David S. Clarke

Pharmacokinetics of Vandetanib: Three Phase I Studies in Healthy Subjects

BACKGROUND Vandetanib is an orally available inhibitor of vascular endothelial growth factor receptor 2 and epidermal growth factor receptor and is rearranged during transfection tyrosine kinase activity. Development has included studies in non-small cell lung cancer and other tumor types. Accurate elimination kinetics were not determined in patient studies, and so the current human volunteer studies were performed to derive detailed kinetic data. OBJECTIVE The aim of this study was to investigate pharmacokinetics, metabolism, excretion, and elimination kinetics after single oral doses of vandetanib in healthy subjects. METHODS Three studies were conducted. In Study A (n = 23), cohorts of 8 subjects were randomized to receive double-blind, ascending doses of vandetanib (300-1200 mg) or placebo (6:2). Study B had a crossover design; subjects (n = 16) received vandetanib 300 mg under fed and fasted conditions. In Study C, subjects (n = 4) received [(14)C] vandetanib 800 mg. Blood samples were collected for pharmacokinetic analysis for up to 28 days after the dose (Studies A and B) and 42 days after the dose (Study C). Plasma (all studies) and urine (Study A only) samples were collected for determination of vandetanib concentrations. In Study C radioactivity was measured in plasma, blood, urine, and feces, and metabolites were identified chromatographically. Tolerability was evaluated by recording of adverse events, clinical chemistry, hematology and urinalysis parameters, vital signs, and ECGs (all studies). RESULTS Study A: mean (SD) age 34.4 (6.9) years; 23/23 male; mean (SD; range) weight 80.6 (8.1; 62-97) kg. Study B: mean (SD) age 35.3 (8.4) years; 15/16 male; mean (SD; range) weight 80.7 (11.2; 57-100) kg. Study C: mean (SD) age 60.3 (7.4) years; 4/4 male; mean (SD; range) weight 78.0 (7.7l; 72-87) kg. Pharmacokinetic parameters were consistent across all studies (Studies A and C, vandetanib 800 mg: geometric mean CL/F, 13.1-13.3 L/h; geometric mean apparent volume of distribution at steady state [V(SS)/F], 3592-4103 L; mean t(½), 215.8-246.6 hours). Vandetanib was absorbed and eliminated slowly after single oral doses. AUC(0-∞) and C(max) were not significantly affected by ingestion of food. Median (range) T(max) was 8 (3-18) hours after food and 6 (5-18) hours after fasting. In plasma, concentrations of total radioactivity were higher than vandetanib concentrations at all time points, indicating the presence of circulating metabolites. Unchanged vandetanib and 2 anticipated metabolites (N-desmethylvandetanib and vandetanib N-oxide) were detected in plasma, urine, and feces. A further trace minor metabolite (glucuronide conjugate) was found in urine and feces. Approximately two thirds of the dose was recovered in feces (44%) and urine (25%) over 21 days, underlining the importance of both routes of elimination. Adverse events were reported by all subjects in Study A apart from 2 at a vandetanib dose of 300 mg; 12/15 (80%) and 14/16 (88%) subjects who took vandetanib under fed and fasted conditions, respectively, in Study B; and 2/4 (50%) subjects in Study C. No serious adverse events were reported. Increasing doses of vandetanib, in Study A, were associated with variable increases in systolic and diastolic blood pressures and variable increases from baseline in QTc interval. Hematuria was reported by 3 subjects (vandetanib 300 mg) in Study A. Small but consistent increases from baseline in serum creatinine were noted in subjects who received vandetanib in these studies. No other clinically important changes were observed in clinical chemistry, hematology and urinalysis parameters, vital signs, and ECGs in any of the studies. CONCLUSIONS The pharmacokinetics of vandetanib after single oral doses to healthy subjects were defined and the metabolic pathway was proposed. Vandetanib was absorbed and eliminated slowly with a t(½) of ∼10 days after single oral doses. The extent of absorption was not significantly affected by the presence of food. Approximately two thirds of the dose was recovered in feces (44%) and urine (25%) over 21 days. Unchanged vandetanib and N-desmethyl and N-oxide metabolites were detected in plasma, urine, and feces. Vandetanib appeared to be was well tolerated in the populations studied.

Use of small-molecule crystal structures to address solubility in a novel series of G protein coupled receptor 119 agonists: optimization of a lead and in vivo evaluation.

G protein coupled receptor 119 (GPR119) is viewed as an attractive target for the treatment of type 2 diabetes and other elements of the metabolic syndrome. During a program toward discovering agonists of GPR119, we herein describe optimization of an initial lead compound, 2, into a development candidate, 42. A key challenge in this program of work was the insolubility of the lead compound. Small-molecule crystallography was utilized to understand the intermolecular interactions in the solid state and resulted in a switch from an aryl sulphone to a 3-cyanopyridyl motif. The compound was shown to be effective in wild-type but not knockout animals, confirming that the biological effects were due to GPR119 agonism.

Design of a potent, soluble glucokinase activator with increased pharmacokinetic half-life.

