Biotransformation and bioactivation reactions of alicyclic amines in drug molecules.

Aliphatic nitrogen heterocycles such as piperazine, piperidine, pyrrolidine, morpholine, aziridine, azetidine, and azepane are well known building blocks in drug design and important core structures in approved drug therapies. These core units have been targets for metabolic attack by P450s and other drug metabolizing enzymes such as aldehyde oxidase and monoamine oxidase (MAOs). The electron rich nitrogen and/or α-carbons are often major sites of metabolism of alicyclic amines. The most common biotransformations include N-oxidation, N-conjugation, oxidative N-dealkylation, ring oxidation, and ring opening. In some instances, the metabolic pathways generate electrophilic reactive intermediates and cause bioactivation. However, potential bioactivation related adverse events can be attenuated by structural modifications. Hence it is important to understand the biotransformation pathways to design stable drug candidates that are devoid of metabolic liabilities early in the discovery stage. The current review provides a comprehensive summary of biotransformation and bioactivation pathways of aliphatic nitrogen containing heterocycles and strategies to mitigate metabolic liabilities.

Discovery of (+)-N-(3-aminopropyl)-N-[1-(5-benzyl-3-methyl-4-oxo-[1,2]thiazolo[5,4-d]pyrimidin-6-yl)-2-methylpropyl]-4-methylbenzamide (AZD4877), a kinesin spindle protein inhibitor and potential anticancer agent.

Structure-activity relationship analysis identified (+)-N-(3-aminopropyl)-N-[1-(5-benzyl-3-methyl-4-oxo-[1,2]thiazolo[5,4-d]pyrimidin-6-yl)-2-methylpropyl]-4-methylbenzamide (AZD4877), from a series of novel kinesin spindle protein (KSP) inhibitors, as exhibiting both excellent biochemical potency and pharmaceutical properties suitable for clinical development. The selected compound arrested cells in mitosis leading to the formation of the monopolar spindle phenotype characteristic of KSP inhibition and induction of cellular death. A favorable pharmacokinetic profile and notable in vivo efficacy supported the selection of this compound as a clinical candidate for the treatment of cancer.

Preclinical pharmacokinetic/pharmacodynamic models to predict synergistic effects of co-administered anti-cancer agents.

PURPOSE: Pharmacokinetic/pharmacodynamic (PK/PD) models have been shown to be useful in predicting tumor growth rates in mouse xenografts. We applied novel PK/PD models to the published anticancer combination therapies of tumor growth inhibition to simulate synergistic changes in tumor growth rates. The parameters from the PK/PD model were further used to estimate clinical doses of the combination. METHODS: A PK/PD model was built that linked the dosing regimen of a compound to the inhibition of tumor growth in mouse xenograft models. Two subsequent PK/PD models were developed to simulate the published tumor growth profiles of combination treatments. Model I predicts the tumor growth curve assuming that the effect of two anticancer drugs, AZD7762 and irinotecan, is synergistic when given in combination. Model II predicts the tumor growth curve assuming that the effect of co-administering flavopiridol and irinotecan is maximally synergistic when dosed at an optimal interval. RESULTS: Model I was able to account for the synergistic effects of AZD7762 following the administration of irinotecan. When Model II was applied to the antitumor activity of irinotecan and flavopiridol combination therapy, the modeling was able to reproduce the optimal dosing interval between administrations of the compounds. Furthermore, Model II was able to estimate the biologically active dose of flavopiridol recommended for phase II studies. CONCLUSIONS: The timing of clinical combination therapy doses is often selected empirically. PK/PD models provide a theoretical structure useful in the design of the optimal clinical dose, frequency of administration and the optimal timing of administration between anticancer agents to maximize tumor suppression.

Discovery of a novel class of 2-ureido thiophene carboxamide checkpoint kinase inhibitors.

Checkpoint kinase-1 (Chk1, CHEK1) is a Ser/Thr protein kinase that mediates the cellular response to DNA-damage. A novel class of 2-ureido thiophene carboxamide urea (TCU) Chk1 inhibitors is described. Inhibitors in this chemotype were optimized for cellular potency and selectivity over Cdk1.

Estimation of human drug clearance using multiexponential techniques.

A multiexponential allometry (MA) method was developed to predict human drug clearance from preclinical data. Separate data sets containing clearances from human and preclinical species were chosen for the study. Human clearance was estimated using the MA technique according to the equation: CL = aBWb + cBWd, where CL is clearance in milliliters/minute, and a, b, c, and d are constants derived from preclinical pharmacokinetic data. Simple allometry (SA) gave the poorest prediction using any data set, and the percentage outliers remained larger than MA or monkey liver blood flow within 1.5-, 2-, and 3-fold error. Analysis of compounds common to both data sets suggested that MA could accurately predict human clearances within approximately 10% of 3-fold error. The analysis also showed that monkey is an important species for scaling, and MA is a better predictor of human clearance when the slope of SA is >0.7.

Reaction phenotyping: current industry efforts to identify enzymes responsible for metabolizing drug candidates.

