of mutation N408K to confer ganciclovir (GCV) and cidofovir (CDV) resistance and of mutation A834P to confer GCV, foscarnet, and CDV resistance. Mutation L737M did not confer resistance to any of the antiviral agents tested. A recombinant strain containing both N408K and A834P demonstrated increased GCV and CDV resistance compared to the levels of resistance of the virus containing only the A834P mutation. The addition of mutation N408K in combination with A834P also partially reconstituted the replication impairment of recombinant virus containing only A834P. This suggests that perturbation of both DNA polymerization (A834P) and exonuclease (N408K) activities contributes to antiviral resistance and altered replication kinetics in these mutant strains. The identification of these multidrug-resistant CMV strains in at-risk seronegative recipients of organs from seropositive donors suggests that improved prophylactic and treatment strategies are required. The additive effect of multiple mutations on antiviral susceptibility suggests that increasing antiviral-resistant phenotypes can result from different virus-antiviral interactions.
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Drew WL, Miner RC, Marousek GI, Chou S. Maribavir sensitivity of cytomegalovirus isolates resistant to ganciclovir, cidofovir or foscarnet. J Clin Virol 2006; 37:124-7. [PMID: 16962820 DOI: 10.1016/j.jcv.2006.07.010] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2006] [Accepted: 07/21/2006] [Indexed: 11/29/2022]
Abstract
BACKGROUND The cytomegalovirus (CMV) UL97 inhibitor drug maribavir (MBV) is undergoing clinical antiviral trials. OBJECTIVES To assess the MBV sensitivity of CMV strains and isolates containing mutations that confer resistance to current antiviral drugs ganciclovir, cidofovir or foscarnet. STUDY DESIGN Resistant clinical isolates and laboratory strains containing UL97 and or UL54 DNA polymerase mutations were tested for sensitivity to all four drugs by standard plaque reduction assay and a reporter-based yield reduction assay. Sensitive control strains were also tested. RESULTS Eleven CMV strains or isolates resistant to GCV, four resistant to FOS and two resistant to CDV, were all sensitive to MBV. These viruses represent four UL97 mutations and three UL54 DNA polymerase mutations. The laboratory derived UL97 L397R mutant was highly MBV-resistant but remained sensitive to the other three drugs. CONCLUSIONS No cross-resistance has been detected between viruses resistant to MBV and those resistant to one or more of the current CMV antiviral drugs, consistent with differences in their mechanisms of action.
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Chou S, Van Wechel LC, Marousek GI. Effect of cell culture conditions on the anticytomegalovirus activity of maribavir. Antimicrob Agents Chemother 2006; 50:2557-9. [PMID: 16801445 PMCID: PMC1489798 DOI: 10.1128/aac.00207-06] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The cytomegalovirus UL97 kinase inhibitor maribavir suppressed viral growth more effectively in lung fibroblasts than in skin fibroblasts, and some cellular kinase inhibitors enhanced its antiviral activity. These effects influence the phenotypic assay of drug susceptibility and suggest the possibility of therapeutically useful combinations of maribavir and cellular kinase inhibitors.
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Prichard MN, Quenelle DC, Bidanset DJ, Komazin G, Chou S, Drach JC, Kern ER. Human cytomegalovirus UL27 is not required for viral replication in human tissue implanted in SCID mice. Virol J 2006; 3:18. [PMID: 16571131 PMCID: PMC1448171 DOI: 10.1186/1743-422x-3-18] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Accepted: 03/29/2006] [Indexed: 11/10/2022] Open
Abstract
Inhibition of the human cytomegalovirus UL97 kinase by maribavir is thought to be responsible for the antiviral activity of this compound. Some mutations that confer resistance to maribavir map to UL97, however additional mutations that also confer resistance to the drug were mapped to UL27. These open reading frames share a low level of homology, yet the function of pUL27 remains unknown. A recombinant virus with a deletion in the UL27 open reading frame was reported previously to exhibit a slight replication deficit, but a more important function in vivo was hypothesized given its homology to the UL97 kinase. The potential for an important function in vivo was investigated by determining if these knockout viruses could replicate in human tissue implanted in SCID mice. None of the AD169 derived viruses replicated well in the implanted thymus/liver tissue, and is consistent with previous observations, although all of the viruses replicated to some degree in retinal tissue implants. Replication of the parent viruses was observed at 7 days post inoculation, whereas no replication was detected with any of the recombinant viruses with deletions in UL27. By day 14, replication was detected in two of the three knockout viruses and in all of the viruses by day 42. These data are consistent with minimal defects observed in cell culture, but are not consistent with an important role for UL27 in vivo. We conclude that UL27 is not required for viral replication in vivo.
