Trial watch: Cardiac glycosides and cancer therapy

Transcriptomic analysis of digitoxin: Synergy with doxorubicin in HER2-overexpressing MDA-MB-453 breast cancer cells

The aim of this research is to further elucidate the mechanism of action of digitoxin and explore its potential synergistic effects with doxorubicin. MDA-MB-453 breast cancer cells, characterized by HER2 overexpression and low ER levels, were exposed to digitoxin at three doses (0.1 (0.13 μM), 0.2, and 1.0 μg/ml). RNA was extracted over 6 and 24-h periods to subject to transcriptomic analysis, using IPA software. To validate the findings, cell growth inhibitory, Western blot, and enzymatic assays were performed. In addition, molecular docking was carried out to assess the interaction of digitoxin and doxorubicin with the Na+/K+-ATPase. IPA analysis indicates that the effects of digitoxin are dose and time-dependent; at the highest dose, digitoxin activates the transcription of cholesterol biosynthetic genes at early times, and the stress response gene ATF3 at later times. Key genes at the central point of the pathways altered by digitoxin include: (activated) TP53, CREB1, and TGFB1 at the highest dose at 6 and 24 h and (repressed) MYCN at the middle dose at 24 h. ATF3 also plays a role in the action of doxorubicin, and digitoxin exhibits synergy with doxorubicin in MDA-MB-453 cells. Molecular docking studies demonstrated binding potential of both digitoxin and doxorubicin to Na+/K+-ATPase, with doxorubicin showing a stronger binding affinity. Our results highlight the role of bioelectric signaling through ion channel proteins, like Na+/K+-ATPase, in cancer development. Our findings suggest it is worthwhile to study the use of digitoxin, alone or combined with doxorubicin, for treating estrogen receptor-negative breast cancer, but caution of possible risks to patients who take both drugs in combination.

HPLC-MS standardization and validation methods for determination of calactin content in dichloromethane fraction of Calotropis gigantea (L.) Dryand. (Niu jiao gua) stem bark and its application in prediction of anticancer activities

Calactin, a doubly-linked cardenolide, is commonly found in Apocynaceae family including Calotropis gigantea (L.) Dryand. (Niu jiao gua, C. gigantea). This phytochemical has gained recognition for its potential as an anticancer agent and a marker for anticancer properties. Our previous reports demonstrated the remarkable anti-liver and anti-colon cancer activities both in vitro and in vivo of the dichloromethane fraction from the stem barks of C. gigantea (CGD). However, quantitative analysis of calactin content in CGD by using a high-performance liquid chromatography (HPLC) - ultraviolet (UV) method was limited. Therefore, this study aimed to develop more sensitive and reliable method for measurement of calactin in CGD by using a HPLC- electrospray ionization mass spectrometry (ESI-MS) for its application on quality control and prediction of anticancer activity of CGD. The study utilized a HPLC-ESI-MS system, negative mode, for standardization and validation. An octadecylsilane column and a mixture of acetonitrile and water containing 0.1 % formic acid in gradient system were used as a stationary phase and a mobile phase, respectively. The method was validated in terms of linearity, accuracy, precision, recovery, limit of detection (LOD), and limit of quantitation (LOQ). The linearity of the developed technique was verified within the calactin concentrations range from 1 to 50 μg/mL, exhibiting a linear coefficient of determination (R2) greater than 0.998. The LOD and LOQ were 0.1 and 1 μg/mL, respectively. The proposed methodology met the acceptance criteria according to the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH) guideline Q2(R1). Therefore, the method was suitable for the quality control of CGD. Additionally, we suggest applying the established protocol to quantify the calactin contents in CGDs collected over a period of one year (12 months) to investigate the correlation to their cytotoxicities against human cell lines derived from colon cancer (HCT116), human hepatoblastoma (HepG2) and human cell line derived from stomach cancer metastasized to liver (MKN74). This will help in predicting its cytotoxicity against HCT116, HepG2 and MKN74. In summary, the established HPLC-ESI-MS method is suitable for both quality control and predicting of CGD anticancer activities for further utilization.

The antiangiogenic effect of digitoxin is dependent on a ROS-elicited RhoA/ROCK pathway activation

We previously showed that digitoxin inhibits angiogenesis and cancer cell proliferation and migration and these effects were associated to protein tyrosine kinase 2 (FAK) inhibition. Considering the interactions between FAK and Rho GTPases regulating cell cytoskeleton and movement, we investigated the involvement of RhoA and Rac1 in the antiangiogenic effect of digitoxin. Phalloidin staining of human umbilical vein endothelial cells (HUVECs) showed the formation of stress fibers in cells treated with 10 nM digitoxin. By Rhotekin- and Pak1- pull down assays, detecting the GTP-bound form of GTPases, we observed that digitoxin (10-25 nM) induced sustained (0.5-6 h) RhoA activation with no effect on Rac1. Furthermore, inhibition of HUVEC migration and capillary-like tube formation by digitoxin was counteracted by hindering RhoA-ROCK axis with RhoA silencing or Y-27632 treatment. Digitoxin did not decrease p190RhoGAP phosphorylation at Tyr1105 (a site targeted by FAK), suggesting that RhoA activation was independent from FAK inhibition. Because increasing evidence points to a redox regulation of RhoA, we measured intracellular ROS and found that digitoxin treatment enhanced ROS levels in a concentration-dependent manner (1-25 nM). Notably, the flavoprotein inhibitor DPI or the pan-NADPH oxidase (NOX) inhibitor VAS-2870 antagonized both ROS increase and RhoA activation by digitoxin. Our results provide evidence that inhibition of HUVEC migration and tube formation by digitoxin is dependent on ROS production by endothelial NOX, which leads to the activation of RhoA/ROCK pathway. Digitoxin effects on proteins regulating cytoskeletal organization and cell motility could have a wider impact on cancer progression, beyond the antiangiogenic activity.

Negative regulation of thyroid adenoma-associated protein (THADA) in the cardiac glycoside-induced anti-cancer effect

Cardiac glycosides, known as inhibitors of Na+,K+-ATPase, have anti-cancer effects such as suppression of cancer cell proliferation and induction of cancer cell death. Here, we examined the signaling pathway elicited by cardiac glycosides in the human hepatocellular carcinoma HepG2 cells and human epidermoid carcinoma KB cells. Three kinds of cardiac glycosides (ouabain, oleandrin, and digoxin) inhibited the cancer cell proliferation and decreased the expression level of thyroid adenoma-associated protein (THADA). Interestingly, the knockdown of THADA inhibited cancer cell proliferation, and the proliferation was significantly rescued by re-expression of THADA in the THADA-knockdown cells. In addition, the THADA-knockdown markedly decreased the expression level of L-type amino acid transporter LAT1. Cardiac glycosides also reduced the LAT1 expression. The LAT1 inhibitor, JPH203, significantly weakened the cancer cell proliferation. These results suggest that the binding of cardiac glycosides to Na+,K+-ATPase negatively regulates the THADA-LAT1 pathway, exerting the anti-proliferative effect in cancer cells.

Trial watch: dexmedetomidine in cancer therapy

Dexmedetomidine (DEX) is a highly selective α2-adrenoceptor agonist that is widely used in intensive and anesthetic care for its sedative and anxiolytic properties. DEX has the capacity to alleviate inflammatory pain while limiting immunosuppressive glucocorticoid stress during major surgery, thus harboring therapeutic benefits for oncological procedures. Recently, the molecular mechanisms of DEX-mediated anticancer effects have been partially deciphered. Together with additional preclinical data, these mechanistic insights support the hypothesis that DEX-induced therapeutic benefits are mediated via the stimulation of adaptive anti-tumor immune responses. Similarly, published clinical trials including ancillary studies described an immunostimulatory role of DEX during the perioperative period of cancer surgery. The impact of DEX on long-term patient survival remains elusive. Nevertheless, DEX-mediated immunostimulation offers an interesting therapeutic option for onco-anesthesia. Our present review comprehensively summarizes data from preclinical and clinical studies as well as from ongoing trials with a distinct focus on the role of DEX in overcoming (tumor microenvironment (TME)-imposed) cancer therapy resistance. The objective of this update is to guide clinicians in their choice toward immunostimulatory onco-anesthetic agents that have the capacity to improve disease outcome.

