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Introduction In recent years, the anesthetized guinea pig has been used increasingly to evaluate the cardiovascular effects of drug-candidate molecules during lead optimization prior to conducting longer, more resource intensive safety pharmacology and toxicology studies. The aim of these studies was to evaluate the correlations between pharmacologically-induced ECG changes in the anesthetized cardiovascular guinea pig (CVGP) with ECG changes in conscious non-rodent telemetry models, human clinical studies and effects on key cardiac ion channels. Methods We compared the effects of 38 agents on ion channel inhibition to their ECG effects in the CVGP. 26 of these agents were also evaluated in non-rodent telemetry and compared to the results in the CVGP. Results The CVGP was highly sensitive for detecting QTc, PR and QRS interval prolongation mediated by inhibition of hERG, hCav1.2 and hNav1.5, respectively. There were robust correlations between ion channel inhibitory potencies and the free plasma concentrations ( Cu ) producing prolongation of the QTc, PR or QRS interval. Further evaluation showed that ECG changes in the CVGP were predictive of their effects on the QTc, PR and QRS intervals in non-rodent telemetry models with 92%, 92% and 100% accuracy, respectively. The CVGP proved to be 100% specific and 88%, 75% and 100% sensitive for QTc, PR and QRS interval prolongation, respectively. Similarly, the Cu that prolonged the QTc, PR and QRS in CVGP and humans correlated well. Discussion The CVGP is a sensitive model for assessing QTc, PR and QRS prolongation elicited by effects on hERG, hCav1.2 and hNav1.5, respectively. ECG changes in the CVGP are predictive of changes in non-rodent telemetry models and in humans (QTc). ECG parameters can be reliably evaluated with the CVGP model which increases the efficiency of CV derisking. Importantly, the design and implementation of this model is consistent with the “3Rs” for animal research.

A series of potent novel 8-hydroxy-3,4-dihydropyrrolo[1,2-a]pyrazine-1(2H)-one HIV-1 integrase inhibitors was identified. These compounds inhibited the strand transfer process of HIV-1 integrase and viral replication in cells. Compound 12 is active against replication of HIV-1 in cell culture with a CIC(95) of 0.31microM. Further SAR exploration led to the preparation of pseudosymmetrical tricyclic pyrrolopyrazine inhibitors 23 and 24 with further improvement in antiviral activity.

Installation of a C2-aminopropyl side chain to the 2,4-diaryl-2,5-dihydropyrrole series of kinesin spindle protein (KSP) inhibitors results in potent, water soluble compounds, but the aminopropyl group induces susceptibility to cellular efflux by P-glycoprotein (Pgp). We show that by carefully modulating the basicity of the amino group by beta-fluorination, this series of inhibitors maintains potency against KSP and has greatly improved efficacy in a Pgp-overexpressing cell line. The discovery that cellular efflux by Pgp can be overcome by carefully modulating the basicity of an amine may be of general use to medicinal chemists attempting to transform leading compounds into cancer cell- or CNS-penetrant drugs.

A 1,6-naphthyridine inhibitor of HIV-1 integrase has been discovered with excellent inhibitory activity in cells, good pharmacokinetics, and an excellent ability to inhibit virus with mutant enzyme.

Optimization of a previously reported thrombin inhibitor, 9-hydroxy-9-fluorenylcarbonyl-l-prolyl-trans-4-aminocyclohexylmethylamide (1), by replacing the aminocyclohexyl P1 group provided a new lead structure, 9-hydroxy-9-fluorenylcarbonyl-l-prolyl-2-aminomethyl-5-chlorobenzylamide (2), with improved potency (K(i) = 0.49 nM for human thrombin, 2x APTT = 0.37 microM in human plasma) and pharmacokinetic properties (F = 39%, iv T(1/2) = 13 h in dogs). An effective strategy for reducing plasma protein binding of 2 and improving efficacy in an in vivo thrombosis model in rats was to replace the lipophilic fluorenyl group in P3 with an azafluorenyl group. Systematic investigation of all possible azafluorenyl P3 isomers and azafluorenyl-N-oxide analogues of 2 led to the identification of an optimal compound, 3-aza-9-hydroxyfluoren-9(R)-ylcarbonyl-l-prolyl-2-aminomethyl-5-chlorobenzylamide (19b), with high potency (K(i) = 0.40 nM, 2x APTT = 0.18 microM), excellent pharmacokinetic properties (F = 55%, T(1/2) = 14 h in dogs), and complete efficacy in the in vivo thrombosis model in rats (inhibition of FeCl(3)-induced vessel occlusions in six of six rats receiving an intravenous infusion of 10 microg/kg/min of 19b). The stereochemistry of the azafluorenyl group in 19b was determined by X-ray crystallographic analysis of its N-oxide derivative (23b) bound in the active site of human thrombin.