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Lurain NS, Fox AM, Lichy HM, Bhorade SM, Ware CF, Huang DD, Kwan SP, Garrity ER, Chou S. Analysis of the human cytomegalovirus genomic region from UL146 through UL147A reveals sequence hypervariability, genotypic stability, and overlapping transcripts. Virol J 2006; 3:4. [PMID: 16409621 PMCID: PMC1360065 DOI: 10.1186/1743-422x-3-4] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Accepted: 01/12/2006] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Although the sequence of the human cytomegalovirus (HCMV) genome is generally conserved among unrelated clinical strains, some open reading frames (ORFs) are highly variable. UL146 and UL147, which encode CXC chemokine homologues are among these variable ORFs. RESULTS The region of the HCMV genome from UL146 through UL147A was analyzed in clinical strains for sequence variability, genotypic stability, and transcriptional expression. The UL146 sequences in clinical strains from two geographically distant sites were assigned to 12 sequence groups that differ by over 60% at the amino acid level. The same groups were generated by sequences from the UL146-UL147 intergenic region and the UL147 ORF. In contrast to the high level of sequence variability among unrelated clinical strains, the sequences of UL146 through UL147A from isolates of the same strain were highly stable after repeated passage both in vitro and in vivo. Riboprobes homologous to these ORFs detected multiple overlapping transcripts differing in temporal expression. UL146 sequences are present only on the largest transcript, which also contains all of the downstream ORFs including UL148 and UL132. The sizes and hybridization patterns of the transcripts are consistent with a common 3'-terminus downstream of the UL132 ORF. Early-late expression of the transcripts associated with UL146 and UL147 is compatible with the potential role of CXC chemokines in pathogenesis associated with viral replication. CONCLUSION Clinical isolates from two different geographic sites cluster in the same groups based on the hypervariability of the UL146, UL147, or the intergenic sequences, which provides strong evidence for linkage and no evidence for interstrain recombination within this region. The sequence of individual strains was absolutely stable in vitro and in vivo, which indicates that sequence drift is not a mechanism for the observed sequence hypervariability. There is also no evidence of transcriptional splicing, although multiple overlapping transcripts extending into the adjacent UL148 and UL132 open reading frames were detected using gene-specific probes.
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Cantero A, Barthakur S, Bushart TJ, Chou S, Morgan RO, Fernandez MP, Clark GB, Roux SJ. Expression profiling of the Arabidopsis annexin gene family during germination, de-etiolation and abiotic stress. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2006; 44:13-24. [PMID: 16531057 DOI: 10.1016/j.plaphy.2006.02.002] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2005] [Indexed: 05/07/2023]
Abstract
Annexins are a multigene family in most plant species and are suggested to play a role in a wide variety of essential cellular processes. In Arabidopsis thaliana there are eight different annexins (AnnAt1-8), which range from 29% to 83% in deduced amino acid sequence identity. As a first step toward clarifying the individual functions of these annexins, in this study we have used quantitative real time reverse transcription PCR to assess their differential expression in different tissues or after different stimuli. We determined which annexins are expressed during germination and early seedling growth by assaying annexin expression levels in dry and germinating seeds and in 7-day-old light-grown seedlings. Our results indicate that transcripts for all eight annexins are present in germinating seeds and that transcript levels for all the annexins increase by 7 days of normal growth. We assayed transcript levels in dark grown roots, cotyledons, and hypocotyls and found that the relative abundance of each annexin varied in these dark-grown tissues. We also examined the effects of red and far red light treatments on annexin expression in 5.5-day-old etiolated seedlings. Light treatments significantly altered transcript levels in hypocotyls and cotyledons for only two members of the gene family. Finally, we monitored annexin expression changes in response to a variety of abiotic stresses. We found that the expression of most of the Arabidopsis annexin genes is differentially regulated by exposure to salt, drought, and high- and low-temperature conditions, indicating a likely role for members of this gene family in stress responses.
