Pyrimido[4,5-d]azepines as potent and selective 5-HT2C receptor agonists: design, synthesis, and evaluation of PF-3246799 as a treatment for urinary incontinence.

New pyrimido[4,5-d]azepines 7 are disclosed as potent 5-HT(2C) receptor agonists. A preferred example, 7b had minimal activation at either the 5-HT(2A) or 5-HT(2B) receptors combined with robust efficacy in a preclinical canine model of stress urinary incontinence (SUI) and attractive pharmacokinetic and safety properties. Based on this profile, 7b (PF-3246799) was identified as a candidate for clinical development for the treatment of SUI. In addition, it proved to be critical to build an understanding of the translation between recombinant cell-based systems, native tissue preparations and in vivo preclinical models. This was a significant undertaking and proved to be crucial in compound selection.

Prostanoid receptors mediating contraction in rat, macaque and human bladder smooth muscle in vitro.

Selective prostaglandin EP1 antagonists have been suggested for the treatment of bladder dysfunction. This study assessed the contractile prostanoid receptor subtypes in human and non-human bladder in vitro. Classical tissue bath studies were conducted using bladder strips exposed to prostanoid agonists and antagonists. Prostaglandin E2 (PGE2) contracted rat, macaque and human bladder smooth muscle strips (pEC50 7.91±0.06 (n=7), 6.40±0.13 (n=7), and 6.07±0.11 (n=5), respectively). The EP1 receptor antagonist, PF2907617 (300nM), caused a rightward shift of the PGE2 concentration-response curve in the rat bladder only (pKB 8.40±0.15, n=3). PGE2 responses in rat and macaque bladders, but not human, were antagonised by the EP3 antagonist CJ24979 (1µM). Sulprostone, a mixed EP1/EP3/FP receptor agonist, induced potent contractions of rat bladder muscle (pEC50 7.94±0.31, n=6). The FP receptor agonist, prostaglandin F2α (PGF2α), induced bladder contraction in all species tested, but with a lower potency in rat. The selective FP receptor agonist latanoprost caused potent contractions of macaque and human bladder strips only. SQ29548, a selective TP antagonist, and GW848687X, a mixed EP1/TP antagonist caused rightward shifts of the concentration-response curves to the selective TP agonist, U46619 (pKB estimates 8.53±0.07 and 7.56±0.06, n=3, respectively). Responses to U46619 were absent in rat preparations. These data suggest significant species differences exist in bladder contractile prostanoid receptor subtypes. We conclude that the EP1 subtype does not represent the best approach to the clinical treatment of bladder disorders targeting inhibition of smooth muscle contraction.

Multiparameter optimization in CNS drug discovery: design of pyrimido[4,5-d]azepines as potent 5-hydroxytryptamine 2C (5-HT2C) receptor agonists with exquisite functional selectivity over 5-HT2A and 5-HT2B receptors.

A series of 4-substituted pyrimido[4,5-d]azepines that are potent, selective 5-HT2C receptor partial agonists is described. A rational medicinal chemistry design strategy to deliver CNS penetration coupled with SAR-based optimization of selectivity and agonist potency provided compounds with the desired balance of preclinical properties. Lead compounds 17 (PF-4479745) and 18 (PF-4522654) displayed robust pharmacology in a preclinical canine model of stress urinary incontinence (SUI) and no measurable functional agonism at the key selectivity targets 5-HT2A and 5-HT2B in relevant tissue-based assay systems. Utilizing recent advances in the structural biology of GPCRs, homology modeling has been carried out to rationalize binding and agonist efficacy of these compounds.