Reaction phenotyping studies to identify specific enzymes involved in the metabolism of drug candidates are increasingly important in drug discovery efforts. Experimental approaches used for CYP reaction phenotyping include incubations with cDNA expressed CYP enzyme systems and incubations containing specific CYP enzyme inhibitors. Since both types of experiments present specific advantages as well as known drawbacks, these studies are generally viewed as complementary approaches. Although glucuronidation pathways are also known to present potential drug-drug interaction issues as well as challenges related to their polymorphic expression, reaction phenotyping approaches for glucuronidation are generally limited to cDNA expressed systems due to lack of availability of specific UGT inhibitors. This article presents a limited review of current approaches to reaction phenotyping studies used within the pharmaceutical industry.

Synthesis and structure-activity relationship of imidazo(1,2-a)thieno(3,2-e)pyrazines as IKK-beta inhibitors.

The identification of a potent series of IKK-beta selective inhibitors based on an imidazothienopyrazine template and the oral efficacy of one such analog (22j) in the LPS-induced TNF-alpha release mouse model are described.

Neurochemical, pharmacokinetic, and behavioral effects of the novel selective serotonin reuptake inhibitor BMS-505130.

BMS-505130 is a potent and selective serotonin transport inhibitor; K(i) for binding to the serotonin transporter = 0.18 nM (K(i) values for binding to the norepinephrine and dopamine transporters = 4.6 and 2.1 microM, respectively). In platelet serotonin uptake studies BMS-505130 (5 mg/kg, p.o.) produced a robust inhibition of serotonin uptake. In microdialysis studies oral dosing with BMS-505130 produced a dose-dependent increase in cortical serotonin levels that reached a maximal effect of 200% above baseline at a dose of 1 mg/kg, p.o.; the peak serotonin response was transient in nature. Following oral administration, peak plasma concentrations of BMS-505130 reached Tmax at 1.6 +/- 0.7 h and then declined to concentrations <10% of Cmax within the following 6 h; plasma half-life following i.v. dosing was 0.46 +/- 0.02 h. Parallel microdialysis and pharmacokinetic studies revealed that changes in serotonin levels in the cortex mirrored changes in the brain concentration of BMS-505130. In a behavioral assay known to be sensitive to selective serotonin reuptake inhibitors (SSRIs), mouse tail suspension, BMS-505130 produced a robust response after either oral or intraperitoneal dosing. BMS-505130 exhibits a pharmacological, neurochemical and behavioral profile consistent with a potent SSRI. Moreover, BMS-505130's short half-life may be advantageous for the treatment of premature ejaculation where an acute effect to delay ejaculation followed by a relatively rapid fall in SSRI plasma concentrations might be desirable.

BMS-345541 is a highly selective inhibitor of I kappa B kinase that binds at an allosteric site of the enzyme and blocks NF-kappa B-dependent transcription in mice.

The signal-inducible phosphorylation of serines 32 and 36 of I kappa B alpha is critical in regulating the subsequent ubiquitination and proteolysis of I kappa B alpha, which then releases NF-kappa B to promote gene transcription. The multisubunit I kappa B kinase responsible for this phosphorylation contains two catalytic subunits, termed I kappa B kinase (IKK)-1 and IKK-2. BMS-345541 (4(2'-aminoethyl)amino-1,8-dimethylimidazo(1,2-a)quinoxaline) was identified as a selective inhibitor of the catalytic subunits of IKK (IKK-2 IC(50) = 0.3 microm, IKK-1 IC(50) = 4 microm). The compound failed to inhibit a panel of 15 other kinases and selectively inhibited the stimulated phosphorylation of I kappa B alpha in cells (IC(50) = 4 microm) while failing to affect c-Jun and STAT3 phosphorylation, as well as mitogen-activated protein kinase-activated protein kinase 2 activation in cells. Consistent with the role of IKK/NF-kappa B in the regulation of cytokine transcription, BMS-345541 inhibited lipopolysaccharide-stimulated tumor necrosis factor alpha, interleukin-1 beta, interleukin-8, and interleukin-6 in THP-1 cells with IC(50) values in the 1- to 5-microm range. Although a Dixon plot of the inhibition of IKK-2 by BMS-345541 showed a non-linear relationship indicating non-Michaelis-Menten kinetic binding, the use of multiple inhibition analyses indicated that BMS-345541 binds in a mutually exclusive manner with respect to a peptide inhibitor corresponding to amino acids 26-42 of I kappa B alpha with Ser-32 and Ser-36 changed to aspartates and in a non-mutually exclusive manner with respect to ADP. The opposite results were obtained when studying the binding to IKK-1. A binding model is proposed in which BMS-345541 binds to similar allosteric sites on IKK-1 and IKK-2, which then affects the active sites of the subunits differently. BMS-345541 was also shown to have excellent pharmacokinetics in mice, and peroral administration showed the compound to dose-dependently inhibit the production of serum tumor necrosis factor alpha following intraperitoneal challenge with lipopolysaccharide. Thus, the compound is effective against NF-kappa B activation in mice and represents an important tool for investigating the role of IKK in disease models.