Metformin reverses stem cell‑like HepG2 sphere formation and resistance to sorafenib by attenuating epithelial‑mesenchymal transformation

Metformin Suppresses Stemness of Non-Small-Cell Lung Cancer Induced by Paclitaxel through FOXO3a

Cancer stem cells (CSCs) play a pivotal role in drug resistance and metastasis. Among the key players, Forkhead box O3a (FOXO3a) acts as a tumor suppressor. This study aimed to unravel the role of FOXO3a in mediating the inhibitory effect of metformin on cancer stemness derived from paclitaxel (PTX)-resistant non-small-cell lung cancer (NSCLC) cells. We showed that CSC-like features were acquired by the chronic induction of resistance to PTX, concurrently with inactivation of FOXO3a. In line with this, knockdown of FOXO3a in PTX-sensitive cells led to changes toward stemness, while overexpression of FOXO3a in PTX-resistant cells mitigated stemness in vitro and remarkably curbed the tumorigenesis of NSCLC/PTX cells in vivo. Furthermore, metformin suppressed the self-renewal ability of PTX-resistant cells, reduced the expression of stemness-related markers (c-MYC, Oct4, Nanog and Notch), and upregulated FOXO3a, events concomitant with the activation of AMP-activated protein kinase (AMPK). All these changes were recapitulated by silencing FOXO3a in PTX-sensitive cells. Intriguingly, the introduction of the AMPK dominant negative mutant offset the inhibitory effect of metformin on the stemness of PTX-resistant cells. In addition, FOXO3a levels were elevated by the treatment of PTX-resistant cells with MK2206 (an Akt inhibitor) and U0126 (a MEK inhibitor). Collectively, our findings indicate that metformin exerts its effect on FOXO3a through the activation of AMPK and the inhibition of protein kinase B (Akt) and MAPK/extracellular signal-regulated kinase (MEK), culminating in the suppression of stemness in paclitaxel-resistant NSCLC cells.

Metformin promotes ferroptosis and sensitivity to sorafenib in hepatocellular carcinoma cells via ATF4/STAT3

BACKGROUND

Hepatocellular carcinoma (HCC) is a common cancer worldwide, and sorafenib is a first-line drug for the treatment of advanced liver cancer. Resistance to sorafenib has become a major challenge in the treatment of hepatocellular carcinoma, however, studies have shown that metformin can promote ferroptosis and sorafenib sensitivity. Therefore, the aim of this study was to investigate the promotion of ferroptosis and sorafenib sensitivity by metformin via ATF4/STAT3 in hepatocellular carcinoma cells.

METHODS

Hepatocellular carcinoma cells Huh7 and Hep3B and induced sorafenib resistance (SR) Huh7/SR and Hep3B/SR cells were used as in vitro cell models. Cells were injected subcutaneously to establish a drug-resistant mouse model. CCK-8 was used to detect cell viability and sorafenib IC50. Western blotting was used to detect the expression of relevant proteins. BODIPY staining was used to analyze the lipid peroxidation level in cells. A scratch assay was used to detect cell migration. Transwell assays were used to detect cell invasion. Immunofluorescence was used to localize the expression of ATF4 and STAT3.

RESULTS

Metformin promoted ferroptosis in hepatocellular carcinoma cells through ATF4/STAT3, decreased sorafenib IC50, increased ROS and lipid peroxidation levels, decreased cell migration and invasion, inhibited the expression of the drug-resistant proteins ABCG2 and P-GP in hepatocellular carcinoma cells, and thus inhibited sorafenib resistance in hepatocellular carcinoma cells. Downregulating ATF4 inhibited the phosphorylated nuclear translocation of STAT3, promoted ferroptosis, and increased the sensitivity of Huh7 cells to sorafenib. Metformin was also shown in animal models to promote ferroptosis and sorafenib sensitivity in vivo via ATF4/STAT3.

CONCLUSION

Metformin promotes ferroptosis and sensitivity to sorafenib in hepatocellular carcinoma cells via ATF4/STAT3, and it inhibits HCC progression.

Clinical and Biological Implications of Cancer Stem Cells in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a malignant tumor with poor prognosis, and is one of the leading causes of cancer-related deaths worldwide. Recently, the development of therapeutic drugs via novel mechanisms of action, involving molecular-targeted drugs and immune checkpoint inhibitors, has progressed in the field of HCC. However, the recurrence rate remains high, and further improvement of the prognosis of patients with HCC is urgently needed. Cancer stem cells (CSCs) are a promising target for further development of novel anti-cancer drugs because they are reportedly involved in tumor initiation, maintenance, recurrence, and resistance to conventional therapies. Although several studies have already been conducted, the functions and roles of CSCs in the development and progression of tumors remain to be elucidated. In this review article, we will clarify the fundamental knowledge of CSCs necessary for the understanding of CSCs and will outline so-far identified markers specific to liver CSCs and the pathological and therapeutic implications of CSCs in HCC.

