Cantharidin, a potent and selective PP2A inhibitor, induces an oxidative stress-independent growth inhibition of pancreatic cancer cells through G2/M cell-cycle arrest and apoptosis

Protein phosphatase 2A as therapeutic targets in various disease models

There are a large number of signalling pathways responsible for transmitting information within the cell. Although cellular signalling is thought to be majorly governed by protein kinases 'cascade effects'; their antagonists protein phosphatases also play a crucial dual role in signal transduction. By dephosphorylating the proteins involved in signalling pathways, phosphatases may lead to their activation and sometimes they may terminate a signal generated by kinases activity. Due to counterbalancing the function of phosphorylation, the protein phosphatases are very important to signal transduction processes and thus the control of phosphatase activity is as significant as kinases, in the regulation of a plethora of cellular processes. In general, the protein phosphatases are comprised of a catalytic subunit with one or more regulatory and/or targeting subunits associated with it. The Protein Phosphatase 2A (PP2A), a member of serine/threonine phosphatases family, is ubiquitously expressed a remarkably conserved enzyme in the cell. Its catalytic activity has been highly regulated and may have enormous therapeutic potential which is still untapped. It has specificities for a number of substrates which witnessed its involvement in various signalling modules of cell cycle regulation, cell morphology and development. Thus it can be an appropriate target for studying different diseases associated with abnormal signal transduction pathways such as neurodegenerative diseases and malignancies. This review will focus on the structure and regulatory pathways of PP2A. The de-regulation of PP2A in some specific pathology such as Cancer, Heart diseases, Neurodegenerative disorders and Diabetes will also be touched upon.

Cantharides poisoning: A retrospective analysis from 1996 to 2016 in China

Cantharides poisoning may cause serious adverse reactions or even death.We attempt to retrieval articles automatically and manually with the key words of "cantharides" and " poisoning " or " side effects ", then summarized and analyzed the cases of cantharides poisoning from 1996 to 2016 in China, to provide some reference for clinical drug use and forensic identification. Finally, 91 cases were conformance to require; general data, clinical data, prognosis, autopsy results were analyzed.We found that the health education of cantharides in primary doctors and people is lackable, the case fatality rate was 18.68% . The death patients of cantharides poisoning had cardiomyocyte necrosis and neuronal apoptosis in the histopathological examination of autopsy , but the toxicological mechanism was unclear. There may be redistribution of cantharidin in vivo after death. Collectively, we hope that an anthropological database for cantharides poisoning established by multicenter cooperation, include medical institutions and forensic identified centers, and conduct more further studies on its cardiotoxicity and neurotoxicity.

Cantharidin-encapsulated thermal-sensitive liposomes coated with gold nanoparticles for enhanced photothermal therapy on A431 cells

Purpose

Plasmonic nanostructure-mediated photothermal therapy (PTT) is a promising alternative therapy for the treatment of skin cancer and other diseases. However, the insufficient efficiency of PTT at irradiation levels tolerable to tissues and the limited biodegradability of nanomaterials are still crucial challenges. In this study, a novel nanosystem for PTT based on liposome–nanoparticle assemblies (LNAs) was established.

Materials and methods

Thermal-sensitive liposomes (TSLs) encapsulating cantharidin (CTD) were coated with gold nanoparticles (GNPs) and used in near-infrared (NIR) illumination-triggered PTT and thermally induced disruption on A431 cells.

Results

The coated GNPs disintegrated into small particles of 5–6 nm after disruption of TSLs, allowing their clearance by the liver and kidneys. CTD encapsulated in the TSLs was released into cytoplasm after PTT. The released CTD increased the apoptosis of PTT-treated tumor cells by blocking the heat shock response (HSR) and inhibiting the expression of HSP70 and BAG3 inhibiting the expression of HSP70 and BAG3 with the synergistic enhancement of CTD, the new nanosystem CTD-encapsulated TSLs coated with GNPs (CTD-TSL@GNPs) had an efficient PTT effect using clinically acceptable irradiation power (200 mW//cm²) on A431 cells.

Conclusion

The developed CTD-TSL@GNPs may be a promising PTT agent for clinical skin cancer therapy.

Role of cantharidin in the activation of IKKα/IκBα/NF‑κB pathway by inhibiting PP2A activity in cholangiocarcinoma cell lines

Cantharidin (CAN), a potent inhibitor of serine/threonine‑protein phosphatase 2A (PP2A), is widely used in clinical practice, particularly in the treatment of advanced cancer due to its specific action on these types of cancer. In the present study, the inhibitory effect of CAN was examined in two cholangiocarcinoma cell lines (QBC939 and Hucc‑t1). Following treatment with CAN, cell viability was effectively reduced in QBC939 and Hucc‑t1 cells and normal human intrahepatic biliary epithelial cells. However, a slight increase in reactive oxygen species levels in QBC939 cells treated with CAN was observed post‑treatment. CAN significantly inhibited cell migration and invasion in a dose‑dependent manner. Western blot analysis demonstrated that the nuclear factor‑κB (NF‑κB) pathway was stimulated by CAN, which was confirmed by the upregulated phosphorylation levels of inhibitor of NF‑κB kinase subunit α (IKKα) and NF‑κB inhibitor α (IκBα) in cells, and an increased NF‑κB p65 subunit level in the nucleus. The expression levels of 72 kDa type IV collagenase (MMP2) and matrix metalloproteinase 9 (MMP9) were downregulated by CAN. Notably, there was a negative association between MMP2 and MMP9 expression levels, and NF‑κB p65, although NF‑κB p65 regulates the expression of MMP2 and MMP9 and has a positive association with these proteins in various types of cancer. Notably, it was observed that CAN exerted specific inhibition on PP2A activity and thereby resulted in the activation of the IKKα/IκBα/NF‑κB pathway. Therefore, CAN‑induced cell inhibition maybe partially dependent on the activation of the IKKα/IκBα/NF‑κB pathway. In conclusion, it was demonstrated that CAN selectively and effectively inhibited cholangiocarcinoma cell migration and invasion. The present study may provide a novel insight into the use of CAN as a therapeutic candidate in the treatment of cholangiocarcinoma.

Cantharidic acid induces apoptosis of human leukemic HL-60 cells via c-Jun N-terminal kinase-regulated caspase-8/-9/-3 activation pathway

Cantharidin, a natural toxin from blister beetles, has shown potent anticancer activities on many solid tumor cells. Recently, cantharidin and its analogue, norcantharidin, were also shown to suppress nonsolid tumors such as chronic myeloid leukemia, acute myeloid leukemia (AML), and leukemic stem cells. However, there is no available information to address the effects of cantharidic acid (CAC), a hydrolysis product of cantharidin, on human AML cells. The present study showed that CAC, at a range of concentrations (0-20 μM), concentration-dependently inhibited cell proliferation in the HL-60 AML cell line. Western blot and flow cytometric assays demonstrated that CAC induced several features of apoptosis such as sub G1-phase cell increase, phosphatidylserine (PS) externalization, and significantly activated proapoptotic signaling including caspase-8, -9, and -3 activation and poly(ADP-ribose) polymerase (PARP) cleavage in HL-60 AML cells. Moreover, treatment of HL-60 cells with CAC induced concentration- and time- dependent activation of p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK). Only JNK-, but not p38 MAPK-specific inhibitor can reverse the CAC-induced activation of the caspase-8, -9, and -3. We concluded that CAC can induce apoptosis in human leukemic HL-60 cells via a caspases-dependent pathway, and that the apoptosis-inducing effect of CAC can be regulated by JNK activation signaling.

