Inhibition of protein kinase C by isojacareubin suppresses hepatocellular carcinoma metastasis and induces apoptosis in vitro and in vivo

Profiling Kinase Activities for Precision Oncology in Diffuse Gastric Cancer

Gastric cancer (GC) remains a leading cause of cancer-related mortality globally. This is due to the fact that majority of the cases of GC are diagnosed at an advanced stage when the treatment options are limited and prognosis is poor. The diffuse subtype of gastric cancer (DGC) under Lauren's classification is more aggressive and usually occurs in younger patients than the intestinal subtype. The concept of personalized medicine is leading to the identification of multiple biomarkers in a large variety of cancers using different combinations of omics technologies. Proteomic changes including post-translational modifications are crucial in oncogenesis. We analyzed the phosphoproteome of DGC by using paired fresh frozen tumor and adjacent normal tissue from five patients diagnosed with DGC. We found proteins involved in the epithelial-to-mesenchymal transition (EMT), c-MYC pathway, and semaphorin pathways to be differentially phosphorylated in DGC tissues. We identified three kinases, namely, bromodomain adjacent to the zinc finger domain 1B (BAZ1B), WNK lysine-deficient protein kinase 1 (WNK1), and myosin light-chain kinase (MLCK) to be hyperphosphorylated, and one kinase, AP2-associated protein kinase 1 (AAK1), to be hypophosphorylated. LMNA hyperphosphorylation at serine 392 (S392) was demonstrated in DGC using immunohistochemistry. Importantly, we have detected heparin-binding growth factor (HDGF), heat shock protein 90 (HSP90), and FTH1 as potential therapeutic targets in DGC, as drugs targeting these proteins are currently under investigation in clinical trials. Although these new findings need to be replicated in larger study samples, they advance our understanding of signaling alterations in DGC, which could lead to potentially novel actionable targets in GC.

The role of PKC and PKD in CXCL12 and CXCL13 directed malignant melanoma and acute monocytic leukemic cancer cell migration

Cancer metastasis is the leading cause of cancer related mortality. Chemokine receptors and proteins in their downstream signalling axis represent desirable therapeutic targets for the prevention of metastasis. Despite this, current therapeutics have experienced limited success in clinical trials due to a lack of insight into the downstream signalling pathway of specific chemokine receptor cascades in different tumours. In this study, we investigated the role of protein kinase C (PKC) and protein kinase D (PKD) in CXCL12 and CXCL13 stimulated SK-MEL-28 (malignant melanoma) and THP-1 (acute monocytic leukaemia) cell migration. While PKC and PKD had no active role in CXCL12 or CXCL13 stimulated THP-1 cell migration, PKC and PKD inhibition reduced CXCL12 stimulated migration and caused profound effects upon the cytoskeleton of SK-MEL-28 cells. Furthermore, only PKC and not PKD inhibition reduced CXCL13 stimulated migration in SK-MEL-28 cells however PKC inhibition failed to stimulate any changes to the actin cytoskeleton. These findings indicate that PKC inhibitors would be a useful therapeutic for the prevention of both CXCL12 and CXCL13 stimulated migration and PKD inhibitors for CXCL12 stimulated migration in malignant melanoma.

Total syntheses of pongaflavone and its natural analogues

The efficient total synthesis of anti-tumor natural product pongaflavone (1) was described starting from commercially available 2,4-dihydroxyacetophenone (9) via seven steps and in 16% overall yield. Its two natural analogues pongachromene (2) and 7,8-(2",2"-dimethylpyrano)-5,3',4'-trihydroxy-3-methoxyflavone (3) were also synthesized following the similar procedure with the yields of 11% and 18%, respectively. Their preliminary anti-tumor activities were evaluated by the inhibition effect on A549 cells. The result showed that this kind of natural products exhibited different levels of anti-tumor activity. Among them, pongachromene (2) displayed the best anti-tumor activity.

