Cancer Therapy: Preclinical Identification of a Novel Small Molecule HIF-1α Translation Inhibitor

Purpose: Hypoxia inducible factor-1 (HIF-1), the central mediator of the cellular response to low oxygen, functions as a transcription factor for a broad range of genes that provide adaptive responses to oxygen deprivation. HIF-1 is overexpressed in cancer and has become an important therapeutic target in solid tumors. In this study, a novel HIF-1α inhibitor was identified and its molecular mechanism was investigated. Experimental Design: Using a HIF-responsive reporter cell–based assay, a 10,000member natural product–like chemical compound library was screened to identify novel HIF-1 inhibitors. This led us to discover KC7F2, a lead compound with a central structure of cystamine. The effects of KC7F2 on HIF-1 transcription, translation, and protein degradation processes were analyzed. Results: KC7F2 markedly inhibited HIF-mediated transcription in cells derived from different tumor types, including glioma, breast, and prostate cancers, and exhibited enhanced cytotoxicity under hypoxia. KC7F2 prevented the activation of HIF-target genes such as carbonic anhydrase IX, matrix metalloproteinase 2 (MMP2), endothelin 1, and enolase 1. An investigation into the mechanism of action of KC7F2 showed that it worked through the down-regulation of HIF-1α protein synthesis, an effect accompanied by the suppression of the phosphorylation of eukaryotic translation initiation factor 4E binding protein 1 and p70 S6 kinase, key regulators of HIF-1α protein synthesis. Conclusion: These results show that KC7F2 is a potent HIF-1 pathway inhibitor and its potential as a cancer therapy agent warrants further study. (Clin Cancer Res 2009;15 (19):6128–36) Hypoxia, a reduction in partial oxygen pressure, is a major hindrance to effective solid tumor therapy. The microenvironment of rapidly growing solid tumors shows increased energy demand and diminished vascular supply, resulting in focal areas of prominent hypoxia (1). The hypoxic fraction of tumors is resistant to traditional therapies. Radiotherapy is compromised because of the reduced reaction of oxygen with radiationinduced DNA free radicals (2). Chemotherapy is hampered by the diffusion-limited drug delivery to hypoxic regions from distant vasculature. Moreover, many anticancer drugs are most effective against rapidly proliferating cells, and hypoxia (and deficiencies in other nutrients such as glucose) can cause a reduction in cell proliferation rate (3). This is compounded by the induction of the multidrug resistance (MDR1) gene product P-glycoprotein in hypoxic tissue (4), further reducing drug efficacy. Hypoxic tumor regions also impede immune responses, and may promote the growth of cancer stem cells (5, 6). Hypoxia drives malignant tumor progression. Tumor hypoxia increases malignant progression and metastasis by promoting angiogenesis through the induction of proangiogenic proteins such as vascular endothelial growth factor (VEGF) and metabolic adaptation through elevation of glycolytic enzymes (7, 8). Hypoxia also generates selective pressure for cells to acquire genetic alterations (e.g., TP53, K-ras) that will circumvent hypoxia-induced apoptosis (9, 10). For all these reasons, it is rational to design novel therapies targeted at the hypoxic fraction in tumors (11). Authors' Affiliations: Laboratory of Molecular Neuro-Oncology, Department of Neurosurgery, Departments of Hematology and Medical Oncology, and Pathology and Laboratory Medicine, Winship Cancer Institute, and Department of Neurology and Center for Neurodegenerative Disease, Emory University, Atlanta, Georgia; and Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, and Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California Received12/7/08; revised6/16/09; accepted 6/18/09; publishedOnlineFirst 9/29/09. Grant support: This research effort was supported in part by grants to E.G. Van Meir from the NIH (DCB APRC supplement to CA86335, CA116804), the American Brain Tumor Association, the Brain Tumor Foundation for Children, the Charlotte Geyer Foundation, EmTechBio, the Southeastern Brain Tumor Foundation, and the Emory University Research Council. Financial support was given to K.C. Nicolaou by the NIH (USA) and to C.F. Gelin through a Governor's Fellowship from the Kellogg School of Science and Technology, The Scripps Research Institute. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/). T.Narita andS.Yindesignedandcarriedoutexperiments.C.S.Morenoanalyzed microarray data,M. Yepes provided the primarymouse neuron cultures, and K.C. Nicolaou and C.F. Gelin synthesized the chemical compounds. E.G. Van Meir conceived the project, discussed the experimental design, analyzed and interpreted the results, and wrote the article with T. Narita and S. Yin. Requests for reprints: Erwin G. Van Meir, Winship Cancer Institute Molecular Pathways and Biomarkers Program, Emory University School of Medicine, 1365C Clifton Road, North East, Room C5078, Atlanta, GA 30322. Phone: 1-404-778-5563; Fax: 1-404-778-5550; E-mail: [email protected]. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-08-3180 6128 Clin Cancer Res 2009;15(19) October 1, 2009 www.aacrjournals.org Research. on April 13, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from Published OnlineFirst September 29, 2009; DOI: 10.1158/1078-0432.CCR-08-3180