Ian Thomson Forbes

In vitro and in vivo profile of SB 206553, a potent 5‐HT2C/5‐HT2B receptor antagonist with anxiolytic‐like properties

1 SB 206553 (5‐methyl‐1‐(3‐pyridylcarbamoyl)‐1,2,3,5‐tetrahydropyrrolo[2,3‐f]indole) displays a high affinity (pK1 7.9) for the cloned human 5‐HT2C receptor expressed in HEK 293 cells and the 5‐HT2B receptor (pA2 8.9) as measured in the rat stomach fundus preparation. SB 206553 has low affinity for cloned human 5‐HT2A receptors expressed in HEK 293 cells (pK1 5.8) and (pK1 <6) for a wide variety of other neurotransmitter receptors. 2 SB 206553 appears to be a surmountable antagonist of 5‐HT‐stimulated phosphoinositide hydrolysis in HEK 293 cells expressing the human 5‐HT2C receptor (pKB 9.0). 3 The compound potently (ID50 5.5 mg kg−1, p.o., 0.27 mg kg−1, i.v.) inhibited the hypolocomotor response to m‐chlorophenylpiperazine (mCPP), a putative model of 5‐HT2C/5‐HT2B receptor function in vivo. 4 At similar doses (2–20 mg kg−1, p.o.) SB 206553 increased total interaction scores in a rat social interaction test and increased punished responding in a rat Geller‐Seifter conflict test. These effects are consistent with the possession of anxiolytic properties. 5 SB 206553 also increased suppressed responding in a marmoset conflict model of anxiety at somewhat higher doses (15 and 20 mg kg−1, p.o.) but also reduced unsuppressed responding. 6 These results suggest that SB 206553 is a potent mixed 5‐HT2C/5‐HT2B receptor antagonist with selectivity over the 5‐HT2A and all other sites studied and possesses anxiolytic‐like properties.

In vivo properties of SB 200646A, a 5-HT2C/2B receptor antagonist.

1 SB 200646A, N‐(1‐methyl‐5‐indolyl)‐N′‐(3‐pyridyl) urea hydrochloride, the first reported selective 5‐HT2C/2B over 5‐HT2A receptor antagonist, (pK1 rat 5‐HT2C receptor 6.9, pA2 rat 5‐HT2B receptor 7.5, pKi rat 5‐HT2A receptor 5.2) dose‐dependently blocked a putative rat model of 5‐HT2C receptor activation; 1‐(3‐chlorophenyl)piperazine (mCPP, 5 mg kg−1, i.p. 20 min pretest)‐induced hypolocomotion (estimated ID50 19.2 mg kg−1, p.o.). 2 SB 200646A also blocked another putative in vivo model of 5‐HT2C receptor function; mCPP (5 mg kg−1, i.p. 20 min pretest)‐induced hypophagia in 23 h food‐deprived rats (estimated ID50 18.3 mg kg−1, p.o.). 3 SB 200646A did not antagonize 1‐(2,5‐dimethoxy‐4‐iodophenyl)‐2‐aminopropane (DOI)‐induced head shakes in rats at doses up to 200 mg kg−1, p.o., an effect thought to be mediated by 5‐HT2A receptors for which SB 200646A has its next highest affinity (50 fold less) after the 5‐HT2C and 5‐HT2B sites. 4 SB 200646A (20, 40 mg kg−1, p.o., 1 h pretest) also reversed mCPP (0.5 mg kg−1, i.p., 30 min pretest)‐induced anxiety in the social interaction test, under low light familiar conditions. 5 When given alone, under high light unfamiliar conditions, SB 200646A (2–40 mg kg−1, p.o.) increased active social interaction without affecting locomotor activity in the rat social interaction test. This is consistent with an anxiolytic action of SB 200646A. 6 These results indicate that SB 200646A has in vivo efficacy and that 5‐HT2C or 5‐HT2B receptors are indeed likely to mediate mCPP‐induced hypolocomotion, hypophagia and anxiogenesis. They also suggest that 5‐HT2C/2B receptor blockade induces anxiolysis.

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.

Functional characterisation of the human cloned 5‐HT7 receptor (long form); antagonist profile of SB‐258719