Involvement of cardiac glycosides targeting Na/K-ATPase in their inhibitory effects on c-Myc expression via its transcription, translation and proteasomal degradation

Cardiac glycosides (CGs) have been used for decades to treat heart failure and arrhythmic diseases. Recent non-clinical and epidemiological findings have suggested that CGs exhibit anti-tumor activities. Therefore, CGs may be repositioned as drugs for the treatment of cancer. A detailed understanding of the anti-cancer mechanisms of CGs is essential for their application to the treatment of targetable cancer types. To elucidate the factors associated with the anti-tumor effects of CGs, we performed transcriptome profiling on human multiple myeloma AMO1 cells treated with periplocin, one of the CGs. Periplocin significantly down-regulated the transcription of MYC (c-Myc), a well-established oncogene. Periplocin also suppressed c-Myc expression at the protein levels. This repression of c-Myc was also observed in several cell lines. To identify target proteins for the inhibition of c-Myc, we generated CG-resistant (C9) cells using a sustained treatment with digoxin. We confirmed that C9 cells acquired resistance to the inhibition of c-Myc expression and cell proliferation by CGs. Moreover, the sequencing of genomic DNA in C9 cells revealed the mutation of D128N in α1-Na/K-ATPase, indicating the target protein. These results suggest that CGs suppress c-Myc expression in cancer cells via α1-Na/K-ATPase, which provides further support for the anti-tumor activities of CGs.

The cardiac glycoside ZINC253504760 induces parthanatos-type cell death and G2/M arrest via downregulation of MEK1/2 phosphorylation in leukemia cells

Overcoming multidrug resistance (MDR) represents a major obstacle in cancer chemotherapy. Cardiac glycosides (CGs) are efficient in the treatment of heart failure and recently emerged in a new role in the treatment of cancer. ZINC253504760, a synthetic cardenolide that is structurally similar to well-known GCs, digitoxin and digoxin, has not been investigated yet. This study aims to investigate the cytotoxicity of ZINC253504760 on MDR cell lines and its molecular mode of action for cancer treatment. Four drug-resistant cell lines (P-glycoprotein-, ABCB5-, and EGFR-overexpressing cells, and TP53-knockout cells) did not show cross-resistance to ZINC253504760 except BCRP-overexpressing cells. Transcriptomic profiling indicated that cell death and survival as well as cell cycle (G2/M damage) were the top cellular functions affected by ZINC253504760 in CCRF-CEM cells, while CDK1 was linked with the downregulation of MEK and ERK. With flow cytometry, ZINC253504760 induced G2/M phase arrest. Interestingly, ZINC253504760 induced a novel state-of-the-art mode of cell death (parthanatos) through PARP and PAR overexpression as shown by western blotting, apoptosis-inducing factor (AIF) translocation by immunofluorescence, DNA damage by comet assay, and mitochondrial membrane potential collapse by flow cytometry. These results were ROS-independent. Furthermore, ZINC253504760 is an ATP-competitive MEK inhibitor evidenced by its interaction with the MEK phosphorylation site as shown by molecular docking in silico and binding to recombinant MEK by microscale thermophoresis in vitro. To the best of our knowledge, this is the first time to describe a cardenolide that induces parthanatos in leukemia cells, which may help to improve efforts to overcome drug resistance in cancer. A cardiac glycoside compound ZINC253504760 displayed cytotoxicity against different multidrug-resistant cell lines. ZINC253504760 exhibited cytotoxicity in CCRF-CEM leukemia cells by predominantly inducing a new mode of cell death (parthanatos). ZINC253504760 downregulated MEK1/2 phosphorylation and further affected ERK activation, which induced G2/M phase arrest.

Involvement of monocyte-derived extracellular vesicle-associated tissue factor activity in convallatoxin-induced hypercoagulability

OBJECTIVES

Convallatoxin (CNT) is a natural cardiac glycoside extracted from lily of the valley ( Convallaria majalis ). Although it is empirically known to cause blood coagulation disorders, the underlying mechanism remains unclear. CNT exerts cytotoxicity and increases tissue factor (TF) expression in endothelial cells. However, the direct action of CNT on blood coagulation remains unclear. Therefore, herein, we investigated the effects of CNT on whole blood coagulation system and TF expression in monocytes.

METHODS

Blood samples were collected from healthy volunteers to measure plasma thrombin-antithrombin complex (TAT) concentration using ELISA and to perform rotational thromboelastometry (ROTEM) and whole-blood extracellular vesicle (EV)-associated TF (EV-TF) analysis. The effects of CNT were also investigated using the monocytic human cell line THP-1. Quantitative real-time PCR and western blotting were performed, and PD98059, a mitogen-activated protein kinase (MAPK) inhibitor, was used to elucidate the action mechanism of CNT-mediated TF production.

RESULTS

CNT treatment increased EV-TF activity, shortened the whole blood clotting time in rotational thromboelastometry analysis, and increased TAT levels, which is an index of thrombin generation. Furthermore, CNT increased TF mRNA expression in THP-1 cells and EV-TF activity in the cell culture supernatant. Therefore, CNT may induce a hypercoagulable state with thrombin generation, in which elevated EV-TF activity derived from monocytes might be involved. These procoagulant effects of CNT were reversed by PD98059, suggesting that CNT-induced TF production in monocytes might be mediated by the MAPK pathway.

CONCLUSIONS

The findings of the present study have further clarified the procoagulant properties of CNT.

Markedly divergent effects of Ouabain on a Temozolomide-resistant (T98G) vs. a Temozolomide-sensitive (LN229) Glioblastoma cell line

BACKGROUND

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor with poor prognosis. GMB are highly recurrent mainly because of radio- and chemoresistance. Radiotherapy with Temozolomide (TMZ) is until today the golden standard adjuvant therapy, however, the optimal treatment of recurrent glioblastoma remains controversial. Ouabain belongs to the Cardiotonic Steroids (CTS) the natural ligands of the Na/K-ATPase (NKA). It is established that the NKA represents a signal transducer with either stimulating or inhibiting cell growth, apoptosis, migration and angiogenesis. Over the last decade evidence grew that CTS have anti-tumor properties especially in GBM.

AIM

Proceeding from recent studies we wanted to further demonstrate a divergent effect of Ouabain on a TMZ-resistant (T98G) as compared to a TMZ-sensitive (LN229) GBM cell line.

METHODS

We analyzed the effect of Ouabain on cell migration and plasma cell membrane potential (PCMP) in the LN229 and T98G GBM cell line as well as underlying mechanisms (Bcl-2 and p-Akt/pan-Akt expression). Moreover, we analyzed the anti-angiogenic effect of Ouabain on human umbilical vein endothelial cells (HUVECs).

RESULTS

T98G cells showed a significant inhibition of cell migration and a significant depolarization of the PCMP at similar Ouabain concentrations (IC50 = 1.67 × 10^-7 M) resp. (IC50 = 2.72 × 10^-7 M) with a strong inverse correlation (R² = 0.95). In contrast, LN229 cells did not respond to Ouabain in these assays at all. Similarly, only T98G but not LN229 cells revealed Bcl-2 down-regulation at nanomolar Ouabain concentrations. This unique response to Ouabain is associated with a down-regulation of pan-Akt in T98G cells 24 h after Ouabain (1.0 × 10^-6 M) treatment. For the first time, the anti-angiogenic effect of Ouabain on HUVEC cells (IC50 = 5.49 × 10^-8 M) was demonstrated which correlated strongly with the anti-migratory effect (R² = 0.85).

CONCLUSION

The TMZ-resistant T98G cell line as compared to the TMZ-sensitive LN229 cell line shows a high sensitivity towards Ouabain. We consider it as a promising new compound especially in recurrent GBM to overcome the resistance to TMZ and irradiation.

3'-epi-12β-hydroxyfroside-mediated autophagy degradation of RIPK1/RIPK3 necrosomes leads to anergy of immunogenic cell death in triple-negative breast cancer cells

Increasing studies have suggested that some cardiac glycosides, such as conventional digoxin (DIG) and digitoxin, can induce immunogenic cell death (ICD) in various tumors. We previously found that 3'-epi-12β-hydroxyfroside (HyFS), a novel cardenolide compound isolated by our group, could induce cytoprotective autophagy through inactivation of the Akt/mTOR pathway. However, whether HyFS can induce ICD remains unknown. In this study, we extend our work to further investigate whether HyFS could induce both autophagy and ICD, and we investigated the relationship between autophagy and ICD in three TNBC cell lines. Unexpectedly, compared to DIG, we found that HyFS could induce complete autophagy flux but not ICD in three human triple-negative breast cancer (TNBC) cell lines and one murine TNBC model. Inhibition of HyFS-induced autophagy resulted in the production of ICD in TNBC MDA-MB-231, MDA-MB-436, and HCC38 cells. A further mechanism study showed that formation of RIPK1/RIPK3 necrosomes was necessary for ICD induction in DIG-treated TNBC cells, while HyFS treatment led to receptor-interacting serine-threonine kinase (RIPK)1/3 necrosome degradation via an autophagy process. Additionally, inhibition of HyFS-induced autophagy by the autophagy inhibitor chloroquine resulted in the reoccurrence of ICD and reversion of the tumor microenvironment, leading to more significant antitumor effects in immunocompetent mice than in immunodeficient mice. These findings indicate that HyFS-mediated autophagic degradation of RIPK1/RIPK3 necrosomes leads to inactivation of ICD in TNBC cells. Moreover, combined treatment with HyFS and an autophagy inhibitor may enhance the antitumor activities, suggesting an alternative therapeutic for TNBC treatment.

