Rohit Chugh

A Preclinical Evaluation of Minnelide as a Therapeutic Agent Against Pancreatic Cancer

Minnelide prevents tumor formation, causes tumor regression, and increases survival in multiple models of pancreatic cancer. Vegetation Is Good for You Your mom always told you to eat your vegetables, but what she probably didn’t tell you is that other plants can be good for you as well. Tripterygium wilfordii, sometimes known as the Thunder God vine, has various uses in traditional Chinese medicine. To better understand and improve upon the healing properties of this vine, the active ingredients have been isolated and characterized. One component of T. wilfordii, triptolide, has shown promising effects against pancreatic cancer cells. New therapies for pancreatic cancer—which is one of the most lethal human malignancies—are desperately needed, but triptolide is poorly soluble in water and thus has limited clinical use. Now, Chugh et al. synthesize a water-soluble form of triptolide, Minnelide, and demonstrate efficacy against pancreatic cancer in multiple animal models. The authors tested Minnelide both in vitro and in multiple preclinical models of pancreatic cancer. Each model has distinct advantages and limitations: Well-studied cancer cell lines and translationally relevant patient tumors were transplanted into mice that lack immune systems, whereas a spontaneous model in immunosufficient mice was, by necessity, a mouse tumor. By combining these approaches, the authors addressed many caveats that frequently plague preclinical studies. Indeed, Minnelide was highly effective in treating pancreatic cancer in all of these complementary models. The next step is to take Minnelide into early clinical trials to see if these results can be reproduced in human patients with pancreatic cancer. Pancreatic cancer is one of the most lethal human malignancies with an all-stage 5-year survival frequency of <5%, which highlights the urgent need for more effective therapeutic strategies. We have previously shown that triptolide, a diterpenoid, is effective against pancreatic cancer cells in vitro as well as in vivo. However, triptolide is poorly soluble in water, limiting its clinical use. We therefore synthesized a water-soluble analog of triptolide, named Minnelide. The efficacy of Minnelide was tested both in vitro and in multiple independent yet complementary in vivo models of pancreatic cancer: an orthotopic model of pancreatic cancer using human pancreatic cancer cell lines in athymic nude mice, a xenograft model where human pancreatic tumors were transplanted into severe combined immunodeficient mice, and a spontaneous pancreatic cancer mouse model (KRasG12D; Trp53R172H; Pdx-1Cre). In these multiple complementary models of pancreatic cancer, Minnelide was highly effective in reducing pancreatic tumor growth and spread, and improving survival. Together, our results suggest that Minnelide shows promise as a potent chemotherapeutic agent against pancreatic cancer, and support the evaluation of Minnelide in clinical trials against this deadly disease.

Triptolide induces cell death in pancreatic cancer cells by apoptotic and autophagic pathways

BACKGROUND & AIMS Pancreatic adenocarcinoma, among the most lethal human malignancies, is resistant to current chemotherapies. We previously showed that triptolide inhibits the growth of pancreatic cancer cells in vitro and prevents tumor growth in vivo. This study investigates the mechanism by which triptolide kills pancreatic cancer cells. METHODS Cells were treated with triptolide and viability and caspase-3 activity were measured using colorimetric assays. Annexin V, propidium iodide, and acridine orange staining were measured by flow cytometry. Immunofluorescence was used to monitor the localization of cytochrome c and Light Chain 3 (LC3) proteins. Caspase-3, Atg5, and Beclin1 levels were down-regulated by exposing cells to their respective short interfering RNA. RESULTS We show that triptolide induces apoptosis in MiaPaCa-2, Capan-1, and BxPC-3 cells and induces autophagy in S2-013, S2-VP10, and Hs766T cells. Triptolide-induced autophagy has a pro-death effect, requires autophagy-specific genes, atg5 or beclin1, and is associated with the inactivation of the Protein kinase B (Akt)/mammalian target of Rapamycin/p70S6K pathway and the up-regulation of the Extracellular Signal-Related Kinase (ERK)1/2 pathway. Inhibition of autophagy in S2-013 and S2-VP10 cells results in cell death via the apoptotic pathway whereas inhibition of both autophagy and apoptosis rescues cell death. CONCLUSIONS This study shows that triptolide kills pancreatic cancer cells by 2 different pathways. It induces caspase-dependent apoptotic death in MiaPaCa-2, Capan-1, and BxPC-3, and induces caspase-independent autophagic death in metastatic cell lines S2-013, S2-VP10, and Hs766T, thereby making it an attractive chemotherapeutic agent against a broad spectrum of pancreatic cancers.

