Oleandrin induces apoptosis via activating endoplasmic reticulum stress in breast cancer cells

Kuwanon C inhibits proliferation and induction of apoptosis via the intrinsic pathway in MDA-MB231 and T47D breast cancer cells

Breast cancer ranks as the most prevalent malignancy, presenting persistent therapeutic challenges encompassing issues such as drug resistance, recurrent occurrences, and metastatic progression. Therefore, there is a need for targeted drugs that are less toxic and more effective against breast cancer. Kuwanon C, an isoamylated flavonoid derived from mulberry resources, has shown promise as a potential candidate due to its strong cytotoxicity against cancer cells. The present study focused on investigating the anticancer activity of kuwanon C in two human breast cancer cell lines, MDA-MB231 and T47D cells. MTS assay results indicated a decrease in cell proliferation with increasing concentrations of kuwanon C. Furthermore, kuwanon C upregulated the expression levels of the cyclin-dependent kinase inhibitor p21 and effectively inhibited cell DNA replication and induced DNA damage. Flow cytometry confirmed that kuwanon C induced cell apoptosis and upregulated the expression levels of pro-apoptotic proteins (Bax and c-caspase3). Additionally, it stimulated the production of reactive oxygen species (ROS) in the cells. Transmission electron microscopy and Fluo-4 AM-calcium ion staining experiments provided insights into the endoplasmic reticulum (ER), revealing that kuwanon C induced ER stress. Kuwanon C upregulated the expression levels of unfolded protein response-related proteins (ATF4, GADD34, HSPA5, and DDIT3). Overall, the present findings suggested that kuwanon C exerts a potent inhibitory effect on breast cancer cell proliferation through modulating of the p21, induction of mitochondrial-mediated apoptosis, activation of ER stress and induction of DNA damage. These results position kuwanon C as a potential targeted therapeutic agent for breast cancer.

The mechanistic role of cardiac glycosides in DNA damage response and repair signaling

Cardiac glycosides (CGs) are a class of bioactive organic compounds well-known for their application in treating heart disease despite a narrow therapeutic window. Considerable evidence has demonstrated the potential to repurpose CGs for cancer treatment. Chemical modification of these CGs has been utilized in attempts to increase their anti-cancer properties; however, this has met limited success as their mechanism of action is still speculative. Recent studies have identified the DNA damage response (DDR) pathway as a target of CGs. DDR serves to coordinate numerous cellular pathways to initiate cell cycle arrest, promote DNA repair, regulate replication fork firing and protection, or induce apoptosis to avoid the survival of cells with DNA damage or cells carrying mutations. Understanding the modus operandi of cardiac glycosides will provide critical information to better address improvements in potency, reduced toxicity, and the potential to overcome drug resistance. This review summarizes recent scientific findings of the molecular mechanisms of cardiac glycosides affecting the DDR signaling pathway in cancer therapeutics from 2010 to 2022. We focus on the structural and functional differences of CGs toward identifying the critical features for DDR targeting of these agents.

Steroidal Saponins: Naturally Occurring Compounds as Inhibitors of the Hallmarks of Cancer

Cancer is a global health burden responsible for an exponentially growing number of incidences and mortalities, regardless of the significant advances in its treatment. The identification of the hallmarks of cancer is a major milestone in understanding the mechanisms that drive cancer initiation, development, and progression. In the past, the hallmarks of cancer have been targeted to effectively treat various types of cancers. These conventional cancer drugs have shown significant therapeutic efficacy but continue to impose unfavorable side effects on patients. Naturally derived compounds are being tested in the search for alternative anti-cancer drugs. Steroidal saponins are a group of naturally occurring compounds that primarily exist as secondary metabolites in plant species. Recent studies have suggested that steroidal saponins possess significant anti-cancer capabilities. This review aims to summarize the recent findings on steroidal saponins as inhibitors of the hallmarks of cancer and covers key studies published between the years 2014 and 2024. It is reported that steroidal saponins effectively inhibit the hallmarks of cancer, but poor bioavailability and insufficient preclinical studies limit their utilization.

