The Drosophila TEAD ortholog Scalloped is required for Yki-mediated overgrowth but is largely dispensable for normal tissue growth, suggesting that its mammalian counterpart may be exploited for ...selective inhibition of oncogenic growth driven by YAP hyperactivation. Here we test this hypothesis genetically and pharmacologically. We show that a dominant-negative TEAD molecule does not perturb normal liver growth but potently suppresses hepatomegaly/tumorigenesis resulting from YAP overexpression or Neurofibromin 2 (NF2)/Merlin inactivation. We further identify verteporfin as a small molecule that inhibits TEAD-YAP association and YAP-induced liver overgrowth. These findings provide proof of principle that inhibiting TEAD-YAP interactions is a pharmacologically viable strategy against the YAP oncoprotein.
Although the protein synthesis inhibitor cycloheximide (CHX) has been known for decades, its precise mechanism of action remains incompletely understood. The glutarimide portion of CHX is seen in a ...family of structurally related natural products including migrastatin, isomigrastatin and lactimidomycin (LTM). We found that LTM, isomigrastatin and analogs have a potent antiproliferative effect on tumor cell lines and selectively inhibit translation. A systematic comparative study of the effects of CHX and LTM on protein synthesis revealed both similarities and differences between the two inhibitors. Both LTM and CHX were found to block the translocation step in elongation. Footprinting experiments revealed protection of a single cytidine nucleotide (C3993) in the E-site of the 60S ribosomal subunit, thus defining a common binding pocket for the two inhibitors in the ribosome. These results shed new light on the molecular mechanism of inhibition of translation elongation by both CHX and LTM.
HIF-1 is a heterodimeric transcription factor that mediates adaptive responses to hypoxia and plays critical roles in cancer progression. Using a cell-based screening assay we have identified ...acriflavine as a drug that binds directly to HIF-1α and HIF-2α and inhibits HIF-1 dimerization and transcriptional activity. Pretreatment of mice bearing prostate cancer xenografts with acriflavine prevented tumor growth and treatment of mice bearing established tumors resulted in growth arrest. Acriflavine treatment inhibited intratumoral expression of angiogenic cytokines, mobilization of angiogenic cells into peripheral blood, and tumor vascularization. These results provide proof of principle that small molecules can inhibit dimerization of HIF-1 and have potent inhibitory effects on tumor growth and vascularization.
Patient‐specific induced pluripotent stem cells (iPSCs) represent a potential source for developing novel drug and cell therapies. Although increasing numbers of disease‐specific iPSCs have been ...generated, there has been limited progress in iPSC‐based drug screening/discovery for liver diseases, and the low gene‐targeting efficiency in human iPSCs warrants further improvement. Using iPSC lines from patients with alpha‐1 antitrypsin (AAT) deficiency, for which there is currently no drug or gene therapy available, we established a platform to discover new drug candidates and correct disease‐causing mutation with a high efficiency. A high‐throughput format screening assay, based on our hepatic differentiation protocol, was implemented to facilitate automated quantification of cellular AAT accumulation using a 96‐well immunofluorescence reader. To expedite the eventual application of lead compounds to patients, we conducted drug screening utilizing our established library of clinical compounds (the Johns Hopkins Drug Library) with extensive safety profiles. Through a blind large‐scale drug screening, five clinical drugs were identified to reduce AAT accumulation in diverse patient iPSC‐derived hepatocyte‐like cells. In addition, using the recently developed transcription activator‐like effector nuclease technology, we achieved high gene‐targeting efficiency in AAT‐deficiency patient iPSCs with 25%‐33% of the clones demonstrating simultaneous targeting at both diseased alleles. The hepatocyte‐like cells derived from the gene‐corrected iPSCs were functional without the mutant AAT accumulation. This highly efficient and cost‐effective targeting technology will broadly benefit both basic and translational applications. Conclusions: Our results demonstrated the feasibility of effective large‐scale drug screening using an iPSC‐based disease model and highly robust gene targeting in human iPSCs, both of which are critical for translating the iPSC technology into novel therapies for untreatable diseases. (HEPATOLOGY 2013;57:2458–2468)