PPP2R2D, a regulatory subunit of protein phosphatase 2A, promotes gastric cancer growth and metastasis via mechanistic target of rapamycin activation

Protein phosphatase 2A (PP2A) is an essential serine/threonine protein phosphatase that regulates the basic activities of eukaryotes by dephosphorylating its substrates. The function and substrate specificity of PP2A are generally determined by its regulatory subunits. In the present study, the clinical significance and roles of PPP2R2D, one of the regulatory subunits of PP2A, were demonstrated in gastric cancer (GC) carcinogenesis. Through a tissue microarray and quantitative polymerase chain reaction analysis, it was demonstrated that PPP2R2D was commonly upregulated in GC samples. This upregulation was positively correlated with the patients' tumor stage (P<0.01), T classification (P<0.01) and N classification (P=0.01). Furthermore, a high expression of PPP2R2D was closely associated with poor prognosis of patients. Knockdown of PPP2R2D significantly inhibited the proliferation and migration of GC cells in vitro, as well as the tumorigenicity and metastasis in vivo in an animal GC model. By contrast, overexpression of PPP2R2D promoted GC cell proliferation and migration in vitro. The analysis of underlying mechanisms indicated that PPP2R2D silencing decreased the phosphorylation level of mechanistic target of rapamycin (mTOR), thereby implicating that PPP2R2D is involved in the regulation of mTOR activity during tumorigenesis. Thus, the findings of the present study suggested that PPP2R2D may serve as a potential oncogene in GC and as a novel target for therapeutic strategies against this disease.

Cantharidin suppresses cell growth and migration, and activates autophagy in human non-small cell lung cancer cells

Cantharidin (CTD), a component of Mylabris (blister beetle), is a traditional Chinese medicine that exerts an anticancer effect in multiple types of cancer cells. The aim of the present study was to investigate whether CTD exhibited anti-metastatic and inhibitory cell proliferation effects against human non-small cell lung cancer (NSCLC) A549 cells, and the possible underlying mechanism by which this occurs. The results of the present study demonstrated that CTD arrested proliferation, suppressed invasion and migration and induced apoptosis in A549 cells in vitro. Alterations of apoptosis-associated protein levels, including B-cell lymphoma-2 (Bcl-2), Bcl-associated X (Bax) and active caspase-3, were detected. Furthermore, the present study demonstrated that CTD activated autophagy through downregulation of p62 expression and upregulation of microtubule-associated proteins 1A/1B light chain 3B and Beclin-1 expression. Additionally, western blot analysis identified that CTD inhibited the phosphatidylinositol 3-kinase (PI3K)/RAC serine/threonine protein kinase (Akt)/mechanistic target of rapamycin (mTOR) signaling pathway in NSCLC, demonstrating that the levels of phosphorylated (p-)Akt, p-mTOR, phosphorylated ribosomal p70S6 protein kinase (p-p70-S6K) and cyclin D1 were significantly decreased following treatment with CTD. In conclusion, the results of the present study indicated that CTD impeded cell growth and migration by inhibiting PI3K/Akt/mTOR signaling in NSCLC, and promoted autophagy and apoptosis. CTD exhibited anticancer activity against NSCLC in vitro, revealing it as a potential candidate for the treatment of NSCLC.

Effects of disodium cantharidinate on dendritic cells of patients with bladder carcinoma

The present study explored the effects of disodium cantharidinate (DC) on the peripheral blood-derived dendritic cells of patients with bladder carcinoma. The peripheral blood mononuclear cells from the 15 cases of urinary bladder carcinoma of middle and advanced stage were separated, and dendritic cells were prepared. The morphological changes of dendritic cells were observed. Flow cytometry was used to detect the expression levels of CD1a and CD83 on dendritic cell surface. MTT assay was utilized to measure the proliferation ability of allogeneic lymphocyte stimulated by DC. Annexin V-FITC/propidium iodide (PI) double staining flow cytometry method was carried out to detect cell apoptosis after treatment with DC. The changes in caspase-3 and PARP expression levels were investigated by western blot method. The high-dose DC resulted in a significant increase in the expressions of dendritic cell phenotyptic molecules CDla and CD83 as compared to control group. In addition, the proliferation index of allogenic lymphocyte stimulated by DC was significantly higher than that of control group. Moreover, MTT assay showed significant inhibition of the growth of BIU-87 cells. After 24 h of DC treatment, double staining flow cytometry confirmed the ability of DC to induce cell apoptosis. Further, western blot method showed a significant elevation of caspase-3 and PARP protein expression after DC treatment. In conclusion, DC treatment could induce dendritic cell maturation of patient with carcinoma of urinary bladder and promote its functional changes. Furthermore, DC was able to inhibit the proliferation of cell BIU-87 and also has the ability to induce cell apoptosis.

Seeing the unseen of Chinese herbal medicine processing (Paozhi): advances in new perspectives

Processing (Paozhi) represents a unique Chinese pharmaceutic technique to facilitate the use of Chinese herbal medicines (CHMs) for a specific clinical need in the guidance of Traditional Chinese Medicine (TCM) theory. Traditionally, most CHMs require a proper processing to meet the needs of specific clinical syndromes before being prescribed by TCM practitioners. During processing, significant changes in chemical profiles occur, which inevitably influence the associated pharmacological properties of a CHM. However, although processing is formed in a long-term practice, the underlying mechanisms remain unclear for most CHMs. The deepening understanding of the mechanism of processing would provide scientific basis for standardization of processing. This review introduced the role of processing in TCM and several typical methods of processing. We also summarized the up-to-date efforts on the mechanistic study of CHM processing. The processing mechanisms mainly include the following aspects: (i) directly reducing contents of toxic constituents; (ii) structural transformation of constituents; (iii) improving solubility of constituents; (iv) physically changing the existing form of constituents; (v) and influence by excipients. These progress may give new insights into future researches.

Omics-Based Platform for Studying Chemical Toxicity Using Stem Cells

The new strategy for chemical toxicity testing and modeling is to use in vitro human cell-based assays in conjunction with quantitative high-throughput screening (qHTS) technology, to identify molecular mechanisms and predict in vivo responses. Stem cells are more physiologically relevant than immortalized cell lines because of their unique proliferation and differentiation potentials. We established a robust two stem cells-two lineages assay system, encompassing human mesenchymal stem cells (hMSCs) along osteogenesis and human induced pluripotent stem cells (hiPSCs) along hepatogenesis. We performed qHTS phenotypic screening of LOPAC1280 and identified 38 preliminary hits for hMSCs. This was followed by validation of a selected number of hits and determination of their IC50 values and mechanistic studies of idarubicin and cantharidin treatments using proteomics and bioinformatics. In general, hiPSCs were more sensitive than hMSCs to chemicals, and differentiated progenies were less sensitive than their progenitors. We showed that chemical toxicity depends on both stem cell types and their differentiation stages. Proteomics identified and quantified over 3000 proteins for both stem cells. Bioinformatics identified apoptosis and G2/M as the top pathways conferring idarubicin toxicity. Our Omics-based assays of stem cells provide mechanistic insights into chemical toxicity and may help prioritize chemicals for in-depth toxicological evaluations.

Ginsenoside Rg3 targets cancer stem cells and tumor angiogenesis to inhibit colorectal cancer progression in vivo

Anti-angiogenic therapy has been successfully applied to treat colorectal cancer (CRC). Ginsenoside Rg3, derived from the Chinese herb ginseng, has anti-vascularization effects and can inhibit tumor growth and metastasis, and can sensitize cancer cells to chemotherapy. Therefore, in the present study, we investigated whether Rg3 could be appropriate for CRC treatment. Growth of CRC cells was assessed by an MTT (methyl thiazolyl tetrazolium) assay in vitro and using orthotopic xenograft models in vivo. mRNA expression was evaluated using real-time PCR. Protein levels were tested by western blotting, flow cytometry and immunohistochemistry. Migration was determined using a wound-healing assay. Stemness was further confirmed using a plate clone formation assay. We found that Rg3 repressed the growth and stemness of CRC cells both in vitro and in vivo. Rg3 also impaired the migration of CRC cells in vitro. Rg3 downregulated the expressions of angiogenesis-related genes, and repressed the vascularization of CRC xenografts. In addition, Rg3 strengthened the cytotoxicity of 5-Fluorouracil and oxaliplatin against orthotopic xenografts in vivo. Moreover, Rg3 downregulated the expressions of B7-H1 and B7-H3, high expressions of which were associated with reduced overall survival (OS) of CRC patients. Hence, Rg3 not only repressed the growth and stemness of CRC cells, but could also remodel the tumor microenvironment through repressing angiogenesis and promoting antitumor immunity. Therefore, Rg3 could be a novel therapeutic for the CRC treatment.

