Randy L. Bell

Correlation of tumor growth suppression and methionine aminopetidase-2 activity blockade using an orally active inhibitor

This laboratory and others have shown that agents that inhibit the in vitro catalytic activity of methionine aminopeptidase-2 (MetAP2) are effective in blocking angiogenesis and tumor growth in preclinical models. However, these prototype MetAP2 inhibitors are clearly not optimized for therapeutic use in the clinic. We have discovered an orally active class of MetAP2 inhibitors, the anthranilic acid sulfonamides exemplified by A-800141, which is highly specific for MetAP2. This orally bioavailable inhibitor exhibits an antiangiogenesis effect and a broad anticancer activity in a variety of tumor xenografts including B cell lymphoma, neuroblastoma, and prostate and colon carcinomas, either as a single agent or in combination with cytotoxic agents. We also have developed a biomarker assay to evaluate in vivo MetAP2 inhibition in circulating mononuclear cells and in tumors. This biomarker assay is based on the N-terminal methionine status of the MetAP2-specific substrate GAPDH in these cells. In cell cultures in vitro, the sulfonamide MetAP2 inhibitor A-800141 caused the formation of GAPDH variants with an unprocessed N-terminal methionine. A-800141 blocked tumor growth and MetAP2 activity in a similar dose–response in mouse models, demonstrating the antitumor effects seen for A-800141 are causally connected to MetAP2 inhibition in vivo. The sulfonamide MetAP2 inhibitor and GAPDH biomarker in circulating leukocytes may be used for the development of a cancer treatment.

Pharmacological modulation of eosinophil influx into the lungs of Brown Norway rats

A model of lung inflammation was developed in Brown Norway rats. Intense lung eosinophilia was induced by a single intravenous injection of Sephadex G-200 particles. The eosinophilia observed was preceded by an increase in cysteinyl leukotrienes found in lung lavage fluids. Theophylline and albuterol were tested in the model and found to be inactive, while dexamethasone was effective. Zileuton, a specific leukotriene inhibitor, was found to effectively inhibit leukotriene formation and the influx of eosinophils into the lungs of these Sephadex-treated animals. Studies with specific leukotriene D4 antagonists of the cysLT1 type receptor indicate that this leukotriene receptor is probably not involved directly in the eosinophilic inflammation. This model appears to be useful in characterizing potential anti-inflammatory effects of inhibitors by evaluating their ability to prevent eosinophil influx into the lung.

Thiazole analogues of the NSAID indomethacin as selective COX-2 inhibitors

The carboxyl group of the NSAID indomethacin was replaced with a variety of substituted thiazoles to obtain a series of potent, selective inhibitors of COX-2. Additional substitutions were made at the 1-position and 5-position of the indole of indomethacin.

Synthesis of indolylalkoxyiminoalkylcarboxylates as leukotriene biosynthesis inhibitors

A series of substituted indolylalkoxyiminoalkylcarboxylates were found to be potent leukotriene biosynthesis inhibitors. The structure-activity relationships were investigated. Representative potent inhibitors identified were the quinolyl 3a (A-86885) and pyridyl 3b (A-86886) congeners with in vitro IC50s of 21 and 9 nM and in vivo leukotriene inhibition in the rat with oral ED50s of 0.9 and 1.7 mg/kg, respectively.

Identification and Characterization of Novel Antagonists of the CCR3 Receptor

Eotaxin, an inducer of eosinophil migration and activation, exerts its activity by binding to CCR3, the C-C chemokine receptor 3. An inhibitor of the eotaxin-CCR3 binding interaction may have potential as an anti-inflammatory drug for treatment of asthma, parasitic infections, and allergic disorders. A radioligand binding assay was developed using HEK cells transfected with CCR3, with 125I eotaxin as the ligand. Whole cells grown on polylysine-coated plates were used as the receptor source for the screen. Screening of more than 200,000 compounds with this assay yielded a number of screening hits, and of these, 2 active novel antagonists were identified. These compounds showed inhibitory effects on eosinophil chemotaxis in both in vitro and in vivo assays. (Journal of Biomolecular Screening 2003:324-331)

Substituted 4-amino-1H-pyrazolo[3,4-d]pyrimidines as multi-targeted inhibitors of insulin-like growth factor-1 receptor (IGF1R) and members of ErbB-family receptor kinases

This Letter describes the lead discovery, optimization, and biological characterization of a series of substituted 4-amino-1H-pyrazolo[3,4-d]pyrimidines as potent inhibitors of IGF1R, EGFR, and ErbB2. The leading compound 11 showed an IGF1R IC(50) of 12 nM, an EGFR (L858R) IC(50) of 31 nM, and an ErbB2 IC(50) of 11 nM, potent activity in cellular functional and anti-proliferation assays, as well as activity in an in vivo pharmacodynamic assay.

Development of multitargeted inhibitors of both the insulin-like growth factor receptor (IGF-IR) and members of the epidermal growth factor family of receptor tyrosine kinases.

Emerging clinical and pre-clinical data indicate that both insulin-like growth factor receptor (IGF-IR) and members of the epidermal growth factor (EGF) family of receptor tyrosine kinases (RTKs) exhibit significant cross-talk in human cancers. Therefore, a small molecule that successfully inhibits the signaling of both classes of oncogenic kinases might provide an attractive agent for chemotherapeutic use. Herein, we disclose the structure activity relationships that led to the synthesis and biological characterization of 14, a novel small molecule inhibitor of both IGF-IR and members of the epidermal growth factor family of RTKs.