Discovery of Isojacareubin as a covalent inhibitor of SARS-CoV-2 main protease using structural and experimental approaches

The ongoing pandemic with the emergence of immune evasion potential and, particularly, the current omicron subvariants intensified the situation further. Although vaccines are available, the immune evasion capabilities of the recent variants demand further efficient therapeutic choices to control the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Hence, considering the necessity of the small molecule inhibitor, we target the main protease (3CLpro), which is an appealing target for the development of antiviral drugs against SARS-CoV-2. High-throughput molecular in silico screening of South African natural compounds database reported Isojacareubin and Glabranin as the potential inhibitors for the main protease. The calculated docking scores were reported to be -8.47 and -8.03 kcal/mol, respectively. Moreover, the structural dynamic assessment reported that Isojacareubin in complex with 3CLpro exhibit a more stable dynamic behavior than Glabranin. Inhibition assay indicated that Isojacareubin could inhibit SARS-CoV-2 3CLpro in a time- and dose-dependent manner, with half maximal inhibitory concentration values of 16.00 ± 1.35 μM (60 min incubation). Next, the covalent binding sites of Isojacareubin on SARS-CoV-2 3CLpro was identified by biomass spectrometry, which reported that Isojacareubin can covalently bind to thiols or Cysteine through Michael addition. To evaluate the inactivation potency of Isojacareubin, the inactivation kinetics was further investigated. The inactivation kinetic curves were plotted according to various concentrations with gradient-ascending incubation times. The KI value of Isojacareubin was determined as 30.71 μM, whereas the Kinact value was calculated as 0.054 min-1 . These results suggest that Isojacareubin is a covalent inhibitor of SARS-CoV-2 3CLpro .

Morin Hydrate Sensitizes Hepatoma Cells and Xenograft Tumor towards Cisplatin by Downregulating PARP-1-HMGB1 Mediated Autophagy

The cross-talk between apoptosis and autophagy influences anticancer drug sensitivity and cellular death in various cancer cell lines. However, the fundamental mechanisms behind this phenomenon are still unidentified. We demonstrated anti-cancerous role of cisplatin (CP) and morin hydrate (Mh) as an individual and/or in combination (CP-Mh) in hepatoma cells and tumor model. Exposure of CP resulted in the production of intracellular reactive oxygen species (ROS)-mediated cellular vacuolization, expansion of mitochondria membrane and activation of endoplasmic reticulum (ER)-stress. Consequently, Cyt c translocation led to the increase of Bax/Bcl-2 ratio, which simultaneously triggered caspase-mediated cellular apoptosis. In addition, CP-induced PARP-1 activation led to ADP-ribosylation of HMGB1, which consequently developed autophagy as evident by the LC3I/II ratio. Chemically-induced inhibition of autophagy marked by increased cell death signified a protective role of autophagy against CP treatment. CP-Mh abrogates the PARP-1 expression and significantly reduced HMGB1-cytoplasmic translocation with subsequent inhibition of the HMGB1-Beclin1 complex formation. In the absence of PARP-1, a reduced HMGB1 mediated autophagy was observed followed by induced caspase-dependent apoptosis. To confirm the role of PARP-1-HMGB1 signaling in autophagy, we used the PARP-1 inhibitor, 4-amino-1,8-naphthalimide (ANI), HMGB1 inhibitor, ethyl pyruvate (EP), autophagy inhibitors, 3-methyl adenine (3-MA) and bafilomycin (baf) and small interfering RNAs (siRNA) to target Atg5 in combination of CP and Mh. Exposure to these inhibitors enhanced the sensitivity of HepG2 cells to CP. Collectively, our findings indicate that CP-Mh in combination served as a prominent regulator of autophagy and significant inducer of apoptosis that maintains a homeostatic balance towards HepG2 cells and the subcutaneous tumor model.

Anti-Tumor Xanthones from Garcinia nujiangensis Suppress Proliferation, and Induce Apoptosis via PARP, PI3K/AKT/mTOR, and MAPK/ERK Signaling Pathways in Human Ovarian Cancers Cells

BACKGROUND

Ovarian cancer (OC) is a serious public health concern in the world. It is important to develop novel drugs to inhibit OC.

PURPOSE

This study investigated the isolation, elucidation, efficiency, molecular docking, and pharmaceutical mechanisms of xanthones isolated from Garcinia nujiangensis.

