Combination of metformin and 9-cis retinoic acid increases apoptosis in C6 glioma stem-like cells

Role of renin angiotensin system inhibitors and metformin in Glioblastoma Therapy: a review

Glioblastoma multiforme (GBM) is a highly aggressive and incurable disease accounting for about 10,000 deaths in the USA each year. Despite the current treatment approach which includes surgery with chemotherapy and radiation therapy, there remains a high prevalence of recurrence. Notable improvements have been observed in persons receiving concurrent antihypertensive drugs such as renin angiotensin inhibitors (RAS) or the antidiabetic drug metformin with standard therapy. Anti-tumoral effects of RAS inhibitors and metformin have been observed in in vitro and in vivo studies. Although clinical trials have shown mixed results, the potential for the use of RAS inhibitors and metformin as adjuvant GBM therapy remains promising. Nevertheless, evidence suggest that these drugs exert multimodal antitumor actions; by particularly targeting several cancer hallmarks. In this review, we highlight the results of clinical studies using multidrug cocktails containing RAS inhibitors and or metformin added to standard therapy for GBM. In addition, we highlight the possible molecular mechanisms by which these repurposed drugs with an excellent safety profile might elicit their anti-tumoral effects. RAS inhibition elicits anti-inflammatory, anti-angiogenic, and immune sensitivity effects in GBM. However, metformin promotes anti-migratory, anti-proliferative and pro-apoptotic effects mainly through the activation of AMP-activated protein kinase. Also, we discussed metformin's potential in targeting both GBM cells as well as GBM associated-stem cells. Finally, we summarize a few drug interactions that may cause an additive or antagonistic effect that may lead to adverse effects and influence treatment outcome.

Current Opportunities for Targeting Dysregulated Neurodevelopmental Signaling Pathways in Glioblastoma

Glioblastoma (GBM) is the most common and highly lethal type of brain tumor, with poor survival despite advances in understanding its complexity. After current standard therapeutic treatment, including tumor resection, radiotherapy and concomitant chemotherapy with temozolomide, the median overall survival of patients with this type of tumor is less than 15 months. Thus, there is an urgent need for new insights into GBM molecular characteristics and progress in targeted therapy in order to improve clinical outcomes. The literature data revealed that a number of different signaling pathways are dysregulated in GBM. In this review, we intended to summarize and discuss current literature data and therapeutic modalities focused on targeting dysregulated signaling pathways in GBM. A better understanding of opportunities for targeting signaling pathways that influences malignant behavior of GBM cells might open the way for the development of novel GBM-targeted therapies.

Metformin induces myeloma cells necrosis and apoptosis and it is considered for therapeutic use

Accumulating evidence, especially in solid tumor, indicated that metformin possessed the potential ability in the proliferation of cancer cells. However, its effects on myeloma cells were relatively rarely clarified. To evaluate the anti-cancer effects of metformin against dexamethasone-resistant and -sensitive myeloma cells. The effects of metformin on myeloma cell lines, including dexamethasone-resistant U266, H929, RPMI 8226 and dexamethasone-sensitive MM.1s, were investigated using the cell counting kit-8 assay for cell proliferation. Apoptosis, necrosis, cell cycle arrest, and cell death mechanisms were explored via flow cytometry (FCM) and Western blot. In addition, the anti-myeloma activity was evaluated in vivo via non-obese diabetic/severe combined immunodeficiency xenograft mouse models. Metformin inhibited proliferation in a dose and time-dependent manner in all the cell lines, while dexamethasone only affected the viability of MM1.s cells. The FCM detection displayed that metformin induced apoptosis in H929, RPMI8226 and MM.1s cells, while for U266 cells, it induced necrosis with Annexin V^-/Propidium iodide⁺. The cell cycle assays showed that metformin arrested G0/G1 phase of H929 and MM.1s cells, or G2/M phase of RPMI8226 cells, but showed no effect on U226 cells. Western blotting analyses demonstrated that the apoptosis-related protein of cleaved caspase 3 was activated; the expressions of Mcl-1, IGF-1R, PI3K, pAKT, and pmTOR proteins were inhibited by metformin in H929, RPMI8226, and MM.1s cells. The necrosis-related protein of iNOS increased in U266 cells while metformin treated. In vivo assay indicated metformin decreased U266 and H929 growth in bone marrow, and thus prolonged mice survival. These data suggested that metformin inhibited the proliferation of myeloma cells via inducing necrosis and apoptosis. This finding indicated that metformin may be served as a potent adjuvant in treating multiple myeloma.

Retinoids as anti-cancer agents and their mechanisms of action

Retinoids (vitamin A) have been reported extensively for anti-cancer properties due to their high receptor-binding affinities and gene regulation abilities. However, the anti-cancer potential of retinoids has not been reviewed in recent years. Thus, this review focused on the anti-cancer effects of retinoids and their synergistic effects with other drugs, together with their mechanisms of action in different types of cancers reported in the past five years. The retinoids were well studied in breast cancer, melanoma, and colorectal cancer. Synthetic retinoids have shown higher selectivity, stronger effectiveness, and lower toxicity than endogenous retinoids. Interestingly, the combination treatment of endogenous retinoids with chemotherapy drugs showed enhanced anti-cancer effects. The mechanisms of action reported for retinoids mainly involved the RAR/RXR signaling pathway. However, limited clinical studies were conducted in recent years. Thus, retinoids which are highly potential anti-cancer agents are worth further study in clinical, especially as a combination therapy with chemotherapy drugs.

Nutrient starvation induces apoptosis and autophagy in C6 glioma stem-like cells

Glioblastoma is a severe cancer with extremely poor survival. Its treatment typically involves a combination of surgery, chemotherapy, and radiation therapy. However, glioma stem-like cells (GSCs)-a subpopulation of tumor-propagating glioblastoma cells-cause post-treatment recurrence and are a major factor in the poor prognosis of the disease. GSCs have higher proliferation than non-GSCs and are more resistant to invasive chemotherapy and radiotherapy. In this study, we subjected GSCs to nutrient starvation (deprived of glucose, glutamine, and calcium) to determine whether cell death can be triggered as a potential strategy to improve treatment outcomes. Flow cytometry revealed that 35.1%, 96.1%, and 99.9% of starved GSCs underwent apoptosis on days 1, 3, and 5, respectively, along with nearly 100% autophagy on all three days. Western blots detected cleaved caspase-3 (an apoptosis marker) and phospho-beclin 1, LC 3B-I, LC 3B-II (autophagy markers) in C6 GSCs after nutrient starvation for 1, 3, 4, and 5 days. Transmission electron microscopic observation of GSC ultrastructure after starvation treatment revealed that compared with control GSCs, starved cells had more pyknotic nuclei, membrane bleb, swollen endoplasmic reticulum, degenerative mitochondria, lipid droplets, and microvilli loss. Thus, nutrient starvation stresses cells by increasing free radicals. Cell stress opens more channels between mitochondria and endoplasmic reticulum. This study demonstrated that nutrient starvation decreases proliferation by approximately 81%, while increasing apoptosis (99.9%) and autophagy (94.6%) in C6 GSCs by the fifth day. Nutrient starvation of GSCs may, therefore, be an effective therapeutic strategy that can trigger apoptotic and autophagic metabolic reprogramming in cancer cells.