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Chou S, Van Wechel LC, Lichy HM, Marousek GI. Phenotyping of cytomegalovirus drug resistance mutations by using recombinant viruses incorporating a reporter gene. Antimicrob Agents Chemother 2005; 49:2710-5. [PMID: 15980340 PMCID: PMC1168698 DOI: 10.1128/aac.49.7.2710-2715.2005] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A new recombinant phenotyping method was developed for the analysis of drug resistance mutations in human cytomegalovirus (CMV). CMV strain T2211 was derived from strain AD169 by inserting unique restriction sites and a secreted alkaline phosphatase (SEAP) reporter gene for rapid viral quantitation. Specific viral UL97 and pol gene mutations were transferred by recombination into T2211, and their drug resistance phenotypes (for ganciclovir, foscarnet, or cidofovir) were determined by the drug concentrations required to reduce supernatant SEAP activity by 50% (IC50). Changes in the IC50 conferred by the mutations tested (UL97 M460V, C592G, A594V, and L595S and pol del981-2) were similar to those previously reported in marker transfer and conventional plaque reduction assays. The combination of UL97 C592G and pol del981-2 conferred much higher ganciclovir resistance than either mutation alone. The UL97 polymorphism D605E had no measurable effect on ganciclovir susceptibility, alone or in combination with common UL97 resistance mutations. Transfer into strain T2211 facilitates the phenotyping of newly observed mutations, combinations of mutations, and clinical CMV sequences without an accompanying viral isolate.
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Springer KL, Chou S, Li S, Giller RH, Quinones R, Shira JE, Weinberg A. How evolution of mutations conferring drug resistance affects viral dynamics and clinical outcomes of cytomegalovirus-infected hematopoietic cell transplant recipients. J Clin Microbiol 2005; 43:208-13. [PMID: 15634973 PMCID: PMC540138 DOI: 10.1128/jcm.43.1.208-213.2005] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Infection with cytomegalovirus (CMV) remains a significant cause of morbidity and mortality among hematopoietic cell transplant (HCT) recipients. We describe two pediatric HCT recipients who developed persistent and severe drug-resistant CMV infections. CMV resistance to foscarnet and ganciclovir was detected after only 6 and 11 weeks of therapy, respectively. Viral pol mutations associated with drug resistance in these patients included T838A (a novel mutation) and D588N, which were shown by marker transfer to confer foscarnet and multidrug resistance, respectively. Each of these mutations significantly reduced in vitro replication of CMV, suggesting that they may decrease viral fitness. This finding was further supported by the disappearance of mutations upon withdrawal of antiviral pressure in one patient. Novel antivirals or combination therapy may be required for the treatment of drug-resistant CMV in HCT recipients and perhaps in other severely immunocompromised patients.
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Weston SJ, Leistikow RL, Reddy KR, Torres M, Wertheimer AM, Lewinsohn DM, Chou S, Davey MP, Corless C, O'Farrelly C, Nelson DR, Rosen HR. Reconstitution of hepatitis C virus-specific T-cellmediated immunity after liver transplantation. Hepatology 2005; 41:72-81. [PMID: 15619226 DOI: 10.1002/hep.20507] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Hepatitis C virus (HCV)-related liver failure is the leading indication for liver transplantation worldwide. After transplantation, virological recurrence is the rule, but the spectrum of histological injury is wide, ranging from the development of allograft cirrhosis within a few years to minimal hepatitis despite long-term follow-up. The immunological correlates of this variable natural history are poorly understood. Here, we studied the kinetics of the cellular immune responses, viral replication, and allograft histology in 24 patients who had undergone liver transplantation for HCV-related liver failure. Using direct ex vivo methodologies (i.e., interferon-gamma ELISPOT and major histocompatibility complex class I-peptide tetrameric complexes), we found that patients who experienced viral eradication after antiviral therapy showed restoration of HCV-specific T-cell responses, whereas patients with progressive HCV recurrence that failed to respond to therapy showed declining frequencies of these viral-specific effector cells. The cytotoxic T lymphocytes that peripherally reconstituted after transplantation were clonotypically identical to those present within the recipient explant liver, defined at the level of the T-cell receptor beta chain (one epitope/one clone). Moreover, the subset of patients who spontaneously demonstrated minimal histologic recurrence had more vigorous CD4+ T-cell responses in the first 3 months, particularly targeting nonstructural proteins. We provide evidence that T-cell responses emerge after liver transplantation, and their presence correlates with improved histological and clinical outcomes. In conclusion, these results may help identify patients more likely to develop severe HCV recurrence and therefore benefit from current antiviral therapy, as well as provide a rationale for the future use of novel immunotherapeutic approaches. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience. wiley.com/jpages/0270-9139/suppmat/index.html).