The continued optimization of a series of glucokinase activators is described, including attempts to understand the interplay between molecular structure and the composite parameter of unbound clearance. These studies resulted in the discovery of a new scaffold for glucokinase activators and further exploration of this scaffold led to the identification of GKA60. GKA60 maintains an excellent balance of potency and physical properties whilst possessing a significantly different, but complimentary, pre-clinical pharmacokinetic profile compared with the previously disclosed compound GKA50.

Property based optimisation of glucokinase activators – discovery of the phase IIb clinical candidate AZD1656

Glucokinase plays a central role in glucose homeostasis and small molecule activators of the glucokinase enzyme have been the subject of significant pharmaceutical research in the quest for agents capable of delivering improved glycaemic control. Here we describe our medicinal chemistry campaign to improve on our previously described development candidate in this area, AZD1092, focussed on removal of Ames liability and improved permeability characteristics. This work culminated in the superior compound AZD1656 which has progressed to phase 2 clinical trials.

Identification of pyrazolo-pyrimidinones as GHS-R1a antagonists and inverse agonists for the treatment of obesity

A pyrazolo-pyrimidinone based series of growth hormone secretagogue receptor type 1a (GHS-R1a) antagonists and inverse agonists were identified using a scaffold hop from known quinazolinone GHS-R1a modulators. Lipophilicity was reduced to decrease hERG activity while maintaining GHS-R1a affinity. SAR exploration of a piperidine substituent was used to identify small cyclic groups as a functional switch from partial agonists to neutral antagonists and inverse agonists. A tool compound was identified which had good overall properties and sufficient oral plasma and CNS exposure to demonstrate reduced food intake in mice through a mechanism involving GHS-R1a.

Discovery, optimisation and in vivo evaluation of novel GPR119 agonists.

GPR119 is increasingly seen as an attractive target for the treatment of type II diabetes and other elements of the metabolic syndrome. During a programme aimed at developing agonists of the GPR119 receptor, we identified compounds that were potent with reduced hERG liabilities, that had good pharmacokinetic properties and that displayed excellent glucose-lowering effects in vivo. However, further profiling in a GPR119 knock-out (KO) mouse model revealed that the biological effects were not exclusively due to GPR119 agonism, highlighting the value of transgenic animals in drug discovery programs.

Circumventing Seizure Activity in a Series of G Protein Coupled Receptor 119 (GPR119) Agonists

Agonism of GPR119 is viewed as a potential therapeutic approach for the treatment of type II diabetes and other elements of metabolic syndrome. During progression of a previously disclosed candidate 1 through mice toxicity studies, we observed tonic-clonic convulsions in several mice at high doses. An in vitro hippocampal brain slice assay was used to assess the seizure liability of subsequent compounds, leading to the identification of an aryl sulfone as a replacement for the 3-cyano pyridyl group. Subsequent optimization to improve the overall profile, specifically with regard to hERG activity, led to alkyl sulfone 16. This compound did not cause tonic-clonic convulsions in mice, had a good pharmacokinetic profile, and displayed in vivo efficacy in murine models. Importantly, it was shown to be effective in wild-type (WT) but not GPR119 knockout (KO) animals, consistent with the pharmacology observed being due to agonism of GPR119.

Conformational restriction in a series of GPR119 agonists: Differences in pharmacology between mouse and human

A series of conformationally restricted GPR119 agonists were prepared based around a 3,8-diazabicyclo[3.2.1]octane scaffold. Examples were found to have markedly different pharmacology in mouse and human despite similar levels of binding to the receptor. This highlights the large effects on GPCR phamacology that can result from small structural changes in the ligand, together with inter-species differences between receptors.

Identification, optimization, and pharmacology of acylurea GHS-R1a inverse agonists.

Ghrelin plays a major physiological role in the control of food intake, and inverse agonists of the ghrelin receptor (GHS-R1a) are widely considered to offer utility as antiobesity agents by lowering the set-point for hunger between meals. We identified an acylurea series of ghrelin modulators from high throughput screening and optimized binding affinity through structure-activity relationship studies. Furthermore, we identified specific substructural changes, which switched partial agonist activity to inverse agonist activity, and optimized physicochemical and DMPK properties to afford the non-CNS penetrant inverse agonist 22 (AZ-GHS-22) and the CNS penetrant inverse agonist 38 (AZ-GHS-38). Free feeding efficacy experiments showed that CNS exposure was necessary to obtain reduced food intake in mice, and it was demonstrated using GHS-R1a null and wild-type mice that this effect operates through a mechanism involving GHS-R1a.

Design of dual-acting thromboxane antagonist-synthase inhibitors by a mutual prodrug approach

Abstract A mutual prodrug approach to dual acting thromboxane receptor antagonist - thromboxane synthase inhibitor compounds is reported in which TXA2 antagonist and inhibitory 1,3-dioxanes with hexenoic acid side chains, were linked by diester and diamide groups. When linking of the components was achieved via di O-alkyl carboxylic esters of catechol, both TXA2 receptor antagonist activity and TXA2 synthase inhibition were observed for a single enantiomer (16) in ex vivo tests following oral dosing to dogs at 5 mg/kg.