METHODS

Xanthones were isolated, and purified by different chromatography, including silica gel, reversed-phase silica gel (ODS-C18), and semipreparative HPLC, then identified by analysis of their spectral data. Three xanthones were estimated for their efficiency on the human OC cells HEY and ES-2. 2 was found to be the most potent cytotoxic xanthones of those tested. Further, its mechanisms of action were explored by molecular docking, cell apoptosis, and Western blotting analysis.

RESULTS

Bioassay-guided fractionation of the fruits of Garcinia nujiangensis led to the separation of a new xanthone named nujiangexanthone G (1) and two known xanthones. Among these, isojacareubin (2) exhibited the most potent cytotoxic compound against the HEY and ES-2 cell lines. The analysis of Western blot suggested that 2 inhibited OC via regulating the PARP, PI3K/AKT/mTOR, and ERK/MAPK signal pathways in the HEY cell lines.

CONCLUSION

In conclusion, isojacareubin (2) might be a potential drug for the treatment of OC.

Cytotoxic Xanthones from Hypericum stellatum, an Ethnomedicine in Southwest China

Hypericum stellatum, a species endemic to China, is used to treat hepatitis by several ethnic groups in Guizhou Province. This research was inspired by the traditional medicinal usage of H. stellatum, and aims to explore the phytochemistry and bioactivity of H. stellatum to explain why local people in Guizhou widely apply H. stellatum for liver protection. In this study, two new prenylated xanthones, hypxanthones A (8) and B (9), together with seven known compounds, were isolated from the aerial parts of the plant. Spectroscopic data as well as experimental and calculated ECD spectra were used to establish the structures of these compounds. Six xanthones isolated in this study, together with four xanthones previously isolated from H. stellatum, were evaluated for their growth-inhibitory activities against five human liver carcinoma cell lines to analyze the bioactivity and structure-activity relationship of xanthones from H. stellatum. Isojacareubin (6) showed significant cytotoxicity against five human liver carcinoma cell lines, with an IC₅₀ value ranging from 1.41 to 11.83 μM, which was stronger than the positive control cisplatin (IC₅₀ = 4.47–20.62 μM). Hypxanthone B (9) showed moderate cytotoxicity to three of the five cell lines. Finally, structure-activity analysis revealed that the prenyl and pyrano substituent groups of these xanthones contributed to their cytotoxicity.

Deranged hepatocyte intracellular Ca2+ homeostasis and the progression of non-alcoholic fatty liver disease to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and the sixth in women. Non-alcoholic fatty liver disease (NAFLD) is now one of the major risk factors for HCC. NAFLD, which involves the accumulation of excess lipid in cytoplasmic lipid droplets in hepatocytes, can progress to non-alcoholic steatosis, fibrosis, and HCC. Changes in intracellular Ca²⁺ constitute important signaling pathways for the regulation of lipid and carbohydrate metabolism in normal hepatocytes. Recent studies of steatotic hepatocytes have identified lipid-induced changes in intracellular Ca²⁺, and have provided evidence that altered Ca²⁺ signaling exacerbates lipid accumulation and may promote HCC. The aims of this review are to summarise current knowledge of the lipid-induced changes in hepatocyte Ca²⁺ homeostasis, to comment on the mechanisms involved, and discuss the pathways leading from altered Ca²⁺ homeostasis to enhanced lipid accumulation and the potential promotion of HCC. In steatotic hepatocytes, lipid inhibits store-operated Ca²⁺ entry and SERCA2b, and activates Ca²⁺ efflux from the endoplasmic reticulum (ER) and its transfer to mitochondria. These changes are associated with changes in Ca²⁺ concentrations in the ER (decreased), cytoplasmic space (increased) and mitochondria (likely increased). They lead to: inhibition of lipolysis, lipid autophagy, lipid oxidation, and lipid secretion; activation of lipogenesis; increased lipid; ER stress, generation of reactive oxygen species (ROS), activation of Ca²⁺/calmodulin-dependent kinases and activation of transcription factor Nrf2. These all can potentially mediate the transition of NAFLD to HCC. It is concluded that lipid-induced changes in hepatocyte Ca²⁺ homeostasis are important in the initiation and progression of HCC. Further research is desirable to better understand the cause and effect relationships, the time courses and mechanisms involved, and the potential of Ca²⁺ transporters, channels, and binding proteins as targets for pharmacological intervention.

