Plumbagin induces apoptosis in human osteosarcoma through ROS generation, endoplasmic reticulum stress and mitochondrial apoptosis pathway

Oxidative Stress Inducers in Cancer Therapy: Preclinical and Clinical Evidence

Reactive oxygen species (ROS) are metabolic byproducts that regulate various cellular processes. However, at high levels, ROS induce oxidative stress, which in turn can trigger cell death. Cancer cells alter the redox homeostasis to facilitate protumorigenic processes; however, this leaves them vulnerable to further increases in ROS levels. This paradox has been exploited as a cancer therapeutic strategy with the use of pro-oxidative drugs. Many chemotherapeutic drugs presently in clinical use, such as cisplatin and doxorubicin, induce ROS as one of their mechanisms of action. Further, various drugs, including phytochemicals and small molecules, that are presently being investigated in preclinical and clinical studies attribute their anticancer activity to ROS induction. Consistently, this review aims to highlight selected pro-oxidative drugs whose anticancer potential has been characterized with specific focus on phytochemicals, mechanisms of ROS induction, and anticancer effects downstream of ROS induction.

Plumbagin induces the apoptosis of drug-resistant oral cancer in vitro and in vivo through ROS-mediated endoplasmic reticulum stress and mitochondrial dysfunction

BACKGROUND

Oral cancer is one of the leading causes of cancer-related deaths worldwide. Chemotherapy is widely used in the treatment of oral cancer, but its clinical efficacy is limited by drug resistance. Hence, novel compounds capable of overcoming drug-resistance are urgently needed.

PURPOSE

Plumbagin (PG), a natural compound isolated from Plumbago zeylanica L, has been used to treat various cancers. In this study, we investigated the anticancer effects of PG on drug-resistant oral cancer (CR-SAS) cells, as well as the underlying mechanism.

METHODS

MTT assays were used to evaluate the effect of PG on the viability of CR-SAS cells. Apoptosis and reactive oxygen species (ROS) production by the cells were determined using flow cytometry. Protein expression levels were detected by western blotting.

RESULTS

The results show that PG reduces the viability and causes the apoptosis of CR-SAS cells. PG is able to induce intracellular and mitochondrial ROS generation that leads to mitochondrial dysfunction. Furthermore, endoplasmic reticulum (ER) stress was triggered in PG-treated CR-SAS cells. The inhibition of ROS using N-acetylcysteine (NAC) abrogated the PG-induced ER stress and apoptosis, as well as the reduction in cell viability. Meanwhile, similar results were observed both in zebrafish and in murine models of drug-resistant oral cancer.

CONCLUSION

Our results indicate that PG induces the apoptosis of CR-SAS cells via the ROS-mediated ER stress pathway and mitochondrial dysfunction. It will be interesting to develop the natural compound PG for the treatment of drug-resistant oral cancer.

Mechanism and Role of Endoplasmic Reticulum Stress in Osteosarcoma

Osteosarcoma is the most common malignant bone tumor, often occurring in children and adolescents. The etiology of most patients is unclear, and the current conventional treatment methods are chemotherapy, radiotherapy, and surgical resection. However, the sensitivity of osteosarcoma to radiotherapy and chemotherapy is low, and the prognosis is poor. The development of new and useful treatment strategies for improving patient survival is an urgent need. It has been found that endoplasmic reticulum (ER) stress (ERS) affects tumor angiogenesis, invasion, etc. By summarizing the literature related to osteosarcoma and ERS, we found that the unfolded protein response (UPR) pathway activated by ERS has a regulatory role in osteosarcoma proliferation, apoptosis, and chemoresistance. In osteosarcoma, the UPR pathway plays an important role by crosstalk with autophagy, oxidative stress, and other pathways. Overall, this article focuses on the relationship between ERS and osteosarcoma and reviews the potential of drugs or gene targets associated with ERS for the treatment of osteosarcoma.

Surfactin induces ER stress-mediated apoptosis via IRE1-ASK1-JNK signaling in human osteosarcoma

Osteosarcoma, one of primary bone tumor in children and young adults, has poor prognosis and drug resistances to chemotherapy. In order to reinforce the conventional therapies and antagonize the osteosarcoma in patients, a novel strategy is required for developing a new treatment. In this study, surfactin, a natural product from Bacillus subtilis, showed the efficiency of cell death in osteosarcoma, but not in normal cells. Surfactin triggers ER stress mechanism by promoting the aberrant Ca²⁺ release from ER lumen and ER-signaling to mitochondrial dysfunction following caspases activation mediating cell apoptosis. Surfactin-induced ER stress not only upregulated of glucose-regulated protein 78/94 and IRE1-ASK1-JNK pathway but also leading to calpains and Bcl-2 proteins family involving the release of cytochrome c. The releases into cytosol trigger the cleavage of caspase-9 and caspase-3 to induce cell apoptosis. In this study, surfactin demonstrated the potential functions to trigger the ER stress, ER stress-associated IRE1-ASK1-JNK signaling pathway, mitochondrial dysfunction, and caspase activations leading to programmed cell apoptosis. Importantly, implicating the signaling pathway that regulates the connection between ER stress and mitochondrial dysfunction causing apoptosis associated with surfactin. These results indicated a potential application of surfactin strengthen current conventional therapies.

