Abstract As solid tumors grow, regions in the tumor become hypoxic because of increased metabolism, heterogeneous and abnormal vasculature delivering oxygen within the tumor, and greater size. In order for the tumor to continue to grow, it depends on survival mechanisms to overcome this hypoxic state, including up-regulation in glycolysis, invasion and metastasis, and angiogenesis, or the growth of new blood vessels. The hypoxia-inducible factor (HIF) transcription factor complex is a major mediator of the cell's response to a hypoxic state and a tumor's survival mechanism under hypoxia. The complex is composed of the hypoxia-dependent HIF-1α subunit and a constitutively expressed HIF-1α subunit, and it requires the co-activator protein p300 to function. In the presence of oxygen, HIF-1α is rapidly degraded. Under hypoxia, HIF-1α forms a complex with HIF-1α and p300 in the nucleus to up-regulate transcription of pro-survival and angiogenic genes. Targeting this transcription factor complex in tumors could circumvent the tumor's hypoxia survival mechanism and lead to growth arrest and cell death. The compounds chetomin, chaetocin, and gliotoxin, members of the epidithiodiketopiperazine (ETP) family of fungal metabolites, have been shown to disrupt the HIF-1α/p300 interaction in an over-expression system. In the following experiments, we sought to validate the disruption of the HIF-1α /p300 transcription factor complex in cells, and to determine the associated downstream cellular effects. By co-immunoprecipitation of the complex from prostate cancer cells, we were able to show that treatment with those select ETPs under hypoxic conditions disrupted the HIF-1α/p300 complex. We performed an enzyme-linked immunosorbent assay (ELISA) to determine the effect of ETPs on levels of secreted vascular endothelial growth factor (VEGF), a major target of HIF transcription. We observed a decrease in VEGF concentration that correlated with ETP treatment under hypoxia. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to examine the transcription levels of other HIF target genes to validate that disruption of the HIF-1α/p300 complex by select ETP treatments indeed affects HIF-mediated transcription. In order to determine the antiangiogenic effects of these agents in vivo, ongoing animal studies in our lab are testing the efficacy of these ETPs in reducing tumor growth and determining feasibility of pre-clinical development. Targeting the HIF complex could circumvent a tumor's survival mechanism under hypoxia, and would be a new treatment strategy in solid tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2331. doi:1538-7445.AM2012-2331