Putative molecular determinants mediating sensitivity or resistance towards carnosic acid tumor cell responses

Novel Class of Proteasome Inhibitors: In Silico and In Vitro Evaluation of Diverse Chloro(trifluoromethyl)aziridines

The ubiquitin-proteasome pathway (UPP) is the major proteolytic system in the cytosol and nucleus of all eukaryotic cells. The role of proteasome inhibitors (PIs) as critical agents for regulating cancer cell death has been established. Aziridine derivatives are well-known alkylating agents employed against cancer. However, to the best of our knowledge, aziridine derivatives showing inhibitory activity towards proteasome have never been described before. Herein we report a new class of selective and nonPIs bearing an aziridine ring as a core structure. In vitro cell-based assays (two leukemia cell lines) also displayed anti-proliferative activity for some compounds. In silico studies indicated non-covalent binding mode and drug-likeness for these derivatives. Taken together, these results are promising for developing more potent PIs.

Transcriptomics, molecular docking, and cross-resistance profiling of nobiletin in cancer cells and synergistic interaction with doxorubicin upon SOX5 transfection

BACKGROUND

Nobiletin is a polymethoxylated flavone from citrus fruit peels. Among other bioactivities, it acts antioxidative, anti-inflammatory, neuroprotective, and cardiovascular-protective. Nobiletin exerts profound anticancer activity in vitro and in vivo but the underlying mechanisms are not well understood.

PURPOSE

The aim was to unravel the multiple modes of action against cancer cells by bioinformatic and transcriptomic techniques and their verification by molecular pharmacological methods.

METHODS

The in silico methods used were COMPARE analysis of transcriptomic data, signaling pathway analysis, transcription factor binding motif analysis in promoter sequences of target genes, and molecular docking. The in vitro methods used were resazurin assay, isobologram analysis, generation of stably SOX5-tranfected cells, and Western blotting.

RESULTS

Nobiletin was cytotoxic against a wide range of cell lines from different tumor types, including diverse phenotypes to established anticancer drugs (e.g., P-glycoprotein, ABCB5, p53, EGFR). Cross-resistance profiling with 83 standard anticancer drugs revealed a correlation to antihormonal anticancer drugs, which can be explained by the phytoestrogenic features of nobiletin. Transcriptomic analysis showed that the responsiveness of tumor cells was predictable by their specific mRNA expression profile. Nobiletin bound to the transcription factor SOX5 in silico. SOX5 conferred resistance to the control drug doxorubicin but collateral sensitivity to nobiletin in HEK293 cells transfected with a lentiviral GFP-tagged pLOCORF-SOX5 vector. The combination of nobiletin and doxorubicin synergistically killed HEK293-SOX5 cells in isobologram analyses, implying attractive new treatment options.

CONCLUSION

Nobiletin represents an interesting candidate for cancer therapy with broad-spectrum activity and multiple modes of action. The identification of novel targets (i.e., SOX5) may allow its use for targeted tumor therapy in individualized treatment protocols.

Investigation of the influence of chirality and halogen atoms on the anticancer activity of enantiopure palladium(ii) complexes derived from chiral amino-alcohol Schiff bases and 2-picolylamine

In order to evaluate the impact of chirality and halogen-substitution pattern on biological activity, four mixed-ligand enantiomeric pairs of Pd(ii) complexes were synthesized and characterized.

Nimbolide inhibits 2D and 3D prostate cancer cells migration, affects microtubules and angiogenesis and suppresses B-RAF/p.ERK-mediated in vivo tumor growth

BACKGROUND

Prostate cancer (PCa) is the most prominent malignancy among men worldwide. PCa cells have a high tendency to metastasize to various distant organs, and this activity is the main cause of PCa mortality. Nimbolide is a promising phytochemical constituent of neem Azadirachta indica (Meliaceae). Previous studies showed that nimbolide exhibited potent anticancer activity however, its role against PCa tumorigenesis has not been fully elucidated.

PURPOSE

Our work aims to explore the role of nimbolide in regulating the essential tumor-associated processes involved in the metastatic cascade in PCa cells.

STUDY DESIGN

Cytotoxicity assay, wound healing and spheroid invasion assays, western blotting, immunofluorescence, tube-formation assay, in vivo and immunohistochemistry.

METHODS

The cytotoxicity of nimbolide towards PCa cell lines was assessed by resazurin assays. The cell mobility and migration of nimbolide-treated DU145 cells were determined by wound healing and spheroid invasion assays. Tubulin network was visualized using U2OS cells and DU145 cells. The effect of nimbolide on E-cadherin, β-catenin, acetylated α-tubulin and HDAC6 protein expressions levels were measured by Western blot. The potentiality of nimbolide to inhibit angiogenesis was revealed by HUVEC tube-formation assay. Nimbolide antitumor effect was studied in a syngeneic model of murine prostate cancer.