The phytochemical plumbagin reciprocally modulates osteoblasts and osteoclasts

Bone metabolism is essential for maintaining bone mineral density and bone strength through a balance between bone formation and bone resorption. Bone formation is associated with osteoblast activity whereas bone resorption is linked to osteoclast differentiation. Osteoblast progenitors give rise to the formation of mature osteoblasts whereas monocytes are the precursors for multi-nucleated osteoclasts. Chronic inflammation, auto-inflammation, hormonal changes or adiposity have the potential to disturb the balance between bone formation and bone loss. Several plant-derived components are described to modulate bone metabolism and alleviate osteoporosis by enhancing bone formation and inhibiting bone resorption. The plant-derived naphthoquinone plumbagin is a bioactive compound that can be isolated from the roots of the Plumbago genus. It has been used as traditional medicine for treating infectious diseases, rheumatoid arthritis and dermatological diseases. Reportedly, plumbagin exerts its biological activities primarily through induction of reactive oxygen species and triggers osteoblast-mediated bone formation. It is plausible that plumbagin's reciprocal actions - inhibiting or inducing death in osteoclasts but promoting survival or growth of osteoblasts - are a function of the synergy with bone-metabolizing hormones calcitonin, Parathormone and vitamin D. Herein, we develop a framework for plausible molecular modus operandi of plumbagin in bone metabolism.

Plumbagin: A Potential Anti-cancer Compound

Cancer is a deadly disease, which has significantly increased in both developed and developing nations. Treatment of cancer utilizing radiotherapy or chemotherapy actuates a few issues which incorporate spewing, sickness, unpalatable reactions, and so forth. In this specific situation, an alternative drug source, which can effectively treat cancer is of prime importance. Products that are obtained from plant sources are utilized for the treatment of various diseases due to their non-harmful nature. Medicinal plants contain different bioactive compounds, which possess an important role in the prevention of different diseases such as cancer. Plumbagin is a bioactive compound, which is mainly present in Plumbaginaceae family and has been explored for its anticancer activity. Plumbagin basically inactivates the Akt/NF-kB, MMP-9 and VEGF pathways that are essential for cancer cell development. Therefore, it is important to review the role of plumbagin in different cancer cells in order to find an alternative drug to overcome this disease. The present review provides a summary of anticancer activity of plumbagin in various cancers and its mode of action.

Kirenol inhibited the cell survival and induced apoptosis in human thyroid cancer cells by altering PI3K/AKT and MAP kinase signaling pathways

The thyroid cancer, especially papillary thyroid cancers are very common among population with high intake of iodine or iodine uptake. Even though several treatment options are available, there is still complication and side effects are still persistent. The role of signaling molecules in cancer signaling is very vast and their significance in progression of disease was increasing which leads to mortality of the patient. The major key players are PI3K, AKT and MAP kinase, involves in cell survival, proliferation, and inhibition of apoptosis and are the promising candidate for cancer treatment target, several researchers focuses these molecule to treat various acute and chronic diseases like cancer. On the other side, various literatures propose that natural compounds derived from plant source are shown potent anticancer property against several cancers. In our study we are looking in to one such active principle obtained from plant source, a diterpenoid compound kirenol, and its role thyroid cancer. Here, we report that kirenol role on various cellular mechanisms like induction of apoptosis, enhancing ROS indirectly by inhibiting antioxidants, altering the signaling mechanism of cell survival and apoptosis. Our study proposes that kirenol involved in the cancer cell cytotoxicity by inducing apoptosis and inhibition of cancer cell survival. Thus, targeting this signaling molecule with kirenol definitely favors and may lead to a therapeutic modality for thyroid cancer.

Cytotoxicity mechanisms of plumbagin in drug-resistant tongue squamous cell carcinoma

OBJECTIVES

To evaluate the inhibitory effect and mechanism of plumbagin (PLB) against drug-resistant tongue squamous cell carcinoma (TSCC), and whether its antitumour effect is not affected by tumour drug resistance.

METHODS

TSCC sensitive CAL27 cells and drug-resistant CAL27/RE cells were used to study the cytotoxicity and mechanism of PLB in vitro, including CCK-8 analysis, colony formation, DAPI staining, flow cytometry assay, transmission electron microscopy, western blotting assay, autophagy, apoptosis and ROS fluorescent probes. BALB/c nude mice xenograft models were used to study the growth inhibitory effect of PLB in vivo.

