Suppression of ER-stress induction of GRP78 as an anti-neoplastic mechanism of the cardiac glycoside Lanatoside C in pancreatic cancer: Lanatoside C suppresses GRP78 stress induction

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.

Lanatoside C Inhibits Proliferation and Induces Apoptosis in Human Prostate Cancer Cells Through the TNF/IL-17 Signaling Pathway

Prostate cancer remains a leading cause of cancer-related morbidity and mortality among men globally, with limited therapeutic options for advanced and metastatic disease. The therapeutic potential of natural compounds has attracted increasing attention in cancer treatment. Lanatoside C (Lan C), a cardiac glycoside derived from Digitalis lanata, has demonstrated promising anticancer activity across various cancer types. However, its role and mechanisms in prostate cancer remain underexplored. In this study, evidence shows that Lan C significantly inhibits the proliferation of prostate cancer cells, as demonstrated by reduced cell viability, suppressed colony formation, and G2/M cell cycle arrest. Additionally, Lan C promotes apoptosis and inhibits the migration and invasion of prostate cancer cells. Mechanistically, transcriptomic analysis identified differentially expressed genes, which were further validated at both the mRNA and protein levels. Our findings suggest that Lan C exerts its effects by modulating the TNF/IL-17 signaling pathway, influencing the tumor microenvironment and regulating key processes involved in tumor progression, immune response, and apoptosis.

Targeting stress induction of GRP78 by cardiac glycoside oleandrin dually suppresses cancer and COVID-19

BACKGROUND

Despite recent therapeutic advances, combating cancer resistance remains a formidable challenge. The 78-kilodalton glucose-regulated protein (GRP78), a key stress-inducible endoplasmic reticulum (ER) chaperone, plays a crucial role in both cancer cell survival and stress adaptation. GRP78 is also upregulated during SARS-CoV-2 infection and acts as a critical host factor. Recently, we discovered cardiac glycosides (CGs) as novel suppressors of GRP78 stress induction through a high-throughput screen of clinically relevant compound libraries. This study aims to test the possibility that agents capable of blocking stress induction of GRP78 could dually suppress cancer and COVID-19.

RESULTS

Here we report that oleandrin (OLN), is the most potent among the CGs in inhibiting acute stress induction of total GRP78, which also results in reduced cell surface and nuclear forms of GRP78 in stressed cells. The inhibition of stress induction of GRP78 is at the post-transcriptional level, independent of protein degradation and autophagy and may involve translational control as OLN blocks stress-induced loading of ribosomes onto GRP78 mRNAs. Moreover, the human Na+/K+-ATPase α3 isoform is critical for OLN suppression of GRP78 stress induction. OLN, in nanomolar range, enhances apoptosis, sensitizes colorectal cancer cells to chemotherapeutic agents, and reduces the viability of patient-derived colon cancer organoids. Likewise, OLN, suppresses GRP78 expression and impedes tumor growth in an orthotopic breast cancer xenograft model. Furthermore, OLN blocks infection by SARS-CoV-2 and its variants and enhances existing anti-viral therapies. Notably, GRP78 overexpression mitigates OLN-mediated cancer cell apoptotic onset and suppression of virus release.

CONCLUSION

Our findings validate GRP78 as a target of OLN anti-cancer and anti-viral activities. These proof-of-principle studies support further investigation of OLN as a readily accessible compound to dually combat cancer and COVID-19.

Lanatoside C induces ferroptosis in non-small cell lung cancer in vivo and in vitro by regulating SLC7A11/GPX4 signaling pathway

Background

Non-small cell lung cancer (NSCLC) is a common malignant tumor worldwide, remaining resistant to chemotherapy drugs. Lanatoside C can inhibit the growth of cancer cell lines. In this study we aimed to investigate the relationship between lanatoside C and ferroptosis, exploring the possible mechanism in NSCLC.

Methods

Experiments in vitro and in vivo were conducted. A549 cells were used for in vitro, including cell counting kit-8 (CCK-8) assay, lactate dehydrogenase (LDH) release, western blotting, flow cytometry, transmission electron microscopy (TEM), and confocal microscopy. In vivo, a subcutaneous tumor model in nude mice using A549 cells was built and body size of the mice was observed. Ki67 immunohistochemistry, hematoxylin-eosin (HE) staining, and western blotting were conducted respectively.