RESULTS

The current study indicated that nimbolide negatively affected the migratory and invasive capacity of DU145 prostate cancer cells in 2D and three-dimensional (3D) spheroid cultures. Interestingly, nimbolide induced downregulation of E-cadherin without any influence on the expression level of β-catenin. Additionally, we demonstrated that nimbolide influenced the microtubule network which was supported by the upregulation of acetylated α-tubulin and the reduction in HDAC6 protein. Moreover, the inhibitory effect of nimbolide on angiogenesis was clearly observed in HUVEC tube formation assay. In vivo experiments revealed the significant suppression of PCa growth and targeting of the B-RAF/p.ERK signaling pathway by nimbolide.

CONCLUSION

Our results showed that nimbolide inhibited 2D and 3D prostate cancer cells migration and downregulated E-cadherin protein expression, a marker for metastatic chemoresistance and tumor recurrence. Nimbolide stabilized the microtubules, combated angiogenesis and suppressed B.RAF/ERK-mediated in vivo tumor growth. Nimbolide may be considered as potential therapeutic agent for metastatic and advanced PCa patients and merits further investigations.

Structure-Activity Relationship of Hydroxycinnamic Acid Derivatives for Cooperating with Carnosic Acid and Calcitriol in Acute Myeloid Leukemia Cells

Plant phenolic compounds have shown the ability to cooperate with one another at low doses in producing enhanced anticancer effects. This may overcome the limitations (e.g., poor bioavailability and high-dose toxicity) in developing these agents as cancer medicines. We have previously reported that the hydroxycinnamic acid derivative (HCAD) methyl-4-hydroxycinnamate and the phenolic diterpene carnosic acid (CA) can synergistically induce massive calcium-dependent apoptosis in acute myeloid leukemia (AML) at non-cytotoxic concentrations of each agent. Here, we explored the chemical nature of the synergy between HCADs and either CA, in inducing cytotoxicity, or the active metabolite of vitamin D (calcitriol), in enhancing the differentiation of AML cells. This was done by determining the structure–activity relationship of a series of hydroxycinnamic acids and their derivatives (methyl hydroxycinnamates and hydroxybenzylideneacetones) in combination with CA or calcitriol. The HCAD/CA synergy required the following critical structural elements of an HCAD molecule: (a) the para-hydroxyl on the phenolic ring, (b) the carbon C7–C8 double bond, and (c) the methyl-esterified carboxyl. Thus, the only HCADs capable of synergizing with CA were found to be methyl-4-hydroxycinnamate and methyl ferulate, which also most potently enhanced calcitriol-induced cell differentiation. Notably, the C7–C8 double bond was the major requirement for this HCAD/calcitriol cooperation. Our findings may contribute to the rational design of novel synergistically acting AML drugs based on prototype combinations of HCADs with other agents studied here.

Curcumin and Carnosic Acid Cooperate to Inhibit Proliferation and Alter Mitochondrial Function of Metastatic Prostate Cancer Cells

Anticancer activities of plant polyphenols have been demonstrated in various models of neoplasia. However, evidence obtained in numerous in vitro studies indicates that proliferation arrest and/or killing of cancer cells require quite high micromolar concentrations of polyphenols that are difficult to reach in vivo and can also be (geno)toxic to at least some types of normal cells. The ability of certain polyphenols to synergize with one another at low concentrations can be used as a promising strategy to effectively treat human malignancies. We have recently reported that curcumin and carnosic acid applied at non-cytotoxic concentrations synergistically cooperate to induce massive apoptosis in acute myeloid leukemia cells, but not in normal hematopoietic and non-hematopoietic cells, via sustained cytosolic calcium overload. Here, we show that the two polyphenols can also synergistically suppress the growth of DU145 and PC-3 metastatic prostate cancer cell cultures. However, instead of cell killing, the combined treatment induced a marked inhibition of cell proliferation associated with G₀/G₁ cell cycle arrest. This was preceded by transient elevation of cytosolic calcium levels and prolonged dissipation of the mitochondrial membrane potential, without generating oxidative stress, and was associated with defective oxidative phosphorylation encompassing mitochondrial dysfunction. The above effects were concomitant with a significant downregulation of mRNA and protein expression of the oncogenic kinase SGK1, the mitochondria-hosted mTOR component. In addition, a moderate decrease in SGK1 phosphorylation at Ser422 was observed in polyphenol-treated cells. The mTOR inhibitor rapamycin produced a similar reduction in SGK1 mRNA and protein levels as well as phosphorylation. Collectively, our findings suggest that the combination of curcumin and carnosic acid at potentially bioavailable concentrations may effectively target different types of cancer cells by distinct modes of action. This and similar combinations merit further exploration as an anticancer modality.

