Deguelin Restores Paclitaxel Sensitivity in Paclitaxel-Resistant Ovarian Cancer Cells via Inhibition of the EGFR Signaling Pathway.

Background: Ovarian cancer is one of women's malignancies with the highest mortality among gynecological cancers. Paclitaxel is used in first-line ovarian cancer chemotherapy. Research on paclitaxel-resistant ovarian cancer holds significant clinical importance. Methods: Cell viability and flow cytometric assays were conducted at different time and concentration points of deguelin and paclitaxel treatment. Immunoblotting was performed to assess the activation status of key signaling molecules important for cell survival and proliferation following treatment with deguelin and paclitaxel. The fluo-3 acetoxymethyl assay for P-glycoprotein transport activity assay and cell viability assay in the presence of N-acetyl-L-cysteine were also conducted. Results: Cell viability and flow cytometric assays demonstrated that deguelin resensitized paclitaxel in a dose- and time-dependent manner. Cotreatment with deguelin and paclitaxel inhibited EGFR and its downstream signaling molecules, including AKT, ERK, STAT3, and p38 MAPK, in SKOV3-TR cells. Interestingly, cotreatment with deguelin and paclitaxel suppressed the expression level of EGFR via the lysosomal degradation pathway. Cotreatment did not affect the expression and function of P-glycoprotein. N-acetyl-L-cysteine failed to restore cell cytotoxicity when used in combination with deguelin and paclitaxel in SKOV3-TR cells. The expression of BCL-2, MCL-1, and the phosphorylation of the S155 residue of BAD were downregulated. Moreover, inhibition of paclitaxel resistance by deguelin was also observed in HeyA8-MDR cells. Conclusion: Our research showed that deguelin effectively suppresses paclitaxel resistance in SKOV3-TR ovarian cancer cells by downregulating the EGFR and its downstream signaling pathway and modulating the BCL-2 family proteins. Furthermore, deguelin exhibits inhibitory effects on paclitaxel resistance in HeyA8-MDR ovarian cancer cells, suggesting a potential mechanism for paclitaxel resensitization that may not be cell-specific. These findings suggest that deguelin holds promise as an anticancer therapeutic agent for overcoming chemoresistance in ovarian cancer.

Downregulation of TRIB3 enhances the sensitivity of lung cancer cells to amino acid deprivation by suppressing AKT activation.

Tribbles pseudokinase 3 (TRIB3), a member of the mammalian Tribbles family, is implicated in multiple biological processes. This study aimed to investigate the biological functions of TRIB3 in lung cancer and its effect on amino acid-deprived lung cancer cells. TRIB3 mRNA expression was elevated in lung cancer tissues and cell lines compared to normal lung tissues and cells. TRIB3 knockdown markedly reduced the viability and proliferation of H1299 lung cancer cells. Deprivation of amino acids, particularly arginine, glutamine, lysine, or methionine, strongly increased TRIB3 expression via ATF4 activation in H1299 lung cancer cells. Knockdown of TRIB3 led to transcriptional downregulation of ATF4 and reduced AKT activation induced by amino acid deprivation, ultimately increasing the sensitivity of H1299 lung cancer cells to amino acid deprivation. Additionally, TRIB3 knockdown enhanced the sensitivity of H1299 cells to V-9302, a competitive antagonist of transmembrane glutamine flux. These results suggest that TRIB3 is a pro-survival regulator of cell viability in amino acid-deficient tumor microenvironments and a promising therapeutic target for lung cancer treatment.

Duloxetine enhances the sensitivity of non-small cell lung cancer cells to EGFR inhibitors by REDD1-induced mTORC1/S6K1 suppression.

