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Addressing the safety aspects of drugs and environmental chemicals has historically been undertaken through animal testing. However, the quantity of chemicals in need of assessment and the challenges of species extrapolation require the development of alternative approaches. Our approach, the US Environmental Protection Agency's ToxCast program, utilizes a large suite of in vitro and model organism assays to interrogate important chemical libraries and computationally analyze bioactivity profiles. Here we evaluated one component of the ToxCast program, the use of primary human cell systems, by screening for chemicals that disrupt physiologically important pathways. Chemical-response signatures for 87 endpoints covering molecular functions relevant to toxic and therapeutic pathways were generated in eight cell systems for 641 environmental chemicals and 135 reference pharmaceuticals and failed drugs. Computational clustering of the profiling data provided insights into the polypharmacology and potential off-target effects for many chemicals that have limited or no toxicity information. The endpoints measured can be closely linked to in vivo outcomes, such as the upregulation of tissue factor in endothelial cell systems by compounds linked to the risk of thrombosis in vivo. Our results demonstrate that assaying complex biological pathways in primary human cells can identify potential chemical targets, toxicological liabilities and mechanisms useful for elucidating adverse outcome pathways.

A new series of 1-(1,3-benzodioxol-5-ylmethyl)-3-[4-(1H-Imidazol-1-yl)phenoxy]-piperidine analogs were designed and identified as potent and selective inhibitors of NO formation based both on the crystal structure of a murine iNOS Delta114 monomer domain/ inhibitor complex and inhibition of the NO formation in human A172 cell assays. Compound 12S showed high potency and high iNOS selectivity versus nNOS and eNOS.

A series of compounds was rationally designed as inhibitors of dimer formation of the inducible isoform of nitric oxide synthase, and subsequent nitric oxide production. The conformation of two fragments obtained from a crystal structure was utilized to design a tether connecting those same two fragments. The resulting compounds were potent dimerization inhibitors that bound to the enzyme in a similar conformation as the fragments.

By the screening of a combinatorial library for inhibitors of nitric oxide (NO) formation by the inducible isoform of nitric oxide synthase (iNOS) using a whole-cell assay, 2-(imidazol-1-yl)pyrimidines were identified. Compounds were found to inhibit the dimerization of iNOS monomers, thus preventing the formation of the dimeric, active form of the enzyme. Optimization led to the selection of the potent, selective, and orally available iNOS dimerization inhibitor, 21b, which significantly ameliorated adjuvant-induced arthritis in a rat model. Analysis of the crystal structure of the 21b--iNOS monomer complex provided a rationalization for both the SAR and the mechanism by which 21b blocks the formation of the protein--protein interaction present in the dimeric form of iNOS.

Hepsin is a type II transmembrane serine protease that is expressed in normal liver, and at lower levels in kidney, pancreas, and testis. Several studies have shown that hepsin mRNA is significantly elevated in most prostate tumors, as well as a significant fraction of ovarian and renal cell carcinomas and hepatomas. Although the overexpression of mRNA in these tumors has been extensively documented, there has been conflicting literature on whether hepsin plays a role in tumor cell growth and progression. Early literature implied a role for hepsin in human tumor cell proliferation, whereas recent studies with a transgenic mouse model for prostate cancer support a role for hepsin in tumor progression and metastases. To evaluate this issue further, we have expressed an activatable form of hepsin, and have generated a set of monoclonal antibodies that neutralize enzyme activity. The neutralizing antibodies inhibit hepsin enzymatic activity in biochemical and cell-based assays. Selected neutralizing and nonneutralizing antibodies were used in cell-based assays with tumor cells to evaluate the effect of antibodies on tumor cell growth and invasion. Neutralizing antibodies failed to inhibit the growth of prostate, ovarian, and hepatoma cell lines in culture. However, potent inhibitory effects of the antibodies were seen on invasion of ovarian and prostate cells in transwell-based invasion assays. These results support a role for hepsin in tumor cell progression but not in primary tumor growth. Consistent with this, immunohistochemical experiments with a mouse monoclonal antibody reveal progressively increased staining of prostate tumors with advanced disease, and in particular, extensive staining of bone metastatic lesions.

Accumulated studies have shown that activation of the Akt pathway plays a pivotal role in malignant transformation and chemoresistance by inducing cell survival, growth, migration, and angiogenesis. Therefore, Akt is believed to be a critical target for cancer intervention. Here, we report the discovery of a small molecule Akt pathway inhibitor, Akt/protein kinase B signaling inhibitor-2 (API-2), by screening the National Cancer Institute Diversity Set. API-2 suppressed the kinase activity and phosphorylation level of Akt. The inhibition of Akt kinase resulted in suppression of cell growth and induction of apoptosis in human cancer cells that harbor constitutively activated Akt due to overexpression of Akt or other genetic alterations such as PTEN mutation. API-2 is highly selective for Akt and does not inhibit the activation of phosphatidylinositol 3'-kinase, phosphoinositide-dependent kinase-1, protein kinase C, serum- and glucocorticoid-inducible kinase, protein kinase A, signal transducer and activators of transcription 3, extracellular signal-regulated kinase-1/2, or c-Jun NH(2)-terminal kinase. Furthermore, API-2 potently inhibited tumor growth in nude mice of human cancer cells in which Akt is aberrantly expressed/activated but not of those cancer cells in which it is not. These findings provide strong evidence for pharmacologically targeting Akt for anticancer drug discovery.