The botanical drug PBI-05204, a supercritical CO2 extract of Nerium oleander, sensitizes alveolar and embryonal rhabdomyosarcoma to radiotherapy in vitro and in vivo

Treatment of rhabdomyosarcoma (RMS), the most common a soft tissue sarcoma in childhood, provides intensive multimodal therapy, with radiotherapy (RT) playing a critical role for local tumor control. However, since RMS efficiently activates mechanisms of resistance to therapies, despite improvements, the prognosis remains still largely unsatisfactory, mainly in RMS expressing chimeric oncoproteins PAX3/PAX7-FOXO1, and fusion-positive (FP)-RMS. Cardiac glycosides (CGs), plant-derived steroid-like compounds with a selective inhibitory activity of the Na+/K+-ATPase pump (NKA), have shown antitumor and radio-sensitizing properties. Herein, the therapeutic properties of PBI-05204, an extract from Nerium oleander containing the CG oleandrin already studied in phase I and II clinical trials for cancer patients, were investigated, in vitro and in vivo, against FN- and FP-RMS cancer models. PBI-05204 induced growth arrest in a concentration dependent manner, with FP-RMS being more sensitive than FN-RMS, by differently regulating cell cycle regulators and commonly upregulating cell cycle inhibitors p21Waf1/Cip1 and p27Cip1/Kip1. Furthermore, PBI-05204 concomitantly induced cell death on both RMS types and senescence in FN-RMS. Notably, PBI-05204 counteracted in vitro migration and invasion abilities and suppressed the formation of spheroids enriched in CD133+ cancer stem cells (CSCs). PBI-05204 sensitized both cell types to RT by improving the ability of RT to induce G2 growth arrest and counteracting the RT-induced activation of both Non‐Homologous End‐Joining and homologous recombination DSBs repair pathways. Finally, the antitumor and radio-sensitizing proprieties of PBI-05204 were confirmed in vivo. Notably, both in vitro and in vivo evidence confirmed the higher sensitivity to PBI-05204 of FP-RMS. Thus, PBI-05204 represents a valid radio-sensitizing agent for the treatment of RMS, including the intrinsically radio-resistant FP-RMS.

Identification of a Cardiac Glycoside Exhibiting Favorable Brain Bioavailability and Potency for Reducing Levels of the Cellular Prion Protein

Several strands of investigation have established that a reduction in the levels of the cellular prion protein (PrP^C) is a promising avenue for the treatment of prion diseases. We recently described an indirect approach for reducing PrP^C levels that targets Na,K-ATPases (NKAs) with cardiac glycosides (CGs), causing cells to respond with the degradation of these pumps and nearby molecules, including PrP^C. Because the therapeutic window of widely used CGs is narrow and their brain bioavailability is low, we set out to identify a CG with improved pharmacological properties for this indication. Starting with the CG known as oleandrin, we combined in silico modeling of CG binding poses within human NKA folds, CG structure-activity relationship (SAR) data, and predicted blood-brain barrier (BBB) penetrance scores to identify CG derivatives with improved characteristics. Focusing on C4'-dehydro-oleandrin as a chemically accessible shortlisted CG derivative, we show that it reaches four times higher levels in the brain than in the heart one day after subcutaneous administration, exhibits promising pharmacological properties, and suppresses steady-state PrP^C levels by 84% in immortalized human cells that have been differentiated to acquire neural or astrocytic characteristics. Finally, we validate that the mechanism of action of this approach for reducing cell surface PrP^C levels requires C4'-dehydro-oleandrin to engage with its cognate binding pocket within the NKA α subunit. The improved brain bioavailability of C4'-dehydro-oleandrin, combined with its relatively low toxicity, make this compound an attractive lead for brain CG indications and recommends its further exploration for the treatment of prion diseases.

Effects of Corchorusoside C on NF-κB and PARP-1 Molecular Targets and Toxicity Profile in Zebrafish

The present study aims to continue the study of corchorusoside C (1), a cardenolide isolated from Streptocaulon juventas, as a potential anticancer agent. A mechanistic study was pursued in a zebrafish model and in DU-145 prostate cancer cells to investigate the selectivity of 1 towards NF-κB and PARP-1 pathway elements. Compound 1 was found to inhibit the expression of IKKα and NF-κB p65 in TNF-α induced zebrafish and inhibit the expression of NIK in vitro. The protein expression levels of XRCC-1 were increased and p53 decreased in DU-145 cells. XIAP protein expression was initially decreased after treatment with 1, followed by an increase in expression at doses higher than the IC₅₀ value. The activity of caspase-1 and the protein expression levels of IL-18 were both decreased following treatment of 1. The binding interactions for 1 to NIK, XRCC-1, p53, XIAP, and caspase-1 proteins were explored in molecular docking studies. Additionally, the toxicity profile of 1 in zebrafish was favorable in comparison to its analog digoxin and other anticancer drugs at the same MTD in zebrafish. Overall, 1 targets the noncanconical NF-κB pathway in vivo and in vitro, and is well tolerated in zebrafish supporting its potential in the treatment of prostate cancer.

Active Biomolecules from Vegetable Extracts with Antitumoral Activity against Pancreas Cancer: A Systematic Review (2011-2021)

The emergence of resistance to pancreatic cancer (PC) current treatment requires the development of new therapeutic strategies. In this context, bioactive molecules from plant extracts have shown excellent properties to improve classical therapy against this type of tumor. This systematic review aims to collect all the in vitro studies related to the antiproliferative activity of isolated plant molecules that support their applicability in PC. A total of 620 articles published in the last 10 years were identified, although only 28 were finally included to meet the inclusion criteria. Our results reflect the most important biomolecules from natural compounds that induce cell death in PC and their essential mechanism of cell death, including apoptosis, pathways activated by the KRAS mutation and cycle cell arrest, among others. These in vitro studies provide an excellent molecule guide showing applications against PC and that should be tested in vivo and in clinical trials to determine their usefulness to reduce PC incidence and to improve the prognosis of these patients. However, natural compounds are isolated in small amounts, which prevents comprehensive drug screening, being necessary the role of organic synthesis for the total synthesis of natural compounds or for the synthesis of their simplified and bioactive analogs.

New opportunities and challenges of natural products research: When target identification meets single-cell multiomics

Natural products, and especially the active ingredients found in traditional Chinese medicine (TCM), have a thousand-year-long history of clinical use and a strong theoretical basis in TCM. As such, traditional remedies provide shortcuts for the development of original new drugs in China, and increasing numbers of natural products are showing great therapeutic potential in various diseases. This paper reviews the molecular mechanisms of action of natural products from different sources used in the treatment of inflammatory diseases and cancer, introduces the methods and newly emerging technologies used to identify and validate the targets of natural active ingredients, enumerates the expansive list of TCM used to treat inflammatory diseases and cancer, and summarizes the patterns of action of emerging technologies such as single-cell multiomics, network pharmacology, and artificial intelligence in the pharmacological studies of natural products to provide insights for the development of innovative natural product-based drugs. Our hope is that we can make use of advances in target identification and single-cell multiomics to obtain a deeper understanding of actions of mechanisms of natural products that will allow innovation and revitalization of TCM and its swift industrialization and internationalization.