Results

The results showed that lanatoside C had an inhibitory effect on the growth of A549 cells, and the dose of lanatoside C used in this experiment was set at 0.4 µM for 24 hours. When A549 cells were treated with lanatoside C, the cell viability was decreased observably (P<0.001) and LDH release was significantly enhanced (P<0.01) compared with the control group. However, when A549 cells were treated together with lanatoside C and five different inhibitors, containing ferroptosis inhibitors, necroptosis inhibitors, apoptosis inhibitors, pyroptosis inhibitors, and autophagy inhibitors, the results showed that the viability of A549 cells with lanatoside C and ferrostatin-1 (Fer-1) was reduced (P>0.05) and the LDH release was significantly enhanced (P<0.05). Besides, TEM and confocal microscopy showed that the mitochondria of A549 cells in the lanatoside C group disappeared and the mitochondrial membrane potential decreased. In vivo, lanatoside C efficiently enhanced the sensitivity of the xenograft tumors, as well as reducing the size and weight of the tumor. Moreover, immunohistochemical staining analysis revealed that the SLC7A11 and GPX4 levels significantly decreased in the lanatoside C group. In addition, the expression of GPX4 and SLC7A11 by western blotting was decreased in lanatoside C group.

Conclusions

Collectively, lanatoside C could inhibit the proliferation and induce ferroptosis, and have a biological effect on inducing ferroptosis in NSCLC.

Incorporating Network Pharmacology and Experimental Validation to Identify Bioactive Compounds and Potential Mechanisms of Digitalis in Treating Anaplastic Thyroid Cancer

Anaplastic thyroid cancer (ATC) is one of the most lethal malignant tumors for which there is no effective treatment. There are an increasing number of studies on herbal medicine for treating malignant tumors, and the classic botanical medicine Digitalis and its active ingredients for treating heart failure and arrhythmias have been revealed to have significant antitumor efficacy against a wide range of malignant tumors. However, the main components of Digitalis and the molecular mechanisms of its anti-ATC effects have not been extensively studied. Here, we screened the main components and core targets of Digitalis and verified the relationship between the active components and targets through network pharmacology, molecular docking, and experimental validation. These experiments showed that the active ingredients of Digitalis inhibit ATC cell activity and lead to ATC cell death through the apoptotic pathway.

Recent advances in small molecule and peptide inhibitors of glucose-regulated protein 78 for cancer therapy

Glucose-regulated protein 78 (GRP78) is one of key endoplasmic reticulum (ER) chaperone proteins that regulates the unfolded protein response (UPR) to maintain ER homeostasis. As a core factor in the regulation of the UPR, GRP78 takes a critical part in the cellular processes required for tumorigenesis, such as proliferation, metastasis, anti-apoptosis, immune escape and chemoresistance. Overexpression of GRP78 is closely correlated with tumorigenesis and poor prognosis in various malignant tumors. Targeting GRP78 is regarded as a potentially promising therapeutic strategy for cancer therapy. Although none of the GRP78 inhibitors have been approved to date, there have been several studies of GRP78 inhibitors. Herein, we comprehensively review the structure, physiological functions of GRP78 and the recent progress of GRP78 inhibitors, and discuss the structures, in vitro and in vivo efficacies, and merits and demerits of these inhibitors to inspire further research. Additionally, the feasibility of GRP78-targeting proteolysis-targeting chimeras (PROTACs), disrupting GRP78 cochaperone interactions, or covalent inhibition are also discussed as novel strategies for drugs discovery targeting GRP78, with the hope that these strategies can provide new opportunities for targeted GRP78 antitumor therapy.

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.

Unveiling the dark side of glucose-regulated protein 78 (GRP78) in cancers and other human pathology: a systematic review

Glucose-Regulated Protein 78 (GRP78) is a chaperone protein that is predominantly expressed in the lumen of the endoplasmic reticulum. GRP78 plays a crucial role in protein folding by assisting in the assembly of misfolded proteins. Under cellular stress conditions, GRP78 can translocate to the cell surface (csGRP78) were it interacts with different ligands to initiate various intracellular pathways. The expression of csGRP78 has been associated with tumor initiation and progression of multiple cancer types. This review provides a comprehensive analysis of the existing evidence on the roles of GRP78 in various types of cancer and other human pathology. Additionally, the review discusses the current understanding of the mechanisms underlying GRP78's involvement in tumorigenesis and cancer advancement. Furthermore, we highlight recent innovative approaches employed in downregulating GRP78 expression in cancers as a potential therapeutic target.