Heat Shock Protein 70 Inhibits Apoptosis in Cancer Cells Through Simultaneous and Independent Mechanisms

BACKGROUND & AIMS Heat shock proteins (HSPs) are highly conserved and serve a multitude of functions that mediate cell survival. HSP70, the only inducible form of the 70-kilodalton subfamily of HSPs, is overexpressed in pancreatic cancer cells and has been shown to inhibit caspase-dependent apoptosis. We aimed to elucidate the mechanism by which HSP70 inhibits apoptosis in cancer cells. METHODS HSP70 expression was down-regulated in cultured pancreatic cancer cells by exposure to quercetin, triptolide, or short interfering RNAs. Intracellular Ca2+, cytosolic cathepsin B activity, caspase-3 activity, cell viability, and lysosome integrity were measured using colorimetric assays. Immunofluorescence assays were used to localize cathepsin B and Lamp2. BAPTA-AM was used to chelate intracellular Ca2+. RESULTS Inhibition of HSP70 increased intracellular Ca2+ levels in pancreatic and colon cancer cell lines and led to loss of lysosome integrity in pancreatic cancer cells. The release of intracellular Ca2+ and lysosomal enzymes activated caspase-dependent apoptosis independently and simultaneously. CONCLUSIONS HSP70 inhibits apoptosis in cancer cells by 2 mechanisms: attenuation of cytosolic calcium and stabilization of lysosomes. HSP70-mediated cell survival might occur in other types of cancer cells.

Triptolide therapy for neuroblastoma decreases cell viability in vitro and inhibits tumor growth in vivo

BACKGROUND Heat shock protein (Hsp)-70 is overexpressed in several human malignancies, and its inhibition has been shown to kill cancer cells. Our objectives were to assess the effectiveness of triptolide, an Hsp-70 inhibitor, in treating neuroblastoma in vitro and in vivo, and to measure the associated effects on Hsp-70 levels and apoptosis markers. METHODS After exposing N2a and SKNSH cell lines to triptolide, cell viability was assessed. Caspase-3 and -9 activities were measured and annexin staining performed to determine if cell death occurred via apoptosis. Hsp-70 protein and mRNA levels were determined using Western blot and real-time polymerase chain reaction. In an orthotopic tumor model, mice received daily triptolide injections and were humanely killed at study completion with tumor measurement. RESULTS Triptolide treatment resulted in dose- and time-dependent N2a cell death and dose-dependent SKNSH killing. Triptolide exposure was associated with dose-dependent increases in caspase activity and annexin staining. Triptolide decreased Hsp-70 protein and mRNA levels in a dose-dependent fashion. Mice receiving triptolide therapy had significantly smaller tumors than controls. CONCLUSION Triptolide therapy decreased neuroblastoma cell viability in vitro and inhibited tumor growth in vivo. Our studies suggest that triptolide killed cells via apoptosis and in association with inhibition of Hsp-70 expression. Triptolide may provide a novel therapy for neuroblastoma.

Triptolide-induced Cell Death in Pancreatic Cancer Is Mediated by O-GlcNAc Modification of Transcription Factor Sp1