Chemistry and the Potential Antiviral, Anticancer, and Anti-Inflammatory Activities of Cardiotonic Steroids Derived from Toads

Cardiotonic steroids (CTS) were first documented by ancient Egyptians more than 3000 years ago. Cardiotonic steroids are a group of steroid hormones that circulate in the blood of amphibians and toads and can also be extracted from natural products such as plants, herbs, and marines. It is well known that cardiotonic steroids reveal effects against congestive heart failure and atrial fibrillation; therefore, the term "cardiotonic" has been coined. Cardiotonic steroids are divided into two distinct groups: cardenolides (plant-derived) and bufadienolides (mainly of animal origin). Cardenolides have an unsaturated five-membered lactone ring attached to the steroid nucleus at position 17; bufadienolides have a doubly unsaturated six-membered lactone ring. Cancer is a leading cause of mortality in humans all over the world. In 2040, the global cancer load is expected to be 28.4 million cases, which would be a 47% increase from 2020. Moreover, viruses and inflammations also have a very nebative impact on human health and lead to mortality. In the current review, we focus on the chemistry, antiviral and anti-cancer activities of cardiotonic steroids from the naturally derived (toads) venom to combat these chronic devastating health problems. The databases of different research engines (Google Scholar, PubMed, Science Direct, and Sci-Finder) were screened using different combinations of the following terms: “cardiotonic steroids”, “anti-inflammatory”, “antiviral”, “anticancer”, “toad venom”, “bufadienolides”, and “poison chemical composition”. Various cardiotonic steroids were isolated from diverse toad species and exhibited superior anti-inflammatory, anticancer, and antiviral activities in in vivo and in vitro models such as marinobufagenin, gammabufotalin, resibufogenin, and bufalin. These steroids are especially difficult to identify. However, several compounds and their bioactivities were identified by using different molecular and biotechnological techniques. Biotechnology is a new tool to fully or partially generate upscaled quantities of natural products, which are otherwise only available at trace amounts in organisms.

Na/K‑ATPase subunit α3 expression is associated with the efficacy of digitoxin treatment in pancreatic cancer cells

The alpha subunits (ATP1A1-3) of Na⁺/K⁺-ATPase binds digitoxin with varying affinity. The expression levels of these subunits dictate the anticancer effects of digitoxin. In the present study, three pancreatic cancer cell lines, AsPC-1, Panc-1 and CFPAC-1, were used to investigate the effects of digitoxin in relation to the expression of the subunits ATP1A1 and ATP1A3. Cell viability and intracellular calcium concentrations was measured in relation to the gene and protein expression of ATP1A1 and ATP1A3. Digitoxin was used to treat the cells at concentrations of 1-100 nM, and the intracellular calcium concentrations increased in a concentration-dependent manner in the Panc-1 and in the CFPAC-1 cells with treatment at 100 nM. In the AsPC-1 cells only the supraphysiological concentration of digitoxin (100 nM) resulted in a decrease in the number of viable cells (unviable cells increased to 22%), whereas it had no effect on intracellular calcium levels. The number of viable Panc-1 and CFPAC-1 cells decreased after digitoxin treatment at 25-100 nM (unviable Panc-1 cells increased to 33-59%; unviable CFPAC-1 cells increased to 22-56%). Digitoxin treatment also affected the transcriptional expression of the ATP1A1 and ATP1A3 subunits. In Panc-1 cells, ATP1A3 gene expression was negatively associated with the digitoxin concentration (25-100 nM). In the AsPC-1 and CFPAC-1 cells, the expression of the ATP1A1 gene increased in the cells treated with the 100 nM digitoxin concentration. The protein expression of ATP1A1 and ATP1A3 was not altered with digitoxin treatment. The basal protein expression of ATP1A1 was high in the AsPC-1 and CFPAC-1 cells, compared to the Panc-1 cells, in contrast to the basal expression of ATP1A3, which was higher in the Panc-1 cells, compared to the other pancreatic cancer cells used. On the whole, the present study demonstrates that the high expression of ATP1A3 renders pancreatic cancer cells more susceptible to digitoxin-induced cell death. The findings suggest that the expression of ATP1A3 may be used as a marker for tumor sensitivity to digitoxin treatment, where a high expression of ATP1A3 is favorable for the anticancer effects of digitoxin.

Investigation of the Mechanism of Periploca forrestii against Rheumatoid Arthritis with Network Pharmacology-Based Analysis

Periploca forrestii Schltr (P. forrestii) is an edible medicinal herb with various health benefits such as treating antirheumatoid arthritis (RA), reducing inflammation, and preventing tumor growth. The active ingredients in P. forrestii responsible for its protective effect against RA, however, remain unknown. In this study, the active ingredient of P. forrestii and its potential mechanism of action against RA were investigated by network pharmacology and enrichment analysis. The methods included predicting target genes of P. forrestii, constructing a protein interaction network, and performing gene-ontology (GO) and Kyoto-encyclopedia of genes and genomes (KEGG) enrichment analysis. We discovered targets of RA through retrieval of OMIM and GeneCards public databases. Cardiac glycosides (CGs) are considered the primarily active ingredients of P. forrestii, and the target genes of GCs were discovered to be overlapped with relevant targets of RA using the Venn diagram. After that, prediction of relevant targets of P. forrestii was accomplished with a network pharmacology-based approach. Through the Venn diagram, we discovered 99 genes shared in the target genes of P. forrestii and RA. Gene enrichment analysis showed that the mechanisms of CGs against RA are associated with 55 signaling pathways, including endocrine resistance, Epstein-Barr virus infection, bladder cancer, prostate cancer, and coronavirus disease (COVID-19) signaling pathways. Coexpression analysis indicated ADSL, ATIC, AR, CCND1, MDM2, and HSP90AA1 as the hub genes between putative targets of P. forrestii-derived CGs and known therapeutic targets of RA. In conclusion, we clarified the mechanism of action of P. forrestii against RA, which would provide a basis for further understanding the clinical application of P. forrestii.

Drug repurposing: An emerging strategy in alleviating skin cancer

Skin cancer is one of the most common forms of cancer. Several million people are estimated to have affected with this condition worldwide. Skin cancer generally includes melanoma and non-melanoma with the former being the most dangerous. Chemotherapy has been one of the key therapeutic strategies employed in the treatment of skin cancer, especially in advanced stages of the disease. It could be also used as an adjuvant with other treatment modalities depending on the type of skin cancer. However, there are several shortfalls associated with the use of chemotherapy such as non-selectivity, tumour resistance, life-threatening toxicities, and the exorbitant cost of medicines. Furthermore, new drug discovery is a lengthy and costly process with minimal likelihood of success. Thus, drug repurposing (DR) has emerged as a new avenue where the drug approved formerly for the treatment of one disease can be used for the treatment of another disease like cancer. This approach is greatly beneficial over the de novo approach in terms of time and cost. Moreover, there is minimal risk of failure of repurposed therapeutics in clinical trials. There are a considerable number of studies that have reported on drugs repurposed for the treatment of skin cancer. Thus, the present manuscript offers a comprehensive overview of drugs that have been investigated as repurposing candidates for the efficient treatment of skin cancers mainly melanoma and its oncogenic subtypes, and non-melanoma. The prospects of repurposing phytochemicals against skin cancer are also discussed. Furthermore, repurposed drug delivery via topical route and repurposed drugs in clinical trials are briefed. Based on the findings from the reported studies discussed in this manuscript, drug repurposing emerges to be a promising approach and thus is expected to offer efficient treatment at a reasonable cost in devitalizing skin cancer.

The expression of the alpha1 subunit of Na+/K+-ATPase is related to tumor development and clinical outcomes in gastric cancer

BACKGROUND

The Na⁺/K⁺-ATPase alpha1 subunit (ATP1A1) is a critical component of Na⁺/K⁺-ATPase (NKA), a membrane pump that maintains a low intracellular Na⁺/K⁺ ratio and retains cellular volume and osmolarity. ATP1A1 was recently implicated in tumor behavior. Therefore, the present study investigated the role of ATP1A1 in patients with gastric cancer (GC).

METHODS

Knockdown experiments were conducted on human GC cell lines using ATP1A1 siRNA, and its effects on proliferation, the cell cycle, apoptosis, and cellular movement were examined. Gene expression profiling was performed by a microarray analysis. Primary tumor samples from 192 GC patients who underwent gastrectomy were subjected to an immunohistochemical analysis.

RESULTS

High ATP1A1 expression levels were observed in NUGC4 and MKN74 cells. Cell proliferation was suppressed and apoptosis was induced by the siRNA-induced knockdown of ATP1A1. The microarray analysis showed that knockdown of ATP1A1 leads to the up-regulated expression of genes involved in the interferon (IFN) signaling pathway, such as STAT1, STAT2, IRF1, and IRF9. Furthermore, the depletion of ATP1A1 altered the phosphorylation of the MAPK pathway. The immunohistochemical analysis revealed that the expression of ATP1A1 was associated with the histological type, venous invasion, and the pathological T stage. Furthermore, the prognostic analysis showed a relationship between high ATP1A1 expression levels and poor postoperative survival.