ER chaperone GRP78/BiP translocates to the nucleus under stress and acts as a transcriptional regulator

Cancer cells are commonly subjected to endoplasmic reticulum (ER) stress. To gain survival advantage, cancer cells exploit the adaptive aspects of the unfolded protein response such as upregulation of the ER luminal chaperone GRP78. The finding that when overexpressed, GRP78 can escape to other cellular compartments to gain new functions regulating homeostasis and tumorigenesis represents a paradigm shift. Here, toward deciphering the mechanisms whereby GRP78 knockdown suppresses EGFR transcription, we find that nuclear GRP78 is prominent in cancer and stressed cells and uncover a nuclear localization signal critical for its translocation and nuclear activity. Furthermore, nuclear GRP78 can regulate expression of genes and pathways, notably those important for cell migration and invasion, by interacting with and inhibiting the activity of the transcriptional repressor ID2. Our study reveals a mechanism for cancer cells to respond to ER stress via transcriptional regulation mediated by nuclear GRP78 to adopt an invasive phenotype.

GRP78 Inhibitor YUM70 Suppresses SARS-CoV-2 Viral Entry, Spike Protein Production and Ameliorates Lung Damage

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of the COVID-19 pandemic, has given rise to many new variants with increased transmissibility and the ability to evade vaccine protection. The 78-kDa glucose-regulated protein (GRP78) is a major endoplasmic reticulum (ER) chaperone that has been recently implicated as an essential host factor for SARS-CoV-2 entry and infection. In this study, we investigated the efficacy of YUM70, a small molecule inhibitor of GRP78, to block SARS-CoV-2 viral entry and infection in vitro and in vivo. Using human lung epithelial cells and pseudoviral particles carrying spike proteins from different SARS-CoV-2 variants, we found that YUM70 was equally effective at blocking viral entry mediated by original and variant spike proteins. Furthermore, YUM70 reduced SARS-CoV-2 infection without impacting cell viability in vitro and suppressed viral protein production following SARS-CoV-2 infection. Additionally, YUM70 rescued the cell viability of multi-cellular human lung and liver 3D organoids transfected with a SARS-CoV-2 replicon. Importantly, YUM70 treatment ameliorated lung damage in transgenic mice infected with SARS-CoV-2, which correlated with reduced weight loss and longer survival. Thus, GRP78 inhibition may be a promising approach to augment existing therapies to block SARS-CoV-2, its variants, and other viruses that utilize GRP78 for entry and infection.

Only one carbon difference determines the pro-apoptotic activity of α-tocopheryl esters

α-Tocopheryl succinate (TS), a redox-silent succinyl ester of natural α-Tocopherol, has emerged as a novel anti-cancer agent. However, the underlying mechanism is unclear. We found that the terminal dicarboxylic moiety of tocopheryl esters contributes to apoptosis induction and thus cytotoxicity. To further examine this relationship, we compared the pro-apoptotic activity of TS, which has four carbon atoms in the terminal dicarboxylic moiety, to that of a newly synthesized, tocopheryl glutarate (Tglu), which has five. Cytotoxicity assays in vitro confirmed that TS stimulated apoptosis, while Tglu was non-cytotoxic. In investigating biological mechanisms leading to these opposing effects, we found that TS caused an elevation of intracellular superoxide, but Tglu did not. TS increased intracellular Ca²⁺ in cultured cells, suggesting induction of endoplasmic reticulum (ER) stress; however, Tglu did not affect Ca²⁺ homeostasis. 1,4,5-trisphosphate (IP₃ ) receptor antagonist 2-Aminoethyl diphenylborinate (2-APB) decreased TS-induced intracellular Ca²⁺ , restored mitochondrial activity and cell viability in TS-treated cells, establishing the ER-mitochondria relationship in apoptosis induction. Moreover, real-time PCR, immunostaining and Western blotting assays revealed that TS downregulated glucose-regulated protein 78 (GRP78), which maintains ER homeostasis and promotes cell survival. Conversely, Tglu upregulates GRP78. Taken together, our results suggest a model in which TS-mediated superoxide production and GRP78 inhibition induce ER stress, which elevates intracellular Ca²⁺ and depolarizes mitochondria, leading to apoptosis. Because Tglu does not affect superoxide generation and increases GRP78 expression, it inhibits ER stress and is thereby non-cytotoxic. Our research provides insight into the structure-activity relationship of tocopheryl esters regarding the induction of apoptosis.