Cytotoxicity of 4-hydroxy-N-(naphthalen-1-yl)-2-oxo-2H-chromene-3-carboxamide in multidrug-resistant cancer cells through activation of PERK/eIF2α/ATF4 pathway

After decades of research, multidrug resistance (MDR) remains a huge challenge in cancer treatment. In this study, the cytotoxic of 4-hydroxy-N-(naphthalen-1-yl)-2-oxo-2H-chromene-3-carboxamide (MCC1734) has been investigated towards multidrug-resistant cancer cell lines. MCC1734 exerted cytotoxicity on cell lines expressing different mechanisms of drug resistance (P-glycoprotein, BCRP, ABCB5, EGFR, p53 knockout) to a different extent. Interestingly, sensitive CCRF-CEM cells and multidrug-resistant P-gp-overexpressing CEM/ADR5000 cells represented similar sensitivity towards MCC1734, indicating MCC1734 can bypass P-gp-mediated resistance. Microarray-based mRNA expression revealed that MCC1734 affected cells by multiple pathways, including cell cycle regulation, mitochondrial dysfunction, apoptosis signaling, and EIF2 signaling. MCC1734 stimulated the generation of excessive reactive oxygen species and the collapse of mitochondria membrane potential in CCRF-CEM cells, companied by the arrest of the cell cycle in the G₂M phase and apoptosis induction as determined by flow cytometry. In addition, our immunoblotting analysis highlighted that MCC1734 triggered endoplasmic reticulum (ER) stress, evidenced by the activation of p-PERK, p-eIF2α, ATF4 and CHOP. The anti-cancer effects of MCC1734 were further observed in vivo using human xenograft tumors transplanted to zebrafish, providing further support for MCC1734 as a promising new candidate for cancer drug development.

A novel moniliformin derivative as pan-inhibitor of histone deacetylases triggering apoptosis of leukemia cells

New and potent agents that evade multidrug resistance (MDR) and inhibit epigenetic modifications are of great interest in cancer drug development. Here, we describe that a moniliformin derivative (IUPAC name: 3-(naphthalen-2-ylsulfanyl)-4-{[(2Z)-1,3,3-trimethyl-2,3-dihydro-1H-indol-2-ylidene]methyl}cyclobut-3-ene-1,2-dione; code: MCC1381) bypasses P-gp-mediated MDR. Using transcriptomics, we identified a large number of genes significantly regulated in response to MCC1381, which affected the cell cycle and disturbed cellular death and survival. The potential targets of MCC1381 might be histone deacetylases (HDACs) as predicted by SwissTargetPrediction. In silico studies confirmed that MCC1381 presented comparable affinity with HDAC1, 2, 3, 6, 8 and 11. Besides, the inhibition activity of HDACs was dose-dependently inhibited by MCC1381. Particularly, a strong binding affinity was observed between MCC1381 and HDAC6 by microscale thermophoresis analysis. MCC1381 decreased the expression of HDAC6, inversely correlated with the increase of acetylated HDAC6 substrates, acetylation p53 and α-tubulin. Furthermore, MCC1381 arrested the cell cycle at the G₂/M phase, induced the generation of reactive oxygen species and collapse of the mitochondrial membrane potential. MCC1381 exhibited in vivo anti-cancer activity in xenografted zebrafish. Collectively, MCC1381 extended cytotoxicity towards P-gp-resistant leukemia cancer cells and may act as a pan-HDACs inhibitor, indicating that MCC1381 is a novel candidate for cancer therapy.

Xylochemical Synthesis and Biological Evaluation of Shancigusin C and Bletistrin G

The biological activities of shancigusin C (1) and bletistrin G (2), natural products isolated from orchids, are reported along with their first total syntheses. The total synthesis of shancigusin C (1) was conducted by employing the Perkin reaction to forge the central stilbene core, whereas the synthesis of bletistrin G (2) was achieved by the Wittig olefination followed by several regioselective aromatic substitution reactions. Both syntheses were completed by applying only renewable starting materials according to the principles of xylochemistry. The cytotoxic properties of shancigusin C (1) and bletistrin G (2) against tumor cells suggest suitability as a starting point for further structural variation.