CONCLUSIONS

ATP1A1 appears to regulate tumor progression by altering IFN signaling, and high ATP1A1 expression levels were associated with poor postoperative survival in GC patients. The present results provide novel insights into the function of ATP1A1 as a mediator and/or biomarker of GC.

Digoxin exerts anticancer activity on human nonsmall cell lung cancer cells by blocking PI3K/Akt pathway

Lung cancer remains the leading cause of cancer mortality because of its metastatic potential and high malignancy. The discovery of new applications for old drugs is a shortcut for cancer therapy. We recently investigated the antitumor effect of digoxin, a well-established drug for treating heart failure, against nonsmall cell lung cancer A549 and H1299 cells. Digoxin inhibited the proliferation and colony-forming ability of the two cell lines and arrested the cell cycle at the G0/G1 phase in A549 cells and the G2/M phase in H1299 cells. Mitochondria-mediated apoptosis was induced in A549 cells but not in H1299 cells after treatment with digoxin. Moreover, digoxin inhibited the migration, invasion, adhesion and epithelial–mesenchymal transition of A549 and H1299 cells. Autophagy was induced in both cell lines after treatment with digoxin, with an increase in autophagosome foci. In addition, digoxin inhibited the phosphorylation of Akt, mTOR and p70S6K, signaling molecules of the PI3K/Akt pathway that are known to be involved in tumor cell survival, proliferation, metastasis and autophagy. Our findings suggest that digoxin has the potential to be used for therapy for human nonsmall cell lung cancer, but further evidence is required.

Protective Effect of Nerium Oleander Distillate and Tarantula Cubensis Alcoholic Extract on Cancer Biomarkers on Colon and Liver Tissues of Rats with Experimental Colon Cancer

BACKGROUND

Colon cancers are among the three major cancer types that result in death. The research for effective treatment continues.

OBJECTIVE

The aim of this study is to determine the effects of Tarantula cubensis alcoholic extract (TCAE) and Nerium oleander (NO) distillate on the levels of midkine, TGF-β, VEGF, AFP, COX-2, IGF and caspase 3 in liver and colon tissues of experimentally induced colon cancer in rats.

METHOD

The liver and colon tissues of the rats were divided into Control, Colon Cancer (AZM), AZM+TCAE and AZM+NO groups and they were homogenized. The levels of midkine, TGF-β, VEGF, AFP, COX-2, IGF and caspase 3 in the colon and liver tissues were measured by ELISA kits.

RESULTS

All parameters levels of colon and liver tissues in the AZM group were generally higher (p<0.05) than the Control group. TCAE and NO prevented (p<0.05) the increases in midkine, TGF-β, VEGF, AFP, COX-2, IGF and caspase-3 levels in the colon. NO prevented increase of all parameters except for IGF level, while TCAE prevented (p<0.05) the increase of all values apart from COX-2 and IGF levels in the liver.

CONCLUSION

NO and TCAE may prevented at the specified marker levels of colon in the AZM induced colon cancer. The increases the level of parameters in the liver are not as severe as in the colon, due to the 18-week study period may not be sufficient for liver metastasis formationIn the future molecular studies should be done to determine the mechanisms and pathways of them more clearly.

Emergence of Cardiac Glycosides as Potential Drugs: Current and Future Scope for Cancer Therapeutics

Cardiac glycosides are natural sterols and constitute a group of secondary metabolites isolated from plants and animals. These cardiotonic agents are well recognized and accepted in the treatment of various cardiac diseases as they can increase the rate of cardiac contractions by acting on the cellular sodium potassium ATPase pump. However, a growing number of recent efforts were focused on exploring the antitumor and antiviral potential of these compounds. Several reports suggest their antitumor properties and hence, today cardiac glycosides (CG) represent the most diversified naturally derived compounds strongly recommended for the treatment of various cancers. Mutated or dysregulated transcription factors have also gained prominence as potential therapeutic targets that can be selectively targeted. Thus, we have explored the recent advances in CGs mediated cancer scope and have considered various signaling pathways, molecular aberration, transcription factors (TFs), and oncogenic genes to highlight potential therapeutic targets in cancer management.

Restoring the Immunity in the Tumor Microenvironment: Insights into Immunogenic Cell Death in Onco-Therapies

Immunogenic cell death (ICD) elicited by cancer therapy reshapes the tumor immune microenvironment. A long-term adaptative immune response can be initiated by modulating cell death by therapeutic approaches. Here, the major hallmarks of ICD, endoplasmic reticulum (ER) stress, and damage-associated molecular patterns (DAMPs) are correlated with ICD inducers used in clinical practice to enhance antitumoral activity by suppressing tumor immune evasion. Approaches to monitoring the ICD triggered by antitumoral therapeutics in the tumor microenvironment (TME) and novel perspective in this immune system strategy are also reviewed to give an overview of the relevance of ICD in cancer treatment.

Periplocin and cardiac glycosides suppress the unfolded protein response

The unfolded protein response (UPR) controls protein homeostasis through transcriptional and translational regulation. However, dysregulated UPR signaling has been associated with the pathogenesis of many human diseases. Therefore, the compounds modulating UPR may provide molecular insights for these pathologies in the context of UPR. Here, we screened small-molecule compounds that suppress UPR, using a library of Myanmar wild plant extracts. The screening system to track X-box binding protein 1 (XBP1) splicing activity revealed that the ethanol extract of the Periploca calophylla stem inhibited the inositol-requiring enzyme 1 (IRE1)-XBP1 pathway. We isolated and identified periplocin as a potent inhibitor of the IRE1-XBP1 axis. Periplocin also suppressed other UPR axes, protein kinase R-like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6). Examining the structure–activity relationship of periplocin revealed that cardiac glycosides also inhibited UPR. Moreover, periplocin suppressed the constitutive activation of XBP1 and exerted cytotoxic effects in the human multiple myeloma cell lines, AMO1 and RPMI8226. These results reveal a novel suppressive effect of periplocin or the other cardiac glycosides on UPR regulation, suggesting that these compounds will contribute to our understanding of the pathological or physiological importance of UPR.

Investigation of the cytotoxic activity of two novel digitoxigenin analogues on H460 lung cancer cells

Cardiac glycosides (CGs) are natural compounds traditionally used for the treatment of heart disorders, and recently new therapeutic possibilities were proposed. Their antitumor reports and clinical trials have notably enhanced, including those targeted for lung cancer, the most lethal type that lacks of new treatment agents, instigating the research of these molecules. The CGs studied here, named C10 {3β-[(N-(2-hydroxyethyl)aminoacetyl]amino-3-deoxydigitoxigenin} and C18 (3β-(aminoacetyl)amino-3-deoxydigitoxigenin), are semisynthetic derivatives prepared from digitoxigenin scaffold. Both compounds demonstrated high cytotoxicity for different cancer cell lines, especially H460 lung cancer cells, and their cytotoxic effects were deeply investigated using different methodological approaches. C10 induced cell death at lower concentrations and during shorter periods of treatment than C18, and increased the number of small and irregular nuclei, which are characteristics of apoptosis. This type of cell death was confirmed by caspase-3/7 assay. Both compounds reduced H460 cells proliferative potential by long-term action, and C10 showed the strongest potential. Moreover, these compounds induced a significant decrease of the area and viability of H460 spheroids providing preclinical favorable profiles to develop new chemotherapeutic agents.

Cytotoxicity of glucoevatromonoside alone and in combination with chemotherapy drugs and their effects on Na+,K+-ATPase and ion channels on lung cancer cells

Cardiac glycosides (CGs) are useful drugs to treat cardiac illnesses and have potent cytotoxic and anticancer effects in cultured cells and animal models. Their receptor is the Na⁺,K⁺ ATPase, but other plasma membrane proteins might bind CGs as well. Herein, we evaluated the short- and long-lasting cytotoxic effects of the natural cardenolide glucoevatromonoside (GEV) on non-small-cell lung cancer H460 cells. We also tested GEV effects on Na⁺,K⁺ -ATPase activity and membrane currents, alone or in combination with selected chemotherapy drugs. GEV reduced viability, migration, and invasion of H460 cells spheroids. It also induced cell cycle arrest and death and reduced the clonogenic survival and cumulative population doubling. GEV inhibited Na⁺,K⁺-ATPase activity on A549 and H460 cells and purified pig kidney cells membrane. However, it showed no activity on the human red blood cell plasma membrane. Additionally, GEV triggered a Cl-mediated conductance on H460 cells without affecting the transient voltage-gated sodium current. The administration of GEV in combination with the chemotherapeutic drugs paclitaxel (PAC), cisplatin (CIS), irinotecan (IRI), and etoposide (ETO) showed synergistic antiproliferative effects, especially when combined with GEV + CIS and GEV + PAC. Taken together, our results demonstrate that GEV is a potential drug for cancer therapy because it reduces lung cancer H460 cell viability, migration, and invasion. Our results also reveal a link between the Na⁺,K⁺-ATPase and Cl^- ion channels.