KEY FINDINGS

The results showed that the cell viability and proliferation inhibition and apoptosis induction abilities of PLB on drug-resistant cells were more obvious than that on sensitive cells. And PLB induced protective autophagy in TSCC cells. Mechanistically, PLB induced apoptosis and autophagy by generating reactive oxygen species to mediate JNK and AKT/mTOR pathways. Finally, the growth inhibitory effect of PLB against drug-resistant TSCC was also confirmed in vivo.

CONCLUSIONS

PLB will be a promising anticancer agent to overcome drug-resistant TSCC without being affected by its drug resistance properties.

Natural Products Targeting the Mitochondria in Cancers

There are abundant sources of anticancer drugs in nature that have a broad prospect in anticancer drug discovery. Natural compounds, with biological activities extracted from plants and marine and microbial metabolites, have significant antitumor effects, but their mechanisms are various. In addition to providing energy to cells, mitochondria are involved in processes, such as cell differentiation, cell signaling, and cell apoptosis, and they have the ability to regulate cell growth and cell cycle. Summing up recent data on how natural products regulate mitochondria is valuable for the development of anticancer drugs. This review focuses on natural products that have shown antitumor effects via regulating mitochondria. The search was done in PubMed, Web of Science, and Google Scholar databases, over a 5-year period, between 2015 and 2020, with a keyword search that focused on natural products, natural compounds, phytomedicine, Chinese medicine, antitumor, and mitochondria. Many natural products have been studied to have antitumor effects on different cells and can be further processed into useful drugs to treat cancer. In the process of searching for valuable new drugs, natural products such as terpenoids, flavonoids, saponins, alkaloids, coumarins, and quinones cover the broad space.

Piperlongumine induces apoptosis and G2/M phase arrest in human osteosarcoma cells by regulating ROS/PI3K/Akt pathway

Previous research has reported that piperlongumine exerts antitumor properties on several types of tumor cells. However, its effect on osteosarcoma cells remains unknown. This study aimed to investigate the antitumor effects of piperlongumine on osteosarcoma cells (MG63 and U2OS cells) in vitro and determined the underlying mechanism. Cell viability was measured using MTT assay. Cell apoptosis was assessed via AO/EB staining and flow cytometry apoptosis as well as western blot analysis. Cell cycle distribution was detected by flow cytometric cell cycle and western blot analysis. In our research, we found that piperlongumine induced apoptosis and G2/M phase arrest of MG63 cells. Western blot analysis not only confirmed the above results, but also demonstrated that piperlongumine induced apoptosis of osteosarcoma cells by activating Caspase-9-dependent apoptotic pathway. Furthermore, we also found that piperlongumine significantly induced apoptosis and cell cycle arrest of osteosarcoma cells by regulating ROS/PI3K/Akt signaling pathway. In summary, our findings suggested that piperlongumine inhibited osteosarcoma progression by promoting apoptosis of osteosarcoma cells. In addition, the underlying mechanism demonstrated that piperlongumine produced potent antitumor properties in osteosarcoma cells by regulating ROS/PI3K/Akt signaling pathway.

Plumbagin Enhances the Anticancer Efficacy of Cisplatin by Increasing Intracellular ROS in Human Tongue Squamous Cell Carcinoma

Cisplatin is widely used in the treatment of tongue squamous cell carcinoma (TSCC), but its clinical efficacy is limited by drug resistance and toxic side effects. Hence, a novel compound capable of enhancing the anticancer effect of cisplatin while reducing the side effects is urgently needed. We have previously shown that plumbagin (PLB), an anticancer phytochemical, is able to inhibit the growth of TSCC in vitro and in vivo. The objective of this study was to investigate the effect of PLB in reversing the resistance of TSCC to cisplatin as well as its molecular mechanisms. Here, we found that PLB enhances cisplatin-induced cytotoxicity, apoptosis, and autophagy in CAL27 and cisplatin-resistant CAL27/CDDP cells. PLB could inhibit the viability and growth of TSCC cells by increasing the production of intracellular reactive oxygen species (ROS). In addition, the combination treatment of PLB and cisplatin resulted in a synergistic inhibition of TSCC viability, apoptosis, and autophagy by increasing intracellular ROS, which may be achieved by activating JNK and inhibiting AKT/mTOR signaling pathways. Finally, the synergistic treatment was also demonstrated in vivo. Therefore, PLB combined with cisplatin is a potential therapeutic strategy against therapy TSCC cisplatin resistance.