The Chemosensitizing Role of Metformin in Anti-Cancer Therapy

Chemoresistance, which leads to the failure of chemotherapy and further tumor recurrence, presents the largest hurdle for the success of anti-cancer therapy. In recent years, metformin, a widely used first-line antidiabetic drug, has attracted increasing attention for its anti-cancer effects. A growing body of evidence indicates that metformin can sensitize tumor responses to different chemotherapeutic drugs, such as hormone modulating drugs, anti-metabolite drugs, antibiotics, and DNA-damaging drugs via selective targeting of Cancer Stem Cells (CSCs), improving the hypoxic microenvironment, and by suppressing tumor metastasis and inflammation. In addition, metformin may regulate metabolic programming, induce apoptosis, reverse Epithelial to Mesenchymal Transition (EMT), and Multidrug Resistance (MDR). In this review, we summarize the chemosensitization effects of metformin and focus primarily on its molecular mechanisms in enhancing the sensitivity of multiple chemotherapeutic drugs, through targeting of mTOR, ERK/P70S6K, NF-κB/HIF-1 α, and Mitogen- Activated Protein Kinase (MAPK) signaling pathways, as well as by down-regulating the expression of CSC genes and Pyruvate Kinase isoenzyme M2 (PKM2). Through a comprehensive understanding of the molecular mechanisms of chemosensitization provided in this review, the rationale for the use of metformin in clinical combination medications can be more systematically and thoroughly explored for wider adoption against numerous cancer types.>.

STAT3 Mediated miR-30a-5p Inhibition Enhances Proliferation and Inhibits Apoptosis in Colorectal Cancer Cells

Signal transducer and activator of transcription 3 (STAT3), a transcriptional factor involved in tumorigenesis and cancer stemness formation, contributes to drug resistance in cancer therapies. STAT3 not only mediates gene transcription but also participates in microRNA suppression. This study identified a STAT3-downstream micro RNA (miRNA) involved in drug resistance against regorafenib in colorectal cancer stem-like tumorspheres. Small RNAseq was used to investigate differential microRNAs in colorectal cancer cell-derived tumorspheres and in a STAT3-knockdown strain. The miRNA-mediated genes were identified by comparing RNAseq data with gene targets predicted using TargetScan. Assays for detecting cell viability and apoptosis were used to validate findings. The formation of colorectal cancer stem-like tumorspheres was inhibited by BBI608, a STAT3 inhibitor, but not by regorafenib. Additional investigations for microRNA expression demonstrated an increase in 10 miRNAs and a decrease in 13 miRNAs in HT29-derived tumorspheres. A comparison of small RNAseq results between tumorspheres and HT29shSTAT3 cells revealed the presence of four STAT3-mediated miRNAs in HT29-derived tumorspheres: hsa-miR-215-5p, hsa-miR-4521, and hsa-miR-215-3p were upregulated, whereas miR-30a-5p was downregulated. Furthermore, hsa-miR-4521 was associated with poor overall survival probability, and miR-30a-5p was associated with better overall survival probability in patients with rectum cancer. Comparisons of RNAseq findings between HCT116- and HT29-derived tumorspheres revealed that HSPA5 were mediated by the STAT3-miR-30a-5p axis, which is overexpressed in colorectal tumorspheres associating to anti-apoptosis. In addition, the transfection of miR-30a-5p and inhibition of HSPA5 by HA15 significantly reduced cell viability and increased apoptosis in HT29 cells. In conclusion, a STAT3-miR-30a-5p-HSPA5 axis was observed against regorafenib-mediated apoptosis in colorectal cancer tumorspheres. The expression of miR-30a-5p was repressed by STAT3; in addition, HSPA5 was identified as the target gene of miR-30a-5p and contributed to both tumorsphere formation and anti-apoptosis.

Molecular mechanism for metformin to enhance pro-apoptotic effect of sorafenib in HepG2 cells

BACKGROUND

Prolonging the survival time of patients with advanced liver cancer is a major clinical challenge. Sorafenib (Sor) is the only targeted drug for the treatment of advanced liver cancer, but drug resistance has become a problem.

AIM

To explore the effect and molecular mechanism of metformin (Met) in enhancing pro-apoptotic effect of Sor in HepG2 cells.

METHODS

MTT assay was used to evaluate the anti-proliferation effects of Met and Sor, alone or in combination. Flow cytometry was employed to analyze cell cycle and cell apoptosis. The expression of Caspase-3, Bax, AMPK, P53, and mTORC1 was evaluated by Western blot.

RESULTS

MTT assay showed that both Met and Sor decreased HepG2 cells viability, and Met combined with Sor had a synergistic inhibitory effect. The relative cell viability rates of the control group, Met group, Sor group, and combination group were 100%, 79.96% ± 4.41%, 85.33% ± 1.00%, and 68.60% ± 4.02%, respectively. Flow cytometry showed that both Met and Sor induced HepG2 cell apoptosis, and Met combined with Sor had a synergistic effect. The apoptosis rates of the control group, Met group, Sor group, and combination group were 4.47% ± 1.93%, 13.73% ± 1.18%, 9.50% ± 0.20%, and 29.03% ± 0.35%, respectively. Western blot analysis showed that both Met and Sor increased the expression of Caspase-3, Bax, P53, and AMPK and decreased the expression of mTORC1.

CONCLUSION

Met can enhance the pro-apoptotic effect of Sor in HepG2 cells.