Although epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) have been effective targeted therapies for non-small cell lung cancer (NSCLC), most advanced NSCLC inevitably develop resistance to these therapies. Combination therapies emerge as valuable approach to preventing, delaying, or overcoming disease progression. Duloxetine, an antidepressant known as a serotonin-noradrenaline reuptake inhibitor, is commonly prescribed for the treatment of chemotherapy-induced peripheral neuropathy. In the present study, we investigated the combined effects of duloxetine and EGFR-TKIs and their possible mechanism in NSCLC cells. Compared with either monotherapy, the combination of duloxetine and EGFR-TKIs leads to synergistic cell death. Mechanistically, duloxetine suppresses 70-kDa ribosomal protein S6 kinase 1 (p70S6K1) activity through mechanistic target of rapamycin complex 1 (mTORC1), and this effect is associated with the synergistic induction of cell death of duloxetine combined with EGFR-TKIs. More importantly, activating transcription factor 4 (ATF4)-induced regulated in development and DNA damage response 1 (REDD1) is responsible for the suppression of mTORC1/S6K1 activation. Additionally, we found that the combination effect was significantly attenuated in REDD1 knockout NSCLC cells. Taken together, our findings reveal that the ATF4/REDD1/mTORC1/S6K1 signaling axis, as a novel mechanism, is responsible for the synergistic therapeutic effect of duloxetine with EGFR-TKIs. These results suggest that combining EGFR-TKIs with duloxetine appears to be a promising way to improve EGFR-TKI efficacy against NSCLC.

Amino acid deprivation induces TXNIP expression by NRF2 downregulation.

Thioredoxin-interacting protein (TXNIP) is sensitive to oxidative stress and is involved in the pathogenesis of various metabolic, cardiovascular, and neurodegenerative disorders. Therefore, several studies have suggested that TXNIP is a promising therapeutic target for several diseases, particularly cancer and diabetes. However, the regulation of TXNIP expression under amino acid (AA)-restricted conditions is not well understood. In the present study, we demonstrated that TXNIP expression was promoted by the deprivation of AAs, especially arginine, glutamine, lysine, and methionine, in non-small cell lung cancer (NSCLC) cells. Interestingly, we determined that increased TXNIP expression induced by AA deprivation was associated with nuclear factor erythroid 2-related factor 2 (NRF2) downregulation, but not with activating transcription factor 4 (ATF4) activation. Furthermore, N-acetyl-l-cysteine (NAC), a scavenger of reactive oxygen species (ROS), suppressed TXNIP expression in NSCLC cells deprived of AA. Collectively, the induction of TXNIP expression by AA deprivation was mediated by ROS production, potentially through NRF2 downregulation. Our findings suggest that TXNIP expression may be associated with the redox homeostasis of AA metabolism and provide a possible rationale for a therapeutic strategy to treat cancer with AA restriction.

Survival analysis of breast cancer patients after diagnosis of second primary malignancies, focusing on the second primary hematologic malignancy.

Purpose: Although the overall survival (OS) of breast cancer patients is increasing with improved detection and therapies, so is the risk of breast cancer patients developing subsequent malignancies. We investigated the OS of breast cancer survivors according to sites of second primary malignancies (SPM). The OS of the second primary hematologic malignancy (SPHM) was then compared with that of metastatic breast cancer (MBC). Methods: We retrospectively analyzed patients diagnosed with primary breast cancer between 1998 and 2019. Only those with SPM were eligible for analysis. First, the OS of patients with SPM diagnosed as the first event after the diagnosis of breast cancer was analyzed. Next, the OS of patients with SPHM, with or without breast cancer relapse, was compared with that of patients with MBC, matched using the propensity score. Results: Patients diagnosed with SPM without breast cancer relapse as the first event had a significantly better OS than did patients with MBC, but the OS of those with SPHM as the first event did not differ significantly from that of patients with MBC (hazard ratio [HR], 1.558; 95% confidence interval [CI], 0.856-2.839; P = 0.147). The OS of patients with SPHM with or without breast cancer relapse was worse than that of the MBC group after propensity score matching (HR, 1.954; 95% CI, 1.045-3.654; P = 0.036). Conclusion: Prognosis of SPM diagnosed as the first event was statistically better than that of MBC, except in case of SPHM. Patients with SPHM, with or without MBC, showed poor OS before and after propensity score matching.

Can chemotherapy be omitted for patients with N0 or N1 endocrine-sensitive breast cancer treated with gonadotropin-releasing hormone agonist and tamoxifen?