Defining Genome-Wide Expression and Phenotypic Contextual Cues in Macrophages Generated by Granulocyte/Macrophage Colony-Stimulating Factor, Macrophage Colony-Stimulating Factor, and Heat-Killed Mycobacteria

Heat-killed (HK) Mycobacterium obuense (NCTC13365) is currently being evaluated in the clinic as an immunotherapeutic agent for cancer treatment. Yet, the molecular underpinnings underlying immunomodulatory properties of HK M. obuense are still largely undefined. To fill this void, we sought to perform immunophenotyping, chemokine/cytokine release analysis and genome-wide characterization of monocyte-derived macrophages (MDM) in which monocytes were originally isolated from healthy donors and differentiated by HK M. obuense (Mob-MDM) relative to macrophage colony-stimulating factor (M-MDM) and granulocyte/macrophage colony-stimulating factor (GM-MDM). Immunophenotyping and cytokine release analysis revealed downregulated surface expression of CD36, decreased spontaneous release of CCL2 and increased spontaneous secretion of CCL5, CXCL8/IL-8, IL-6, and TNF-α in Mob-MDM relative to M-MDM and GM-MDM. Analysis of cytostatic activity showed that Mob-MDM exhibited similar growth inhibitory effects on immortalized and malignant epithelial cells compared with GM-MDM but at an elevated rate relative to M-MDM. To understand global cues in Mob-MDM, we performed comparative RNA-sequencing (RNA-Seq) analysis of Mob-MDM relative to GM-MDM and M-MDM (n = 4 donors). Clustering analysis underscored expression profiles (n = 256) that were significantly modulated in Mob-MDM versus both M-MDM and GM-MDM including, among others, chemokines/cytokines and their receptors, enzymes and transcriptions factors. Topological functional analysis of these profiles identified pathways and gene sets linked to Mob-MDM phenotype including nitric oxide production, acute phase response signaling and microbe recognition pathways as well as signaling cues mediated by the proinflammatory cytokine, interferon-gamma, and the intracellular pattern recognition receptor, nucleotide-binding oligomerization domain-containing protein 2. Taken together, our study highlights molecular immune phenotypes and global signaling cues in Mob-MDM that may underlie immunomodulatory properties of HK M. obuense. Such properties could be of valuable use in immunotherapy approaches such as adoptive cell therapy against cancer.

Attribution of Bax and mitochondrial permeability transition pore on cantharidin-induced apoptosis of Sf9 cells

To investigate the insecticidal mechanism of cantharidin, a promising biological pesticide substance from blister beetle, on Sf9 cells, a cultured cell line derived from fall armyworm, Spodoptera frugiperda, we preliminary studied the attribution of Bax channel and mitochondrial permeability transition pore on cantharidin-induced mitochondrial apoptosis signal pathway. Changes in cell morphology, activity of mitochondrial dehydrogenases, release of cytochrome C and mitochondrial transmembrane potential were detected when the two channels were blocked by specific inhibitors, Bax channel blocker and cyclosporin A. Results showed that cantharidin-induced apoptotic features, including changes in the cell morphology, release of cytochrome C and decrease in mitochondrial transmembrane potential could be significantly inhibited by Bax channel blocker, while cyclosporin A accelerated the downward trend of mitochondrial dehydrogenases activity and caused a decrease of Ca²⁺ in mitochondria. In summary, Bax might be necessary but not exclusively for the apoptosis induced by cantharidin and the attribution of these channels seems to be more complexity.

Cantharidin suppressed breast cancer MDA-MB-231 cell growth and migration by inhibiting MAPK signaling pathway

As an active constituent of the beetle Mylabris used in traditional Chinese medicine, cantharidin is a potent and selective inhibitor of protein phosphatase 2A (PP2A) that plays a crucial role in cell cycle progression, apoptosis, and cell fate. The role and possible mechanisms exerted by cantharidin in cell growth and metastasis of breast cancer were investigated in this study. Cantharidin was found to inhibit cell viability and clonogenic potential in a time- and dose-dependent manner. Cell cycle analysis revealed that cell percentage in G2/M phase decreased, whereas cells in S and G1 phases progressively accumulated with the increasing doses of cantharidin treatment. In a xenograft model of breast cancer, cantharidin inhibited tumor growth in a dose-dependent manner. Moreover, high doses of cantharidin treatment inhibited cell migration in wound and healing assay and downregulated protein levels of major matrix metalloproteinases (MMP)-2 and MMP-9. MDA-MB-231 cell migration and invasion were dose-dependently inhibited by cantharidin treatment. Interestingly, the members of the mitogen-activated protein kinase (MAPK) signaling family were less phosphorylated as the cantharidin dose increased. Cantharidin was hypothesized to exert its anticancer effect through the MAPK signaling pathway. The data of this study also highlighted the possibility of using PP2A as a therapeutic target for breast cancer treatment.

Roles of p38 and JNK protein kinase pathways activated by compound cantharidin capsules containing serum on proliferation inhibition and apoptosis of human gastric cancer cell line

The aim of the present study was to investigate the inhibitory effect of compound cantharides capsules (CCCs) on the viability and apoptosis of human gastric cancer cell lines, BGC-823 and SGC-7901, and to detect its regulation of gene expression levels, as well as its inhibition mechanisms. Each cell line was grouped into a control group, CCC serum group, 5-fluorouracil (5-FU) group, combination therapy group (CCC serum + 5-FU) and serum control group. Growth curves were measured and flow cytometry was used to detect cell apoptosis and cell viability. The mRNA expression level of proliferation-related C-MYC and p53 genes were assayed by reverse transcription-quantitative polymerase chain reaction. Protein phosphorylation levels of proliferating cell nuclear antigen, p38 mitogen-activated protein kinase, extracellular signal-related kinase 1/2, c-Jun N-terminal kinase (JNK) and IκB were assayed by western blotting. The combined CCC serum and 5-FU group exhibited a higher inhibition rate in both cell lines and CCC serum therapy demonstrated a similar effect to 5-FU treatment, as demonstrated in the MTT and cell growth assay. Combined therapy significantly decreased the C-MYC mRNA expression levels and increased p53 mRNA expression levels (P<0.05). Combined therapy of 5-FU and CCC was more significant compared with CCC serum or 5-FU only (P<0.05). P38 and JNK-related protein phosphorylation are involved in apoptosis initiated by CCC combined 5-FU therapy. Combined therapy was able to significantly inhibit human gastric cancer cell growth (P<0.05), and advance cell apoptosis compared with CCC serum only. CCC serum resulted in downregulation of the c-Myc gene and upregulation of the p53 gene. p38 and JNK-related protein phosphorylation is involved in the inhibition of cell viability and apoptosis of human gastric cancer cell lines.

Augmented Anticancer Effects of Cantharidin with Liposomal Encapsulation: In Vitro and In Vivo Evaluation

PEGylated liposomes have received much attention as pharmaceutical carriers to deliver chemotherapeutic agents for therapeutic purpose. The aim of this study was to prepare and characterize PEGylated liposome of cantharidin and investigate its therapeutic effect on human hepatocellular carcinoma treatment in vitro and in vivo. Liposomal cantharidin was evaluated for their anticancer effects in vitro using human hepatocellular carcinoma HepG2 cells and in vivo using HepG2-bearing nude mice compared to free drug. PEGylated liposome of cantharidin had a particle size of 129.9 nm and a high encapsulation efficacy of approximately 88.9%. The liposomal cantharidin had a higher anti-proliferative effect vis-à-vis free cantharidin in inducing G2/M cell cycle arrest and apoptosis. Liposomal cantharidin killed more HepG2 cancer cells at the same concentration equivalent to free cantharidin. Further study in vivo also showed that liposomal cantharidin achieved a higher tumor growth inhibition efficacy than free drug on hepatocellular carcinoma. As our study exhibited enhanced cytotoxicity against HepG2 cells and augmented tumor inhibitory effects in vivo, the results validate the potential value of cantharidin-liposome in improving the therapeutic efficacy of cantharidin for liver cancer.