2α-Hydroxyalantolactone from Pulicaria undulata: activity against multidrug-resistant tumor cells and modes of action

BACKGROUND

Sesquiterpene lactones having α-methylene-γ-lactone moiety are promising natural metabolites showing various biological activity. One of the major metabolites isolated from Pulicaria undulata, 2α-hydroxyalantolactone (PU-1), has not been investigated in detail yet. Multidrug resistance (MDR) represents a major obstacle for cancer chemotherapy and the capability of novel natural products to overcoming MDR is of great interest.

PURPOSE

Exploring the molecular modes of action for potent natural product metabolites.

METHODS

The resazurin reduction assay was employed to evaluate the cytotoxicity of PU-1 on sensitive and their corresponding drug-resistant cell lines (overexpressing P-glycoprotein, BCRP, ABCB5, ΔEGFR, or TP53 knockout). Gene expression profiling was performed by transcriptome-wide mRNA microarray in the human CCRF-CEM leukemic cells after treatment with PU-1. The top significantly up- or down-regulated genes were identified by Chipster program and analyzed using Ingenuity Pathway Analysis (IPA) software. Finally, flow cytometry and Western blotting were performed for cell cycle analyses and apoptosis detection.

RESULTS

The sesquiterpene lactone, PU-1, showed potent cytotoxicity towards the drug-sensitive and -resistant cell lines. Transcriptome-wide mRNA expression profiling and pathway analysis pointed to genes involved in DNA damage response and G2/M cell cycle arrest. G2/M arrest was verified by flow cytometry and further confirmed by the upregulation of p21 and downregulation of p-CDC25C expression in Western blotting. Moreover, the suggested DNA damage checkpoint regulation was confirmed by immunofluorescence and Western blotting by upregulation of pS345 Chk1, p-H3 and γ-H2AX. Furthermore, PU-1 inhibited PI3K/AKT pathway, which is involved in signaling DNA damage and G2/M arrest. Cells ultimately induced apoptosis upon PU-1 treatment.

CONCLUSIONS

PU-1 is a potent natural product inhibiting otherwise drug-resistant human tumor cell growth through DNA damage, G2/M cell cycle arrest and apoptosis.

Cytotoxicity of apigenin toward multiple myeloma cell lines and suppression of iNOS and COX-2 expression in STAT1-transfected HEK293 cells

BACKGROUND

Apigenin is one of the most abundant dietary flavonoids that possesses multiple bio-functions.

PURPOSE

This study was designed to determine the influence of apigenin on gene expressions, cancer cells, as well as STAT1/COX-2/iNOS pathway mediated inflammation and tumorigenesis in HEK293-STAT1 cells. Furthermore, the cytotoxic activity toward multiple myeloma (MM) cell lines was investigated.

METHODS

Bioinformatic analyses were used to predict the sensitivity and resistance of tumor cells toward apigenin and to determine cellular pathways influenced by this compound. The cytotoxic and ferroptotic activity of apigenin was examined by the resazurin reduction assay. Additionally, we evaluated apoptosis, and cell cycle distribution, induction of reactive oxygen species (ROS) and loss of integrity of mitochondrial membrane (MMP) by using the flow cytometry analysis. DAPI staining was used to detect characteristic apoptotic features. Furthermore, we verified its anti-inflammatory and additional mechanism of cell death by western blotting.

RESULTS

COMPARE and hierarchical cluster analyses exhibited that 29 of 55 tumor cell lines were sensitive against apigenin (p < 0.001). The Ingenuity Pathway Analysis data showed that important bio-functions affected by apigenin were: gene expression, cancer, hematological system development and function, inflammatory response, and cell cycle. The STAT1 transcription factor was chosen as target protein on the basis of gene promoter binding motif analyses. Apigenin blocked cell proliferation of wild-type HEK293 and STAT1 reporter cells (HEK293-STAT1), promoted STAT1 suppression and subsequent COX-2 and iNOS inhibition. Apigenin also exhibited synergistic activity in combination with doxorubicin toward HEK293-STAT1 cells. Apigenin exerted excellent growth-inhibitory activity against MM cells in a concentration-dependent manner with the greatest activity toward NCI-H929 (IC₅₀ value: 10.73 ± 3.21 μM). Apigenin induced apoptosis, cell cycle arrest, ferroptosis and autophagy in NCI-H929 cells.

CONCLUSION

Apigenin may be a suitable candidate for MM treatment. The inhibition of the STAT1/COX-2/iNOS signaling pathway by apigenin is an important mechanism not only in the suppression of inflammation but also in induction of apoptosis.