Purpose: Whether administering chemotherapy followed by tamoxifen plus a gonadotropin-releasing hormone (GnRH) agonist to treat patients with lower-risk hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer provides a greater benefit than administering tamoxifen plus GnRH agonist alone remains unclear. This study aimed to compare the outcomes of propensity score-matched (PSM) patients who underwent these 2 types of treatment plans. Methods: This retrospective study included patients treated at our institution between 2009 and 2019. Eligible patients had HR-positive, HER2-negative, invasive breast cancer who had undergone surgery. There were 579 patients with HR-positive, HER2-negative breast cancer who were treated with a GnRH agonist and tamoxifen; patients with pathologic N2 and those who received neoadjuvant chemotherapy were excluded. After 1:1 PSM of patients who underwent GnRH agonist treatment and tamoxifen with versus without chemotherapy, 122 patients from these 2 groups were analyzed. Survival rates were calculated using the Kaplan-Meier method and compared via the log-rank test. Results: After PSM, there were no significant differences in several baseline characteristics between the 2 groups. After a median follow-up of 62.8 months, the patients in both groups demonstrated similar outcomes with no significant difference in disease-free survival (P = 0.596). Conclusion: Patients derived no significant survival benefit from undergoing a chemotherapy regimen before receiving tamoxifen and GnRH agonist therapy compared to forgoing such chemotherapy.

Nebivolol Sensitizes BT-474 Breast Cancer Cells to FGFR Inhibitors.

BACKGROUND/AIM: The fibroblast growth factor receptor (FGFR) signaling pathway is abnormally activated in human cancers, including breast cancer. Therefore, targeting the FGFR signaling pathway is a potent strategy to treat breast cancer. The purpose of this study was to find drugs that could increase sensitivity to FGFR inhibitor effects in BT-474 breast cancer cells, and to investigate the combined effects and underlying mechanisms of these combinations for BT-474 breast cancer cell survival. MATERIALS AND METHODS: Cell viability was measured by MTT assay. Protein expression was determined by western blot analysis. mRNA expression was detected by Real-time PCR. Drug synergy effect was determined by isobologram analysis. RESULTS: Nebivolol, a third generation ß1-blocker, synergistically increased the sensitivity of BT-474 breast cancer cells to the potent and selective FGFR inhibitors erdafitinib (JNJ-42756493) and AZD4547. A combination of nebivolol and erdafitinib markedly reduced AKT activation. Suppression of AKT activation using specific siRNA and a selective inhibitor further enhanced cell sensitivity to combined treatment with nebivolol and erdafitinib, whereas SC79, a potent activator of AKT, reduced cell sensitivity to nebivolol and erdafitinib. CONCLUSION: Enhanced sensitivity of BT-474 breast cancer cells to nebivolol and erdafitinib was probably associated with down-regulation of AKT activation. Combined treatment with nebivolol and erdafitinib is a promising strategy for breast cancer treatment.

The Significance of p-AKT1 as a Prognostic Marker and Therapeutic Target in Patients With Hormone Receptor-Positive and Human Epidermal Growth Factor Receptor-2-Positive Early Breast Cancer.

PURPOSE: Phosphorylated AKT1 (p-AKT1) at Ser473 is a functional isoform of AKT and a key component of the PI3K/mTOR/AKT pathway. This study aimed to evaluate the prognostic significance of p-AKT1 (Ser473) based on the molecular subtypes of breast cancer. METHODS: To investigate the prognostic value of p-AKT1 (Ser473), we performed a retrospective chart review of patients with breast cancer. Data on p-AKT1 (Ser473) positivity, hormone receptor (HR) status, human epidermal growth factor receptor 2 (HER2) expression status, and other clinicopathological factors were obtained. Furthermore, the therapeutic effect of blocking p-AKT1 (Ser473) in breast cancer cells was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, cell apoptosis assay, apoptosis protein array, and western blot analysis. RESULTS: A total of 3,044 patients were evaluated, and the median follow-up time was 43 (range: 0-125) months. In patients with HR-positive and HER2-positive disease, the p-AKT1 (Ser473)-positive group had worse disease-free survival (DFS) than the p-AKT1 (Ser473)-negative group (hazard ratio, 1.9; 95% confidence interval, 1.1-3.5; p = 0.024). In the multivariate analysis, p-AKT1 (Ser473) remained a significantly worse prognostic factor in patients with HR-positive/HER2-positive breast cancer (p = 0.03). There was no difference in DFS according to p-AKT1 (Ser473) status among patients with other breast cancer subgroups. In vitro analysis showed that blocking p-AKT1 (Ser473) levels enhanced trastuzumab-induced cell death in HR-positive/HER2-positive and p-AKT1 (Ser473)-positive breast cancer cells. CONCLUSION: p-AKT1 (Ser473) is a prognostic marker for poor outcomes in patients with HR-positive/HER2-positive breast cancer and may have a potential value as a therapeutic target.

