In vitro Cytochrome P450 Reaction Phenotyping for Metabolism‐linked hemotoxicity of NPC1161B, a novel 8‐aminoquinoline antimalarial agent

Abstract

8‐Aminoquinolines are important class of drugs, holding promise in many infectious diseases. Primaquine is a prototype of this class, while its 5‐dichlorophenoxy derivative, NPC1161B has been identified as a promising candidate with enantioselective toxicity and efficacy profiles. Use of 8‐AQs is restricted due to their hematological toxicities, for which biotransformation seems to be a prerequisite. Earlier metabolic studies have been hindered due to the unstable nature of hematotoxic intermediates. An in vitro metabolism‐linked hematoxicity assay has been employed to evaluate generation of methemoglobin and other hematotoxic responses by 8‐AQs. Direct incubation of the drug with microsomes or recombinant human CYP isoforms afforded in situ generation of toxic metabolites that mediate a robust hemoglobin oxidation. Three main approaches of reaction phenotyping i.e., correlation analysis, chemical inhibition and recombinant CYPs were employed to investigate hematoxicity of NPC1161B. CYP3A4 selectively metabolized NPC1161B leading to methemoglobin toxicity. It also correlated with CYP3A4 content of different batches of human liver microsomes. Inhibitors of CYP3A4 dramatically reduced methemoglobin formation in in vitro and in vivo studies. Data provide the basis for a mechanism based approach to abrogate hematotoxicity of NPC1161B, currently under evaluation for clinical advancement.