Cardiac glycoside neriifolin exerts anti-cancer activity in prostate cancer cells by attenuating DNA damage repair through endoplasmic reticulum stress

Prostate cancer (PCa) is one of the most common cancers in men. Patients with recurrent disease initially respond to androgen-deprivation therapy, but the tumor eventually progresses into castration-resistant PCa. Thus, new therapeutic approaches for PCa resistance to current treatments are urgently needed. Here, we report that cardiac glycoside neriifolin suppresses the malignancy of cancer cells via increasing DNA damage and apoptosis through activation of endoplasmic reticulum stress (ERS) in prostate cancers. We found that cardiac glycoside neriifolin markedly inhibited the cell growth and induced apoptosis in prostate cancer cells. Transcriptome sequence analysis revealed that neriifolin significantly induced DNA damage and double strand breaks (DSBs), validated with attenuation expression of genes in DSBs repair and increasing phosphorylated histone H2AX (γ-H2AX) foci formation, a quantitative marker of DSBs. Moreover, we found that neriifolin also activated ERS, evidenced by upregulation and activation of ERS related proteins, including eukaryotic initiation factor 2α (eIF2α), protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) and C/EBP homologous protein (CHOP) as well as downregulation of CCAATenhancerbinding protein alpha (C/EBP-α), a transcriptional factor that forms heterodimers with CHOP. In addition, neriifolin treatment dramatically inhibited the by tumor growth, which were reversed by CHOP loss or overexpression of C/EBP-α in nude mice. Mechanistically, neriifolin suppressed the tumor growth by increasing DNA damage and apoptosis through CHOP-C/EBP-α signaling axis of ERS in prostate cancers. Taken together, these results suggest that cardiac glycoside neriifolin may be a potential tumor-specific chemotherapeutic agent in prostate cancer treatment.

Application of advanced technology in traditional Chinese medicine for cancer therapy

Although cancer has seriously threatened people’s health, it is also identified by the World Health Organization as a controllable, treatable and even curable chronic disease. Traditional Chinese medicine (TCM) has been extensively used to treat cancer due to its multiple targets, minimum side effects and potent therapeutic effects, and thus plays an important role in all stages of tumor therapy. With the continuous progress in cancer treatment, the overall efficacy of cancer therapy has been significantly improved, and the survival time of patients has been dramatically prolonged. In recent years, a series of advanced technologies, including nanotechnology, gene editing technology, real-time cell-based assay (RTCA) technology, and flow cytometry analysis technology, have been developed and applied to study TCM for cancer therapy, which efficiently improve the medicinal value of TCM and accelerate the research progress of TCM in cancer therapy. Therefore, the applications of these advanced technologies in TCM for cancer therapy are summarized in this review. We hope this review will provide a good guidance for TCM in cancer therapy.

Pro-Apoptotic and Pro-Autophagic Properties of Cardenolides from Aerial Parts of Pergularia tomentosa

Pergularia tomentosa L., a milkweed tropical plant belonging to the family Asclepiadaceae, is a rich source of unusual cardiac glycosides, characterised by transfused A/B rings and a sugar moiety linked by a double link, generating a dioxanoid structure. In the present report, five cardenolides isolated from the aerial parts of the plant (calactin, calotropin, 12β-hydroxycalactin, 12β,6'-dihydroxycalotropin, and 16α-hydroxycalotropin) were investigated for their biological effects on a human hepatocarcinoma cell line. Cell viability was monitored by an MTT assay. The occurrence of apoptosis was evaluated by detecting caspase-3 activation and chromatin fragmentation. The ability of these compounds to induce autophagy was analysed by monitoring two markers of the autophagic process, LC3 and p62. Our results indicated that all cardenolides had cytotoxic effects, with IC₅₀ ranging from 0.127 to 6.285 μM. All compounds were able to induce apoptosis and autophagy, calactin being the most active one. Some of them also caused a reduction in cell migration and a partial block of the cell cycle into the S-phase. The present study suggests that selected cardenolides from aerial parts of P. tomentosa, particularly calactin, possess potentially desirable properties for further investigation as anticancer agents.