Inhibition of Glutamine Uptake Resensitizes Paclitaxel Resistance in SKOV3-TR Ovarian Cancer Cell via mTORC1/S6K Signaling Pathway.

Ovarian cancer is a carcinoma that affects women and that has a high mortality rate. Overcoming paclitaxel resistance is important for clinical application. However, the effect of amino acid metabolism regulation on paclitaxel-resistant ovarian cancer is still unknown. In this study, the effect of an amino acid-deprived condition on paclitaxel resistance in paclitaxel-resistant SKOV3-TR cells was analyzed. We analyzed the cell viability of SKOV3-TR in culture conditions in which each of the 20 amino acids were deprived. As a result, the cell viability of the SKOV3-TR was significantly reduced in cultures deprived of arginine, glutamine, and lysine. Furthermore, we showed that the glutamine-deprived condition inhibited mTORC1/S6K signaling. The decreased cell viability and mTORC1/S6K signaling under glutamine-deprived conditions could be restored by glutamine and α-KG supplementation. Treatment with PF-4708671, a selective S6K inhibitor, and the selective glutamine transporter ASCT2 inhibitor V-9302 downregulated mTOR/S6K signaling and resensitized SKOV3-TR to paclitaxel. Immunoblotting showed the upregulation of Bcl-2 phosphorylation and a decrease in Mcl-1 expression in SKOV3-TR via the cotreatment of paclitaxel with PF-4708671 and V-9302. Collectively, this study demonstrates that the inhibition of glutamine uptake can resensitize SKOV3-TR to paclitaxel and represents a promising therapeutic target for overcoming paclitaxel resistance in ovarian cancer.

Knockdown of NUPR1 Enhances the Sensitivity of Non-small-cell Lung Cancer Cells to Metformin by AKT Inhibition.

BACKGROUND/AIM: Metformin is a widely used drug for type 2 diabetes mellitus and has recently attracted broad attention for its therapeutic effects on many cancers. This study aimed to investigate the molecular mechanism of metformin's anticancer activity. MATERIALS AND METHODS: Cell viability was measured by MTT assay. Gene and protein expression levels were determined by reverse transcription-polymerase chain reaction and western blot analyses, respectively. RESULTS: Metformin and phenformin markedly induced NUPR1 expression in a dose- and time-dependent manner in H1299 non-small-cell lung cancer (NSCLC) cells. The silencing of NUPR1 in H1299 NSCLC cells enhanced cell sensitivity to metformin or ionizing radiation. Our previous report showed that metformin induces AKT serine/threonine kinase (AKT) activation in an activating transcription factor 4 (ATF4)-dependent manner and that the inhibition of AKT promotes cell sensitivity to metformin in H1299 NSCLC cells. Interestingly, ATF4-induced AKT activation in H1299 NSCLC cells treated with metformin was suppressed by the knockdown of NUPR1. CONCLUSION: Targeting NUPR1 could enhance the sensitivity of H1299 NSCLC cells to metformin by AKT inhibition.

Melatonin increases growth properties in human dermal papilla spheroids by activating AKT/GSK3ß/ß-Catenin signaling pathway.

