Alexander J. Stevens

Improving the in Vitro Prediction of in Vivo Central Nervous System Penetration: Integrating Permeability, P-glycoprotein Efflux, and Free Fractions in Blood and Brain

This work examines the inter-relationship between the unbound drug fractions in blood and brain homogenate, passive membrane permeability, P-glycoprotein (Pgp) efflux ratio, and log octanol/water partition coefficients (cLogP) in determining the extent of central nervous system (CNS) penetration observed in vivo. The present results demonstrate that compounds often considered to be Pgp substrates in rodents (efflux ratio greater than 5 in multidrug resistant Madin-Darby canine kidney cells) with poor passive permeability may still exhibit reasonable CNS penetration in vivo; i.e., where the unbound fractions and nonspecific tissue binding act as a compensating force. In these instances, the efflux ratio and in vitro blood-brain partition ratio may be used to predict the in vivo blood-brain ratio. This relationship may be extended to account for the differences in CNS penetration observed in vivo between mdr1a/b wild type and knockout mice. In some instances, cross-species differences that might initially seem to be related to differing transporter expression can be rationalized from knowledge of unbound fractions alone. The results presented in this article suggest that the information exists to provide a coherent picture of the nature of CNS penetration in the drug discovery setting, allowing the focus to be shifted away from understanding CNS penetration toward the more important aspect of understanding CNS efficacy.

SB-656104-A, a novel selective 5-HT7 receptor antagonist, modulates REM sleep in rats

(6‐((R)‐2‐{2‐[4‐(4‐Chloro‐phenoxy)‐piperidin‐1‐yl]‐ethyl}‐pyrrolidine‐1‐sulphonyl)‐1H‐indole hydrochloride) (SB‐656104‐A), a novel 5‐hydroxytryptamine (5‐HT7) receptor antagonist, potently inhibited [3H]‐SB‐269970 binding to the human cloned 5‐HT7(a) (pKi 8.7±0.1) and 5‐HT7(b) (pKi 8.5±0.2) receptor variants and the rat native receptor (pKi 8.8±0.2). The compound displayed at least 30‐fold selectivity for the human 5‐HT7(a) receptor versus other human cloned 5‐HT receptors apart from the 5‐HT1D receptor (∼10‐fold selective). SB‐656104‐A antagonised competitively the 5‐carboxamidotryptamine (5‐CT)‐induced accumulation of cyclic AMP in h5‐HT7(a)/HEK293 cells with a pA2 of 8.5. Following a constant rate iv infusion to steady state in rats, SB‐656104 had a blood clearance (CLb) of 58±6 ml min−1 kg−1 and was CNS penetrant with a steady‐state brain : blood ratio of 0.9 : 1. Following i.p. administration to rats (10 mg kg−1), the compound displayed a t1/2 of 1.4 h with mean brain and blood concentrations (at 1 h after dosing) of 0.80 and 1.0 μM, respectively. SB‐656104‐A produced a significant reversal of the 5‐CT‐induced hypothermic effect in guinea pigs, a pharmacodynamic model of 5‐HT7 receptor interaction in vivo (ED50 2 mg kg−1). SB‐656104‐A, administered to rats at the beginning of the sleep period (CT 0), significantly increased the latency to onset of rapid eye movement (REM) sleep at 30 mg kg−1 i.p. (+93%) and reduced the total amount of REM sleep at 10 and 30 mg kg−1 i.p. with no significant effect on the latency to, or amount of, non‐REM sleep. SB‐269970‐A produced qualitatively similar effects in the same study. In summary, SB‐656104‐A is a novel 5‐HT7 receptor antagonist which has been utilised in the present study to provide further evidence for a role for 5‐HT7 receptors in the modulation of REM sleep.

SB-656104-A: A novel 5-HT7 receptor antagonist with improved In vivo properties

A focused SAR study around the previously reported selective 5-HT(7) receptor antagonist, SB-269970-A has resulted in the identification of a structurally related analogue having an improved pharmacokinetic profile. Replacement of the phenolic group in SB-269970-A with an indole moiety, and replacement of the piperidinyl 4-methyl group with a heterocyclic ring system proved to be the key changes leading to the identification of SB-656104-A.

Design and synthesis of 6-phenylnicotinamide derivatives as antagonists of TRPV1

6-Phenylnicotinamide (2) was previously identified as a potent TRPV1 antagonist with activity in an in vivo model of inflammatory pain. Optimization of this lead through modification of both the biaryl and heteroaryl components has resulted in the discovery of 6-(4-fluorophenyl)-2-methyl-N-(2-methylbenzothiazol-5-yl)nicotinamide (32; SB-782443) which possesses an excellent overall profile and has been progressed into pre-clinical development.