PP2A inhibition from LB100 therapy enhances daunorubicin cytotoxicity in secondary acute myeloid leukemia via miR-181b-1 upregulation

Patients with secondary acute myeloid leukemia (sAML) arising from myelodysplastic syndromes have a poor prognosis marked by an increased resistance to chemotherapy. An urgent need exists for adjuvant treatments that can enhance or replace current therapeutic options. Here we show the potential of LB100, a small-molecule protein phosphatase 2 A (PP2A) inhibitor, as a monotherapy and chemosensitizing agent for sAML using an in-vitro and in-vivo approach. We demonstrate that LB100 decreases cell viability through caspase activation and G2/M cell-cycle arrest. LB100 enhances daunorubicin (DNR) cytotoxicity resulting in decreased xenograft volumes and improved overall survival. LB100 profoundly upregulates miR-181b-1, which we show directly binds to the 3′ untranslated region of Bcl-2 mRNA leading to its translational inhibition. MiR-181b-1 ectopic overexpression further diminishes Bcl-2 expression leading to suppression of sAML cell growth, and enhancement of DNR cytotoxicity. Our research highlights the therapeutic potential of LB100, and provides new insights into the mechanism of LB100 chemosensitization.

Cantharidin alters the expression of genes associated with the NKG2D-associated immune response in TSGH-8301 human bladder carcinoma cells

Cantharidin (CTD) is a natural toxin in beetles of the Mylabris genus (blister beetle), which has been revealed to induce cell death in various types of human cancer cells. However, to the best of our knowledge, no previous studies have investigated the effect of CTD on the expression of genes and their associated signaling pathways in human bladder carcinoma cells. In the present study, CTD-induced cell morphological changes and apoptosis were observed using phase-contrast microscopy and the terminal deoxynucleotidyl transferase dUTP nick end labeling assay, respectively, in TSGH-8301 human bladder carcinoma cells. In addition, a complementary DNA microarray analysis demonstrated that CTD treatment led to a >2-fold upregulation of 269 genes. For example, the DNA damage-associated gene DNA-damage-inducible transcript 3 had a 4.75-fold upregulation. Furthermore, another 286 genes were >2-fold downregulated in response to CTD treatment. Matrix-remodeling associated 5, which is associated with cell migration and invasion, was downregulated 7.98-fold.

Role of S100A3 in human hepatocellular carcinoma and the anticancer effect of sodium cantharidinate

The fifth most common cancer worldwide is hepatocellular carcinoma (HCC), which has an annual mortality rate of ~800,000. Although surgical procedures for HCC, such as hepatic resection and liver transplantation, have progressed and the outcomes of patients have improved, HCC is still characterized by frequent recurrence, even after liver transplantation. In the present study the expression of the protein coding gene, S100 calcium binding protein A3 (S100A3), was observed in 62 HCC tissues and tumor-surrounding tissues. The present study indicated that S100A3 activation was involved in tumorigenesis and tumor aggressiveness. The protein and mRNA expression levels of S100A3 in the human HCC cell line (HepG2) were investigated using western blotting and reverse transcription-quantitative polymerase chain reaction analysis, respectively. The function of sodium cantharidinate in inducing HCC cell apoptosis was also investigated. Sodium cantharidinate inhibited the protein and gene expression of S100A3 in HepG2 cells in vitro. These data suggested that S100A3 has an important role in human HCC. The present study indicates that the functional properties of sodium cantharidinate are promising for the development of a novel drug that may control the expression of S100A3 and improve the treatment of human HCC in the near future.

Anticancer effects of cantharidin in A431 human skin cancer (Epidermoid carcinoma) cells in vitro and in vivo

Cantharidin (CTD), a potential anticancer agent of Traditional Chinese Medicine has cytotxic effects in different human cancer cell lines. The cytotoxic effects of CTD on A431 human skin cancer (epidermoid carcinoma) cells in vitro and in A431 cell xenograft mouse model were examined. In vitro, A431 human skin cell were treated with CTD for 24 and 48 h. Cell phase distribution, ROS production, Ca²⁺ release, Caspase activity and the level of apoptosis associated proteins were measured. In vivo, A431 cell xenograft mouse model were examined. CTD-induced cell morphological changes and decreased percentage of viable A431 cells via G0/G1 phase arrest and induced apoptosis. CTD-induced G0/G1 phase arrest through the reduction of protein levels of cyclin E, CDK6, and cyclin D in A431 cells. CTD-induced cell apoptosis of A431 cells also was confirm by DNA gel electrophoresis showed CTD-induced DNA fragmentation. CTD reduced the mitochondrial membrane potential and stimulated release of cytochrome c, AIF and Endo G in A431 cells. Flow cytometry demonstrated that CTD increased activity of caspase-8, -9 and -3. However, when cells were pretreated with specific caspase inhibitors activity was reduced and cell viability increased. CTD increased protein levels of death receptors such as DR4, DR5, TRAIL and levels of the active form of caspase-8, -9 and -3 in A431 cells. AIF and Endo G proteins levels were also enhanced by CTD. In vivo studies showed that CTD significantly inhibited A431 cell xenograft tumors in mice. Taken together, these in vitro and in vivo results provide insight into the mechanisms of CTD on cell growth and tumor production. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 723-738, 2017.

Alpha-Synuclein Suppresses Retinoic Acid-Induced Neuronal Differentiation by Targeting the Glycogen Synthase Kinase-3β/β-Catenin Signaling Pathway

Alpha-synuclein (α-SYN) is expressed during neuronal development and is mainly involved in the modulation of synaptic transmission. Missense mutations and amplifications of this gene have been associated with the pathogenesis of Parkinson's disease. Here, we evaluate whether α-SYN plays a detrimental role in the phenotypic and morphological regulation of neurons. We also identify the underlying mechanisms of this process in all-trans-retinoic acid (RA)-induced differentiated SH-SY5Y cells, which represents dopaminergic (DAergic) phenotype. Our results indicate that overexpression of wild-type or mutant A53T α-SYN attenuated the RA-induced upregulation of tyrosine hydroxylase and dopamine transporter as well as neurite outgrowth in SH-SY5Y cells. In addition, GSK-3β inactivation and downstream β-catenin stabilization were associated with RA-induced differentiation, which was attenuated by α-SYN. Moreover, protein phosphatase 2A was positively regulated by α-SYN and was implicated in the α-SYN-mediated interference with RA signaling. The results obtained from SH-SY5Y cells were verified in primary cultures of mesencephalic DAergic neurons from A53T α-SYN transgenic mice, which represent high levels of α-SYN and protein phosphatase 2A in the midbrain. The number and length of neurites in tyrosine hydroxylase-positive as well as Tau-positive cells from A53T α-SYN transgenic mice were significantly lower than those in littermate controls. The current results provide novel insight into the role of α-SYN in the regulation of neuronal differentiation, including DAergic neurons. Identifying the signaling pathway involved in the α-SYN-mediated dysregulation of neuronal differentiation could lead to a better understanding of the developmental processes underlying α-SYN-related pathologies and facilitate the discovery of specifically targeted therapeutics.

