John G. Houston

Discovery and Evaluation of BMS-708163, a Potent, Selective and Orally Bioavailable γ-Secretase Inhibitor

During the course of our research efforts to develop a potent and selective γ-secretase inhibitor for the treatment of Alzheimers disease, we investigated a series of carboxamide-substituted sulfonamides. Optimization based on potency, Notch/amyloid-β precursor protein selectivity, and brain efficacy after oral dosing led to the discovery of 4 (BMS-708163). Compound 4 is a potent inhibitor of γ-secretase (Aβ40 IC50 = 0.30 nM), demonstrating a 193-fold selectivity against Notch. Oral administration of 4 significantly reduced Aβ40 levels for sustained periods in brain, plasma, and cerebrospinal fluid in rats and dogs.

γ-Secretase Inhibitors for Alzheimer’s Disease

The amyloid hypothesis, which states that β-amyloid (Aβ) aggregates cause the onset and progression of Alzheimer’s disease (AD), is a leading proposal to explain AD aetiology. Based on this hypothesis, compounds that inhibit γ-secretase, one of the enzymes responsible for forming Aβ, are potential therapeutics for AD. Preclinical studies clearly establish that γ-secretase inhibitors can reduce brain Aβ in rodent models. The initial investigation of the effects of a γ-secretase inhibitor on Aβ-induced cognitive deficits in transgenic mice showed that modest Aβ reductions (15–30%) are sufficient to reverse Aβ-induced cognitive deficits in Tg2576 mice. Extending these studies to other γ-secretase inhibitors and other models with Aβ-induced cognitive deficits will be important. Unfortunately, γ-secretase inhibitors also cause abnormalities in the gastrointestinal tract, thymus and spleen in rodents. These changes likely result from inhibition of Notch cleavage, a transmembrane receptor involved in regulating cell-fate decisions. Two recent studies in rodents suggest that Aβ reduction using γ-secretase inhibitors can be partially separated from Notch inhibition. Given the uncertain Aβ reduction target and the potential for mechanism-based toxicity, biomarkers for efficacy and toxicity would be helpful in clinical trials. The first report of γ-secretase inhibitors in clinical trials was recently published. In this study, LY-450139 reduced plasma Aβ, but not cerebrospinal fluid Aβ. Taken together, the results of studies to date suggest that γ-secretase inhibitors have the potential to address a large unmet medical need if the technical challenges can be overcome.

Case study: impact of technology investment on lead discovery at Bristol–Myers Squibb, 1998–2006

We review strategic approaches taken over an eight-year period at BMS to implement new high-throughput approaches to lead discovery. Investments in compound management infrastructure and chemistry library production capability allowed significant growth in the size, diversity and quality of the BMS compound collection. Screening platforms were upgraded with robust automated technology to support miniaturized assay formats, while workflows and information handling technologies were streamlined for improved performance. These technology changes drove the need for a supporting organization in which critical engineering, informatics and scientific skills were more strongly represented. Taken together, these investments led to significant improvements in speed and productivity as well a greater impact of screening campaigns on the initiation of new drug discovery programs.

Pharmacodynamics of Selective Inhibition of γ -Secretase by Avagacestat

A hallmark of Alzheimer’s disease (AD) pathology is the accumulation of brain amyloid β-peptide (Aβ), generated by γ-secretase-mediated cleavage of the amyloid precursor protein (APP). Therefore, γ-secretase inhibitors (GSIs) may lower brain Aβ and offer a potential new approach to treat AD. As γ-secretase also cleaves Notch proteins, GSIs can have undesirable effects due to interference with Notch signaling. Avagacestat (BMS-708163) is a GSI developed for selective inhibition of APP over Notch cleavage. Avagacestat inhibition of APP and Notch cleavage was evaluated in cell culture by measuring levels of Aβ and human Notch proteins. In rats, dogs, and humans, selectivity was evaluated by measuring plasma blood concentrations in relation to effects on cerebrospinal fluid (CSF) Aβ levels and Notch-related toxicities. Measurements of Notch-related toxicity included goblet cell metaplasia in the gut, marginal-zone depletion in the spleen, reductions in B cells, and changes in expression of the Notch-regulated hairy and enhancer of split homolog-1 from blood cells. In rats and dogs, acute administration of avagacestat robustly reduced CSF Aβ40 and Aβ42 levels similarly. Chronic administration in rats and dogs, and 28-day, single- and multiple-ascending–dose administration in healthy human subjects caused similar exposure-dependent reductions in CSF Aβ40. Consistent with the 137-fold selectivity measured in cell culture, we identified doses of avagacestat that reduce CSF Aβ levels without causing Notch-related toxicities. Our results demonstrate the selectivity of avagacestat for APP over Notch cleavage, supporting further evaluation of avagacestat for AD therapy.