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Murphy MD, Marousek GI, Chou S. HIV protease mutations associated with amprenavir resistance during salvage therapy: importance of I54M. J Clin Virol 2004; 30:62-7. [PMID: 15072756 DOI: 10.1016/j.jcv.2003.08.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2003] [Revised: 08/07/2003] [Accepted: 08/21/2003] [Indexed: 10/26/2022]
Abstract
OBJECTIVE To examine the clinical significance of HIV protease mutations detected before and after therapy with amprenavir. STUDY DESIGN Serial plasma HIV loads and protease gene mutations were monitored in 31 patients who received amprenavir, including 19 who had been exposed to other protease inhibitors (salvage therapy). Recombinant phenotyping was used to assess the significance of new mutations appearing after amprenavir therapy. RESULTS After 6-8 months of amprenavir, 4 treatment-naïve and 5 salvage patients had an undetectable plasma HIV load, while 12 other salvage patients showed less than 10-fold HIV load reduction. HIV protease mutations associated with amprenavir resistance included I84V, I50V, I47V, V32I, and I54M. Among mutations newly detected after amprenavir treatment, I54M occurred in six cases, I54L in two cases, M46I in two cases, I47V in one case and I50V in one case. When compared with pretreatment plasma without the mutation, recombinant phenotyping showed that I54M increased the amprenavir resistance by at least 6-fold, resulting in up to 48-fold resistance over a drug-sensitive control. CONCLUSIONS Protease I54M frequently appears after amprenavir therapy, and when combined with pre-existing mutations, leads to high-level amprenavir resistance and treatment failure.
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Chou S, Marousek GI, Senters AE, Davis MG, Biron KK. Mutations in the human cytomegalovirus UL27 gene that confer resistance to maribavir. J Virol 2004; 78:7124-30. [PMID: 15194788 PMCID: PMC421656 DOI: 10.1128/jvi.78.13.7124-7130.2004] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previous drug selection experiments resulted in the isolation of a human cytomegalovirus (CMV) UL97 phosphotransferase mutant resistant to the benzimidazole compound maribavir (1263W94), reflecting the anti-UL97 effect of this drug. Three other CMV strains were plaque purified during these experiments. These strains showed lower-grade resistance to maribavir than the UL97 mutant. Extensive DNA sequence analyses showed no changes from the baseline strain AD169 in UL97, the genes involved in DNA replication, and most structural proteins. However, changes were identified in UL27 where each strain contained a different mutation (R233S, W362R, or a combination of A406V and a stop at codon 415). The mutation at codon 415 is predicted to truncate the expressed UL27 protein by 193 codons (32% of UL27) with a loss of nuclear localization. The expression of full-length UL27 as a green fluorescent fusion protein in uninfected fibroblasts resulted in nuclear and nucleolar fluorescence, whereas cytoplasmic localization was observed when codons 1 to 415 were similarly expressed. Viable UL27 deletion mutants were created by recombination and showed slight growth attenuation and maribavir resistance in cell culture. Marker transfer experiments confirmed that UL27 mutations conferred maribavir resistance. The UL27 sequence was well conserved in a sample of 16 diverse clinical isolates. Mutation in UL27, a betaherpesvirus-specific early gene of unknown biological function, may adapt the virus for growth in the absence of UL97 activity.
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