Everolimus and mycophenolate mofetil are potent inhibitors of fibroblast proliferation after lung transplantation

Background. Dysregulated fibroblast proliferation is thought to play an important role in the progression of bronchiolitis obliterans (BO) after lung transplantation. Augmented immunosuppression is often used to treat BO. We investigated the effect of methylprednisolone (mPRED), cyclosporine A (CsA), tacrolimus (FK506), azathioprine (AZA), mycophenolate mofetil (MMF), and everolimus (rapamycin derivative [RAD]) on the proliferative capacity of fibroblasts cultured from transbronchial biopsies of lung transplant recipients. Methods. Primary cultures of human lung fibroblasts were obtained from 14 transbronchial biopsies of lung transplant recipients. Subconfluent cells were serum starved for 24 hr followed by growth stimulation in the presence or absence of the respective drug in six concentrations ranging as follows: 0.01 to 100 mg/L for mPRED; 0.01 to 50 mg/L for CsA and AZA; 0.001 to 5 mg/L for FK506 and MMF; and 0.00001 to 1 mg/L for RAD. Proliferation was quantified by [H-3]thymidine incorporation and direct cell count. A toxic drug effect was excluded by trypan blue. Results. Drug concentrations (mg/L) causing a 50% inhibition of fibroblast proliferation were mPRED 4; CsA 20; FK506 0.3; AZA 7; MMF 0.3; and RAD 0.0006. Drug concentrations (mg/L) causing inhibition of fetal bovine serum-induced proliferation were mPRED 60; CsA 45; FK506 3; AZA 35; MMF 1; and RAD 0.003. Conclusions. RAD and MMF were the most potent antifibroproliferative drugs and were effective at concentrations achieved clinically, supporting their use for the treatment of patients with early BO. Our method holds promise as an in vitro model to assess the likely in vivo responses of human lung fibroblasts to specific immunosuppressive drugs.