The antiangiogenic agent bevacizumab has been approved for the treatment of non-small cell lung cancer (NSCLC), although the survival benefit associated with this agent is marginal, and toxicities ...and cost are substantial. A recent screen for selective inhibitors of endothelial cell proliferation identified the oral antifungal drug itraconazole as a novel agent with potential antiangiogenic activity. In this article, we define and characterize the antiangiogenic and anticancer activities of itraconazole in relevant preclinical models of angiogenesis and lung cancer. Itraconazole consistently showed potent, specific, and dose-dependent inhibition of endothelial cell proliferation, migration, and tube formation in response to both VEGF- and basic fibroblast growth factor-mediated angiogenic stimulation. In vivo, using primary xenograft models of human NSCLC, oral itraconazole showed single-agent growth-inhibitory activity associated with induction of tumor hypoxia-inducible factor 1 alpha expression and marked inhibition of tumor vascularity. Itraconazole significantly enhanced the antitumor efficacy of the chemotherapeutic agent cisplatin in the same model systems. Taken together, these data suggest that itraconazole has potent and selective inhibitory activity against multiple key aspects of tumor-associated angiogenesis in vitro and in vivo, and strongly support clinical translation of its use. Based on these observations, we have initiated a randomized phase II study comparing the efficacy of standard cytotoxic therapy with or without daily oral itraconazole in patients with recurrent metastatic NSCLC.
Triptolide (1) is a structurally unique diterpene triepoxide isolated from a traditional Chinese medicinal plant with anti-inflammatory, immunosuppressive, contraceptive and antitumor activities. Its ...molecular mechanism of action, however, has remained largely elusive to date. We report that triptolide covalently binds to human XPB (also known as ERCC3), a subunit of the transcription factor TFIIH, and inhibits its DNA-dependent ATPase activity, which leads to the inhibition of RNA polymerase II-mediated transcription and likely nucleotide excision repair. The identification of XPB as the target of triptolide accounts for the majority of the known biological activities of triptolide. These findings also suggest that triptolide can serve as a new molecular probe for studying transcription and, potentially, as a new type of anticancer agent through inhibition of the ATPase activity of XPB.
Cholesterol is an important modulator of membrane protein function and signaling in endothelial cells, thus making it an emerging target for anti-angiogenic agents. In this study, we employed a ...phenotypic screen that detects intracellular cholesterol distribution in endothelial cells (HUVEC) and identified 13 existing drugs as cholesterol trafficking inhibitors. Cepharanthine, an approved drug for anti-inflammatory and cancer management use, was amongst the candidates, which was selected for in-depth mechanistic studies to link cholesterol trafficking and angiogenesis. Cepharanthine inhibited the endolysosomal trafficking of free-cholesterol and low-density lipoprotein in HUVEC by binding to Niemann-Pick disease, type C1 (NPC1) protein and increasing the lysosomal pH. The blockade of cholesterol trafficking led to a cholesterol-dependent dissociation of mTOR from the lysosomes and inhibition of its downstream signaling. Cepharanthine inhibited angiogenesis in HUVEC and in zebrafish in a cholesterol-dependent manner. Furthermore, cepharanthine suppressed tumor growth in vivo by inhibiting angiogenesis and it enhanced the antitumor activity of the standard chemotherapy cisplatin in lung and breast cancer xenografts in mice. Altogether, these results strongly support the idea that cholesterol trafficking is a viable drug target for anti-angiogenesis and that the inhibitors identified among existing drugs, such as cepharanthine, could be potential anti-angiogenic and antitumor agents.