NADPH: Quinone oxidoreductase 1 (NQO1) mediated anti-cancer effects of plumbagin in endocrine resistant MCF7 breast cancer cells

BACKGROUND

PLB is a natural naphthoquinone compound isolated from the roots of Plumbago indica plant. Our previous study reported the inhibitory effect of Plumbagin (PLB) on human endocrine resistant breast cancer cell growth and cell invasion.

HYPOTHESIS/PURPOSE

Since PLB is a naphthoquinone compound, it can be reduced by the cytosolic NADPH: quinone oxidoreductase 1 (NQO1) enzyme. NQO1 expression is upregulated in various types of aggressive cancer including breast cancer. This study investigated the impact of NQO1 on anti-cancer effects of PLB in endocrine-resistant breast cancer cells.

STUDY DESIGN

This study was an in vitro study using ER-positive cell line (MCF7) and endocrine-resistant cell lines (MCF7/LCC2 and MCF7/LCC9 cells).

METHODS

The roles of NQO1 in anti-cancer activity of PLB were investigated by using NQO1 knockdown cells, NQO1 inhibitor and NQO1 overexpressed cells. To study the impact of NQO1 on the effects of PLB on cell viability, apoptosis, invasion and generation of ROS, the following assays were used: MTT assays, annexin V-PE/7-ADD staining flow cytometry, matrigel invasion assays and DCFHDA assays. To study the mechanism of how NQO1 mediated PLB effects in tamoxifen response and apoptosis, we assessed the levels of mRNA expression by using qRT-PCR.

RESULTS

1. In this study, NQO1 was upregulated in endocrine-resistant cells. 2. PLB did not change the expression of NQO1 but it was able to increase NQO1 activity. 3. The inhibitory effects of PLB on cell proliferation, cell invasion and expression of tamoxifen resistant gene were attenuated in NQO1 knockdown cells or in the presence of NQO1 inhibitor. 4. The effects of PLB to induce apoptosis and generate ROS were also decreased when NQO1 activity was inhibited or when the NQO1 expression was reduced. 5. The anti-cancer effects of PLB increased when NQO1 was upregulated.

CONCLUSION

The effects of PLB in endocrine-resistant breast cancer cells is dependent on NQO1's activity.

Tomentosin Displays Anti-Carcinogenic Effect in Human Osteosarcoma MG-63 Cells via the Induction of Intracellular Reactive Oxygen Species

Tomentosin is a natural sesquiterpene lactone extracted from various plants and is widely used as a medicine because it exhibits essential therapeutic properties. In this study, we investigated the anti-carcinogenic effects of tomentosin in human osteosarcoma MG-63 cells by performing cell migration/viability/proliferation, apoptosis, and reactive oxygen species (ROS) analysis assays. MG-63 cells were treated with various doses of tomentosin. After treatment with tomentosin, MG-63 cells were analyzed using the MTT assay, colony formation assay, cell counting assay, wound healing assay, Boyden chamber assay, zymography assay, cell cycle analysis, FITC Annexin V apoptosis assay, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, western blot analysis, and ROS detection analysis. Our results indicated that tomentosin decreased cell viability and migration ability in MG-63 cells. Moreover, tomentosin induced apoptosis, cell cycle arrest, DNA damage, and ROS production in MG-63 cells. Furthermore, tomentosin-induced intracellular ROS decreased cell viability and induced apoptosis, cell cycle arrest, and DNA damage in MG-63 cells. Taken together, our results suggested that tomentosin exerted anti-carcinogenic effects in MG-63 cells by induction of intracellular ROS.

Emerging role of plumbagin: Cytotoxic potential and pharmaceutical relevance towards cancer therapy

Plumbagin is a naphthoquinone derived yellow crystalline phytochemical. Plumbagin has a wide range of biological effects including cytotoxicity against cancer cells both in vitro and in vivo. Due to the pleiotropic nature of plumbagin, it shows the anticancer effect by targeting several molecular mechanisms including apoptosis and autophagic pathways, cell cycle arrest, anti-angiogenic pathways, anti-invasion and anti-metastasis pathways. Among many signaling pathways the key regulatory genes regulated by plumbagin are NF-kβ, STAT3, and AKT, etc. Plumbagin is also a potent inducer of ROS, suppressor of cellular glutathione, and causes DNA strand break by oxidative DNA base damages. In vivo studies suggested that plumbagin significantly reduces the tumor weight and volume in dose-dependent manner without any side effects in tested model organisms. Another exciting aspect of plumbagin is the ability to re-sensitize the chemo and radioresistant cancer cells when used in combination or alone. Nano encapsulation of plumbagin overcomes the poor water solubility and bioavailability obstacles, enhancing the pharmaceutical relevance with better therapeutic efficacy. Moreover, plumbagin can be introduced as a future phytotherapeutic anticancer drug after fully satisfied preclinical and clinical trials.