Apoptosis Induction Associated with Enhanced ER Stress Response and Up-Regulation of c-Jun/p38 MAPK Proteins in Human Cervical Cancer Cells by Colocasia esculenta var. aquatilis Hassk Extract

Colocasia esculenta var. Aquatilis Hassk, elephant ear (CF-EE) has been widely used as traditional food and medicine. It also shows other therapeutic properties, such as antimicrobial and anti-cancer activity. In this study, we aim to investigate the effect of CF-EE extract on apoptosis induction associated with ER stress in cervical cancer HeLa cells. Cell viability was determined by MTT assay. Assessments of nuclear morphological changes, mitochondrial membrane potential, and intracellular reactive oxygen species (ROS) production were conducted by hoeshst33342, JC-1, and DCFH-DA fluorescence staining, respectively. Sub-G1 DNA content was analyzed by flow cytometry, and protein expression was determined by Western blotting. The results demonstrate that CF-EE extract suppressed HeLa cell growth and induced nuclear condensation and apoptotic bodies. There was also a loss of mitochondrial membrane potential and increased apoptosis marker protein expression, including Bax, cleaved-caspase-7, and cleaved-PARP. In addition, the results show that CF-EE extract induced ROS, increased ER stress proteins (GRP78 and CHOP), enhanced p38 and c-Jun phosphorylation, and inhibited Akt expression in HeLa cells. In summary, CF-EE extract induced apoptotic cell death-associated ROS-induced ER stress and the MAPK/AKT signaling pathway. Therefore, CF-EE extract has anticancer therapeutic potential for cervical cancer treatment in the future.

Antitumor effects of oleandrin in different types of cancers: Systematic review

Oleandrin, a cardiac glycoside isolated from the leaves of Nerium oleander, has known effects on the heart. Evidence from recent studies have highlighted its potential for anticancer properties. Therefore, we aimed to investigate the effects of oleandrin on cancer cell proliferation, viability and apoptosis in vitro and in vivo. We performed a systematic search in six electronic databases up to Jan 2022. We extracted information about the effects of oleandrin on cell proliferation, cell viability, apoptosis and/or cell cycle arrest in in vitro studies, and the effects on tumor size and volume in animal experimental models. We have retrieved 775 scientific studies. 14 studies met the inclusion criteria. They investigated the effects of oleandrin on breast, lung, pancreatic, colon, prostate, colorectal, oral, ovarian, glioma, melanoma, glioblastoma, osteosarcoma, and histiocytic lymphoma cancers. Overall, in vitro studies demonstrated that oleandrin was able to inhibit cell proliferation, decrease cell viability, and induce apoptosis and/or cell cycle arrest. In addition, oleandrin had an effect on reducing mean tumor size and volume in animal studies. Oleandrin, as a cytotoxic agent, demonstrated antitumor effects in different types of cancers, however important clinical limitations remain a concern. These results encourage future studies to verify the applicability of oleandrin in antineoplastic therapeutic protocols human and veterinary medicine, the investigation of antimetastatic properties, as well as the potential increase in patient survival and the decrease of tumor markers.

BAY-885, a mitogen-activated protein kinase kinase 5 inhibitor, induces apoptosis by regulating the endoplasmic reticulum stress/Mcl-1/Bim pathway in breast cancer cells

