Macitentan in the Treatment of Organ Rejection After Lung Transplantation

Preliminary studies employing a "rat tracheal allograft transplant model" have demonstrated amelioration of the fibrous airway obliteration associated with blockade of the renin-angiotension and the endothelin system implementing the ERA antagonist, BOSENTAN (100 mg/kg). Clinical studies have indeed demonstrated that the mitogenic and profibrotic peptide, ET-1, may represent a potential biomarker in clinical BOS. Detection of levels of ET-1 mRNA were significantly increased in the lung allografts of those with versus those without BOS at 3 and 12 months post-transplantation while ET-1 concentrations were significantly elevated both in serum and bronchoalveolar lavage fluid (BALF) from patients with BOS. Additional studies have further demonstrated a pronounced inhibitory effect elicited by chronic ET(A) receptor blockade in the absence of immunosuppressive therapy, on both plasma levels and transcriptional regulation of inflammatory chemokines in a rat heterotopic heart transplant model of chronic rejection . MACITENTAN, a novel, competitive ERA with significantly slower receptor dissociation kinetics than currently approved ERAs, may represent a renewed hope for patients suffering from progressive CLAD post-transplantation. The efficacy of MACITENTAN was not realized in the exploratory Phase II MUSIC Trial for IPF for the primary endpoint measure of forced vital capacity (FVC), nevertheless, mechanistic disparities in the pathobiology of CLAD versus IPF, therefore should not preclude a separate therapeutic trial. Further, in vitro treatment with MACITENTAN and its major metabolite (ACT-132577) decreases alpha smooth muscle actin elaboration by dermal fibroblasts in systemic sclerosis fibrotic skin lesions, therefore offering significant promise for potential disease modulation. Most importantly, the MUSIC Trial has further demonstrated the "clinical safety" of this pharmacologic therapy in 178 patients with IPF with mean drug exposure of approximately 14 months and without statistical differences in incidence of abnormal liver function studies. Recent pharmacokinetic studies of MACITENTAN have suggested no "clinically significant" drug-drug interaction with respect to Cytochrome P4503A4 for concurrent post-transplant immunosuppressive type therapies, such as cyclosporine, tacrolimus and mycophenolate mofetil; while insignificant interaction with the frequently implemented "azole-type antibiotics" was also observed.