Background: Preclinical evaluation of triptolide shows pancreatic tumor regression in animal models. Results: Triptolide deregulates glycosylation of Sp1, leading to its decreased activity and causing pancreatic cancer cell death associated with down-regulating HSP70. Conclusion: Triptolide down-regulation of HSP70 is associated with inhibition of Sp1 activity in pancreatic cancer. Significance: This mechanism is of relevance, as its water-soluble prodrug, Minnelide, is currently under Phase 1 clinical trial. Pancreatic cancer, the fourth most prevalent cancer-related cause of death in the United States, is a disease with a dismal survival rate of 5% 5 years after diagnosis. One of the survival proteins responsible for its extraordinary ability to evade cell death is HSP70. A naturally derived compound, triptolide, and its water-soluble prodrug, Minnelide, down-regulate the expression of this protein in pancreatic cancer cells, thereby causing cell death. However, the mechanism of action of triptolide has not been elucidated. Our study shows that triptolide-induced down-regulation of HSP70 expression is associated with a decrease in glycosylation of the transcription factor Sp1. We further show that triptolide inhibits glycosylation of Sp1, inhibiting the hexosamine biosynthesis pathway, particularly the enzyme O-GlcNAc transferase. Inhibition of O-GlcNAc transferase prevents nuclear localization of Sp1 and affects its DNA binding activity. This in turn down-regulates prosurvival pathways like NF-κB, leading to inhibition of HSF1 and HSP70 and eventually to cell death. In this study, we evaluated the mechanism by which triptolide affects glycosylation of Sp1, which in turn affects downstream pathways controlling survival of pancreatic cancer cells.

Prosurvival role of heat shock factor 1 in the pathogenesis of pancreatobiliary tumors

Several mechanisms have evolved to ensure the survival of cells under adverse conditions. The heat shock response is one such evolutionarily conserved survival mechanism. Heat shock factor-1 (HSF1) is a transcriptional regulator of the heat shock response. By the very nature of its prosurvival function, HSF1 may contribute to the pathogenesis of cancer. The current study investigates the role of HSF1 in the pathogenesis of pancreatobiliary tumors. HSF1 was downregulated in pancreatic cancer (MIA PaCa-2 and S2-013) and cholangiocarcinoma (KMBC and KMCH) cell lines by HSF1-specific small interfering RNA (siRNA). Nonsilencing siRNA was used as control. The effect of HSF1 downregulation on viability and apoptosis parameters, i.e., annexin V, terminal deoxynucleotidyl transferase dUTP-mediated nick end labeling (TUNEL), and caspase-3, was measured. To evaluate the cancer-specific effects of HSF1, the effect of HSF1 downregulation on normal human pancreatic ductal cells was also evaluated. HSF1 is abundantly expressed in human pancreatobiliary cancer cell lines, as well as in pancreatic cancer tissue, as demonstrated by Western blot and immunohistochemistry, respectively. Inhibition of HSF1 expression by the HSF1 siRNA sequences leads to time-dependent death in pancreatic and cholangiocarcinoma cell lines. Downregulation of HSF1 expression induces annexin V and TUNEL positivity and caspase-3 activation, suggesting activation of a caspase-dependent apoptotic pathway. Although caspase-3 inhibition protects against cell death induced by HSF1 expression, it does not completely prevent it, suggesting a role for caspase-independent cell death. HSF1 plays a prosurvival role in the pathogenesis of pancreatobiliary tumors. Modulation of HSF1 activity could therefore emerge as a novel therapeutic strategy for cancer treatment.

Sorafenib and triptolide as combination therapy for hepatocellular carcinoma

INTRODUCTION Sorafenib is the only drug approved by the Food and Drug Administration for metastatic hepatocellular carcinoma (HCC). Triptolide, a diterpene triepoxide, exhibits antineoplastic properties in multiple tumor cell types. In this study, we examined the effects of these agents and their combination on HCC in vitro and in vivo models. METHODS HuH-7 and PLC/PRF/5 cells were treated with triptolide (50 nM), sorafenib (1.25 or 2.5 μM), or a combination of both. Cell viability assay (CCK-8), caspase 3&7 activation, and nuclear factor κB assays were performed. For in vivo studies, 40 mice were implanted with subcutaneous HuH7 tumors and divided into four treatment groups (n = 10); saline control, sorafenib 10 mg/kg PO daily (S), Minnelide (a prodrug of triptolide) 0.21 mg/kg intraperitoneally7 daily (M), and combination of both (C). Tumor volumes were assessed weekly. RESULTS The combination of triptolide and sorafenib was superior to either drug alone in inducing apoptosis and decreasing viability, whereas triptolide alone was sufficient to decrease nuclear factor κB activity. After 2 weeks of treatment, tumor growth inhibition rates were S = 59%, M = 84%, and C = 93%, whereas tumor volumes in control animals increased by 9-fold. When crossed over to combination treatment, control mice tumor growth volumes plateaued over the following 4 weeks. CONCLUSION The combination of sorafenib and triptolide is superior to single drug treatment in increasing cell death and apoptosis in vitro. Combining sorafenib with Minnelide inhibited tumor growth with greater efficacy than single-agent treatments. Importantly, in vivo combination treatment allowed for using a lesser dose of sorafenib (10 mg/kg), which is less than 10% of currently prescribed dose for HCC patients. Therefore, combination treatment could have translational potential in the management of HCC.

