Structure-Activity Relationships, Pharmacokinetics, and in Vivo Activity of CYP11B2 and CYP11B1 Inhibitors.

CYP11B2, the aldosterone synthase, and CYP11B1, the cortisol synthase, are two highly homologous enzymes implicated in a range of cardiovascular and metabolic diseases. We have previously reported the discovery of LCI699, a dual CYP11B2 and CYP11B1 inhibitor that has provided clinical validation for the lowering of plasma aldosterone as a viable approach to modulate blood pressure in humans, as well normalization of urinary cortisol in Cushing's disease patients. We now report novel series of aldosterone synthase inhibitors with single-digit nanomolar cellular potency and excellent physicochemical properties. Structure-activity relationships and optimization of their oral bioavailability are presented. An illustration of the impact of the age of preclinical models on pharmacokinetic properties is also highlighted. Similar biochemical potency was generally observed against CYP11B2 and CYP11B1, although emerging structure-selectivity relationships were noted leading to more CYP11B1-selective analogs.

In vitro metabolism of CP-122,721 ((2S,3S)-2-phenyl-3-[(5-trifluoromethoxy-2-methoxy)benzylamino]piperidine), a non-peptide antagonist of the substance P receptor.

The metabolism of CP-122,721, a neurokinin-1 antagonist, has been examined in vitro using hepatic microsomes from human and animal species, and recombinant heterologously expressed P450 enzymes. Metabolism occurs primarily via O-demethylation and N-dealkylation reactions. In human liver microsomes, O-demethylation was shown to be catalyzed by CYP2D6 with a low K(M) value. N-dealkyation was shown to be catalyzed primarily by CYP3A4. When scaled to in vivo, in vitro intrinsic clearance data yielded a reasonable correlation across species. CP-122,721 was shown to be metabolized by parallel pathways to 5-trifluoromethoxysalicylic acid, which had been observed as a major circulating metabolite in humans after oral administration of CP-122,721. The involvement of CYP1A2, CYP3A4, and MAO-B was demonstrated in the pathways leading to 5-trifluoromethoxysalicylic acid. The O-desmethyl metabolite of CP-122,721 was shown to undergo a P450 catalyzed O-detrifluoromethylation reaction yielding a p-hydroquinone metabolite. The reaction was shown to be catalyzed by CYP3A4. Incubation under (18)O(2) yielded the hydroquinone containing O-18, consistent with this reaction occurring via an ispo substitution mechanism. Combined, these findings provide a comprehensive understanding of the metabolism of this new agent.

The impact of P-glycoprotein on the disposition of drugs targeted for indications of the central nervous system: evaluation using the MDR1A/1B knockout mouse model.

Thirty-two structurally diverse drugs used for the treatment of various conditions of the central nervous system (CNS), along with two active metabolites, and eight non-CNS drugs were measured in brain, plasma, and cerebrospinal fluid in the P-glycoprotein (P-gp) knockout mouse model after subcutaneous administration, and the data were compared with corresponding data obtained in wild-type mice. Total brain-to-plasma (B/P) ratios for the CNS agents ranged from 0.060 to 24. Of the 34 CNS-active agents, only 7 demonstrated B/P area under the plasma concentration curve ratios between P-gp knockout and wild-type mice that did not differ significantly from unity. Most of the remaining drugs demonstrated 1.1- to 2.6-fold greater B/P ratios in P-gp knockout mice versus wild-type mice. Three, risperidone, its active metabolite 9-hydroxyrisperidone, and metoclopramide, showed marked differences in B/P ratios between knockout and wild-type mice (6.6- to 17-fold). Differences in B/P ratios and cerebrospinal fluid/plasma ratios between wild-type and knockout animals were correlated. Through the use of this model, it appears that most CNS-active agents demonstrate at least some P-gp-mediated transport that can affect brain concentrations. However, the impact for the majority of agents is probably minor. The example of risperidone illustrates that even good P-gp substrates can still be clinically useful CNS-active agents. However, for such agents, unbound plasma concentrations may need to be greater than values projected using receptor affinity data to achieve adequate receptor occupancy for effect.