Epidithiodiketopiperazines (ETPs) exhibit in vitro antiangiogenic and in vivo antitumor activity by disrupting the HIF-1α/p300 complex in a preclinical model of prostate cancer

Abstract

The downstream targets of hypoxia inducible factor-1 alpha (HIF-1α) play an important role in tumor progression and angiogenesis. Therefore, inhibition of HIF-mediated transcription has potential in the treatment of cancer. One attractive strategy for inhibiting HIF activity is the disruption of the HIF-1α/p300 complex, as p300 is a crucial coactivator of hypoxia-inducible transcription. Several members of the epidithiodiketopiperazine (ETP) family of natural products have been shown to disrupt the HIF-1α/p300 complex in vitro; namely, gliotoxin, chaetocin, and chetomin. Here, we further characterized the molecular mechanisms underlying the antiangiogenic and antitumor effects of these ETPs using a preclinical model of prostate cancer. In the rat aortic ring angiogenesis assay, gliotoxin, chaetocin, and chetomin significantly inhibited microvessel outgrowth at a GI50 of 151, 8, and 20 nM, respectively. In vitro co-immunoprecipitation studies in prostate cancer cell extracts demonstrated that these compounds disrupted the HIF-1α/p300 complex. The downstream effects of inhibiting the HIF-1α/p300 interaction were evaluated by determining HIF-1α target gene expression at the mRNA and protein levels. Dose-dependent decreases in levels of secreted VEGF were detected by ELISA in the culture media of treated cells, and the subsequent downregulation of VEGFA, LDHA, and ENO1 HIF-1α target genes were confirmed by semi-quantitative real-time PCR. Finally, treatment with ETPs in mice bearing prostate tumor xenografts resulted in significant inhibition of tumor growth. These results suggest that directly targeting the HIF-1α/p300 complex with ETPs may be an effective approach for inhibiting angiogenesis and tumor growth.

Resistance is not futile: gliotoxin biosynthesis, functionality and utility

“…Tumor cells must adapt to a hypoxic environment to survive and grow. This is mediated by hypoxia-inducible factor (HIF-1), whereby the O 2 -regulated HIF-1a subunit of the HIF-1 transcription factor is required for activation of multiple genes involved in tumor progression and angiogenesis [69]. Under hypoxic conditions, HIF-1a undergoes nuclear translocation where it interacts with HIF-1b and binds to target DNA sequences.…”

“…Indeed, Zn 2+ supplementation of ruminant diets is an effective prophylactic treatment for this disease [73]; it is tempting to speculate that this could be effected via disruption of the HIF-1a-p300 adaptive response. More recently it has been shown that gliotoxin, chaetocin, and chetomin could significantly decrease tumor growth in a prostate cancer xenograft model system [69]. Although gliotoxin exposure did not impact on the expression of HIF-1a regulated genes, these authors speculated that the antitumor activity of gliotoxin could be mediated via farnesyltransferase inhibition because inhibition of this enzyme can attenuate angiogenesis by interfering with endothelial cell migration [74].…”

Targeting protein–protein interactions (PPIs) of transcription factors: Challenges of intrinsically disordered proteins (IDPs) and regions (IDRs)

“…Several compounds have been reported to inhibit activity of HIF-1. Kwon et al, 2012; In particular, natural products such as Chetomin, (Kung et al, 2004) and other epidithioketopiperazine (ETP)-containing small molecules (Reece et al, 2014) have been reported to be potent HIF-1α:p300 inhibitors. However, the ETP motif has been shown to chelate one of the structurally important zinc atoms in p300/CBP, so this class of molecules are unlikely to be selective inhibitors.…”

Hypoxia-inducible factor–1 and associated upstream and downstream proteins in the pathophysiology and management of glioblastoma

“…In fact, studies have effectively demonstrated inhibitors of this interaction in different cancers. 116,158,187,207 In several glioma cell lines, the inhibitor arylsulfonamide interfered with HIF-1 signaling and disrupted HIF-1a interaction with the nuclear cofactors CBP/p300, inhibiting in vivo glioma growth, 247 further suggesting the potential of the HIF-1a/CBP/p300 interaction as a therapeutic target in GBM.…”