Preclinical and clinical pharmacology of TPA023B, a GABAA receptor α2/α3 subtype-selective partial agonist.

In the accompanying paper we describe how MRK-409 unexpectedly produced sedation in man at relatively low levels of GABA(A) receptor occupancy (∼10%). Since it was not clear whether this sedation was mediated via the α2/α3 or α1 GABA(A) subtype(s), we characterized the properties of TPA023B, a high-affinity imidazotriazine which, like MRK-409, has partial agonist efficacy at the α2 and α3 subtype but is an antagonist at the α1 subtype, at which MRK-409 has weak partial agonism. TPA023B gave dose- and time-dependent occupancy of rat brain GABA(A) receptors as measured using an in vivo [(3)H]flumazenil binding assay, with 50% occupancy corresponding to a respective dose and plasma drug concentration of 0.09 mg/kg and 19 ng/mL, the latter of which was similar to that observed in mice (25 ng/mL) and comparable to values obtained in baboon and man using [(11)C]flumazenil PET (10 and 5.8 ng/mL, respectively). TPA023B was anxiolytic in rodent and primate (squirrel monkey) models of anxiety (elevated plus maze, fear-potentiated startle, conditioned suppression of drinking, conditioned emotional response) yet had no significant effects in rodent or primate assays of ataxia and/or myorelaxation (rotarod, chain-pulling, lever pressing), up to doses (10 mg/kg) corresponding to occupancy of greater than 99%. In man, TPA023B was well tolerated at a dose (1.5 mg) that produced occupancy of >50%, suggesting that the sedation previously seen with MRK-409 is due to the partial agonist efficacy of that compound at the α1 subtype, and highlighting the importance of antagonist efficacy at this particular GABA(A) receptor population for avoiding sedation in man.

3-(4-Fluoropiperidin-3-yl)-2-phenylindoles as high affinity, selective, and orally bioavailable h5-HT(2A) receptor antagonists.

The development of very high affinity, selective, and bioavailable h5-HT(2A) receptor antagonists is described. By investigation of the optimal position for the basic nitrogen in a series of 2-phenyl-3-piperidylindoles, it was found that with the basic nitrogen at the 3-position of the piperidine it was not necessary to further substitute the piperidine in order to obtain good binding at h5-HT(2A) receptors. This meant the compounds no longer had high affinity at the IKr potassium channel, an issue with previous series of 2-aryl-3-(4-piperidyl)indoles. Improvements could be made to oral bioavailability in this series by reduction of the pK(a) of the basic nitrogen, by adding a fluorine atom to the piperidine ring, leading to 3-(4-fluoropiperidin-3-yl)-2-phenyl-1H-indole (17). Metabolic studies with this compound identified oxidation at the 6-position of the indole as a major route in vitro and in vivo in rats. Blocking this position with a fluorine atom led to 6-fluoro-3-(4-fluoropiperidin-3-yl)-2-phenyl-1H-indole (22), an antagonist with 0.06 nM affinity for h5-HT(2A) receptors, with bioavailability of 80% and half-life of 12 h in rats.

Mutagenicity and chemical analysis of aliphatic and aromatic fractions of Prudhoe Bay crude oil and fuel oil no. 2.

The mutagenicity of aliphatic (fraction 1), one- to three-ring aromatic (fraction 3), and four- to five-ring aromatic (fraction 4) fractions of Prudhoe Bay crude oil and of a fuel oil no. 2 was investigated with a battery of in vitro mammalian and microbial assays. Chemical analysis of the fractions was carried out by gas capillary chromatography-mass spectrometry. In the Salmonella/mammalian microsome test, both first fractions were negative, while fraction 3 of Prudhoe Bay crude and fraction 4 of both oils exhibited mutagenic activity with metabolic activation. In Chinese hamster ovary cells, all of the aromatic fractions, in the presence of metabolic activation, caused a significant increase in the number of sister chromatid exchanges. Chromosome aberrations were not caused by any of the aromatic fractions; however, fraction 3 of fuel oil no. 2 induced endoreduplication in the presence of metabolic activation.

Total organically-bound chlorine and bromine in Lake Ontario herring gull eggs, 1977, by instrumental neutron activation and chromatographic methods.

In order to determine the extent to which organically-bound chlorine in Herring Gull eggs from Lake Ontario can be accounted for by gas chromatographic analysis, comparison was made with values obtained for total chlorine using instrumental neutron activation analysis (INAA). Total chlorine and bromine (mg/kg fresh weight of egg) was determined by INAA on crude extract (Cl, 65 +/- 35; Br, 1.03 +/- 1.00), Florisil-chromatography treated extracts (Cl, 46 +/- 10; Br, 0.93 +/- 0.82) and H2SO4-treated extracts (Cl, 43 +/- 11; Br, 0.44 +/- 0.22) of eggs collected from seven colonies around Lake Ontario in 1977. Levels of chlorine were also determined by gas chromatography using the Hall electrolytic conductivity detector (51 +/- 11 mg/kg) and estimated by conversion of levels of individual residues determined by electron-capture gas chromatography (61 +/- 12 mg/kg). The agreement between the various determinations indicated that PCBs, DDE, mirex and photomirex accounted for most of the organically-bound chlorine. Two colonies had total chlorine levels in crude extracts 2--4 times higher than could be accounted for by know compounds. The "excess" chlorine was removed by H2SO4-treatment or Florisil clean-up. The same two samples had abnormally high bromine levels, possibly indicating the presence of compounds formed during aqueous chlorination processes.