Discovery and structure-activity relationships of a series of pyroglutamic acid amide antagonists of the P2X7 receptor.

A computational lead-hopping exercise identified compound 4 as a structurally distinct P2X(7) receptor antagonist. Structure-activity relationships (SAR) of a series of pyroglutamic acid amide analogues of 4 were investigated and compound 31 was identified as a potent P2X(7) antagonist with excellent in vivo activity in animal models of pain, and a profile suitable for progression to clinical studies.

Discovery of N-(3-Fluorophenyl)-1-[(4-([(3S)-3-methyl-1-piperazinyl]methyl)phenyl)acetyl]-4-piperidinamine (GSK962040), the First Small Molecule Motilin Receptor Agonist Clinical Candidate

N-(3-fluorophenyl)-1-[(4-([(3S)-3-methyl-1-piperazinyl]methyl)phenyl)acetyl]-4-piperidinamine 12 (GSK962040) is a novel small molecule motilin receptor agonist. It possesses excellent activity at the recombinant human motilin receptor and also at the native rabbit motilin receptor where its agonist activity results in potentiation of the amplitude of neuronal-mediated contractions of isolated gastric antrum tissue. Compound 12 also possesses highly promising pharmacokinetic profiles in both rat and dog, and these results, in combination with further profiling in human native tissue and an in vivo model of gastrointestinal transit in the rabbit, have led to its selection as a candidate for further development.

Synthesis and structure-activity relationships of a series of (1H-pyrazol-4-yl)acetamide antagonists of the P2X7 receptor

High-throughput screening identified compound 1 as a potent P2X(7) receptor antagonist suitable for lead optimisation. Structure-activity relationships (SAR) of a series of (1H-pyrazol-4-yl)acetamides were investigated and compound 32 was identified as a potent P2X(7) antagonist with enhanced potency and favourable physicochemical and pharmacokinetic properties.

Structure-activity relationships and in vivo activity of (1H-pyrazol-4-yl)acetamide antagonists of the P2X7 receptor

Structure-activity relationships (SAR) of analogues of lead compound 1 were investigated and compound 16 was selected for further study in animal models of pain. Compound 16 was shown to be a potent antihyperalgesic agent in both the rat acute complete Freunds adjuvant (CFA) model of inflammatory pain [Iadarola, M. J.; Douglass, J.; Civelli, O.; Naranjo, J. R. rain Res.1988, 455, 205] and the knee joint model of chronic inflammatory pain [Wilson, A. W.; Medhurst, S. J.; Dixon, C. I.; Bontoft, N. C.; Winyard, L. A.; Brackenborough, K. T.; De Alba, J.; Clarke, C. J.; Gunthorpe, M. J.; Hicks, G. A.; Bountra, C.; McQueen, D. S.; Chessell, I. P. Eur. J. Pain2006, 10, 537].

Identification of [4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)-2-pyrimidinyl] amines and ethers as potent and selective cyclooxygenase-2 inhibitors.

A novel series of [4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)-2-pyrimidine-based cyclooxygenase-2 (COX-2) inhibitors, which have a different arrangement of substituents compared to the more common 1,2-diarylheterocycle based molecules, have been discovered. For example, 2-(butyloxy)-4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)pyrimidine (47), a member of the 2-pyrimidinyl ether series, has been shown to be a potent and selective inhibitor with a favourable pharmacokinetic profile, high brain penetration and good efficacy in rat models of hypersensitivity.

Optimization of Sphingosine-1-phosphate-1 Receptor Agonists: Effects of Acidic, Basic, and Zwitterionic Chemotypes on Pharmacokinetic and Pharmacodynamic Profiles

The efficacy of the recently approved drug fingolimod (FTY720) in multiple sclerosis patients results from the action of its phosphate metabolite on sphingosine-1-phosphate S1P1 receptors, while a variety of side effects have been ascribed to its S1P3 receptor activity. Although S1P and phospho-fingolimod share the same structural elements of a zwitterionic headgroup and lipophilic tail, a variety of chemotypes have been found to show S1P1 receptor agonism. Here we describe a study of the tolerance of the S1P1 and S1P3 receptors toward bicyclic heterocycles of systematically varied shape and connectivity incorporating acidic, basic, or zwitterionic headgroups. We compare their physicochemical properties, their performance in in vitro and in vivo pharmacokinetic models, and their efficacy in peripheral lymphocyte lowering. The campaign resulted in the identification of several potent S1P1 receptor agonists with good selectivity vs S1P3 receptors, efficacy at <1 mg/kg oral doses, and developability properties suitable for progression into preclinical development.