The mitogen-activated protein kinase kinase 5 (MEK5)/extracellular signal-regulated kinase 5 (ERK5) axis has been reported to promote tumorigenesis in breast cancer (BC). Therefore, targeting the MEK5/ERK5 axis is a potential strategy against BC. BAY-885 is a novel inhibitor of ERK5; however, to date, its anti-tumor effects in BC have not been investigated. This study aimed to assess the anti-tumor effects of BAY-885 in BC and identify its underlying mechanisms of action. Unlike other ERK5 inhibitors, which frequently failed to mimic ERK5 genetic ablation phenotypes, the BAY-885 treatment effectively recapitulated ERK5 depletion effects in BC cells. Results revealed that BAY-885 affected the viability and induced apoptosis in BC cells. Moreover, the BAY-885-mediated downregulation of myeloid cell leukemia-1 (Mcl-1) and upregulation of Bim were dependent on ERK5 inhibition. Furthermore, BAY-885 triggered activation of endoplasmic reticulum (ER) stress, which further led to the upregulation of Bim and downregulation of Mcl-1. ER stress was induced in an ERK5 inhibition-dependent manner. These findings suggested that BAY-885 induced apoptosis in BC cells via ER stress/Mcl-1/Bim axis, suggesting that BAY-885 may serve as a therapeutic agent for BC.

Targeting regulated cell death (RCD) with small-molecule compounds in triple-negative breast cancer: a revisited perspective from molecular mechanisms to targeted therapies

Triple-negative breast cancer (TNBC) is a subtype of human breast cancer with one of the worst prognoses, with no targeted therapeutic strategies currently available. Regulated cell death (RCD), also known as programmed cell death (PCD), has been widely reported to have numerous links to the progression and therapy of many types of human cancer. Of note, RCD can be divided into numerous different subroutines, including autophagy-dependent cell death, apoptosis, mitotic catastrophe, necroptosis, ferroptosis, pyroptosis and anoikis. More recently, targeting the subroutines of RCD with small-molecule compounds has been emerging as a promising therapeutic strategy, which has rapidly progressed in the treatment of TNBC. Therefore, in this review, we focus on summarizing the molecular mechanisms of the above-mentioned seven major RCD subroutines related to TNBC and the latest progress of small-molecule compounds targeting different RCD subroutines. Moreover, we further discuss the combined strategies of one drug (e.g., narciclasine) or more drugs (e.g., torin-1 combined with chloroquine) to achieve the therapeutic potential on TNBC by regulating RCD subroutines. More importantly, we demonstrate several small-molecule compounds (e.g., ONC201 and NCT03733119) by targeting the subroutines of RCD in TNBC clinical trials. Taken together, these findings will provide a clue on illuminating more actionable low-hanging-fruit druggable targets and candidate small-molecule drugs for potential RCD-related TNBC therapies.

Promoting Apoptosis, a Promising Way to Treat Breast Cancer With Natural Products: A Comprehensive Review

Breast cancer is one of the top-ranked malignant carcinomas associated with morbidity and mortality in women worldwide. Chemotherapy is one of the main approaches to breast cancer treatment. Breast cancer initially responds to traditional first- and second-line drugs (aromatase inhibitor, tamoxifen, and carboplatin), but eventually acquires resistance, and certain patients relapse within 5 years. Chemotherapeutic drugs also have obvious toxic effects. In recent years, natural products have been widely used in breast cancer research because of their low side effects, low toxicity, and good efficacy based on their multitarget therapy. Apoptosis, a programmed cell death, occurs as a normal and controlled process that promotes cell growth and death. Inducing apoptosis is an important strategy to control excessive breast cancer cell proliferation. Accumulating evidence has revealed that natural products become increasingly important in breast cancer treatment by suppressing cell apoptosis. In this study, we reviewed current studies on natural product–induced breast cancer cell apoptosis and summarized the proapoptosis mechanisms including mitochondrial, FasL/Fas, PI3K/AKT, reactive oxygen species, and mitogen-activated protein kinase–mediated pathway. We hope that our review can provide direction in the search for candidate drugs derived from natural products to treat breast cancer by promoting cell apoptosis.

Efficacy of oleandrin and PBI-05204 against bovine viruses of importance to commercial cattle health

Background

Bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus (BRSV). and bovine coronavirus (BCV) threaten the productivity of cattle worldwide. Development of therapeutics that can control the spread of these viruses is an unmet need. The present research was designed to explore the in vitro antiviral activity of the Nerium oleander derived cardiac glycoside oleandrin and a defined N. oleander plant extract (PBI-05204) containing oleandrin.