Triptolide sensitizes pancreatic cancer cells to TRAIL-induced activation of the Death Receptor pathway

The tumor necrosis factor related apoptosis-inducing ligand (TRAIL) causes cancer cell death, but many cancers, including pancreatic cancer, are resistant to TRAIL therapy. A combination of TRAIL and the diterpene triepoxide, triptolide, is effective in inducing pancreatic cancer cell death. Triptolide increases levels of death receptor DR5 and decreases the pro-survival FLICE-like inhibitory protein (c-FLIP), which contribute to the activation of caspase-8. This combination further causes both lysosomal and mitochondrial membrane permeabilization, resulting in cell death. Our study provides a mechanism by which triptolide sensitizes TRAIL resistant cells, which may become a novel therapeutic strategy against pancreatic cancer.

TRAIL and Triptolide: An Effective Combination that Induces Apoptosis in Pancreatic Cancer Cells

IntroductionAn emerging therapy in oncology is the induction of apoptotic cell death through anti-death receptor therapy. However, pancreatic cancer is resistant to apoptosis including anti-death receptor therapy. We have previously described how triptolide decreases resistance to apoptosis in pancreatic cancer cells in vitro and in vivo. We hypothesized that triptolide decreases tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resistance in pancreatic cancer cells. The aim of this study was to evaluate the effects that combined therapy with TRAIL and triptolide have on different parameters of apoptosis.MethodsFour different pancreatic cancer cell lines were exposed to triptolide, TRAIL, or a combination of both drugs. We assessed the effects that combined therapy with TRAIL and triptolide has on cell viability, apoptosis, caspase-3 and caspase-9 activities, and poly(ADP)-ribose polymerase cleavage.ResultsPancreatic cancer cells were resistant to TRAIL therapy; however, combined therapy with triptolide and TRAIL significantly decreased the cell viability in all the cell lines and increased apoptotic cell death as a result of caspase-3 and caspase-9 activation.ConclusionsPancreatic cancer is highly resistant to anti-death receptor therapy, but combined therapy with TRAIL and triptolide is an effective therapy that induces apoptotic cell death in pancreatic cancer cells.

Triptolide activates unfolded protein response leading to chronic ER stress in pancreatic cancer cells

Pancreatic cancer is a devastating disease with a survival rate of <5%. Moreover, pancreatic cancer aggressiveness is closely related to high levels of prosurvival mediators, which can ultimately lead to rapid disease progression. One of the mechanisms that enables tumor cells to evade cellular stress and promote unhindered proliferation is the endoplasmic reticulum (ER) stress response. Disturbances in the normal functions of the ER lead to an evolutionarily conserved cell stress response, the unfolded protein response (UPR). The UPR initially compensates for damage, but it eventually triggers cell death if ER dysfunction is severe or prolonged. Triptolide, a diterpene triepoxide, has been shown to be an effective compound against pancreatic cancer. Our results show that triptolide induces the UPR by activating the PKR-like ER kinase-eukaryotic initiation factor 2α axis and the inositol-requiring enzyme 1α-X-box-binding protein 1 axis of the UPR and leads to chronic ER stress in pancreatic cancer. Our results further show that glucose-regulated protein 78 (GRP78), one of the major regulators of ER stress, is downregulated by triptolide, leading to cell death by apoptosis in MIA PaCa-2 cells and autophagy in S2-VP10 cells.