title: Anti-BK virus mechanisms of sirolimus and leflunomide alone and in combination: toward a new therapy for BK virus infection.
abstract: BACKGROUND
  Human BK polyomavirus is the causative agent of BK nephropathy which is now the leading cause of early renal graft loss. Although no randomized clinical trials have supported this therapy, reduction of immunosuppressive drugs is the current BK nephropathy treatment. We hypothesized that inhibition of the intracellular protein kinase pathways activated by BK virus may be a more effective therapeutic strategy than reduction of immunosuppression.
  
  
  RESULTS
  Four days after infection of renal epithelial cells lines CCD1103, CCD1105 and human primary tubular epithelial cells with BK virus, we found increased phosphorylation of 3'-phosphoinositide-dependent kinase-1 (PDK-1), the protein kinase Akt (Akt), mammalian target of rapamycin (mTOR), and 70 kDa ribosomal protein S6 kinase (p70S6K). To inhibit this pathway, we used sirolimus, which repressed p70S6K phosphorylation and reduced BK virus large T antigen expression in a dose-dependent manner. We then used the tyrosine kinase inhibitor leflunomide (using the active metabolite A77 1726), which decreased PDK1 and Akt phosphorylation and inhibited BK virus genome replication and early gene expression. The combination of sirolimus and leflunomide inhibited BK virus genome replication, large T antigen expression, PDK1, Akt, mammalian target of rapamycin, and p70S6K phosphorylation.
  
  
  CONCLUSIONS
  On the basis of these results, we suggest that inhibition of protein kinase pathways with a combination of sirolimus and leflunomide may be an effective therapy for BK virus reactivation. Because both sirolimus and leflunomide possess immunosuppressive activity, combination therapy may reduce BK pathogenesis while maintaining appropriate transplant immunosuppression.
authors.affiliation: Faculty of Medicine, Institute of Infection, Immunity and Inflammation, University of Calgary, Calgary, AB, Canada.
authors.forename: Abdelhamid
authors.initials: A
authors.lastname: Liacini
authors.forename: Mark E
authors.initials: ME
authors.lastname: Seamone
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Muruve
authors.forename: Lee Anne
authors.initials: LA
authors.lastname: Tibbles
mesh_terms: D000956:Antigens, Viral / Q000276:immunology; D000957:Antigens, Viral, Tumor / Q000187:drug effects / Q000276:immunology; D000998:Antiviral Agents / Q000627:therapeutic use*; D001739:BK Virus / Q000187:drug effects / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D002460:Cell Line; D004359:Drug Therapy, Combination; D004847:Epithelial Cells / Q000821:virology; D006801:Humans; D007166:Immunosuppressive Agents / Q000627:therapeutic use; D007555:Isoxazoles / Q000627:therapeutic use*; D016030:Kidney Transplantation / Q000009:adverse effects* / Q000276:immunology; D007684:Kidney Tubules / Q000821:virology; D000077339:Leflunomide; D016133:Polymerase Chain Reaction; D027601:Polyomavirus Infections / Q000276:immunology* / Q000517:prevention & control; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000627:therapeutic use*; D014181:Transplantation Immunology / Q000187:drug effects
chemical_list: D000956:Antigens, Viral; D000957:Antigens, Viral, Tumor; D000998:Antiviral Agents; D007166:Immunosuppressive Agents; D007555:Isoxazoles; D000077339:Leflunomide; D020123:Sirolimus