The active fraction from the tuber of Bolboschoenus yagara inhibits melanoma B16 cells metastasis LPS-induced in vitro and in vivo

This study was to identify anti-metastatic active fractions and compounds of Bolboschoenus yagara (B. yagara). The results indicated that 50 µg/mL ethyl acetate fraction (Et) can dramatically inhibit mouse melanoma B16 cells migration and invasion in vitro. In B16 cells pulmonary and hepatic metastasis assays, 50 µg/mL Et alleviated mouse lung and liver weights, the number of metastatic nodules and the levels of TNF-α and IL-6 in mouse serum and organs. Histological studies showed that Et fraction was able to prevent liver and lung metastasis. And the inhibition of 50 µg/mL Et fraction against hepatic metastasis was almost equivalent to that of 1 µM TAK242. In addition, fourteen compounds of Et were quantified by HPLC analysis, in which, isocoumarins, stilbenes and xanthones obviously abated LPS-modulated B16 cells migration and invasion.[Formula: see text].

Synthesis and biological evaluation of α-santonin derivatives as anti-hepatoma agents

A series of α-santonin-derived compounds as potentially anti-hepatoma agents were designed and synthesized in an effort to find novel therapeutic agents. Among them, derivative 5h was more potent than the positive control 5-fluorouracil (5-Fu) on HepG-2, QGY-7703 and SMMC-7721 with IC₅₀ values of 7.51, 3.06 and 4.08 μM, respectively. The structure-activity relationships (SARs) of these derivatives were discussed. In addition, flow cytometry and western blot assay revealed that the derivatives induced hepatoma cells apoptosis by facilitating apoptosis-related proteins expressions. Our findings suggested that these α-santonin-derived analogues hold promise as chemotherapeutic agents for the treatment of human hepatocellular cancer.

The antitumor natural product tanshinone IIA inhibits protein kinase C and acts synergistically with 17-AAG

Tanshinone IIA (Tan IIA), the primary bioactive compound derived from the traditional Chinese medicine (TCM) Salvia miltiorrhiza Bunge, has been reported to possess antitumor activity. However, its antitumor mechanisms are not fully understood. To resolve the potential antitumor mechanism(s) of Tan IIA, its gene expression profiles from our database was analyzed by connectivity map (CMAP) and the CMAP-based mechanistic predictions were confirmed/validated in further studies. Specifically, Tan IIA inhibited total protein kinase C (PKC) activity and selectively suppressed the expression of cytosolic and plasma membrane PKC isoforms ζ and ε. The Ras/MAPK pathway that is closely regulated by the PKC signaling is also inhibited by Tan IIA. While Tan IIA did not inhibit heat shock protein 90 (Hsp90), it synergistically enhanced the antitumor efficacy of the Hsp90 inhibitors 17-AAG and ganetespib in human breast cancer MCF-7 cells. In addition, Tan IIA significantly inhibited PI3K/Akt/mTOR signaling, and induced both cell cycle arrest and autophagy. Collectively, these studies provide new insights into the molecular mechanisms responsible for antitumor activity of Tan IIA.

Therapeutic targeting of oncogenic transcription factors by natural products in eye cancer