•A phenotypic screen identified 13 existing drugs, including cepharanthine, as cholesterol trafficking inhibitors.•Cepharanthine inhibited lysosomal cholesterol trafficking by binding to NPC1 protein and increasing the lysosomal pH.•The blockade of cholesterol trafficking led to a cholesterol-dependent dissociation of mTOR from the lysosomes.•Cepharanthine inhibited angiogenesis in HUVEC and in zebrafish in a cholesterol-dependent manner.•Cepharanthine treatment enhanced the antitumor activity of cisplatin in lung and breast cancer xenografts in mice.
Itraconazole, a clinically used antifungal drug, was found to possess potent antiangiogenic and anticancer activity that is unique among the azole antifungals. Previous mechanistic studies have shown ...that itraconazole inhibits the mechanistic target of rapamycin (mTOR) signaling pathway, which is known to be a critical regulator of endothelial cell function and angiogenesis. However, the molecular target of itraconazole that mediates this activity has remained unknown. Here we identify the major target of itraconazole in endothelial cells as the mitochondrial protein voltage-dependent anion channel 1 (VDAC1), which regulates mitochondrial metabolism by controlling the passage of ions and small metabolites through the outer mitochondrial membrane. VDAC1 knockdown profoundly inhibits mTOR activity and cell proliferation in human umbilical vein cells (HUVEC), uncovering a previously unknown connection between VDAC1 and mTOR. Inhibition of VDAC1 by itraconazole disrupts mitochondrial metabolism, leading to an increase in the cellular AMP:ATP ratio and activation of the AMP-activated protein kinase (AMPK), an upstream regulator of mTOR. VDAC1-knockout cells are resistant to AMPK activation and mTOR inhibition by itraconazole, demonstrating that VDAC1 is the mediator of this activity. In addition, another known VDAC-targeting compound, erastin, also activates AMPK and inhibits mTOR and proliferation in HUVEC. VDAC1 thus represents a novel upstream regulator ofmTOR signaling in endothelial cells and a promising target for the development of angiogenesis inhibitors.
Blockade of lysosomal calcium release due to lysosomal lipid accumulation has been shown to inhibit mTORC1 signaling. However, the mechanism by which lysosomal calcium regulates mTORC1 has remained ...undefined. Herein we report that proper lysosomal calcium release through the calcium channel TRPML1 is required for mTORC1 activation. TRPML1 depletion inhibits mTORC1 activity, while overexpression or pharmacologic activation of TRPML1 has the opposite effect. Lysosomal calcium activates mTORC1 by inducing association of calmodulin (CaM) with mTOR. Blocking the interaction between mTOR and CaM by antagonists of CaM significantly inhibits mTORC1 activity. Moreover, CaM is capable of stimulating the kinase activity of mTORC1 in a calcium-dependent manner
. These results reveal that mTOR is a new type of CaM-dependent kinase, and TRPML1, lysosomal calcium and CaM play essential regulatory roles in the mTORC1 signaling pathway.
Mammalian target of rapamycin (mTOR) constitutes a nodal point of a signaling network that regulates cell growth and proliferation in response to various environmental cues ranging from growth factor ...stimulation to nutrients to stress. Whether mTOR is also affected by cholesterol homeostasis, however, has remained unknown. We report that blockade of cholesterol trafficking through lysosome by a newly identified inhibitor of angiogenesis, itraconazole, leads to inhibition of mTOR activity in endothelial cells. Inhibition of mTOR by itraconazole but not rapamycin can be partially restored by extracellular cholesterol delivered by cyclodextrin. Moreover, other known inhibitors of endosomal/lysosomal cholesterol trafficking as well as siRNA knockdown of Niemann-Pick disease type C (NPC) 1 and NPC2 also cause inhibition of mTOR in endothelial cells. In addition, both the accumulation of cholesterol in the lysosome and inhibition of mTOR caused by itraconazole can be reversed by thapsigarin. These observations suggest that mTOR is likely to be involved in sensing membrane sterol concentrations in endothelial cells, and the cholesterol trafficking pathway is a promising target for the discovery of inhibitors of angiogenesis.
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