George Chang

CP-346086 an MTP inhibitor that lowers plasma cholesterol and triglycerides in experimental animals and in humans

A microsomal triglyceride transfer protein (MTP) inhibitor, CP-346086, was identified that inhibited both human and rodent MTP activity [concentration giving half-maximal inhibition (IC50) 2.0 nM]. In Hep-G2 cells, CP-346086 inhibited apolipoprotein B (apoB) and triglyceride secretion (IC50 2.6 nM) without affecting apoA-I secretion or lipid synthesis. When administered orally to rats or mice, CP-346086 lowered plasma triglycerides [dose giving 30% triglyceride lowering (ED30) 1.3 mg/kg] 2 h after a single dose. Coadministration with Tyloxapol demonstrated that triglyceride lowering was due to inhibition of hepatic and intestinal triglyceride secretion. A 2 week treatment with CP-346086 lowered total, VLDL, and LDL cholesterol and triglycerides dose dependently with 23%, 33%, 75%, and 62% reductions at 10 mg/kg/day. In these animals, MTP inhibition resulted in increased liver and intestinal triglycerides when CP-346086 was administered with food. When dosed away from meals, however, only hepatic triglycerides were increased. When administered as a single oral dose to healthy human volunteers, CP-346086 reduced plasma triglycerides and VLDL cholesterol dose dependently with ED50s of 10 mg and 3 mg, and maximal inhibition (100 mg) of 66% and 87% when measured 4 h after treatment. After a 2 week treatment (30 mg/day), CP-346086 reduced total and LDL cholesterol and triglycerides by 47%, 72%, and 75%, relative to either individual baselines or placebo, with little change in HDL cholesterol. Together, these data support further evaluation of CP-346086 in hyperlipidemia.

Physicochemical space for optimum oral bioavailability: contribution of human intestinal absorption and first-pass elimination.

Oral bioavailability (F) is a product of fraction absorbed (Fa), fraction escaping gut-wall elimination (Fg), and fraction escaping hepatic elimination (Fh). In this study, using a database comprised of Fa, Fg, Fh, and F values for 309 drugs in humans, an analysis of the interrelation of physicochemical properties and the individual parameters was carried out in order to define the physicochemical space for optimum human oral bioavailability. Trend analysis clearly indicated molecular weight (MW), ionization state, lipophilicity, polar descriptors, and free rotatable bonds (RB) influence bioavailability. These trends were due to a combination of effects of the properties on Fa and first-pass elimination (Fg and Fh). Higher MW significantly impacted Fa, while Fg and Fh decreased with increasing lipophilicity. Parabolic trends were observed for bioavailability with polar descriptors. Interestingly, RB has a negative effect on all three parameters, leading to its pronounced effect on bioavailability. In conclusion, physicochemical properties influence bioavailability with typically opposing effects on Fa and first-pass elimination. This analysis may provide a rational judgment on the physicochemical space to optimize oral bioavailability.

Species Independence in Brain Tissue Binding Using Brain Homogenates

Species independence of brain tissue binding was assessed with a large number of structurally diverse compounds using equilibrium dialysis with brain homogenates of seven species and strains (Wistar Han rat, Sprague-Dawley rat, CD-1 mouse, Hartley guinea pig, beagle dog, cynomolgus monkey, and human). The results showed that the fractions unbound of the seven species and strains were strongly correlated with correlation coefficients ranging from 0.93 to 0.99. The cross-species/strain correlations were not significantly different from the interassay correlation with the same species. The linear correlation between Wistar Han and other species had a slope close to 1 and an intercept near 0. Based on orthogonal statistical analysis, no correction is needed for extrapolation of fraction unbound from Wistar Han rat to the other species or strains. Hence, brain tissue binding of Wistar Han rat can be used to obtain binding of other species and strains in drug discovery.