Insulin-like Growth Factor-1 Receptor and ErbB Kinase Inhibitor Combinations Block Proliferation and Induce Apoptosis through Cyclin D1 Reduction and Bax Activation

The insulin-like growth factor-1 receptor (IGF-1R) and ErbB family of receptors are receptor tyrosine kinases that play important roles in cancer. Lack of response and resistance to therapies targeting ErbB receptors occur and are often associated with activation of the IGF-1R pathway. Combinations of agents that inhibit IGF-1R and ErbB receptors have been shown to synergistically block cancer cell proliferation and xenograft tumor growth. To determine the mechanism by which targeting both IGF-1R and ErbB receptors causes synergistic effects on cell growth and survival, we investigated the effects of combinations of selective IGF-1R and ErbB kinase inhibitors on proliferative and apoptotic signaling. We identified A431 squamous cell carcinoma cells as most sensitive to combinations of ErbB and IGF-1R inhibitors. The inhibitor combinations resulted in not only blockade of A431 cell proliferation, but also induced apoptosis, which was not seen with either agent alone. Upon examining phosphorylation states and expression levels of proteins in the IGF-1R and ErbB signaling pathways, we found a correlation between the ability of combinations to inhibit proliferation and to decrease levels of phosphorylated Akt and cyclin D1. In addition, the massive cell death induced by combined IGF-1R/ErbB inhibition was associated with Mcl-1 reduction and Bax activation. Thus, targeting both IGF-1R and ErbB receptors simultaneously results in cell cycle arrest and apoptosis through combined effects on Akt, cyclin D1, and Bax activation.

Discovery, identification, and characterization of candidate pharmacodynamic markers of methionine aminopeptidase-2 inhibition.

The catalytic activity of methionine aminopeptidase-2 (MetAP2) has been pharmacologically linked to cell growth, angiogenesis, and tumor progression, making this an attractive target for cancer therapy. An assay for monitoring specific protein changes in response to MetAP2 inhibition, allowing pharmacokinetic (PK)/pharmacodynamic (PD) models to be established, could dramatically improve clinical decision-making. Candidate MetAP2-specific protein substrates were discovered from undigested cell culture-derived proteomes by MALDI-/SELDI-MS profiling and a biochemical method using (35)S-Met labeled protein lysates. Substrates were identified either as intact proteins by FT-ICR-MS or applying in-gel protease digestions followed by LC-MS/MS. The combination of these approaches led to the discovery of novel MetAP2-specific substrates including thioredoxin-1 (Trx-1), SH3 binding glutamic acid rich-like protein (SH3BGRL), and eukaryotic elongation factor-2 (eEF2). These studies also confirmed glyceraldehye 3-phosphate dehydrogenase (GAPDH) and cyclophillin A (CypA) as MetAP2 substrates. Additional data in support of these proteins as MetAP2-specific substrates were provided by in vitro MetAP1/MetAP2 enzyme assays with the corresponding N-terminal derived peptides and 1D/2D Western analyses of cellular and tissue lysates. FT-ICR-MS characterization of all intact species of the 18 kDa substrate, CypA, enabled a SELDI-MS cell-based assay to be developed for correlating N-terminal processing and inhibition of proliferation. The MetAP2-specific protein substrates discovered in this study have diverse properties that should facilitate the development of reagents for testing in preclinical and clinical environments.

Reversal of oncogene transformation and suppression of tumor growth by the novel IGF1R kinase inhibitor A-928605

BackgroundThe insulin-like growth factor (IGF) axis is an important signaling pathway in the growth and survival of many cell and tissue types. This pathway has also been implicated in many aspects of cancer progression from tumorigenesis to metastasis. The multiple roles of IGF signaling in cancer suggest that inhibition of the pathway might yield clinically effective therapeutics.MethodsWe describe A-928605, a novel pyrazolo [3,4-d]pyrimidine small molecule inhibitor of the receptor tyrosine kinases (IGF1R and IR) responsible for IGF signal transduction. This compound was first tested for its activity and selectivity via conventional in vitro kinome profiling and cellular IGF1R autophosphorylation. Additionally, cellular selectivity and efficacy of A-928605 were analyzed in an IGF1R oncogene-addicted cell line by proliferation, signaling and microarray studies. Finally, in vivo efficacy of A-928605 was assessed in the oncogene-addicted cell line and in a neuroblastoma model as a single agent as well as in combination with clinically approved therapeutics targeting EGFR in models of pancreatic and non-small cell lung cancers.ResultsA-928605 is a selective IGF1R inhibitor that is able to abrogate activation of the pathway both in vitro and in vivo. This novel compound dosed as a single agent is able to produce significant growth inhibition of neuroblastoma xenografts in vivo. A-928605 is also able to provide additive effects when used in combination with clinically approved agents directed against EGFR in non-small cell lung and human pancreatic tumor models.ConclusionThese results suggest that a selective IGF1R inhibitor such as A-928605 may provide a useful clinical therapeutic for IGF pathway affected tumors and warrants further investigation.