Antihepatoma activity of chaetocin due to deregulated splicing of hypoxia-inducible factor 1α pre-mRNA in mice and in vitro

Abstract

Chaetocin, an antibiotic produced by Chaetomium species fungi, was recently found to have antimyeloma activity. Here we examined whether chaetocin has anticancer activities against solid tumors. Chaetocin inhibited the growth of mouse and human hepatoma grafts in nude mice. Immunohistochemical analyses revealed that chaetocin inhibits hypoxia-inducible factor-1a (HIF-1a) expression and vessel formation in the tumors. Chaetocin also showed antiangiogenic anticancer activities in HIF-1a(1/1) fibrosarcoma grafted in mice, but not in HIF-1a(2/2) fibrosarcoma. Biochemical analyses showed that chaetocin down-regulated HIF-1a and the transcripts of HIF-1 target genes including vascular endothelial growth factor in hepatoma tissues and in various hepatoma cell lines. Based on the reported literature, unsuccessful efforts were made to determine the mechanism underlying the action of chaetocin. Unexpectedly, chaetocin was found to cause the accumulation of HIF-1a premessenger RNA (pre-mRNA) but to reduce mature mRNA levels in hepatoma cells and tissues. Such an effect of chaetocin was not observed in cell lines derived from normal cells, and was cell type-dependent even among cancer cell lines. Conclusions: Our results suggest that chaetocin could be developed as an anticancer agent to target HIF-1 in some cancers including hepatoma. It is also suggested that the HIF-1a premRNA splicing is a novel therapeutic target for controlling HIF-1-mediated pathological processes. (HEPATOLOGY 2011;53:171-180) H epatocellular carcinoma (also called malignant hepatoma) is one of the most common malignant tumors and the third leading cause of cancer mortality worldwide.1 Despite many efforts to develop various classes of agents, systemic chemotherapy and hormone therapy have failed to significantly increase the survival of patients with advanced hepatoma. However, recent advances in the understanding of hepatoma progression have led to the development of novel molecularly targeted therapies.2 Because angiogenesis is pivotal for the development and progression of hepatoma, key molecules regulating angiogenesis are regarded as promising targets for treating hepatoma. Hypoxia inevitably develops in rapidly growing tumors and is an important microenvironment that forces changes in tumor behavior. In particular, hypoxia activates hypoxia-inducible factor-1a (HIF-1a), which promotes the progression of malignancy by stimulating angiogenesis and by augmenting the ability of tumors to survive. 4,5 The roles of HIF-1a have been extensively investigated in cancer patients and in tumor-bearing mice. 6,7 Consequently, HIF-1a is believed to be a valid target for the treatment of aggressive tumors, and many efforts have been made to identify suitable HIF-1a inhibitors. 8 Chaetocin, which is produced by Chaetomium sp., is an antibiotic having the thiodioxopiperazine structure (a disulfide-bridged piperazine).9 Other thiodioxopiperazines are known to have antimicrobial, antiviral, Abbreviations: ATP, adenosine triphosphate; CA9, carbonic anhydrase 9...

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

“…Thus, the observed decrease in the amount of HIF-1α in the p300 immunoprecipitates upon treatment with gliotoxin and chetomin demonstrates their ability to disrupt the interaction between HIF-1α and p300 in cells. In accordance with a previous study [26], chaetocin treatment inhibited HIF-1α expression in a dose-dependent manner (data not shown); thus, co-immunoprecipitations could not be performed from chaetocin-treated cells.…”

“…A similar effect was seen in a study by Lee et al . [26], which demonstrated that the hypoxic induction of HIF-1α was attenuated by chaetocin in human hepatoma cell lines. The authors later concluded that the antiangiogenic and anticancer effects of chaetocin against hepatoma were via deregulation of HIF-1α premessenger RNA splicing.…”

Cytotoxic Dimeric Epipolythiodiketopiperazines from the Ascomycetous Fungus Preussia typharum

“…3−15 Some of the ETPs were also found to inhibit the growth of tumor xenografts in mice. 4−7,10,12 One of the most widely studied ETPs, chaetocin, has displayed a wide spectrum of in vivo antitumor activities against SK-OV-3 human ovarian cancer, 4 U937 human leukemia, 5 RPMI 8226 human myeloma, 6 and mouse and human hepatomas. 10 These observations suggest the ETPs may have utility as lead molecules for drug development and/or molecular tools.…”

“…4−7,10,12 One of the most widely studied ETPs, chaetocin, has displayed a wide spectrum of in vivo antitumor activities against SK-OV-3 human ovarian cancer, 4 U937 human leukemia, 5 RPMI 8226 human myeloma, 6 and mouse and human hepatomas. 10 These observations suggest the ETPs may have utility as lead molecules for drug development and/or molecular tools. In this report, we describe the isolation, structural determination, absolute configuration assignments, and conformational analyses of two new ETPs, preussiadins A ( 1 ) and B ( 2 ), together with two known diastereomers, leptosins C ( 6 ) and A ( 7 ), from Preussia typharum .…”

FBXO11 represses cellular response to hypoxia by destabilizing hypoxia-inducible factor-1α mRNA

“…These results implied that FBXO11 may regulate HIF-1α transcription or mRNA stability. To check the newly synthesized HIF-1α mRNA, specific primers for the pre-mRNAs including those from exon 3 or exon 4 were used for RT-qPCR [13]. The amounts of pre-mRNAs of HIF-1α were not changed by FBXO11 knock-down (Fig.…”