1 The functional profile of the long form of the human cloned 5‐HT7 receptor (designated h5‐HT7(a)) was investigated using a number of 5‐HT receptor agonists and antagonists and compared with its binding profile. Receptor function was measured using adenylyl cyclase activity in washed membranes from HEK293 cells stably expressing the recombinant h5‐HT7(a) receptor. 2 The receptor binding profile, determined by competition with [3H]‐5‐CT, was consistent with that previously reported for the h5‐HT7(a) receptor. The selective 5‐HT7 receptor antagonist SB‐258719 ((R)‐3,N‐Dimethyl‐N‐[1‐methyl‐3‐(4‐methylpiperidin‐1‐yl)propyl]benzene sulfonamide) displayed high affinity (pKi 7.5) for the receptor. 3 In the adenylyl cyclase functional assay, 5‐CT and 8‐OH‐DPAT were both full agonists compared to 5‐HT and the rank order of potency for agonists (5‐CT>5‐HT>8‐OH‐DPAT) was the same in functional and binding studies. 4 Risperidone, methiothepin, mesulergine, clozapine, olanzapine, ketanserin and SB‐258719 antagonised surmountably 5‐CT‐stimulated adenylyl cyclase activity. Schild analysis of the antagonism by SB‐258719 gave a pA2 of 7.2±0.2 and slope not significantly different from 1, consistent with competitive antagonism. 5 The same antagonists also inhibited basal adenylyl cyclase activity with a rank order of potency in agreement with those for antagonist potency and binding affinity. Both SB‐258719 and mesulergine displayed apparent partial inverse agonist profiles compared to the other antagonists tested. These inhibitory effects of antagonists appear to be 5‐HT7 receptor‐mediated and to reflect inverse agonism. 6 It is concluded that in this expression system, the h5‐HT7(a) receptor shows the expected binding and functional profile and displays constitutive activity, revealing inverse agonist activity for a range of antagonists.

Characterization of a CNS penetrant, selective M1 muscarinic receptor agonist, 77-LH-28-1

M1 muscarinic ACh receptors (mAChRs) represent an attractive drug target for the treatment of cognitive deficits associated with diseases such as Alzheimers disease and schizophrenia. However, the discovery of subtype‐selective mAChR agonists has been hampered by the high degree of conservation of the orthosteric ACh‐binding site among mAChR subtypes. The advent of functional screening assays has enabled the identification of agonists such as AC‐42 (4‐n‐butyl‐1‐[4‐(2‐methylphenyl)‐4‐oxo‐1‐butyl]‐piperidine), which bind to an allosteric site and selectively activate the M1 mAChR subtype. However, studies with this compound have been limited to recombinantly expressed mAChRs.

Probing the Molecular Mechanism of Interaction between 4-n-Butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine (AC-42) and the Muscarinic M1 Receptor: Direct Pharmacological Evidence That AC-42 Is an Allosteric Agonist

4-n-Butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine hydrogen chloride (AC-42) is a selective agonist of the muscarinic M1 receptor previously suggested to interact with an “ectopic” site on this receptor. However, the pharmacological properties of this site (i.e., whether it overlaps to any extent with the classic orthosteric site or represents a novel allosteric site) remain undetermined. In the present study, atropine or pirenzepine significantly inhibited the ability of either carbachol or AC-42 to stimulate inositol phosphate accumulation or intracellular calcium mobilization in Chinese hamster ovary (CHO) cells stably expressing the human M1 receptor. However, the interaction between either of these antagonists and AC-42 was characterized by Schild slopes significantly less than unity. Increasing the concentrations of atropine revealed that the Schild regression was curvilinear, consistent with a negative allosteric interaction. More direct evidence for an allosteric mode of action of AC-42 was obtained in [3H]N-methylscopolamine ([3H]NMS) binding studies, in that both AC-42 and the prototypical modulator gallamine failed to fully inhibit specific [3H]NMS binding in a manner that was quantitatively described by an allosteric model applied to both modulator data sets. Furthermore, AC-42 and gallamine significantly retarded the rate of [3H]NMS dissociation from CHO-hM1 cell membranes, conclusively demonstrating their ability to bind to a topographically distinct site to change M1 receptor conformation. These data provide the first direct evidence that AC-42 is an allosteric agonist that activates M1 receptors in the absence of the orthosteric agonist.

CCR2B receptor antagonists : Conversion of a weak HTS hit to a potent lead compound

A weak HTS hit at the CCR2B receptor has been converted into a potent antagonist by array SAR studies. Selectivity over the closely related CCR5 receptor is also achieved.

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.

Conformationally restricted indolopiperidine derivatives as potent CCR2B receptor antagonists

The preparation and biological evaluation of a series of indolopiperidine CCR2B receptor antagonists possessing a conformationally restricted C-5 linker chain in combination with a restricted piperidine ring are described. Compared to the parent compound 1, analogue 8 shows a dramatic improvement in selectivity against a range of 5-HT and dopaminergic receptors.

Novel N-Substituted Benzimidazolones as Potent, Selective, CNS-Penetrant, and Orally Active M1 mAChR Agonists

Virtual screening of the corporate compound collection yielded compound 1 as a subtype selective muscarinic M1 receptor agonist hit. Initial optimization of the N-capping group of the central piperidine ring resulted in compounds 2 and 3 with significantly improved potency and selectivity. Subsequent optimization of substituents on the phenyl ring of the benzimidazolone moiety led to the discovery of novel muscarinic M1 receptor agonists 4 and 5 with excellent potency, general and subtype selectivity, and pharmacokinetic (PK) properties including good central nervous system (CNS) penetration and oral bioavailability. Compound 5 showed robust in vivo activities in animal models of cognition enhancement. The combination of high potency, excellent selectivity, and good PK properties makes compounds 4 and 5 valuable tool compounds for investigating and validating potential therapeutic benefits resulting from selective M1 activation.