Methods

Madin Darby Bovine Kidney (MDBK) cells, Bovine Turbinate (BT) cells, and Human Rectal Tumor-18 (HRT-18) cells were used as in vitro culture systems for BVDV, BRSV and BCV, respectively. Cytotoxicity was established using serial dilutions of oleandrin or PBI-05204. Noncytotoxic concentrations of each drug were used either prior to or at 12 h and 24 h following virus exposure to corresponding viruses. Infectious virus titers were determined following each treatment.

Results

Both oleandrin as well as PBI-05204 demonstrated strong antiviral activity against BVDV, BRSV, and BCV, in a dose-dependent manner, when added prior to or following infection of host cells. Determination of viral loads by PCR demonstrated a concentration dependent decline in virus replication. Importantly, the relative ability of virus produced from treated cultures to infect new host cells was reduced by as much as 10,000-fold at noncytotoxic concentrations of oleandrin or PBI-05204.

Conclusions

The research demonstrates the potency of oleandrin and PBI-05204 to inhibit infectivity of three important enveloped bovine viruses in vitro. These data showing non-toxic concentrations of oleandrin inhibiting infectivity of three bovine viruses support further investigation of in vivo antiviral efficacy.

Cdc25C/cdc2/cyclin B, raf/MEK/ERK and PERK/eIF2α/CHOP pathways are involved in forskolin-induced growth inhibition of MM.1S cells by G2/M arrest and mitochondrion-dependent apoptosis

Multiple myeloma (MM) remains an incurable hematological malignancy characterized by proliferation and accumulation of plasma cells in the bone marrow. Innovative and effective therapeutic approaches that are able to improve the outcome and the survival of MM sufferers, especially the identification of novel natural compounds and investigation of their anti-MM mechanisms, are needed. Here, we investigated the effects and the potential mechanisms against MM of forskolin, a diterpene derived from the medicinal plant Coleus forskohlii, in MM cell line MM.1S. CCK-8 assay showed that forskolin significantly inhibited MM.1S cells viability in a time- and dose-dependent manner. Furthermore, we demonstrated that forskolin induced G2/M phase arrest with a remarkable increase of p-cdc25c, p-cdc2, and a decrease of cyclin B1, indicating the suppression of cdc25C/cdc2/cyclin B pathway. Moreover, we found that forskolin induced mitochondrion-dependent apoptosis which was accompanied by the increase of pro-apoptotic proteins Bax, Bad, Bim and Bid, the decrease of anti-apoptotic proteins Bcl-2 and Bcl-xl, the changes of the mitochondrial membrane potential (MMP) and increase of cleaved caspase-9, cleaved caspase-3 and cleaved PARP. Of note, we demonstrated that forskolin induced a decrease of p-C-Raf, p-MEK, p-ERK1/2 and p-p90Rsk, and an increase of p-PERK, p-eIF2α and CHOP, which indicated that the inhibition of Raf/MEK/ERK pathway and activation of PERK/eIF2α/CHOP pathway were involved, at least partially, in forskolin-induced MM.1S cells apoptosis. These findings confirm the anti-MM action of forskolin and extend the understanding of its anti-MM mechanism in MM.1S cells, as well as reinforcing the evidence for forskolin as a natural chemotherapeutic compound against MM.

Calotropis gigantea stem bark extract induced apoptosis related to ROS and ATP production in colon cancer cells

