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.

Identification of a novel, non-tetrahydroquinoline variant of the cholesteryl ester transfer protein (CETP) inhibitor torcetrapib, with improved aqueous solubility.

1. Elaborate studies of cholesteryl ester transfer protein (CETP) polymorphisms and genetic deficiency in humans suggest direct links between CETP, high-density lipoprotein cholesterol (HDL-c) levels and coronary heart diseases. The hypothesis that CETP inhibition by small molecule inhibitors raises HDL-c has been validated clinically with structurally-diverse CETP inhibitors such as torcetrapib, anacetrapib, dalcetrapib and evacetrapib. 2. Despite promising phase 2 results with respect to HDL-c elevation, torcetrapib was discontinued in phase 3 trials due to increased mortality rates in the cardiovascular outcomes study. Emerging evidence for the adverse effects hints at off-target chemotype-specific cardiovascular toxicity, possibly related to the pressor effects of torcetrapib, since structurally diverse CETP inhibitors such as anacetrapib, evacetrapib and dalcetrapib are not associated with blood pressure increases in humans. Nonclinical follow-up studies showed that torcetrapib induces aldosterone biosynthesis and secretion in vivo and in vitro, an effect which is not observed with other CETP inhibitors in clinical development. 3. As part of ongoing efforts to identify novel CETP inhibitors devoid of pressor effects, strategies were implemented towards the design of compounds, which lack the 1,2,3,4-tetrahydroquinoline (THQ) scaffold present in torcetrapib. In this article, we disclose results of structure-activity relationship studies for a series of novel non-THQ CETP inhibitors, which resulted in the identification of a novel isonipecotic acid derivative 10 (also referred to as PF-04445597) with vastly improved oral pharmacokinetic properties mainly as a result of improved aqueous solubility. This feature is attractive in that, it bypasses significant investments needed to develop compatible solubilizing formulation(s) for oral drug delivery of highly lipophilic and poorly soluble compounds; attributes, which are usually associated with small molecule CETP inhibitors. PF-04445597 was also devoid of aldosterone secretion in human H295R adrenal carcinoma cells.

In Vitro-In Vivo Extrapolation and Scaling Factors for Clearance of Human and Preclinical Species with Liver Microsomes and Hepatocytes.

In vitro-in vivo extrapolation ((IVIVE) and empirical scaling factors (SF) of human intrinsic clearance (CLint) were developed using one of the largest dataset of 455 compounds with data from human liver microsomes (HLM) and human hepatocytes (HHEP). For extended clearance classification system (ECCS) class 2/4 compounds, linear SFs (SFlin) are approximately 1, suggesting enzyme activities in HLM and HHEP are similar to those in vivo under physiological conditions. For ECCS class 1A/1B compounds, a unified set of SFs was developed for CLint. These SFs contain both SFlin and an exponential SF (SFß) of fraction unbound in plasma (fu,p). The unified SFs for class 1A/1B eliminate the need to identify the transporters involved prior to clearance prediction. The underlying mechanisms of these SFs are not entirely clear at this point, but they serve practical purposes to reduce biases and increase prediction accuracy. Similar SFs have also been developed for preclinical species. For HLM-HHEP disconnect (HLM > HHEP) ECCS class 2/4 compounds that are mainly metabolized by cytochrome P450s/FMO, HLM significantly overpredicted in vivo CLint, while HHEP slightly underpredicted and geometric mean of HLM and HHEP slightly overpredicted in vivo CLint. This observation is different than in rats, where rat liver microsomal CLint correlates well with in vivo CLint for compounds demonstrating permeability-limited metabolism. The good CLint IVIVE developed using HLM and HHEP helps build confidence for prospective predictions of human clearance and supports the continued utilization of these assays to guide structure-activity relationships to improve metabolic stability.