Therapeutic arthropods and other, largely terrestrial, folk-medicinally important invertebrates: a comparative survey and review

Traditional healing methods involving hundreds of insect and other invertebrate species are reviewed. Some of the uses are based on the tenet of "similia similibus" (let likes be cured by likes), but not all non-conventional health promoting practices should be dismissed as superstition or wishful thinking, for they have stood the test of time. Two questions are addressed: how can totally different organ systems in a human possibly benefit from extracts, potions, powders, secretions, ashes, etc. of a single species and how can different target organs, e.g. bronchi, lungs, the urinary bladder, kidneys, etc. apparently respond to a range of taxonomically not even closely related species? Even though therapeutically used invertebrates are generally small, they nevertheless possess organs for specific functions, e.g. digestion, gas exchange, reproduction. They have a nervous system, endocrine glands, a heart and muscle tissue and they contain a multitude of different molecules like metabolites, enzymes, hormones, neurotransmitters, secretions, etc. that have come under increased scientific scrutiny for pharmacological properties. Bearing that in mind it seems likely that a single species prepared and used in different ways could have a multitude of uses. But how, for example, can there be remedies for breathing and other problems, involving earthworms, molluscs, termites, beetles, cockroaches, bugs, and dragonflies? Since invertebrates themselves can suffer from infections and cancers, common defence reactions are likely to have evolved in all invertebrates, which is why it would be far more surprising to find that each species had evolved its own unique disease fighting system. To obtain a more comprehensive picture, however, we still need information on folk medicinal uses of insects and other invertebrates from a wider range of regions and ethnic groups, but this task is hampered by western-based medicines becoming increasingly dominant and traditional healers being unable and sometimes even unwilling to transmit their knowledge to the younger generation. However, collecting and uncontrolled uses of therapeutic invertebrates can put undue pressure on certain highly sought after species and this is something that has to be borne in mind as well.

TNF-α sensitizes chemotherapy and radiotherapy against breast cancer cells

Purpose

Despite new developments in cancer therapy, chemotherapy and radiotherapy remain the cornerstone of breast cancer treatment. Therefore, finding ways to reduce the toxicity and increase sensitivity is particularly important. Tumor necrosis factor alpha (TNF-α) exerts multiple functions in cell proliferation, differentiation and apoptosis. In the present study, we investigated whether TNF-α could enhance the effect of chemotherapy and radiotherapy against breast cancer cells.

Methods

Cell growth was determined by MTT assay in vitro, and by using nude mouse tumor xenograft model in vivo. Cell cycle and apoptosis/necrosis were evaluated by flow cytometry. DNA damage was visualized by phospho-Histone H2A.X staining. mRNA expression was assessed by using real-time PCR. Protein expression was tested by Western blot assay.

Results

TNF-α strengthened the cytotoxicity of docetaxel, 5-FU and cisplatin against breast cancer cells both in vitro and in vivo. TNF-α activated NF-κB pathway and dependently up-regulated expressions of CyclinD1, CyclinD2, CyclinE, CDK2, CDK4 and CDK6, the key regulators participating in G1→S phase transition. As a result, TNF-α drove cells out of quiescent G0/G1 phase, entering vulnerable proliferating phases. Treatment of TNF-α brought more DNA damage after Cs¹³⁷-irradiation and strengthened G2/M and S phase cell cycle arrest induced by docetaxel and cisplatin respectively. Moreover, the up-regulation of RIP3 (a necroptosis marker) by 5-FU, and the activation of RIP3 by TNF-α, synergistically triggered necroptosis (programmed necrosis). Knockdown of RIP3 attenuated the synergetic effect of TNF-α and 5-FU.

Conclusion

TNF-α presented radiotherapy- and chemotherapy-sensitizing effects against breast cancer cells.

Inflammatory stimuli promote growth and invasion of pancreatic cancer cells through NF-κB pathway dependent repression of PP2Ac

Previous studies have indicated that inflammatory stimulation represses protein phosphatase 2A (PP2A), a well-known tumor suppressor. However, whether PP2A repression participates in pancreatic cancer progression has not been verified. We used lipopolysaccharide (LPS) and macrophage-conditioned medium (MCM) to establish in vitro inflammation models, and investigated whether inflammatory stimuli affect pancreatic cancer cell growth and invasion PP2A catalytic subunit (PP2Ac)-dependently. Via nude mouse models of orthotopic tumor xenografts and dibutyltin dichloride (DBTC)-induced chronic pancreatitis, we evaluated the effect of an inflammatory microenvironment on PP2Ac expression in vivo. We cloned the PP2Acα and PP2Acβ isoform promoters to investigate the PP2Ac transcriptional regulation mechanisms. MCM accelerated pancreatic cancer cell growth; MCM and LPS promoted cell invasion. DBTC promoted xenograft growth and metastasis, induced tumor-associated macrophage infiltration, promoted angiogenesis, activated the nuclear factor-κB (NF-κB) pathway, and repressed PP2Ac expression. In vitro, LPS and MCM downregulated PP2Ac mRNA and protein. PP2Acα overexpression attenuated JNK, ERK, PKC, and IKK phosphorylation, and impaired LPS/MCM-stimulated cell invasion and MCM-promoted cell growth. LPS and MCM activated the NF-κB pathway in vitro. LPS and MCM induced IKK and IκB phosphorylation, leading to p65/RelA nuclear translocation and transcriptional activation. Overexpression of the dominant negative forms of IKKα attenuated LPS and MCM downregulation of PP2Ac, suggesting inflammatory stimuli repress PP2Ac expression NF-κB pathway-dependently. Luciferase reporter gene assay verified that LPS and MCM downregulated PP2Ac transcription through an NF-κB-dependent pathway. Our study presents a new mechanism in inflammation-driven cancer progression through NF-κB pathway-dependent PP2Ac repression.

Cantharidin Induced Oral Squamous Cell Carcinoma Cell Apoptosis via the JNK-Regulated Mitochondria and Endoplasmic Reticulum Stress-Related Signaling Pathways

Oral cancer is a subtype of head and neck cancer which represents 2.65% of all human malignancies. Most of oral cancer is histopathologically diagnosed as oral squamous cell carcinoma (OSCC). OSCC is characterized by a high degree of local invasion and a high rate of metastasis to the cervical lymph nodes. How to prevention and treatment of OSCC is important and imperative. Here, we investigated the therapeutic effect and molecular mechanism of cantharidin, an active compound isolated from blister beetles, on OSCC in vitro. Results showed that cantharidin significantly decreased cell viability in human tongue squamous carcinoma-derived SAS, CAL-27, and SCC-4 cell lines. The further mechanistic studies were carried out in SAS cells. Cantharidin also significantly increased apoptosis-related signals, including caspase-9, caspase-7 and caspase-3 proteins. Besides, cantharidin decreased mitochondrial transmembrane potential (MMP) and induced cytochrome c and apoptosis inducing factor (AIF) release. Cantharidin also increased Bax, Bid, and Bak protein expressions and decreased Bcl-2 protein expression. Cantharidin could also increase the endoplasmic reticulum (ER) stress signals, including the expressions of phosphorylated eIF-2α and CHOP, but not Grp78 and Grp94. Furthermore, cantharidin reduced pro-caspase-12 protein expression. In signals of mitogen-activated protein kinases, cantharidin increased the phosphorylation of JNK, but not ERK and p38. Transfection of shRNA-JNK to OSCC cells effectively reversed the cantharidin-induced cell apoptotic signals, including the mitochondrial and ER stress-related signaling molecules. Taken together, these findings suggest that cantharidin induces apoptosis in OSCC cells via the JNK-regulated mitochondria and ER stress-related signaling pathways.

Cantharidin Overcomes Imatinib Resistance by Depleting BCR-ABL in Chronic Myeloid Leukemia

Cantharidin (CTD) is an active compound isolated from the traditional Chinese medicine blister beetle and displayed anticancer properties against various types of cancer cells. However, little is known about its effect on human chronic myeloid leukemia (CML) cells, including imatinib-resistant CML cells. The objective of this study was to investigate whether CTD could overcome imatinib resistance in imatinib-resistant CML cells and to explore the possible underlying mechanisms associated with the effect. Our results showed that CTD strongly inhibited the growth of both imatinib-sensitive and imatinib-resistant CML cells. CTD induced cell cycle arrest at mitotic phase and triggered DNA damage in CML cells. The ATM/ATR inhibitor CGK733 abrogated CTD-induced mitotic arrest but promoted the cytotoxic effects of CTD. In addition, we demonstrated that CTD downregulated the expression of the BCR-ABL protein and suppressed its downstream signal transduction. Real-time quantitative PCR revealed that CTD inhibited BCR-ABL at transcriptional level. Knockdown of BCR-ABL increased the cell-killing effects of CTD in K562 cells. These findings indicated that CTD overcomes imatinib resistance through depletion of BCR-ABL. Taken together, CTD is an important new candidate agent for CML therapy.

