Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by complement-mediated intravascular hemolysis due to the absence of complement regulators CD55 and CD59 on affected erythrocytes. Danicopan is a first-in-class oral proximal, complement alternative pathway factor D inhibitor. Therapeutic factor D inhibition was designed to control intravascular hemolysis and prevent C3-mediated extravascular hemolysis. In this open-label, phase II, dose-finding trial, ten untreated PNH patients with hemolysis received danicopan monotherapy (100-200 mg thrice daily). Endpoints included changes in the concentrations of lactate dehydrogenase (LDH) at day 28 (primary endpoint), of LDH at day 84, and of hemoglobin. Safety, pharmacokinetics/pharmacodynamics, and patient-reported outcomes were assessed. Ten patients reached the primary endpoint; two later discontinued treatment: one because of a serious adverse event (elevated aspartate aminotransferase/alanine aminotransferase coincident with breakthrough hemolysis, resolving without sequelae) and one for personal reasons unrelated to safety. Eight patients completed treatment. Intravascular hemolysis was inhibited, as demonstrated by a mean decrease of LDH (5.7 times upper limit of normal [ULN] at baseline vs. 1.8 times ULN at day 28 and 2.2 times ULN at day 84; both P<0.001). Mean baseline hemoglobin, 9.8 g/dL, increased by 1.1 (day 28) and 1.7 (day 84) g/dL (both P<0.005). No significant C3 fragment deposition occurred on glycosylphosphatidylinositol-deficient erythrocytes. Mean baseline Functional Assessment of Chronic Illness Therapy–Fatigue score, 34, increased by 9 (day 28) and 13 (day 84) points. The most common adverse events were headache and upper respiratory tract infection. These phase II, monotherapy data show that proximal inhibition with danicopan provides clinically meaningful inhibition of intravascular hemolysis and increases hemoglobin concentration in untreated PNH patients, without evidence of C3-mediated extravascular hemolysis. This trial was registered at www.clinicaltrials.gov (#NCT03053102).
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