Renal clearance in drug discovery and development: molecular descriptors, drug transporters and disease state

Importance of the field: Kidney plays a key role in the elimination of xenobiotics and metabolic products from the body, where renal clearance is determined by glomerular filtration, tubular secretion and reabsorption processes. The proximal tubule of the nephron is equipped with multi-specificity uptake and efflux transporters for the secretion of a broad range of xenobiotics, while the compound physicochemical space drives the tubular reabsorption. Due to involvement of transporters, renal clearance is possibly associated with renal drug–drug interactions (DDIs) in clinical situations. Nevertheless, renal insufficiency in diseased population is associated with altered transporter activity and evidently affects the pharmacokinetics of both renally and non-renally cleared compounds. Thus, early information on renal clearance is critical for successful development of compounds in certain chemical space. Areas covered in this review: This review provides updated information on the influence of physicochemical properties and the relevance of transporters in renal clearance and the associated drug interactions. In silico tools to predict the renal clearance at the discovery stage along with the potential alterations in drug disposition in the renal disease state are discussed with preclinical and clinical examples. What the reader will gain: The review provides comprehensive knowledge with recent examples to moderate renal disposition concerns in the drug discovery and development settings. Take home message: Consideration of clearance pathways early in the discovery process has become critical for successful development of compounds. Although significant progress has been made in elucidating the physicochemical drivers and biochemical processes for this pathway, the predictive ability remains a challenge. Furthermore, development of renally cleared compounds should progress with a clear understanding of possible issues including transporter-mediated DDI and disease state.

Mechanistic insights from comparing intrinsic clearance values between human liver microsomes and hepatocytes to guide drug design

Metabolic stability of drug candidates are often determined in both liver microsome and hepatocyte assays. Comparison of intrinsic clearance values between the two assays provides additional information to guide drug design. Intrinsic clearance values from human liver microsomes and hepatocytes were compared for a set of commercial drugs with known metabolic pathways and transporter characteristics. The results showed that for compounds that were predominately metabolized by CYP mediated mechanisms, the intrinsic clearance values from the two assays were comparable. For compounds with non-CYP pathways, such as UGT and AO, intrinsic clearance was faster in hepatocytes than in microsomes. Substrates of uptake or efflux transporters in this study did not have significant differences of intrinsic clearance between microsomes and hepatocytes, when uptake into the hepatocytes was not the rate-limiting step. When hepatic uptake was rate limiting, intrinsic clearance in microsomes was faster than that in hepatocytes, which was more prevalent for compounds with rapid metabolism. Low passive permeability can limit the exposure to drug molecules to the metabolizing enzymes in the hepatocytes in relationship to the rate of metabolism. The faster the rate of metabolism, the higher permeability is needed for molecule to enter the cells and not becoming rate-limiting. The findings are very useful for drug discovery programs to gain additional insights on mechanistic information to help drug design without added experiments. Follow-up studies can then be designed to address specific questions.

Extraction of tacit knowledge from large ADME data sets via pairwise analysis

Pharmaceutical companies routinely collect data across multiple projects for common ADME endpoints. Although at the time of collection the data is intended for use in decision making within a specific project, knowledge can be gained by data mining the entire cross-project data set for patterns of structure-activity relationships (SAR) that may be applied to any project. One such data mining method is pairwise analysis. This method has the advantage of being able to identify small structural changes that lead to significant changes in activity. In this paper, we describe the process for full pairwise analysis of our high-throughput ADME assays routinely used for compound discovery efforts at Pfizer (microsomal clearance, passive membrane permeability, P-gp efflux, and lipophilicity). We also describe multiple strategies for the application of these transforms in a prospective manner during compound design. Finally, a detailed analysis of the activity patterns in pairs of compounds that share the same molecular transformation reveals multiple types of transforms from an SAR perspective. These include bioisosteres, additives, multiplicatives, and a type we call switches as they act to either turn on or turn off an activity.