Suppression of head and neck cancer cell survival and cisplatin resistance by GRP78 small molecule inhibitor YUM70

Background

Head and neck squamous cell carcinoma (HNSCC) is one of the leading causes of cancer-related death worldwide. Surgical resection, radiation and chemotherapy are the mainstay of HNSCC treatment but are often unsatisfactory. Cisplatin is a commonly used chemotherapy in HNSCC; however, cisplatin resistance is a major cause of relapse and death. The 78-kD glucose-regulated protein (GRP78) is the master regulator of the unfolded protein response (UPR) and is implicated in therapeutic resistance in cancer. The role of GRP78 in cisplatin resistance in HNSCC remains unclear. YUM70 is a newly discovered hydroxyquinoline analogue and found to be an inhibitor of GRP78. The effect of YUM70 in HNSCC cell lines is unknown.

Method

Knockdown of GRP78 by siRNAs was performed to investigate the effect of GRP78 reduction in endoplasmic reticulum (ER)-stress induced and general apoptosis. Western blots examining apoptotic markers were performed on three HPV-negative HNSCC cell lines. WST-1 assay was performed to determine cell viability. In reverse, we utilized AA147, an ER proteostasis regulator to upregulate GRP78, and apoptotic markers and cell viability were determined. To test the ability of YUM70 to reverse cisplatin resistance, cisplatin-resistant HNSCC cell lines were generated by prolonged, repeated exposure to increasing concentrations of cisplatin. Colony formation assay using the cisplatin-resistant HNSCC cell line was performed to assess the in vitro reproductive cell survival. Furthermore, to test the ability of YUM70 to reverse cisplatin resistance in a physiologically relevant system, we subjected the 3D spheroids of the cisplatin-resistant HNSCC cell line to cisplatin treatment with or without YUM70 and monitored the onset of apoptosis.

Results

Reduction of GRP78 level induced HNSCC cell death while GRP78 upregulation conferred higher resistance to cisplatin. Combined cisplatin and YUM70 treatment increased apoptotic markers in the cisplatin-resistant HNSCC cell line, associating with reduced cell viability and clonogenicity. The combination treatment also increased apoptotic markers in the 3D spheroid model.

Conclusion

The GRP78 inhibitor YUM70 reduced HNSCC cell viability and re-sensitized cisplatin-resistant HNSCC cell line in both 2D and 3D spheroid models, suggesting the potential use of YUM70 in the treatment of HNSCC, including cisplatin-resistant HNSCC.

Targeting GRP78 suppresses oncogenic KRAS protein expression and reduces viability of cancer cells bearing various KRAS mutations

KRAS is the most commonly mutated oncogene in human cancers with limited therapeutic options, thus there is a critical need to identify novel targets and inhibiting agents. The 78-kDa glucose-regulated protein GRP78, which is upregulated in KRAS cancers, is an essential chaperone and the master regulator of the unfolded protein response (UPR). Following up on our recent discoveries that GRP78 haploinsufficiency suppresses both KRASG12D-driven pancreatic and lung tumorigenesis, we seek to determine the underlying mechanisms. Here, we report that knockdown of GRP78 via siRNA reduced oncogenic KRAS protein level in human lung, colon, and pancreatic cancer cells bearing various KRAS mutations. This effect was at the post-transcriptional level and is independent of proteasomal degradation or autophagy. Moreover, targeting GRP78 via small molecule inhibitors such as HA15 and YUM70 with anti-cancer activities while sparing normal cells significantly suppressed oncogenic KRAS expression in vitro and in vivo, associating with onset of apoptosis and loss of viability in cancer cells bearing various KRAS mutations. Collectively, our studies reveal that GRP78 is a previously unidentified regulator of oncogenic KRAS expression, and, as such, augments the other anti-cancer activities of GRP78 small molecule inhibitors to potentially achieve general, long-term suppression of mutant KRAS-driven tumorigenesis.

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.