Cantharidin induces apoptosis of human multiple myeloma cells via inhibition of the JAK/STAT pathway

Design and synthesis of cantharidin derivative DCZ5418 as a TRIP13 inhibitor with anti-multiple myeloma activity in vitro and in vivo

Natural product cantharidin can inhibit multiple myeloma cell growth in vitro, while serious adverse effects limited its clinical application. Therefore, the structural modification of cantharidin is needed. Herein, inspired by the structural similarity of the aliphatic endocyclic moiety in cantharidin and TRIP13 inhibitor DCZ0415, we designed and synthesized DCZ5418 and its nineteen derivatives. The molecular docking study indicated that DCZ5418 had a similar binding mode to TRIP13 protein as DCZ0415 while with a stronger docking score. Moreover, the bioassay studies of the MM-cells viability inhibition, TRIP13 protein binding affinity and enzyme inhibiting activity showed that DCZ5418 had good anti-MM activity in vitro and definite interaction with TRIP13 protein. The acute toxicity test of DCZ5418 showed less toxicity in vivo than cantharidin. Furthermore, DCZ5418 showed good anti-MM effects in vivo with a lower dose administration than DCZ0415 (15 mg/kg vs 25 mg/kg) on the tumor xenograft models. Thus, we obtained a new TRIP13 inhibitor DCZ5418 with improved safety and good activity in vivo, which provides a new example of lead optimization by using the structural fragments of natural products.

Altering phosphorylation in cancer through PP2A modifiers

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase integral to the regulation of many cellular processes. Due to the deregulation of PP2A in cancer, many of these processes are turned toward promoting tumor progression. Considerable research has been undertaken to discover molecules capable of modulating PP2A activity in cancer. Because PP2A is capable of immense substrate specificity across many cellular processes, the therapeutic targeting of PP2A in cancer can be completed through either enzyme inhibitors or activators. PP2A modulators likewise tend to be effective in drug-resistant cancers and work synergistically with other known cancer therapeutics. In this review, we will discuss the patterns of PP2A deregulation in cancer, and its known downstream signaling pathways important for cancer regulation, along with many activators and inhibitors of PP2A known to inhibit cancer progression.

Hepatotoxic mechanism of cantharidin: insights and strategies for therapeutic intervention

Cantharidin (CTD), a natural compound derived from Mylabris, is widely used in traditional Oriental medicine for its potent anticancer properties. However, its clinical application is restricted due to its high toxicity, particularly towards the liver. This review provides a concise understanding of the hepatotoxic mechanisms of CTD and highlights novel therapeutic strategies to mitigate its toxicity while enhancing its anticancer efficacy. We systematically explore the molecular mechanisms underlying CTD-induced hepatotoxicity, focusing on the involvement of apoptotic and autophagic processes in hepatocyte injury. We further discuss the endogenous and exogenous pathways implicated in CTD-induced liver damage and potential therapeutic targets. This review also summarizes the structural modifications of CTD derivatives and their impact on anticancer activity. Additionally, we delve into the advancements in nanoparticle-based drug delivery systems that hold promise in overcoming the limitations of CTD derivatives. By offering valuable insights into the hepatotoxic mechanisms of CTD and outlining potential avenues for future research, this review contributes to the ongoing efforts to develop safer and more effective CTD-based therapies.

Small in Size, but Large in Action: microRNAs as Potential Modulators of PTEN in Breast and Lung Cancers

MicroRNAs (miRNAs) are well-known regulators of biological mechanisms with a small size of 19–24 nucleotides and a single-stranded structure. miRNA dysregulation occurs in cancer progression. miRNAs can function as tumor-suppressing or tumor-promoting factors in cancer via regulating molecular pathways. Breast and lung cancers are two malignant thoracic tumors in which the abnormal expression of miRNAs plays a significant role in their development. Phosphatase and tensin homolog (PTEN) is a tumor-suppressor factor that is capable of suppressing the growth, viability, and metastasis of cancer cells via downregulating phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling. PTEN downregulation occurs in lung and breast cancers to promote PI3K/Akt expression, leading to uncontrolled proliferation, metastasis, and their resistance to chemotherapy and radiotherapy. miRNAs as upstream mediators of PTEN can dually induce/inhibit PTEN signaling in affecting the malignant behavior of lung and breast cancer cells. Furthermore, long non-coding RNAs and circular RNAs can regulate the miRNA/PTEN axis in lung and breast cancer cells. It seems that anti-tumor compounds such as baicalein, propofol, and curcumin can induce PTEN upregulation by affecting miRNAs in suppressing breast and lung cancer progression. These topics are discussed in the current review with a focus on molecular pathways.