Physicochemical Property Space of Hepatobiliary Transport and Computational Models for Predicting Rat Biliary Excretion

Biliary excretion (BE) is a major elimination pathway, and its prediction is particularly important for optimization of systemic and/or target-site exposure of new molecular entities. The objective is to characterize the physicochemical space associated with hepatobiliary transport and rat BE and to develop in silico models. BE of 123 in-house compounds was obtained using the bile-duct cannulated rat model. Human and rat hepatic uptake transporters (hOATP1B1, hOATP1B3, hOATP2B1, and rOatp1b2) substrates (n = 183) were identified using transfected cells. Furthermore, the datasets were extended by adding BE of 163 compounds and 97 organic anion transporting polypeptide (OATP) substrates from the literature. Approximately 60% of compounds showing percentage of BE (%BE) ≥ 10 are anions, with mean BE of anions (36%) more than 3-fold higher than that of nonacids (11%). Compounds with %BE ≥ 10 are found to have high molecular mass, large polar surface area, more rotatable bonds, and high H-bond count, whereas the lipophilicity and passive membrane permeability are lower compared with compounds with %BE < 10. According to statistical analysis and principal component analysis, hOATPs and rOatp1b2 substrates showed physicochemical characteristics that were similar to those of the %BE ≥ 10 dataset. We further build categorical in silico models to predict rat BE, and the models (gradient boosting machine and scoring function) developed showed 80% predictability in identifying the rat BE bins (%BE ≥ 10 or < 10). In conclusion, the significant overlap of the property space of OATP substrates and rat BE suggests a predominant role of sinusoidal uptake transporters in biliary elimination. Categorical in silico models to predict rat BE were developed, and successful predictions were achieved.

Assessment of in silico models for fraction of unbound drug in human liver microsomes.

Importance of the field: Fraction of unbound drug in human liver microsome (fumic) incubation media is an important parameter for accurate assessment of hepatic intrinsic clearance and drug–drug interactions. In recent years, there have been considerable advances in understanding structure–microsomal binding relationships. Areas covered in the review: This review highlights the in silico modeling techniques for fumic including physicochemical properties-based modeling, pharmacophore feature-based classification modeling and more complex statistical method-based modeling. The application of these modeling techniques to the understanding of the structure-binding relationships is also discussed. What the reader will gain: The reader will gain an understanding of the modeling techniques used for prediction of binding to human liver microsomes (fumic). The reader will also understand the molecular structure–microsomal protein binding relationships. In all of these models, lipophilicity is the most important molecular property underlying the structure-binding relationship. Other molecular properties such as charge type (positive vs negative) and hydrogen bonding are also important factors for microsomal binding. Take home message: The predictive accuracy of fumic models in the high lipophilicity and tight microsomal binding ranges still needs to be further improved. However, in silico models are still valuable tools to aid chemical library design and prioritize multiple chemical series, which could provide efficiency and decrease knowledge cycle times in drug discovery.

The conversion of alcohols to halides using a filterable phosphine source

Abstract The conversion of primary and secondary alcohols to chlorides and bromides using 1,2-bis(diphenylphosphino)ethane (diphos) is described. Use of this reagent in lieu of the typical triphenylphosphine–carbontetrahalide complex provides a facile means of purifying the desired halide from the phosphine–oxide byproduct.

Discovery of a Highly Selective Glycogen Synthase Kinase-3 Inhibitor (PF-04802367) That Modulates Tau Phosphorylation in the Brain: Translation for PET Neuroimaging.

Glycogen synthase kinase-3 (GSK-3) regulates multiple cellular processes in diabetes, oncology, and neurology. N-(3-(1H-1,2,4-triazol-1-yl)propyl)-5-(3-chloro-4-methoxyphenyl)oxazole-4-carboxamide (PF-04802367 or PF-367) has been identified as a highly potent inhibitor, which is among the most selective antagonists of GSK-3 to date. Its efficacy was demonstrated in modulation of tau phosphorylation in vitro and in vivo. Whereas the kinetics of PF-367 binding in brain tissues are too fast for an effective therapeutic agent, the pharmacokinetic profile of PF-367 is ideal for discovery of radiopharmaceuticals for GSK-3 in the central nervous system. A (11) C-isotopologue of PF-367 was synthesized and preliminary PET imaging studies in non-human primates confirmed that we have overcome the two major obstacles for imaging GSK-3, namely, reasonable brain permeability and displaceable binding.