Background: Melatonin, a neurohormone, maybe involved in physiological processes, such as antioxidation, anti-inflammation, and hair growth. In the present study, we investigated the effects of melatonin on proliferation and intracellular signaling in DP cells using a three-dimensional (3D) spheroid culture system that mimics the in vivo hair follicle system. Methods: DP cells were incubated in monolayer (2D) and 3D spheroid culture systems. The expression levels of melatonin receptors in DP cells were analyzed using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blotting. The effect of melatonin on the hair-inductive property of DP cells was analyzed using a WST-1-based proliferation assay, determination of DP spheroid size, expression analysis of DP signature genes, and determination of ß-catenin stabilization in DP cells. The AKT/GSK3ß/ß-catenin signaling pathway associated with melatonin-induced ß-catenin stabilization in DP cells was investigated by analyzing changes in upstream regulator proteins, including AKT, GSK3ß, and their phosphorylated forms. Results: The expression levels of the melatonin receptors were higher in human DP cells than in human epidermal keratinocytes and human dermal fibroblast cells. Comparing the expression level according to the human DP cell culture condition, melatonin receptor expression was upregulated in the 3D culture system compared to the traditional two-dimensional monolayer culture system. Cell viability analysis showed that melatonin concentrations up to 1 mM did not affect cell viability. Moreover, melatonin increased the diameter of DP cell 3D spheroids in a dose-dependent manner. Immunoblotting and qRT-PCR analysis revealed that melatonin upregulated the expression of hair growth-related genes, including alkaline phosphatase, bone morphogenetic protein 2, versican, and wingless-int 5A, in a melatonin receptor-dependent manner. Cell fractionation analysis showed that melatonin increased the nuclear localization of ß-catenin. This result correlated with the increased transcriptional activation of T-cell factor/lymphoid enhancer factor-responsive luciferase induced by melatonin treatment. Interestingly, melatonin induced the phosphorylation of protein kinase B/AKT at serine 473 residue and GSK-3ß at serine 9 residue. To determine whether AKT phosphorylation at serine 473 induced ß-catenin nuclear translocation through GSK3ß phosphorylation at serine 9, the PI3K/AKT inhibitor LY294002 was cotreated with melatonin. Immunoblotting showed that LY294002 inhibited melatonin-induced phosphorylation of GSK3ß at serine 9 residue and ß-catenin activation. Conclusion: Collectively, this report suggests that melatonin promotes growth properties by activating the AKT/GSK3ß/ß-catenin signaling pathway through melatonin receptors.

Daphnetin inhibits α-MSH-induced melanogenesis via PKA and ERK signaling pathways in B16F10 melanoma cells.

Daphnetin is a dehydroxylated derivative of coumarin isolated from Daphne species. However, the effect of daphnetin on melanogenesis has not been elucidated. This study aims to investigate the inhibitory effect of daphnetin on melanogenesis in α-melanocyte stimulating hormone (α-MSH)-treated B16F10 cells and its potential mechanism. Melanin content analysis and cellular tyrosinase activity assay showed that daphnetin inhibited melanin biosynthesis in α-MSH-treated B16F10 cells. Immunoblotting and qRT-PCR also indicated that daphnetin suppressed the expression of microphthalmia-associated transcription factor, a mastering transcription factor of melanogenesis and its downstream melanogenic enzymes including tyrosinase and tyrosinase-related proteins. Moreover, daphnetin downregulated the phosphorylation of PKA, ERK, MSK1, and CREB. Additionally, daphnetin inhibited melanin synthesis in UVB-irradiated HaCaT conditioned medium system suggesting that daphnetin has potential as an antipigmentation activity in a physiological skin condition. Our data propose that daphnetin inhibits melanogenesis via modulating both the PKA/CREB and the ERK/MSK1/CREB pathways.

Knockdown of YAP/TAZ sensitizes tamoxifen-resistant MCF7 breast cancer cells.

Although endocrine therapy with tamoxifen has improved survival in breast cancer patients, resistance to this therapy remains one of the major causes of breast cancer mortality. In the present study, we found that the expression level of YAP/TAZ in tamoxifen-resistant MCF7 (MCF7-TR) breast cancer cells was significantly increased compared with that in MCF7 cells. Knockdown of YAP/TAZ with siRNA sensitized MCF7-TR cells to tamoxifen. Furthermore, siRNA targeting PSAT1, a downstream effector of YAP/TAZ, enhanced sensitivity to tamoxifen in MCF7-TR cells. Additionally, mTORC1 activity and survivin expression were significantly decreased during cell death induced by combination treatment with YAP/TAZ or PSAT1 siRNA and tamoxifen. In conclusion, targeting the YAP/TAZ-PSAT1 axis could sensitize tamoxifen-resistant MCF7 breast cancer cells by modulating the mTORC1-survivin axis.