Conventional chemotherapeutic agents for colorectal cancer (CRC) cause systemic side effects and eventually become less efficacious owing to the development of drug resistance in cancer cells. Therefore, new therapeutic regimens have focused on the use of natural products. The anticancer activity of several parts of Calotropis gigantea has been reported; however, the effects of its stem bark extract on inhibition of cancer cell proliferation have not yet been examined. In this study, the anticancer activity of C. gigantea stem bark extract, both alone and in combination with 5-fluorouracil (5-FU), was evaluated. A crude ethanolic extract was prepared from dry, powdered C. gigantea barks using 95% ethanol. This was then partitioned to obtain dichloromethane (CGDCM), ethyl acetate, and water fractions. Quantitative analysis of the constituent secondary metabolites and calotropin was performed. These fractions exhibited cytotoxicity in HCT116 and HT-29 cells, with CGDCM showing the highest potency in both the cell lines. A combination of CGDCM and 5-FU significantly enhanced the cytotoxic effect. Moreover, the resistance of normal fibroblast, HFF-1, cells to this combination demonstrated its safety in normal cells. The combination significantly enhanced apoptosis through the mitochondria-dependent pathway. Additionally, the combination reduced adenosine triphosphate production and increased the production of reactive oxygen species, demonstrating the mechanisms involved in the induction of apoptosis. Our results suggest that CGDCM is a promising anti-cancer agent and may enhance apoptosis induction by 5-FU in the treatment of CRC, while minimizing toxicity toward healthy cells.

Oleandrin, a cardiac glycoside, induces immunogenic cell death via the PERK/elF2α/ATF4/CHOP pathway in breast cancer

Chemotherapeutic agents have been linked to immunogenic cell death (ICD) induction that is capable of augmenting anti-tumor immune surveillance. The cardiac glycoside oleandrin, which inhibits Na⁺/K⁺-ATPase pump (NKP), has been shown to suppress breast cancer growth via inducing apoptosis. In the present study, we showed that oleandrin treatment triggered breast cancer cell ICD by inducing calreticulin (CRT) exposure on cell surface and the release of high-mobility group protein B1 (HMGB1), heat shock protein 70/90 (HSP70/90), and adenosine triphosphate (ATP). The maturation and activation of dendritic cells (DCs) were increased by co-culturing with the oleandrin-treated cancer cells, which subsequently enhanced CD8⁺ T cell cytotoxicity. Murine breast cancer cell line EMT6 was engrafted into BALB/c mice, and tumor-bearing mice were administered with oleandrin intraperitoneally every day. Oleandrin inhibited tumor growth and increased tumor infiltrating lymphocytes including DCs and T cells. Furthermore, the differential mRNA expression incurred by oleandrin was investigated by mRNA sequencing and subsequently confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. Mechanistically, oleandrin induced endoplasmic reticulum (ER) stress-associated, caspase-independent ICD mainly through PERK/elF2α/ATF4/CHOP pathway. Pharmacological and genetic inhibition of protein kinase R-like ER kinase (PERK) suppressed oleandrin-triggered ICD. Taken together, our findings showed that oleandrin triggered ER stress and induced ICD-mediated immune destruction of breast cancer cells. Oleandrin combined with immune checkpoint inhibitors might improve the efficacy of immunotherapy.

Cytotoxicity of Oleandrin Is Mediated by Calcium Influx and by Increased Manganese Uptake in Saccharomyces cerevisiae Cells

Oleandrin, the main component of Nerium oleander L. extracts, is a cardiotoxic glycoside with multiple pharmacological implications, having potential anti-tumoral and antiviral characteristics. Although it is accepted that the main mechanism of oleandrin action is the inhibition of Na⁺/K⁺-ATPases and subsequent increase in cell calcium, many aspects which determine oleandrin cytotoxicity remain elusive. In this study, we used the model Saccharomyces cerevisiae to unravel new elements accounting for oleandrin toxicity. Using cells expressing the Ca²⁺-sensitive photoprotein aequorin, we found that oleandrin exposure resulted in Ca²⁺ influx into the cytosol and that failing to pump Ca²⁺ from the cytosol to the vacuole increased oleandrin toxicity. We also found that oleandrin exposure induced Mn²⁺ accumulation by yeast cells via the plasma membrane Smf1 and that mutants with defects in Mn²⁺ homeostasis are oleandrin-hypersensitive. Our data suggest that combining oleandrin with agents which alter Ca²⁺ or Mn²⁺ uptake may be a way of controlling oleandrin toxicity.