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The synthesis and optimisation of HCV NS5B polymerase inhibitors with improved potency versus the existing compound 1 is described. Substitution in the benzothiadiazine portion of the molecule, furnishing improvement in potency in the high protein Replicon assay, is highlighted, culminating in the discovery of 12h, a highly potent oxyacetamide derivative.

N-tert-Butyl isoquine (4) (GSK369796) is a 4-aminoquinoline drug candidate selected and developed as part of a public-private partnership between academics at Liverpool, MMV, and GSK pharmaceuticals. This molecule was rationally designed based on chemical, toxicological, pharmacokinetic, and pharmacodynamic considerations and was selected based on excellent activity against Plasmodium falciparum in vitro and rodent malaria parasites in vivo. The optimized chemistry delivered this novel synthetic quinoline in a two-step procedure from cheap and readily available starting materials. The molecule has a full industry standard preclinical development program allowing first into humans to proceed. Employing chloroquine (1) and amodiaquine (2) as comparator molecules in the preclinical plan, the first preclinical dossier of pharmacokinetic, toxicity, and safety pharmacology has also been established for the 4-aminoquinoline antimalarial class. These studies have revealed preclinical liabilities that have never translated into the human experience. This has resulted in the availability of critical information to other drug development teams interested in developing antimalarials within this class.

The disposition of three 4-aminoquinoline leads, namely isoquine (ISO), des-ethyl isoquine (DEI) and N-tert-butyl isoquine (NTBI), were studied in a range of in vivo and in vitro assays to assist in selecting an appropriate candidate for further development. Analogous to amodiaquine (ADQ), ISO undergoes oxidative N-dealkylation to form DEI in vivo. Blood clearance of DEI was as much as 10-fold lower than that of ISO in animals and after oral administration, metabolite exposure exceeded that of parent by as much as 14-fold. Replacement of the N-ethyl with an N-tert-butyl substituent substantially reduced N-dealkylation as blood clearance of NTBI was approximately 2 to 3-fold lower than DEI in mouse, rat, dog and monkey. Mean NTBI oral bioavailability was generally higher than the other leads (/=68%). Blood cell association was substantial for NTBI, particularly in dog and monkey, where blood to plasma concentration ratios4 were observed. Human plasma protein binding was similar for NTBI, DEI, and des-ethyl amodiaquine (DEA). Allometric scaling predicted human blood clearance (CL) for NTBI to be low ( approximately 12% liver blood flow). All the 4-aminoquinolines inhibited recombinant human cytochrome P450 2D6 with similar potency; DEI also inhibited 1A2. On balance, NTBI appeared the most promising lead to progress towards full development.

The pharmacokinetics and brain penetration of the novel neurokinin (NK)-1 receptor antagonist casopitant [1-piperidinecarboxamide, 4-(4-acetyl-1-piperazinyl)-N-((1R)-1-(3,5-bis(trifluoromethyl)phenyl)ethyl)-2-(4-fluoro-2-methylphenyl)-N-methyl-, (2R,4S)-; GW679769] were examined in ferrets. The ferret is known to respond to the full spectrum of agents recognized to induce emesis in humans, and the cisplatin-induced emesis models in the ferret have been used to establish the antiemetic potential of casopitant. Following single i.p. dosing to the ferret, casopitant was rapidly absorbed, with plasma and brain concentrations being approximately equal at 2 h postdose. The predominant radioactive component present in the ferret brain after a single dose of [(14)C]casopitant was parent compound, accounting for approximately 76% of the radioactivity. The major metabolites present in brain tissue following administration of [(14)C]casopitant were hydroxylated casopitant (M1) and the corresponding ketone product of the M1 metabolite (M2), which accounted for approximately 19 and 3% of the radioactivity in the brain extracts, respectively. All three molecules had relatively similar potency against ferret brain cortical NK-1, suggesting that the pharmacologic activity of casopitant in the ferret is largely attributable to parent compound and, to a lesser extent, to its oxidative metabolites. Because casopitant is intended to be administered in combination with ondansetron and because therapeutic synergy has been observed with this combination in the ferret, a drug interaction study was conducted. The additional pharmacodynamic benefit of the combination dose was not because of an alteration in the pharmacokinetics of either agent but is likely the result of the complementary mechanisms of pharmacologic action of the two drugs.

1. The in vivo clearance (CL) for 498 compounds representing more than 40 lead optimization programmes were compared in the rat and mouse. 2. A total of 278 of the compounds had similar CL values in rat and mouse and 41 compounds had a high CL in one rodent species and a low CL in the other (median seven-fold difference). For this latter subset, comparative in vitro plasma protein binding, liver microsomal or hepatocyte intrinsic CL provided plausible explanations for the observed in vivo differences in many cases. 3. A considerable proportion of compounds with substantially different CL in rodents, and those with a high CL in both rat and mouse, had a low-to-moderate CL in dog and/or monkey (43%). A larger proportion (71%) had promising pharmacokinetics in higher species when CL was low in both rat and mouse. 4. Drug-discovery scientists should consider the potential for there to be substantial differences in the disposition of leads in different rodent species and design screening cascades to explore this possibility.

Recently, we disclosed a new class of HCV polymerase inhibitors discovered through high-throughput screening (HTS) of the GlaxoSmithKline proprietary compound collection. This interesting class of 3-(1,1-dioxo-2H-1,2,4-benzothiadiazin-3-yl)-4-hydroxy-2(1H)-quinolinones potently inhibits HCV polymerase enzymatic activity and inhibits the ability of the subgenomic HCV replicon to replicate in Huh-7 cells. This report will focus on the structure-activity relationships (SAR) of substituents on the quinolinone ring, culminating in the discovery of 1-(2-cyclopropylethyl)-3-(1,1-dioxo-2H-1,2,4-benzothiadiazin-3-yl)-6-fluoro-4-hydroxy-2(1H)-quinolinone (130), an inhibitor with excellent potency in biochemical and cellular assays possessing attractive molecular properties for advancement as a clinical candidate. The potential for development and safety assessment profile of compound 130 will also be discussed.

Potent inhibitors of PLK1 with acceptable solubility, mouse iv clearance, and reduced CYP450 inhibition were identified. Drug-like properties were improved using a heteroaryl ring as a functional handle for manipulation of inhibitors' physiochemical and DMPK properties.

GW844520 is a potent and selective inhibitor of the cytochrome bc1 complex of mitochondrial electron transport in P. falciparum, the parasite primarily responsible for the mortality associated with malaria worldwide. GW844520 is fully active against the parasite including resistance isolates, showing no cross resistance with agents in use. To evaluate full potential of this development candidate, we conducted drug metabolism and pharmacokinetic studies of this novel anti-malarial. GW844520 had low blood clearance of about 0.5-4% of hepatic blood flow and a steady-state volume of distribution of 2-4 times total body water in mouse, rat, dog, and monkey. Oral bioavailability was high (51-100%). Consistent with the in vivo data, GW844520 had low intrinsic clearance in liver microsomes and hepatocytes of animal and human origin, high passive cellular permeability and was not a P-glycoprotein substrate. GW844520 did not associate appreciably with blood cells but was highly bound to plasma proteins (>99%) in all species. GW844520 was a substrate and inhibitor of human CYP2D6 but not of CYP1A2, 2C9, 2C19, and 3A4. This conjunctive analysis supports continued evaluation of this compound in definitive pre-IND studies and exemplifies our strategy supporting the discovery of novel agents to treat diseases of the developing world.