High Throughput Screening Identified a Substituted Imidazole as a Novel RANK Pathway-Selective Osteoclastogenesis Inhibitor

Anti-Microbial Drug Metronidazole Promotes Fracture Healing: Enhancement in the Bone Regenerative Efficacy of the Drug by a Biodegradable Sustained-Release In Situ Gel Formulation

Nitroimidazoles comprise a class of broad-spectrum anti-microbial drugs with efficacy against parasites, mycobacteria, and anaerobic Gram-positive and Gram-negative bacteria. Among these drugs, metronidazole (MTZ) is commonly used with other antibiotics to prevent infection in open fractures. However, the effect of MTZ on bone remains understudied. In this paper, we evaluated six nitroimidazole drugs for their impact on osteoblast differentiation and identified MTZ as having the highest osteogenic effect. MTZ enhanced bone regeneration at the femur osteotomy site in osteopenic ovariectomized (OVX) rats at the human equivalent dose. Moreover, in OVX rats, MTZ significantly improved bone mass and strength and improved microarchitecture compared to the vehicle-treated rats, which was likely achieved by an osteogenic mechanism attributed to the stimulation of the Wnt pathway in osteoblasts. To mitigate the reported neurological and genotoxic effects of MTZ, we designed an injectable sustained-release in situ gel formulation of the drug that improved fracture healing efficacy by 3.5-fold compared to oral administration. This enhanced potency was achieved through a significant increase in the circulating half-life and bioavailability of MTZ. We conclude that MTZ exhibits osteogenic effects, further accentuated by our sustained-release delivery system, which holds promise for enhancing bone regeneration in open fractures.

Pharmacological characterization of AS2690168, a novel small molecule RANKL signal transduction inhibitor

Pathological osteolysis is associated with excessive bone resorption by activated osteoclasts. Given that receptor activator of NF-kB and its ligand (RANKL) are key players in the differentiation and activation of osteoclasts, the RANKL/RANK signaling pathway is considered a promising target for the development of effective osteoclastogenesis inhibitors. We previously found that the orally available compound, AS2690168, suppresses RANKL-induced osteoclastogenesis of RAW264 cells. In this report, we further characterized the pharmacological profiles of AS2690168 in vitro and in vivo. AS2690168 suppressed soluble RANKL (sRANKL)-induced NFATc1 mRNA expression in RAW264 cells at 0.3 and 3.0 μM. It also suppressed calcium release from parathyroid hormone-stimulated mouse calvaria with an IC₅₀ value of 0.46 μM. Oral administration of AS2690168 completely suppressed the decrease in femoral bone mineral content in an sRANKL-induced osteopenic mice model at 3.0 mg/kg. It also significantly suppressed the decrease in femoral bone mineral density and increase in serum tartrate-resistant acid phosphatase-5b levels in ovariectomized rats at doses of 0.3, 1 and 3 mg/kg. Finally, AS260168 suppressed the increase in urine deoxypyridinoline in a rat prednisolone-induced osteoporosis model at 10 mg/kg. These results suggest that AS2690168 is a promising treatment for bone disorders with excessive bone resorption.

Inhibitory Effect of KP-A038 on Osteoclastogenesis and Inflammatory Bone Loss Is Associated With Downregulation of Blimp1

Excessive osteoclastic activity results in pathological bone resorptive diseases, such as osteoporosis, periodontitis, and rheumatoid arthritis. As imidazole-containing compounds possess extensive therapeutic potential for the management of diverse diseases, we synthesized a series of imidazole derivatives and investigated their effects on osteoclast differentiation and function. In the present study, we found that a novel imidazole derivative, KP-A038, suppressed receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclastogenesis and bone-resorbing activity in vitro and attenuated lipopolysaccharide (LPS)-induced bone destruction in vivo. KP-A038 significantly inhibited the induction of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) and the expression of its target genes, including tartrate-resistant acid phosphatase (Acp5), cathepsin K (Ctsk), dendritic cell-specific transmembrane protein (Dcstamp), and matrix metallopeptidase 9 (Mmp9). KP-A038 upregulated the expression of negative regulators of osteoclast differentiation, such as interferon regulatory factor-8 (Irf8) and B-cell lymphoma 6 (Bcl6). Consistently, KP-A038 downregulated the expression of B lymphocyte-induced maturation protein-1 (Blimp1 encoded by Prdm1), a repressor for Irf8 and Bcl6. Moreover, administration of KP-A038 reduced LPS-induced bone erosion by suppressing osteoclast formation in vivo. Thus, our findings suggest that KP-A038 may serve as an effective therapeutic agent for the treatment and/or prevention of bone loss in pathological bone diseases, including osteoporosis and periodontitis.

Predicting cytotoxicity from heterogeneous data sources with Bayesian learning

BACKGROUND

We collected data from over 80 different cytotoxicity assays from Pfizer in-house work as well as from public sources and investigated the feasibility of using these datasets, which come from a variety of assay formats (having for instance different measured endpoints, incubation times and cell types) to derive a general cytotoxicity model. Our main aim was to derive a computational model based on this data that can highlight potentially cytotoxic series early in the drug discovery process.