Carcinogenesis has a multifactorial etiology, and the underlying molecular pathogenesis is still not entirely understood, especially for eye cancers. Primary malignant intraocular neoplasms are relatively rare, but delayed detection and inappropriate management contribute to poor outcomes. Conventional treatment, such as orbital exenteration, chemotherapy, or radiotherapy, alone results in high mortality for many of these malignancies. Recent sequential multimodal therapy with a combination of high-dose chemotherapy, followed by appropriate surgery, radiotherapy, and additional adjuvant chemotherapy has helped dramatically improve management. Transcription factors are proteins that regulate gene expression by modulating the synthesis of mRNA. Since transcription is a dominant control point in the production of many proteins, transcription factors represent key regulators for numerous cellular functions, including proliferation, differentiation, and apoptosis, making them compelling targets for drug development. Natural compounds have been studied for their potential to be potent yet safe chemotherapeutic drugs. Since the ancient times, plant-derived bioactive molecules have been used to treat dreadful diseases like cancer, and several refined pharmaceutics have been developed from these compounds. Understanding targeting mechanisms of oncogenic transcription factors by natural products can add to our oncologic management toolbox. This review summarizes the current findings of natural products in targeting specific oncogenic transcription factors in various types of eye cancer.

MZF-1/Elk-1/PKCα is Associated with Poor Prognosis in Patients with Hepatocellular Carcinoma

Background: Protein kinase C alpha (PKCα) is a key signaling molecule in human cancer development. As a therapeutic strategy, targeting PKCα is difficult because the molecule is ubiquitously expressed in non-malignant cells. PKCα is regulated by the cooperative interaction of the transcription factors myeloid zinc finger 1 (MZF-1) and Ets-like protein-1 (Elk-1) in human cancer cells.

Methods: By conducting tissue array analysis, herein, we determined the protein expression of MZF-1/Elk-1/PKCα in various cancers.

Results: The data show that the expression of MZF-1/Elk-1 is correlated with that of PKCα in hepatocellular carcinoma (HCC), but not in bladder and lung cancers. In addition, the PKCα down-regulation by shRNA Elk-1 was only observed in the HCC SK-Hep-1 cells. Blocking the interaction between MZF-1 and Elk-1 through the transfection of their binding domain MZF-1_60-72 decreased PKCα expression. This step ultimately depressed the epithelial-mesenchymal transition potential of the HCC cells.

Conclusion: These findings could be used to develop an alternative therapeutic strategy against patients with the PKCα-derived HCC.

Benzophenones and xanthone derivatives from Garcinia schomburgkiana-induced P-glycoprotein overexpression in human colorectal Caco-2 cells via oxidative stress-mediated mechanisms

BACKGROUND

Up-regulation of P-gp is an adaptive survival mechanism of cancer cells from chemotherapy. Three new phytochemicals including two benzophenones, guttiferone K (GK) and oblongifolin C (OC), and a xanthone, isojacaruebin (ISO), are potential anti-cancer agents. However, the capability of these compounds to increase multidrug-resistance (MDR) through P-gp up-regulation in cancer cells has not been reported.

PURPOSE

This study was to investigate the effects of GK, OC and ISO on P-gp up-regulation in colorectal adenocarcinoma cells (Caco-2 cells). In addition, the mechanisms underlying their inductive effect were also determined.

METHODS

The inductive effect of GK, OC and ISO on P-gp expression at transcription level was measured by real-time reverse transcription polymerase chain reaction. The reactive oxygen species production was determined by 2', 7'-dichlorofluorescin diacetate assay. The protein content of P-gp and involvement of mitogen-activated protein kinases (MAPK) pathway was evaluated by western blot analysis.

RESULTS

GK, OC and ISO (50 µM, 24 h) were able to increase the amount of MDR1 mRNA and protein in Caco-2 cells. The presence of N-acetyl-l-cysteine significantly prevented the inductive effect of GK, OC and ISO on MDR1 mRNA level. Moreover, MAPK inhibitors including U0126 (an ERK1/2/MAPK inhibitor) and SB202190 (p38/MAPK inhibitor) suppressed an increase of MDR1 mRNA levels in the cells treated with benzophenones (GK, OC) and xanthone ISO, respectively. These findings were in agreement with the increase of phosphorylated form of either ERK1/2 (p-ERK1/2) or p38 (p-p38) upon treatment of the cells with these three compounds. In addition, OC and ISO, but not GK, increased mRNA of c-Jun level.

CONCLUSION

The benzophenones GK, OC and xanthone ISO are likely MDR inducers through up-regulation of P-gp expression at transcription level. Their molecular mechanisms involve oxidative stress-mediated activation of MAPK signaling pathway.