Functional characterization of STATa/b genes encoding transcription factors from Branchiostoma belcheri

The signal transducer and activator of transcription (STAT), as an important transcription factor of the Janus kinase (JAK)-STAT signaling pathway, is pivotal for development and immunity and well documented in vertebrates. However, the STAT gene has not been reported in chordate amphioxus (Branchiostoma belcheri). In this study, we firstly identify and characterize two STAT genes from Branchiostoma belcheri (designed as AmphiSTATa and AmphiSTATb). Secondly, our results reveal that AmphiSTATa is clustered with vertebrate STAT1, STAT2, STAT3 and STAT4, whereas AmphiSTATb is grouped with STAT5 and STAT6 based on phylogenetic analysis. Thirdly, AmphiSTATa and AmphiSTATb are found to widely express in five representative tissues of amphioxus (gill, hepatic cecum, intestine, muscle and notochord) by RT-qPCR analysis. Importantly, both AmphiSTATa and AmphiSTATb can be involved in innate immune responses to LPS stimulation. Fourthly, we demonstrate that AmphiSTATa and AmphiSTATb can form homodimers or heterodimers by Co-IP and Native-PAGE assay, and that AmphiSTATa and AmphiSTATb proteins can also distribute in cytoplasm and nucleus by the subcellular localization. Taken together, our findings not only reveal the roles of AmphiSTATa and AmphiSTATb in amphioxus innate immune responses to LPS stimulation, but provide a new insight into further elucidating the evolution and function of STATs in animals.

Natural products as important tyrosine kinase inhibitors

As an important source of drugs, natural products play an important role in the discovery and development of new drugs. More than 60% of anti-tumor drugs are closely related to natural products. At the same time, as the main cause of tumors, the abnormal activity of tyrosine kinase has become an important target for clinical treatment. Although, small molecule targeted drugs dominate the cancer treatment. Natural active products are driving the development of new tyrosine kinase inhibitors with their unique mode of action and molecular structure diversity. Obtaining new chemical entities with tyrosine kinase inhibitory activity from natural active products will bring new breakthroughs in the research of anticancer drugs. In this paper, different tyrosine kinases are mainly classified as targets, and natural products and derivatives which have been found to inhibit tyrosine kinase activity have been described. It is hoped that by analyzing the different aspects of the source, structural characteristics, mechanism of action and biological activity of these natural products, we will find new members that can be developed into drugs and promote the development of anti-tumor drugs.

Cantharidin decreased viable cell number in human osteosarcoma U-2 OS cells through G2/M phase arrest and induction of cell apoptosis

Cantharidin (CTD), a sesquiterpenoid bioactive substance, has been reported to exhibit anticancer activity against various types of cancer cells. The aim of the present study was to investigate the apoptosis effects and the underlying mechanisms of CTD on osteosarcoma U-2 OS cells. Results showed that CTD induced cell morphologic changes, reduced total viable cells, induced DNA damage, and G₂/M phase arrest. CTD increased the production of reactive oxygen species and Ca²⁺, and elevated the activities of caspase-3 and -9, but decreased the level of mitochondrial membrane potential. Furthermore, CTD increased the ROS- and ER stress-associated protein expressions and increased the levels of pro-apoptosis-associated proteins, but decreased that of anti-apoptosis-associated proteins. Based on these observations, we suggested that CTD decreased cell number through G₂/M phase arrest and the induction of cell apoptosis in U-2 OS cells and CTD could be a potential candidate for osteosarcoma treatments.

Anticancer Activity and Underlying Mechanism of Phytochemicals against Multiple Myeloma

Multiple myeloma (MM)-a common hematologic malignancy of plasma cells-accounts for substantial mortality and morbidity rates. Due to the advent of novel therapies such as immunomodulatory drugs (IMiDs), proteasome inhibitors (PIs), and monoclonal antibodies (mAbs), response rates were increased and free survival and overall survival have been elevated. However, adverse events including toxicity, neuropathy or continuous relapse are still problems. Thus, development of novel drugs which have less side effects and more effective is needed. This review aims to recapitulate the pharmacologic anti-MM mechanisms of various phytochemicals, elucidating their molecular targets. Keywords related to MM and natural products were searched in PUBMED/MEDLINE. Phytochemicals have been reported to display a variety of anti-MM activities, including apoptosis, cell cycle arrest, antiangiogenesis, and miRNA modulation. Some phytochemicals sensitize the conventional therapies such as dexamethasone. Also, there are clinical trials with phytochemicals such as agaricus, curcumin, and Neovastat regarding MM treatment. Taken together, this review elucidated and categorized the evidences that natural products and their bioactive compounds could be potent drugs in treating MM.

Beetles as Model Organisms in Physiological, Biomedical and Environmental Studies - A Review