Prospects and Therapeutic Applications of Cardiac Glycosides in Cancer Remediation

Active metabolites from natural sources are the predominant molecular targets in numerous biological studies owing to their appropriate compatibility with biological systems and desirable selective toxicities. Thus, their potential for therapeutic development could span a broad scope of disease areas, including pathological and neurological dysfunctions. Cardiac glycosides are a unique class of specialized metabolites that have been extensively applied as therapeutic agents for the treatment of numerous heart conditions, and more recently, they have also been explored as probable antitumor agents. They are a class of naturally derived compounds that bind to and inhibit Na⁺/K⁺-ATPase. This study presents cardiac glycosides and their analogues with highlights on their applications, challenges, and prospects as lead compounds for cancer treatment.

Biological and Pharmacological Effects of Synthetic Saponins

Saponins are amphiphilic molecules consisting of carbohydrate and either triterpenoid or steroid aglycone moieties and are noted for their multiple biological activities-Fungicidal, antimicrobial, antiviral, anti-inflammatory, anticancer, antioxidant and immunomodulatory effects have all been observed. Saponins from natural sources have long been used in herbal and traditional medicines; however, the isolation of complexed saponins from nature is difficult and laborious, due to the scarce amount and structure heterogeneity. Chemical synthesis is considered a powerful tool to expand the structural diversity of saponin, leading to the discovery of promising compounds. This review focuses on recent developments in the structure optimization and biological evaluation of synthetic triterpenoid and steroid saponin derivatives. By summarizing the structure-activity relationship (SAR) results, we hope to provide the direction for future development of saponin-based bioactive compounds.

Digoxin use is associated with pancreatic cancer risk but does not affect survival

PURPOSE

Digoxin affects several cellular pathways involved in tumorigenesis. We sought to determine the association between digoxin use and pancreatic cancer risk and survival.

METHODS

A nested case-control study using The Health Improvement Network (THIN), a population-representative database from the United Kingdom (UK). Cases included all individuals with incident diagnosis of pancreatic cancer. Each case was matched to up to four controls using incidence density sampling based on age, sex, practice site, calendar time, and duration of follow-up. Exposure of interest was digoxin therapy before cancer diagnosis. Odds ratios (ORs) and 95% confidence intervals (CIs) for the association between digoxin use and pancreatic cancer risk were estimated using conditional logistic regression. We further conducted a retrospective cohort study among pancreatic cancer cases using Cox regression model in order to evaluate the association between digoxin use and overall survival.

RESULTS

We identified 4,113 cases with incident pancreatic cancer and 16,072 matched controls. The adjusted OR for diagnosis of pancreatic cancer among active digoxin users was 1.41 (95% CI 1.16-1.72). The risk did not change among active users with duration of therapy of more than 1 year (adjusted OR of 1.39, 95% CI 1.11-1.76). Digoxin was not associated with change in overall survival with an adjusted hazard ratio of 0.97 (95% CI 0.81-1.18).

CONCLUSIONS

Digoxin use was associated with modestly increased pancreatic cancer risk but did not affect overall survival.

Anticancer and Antiviral Properties of Cardiac Glycosides: A Review to Explore the Mechanism of Actions

Cardiac glycosides (CGs) have a long history of treating cardiac diseases. However, recent reports have suggested that CGs also possess anticancer and antiviral activities. The primary mechanism of action of these anticancer agents is by suppressing the Na+/k+-ATPase by decreasing the intracellular K+ and increasing the Na+ and Ca2+. Additionally, CGs were known to act as inhibitors of IL8 production, DNA topoisomerase I and II, anoikis prevention and suppression of several target genes responsible for the inhibition of cancer cell proliferation. Moreover, CGs were reported to be effective against several DNA and RNA viral species such as influenza, human cytomegalovirus, herpes simplex virus, coronavirus, tick-borne encephalitis (TBE) virus and Ebola virus. CGs were reported to suppress the HIV-1 gene expression, viral protein translation and alters viral pre-mRNA splicing to inhibit the viral replication. To date, four CGs (Anvirzel, UNBS1450, PBI05204 and digoxin) were in clinical trials for their anticancer activity. This review encapsulates the current knowledge about CGs as anticancer and antiviral drugs in isolation and in combination with some other drugs to enhance their efficiency. Further studies of this class of biomolecules are necessary to determine their possible inhibitory role in cancer and viral diseases.

In Silico Screening of Potential Spike Glycoprotein Inhibitors of SARS-CoV-2 with Drug Repurposing Strategy

Objective

To select potential molecules that can target viral spike proteins, which may potentially interrupt the interaction between the human angiotension-converting enzyme 2 (ACE2) receptor and viral spike protein by virtual screening.

Methods

The three-dimensional (3D)-coordinate file of the receptor-binding domain (RBD)-ACE2 complex for searching a suitable docking pocket was firstly downloaded and prepared. Secondly, approximately 15,000 molecular candidates were prepared, including US Food and Drug Administration (FDA)-approved drugs from DrugBank and natural compounds from Traditional Chinese Medicine Systems Pharmacology (TCMSP), for the docking process. Then, virtual screening was performed and the binding energy in Autodock Vina was calculated. Finally, the top 20 molecules with high binding energy and their Chinese medicine (CM) herb sources were listed in this paper.

Results

It was found that digitoxin, a cardiac glycoside in DrugBank and bisindigotin in TCMSP had the highest docking scores. Interestingly, two of the CM herbs containing the natural compounds that had relatively high binding scores, Forsythiae fructus and Isatidis radix, are components of Lianhua Qingwen (莲花清瘟), a CM formula reportedly exerting activity against severe acute respiratory syndrome (SARS)-Cov-2. Moreover, raltegravir, an HIV integrase inhibitor, was found to have a relatively high binding score.

Conclusions

A class of compounds, which are from FDA-approved drugs and CM natural compounds, that had high binding energy with RBD of the viral spike protein. Our work provides potential candidates for other researchers to identify inhibitors to prevent SARS-CoV-2 infection, and highlights the importance of CM and integrative application of CM and Western medicine on treating COVID-19.

Triple-Negative Breast Cancer Cells Exhibit Differential Sensitivity to Cardenolides from Calotropis gigantea

Triple-negative breast cancers (TNBC) are aggressive and heterogeneous cancers that lack targeted therapies. We implemented a screening program to identify new leads for subgroups of TNBC using diverse cell lines with different molecular drivers. Through this program, we identified an extract from Calotropis gigantea that caused selective cytotoxicity in BT-549 cells as compared to four other TNBC cell lines. Bioassay-guided fractionation of the BT-549 selective extract yielded nine cardenolides responsible for the selective activity. These included eight known cardenolides and a new cardenolide glycoside. Structure-activity relationships among the cardenolides demonstrated a correlation between their relative potencies toward BT-549 cells and Na+/K+ ATPase inhibition. Calotropin, the compound with the highest degree of selectivity for BT-549 cells, increased intracellular Ca2+ in sensitive cells to a greater extent than in the resistant MDA-MB-231 cells. Further studies identified a second TNBC cell line, Hs578T, that is also highly sensitive to the cardenolides, and mechanistic studies were conducted to identify commonalities among the sensitive cell lines. Experiments showed that both cardenolide-sensitive cell lines expressed higher mRNA levels of the Na+/Ca2+ exchanger NCX1 than resistant TNBC cells. This suggests that NCX1 could be a biomarker to identify TNBC patients that might benefit from the clinical administration of a cardiac glycoside for anticancer indications.