Synergism of a novel MCL­1 downregulator, acriflavine, with navitoclax (ABT­263) in triple­negative breast cancer, lung adenocarcinoma and glioblastoma multiforme.

Myeloid cell leukemia sequence 1 (MCL­1), an anti­apoptotic B­cell lymphoma 2 (BCL­2) family molecule frequently amplified in various human cancer cells, is known to be critical for cancer cell survival. MCL­1 has been recognized as a target molecule for cancer treatment. While various agents have emerged as potential MCL­1 blockers, the present study presented acriflavine (ACF) as a novel MCL­1 inhibitor in triple­negative breast cancer (TNBC). Further evaluation of its treatment potential on lung adenocarcinoma and glioblastoma multiforme (GBM) was also investigated. The anticancer effect of ACF on TNBC cells was demonstrated when MDA­MB­231 and HS578T cells were treated with ACF. ACF significantly induced typical intrinsic apoptosis in TNBCs in a dose­ and time­dependent manner via MCL­1 downregulation. MCL­1 downregulation by ACF treatment was revealed at each phase of protein expression. Initially, transcriptional regulation via reverse transcription­quantitative PCR was validated. Then, post­translational regulation was explained by utilizing an inhibitor against protein biosynthesis and proteasome. Lastly, immunoprecipitation of ubiquitinated MCL­1 confirmed the post­translational downregulation of MCL­1. In addition, the synergistic treatment efficacy of ACF with the well­known MCL­1 inhibitor ABT­263 against the TNBC cells was explored [combination index (CI)<1]. Conjointly, the anticancer effect of ACF was assessed in GBM (U87, U251 and U343), and lung cancer (A549 and NCI­H69) cell lines as well, using immunoblotting, cytotoxicity assay and FACS. The effect of the combination treatment using ACF and ABT­263 was estimated in GBM (U87, U343 and U251), and non­small cell lung cancer (A549) cells likewise. The present study suggested a novel MCL­1 inhibitory function of ACF and the synergistic antitumor effect with ABT­263.

Pancreatic adenocarcinoma with atypical imaging features mimicking chronic pancreatitis in a dog.

An 11-year-old intact female Pomeranian dog was referred for jaundice, anorexia, and vomiting. The blood analysis revealed increased alanine aminotransferase, alkaline phosphatase, and gamma-glutamyl transpeptidase. The serum canine pancreatic lipase immunoreactivity was within the normal reference range. The radiography revealed no significant findings. On ultrasound, the gallbladder was enlarged with a markedly distended common bile duct (CBD) measuring up to 6 mm in diameter. The pancreas had an irregular contour, a hypoechoic peripheral rim, multiple hyperechoic foci with acoustic shadowing, and showed increased echogenicity of the adjacent mesentery. Based on these results, an extrahepatic biliary obstruction secondary to the presumed chronic pancreatitis was diagnosed. The computed tomography (CT) images showed a hypoattenuating pancreatic parenchyma compared to the liver in the early phase, as well as multiple calcifications. A laparotomy was performed to reserve the patency of the CBD. The histopathological examination of the pancreas revealed exocrine pancreatic adenocarcinoma. While various appearances of exocrine pancreatic adenocarcinoma on CT have been reported in humans, CT features of pancreatic adenocarcinoma have not been well-established in dogs. The purpose of this report is to describe the atypical imaging features of pancreatic adenocarcinoma that are similar to those of chronic pancreatitis in a dog.

Amino acid deprivation induces AKT activation by inducing GCN2/ATF4/REDD1 axis.

Amino acid availability is sensed by various signaling molecules, including general control nonderepressible 2 (GCN2) and mechanistic target of rapamycin complex 1 (mTORC1). However, it is unclear how these sensors are associated with cancer cell survival under low amino acid availability. In the present study, we investigated AKT activation in non-small cell lung cancer (NSCLC) cells deprived of each one of 20 amino acids. Among the 20 amino acids, deprivation of glutamine, arginine, methionine, and lysine induced AKT activation. AKT activation was induced by GCN2/ATF4/REDD1 axis-mediated mTORC2 activation under amino acid deprivation. In CRISPR-Cas9-mediated REDD1-knockout cells, AKT activation was not induced by amino acid deprivation, indicating that REDD1 plays a major role in AKT activation under amino acid deprivation. Knockout of REDD1 sensitized cells cultured under glutamine deprivation conditions to radiotherapy. Taken together, GCN2/ATF4/REDD1 axis induced by amino acid deprivation promotes cell survival signal, which might be a potential target for cancer therapy.

miR-3188 Enhances Sensitivity of Breast Cancer Cells to Ionizing Radiation by Down-regulating Rictor.