Model organisms are often used in biological, medical and environmental research. Among insects, Drosophila melanogaster, Galleria mellonella, Apis mellifera, Bombyx mori, Periplaneta americana, and Locusta migratoria are often used. However, new model organisms still appear. In recent years, an increasing number of insect species has been suggested as model organisms in life sciences research due to their worldwide distribution and environmental significance, the possibility of extrapolating research studies to vertebrates and the relatively low cost of rearing. Beetles are the largest insect order, with their representative - Tribolium castaneum - being the first species with a completely sequenced genome, and seem to be emerging as new potential candidates for model organisms in various studies. Apart from T. castaneum, additional species representing various Coleoptera families, such as Nicrophorus vespilloides, Leptinotarsa decemlineata, Coccinella septempunctata, Poecilus cupreus, Tenebrio molitor and many others, have been used. They are increasingly often included in two major research aspects: biomedical and environmental studies. Biomedical studies focus mainly on unraveling mechanisms of basic life processes, such as feeding, neurotransmission or activity of the immune system, as well as on elucidating the mechanism of different diseases (neurodegenerative, cardiovascular, metabolic, or immunological) using beetles as models. Furthermore, pharmacological bioassays for testing novel biologically active substances in beetles have also been developed. It should be emphasized that beetles are a source of compounds with potential antimicrobial and anticancer activity. Environmental-based studies focus mainly on the development and testing of new potential pesticides of both chemical and natural origin. Additionally, beetles are used as food or for their valuable supplements. Different beetle families are also used as bioindicators. Another important research area using beetles as models is behavioral ecology studies, for instance, parental care. In this paper, we review the current knowledge regarding beetles as model organisms and their practical application in various fields of life science.

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.

Identification of the APC/C co-factor FZR1 as a novel therapeutic target for multiple myeloma

Multiple Myeloma (MM) is a haematological neoplasm characterised by the clonal proliferation of malignant plasma cells in the bone marrow. The success of proteasome inhibitors in the treatment of MM has highlighted the importance of the ubiquitin proteasome system (UPS) in the pathogenesis of this disease. In this study, we analysed gene expression of UPS components to identify novel therapeutic targets within this pathway in MM. Here we demonstrate how this approach identified previously validated and novel therapeutic targets. In addition we show that FZR1 (Fzr), a cofactor of the multi-subunit E3 ligase complex anaphase-promoting complex/cyclosome (APC/C), represents a novel therapeutic target in myeloma. The APC/C associates independently with two cofactors, Fzr and Cdc20, to control cell cycle progression. We found high levels of FZR1 in MM primary cells and cell lines and demonstrate that expression is further increased on adhesion to bone marrow stromal cells (BMSCs). Specific knockdown of either FZR1 or CDC20 reduced viability and induced growth arrest of MM cell lines, and resulted in accumulation of APC/C^Fzr substrate Topoisomerase IIα (TOPIIα) or APC/C^Cdc20 substrate Cyclin B. Similar effects were observed following treatment with proTAME, an inhibitor of both APC/C^Fzr and APC/C^Cdc20. Combinations of proTAME with topoisomerase inhibitors, etoposide and doxorubicin, significantly increased cell death in MM cell lines and primary cells, particularly if TOPIIα levels were first increased through pre-treatment with proTAME. Similarly, combinations of proTAME with the microtubule inhibitor vincristine resulted in enhanced cell death. This study demonstrates the potential of targeting the APC/C and its cofactors as a therapeutic approach in MM.

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.

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.

The DEAD box protein p68: a novel coactivator of Stat3 in mediating oncogenesis

DEAD box RNA helicase p68 acts as a transcriptional coactivator of several oncogenic transcription factors apart from being a vital player of RNA metabolism. Signal transducer and activator of transcription 3 (Stat3) is a major oncogenic contributor of diverse cancers, including that of colon. Deciphering the mechanistic insights of coactivation of Stat3 transcriptional activity may aid in improved therapeutic strategies. Here we report for the first time a novel mechanism of alliance between p68 and Stat3 in stimulating transcriptional activity of Stat3. Interestingly, we observed that the expression of p68 and Stat3 bears strong positive correlation and significant colocalization in normal and colon carcinoma patient samples. We demonstrated that p68 directly interacts with Stat3 in HEK293 cells as well as multiple colon cancer cell lines. Additionally, p68 positively modulated both mRNA and protein expression levels of Stat3 target genes; promoter activity of Stat3 target gene Mcl-1 in multiple colon cancer cell lines. Also, p68 occupied the promoters of multiple Stat3 target genes in enhancing Stat3-dependent transcription. Moreover, the strong positive correlation between the abundance of p68 and Stat3 target genes in the same set of colon carcinoma samples further supported our observations. Enhanced expression levels of Stat3 target genes observed in primary tumors and metastatic lung nodules, generated in mice colorectal allograft model using syngeneic cells stably expressing p68, further reinforced our in vitro findings. Hence, this study unravels novel modes of p68-mediated oncogenesis through coactivation of Stat3 and enhancing Stat3 signaling.

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.

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.