Natural products and their derivatives: Promising modulators of tumor immunotherapy

A wealth of evidence supports the role of tumor immunotherapy as a vital therapeutic option in cancer. In recent decades, accumulated studies have revealed the anticancer activities of natural products and their derivatives. Increasing interest has been driven toward finding novel potential modulators of tumor immunotherapy from natural products, a hot research topic worldwide. These works of research mainly focused on natural products, including polyphenols (e.g., curcumin, resveratrol), cardiotonic steroids (e.g., bufalin and digoxin), terpenoids (e.g., paclitaxel and artemisinins), and polysaccharide extracts (e.g., lentinan). Compelling data highlight that natural products have a promising future in tumor immunotherapy. Considering the importance and significance of this topic, we initially discussed the integrated research progress of natural products and their derivatives, including target T cells, macrophages, B cells, NKs, regulatory T cells, myeloid‐derived suppressor cells, inflammatory cytokines and chemokines, immunogenic cell death, and immune checkpoints. Furthermore, these natural compounds inactivate several key pathways, including NF‐κB, PI3K/Akt, MAPK, and JAK/STAT pathways. Here, we performed a deep generalization, analysis, and summarization of the previous achievements, recent progress, and the bottlenecks in the development of natural products as tumor immunotherapy. We expect this review to provide some insight for guiding future research.

Inhibitors of Na+/K+ ATPase exhibit antitumor effects on multicellular tumor spheroids of hepatocellular carcinoma

Hepatocellular carcinoma (HCC), one of the most common malignant cancers worldwide, is associated with substantial mortality. Because HCCs have strong resistance to conventional chemotherapeutic agents, novel therapeutic strategies are needed to improve survival in patients with HCC. The multicellular tumor spheroid (MCTS) model is a powerful method for anticancer research because of its ability to mimic the complexity and heterogeneity of tumor tissue, the three-dimensional cellular context of tumor tissue, and the pathophysiological gradients of in vivo tumors. However, it is difficult to obtain meaningful results from the MCTS model without considering the conditions of clinical tumors. We, therefore, provided a proof of concept to determine whether spheroid models simulate in vivo tumor microenvironments. Through a high-throughput screening for HCC therapy using the MCTS model, we selected inhibitors of Na⁺/K⁺-ATPase (ouabain and digoxin) that could suppress cell growth and migration via inhibition of the epithelial-mesenchymal transition of HCC in vivo and in vitro. The results showed that this model provides a new paradigm for high-throughput drug screening and will significantly improve the efficiency of identifying new drugs for HCC treatment. Through utilization of MCTS models, here we found that inhibitors of Na⁺/K⁺-ATPase may be feasible as a novel target to sensitize HCC cells.

New drugs are not enough‑drug repositioning in oncology: An update

Drug repositioning refers to the concept of discovering novel clinical benefits of drugs that are already known for use treating other diseases. The advantages of this are that several important drug characteristics are already established (including efficacy, pharmacokinetics, pharmacodynamics and toxicity), making the process of research for a putative drug quicker and less costly. Drug repositioning in oncology has received extensive focus. The present review summarizes the most prominent examples of drug repositioning for the treatment of cancer, taking into consideration their primary use, proposed anticancer mechanisms and current development status.

Consensus guidelines for the definition, detection and interpretation of immunogenic cell death

Cells succumbing to stress via regulated cell death (RCD) can initiate an adaptive immune response associated with immunological memory, provided they display sufficient antigenicity and adjuvanticity. Moreover, multiple intracellular and microenvironmental features determine the propensity of RCD to drive adaptive immunity. Here, we provide an updated operational definition of immunogenic cell death (ICD), discuss the key factors that dictate the ability of dying cells to drive an adaptive immune response, summarize experimental assays that are currently available for the assessment of ICD in vitro and in vivo, and formulate guidelines for their interpretation.

Digoxin Enhances the Anticancer Effect on Non-Small Cell Lung Cancer While Reducing the Cardiotoxicity of Adriamycin

Digoxin is widely used to treat heart failure. Epidemiological studies suggested it might be used as an anticancer drug or sensitizing agent for cancer therapy. Adriamycin is a well-known anticancer drug, but often causes cardiotoxicity which limits its use. We recently investigated the anticancer effects of digoxin alone or in combination with adriamycin on human non-small cell lung cancer in vitro and in vivo. Digoxin reduced the viability of A549 and H1299 cells in vitro, increased DNA damage by promoting ROS generation and inhibiting both DNA double strand break (DSB) and single strand break (SSB) repair. Combination with adriamycin showed synergistic antiproliferative effects at the ratios of 1/2IC50_DIG:IC50_ADR and IC50_DIG:IC50_ADR on A549 and H1299 cells, respectively. In vivo, digoxin potently inhibited A549 growth in both zebrafish and nude mouse xenograft model. Co-treatment with adriamycin not only enhanced the antitumor efficacy, but also reduced the cardiotoxicity. Our findings suggest that digoxin has the potential to be applied as an antitumor drug via inhibiting both DNA DSB and SSB repair, and combination with adriamycin for therapy of human non-small cell lung cancer is reasonable.

Peruvoside targets apoptosis and autophagy through MAPK Wnt/β-catenin and PI3K/AKT/mTOR signaling pathways in human cancers

AIM

To investigate the cytotoxic effect of Peruvoside and mechanism of action in human cancers.

MAIN METHODS

Cell viability was measured by MTT assay and the cell cycle arrest was identified by FACS. Real-time qPCR and western blotting studies were performed to identify important gene and protein expressions in the different pathways leading to apoptosis. Immunofluorescence was performed to understand protein localization and molecular docking studies were performed to identify protein-ligand interactions.

KEY FINDINGS

Peruvoside showed significant anti-proliferative activities against human breast, lung, and liver cancer cells in dose-dependent manner. The anti-cancer mechanism was further confirmed by DNA damage and cell cycle arrest at the G0/G1 phase. Dysregulation of Wnt/β-catenin signaling with Peruvoside treatment resulted in inhibition of cyclin D1 and c-Myc also observed in this study. Furthermore, we identified that Peruvoside can inhibit autophagy by PI3K/AKT/mTOR signaling and through downregulating MEK1. Moreover, Peruvoside has the ability to modulate the expressions of key proteins from the cell cycle, MAPK, NF-kB, and JAK-STAT signaling. In silico studies revealed that Peruvoside has the ability to interact with crucial proteins from different biochemical signaling pathways.

SIGNIFICANCE

Our results demonstrated that Peruvoside has the ability to inhibit cancer cell proliferation by modulating the expression of various key proteins involved in cell cycle arrest, apoptosis, and autophagic cell death. Clinical data generated from the present study might provide a novel impetus for targeting several human cancers. Conclusively, our findings suggest that the Peruvoside possesses a broad spectrum of anticancer activity in breast, lung, and liver cancers, which provides an impetus for further investigation of the anticancer potentiality of this biomolecule.

Cloning and characterization of a glycosyltransferase from Catharanthus roseus for glycosylation of cardiotonic steroids and phenolic compounds

OBJECTIVES

To characterize a glycosyltransferase (UGT74AN3) from Catharanthus roseus and investigate its specificity toward cardiotonic steroids and phenolic compounds.

RESULTS

UGT74AN3, a novel permissive GT from C. roseus, displayed average high conversion rate (> 90%) toward eight structurally different cardiotonic steroids. Among them, resibufogenin, digitoxigenin, and uzarigenin gave 100% yield. Based on LC-MS, ¹H-NMR and ¹³C-NMR analysis, structure elucidation of eight glycosides was consistent with 3-O-β-D-glucosides. We further confirmed UGT74AN3 was permissive enough to glycosylate curcumin, resveratrol, and phloretin. The cDNA sequence of UGT74AN3 contained an ORF of 1,425 nucleotides encoding 474 amino acids. UGT74AN3 performed the maximum catalytic activity at 40 °C, pH 8.0, and was divalent cation-independent. K_m values of UGT74AN3 toward resibufogenin, digitoxigenin, and uzarigenin were 7.0 µM, 12.3 µM, and 17.4 µM, respectively.

CONCLUSIONS

UGT74AN3, a glycosyltransferase from a noncardenolide-producing plant, displayed catalytic efficiency toward cardiotonic steroids and phenolic compounds, which would make it feasible for glycosylation of bioactive molecules.

