PMX-53 (3D53) is a synthetic peptidic and a potent and orally active complement C5a receptor (CD88) antagonist with an IC50 of 20 nM. PMX-53 is also a low-affinity MrgX2 agonist that stimulates MrgX2-mediated mast cell degranulation. PMX-53 specifically binds to C5aR1 and does not bind to the second C5aR (C5L2) and C3aR. PMX-53 has anti-inflammatory, anticancer and antiatherosclerotic effects.