Cantharidin modulates the E2F1/MCM7-miR-106b-93/p21-PTEN signaling axis in MCF-7 breast cancer cells

Cantharidin (CTD) is one of numerous natural products used in traditional Chinese medicine for the treatment of cancer. The aim of the present study was to investigate the effects of CTD on changes in the expression of microRNAs (miRNAs/miRs) and to explore its anti-proliferative effect on MCF-7 breast cancer cells. The proliferation of MCF-7 cells was measured by performing an MTT assay. MCF-7 cells were treated with various concentrations of CTD for 48 h, and the expression profiles of miRNAs in CTD-treated and -untreated MCF-7 cells were detected using miRNA microarray chips. The array data were confirmed by reverse transcription-quantitative polymerase chain reaction and protein expression levels were measured by western blot analysis. The 50% inhibitory concentration of CTD was 1.75 µg/ml following treatment for 48 h and CTD significantly inhibited the proliferation of MCF-7 cells in a dose-dependent manner (P<0.01). Furthermore, microarray analysis identified 35 miRNAs that were up-regulated (fold change ≥2.0 and P<0.01) and 45 miRNAs that were down-regulated (fold change ≤ 0.5 and P<0.01) in response to CTD treatment. Thus, numerous CTD-induced miRNAs appeared to be associated with breast cancer. Notably, CTD repressed the expression of miR-106b-93, its host gene MCM7 and its transcription factor E2F1. In addition, CTD induced an increase in the protein expression levels of miR-106b-93 target genes p21 and phosphatase and tensin homolog. These observations suggested that the modulation of miRNA expression is an important mechanism underlying the biological effects of CTD in breast cancer.

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.

Cantharidin Induces Apoptosis Through the Calcium/PKC-Regulated Endoplasmic Reticulum Stress Pathway in Human Bladder Cancer Cells

Bladder cancer is a common malignancy worldwide. However, there is still no effective therapy for bladder cancer. In this study, we investigated the cytotoxic effects of cantharidin [a natural toxin produced (pure compound) from Chinese blister beetles (Mylabrisphalerata or Mylabriscichorii) and Spanish flies (Cantharis vesicatoria)] in human bladder cancer cell lines (including: T24 and RT4 cells). Treatment of human bladder cancer cells with cantharidin significantly decreased cell viability. The increase in the expressions of caspase-3 activity and cleaved form of caspase-9/-7/-3 were also increased in cantharidin-treated T24 cells. Furthermore, cantharidin increased the levels of phospho-eIF2α and Grp78 and decreased the protein expression of procaspase-12, which was accompanied by the increase in calpain activity in T24 cells. Cantharidin was capable of increasing the intracellular Ca 2+ and the phosphorylation of protein kinase C (PKC) in T24 cells. The addition of BAPTA/AM (a Ca 2+ chelator) and RO320432 (a selective cell-permeable PKC inhibitor) effectively reversed the increase in caspase-3 and calpain activity, the phosphorylation levels of PKC and eIF2α and Grp78 protein expression, and the decrease in procaspase-12 expression induced by cantharidin. Importantly, cantharidin significantly decreased the tumor volume (a dramatic 71% reduction after 21 days of treatment) in nude mice xenografted with T24 cells. Taken together, these results indicate cantharidin induced human bladder cancer cell apoptosis through a calcium/PKC-regulated ER stress pathway. These findings suggest that cantharidin may be a novel and potential anticancer agent targeting on bladder cancer cells.

Interferon-gamma and interlukin-4 patterns in BALB/c mice suffering from cutaneous leishmaniasis treated with cantharidin

Background:

Cutaneous leishmaniasis is a health problem in the world. Lesions should be treated on cosmetically or functionally important sites, such as the face and hands. Cantharidin is a terpenoid compound produced naturally by beetles of Meloidae and Oedemeridae families.

Objectives:

The current study aimed to investigate the effect of cantharidin on Cutaneous Leishmaniasis (CL) lesions and IFN-γ and IL-4 patterns in infected BALB/c mice.

Materials and Methods:

Infected BALB/c mice were divided into five groups as: untreated (control group), eucerin-treated and 0.05%, 0.1% and 0.5% cantharidin-treated. Lesions diameter was measured by Vernier caliper every three days for four weeks. Cytokines levels were measured by enzyme-linked immunosorbent assay (ELISA) using U-CyTech kit.

Results:

The results indicated that treatment with cantharidin exacerbates lesions compared with the controls, except for 0.05% cantharidin dose that restrained lesion growth significantly. Interferon gamma level in cantharidin-treated groups was significantly less than that of the control group. But interlukin-4 level was similar among the groups.

Conclusions:

The current study results indicated that high doses of cantharidin exacerbates leishmaniasis lesion, but low dose of cantharidin inhibits lesion growth.

Cantharidin induces G2/M phase arrest and apoptosis in human gastric cancer SGC-7901 and BGC-823 cells

The aim of the present study was to investigate the effect of cantharidin (CTD) on human gastric cancer cells and to explore the underlying mechanisms of these effects. The human gastric cancer SGC-7901 and BGC-823 cell lines were treated with CTD. MTS assays were then employed to examine cellular proliferation, flow cytometry was used to analyze the cell cycle and apoptosis, and western blot analysis was used to determine protein expression levels. It was found that CTD inhibited the proliferation of the human gastric cancer SGC-7901 and BGC-823 cells in a dose- and time-dependent manner in vitro. CTD also induced G₂/M phase arrest and cellular apoptosis in a dose-dependent manner. In addition, CTD increased the levels of p21, caspase-7, -8 and -9, activated caspase-3, poly ADP ribose polymerase and Bad, but decreased the levels of cyclin-dependent kinase 1, cyclin A and B, B-cell lymphoma-2 (Bcl-2) and Bid. The present results suggested that CTD may inhibit the proliferation of human gastric cancer SGC-7901 and BGC-823 cells in vitro by inducing G₂/M phase arrest and cell apoptosis. CTD may induce cellular G₂/M phase arrest by regulating cycle-associated proteins and induce apoptosis by activating a caspase cascade or regulating the Bcl-2 family proteins.