Comedications influence immune infiltration and pathological response to neoadjuvant chemotherapy in breast cancer

Immunosurveillance plays an important role in breast cancer (BC) prognosis and progression, and can be geared by immunogenic chemotherapy. In a cohort of 1023 BC patients treated with neoadjuvant chemotherapy (NAC), 40% of the individuals took comedications mostly linked to aging and comorbidities. We systematically analyzed the off-target effects of 1178 concurrent comedications (classified according to the Anatomical Therapeutic Chemical (ATC) Classification System) on the density of tumor-infiltrating lymphocytes (TILs) and pathological complete responses (pCR). At level 1 of the ATC system, the main anatomical classes of drugs were those targeting the nervous system (class N, 39.1%), cardiovascular disorders (class C, 26.6%), alimentary and metabolism (class A, 16.9%), or hormonal preparations (class H, 6.5%). At level 2, the most frequent therapeutic classes were psycholeptics (N05), analgesics (N02), and psychoanaleptics (N06). Pre-NAC TIL density in triple-negative BC (TNBC) was influenced by medications from class H, N, and A, while TIL density in HER2⁺ BC was associated with the use of class C. Psycholeptics (N05) and agents acting on the renin-angiotensin system (C09) were independently associated with pCR in the whole population of BC or TNBC, and in HER2-positive BC, respectively. Importantly, level 3 hypnotics (N05C) alone were able to reduce tumor growth in BC bearing mice and increased the anti-cancer activity of cyclophosphamide in a T cell-dependent manner. These findings prompt for further exploration of drugs interactions in cancer, and for prospective drug-repositioning strategies to improve the efficacy of NAC in BC.

Cardiac glycoside sensitized hepatocellular carcinoma cells to TRAIL via ROS generation, p38MAPK, mitochondrial transition, and autophagy mediation

A major concern in the clinical application of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) in tumors is the development of resistance. Therefore, agents that can potentially restore TRAIL sensitivity are important therapeutic targets for cancer treatment. Herein, we evaluated lanatoside c and digoxin, both of which are widely used cardiac glycosides (CGs), for their ability to sensitize human hepatocellular carcinoma cells (Huh-7 and HepG2) through TRAIL-induced apoptosis. CGs functionalize TRAIL as shown by its effect on intracellular reactive oxygen species (ROS) generation, which damages mitochondrial integrity and thereby confers intrinsic apoptotic caspase cascade during combined treatment. Caspase activation is dependent on ROS as shown by the ability of CGs to generate ROS and the ROS-N-acetylcysteine (NAC) relationship, which inhibits apoptosis during cotreatment by preventing the formation of caspase-8 and -3. Furthermore, CGs triggered p38MAPK phosphorylation and NAC pre-exposure blocked p38MAPK phosphorylation, which demonstrated that p38MAPK was dependent upon ROS generation. Additionally, CGs were found to be potent inducers of AMPK-mediated protective autophagy as pharmacological and genetic autophagy inhibition reached the higher threshold of TRAIL-mediated apoptosis. Finally, CGs downregulated the expression of the antiapoptotic protein Bcl-2 and increased the translocation of proapoptotic protein cytochrome c, thereby inducing apoptosis. Collectively, these results indicate that CGs potentiate the enhanced cytotoxic capacity to TRAIL through ROS generation, p38MAPK phosphorylation, cell survival protein downregulation, and protective autophagy inhibition.

Caspase-Dependent Apoptosis in Prostate Cancer Cells and Zebrafish by Corchorusoside C from Streptocaulon juventas

Corchorusoside C (1), isolated from Streptocaulon juventas collected in Vietnam, was found to be nontoxic in a zebrafish ( Danio rerio) model and to induce cytotoxicity in several cancer cell lines with notable selective activity against prostate DU-145 cancer cells (IC50 0.08 μM). Moreover, corchorusoside C induced DU-145 cell shrinkage and cell detachment. In CCD-112CoN colon normal cells, 1 showed significantly reduced cytotoxic activity (IC50 2.3 μM). A preliminary mechanistic study indicated that 1 inhibits activity and protein expression of NF-κB (p50 and p65), IKK (α and β), and ICAM-1 in DU-145 cells. ROS concentrations increased at 5 h post-treatment, and MTP decreased in a dose-dependent manner. Moreover, decreased protein expression of Bcl-2 and increased expression of PARP-1 was observed. Furthermore, corchorusoside C increased both the activity and protein levels of caspases 3 and 7. Additionally, 1 induced sub-G1 population increase of DU-145 cells and modulated caspases in zebrafish with nondifferential morphological effects. Therefore, corchorusoside C (1) induces apoptosis in DU-145 cells and targets the same pathways both in vitro and in vivo in zebrafish. Thus, the use of zebrafish assays seems worthy of wider application than is currently employed for the evaluation of potential anticancer agents of natural origin.

Cardiac glycoside cerberin exerts anticancer activity through PI3K/AKT/mTOR signal transduction inhibition

Natural products possess a significant role in anticancer therapy and many currently-used anticancer drugs are of natural origin. Cerberin (CR), a cardenolide isolated from the fruit kernel of Cerbera odollam, was found to potently inhibit cancer cell growth (GI₅₀ values < 90 nM), colony formation and migration. Significant G2/M cell cycle arrest preceded time- and dose-dependent apoptosis-induction in human cancer cell lines corroborated by dose-and time-dependent PARP cleavage and caspase 3/7 activation, in addition to reduced Bcl-2 and Mcl-1 expression. CR potently inhibited PI3K/AKT/mTOR signalling depleting polo-like kinase 1 (PLK-1), c-Myc and STAT-3 expression. Additionally, CR significantly increased the generation of reactive oxygen species (ROS) producing DNA double strand breaks. Preliminary in silico biopharmaceutical assessment of CR predicted >60% bioavailability and rapid absorption; doses of 1-10 mg/kg CR were predicted to maintain efficacious unbound plasma concentrations (>GI₅₀ value). CR's potent and selective anti-tumour activity, and its targeting of key signalling mechanisms pertinent to tumourigenesis support further preclinical evaluation of this cardiac glycoside.

Oleandrin and Its Derivative Odoroside A, Both Cardiac Glycosides, Exhibit Anticancer Effects by Inhibiting Invasion via Suppressing the STAT-3 Signaling Pathway

The cardiac glycosides oleandrin and odoroside A, polyphenolic monomer compounds extracted from Nerium oleander, have been found to have antitumor effects on various tumors at low doses. However, the mechanisms of anticancer effects of oleandrin and odoroside A are not well known. Therefore, in this study, we aimed to investigate the anticancer effects of oleandrin and odoroside A and their associated mechanisms in highly metastatic MDA-MB-231 breast cancer cells and radiotherapy-resistant (RT-R) MDA-MB-231 cells. Our results showed that oleandrin and odoroside A dose-dependently decreased the colony formation and the invasion of both cell lines at nanomolar ranges. Furthermore, oleandrin (50 nM) and odoroside A (100 nM) reduced octamer-binding transcription factor 3/4 (OCT3/4) and β-catenin levels and matrix metalloproteinase-9 (MMP-9) activity. Finally, we found that phospho-STAT-3 levels were increased in MDA-MB-231 and RT-R-MDA-MB-231, but not in endothelial cells (ECs), and that the levels were significantly decreased by oleandrin (50 nM) and odoroside A (100 nM). Inhibition of phospho-signal transducer and activator of transcription (STAT)-3 significantly reduced OCT3/4 and β-catenin levels and MMP-9 activity, ultimately resulting in reduced invasion. These results suggest that the anticancer effects of oleandrin and odoroside A might be due to the inhibition of invasion through of phospho-STAT-3-mediated pathways that are involved in the regulation of invasion-related molecules.

Crosstalk between Na+,K+-ATPase and a volume-regulated anion channel in membrane microdomains of human cancer cells

Low concentrations of cardiac glycosides including ouabain, digoxin, and digitoxin block cancer cell growth without affecting Na⁺,K⁺-ATPase activity, but the mechanism underlying this anti-cancer effect is not fully understood. Volume-regulated anion channel (VRAC) plays an important role in cell death signaling pathway in addition to its fundamental role in the cell volume maintenance. Here, we report cardiac glycosides-induced signaling pathway mediated by the crosstalk between Na⁺,K⁺-ATPase and VRAC in human cancer cells. Submicromolar concentrations of ouabain enhanced VRAC currents concomitantly with a deceleration of cancer cell proliferation. The effects of ouabain were abrogated by a specific inhibitor of VRAC (DCPIB) and knockdown of an essential component of VRAC (LRRC8A), and they were also attenuated by the disruption of membrane microdomains or the inhibition of NADPH oxidase. Digoxin and digitoxin also showed anti-proliferative effects in cancer cells at their therapeutic concentration ranges, and these effects were blocked by DCPIB. In membrane microdomains of cancer cells, LRRC8A was found to be co-immunoprecipitated with Na⁺,K⁺-ATPase α1-isoform. These ouabain-induced effects were not observed in non-cancer cells. Therefore, cardiac glycosides were considered to interact with Na⁺,K⁺-ATPase to stimulate the production of reactive oxygen species, and they also apparently activated VRAC within membrane microdomains, thus producing anti-proliferative effects.