BACKGROUND/AIM: Rictor is an adaptor protein essential for mTORC2, which regulates cell growth and survival. The aim of this study was to identify microRNAs (miR) that down-regulate Rictor and investigate their function on breast cancer cell survival. MATERIALS AND METHODS: Trypan blue assay, MTT assay, polymerase chain reaction analysis, luciferase reporter assay and western blot analysis were carried out in breast cancer cell lines HCC1954, MDA-MB-231, SK-BR-3, and BT474. RESULTS: miR-3188 overexpression suppressed the expression of Rictor and inhibited cell viability in HCC1954 and MDA-MB-231, highly Rictor-expressing breast cancer cells. In addition, miR-3188 overexpression decreased the protein level of p-AKT at Ser473, a substrate of mTORC2. Moreover, miRNA-3188 overexpression sensitized breast cancer cells to ionizing radiation (IR) by down-regulating Rictor and p-AKT. CONCLUSION: miR-3188 enhances IR sensitivity by affecting the mTORC2/AKT signalling pathway by altering the expression of Rictor, which could be a promising therapeutic strategy for the future treatment of breast cancer.

Inhibition of mTORC1 through ATF4-induced REDD1 and Sestrin2 expression by Metformin.

BACKGROUND: Although the major anticancer effect of metformin involves AMPK-dependent or AMPK-independent mTORC1 inhibition, the mechanisms of action are still not fully understood. METHODS: To investigate the molecular mechanisms underlying the effect of metformin on the mTORC1 inhibition, MTT assay, RT-PCR, and western blot analysis were performed. RESULTS: Metformin induced the expression of ATF4, REDD1, and Sestrin2 concomitant with its inhibition of mTORC1 activity. Treatment with REDD1 or Sestrin2 siRNA reversed the mTORC1 inhibition induced by metformin, indicating that REDD1 and Sestrin2 are important for the inhibition of mTORC1 triggered by metformin treatment. Moreover, REDD1- and Sestrin2-mediated mTORC1 inhibition in response to metformin was independent of AMPK activation. Additionally, lapatinib enhances cell sensitivity to metformin, and knockdown of REDD1 and Sestrin2 decreased cell sensitivity to metformin and lapatinib. CONCLUSIONS: ATF4-induced REDD1 and Sestrin2 expression in response to metformin plays an important role in mTORC1 inhibition independent of AMPK activation, and this signalling pathway could have therapeutic value.

Inhibition of AKT Enhances the Sensitivity of NSCLC Cells to Metformin.

BACKGROUND/AIM: Metformin is an antidiabetic drug that has been reported to have antitumor activity in many cancer types. This study investigated the molecular mechanisms underlying the antitumor effect of metformin. MATERIALS AND METHODS: We investigated the molecular mechanism of the antitumor effect of metformin alone and in combination with AKT serine/threonine kinase (AKT) inhibition via cell viability and western blot analyses. RESULTS: Notably, metformin increased the phosphorylation of AKT at serine 473 using protein array screening. Metformin-induced AKT activation was markedly suppressed by siRNA targeting activating transcription factor 4 (ATF4) but not AMP-activated protein kinase α. These results indicate that AKT activation by metformin was induced in an ATF4-dependent and AMPKα-independent manner. Treatment using metformin combined with MK-2206, an AKT inhibitor, or a siRNA for AKT markedly reduced the viability of cells compared with those cells treated with these agents alone. In addition, MK-2206 increased cell sensitivity to the combination of metformin with ionizing radiation or cisplatin. CONCLUSION: Inhibition of AKT can enhance the antitumor effect of metformin and would be a promising strategy to sensitize non-small-cell lung cancer to a combination of metformin with radiation or cisplatin.