Cantharidin induces G2/M phase arrest by inhibition of Cdc25c and Cyclin A and triggers apoptosis through reactive oxygen species and the mitochondria‑dependent pathways of A375.S2 human melanoma cells

Cantharidin (CTD), a component of natural mylabris (Mylabris phalerata Pallas) was reported to have high cytotoxicity in many human cancer cell lines. However, it was not reported to affect human melanoma A375.S2 cells. In the present study, we found that CTD induced cell morphological changes and decreased the percentage of viable cells and induced G2/M phase arrest and induction of apoptosis in A375.S2 cells. Results also showed that CTD induced the generation of reactive oxygen species (ROS) and Ca2+ and decreased mitochondria membrane potential and lead to the release of cytochrome c, AIF and Endo G. Further investigation revealed that CTD induced A375.S2 cells with an increase of caspase activation and caspase-dependent apoptotic proteins to trigger correlated pathway mechanisms according to western blotting results. Western blotting was used for examining the changes of G2/M phase arrest and apoptosis-associated protein expression and confocal laser microscopy was used to examine the translocation apoptosis-associated protein. Results showed that CTD increased the protein expression of caspase-3, -8 and -9, cytochrome c, Bax, Bid, Endo G and AIF but inhibited the levels of Bcl-2 and Bcl-x. CTD induced ER stress-associated protein expression such as GRP78, IRE1β, ATF6α and caspase-12. Based on those observations, we suggest that CTD may have potential as a novel anti-cancer agent for the treatment of skin cancer.

Cantharidin induces apoptosis of H460 human lung cancer cells through mitochondria-dependent pathways

Lung cancer is one of the leading causes of death in cancer-related diseases. Cantharidin (CTD) is one of the components of natural mylabris (Mylabris phalerata Pallas). Numerous studies have shown that CTD induced cytotoxic effects on cancer cells. However, there is no report to demonstrate that CTD induced apoptosis in human lung cancer cells. Herein, we investigated the effect of CTD on the cell death via the induction of apoptosis in H460 human lung cancer cells. Flow cytometry assay was used for examining the percentage of cell viability, sub-G1 phase of the cell cycle, reactive oxygen species (ROS) and Ca²⁺ productions and the levels of mitochondrial membrane potential (∆Ψm). Annexin V/PI staining and DNA gel electrophoresis were also used for examining cell apoptosis. Western blot analysis was used to examine the changes of apoptosis associated protein expression and confocal microscopy for examining the translocation apoptosis associated protein. Results indicated that CTD significantly induced cell morphological changes and decreased the percentage of viable H460 cells. CTD induced apoptosis based on the occurrence of sub-G1 phase and DNA fragmentation. We found that CTD increased gene expression (mRNA) of caspase-3 and -8. Moreover, CTD increased ROS and Ca2+ production and decreased the levels of ∆Ψm. Western blot analysis results showed that CTD increased the expression of cleavage caspase-3 and -8, cytochrome c, Bax and AIF but inhibited the levels of Bcl-xL. CTD promoted ER stress associated protein expression such as GRP78, IRE1α, IRE1β, ATF6α and caspase-4 and it also promoted the expression of calpain 2 and XBP-1, but inhibited calpain 1 that is associated with apoptosis pathways. Based on those observations, we suggest that CTD may be used as a novel anticancer agent for the treatment of lung cancer in the future.

The natural compound cantharidin induces cancer cell death through inhibition of heat shock protein 70 (HSP70) and Bcl-2-associated athanogene domain 3 (BAG3) expression by blocking heat shock factor 1 (HSF1) binding to promoters

Heat shock factor 1 (HSF1) enhances the survival of cancer cells under various stresses. The knock-out of HSF1 impairs cancer formation and progression, suggesting that HSF1 is a promising therapeutic target. To identify inhibitors of HSF1 activity, we performed cell-based screening with a library of marketed and experimental drugs and identified cantharidin as an HSF1 inhibitor. Cantharidin is a potent antitumor agent from traditional Chinese medicine. Cantharidin inhibited heat shock-induced luciferase activity with an IC50 of 4.2 μm. In contrast, cantharidin did not inhibit NF-κB luciferase reporter activity, demonstrating that cantharidin is not a general transcription inhibitor. When the HCT-116 colorectal cancer cells were exposed to heat shock in the presence of cantharidin, the induction of HSF1 downstream target proteins, such as HSP70 and BAG3 (Bcl-2-associated athanogene domain 3), was suppressed. HSP70 and its co-chaperone BAG3 have been reported to protect cells from apoptosis by stabilizing anti-apoptotic Bcl-2 family proteins. As expected, treating HCT-116 cancer cells with cantharidin significantly decreased the amounts of BCL-2, BCL-xL, and MCL-1 protein and induced apoptotic cell death. Chromatin immunoprecipitation analysis showed that cantharidin inhibited the binding of HSF1 to the HSP70 promoter and subsequently blocked HSF1-dependent p-TEFb recruitment. Therefore, the p-TEFb-dependent phosphorylation of the C-terminal domain of RNA polymerase II was blocked, arresting transcription at the elongation step. Protein phosphatase 2A inhibition with PP2CA siRNA or okadaic acid did not block HSF1 activity, suggesting that cantharidin inhibits HSF1 in a protein phosphatase 2A-independent manner. We show for the first time that cantharidin inhibits HSF1 transcriptional activity.