RACK1 stabilises the activity of PP2A to regulate the transformed phenotype in mammary epithelial cells

Conflicting reports implicate the scaffolding protein RACK1 in the progression of breast cancer. RACK1 has been identified as a key regulator downstream of growth factor and adhesion signalling and as a direct binding partner of PP2A. Our objective was to further characterise the interaction between PP2A and RACK1 and to advance our understanding of this complex in breast cancer cells. We examined how the PP2A holoenzyme is assembled on the RACK1 scaffold in MCF-7 cells. We used immobilized peptide arrays representing the entire PP2A-catalytic subunit to identify candidate amino acids on the C subunit of PP2A that might be involved in binding of RACK1. We identified the RACK1 interaction sites on PP2A. Stable cell lines expressing PP2A with FR69/70AA, R214A and Y218F substitutions were generated and it was confirmed that the RACK1/PP2A interaction is essential to stabilise PP2A activity. We used Real-Time Cell Analysis and a series of assays to demonstrate that disruption of the RACK1/PP2A complex also reduces the adhesion, proliferation, migration and invasion of breast cancer cells and plays a role in maintenance of the cancer phenotype. This work has significantly advanced our understanding of the RACK1/PP2A complex and suggests a pro-carcinogenic role for the RACK1/PP2A interaction. This work suggests that approaches to target the RACK1/PP2A complex are a viable option to regulate PP2A activity and identifies a novel potential therapeutic target in the treatment of breast cancer.

Non-dioxin-like organic toxicant PCB153 modulates sphingolipid metabolism in liver progenitor cells: its role in Cx43-formed gap junction impairment

The non-dioxin-like environmental toxicant 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153), member of a group of persistent organic pollutants wide-spread throughout the environment, reduces gap junction intercellular communication (GJIC), an event possibly associated with tumor promotion. Since very few studies have investigated the signaling effectors and mode(s) of action of PCB153, and it is known that the gap junction (GJ) protein Cx43 can be regulated by the bioactive sphingolipid (SL) sphingosine 1-phosphate (S1P), this in vitro study mainly addresses whether SL metabolism is affected by PCB153 in rat liver epithelial WB-F344 cells. PCB153 treatment obtained significant changes in the S1P/ceramide (Cer) ratio, known to be crucial in determining cell fate. In particular, an increase in S1P at 30 min and a decrease of the bioactive lipid at 3 h were observed, whereas Cer level increased at 1 h and 24 h. Notably, a time-dependent modulation of sphingosine kinase (SphK), the enzyme responsible for S1P synthesis, and of its regulators, ERK1/2 and protein phosphatase PP2A, supports the involvement of these signaling effectors in PCB153 toxicity. Electrophysiological analyses, furthermore, indicated that the lipophilic environmental toxicant significantly reduced GJ biophysical properties, affecting both voltage-dependent (such as those formed by Cx43 and/or Cx32) and voltage-independent channels, thereby demonstrating that PCB153 may act differently on GJs formed by distinct Cx isoforms. SphK down-regulation alone induced GJIC impairment, and, when combined with PCB153, the acute effect on GJ suppression was additive. Moreover, after enzyme-specific gene silencing, the SphK1 isoform appears to be responsible for down-regulating Cx43 expression, while being the target of PCB153 at short-term exposure. In conclusion, we provide the first evidence of novel effectors in PCB153 toxic action in rat liver stem-like cells, leading us to consider SLs as potential markers for preventing GJIC deregulation and, thus, the tumorigenic action elicited by this environmental toxicant.

PP2A inhibitors arrest G2/M transition through JNK/Sp1- dependent down-regulation of CDK1 and autophagy-dependent up-regulation of p21

Protein phosphatase 2A (PP2A) plays an important role in the control of the cell cycle. We previously reported that the PP2A inhibitors, cantharidin and okadaic acid (OA), efficiently repressed the growth of cancer cells. In the present study, we found that PP2A inhibitors arrested the cell cycle at the G2 phase through a mechanism that was dependent on the JNK pathway. Microarrays further showed that PP2A inhibitors induced expression changes in multiple genes that participate in cell cycle transition. To verify whether these expression changes were executed in a PP2A-dependent manner, we targeted the PP2A catalytic subunit (PP2Ac) using siRNA and evaluated gene expression with a microarray. After the cross comparison of these microarray data, we identified that CDK1 was potentially the same target when treated with either PP2A inhibitors or PP2Ac siRNA. In addition, we found that the down-regulation of CDK1 occurred in a JNK-dependent manner. Luciferase reporter gene assays demonstrated that repression of the transcription of CDK1 was executed through the JNK-dependent activation of the Sp1 transcription factor. By constructing deletion mutants of the CDK1 promoter and by using ChIP assays, we identified an element in the CDK1 promoter that responded to the JNK/Sp1 pathway after stimulation with PP2A inhibitors. Cantharidin and OA also up-regulated the expression of p21, an inhibitor of CDK1, via autophagy rather than PP2A/JNK pathway. Thus, this present study found that the PP2A/JNK/Sp1/CDK1 pathway and the autophagy/p21 pathway participated in G2/M cell cycle arrest triggered by PP2A inhibitors.

High Performance Liquid Chromatography-mass Spectrometry Analysis of High Antioxidant Australian Fruits with Antiproliferative Activity Against Cancer Cells

BACKGROUND

High antioxidant capacities have been linked to the treatment and prevention of several cancers. Recent reports have identified several native Australian fruits with high antioxidant capacities. Despite this, several of these species are yet to be tested for anticancer activity.

MATERIALS AND METHODS

Solvent extracts prepared from high antioxidant native Australian fruits were analyzed for antioxidant capacity by the di (phenyl)-(2,4,6-trinitrophenyl) iminoazanium free radical scavenging assay. Antiproliferative activities against CaCo2 and HeLa cancer cells were determined by a multicellular tumor spheroid-based cell proliferation assay. Toxicity was determined by Artemia franciscana bioassay.

RESULTS

Methanolic extracts of all plant species displayed high antioxidant contents (equivalent to approximately 7-16 mg of vitamin C per gram of fruit extracted). Most aqueous extracts also contained relatively high antioxidant capacities. In contrast, the ethyl acetate, chloroform, and hexane extracts of most species (except lemon aspen and bush tomato) had lower antioxidant contents (below 1.5 mg of vitamin C equivalents per gram of plant material extracted). The antioxidant contents correlated with the ability of the extracts to inhibit proliferation of CaCo2 and HeLa cancer cell lines. The high antioxidant methanolic extracts of all species were potent inhibitors of cell proliferation. The methanolic lemon aspen extract was particularly effective, with IC50 values of 480 and 769 μg/mL against HeLa and CaCo2 cells, respectively. In contrast, the lower antioxidant ethyl acetate and hexane extracts (except the lemon aspen ethyl acetate extract) generally did not inhibit cancer cell proliferation or inhibited to only a minor degree. Indeed, most of the ethyl acetate and hexane extracts induced potent cell proliferation. The native tamarind ethyl acetate extract displayed low-moderate toxicity in the A. franciscana bioassay (LC50 values below 1000 μg/mL). All other extracts were nontoxic. A total of 145 unique mass signals were detected in the lemon aspen methanolic and aqueous extracts by nonbiased high-performance liquid chromatography-mass spectrometry analysis. Of these, 20 compounds were identified as being of particular interest due to their reported antioxidant and/or anticancer activities.

CONCLUSIONS

The lack of toxicity and antiproliferative activity of the high antioxidant plant extracts against HeLa and CaCo2 cancer cell lines indicates their potential in the treatment and prevention of some cancers.