RESULTS

We developed Bayesian models for each assay using Scitegic FCFP_6 fingerprints together with the default physical property descriptors. Pairs of assays that are mutually predictive were identified by calculating the ROC score of the model derived from one predicting the experimental outcome of the other, and vice versa. The prediction pairs were visualised in a network where nodes are assays and edges are drawn for ROC scores >0.60 in both directions. We observed that, if assay pairs (A, B) and (B, C) were mutually predictive, this was often not the case for the pair (A, C). The results from 48 assays connected to each other were merged in one training set of 145590 compounds and a general cytotoxicity model was derived. The model has been cross-validated as well as being validated with a set of 89 FDA approved drug compounds.

CONCLUSIONS

We have generated a predictive model for general cytotoxicity which could speed up the drug discovery process in multiple ways. Firstly, this analysis has shown that the outcomes of different assay formats can be mutually predictive, thus removing the need to submit a potentially toxic compound to multiple assays. Furthermore, this analysis enables selection of (a) the easiest-to-run assay as corporate standard, or (b) the most descriptive panel of assays by including assays whose outcomes are not mutually predictive. The model is no replacement for a cytotoxicity assay but opens the opportunity to be more selective about which compounds are to be submitted to it. On a more mundane level, having data from more than 80 assays in one dataset answers, for the first time, the question - "what are the known cytotoxic compounds from the Pfizer compound collection?" Finally, having a predictive cytotoxicity model will assist the design of new compounds with a desired cytotoxicity profile, since comparison of the model output with data from an in vitro safety/toxicology assay suggests one is predictive of the other.

Discovery of novel benzopyranyl tetracycles that act as inhibitors of osteoclastogenesis induced by receptor activator of NF-κB ligand

A novel benzopyran-fused molecular framework 7ai was discovered as a specific inhibitor of RANKL-induced osteoclastogenesis using a cell-based TRAP activity assay from drug-like small-molecule libraries constructed by diversity-oriented synthesis. Its inhibitory activity was confirmed by in vitro evaluations including specific inhibition of RANKL-induced ERK phosphorylation and NF-κB transcriptional activation. 7ai can serve as a specific small-molecule modulator for mechanistic studies of RANKL-induced osteoclast differentiation as well as a potential lead for the development of antiresorptive drugs.

Development of a cell-based assay to quantify the inflammatory potential of test substances and screen compound libraries for anti-cancer drug candidates in a high-throughput format

Despite the current availability of an impressive in vitro assay battery developed to quantitatively analyze the broad panel of small compounds and macromolecules that possess the inflammatory potential, little methodology exists nowadays that affords a researcher or clinician to quantify the ultimate output on the level of cell signaling response caused by inflammatory pathway stimulation. As a matter of fact, majority of analytical tools measure bona fide inflammatory substances (e.g., cytokines or chemokines) by their direct binding to secondary reagents such as specific antibodies or other selectively affine substrates with the final readout generated via quantification of the resulting complexes. Although specific and highly reproducible, this approach provides no discrimination between biologically active versus inactive input analyte nor does it address the differential biological potential for the questioned substances related to their in vivo stability and biodistribution. In a search for alternative solutions, a novel strategy is emerging that employs cell-based methods of inflammatory substance measurements allowing to detect and quantify the downstream effects of analyte's activity translated in terms of inflammatory pathways stimulation. In addition, application of cell based assays simultaneously permits entry level evaluation of compound toxicity and endows with a powerful approach to perform high-throughput screenings of, e.g., small molecule libraries in a quest for novel compounds capable of influencing the inflammation process.

An improved beta-lactamase reporter assay: multiplexing with a cytotoxicity readout for enhanced accuracy of hit identification

A problem inherent to the use of cellular assays for drug discovery is their sensitivity to cytotoxic compounds, which can result in false hits from certain compound screens. To alleviate the need to follow-up hits from a reporter assay with a separate cytotoxicity assay, the authors have developed a multiplexed assay that combines the readout of a beta-lactamase reporter with that of a homogeneous cytotoxicity indicator. Important aspects to the development of the multiplexed format are addressed, including results that demonstrate that the IC(50) values of 40 select compounds in a beta-lactamase reporter assay for nuclear factor kappa B and SIE pathway antagonists are not affected by the addition of the cytotoxicity indicator. To demonstrate the improvement in hit confirmation, the multiplexed assay was used to perform a small-library screen (7728 compounds) for serotonin 5HT1A receptor antagonists. Hits identified from analysis of the beta-lactamase reporter data alone were compared to those hits determined when the reporter and cytotoxicity data generated from the multiplexed assay were combined. Confirmation rates were determined from compound follow-up using dose-response analysis of the potential antagonist hits identified by the initial screen. In this representative screen, the multiplexed assay approach yielded a 19% reduction in the number of compounds flagged for follow-up, with a 37% decrease in the number of false hits, demonstrating that multiplexing a beta-lactamase reporter assay with a cytotoxicity readout is a highly effective strategy for reducing false hit rates in cell-based compound screening assays.