Activation of the Janus kinase/signal transducer and activator of transcription pathway in multiple myeloma is not related to point mutations in kinase and pseudokinase domains of JAK1

Abstract Considering the recent impact of tyrosine kinase inhibitors in the treatment of myeloproliferative disorders carrying a recurrent JAK2 mutation not identified in multiple myeloma (MM), this study aimed to search for mutations in kinase and pseudokinase domains of the JAK1 gene in an attempt to define any critical and recurring change that can be used as a therapeutic target. We obtained CD138 + purified cells from 27 bone marrow aspirates of untreated MM, four normal controls and four MM cell lines. After amplification of kinase and pseudokinase domains of JAK1 in cDNA samples, the fragments were automatically sequenced. Seventy-eight percent of MM cases showed at least one polymorphism, all being synonymous single nucleotide polymorphisms (SNPs), with allele frequencies consistent with previous studies in normal European, African American and Asian populations. The four cell lines also showed only synonymous SNPs. Mutations in the kinase and pseudokinase domains of the JAK1 gene do not seem to be important for activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway because we were not able to find any recurrent mutation in a case series of 27 patients and four MM cell lines.

Cantharidin and its anhydride-modified derivatives: relation of structure to insecticidal activity

Cantharidin is a natural compound of novel structure with ideal insecticidal activity. However, the relationship of structure to insecticidal activity of cantharidin and its derivatives has not been ever clarified. To explore what determines the insecticidal activity structurally of cantharidin-related compounds, two series target compounds 6 and 7 were synthesized by replacing the anhydride ring of norcantharidin with an aromatic amine or fatty amine with different electron density, respectively. The structures of these compounds were characterized by 1H NMR, 13C NMR and HRMS-ESI. A bioassay showed that compounds 6 (a-m) lacked any larvicidal activity against Plutella xylostella; whereas their ring-opened partners 7 (a-m) provided a variety of larvicidal activities against P. xylostella, and compound 7f indicated the highest larvicidal activity with LC(50) value of 0.43 mM. The present work demonstrated that the form of the compound (cyclic or ring-opened) or their ability to hydrolyze facilely was the key to determine whether it exhibits larvicidal activity. Moreover, it revealed that the improvement of insecticidal activity required a reasonable combination of both aliphatic amide and aromatic amide moieties, and the type of substituent Y on the aniline ring was critical.

Prostate cancer cells and bone stromal cells mutually interact with each other through bone morphogenetic protein-mediated signals

Functional interactions between cancer cells and the bone microenvironment contribute to the development of bone metastasis. Although the bone metastasis of prostate cancer is characterized by increased ossification, the molecular mechanisms involved in this process are not fully understood. Here, the roles of bone morphogenetic proteins (BMPs) in the interactions between prostate cancer cells and bone stromal cells were investigated. In human prostate cancer LNCaP cells, BMP-4 induced the production of Sonic hedgehog (SHH) through a Smad-dependent pathway. In mouse stromal MC3T3-E1 cells, SHH up-regulated the expression of activin receptor IIB (ActR-IIB) and Smad1, which in turn enhanced BMP-responsive reporter activities in these cells. The combined stimulation with BMP-4 and SHH of MC3T3-E1 cells cooperatively induced the expression of osteoblastic markers, including alkaline phosphatase, bone sialoprotein, collagen type II α1, and osteocalcin. When MC3T3-E1 cells and LNCaP cells were co-cultured, the osteoblastic differentiation of MC3T3-E1 cells, which was induced by BMP-4, was accelerated by SHH from LNCaP cells. Furthermore, LNCaP cells and BMP-4 cooperatively induced the production of growth factors, including fibroblast growth factor (FGF)-2 and epidermal growth factor (EGF) in MC3T3-E1 cells, and these may promote the proliferation of LNCaP cells. Taken together, our findings suggest that BMPs provide favorable circumstances for the survival of prostate cancer cells and the differentiation of bone stromal cells in the bone microenvironment, possibly leading to the osteoblastic metastasis of prostate cancer.