SUMMARY

Australian fruit extracts with high antioxidant contents were potent inhibitors of CaCo2 and HeLa carcinoma cell proliferationMethanolic lemon aspen extract was particularly potent, with IC50 values of 480 μg/mL (HeLa) and 769 μg/mL (CaCo2)High-performance liquid chromatography-mass spectrometry-quadrupole time-of-flight analysis highlighted and putatively identified 20 compounds in the antiproliferative lemon aspen extractsIn contrast, lower antioxidant content extracts stimulated carcinoma cell proliferationAll extracts with antiproliferative activity were nontoxic in the Artemia nauplii assay. Abbreviations used: DPPH: di (phenyl)- (2,4,6-trinitrophenyl) iminoazanium, HPLC: High-performance liquid chromatography, IC50: The concentration required to inhibit by 50%, LC50: The concentration required to achieve 50% mortality, MS: Mass spectrometry.

Regulation of Receptor for Advanced Glycation End Products (RAGE) Ectodomain Shedding and Its Role in Cell Function

The receptor for advanced glycation end products (RAGE) is a multiligand transmembrane receptor that can undergo proteolysis at the cell surface to release a soluble ectodomain. Here we observed that ectodomain shedding of RAGE is critical for its role in regulating signaling and cellular function. Ectodomain shedding of both human and mouse RAGE was dependent on ADAM10 activity and induced with chemical activators of shedding (ionomycin, phorbol 12-myristate 13-acetate, and 4-aminophenylmercuric acetate) and endogenous stimuli (serum and RAGE ligands). Ectopic expression of the splice variant of RAGE (RAGE splice variant 4), which is resistant to ectodomain shedding, inhibited RAGE ligand dependent cell signaling, actin cytoskeleton reorganization, cell spreading, and cell migration. We found that blockade of RAGE ligand signaling with soluble RAGE or inhibitors of MAPK or PI3K blocked RAGE-dependent cell migration but did not affect RAGE splice variant 4 cell migration. We finally demonstrated that RAGE function is dependent on secretase activity as ADAM10 and γ-secretase inhibitors blocked RAGE ligand-mediated cell migration. Together, our data suggest that proteolysis of RAGE is critical to mediate signaling and cell function and may therefore emerge as a novel therapeutic target for RAGE-dependent disease states.

Synthesis of Canthardin Sulfanilamides and Their Acid Anhydride Analogues via a Ring-Opening Reaction of Activated Aziridines and Their Associated Pharmacological Effects

The cantharidinimide derivatives, 5a-h, including sulfanilamides containing pyrimidyl, pyrazinyl, hydrogen, thiazolyl, and oxazolyl groups were synthesized. Modification of cantharidinimide by means of the reaction of activated aziridine ring opening led to the discovery of a novel class of antitumor compounds. The analogues 10i-k, 11l-n, 12o-p, and 16q-s were obtained from treating cantharidinimide 6 and analogues (7, 8, and 13) with activated aziridines, which produced a series of ring-opened products including normal and abnormal types. Some of these compounds showed cytotoxic effects in vitro against HL-60, Hep3B, MCF7, and MDA-MB-231 cancer cells. The most potent cytostatic compound, N-cantharidinimido-sulfamethazine (5a), exhibited anti-HL-60 and anti-Hep3B cell activities. Two compounds 5g and 5h displayed slight effects on the Hep3B cell line, while the other compounds produced no response in these four cell lines.

Synthesis and Biological Evaluation of Norcantharidin Derivatives Possessing an Aromatic Amine Moiety as Antifungal Agents

Based on the structure of naturally produced cantharidin, different arylamine groups were linked to the norcantharidin scaffold to provide thirty six compounds. Their structures were confirmed by melting point, ¹H-NMR, (13)C-NMR and HRMS-ESI studies. These synthetic compounds were tested as fungistatic agents against eight phytopathogenic fungi using the mycelium growth rate method. Of these thirty six derivatives, seven displayed stronger antifungal activity than did norcantharidin, seven showed higher activity than did cantharidin and three exhibited more significant activity than that of thiabendazole. In particular, 3-(3'-chloro-phenyl)carbamoyl norcantharidate II-8 showed the most significant fungicidal activity against Sclerotinia fructigena and S. sclerotiorum, with IC50 values of 0.88 and 0.97 μg/mL, respectively. The preliminary structure-activity relationship data of these compounds revealed that: (1) the benzene ring is critical for the improvement of the spectrum of antifungal activity (3-phenylcarbamoyl norcantharidate II-1 vs norcantharidin and cantharidin); (2) among the three sites, including the C-2', C-3' and C-4' positions of the phenyl ring, the presence of a halogen atom at the C-3'position of the benzene ring caused the most significant increase in antifungal activity; (3) compounds with strongly electron-drawing or electron-donating groups substitutions were found to have a poor antifungal activity; and (4) compared with fluorine, bromine and iodine, chlorine substituted at the C-3' position of the benzene ring most greatly promoted fungistatic activity. Thus, compound II-8 has emerged as new lead structure for the development of new fungicides.

Crosstalk between PI3K and Ras pathways via protein phosphatase 2A in human ovarian clear cell carcinoma

Hypoxia-inducible factor-1 (HIF-1) is one of the most promising pharmacological targets for all types of cancer, including ovarian cancer. Ovarian clear cell carcinoma (OCCC) has poor prognosis because of its insensitivity to chemotherapy. To elucidate the characteristics of this troublesome cancer, we examined HIF-1α expression under normoxia or hypoxia in various ovarian cancer cell lines. HIF-1α was highly expressed under normoxia only in RMG-1, an OCCC cell line. To examine whether HIF-1 is involved in the tumorigenesis of RMG-1 cells, we established HIF-1α-silenced cells, RMG-1HKD. The proliferation rate of RMG-1HKD cells was faster than that of RMG-1 cells. Furthermore, the activity of MEK/ERK in the Ras pathway increased in RMG-1HKD cells, whereas that of mTOR in the PI3K pathway did not change. Activation of the Ras pathway was attributable to the increase in phosphorylated MEK via PP2A inactivation. To confirm the crosstalk between the PI3K and Ras pathways in vivo, RMG-1 or RMG-1HKD cells were transplanted into the skin of nude mice with rapamycin (an inhibitor of mTOR), PD98059 (an inhibitor of MEK), or both. RMG-1HKD cells showed higher sensitivity to PD98059 than that observed in RMD-1 cells, whereas the combination therapy resulted in synergistic inhibition of both cells. These findings suggest that inhibition of HIF-1, a downstream target of mTOR in the PI3K pathway, activates the Ras pathway on account of the increase in MEK phosphorylation via PP2A inactivation, and the crosstalk between the 2 pathways could be applied in the combination therapy for HIF-1-overexpressing cancers such as OCCC.

Negative Regulation of p21Waf1/Cip1 by Human INO80 Chromatin Remodeling Complex Is Implicated in Cell Cycle Phase G2/M Arrest and Abnormal Chromosome Stability

We previously identified an ATP-dependent human Ino80 (INO80) chromatin remodeling complex which shares a set of core subunits with yeast Ino80 complex. Although research evidence has suggested that INO80 complex functions in gene transcription and genome stability, the precise mechanism remains unclear. Herein, based on gene expression profiles from the INO80 complex-knockdown in HeLa cells, we first demonstrate that INO80 complex negatively regulates the p21^Waf1/Cip1 (p21) expression in a p53-mediated mechanism. In chromatin immunoprecipitation (ChIP) and a sequential ChIP (Re-ChIP) assays, we determined that the INO80 complex and p53 can bind to the same promoter region of p21 gene (-2.2kb and -1.0kb upstream of the p21 promoter region), and p53 is required for the recruitment of the INO80 complex to the p21 promoter. RNAi knockdown strategies of INO80 not only led to prolonged progression of cell cycle phase G2/M to G1, but it also resulted in abnormal chromosome stability. Interestingly, high expression of p21 was observed in most morphologically-changed cells, suggesting that negative regulation of p21 by INO80 complex might be implicated in maintaining the cell cycle process and chromosome stability. Together, our findings will provide a theoretical basis to further elucidate the cellular mechanisms of the INO80 complex.

