Immunosuppressive TOR kinase inhibitor everolimus (RAD) suppresses growth of cells derived from posttransplant lymphoproliferative disorder at allograft-protecting doses

Background. Posttransplant lymphoproliferative disorders (PTLDs) represent a life-threatening complication of standard immunosuppressive therapy. The impact of novel, rapamycin-related immunosuppressive drugs on the pathogenesis of PTLDs remains undefined. Methods. We tested the effect of everolimus (RAD, Novartis Pharma AG, Basel, Switzerland) on human PTLD-derived cells using in vitro. assays and an in vivo severe combined immunodeficiency disease mouse xenotransplant model. Results. Everolimus profoundly inhibited the proliferation, cell-cycle progression, and survival of the PTLD-1 cell line established from a pulmonary PTLD. Equally profound inhibition of PTLD-1 growth was achieved in-vivo at well-tolerated everolimus doses of 0.5 to 5 mg/kg per day. Five mg/kg per day of everolimus, given once per day, inhibited PTLD-1 tumor volume gain by more than 10-fold in treated mice compared with untreated mice. Because the subsequent pharmacokinetic analysis indicated rapid everolimus absorption, distribution, and clearance in mice (with a half-life of 3 to 6 hr and maximum drug blood concentration reached after 0.5 to 1 hr), treatment was changed to a twice-daily regimen. Everolimus given twice daily at 0.5 mg/kg,per dose inhibited tumor-volume gain by more than 60-fold and at 0.25 mg/kg per dose by more than 10-fold. Similar everolimus doses were required to prevent graft rejection in a mouse heart allotransplantation model; the highest dose tested (1.5 mg/kg twice daily) resulted in long-term graft survival in all mice that underwent transplantation. Conclusions. Everolimus displays a potent inhibitory effect on PTLD-derived cells in vitro and in vivo in a dose range leading to prevention of. allograft rejection and may prove effective in both the prevention and treatment of PTLDS in transplant patients.