Norcantharidin impairs medulloblastoma growth by inhibition of Wnt/β-catenin signaling

Medulloblastoma is one of the leading causes of morbidity and mortality in pediatric cancer. Wnt-active tumors, an independent molecular subgroup in medulloblastoma, are characterized by a distinct pattern of genomic aberrations. We assessed the anticancer activity of cantharidin and norcantharidin against medulloblastoma, as cell lines in vitro and in athymic nude mice in vivo. Cantharidin and norcantharidin treatment impaired the growth of DAOY and UW228 medulloblastoma cells and promoted the loss of β-catenin activation and the β-catenin nuclearization linked to N-cadherin impairment in vitro. Intra-peritoneal administration of norcantharidin inhibited the growth of intra-cerebellum tumors in orthotopic xenograft nude mice. Analysis of the xenograft tissues revealed enhanced neuronal differentiation and reduced β-catenin expression. Our findings suggest that norcantharidin has potential therapeutic applications in the treatment of medulloblastoma as a result of its ability to cross the blood-brain barrier and its impairment of Wnt-β-catenin signaling.

PP2A inhibitors induce apoptosis in pancreatic cancer cell line PANC-1 through persistent phosphorylation of IKKα and sustained activation of the NF-κB pathway

Serine/threonine protein phosphatase 2A (PP2A), is thought to be a cancer suppresser, as inhibition of PP2A can induce phosphorylation and activation of substrate kinases, most of which can accelerate growth. Interestingly, cantharidin potently inhibits PP2A but efficiently represses various cancer cells. In the present study, we found that PP2A inhibitors, cantharidin or Okadaic acid, inhibited cell viability and triggered apoptosis in PANC-1 pancreatic cancer cell line dependent on PP2A/IKKα/IκBα/p65 NF-κB pathway. The activation of NF-κB pathway up-regulated downstream pro-apoptotic genes, TNF-α, TRAILR1 and TRAILR2, and triggered apoptosis through the extrinsic pathway, indicating that PP2A is a potential target for pancreatic cancer treatment.

Matrine induces apoptosis of human multiple myeloma cells via activation of the mitochondrial pathway

Multiple myeloma (MM) is a hematological malignancy characterized by the uncontrolled proliferation of clonal plasma cells in bone marrow in the elderly. Although there have been tremendous advances in the treatment of MM, it remains an incurable disease. Matrine, a main alkaloid of the traditional Chinese herb Sophora flavescens Ait, has been shown to inhibit cellular proliferation and induce apoptosis of various cancer cells. The aim of this study was to investigate the possibility of matrine as a novel therapeutic agent for patients with MM. We investigated the effects of matrine for its anti-myeloma activity in vitro, and further examined the mechanisms of apoptosis induced by matrine. Matrine inhibited the proliferation of human myeloma cell lines as well as freshly isolated myeloma cells from patients in a dose- and time-dependent manner. Matrine showed a potent induction of apoptosis of myeloma cells. Mitochondrial membrane potential (Deltapsim) was lost and cytochrome c (cyt c) was released from mitochondria to cytosol in myeloma cells treated by matrine for 24 h in a dose-dependent manner. The ratio of Bcl-2/Bax protein decreased, and the percentage of activated caspase-3 increased in myeloma cells treated by matrine for 48 h, but this matrine-induced activity of caspase-3 was completely canceled by the addition of Z-Asp(O-Me)-Glu(O-Me)-Val-Asp(O-Me) fluoromethyl ketone (Z-DEVD-FMK), a caspase-3 inhibitor. The addition of Z-DEVD-FMK partially blocked the apoptotic effect of matrine on myeloma cells. These data indicated that matrine could exert antiproliferative effects on myeloma cells and induce apoptosis of myeloma cells in vitro. The induction of apoptosis appeared to proceed via the mitochondrial pathway, including down-regulation of Bcl-2/Bax ratio, loss of Deltapsim, release of cyt c from mitochondria to cytosol, and activation of caspase-3. These findings support the view that matrine may be a useful candidate as a chemotherapeutic agent against MM.

The antiplasmodial activity of norcantharidin analogs

The antiplasmodial activities of sixty norcantharidin analogs were tested in vitro against a chloroquine sensitive (D6, Sierra Leone) and chloroquine resistant (W2) strains of Plasmodium falciparum. Forty analogs returned IC(50) values <500 μM against at least one of the P. falciparum strains examined. The ring open compound 24 ((1S,4R)-3-(allylcarbamoyl)-7-oxabicyclo[2.2.1]heptane-2-carboxylic acid) is the most active aliphatic analog (D6 IC(50)=3.0±0.0 and W2 IC(50)=3.0±0.8 μM) with a 20-fold enhancement relative to norcantharidin. Surprisingly, seven norcantharimides also displayed good antiplasmodial activity with the most potent, 5 returning D6=8.9±0.9 and W2 IC(50)=12.5±2.2 μM, representing a fivefold enhancement over norcantharidin.

