Altering metabolic profiles of drugs by precision deuteration: reducing mechanism-based inhibition of CYP2D6 by paroxetine.

Selective deuterium substitution as a means of ameliorating clinically relevant pharmacokinetic drug interactions is demonstrated in this study. Carbon-deuterium bonds are more stable than corresponding carbon-hydrogen bonds. Using a precision deuteration platform, the two hydrogen atoms at the methylenedioxy carbon of paroxetine were substituted with deuterium. The new chemical entity, CTP-347 [(3S,4R)-3-((2,2-dideuterobenzo[d][1,3]dioxol-5-yloxy)methyl)-4-(4-fluorophenyl)piperidine], demonstrated similar selectivity for the serotonin receptor, as well as similar neurotransmitter uptake inhibition in an in vitro rat synaptosome model, as unmodified paroxetine. However, human liver microsomes cleared CTP-347 faster than paroxetine as a result of decreased inactivation of CYP2D6. In phase 1 studies, CTP-347 was metabolized more rapidly in humans and exhibited a lower pharmacokinetic accumulation index than paroxetine. These alterations in the metabolism profile resulted in significantly reduced drug-drug interactions between CTP-347 and two other CYP2D6-metabolized drugs: tamoxifen (in vitro) and dextromethorphan (in humans). Our results show that precision deuteration can improve the metabolism profiles of existing pharmacotherapies without affecting their intrinsic pharmacologies.