Cantharidin induces DNA damage and inhibits DNA repair-associated protein levels in NCI-H460 human lung cancer cells

Cantharidin is one of the major compounds from mylabris and it has cytotoxic effects in many different types of human cancer cells. Previously, we found that cantharidin induced cell death through cell cycle arrest and apoptosis induction in human lung cancer NCI-H460 cells. However, cantharidin-affected DNA damage, repair, and associated protein levels in NCI-H460 cells have not been examined. In this study, we determined whether cantharidin induced DNA damage and condensation and altered levels of proteins in NCI-H460 cells in vitro. Incubation of NCI-H460 cells with 0, 2.5, 5, 10, and 15 μM of cantharidin caused a longer DNA migration smear (comet tail). Cantharidin also increased DNA condensation. These effects were dose-dependent. Cantharidin (5, 10, and 15 μM) treatment of NCI-H460 cells reduced protein levels of ataxia telangiectasia mutated (ATM), breast cancer 1, early onset (BRCA-1), 14-3-3 proteins sigma (14-3-3σ), DNA-dependent serine/threonine protein kinase (DNA-PK), O(6) -methylguanine-DNA methyltransferase (MGMT), and mediator of DNA damage checkpoint protein 1 (MDC1). Protein translocation of p-p53, p-H2A.X (S140), and MDC1 from cytoplasm to nucleus was induced by cantharidin in NCI-H460 cells. Taken together, this study showed that cantharidin caused DNA damage and inhibited levels of DNA repair-associated proteins. These effects may contribute to cantharidin-induced cell death in vitro.

Insights into the key interactions between human protein phosphatase 5 and cantharidin using molecular dynamics and site-directed mutagenesis bioassays

Serine/threonine protein phosphatase 5 (PP5) is a promising novel target for anticancer therapies. This work aims to uncover the key interactions at the atomic level between PP5 and three inhibitors (cantharidin, norcantharidin and endothall). We found that, unlike previous report, Arg 100 contributes less to PP5-inhibitor binding, and the residues His 69, Asn 128, His 129, Arg 225, His 252 and Arg 250 are of importance to PP5-inhibitor binding. The hydrophobic interactions established between the residues Val 254, Phe 271 and Tyr 276, especially Glu 253, are very important to enhance the inhibitive interaction. We suggested that, to increase the inhibitory activity, the interactions of inhibitor with three negatively charged unfavorable interaction residues, Asp 99, Glu 130 and Asp 213, should be avoided. However, the interactions of inhibitor with favorable interaction residue Arg 250 could enhance the inhibitory activity. The Manganese ion 2 (MN2) unfavorably contribute to the total interaction free energies. The coordination between MN2 and chemical group of inhibitor should be eliminated. This work provides insight into how cantharidin and its analogs bind to PP5c at the atomic level and will facilitate modification of cantharidin-like chemicals to rationally develop more specific and less cytotoxic anti-cancer drugs.

Cantharidin represses invasion of pancreatic cancer cells through accelerated degradation of MMP2 mRNA

Cantharidin is an active constituent of mylabris, a traditional Chinese medicine, and is a potent and selective inhibitor of protein phosphatase 2A (PP2A) that plays an important role in cell cycle control, apoptosis, and cell-fate determination. In the present study, we found that cantharidin repressed the invasive ability of pancreatic cancer cells and downregulated matrix metalloproteinase 2 (MMP2) expression through multiple pathways, including ERK, JNK, PKC, NF-κB, and β-catenin. Interestingly, transcriptional activity of the MMP2 promoter increased after treatment with PP2A inhibitors, suggesting the involvement of a posttranscriptional mechanism. By using an mRNA stability assay, we found accelerated degradation of MMP2 mRNA after treatment of cantharidin. Microarray analyses revealed that multiple genes involved in the 3' → 5' decay pathway were upregulated, especially genes participating in cytoplasmic deadenylation. The elevation of these genes were further demonstrated to be executed through ERK, JNK, PKC, NF-κB, and β-catenin pathways. Knockdown of PARN, RHAU, and CNOT7, three critical members involved in cytoplasmic deadenylation, attenuated the downregulation of MMP2. Hence, we present the mechanism of repressed invasion by cantharidin and other PP2A inhibitors through increased degradation of MMP2 mRNA by elevated cytoplasmic deadenylation.

When Cancer Fights Back: Multiple Myeloma, Proteasome Inhibition, and the Heat-Shock Response

Multiple myeloma is a plasma cell malignancy with an estimated 26,850 new cases and 11,240 deaths in 2015 in the United States. Two main classes of agents are the mainstays of therapy-proteasome inhibitors (PI) and immunomodulatory drugs (IMiD). Other new targets are emerging rapidly, including monoclonal antibodies and histone deacetylase (HDAC) inhibitors. These therapeutic options have greatly improved overall survival, but currently only 15% to 20% of patients experience long-term progression-free survival or are cured. Therefore, improvement in treatment options is needed. One potential means of improving clinical options is to target resistance mechanisms for current agents. For example, eliminating the cytoprotective heat-shock response that protects myeloma cells from proteasome inhibition may enhance PI-based therapies. The transcription factor heat-shock factor 1 (HSF1) is the master regulator of the heat-shock response. HSF1 is vital in the proteotoxic stress response, and its activation is controlled by posttranslational modifications (PTM). This review details the mechanisms of HSF1 regulation and discusses leveraging that regulation to enhance PI activity.

Participation of autophagy in the cytotoxicity against breast cancer cells by cisplatin

Breast cancer is one of the most common cancers affecting women worldwide. Conventional chemotherapy is still one of the major approaches to the treatment of breast cancer. Autophagy, also termed as type II programmed cell death (PCD), exhibits either a protumorigenic or antitumorigenic function. In the present study, we investigated whether autophagy could be involved in the effect of chemotherapy against breast cancer. Epirubicin, docetaxel, methotrexate, cyclophosphamide, fluorouracil (5-FU) and cisplatin were applied in the present investigation. All of these chemotherapeutics presented cytotoxicity against breast cancer cells. DsRed-LC3 reporter assay revealed that only docetaxel and cisplatin induced autophagy. Autophagy inhibitor 3-methyladenine (3-MA) strengthened the cytotoxicity of docetaxel, yet impaired the cytotoxicity of cisplatin, suggesting that docetaxel stimulates protumorigenic autophagy, while cisplatin-induced autophagy could be antitumorigenic. Real-time PCR revealed that cisplatin upregulated multiple autophagy-related genes, including AMBRA1, ATG3, ATG4C, ATG4D, ATG5, ATG7, ATG13, ATG14, ATG16L2, Beclin1, DRAM1, GABARAP, GABARAPL1, GABARAPL2, HDAC6, IRGM, MAP1LC3B and ULK1, indicating that cisplatin induced autophagy through a multiple mechanism involved manner.

Inhibition of protein phosphatase 2A with the small molecule LB100 overcomes cell cycle arrest in osteosarcoma after cisplatin treatment

Osteosarcoma is the most common primary malignant bone tumor and affects a significant portion of pediatric oncology patients. Although surgery and adjuvant chemotherapy confer significant survival benefits, many patients go on to develop metastatic disease, particularly to the lungs, secondary to development of drug resistance. Inhibition of protein phosphatase 2A with the small molecule, LB100, has demonstrated potent chemo- and radio-sensitizing properties in numerous pre-clinical tumor models. In this study, we showed that LB100 overcame DNA repair mechanisms in osteosarcoma cells treated with cisplatin, in vitro, and recapitulated these findings in an in vivo xenograft model. Notably, the addition of LB100 to cisplatin prevented development of pulmonary metastases in the majority of treated animals. Our data indicated the mechanism of chemo-sensitization by LB100 involved abrogation of the ATM/ATR-activated DNA damage response, leading to hyperphosphorylation of Chk proteins and persistent cyclin activity. In addition, LB100 exposure suppressed Akt signaling, leading to Mdm2-mediated proteasomal degradation of functional p53. Taken together, LB100 prevented repair of cisplatin-induced DNA damage, resulting in mitotic catastrophe and cell death.