The gold compound auranofin induces apoptosis of human multiple myeloma cells through both down-regulation of STAT3 and inhibition of NF-κB activity

Constitutive activation of NF-κB and STAT3 plays an important role in the cellular proliferation and survival of multiple myeloma cells. We first found that auranofin (AF), a coordinated gold compound, induced a significant level of cell cycle arrest at G1 phase and subsequent apoptosis of myeloma cells. Further, AF inhibited constitutive and IL-6-induced activation of JAK2 and phosphorylation of STAT3 followed by the decreased expression of Mcl-1. AF down-regulated the activation of NF-κB, and the combination of AF and a specific NF-κB inhibitor resulted in a marked decrease of Mcl-1 expression. These results suggest that AF inhibits both IL-6 induced-JAK/STAT pathway and NF-κB activation in myeloma cells.

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

Cantharidin is an active constituent of mylabris, a traditional Chinese medicine. It is a potent and selective inhibitor of protein phosphatase 2A (PP2A) that plays an important role in control of cell cycle, apoptosis, and cell-fate determination. Owing to its antitumor activity, cantharidin has been frequently used in clinical practice. In the present study, we investigated the therapeutic potential of cantharidin in pancreatic cancer. Cantharidin efficiently inhibited the growth of pancreatic cancer cells, but presented a much lighter toxicity effect against normal pancreatic duct cells. It caused G2/M cell-cycle arrest that was accompanied by the down-regulation of cyclin-dependent kinase 1 (CDK1) and up-regulation of p21 expression. It induced apoptosis and elevated the expressions of pro-apoptotic factors tumor necrosis factor-alpha (TNF-alpha), TNF-related apoptosis inducing receptor 1 (TRAILR1), TRAILR2, Bad, Bak, and Bid, and decreased the expression of anti-apoptotic Bcl-2. Activation of caspase-8 and caspase-9 suggested that both extrinsic and intrinsic pathways are involved in the induction of apoptosis. Interestingly, unlike previous studies on other cancer cells, we found that the inhibitory role of cantharidin is independent of oxidative stress in pancreatic cancer cells. Mitogen-activated protein kinases (MAPKs), including ERK, JNK, and p38, were activated after treatment with cantharidin. Inhibition of JNK, but not ERK or p38, alleviated the cytotoxity effect of cantharidin, suggesting cantharidin exerted its anticancer effect through the JNK-dependent way. Hence, in addition to being an attractive candidate compound with therapeutic potential, cantharidin also highlighted the possibility of using PP2A as a therapeutic target for pancreatic cancer treatment.

Constitutive down-regulation of Osterix in osteoblasts from myeloma patients: in vitro effect of Bortezomib and Lenalidomide

Bortezomib and Lenalidomide have been shown to be effective in the control of multiple myeloma (MM) progression. We have investigated their role in the in vitro expression of Osterix by primary osteoblast cultures from MM patients and found that Osterix RNA was constitutively down-regulated in these cells. Treatment of osteoblasts with Bortezomib resulted in an increase of Osterix RNA and in enhanced activity of both BMP-2 and Runx2. Instead, Lenalidomide was unable to modify Osterix transcription. These findings provide additional evidence suggesting that, at least in vitro, Bortezomib promotes the osteoblast maturation whereas Lenalidomide is ineffective.

Innate immune signaling pathways in animals: beyond reductionism

The immune system plays a crucial role in the maintenance of the stability and equilibrium of the internal environment in living organisms. The field of animal innate immunity has been the global focus of immunological research for decades. It is now known that the functions of innate immunity inevitably rely on the action of the molecular machines of the cascades or network of immune signaling pathways. Up to date, many researches on the immune signaling pathways in animals were focused on identifying the component functions or cascade molecules in details, which essentially followed a reductionist paradigm without paying high attention to the integrated features. The main purpose of this article was dedicated to accentuating the shift of this field from a reductionist to a systemic view. First, the former part of this article made efforts to summarize the main aspects of the signaling pathways of animal innate immunity including the web resources, the recapitulation of highlighted pathways, the cross-talks, and the evolutionary considerations, which heavily emphasized the integrated characteristics of the immune signaling pathways. Subsequently, the later part of this article was based on the holistic feature of the immune signaling pathways, mainly dedicated to propose a novel hypothesis. From a whole perspective, the oscillating balance hypothesis was deliberately formulated to characterize the holistic pattern of the signaling transduction network of animal innate immune system, which might help to understand some immunological phenomena through the integral principle of the immune network.

Structural basis of serine/threonine phosphatase inhibition by the archetypal small molecules cantharidin and norcantharidin

The inhibition of a subgroup of human serine/threonine protein phosphatases is responsible for the cytotoxicity of cantharidin and norcantharidin against tumor cells. It is shown that the anhydride rings of cantharidin and norcantharidin are hydrolyzed when bound to the catalytic domain of the human serine/threonine protein phosphatases 5 (PP5c), and the high-resolution crystal structures of PP5c complexed with the corresponding dicarboxylic acid derivatives of the two molecules are reported. Norcantharidin shows a unique binding conformation with the catalytically active Mn2PP5c, while cantharidin is characterized by a double conformation in its binding mode to the protein. Different binding modes of norcantharidin are observed depending of whether the starting ligand is in the anhydride or in the dicarboxylic acid form. All these structures will provide the basis for the rational design of new cantharidin-based drugs.