Best Practices in Compound Management for Preserving Compound Integrity and Accurately Providing Samples for Assays

Preserving the integrity of the compound collection and providing high-quality materials for drug discovery in an efficient and cost-effective manner are 2 major challenges faced by compound management (CM) at Bristol-Myers Squibb (BMS). The demands on CM include delivering hundreds of thousands of compounds a year to a variety of operations. These operations range from single-compound requests to hit identification support and just-in-time assay plate provision for lead optimization. Support needs for these processes consist of the ability to rapidly provide compounds as solids or solutions in a variety of formats, establishing proper long- and short-term storage conditions and creating appropriate methods for handling concentrated, potent compounds for delivery to sensitive biological assays. A series of experiments evaluating the effects of processing compounds with volatile solvents, storage conditions that can induce freeze/thaw cycles, and the delivery of compounds were performed. This article presents the results of these experiments and how they affect compound integrity and the accuracy of compound management processes. (Journal of Biomolecular Screening 2009:476-484)

Discovery of (5S,6S,9R)-5-Amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridin-9-yl 4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin-1-yl)piperidine-1-carboxylate (BMS-927711): An Oral Calcitonin Gene-Related Peptide (CGRP) Antagonist in Clinical Trials for Treating Migraine

Calcitonin gene-related peptide (CGRP) receptor antagonists have demonstrated clinical efficacy in the treatment of acute migraine. Herein, we describe the design, synthesis, and preclinical characterization of a highly potent, oral CGRP receptor antagonist BMS-927711 (8). Compound 8 has good oral bioavailability in rat and cynomolgus monkey, attractive overall preclinical properties, and shows dose-dependent activity in a primate model of CGRP-induced facial blood flow. Compound 8 is presently in phase II clinical trials.

Efficient and Effective Compound Management to Support Lead Optimization

The introduction of lean thinking and Six Sigma methodologies into the drug discovery process has become an important approach for ensuring efficient workflows while containing costs. For the compound management department at Bristol-Myers Squibb, this has resulted in a partnership with the research community to evaluate and streamline processes to enable cost-disciplined science. The authors describe the results of Lean Six Sigma approaches in the automation and informatics environment that have been optimized to support parallel processing of compounds. This new platform facilitates the rapid and simultaneous data generation from structure activity and structure liability assays. As a result of these compound management improvements, reduction of timelines and quicker decision making has been achieved in the lead optimization process.

Gamma-secretase inhibitors have intrinsically different potencies against Aβ production and Notch signaling

immunohistochemistry. The peptide capturing antibody (11A50) showed preferential affinity (32.5 nM) to monomeric Ab40, but did not bind to Ab40 fibrils, whereas antibodies 6E10 and 4G8 had moderate affinity to monomeric Ab40 (22.3 and 30.1 nM, respectively). 4G8, which labels diffuse plaques better than 6E10, had a higher association rate constant than 6E10 but showed similar association and dissociation kinetics compared to 11A50. Enzymatic digestion of IgG4.1 to the F(ab)24.1 fragments or their polyamine-modified derivatives that enhance blood brain barrier permeability did not affect the kinetic properties of the antigen binding site. Conclusions: These differences in kinetic binding to monomeric and fibrillar Ab among various antibodies could be utilized to distinguish mAbs that might be useful for immunotherapy or amyloid plaque imaging versus those that could be utilized for bioanalytical techniques.