Dual targeting of BCL-2 and MCL-1 in the presence of BAX breaks venetoclax resistance in human small cell lung cancer.

BACKGROUND: No targeted drugs are currently available against small cell lung cancer (SCLC). BCL-2 family members are involved in apoptosis regulation and represent therapeutic targets in many malignancies. METHODS: Expression of BCL-2 family members in 27 SCLC cell lines representing all known four SCLC molecular subtypes was assessed by qPCR, Western blot and mass spectrometry-based proteomics. BCL-2 and MCL-1 inhibition (venetoclax and S63845, respectively) was assessed by MTT assay and flow cytometry and in mice bearing human SCLC tumours. Drug interactions were calculated using the Combenefit software. Ectopic BAX overexpression was achieved by expression plasmids. RESULTS: The highest BCL-2 expression levels were detected in ASCL1- and POU2F3-driven SCLC cells. Although sensitivity to venetoclax was reflected by BCL-2 levels, not all cell lines responded consistently despite their high BCL-2 expression. MCL-1 overexpression and low BAX levels were both characteristic for venetoclax resistance in SCLC, whereas the expression of other BCL-2 family members did not affect therapeutic efficacy. Combination of venetoclax and S63845 resulted in significant, synergistic in vitro and in vivo anti-tumour activity and apoptosis induction in double-resistant cells; however, this was seen only in a subset with detectable BAX. In non-responding cells, ectopic BAX overexpression sensitised to venetoclax and S63845 and, furthermore, induced synergistic drug interaction. CONCLUSIONS: The current study reveals the subtype specificity of BCL-2 expression and sheds light on the mechanism of venetoclax resistance in SCLC. Additionally, we provide preclinical evidence that combined BCL-2 and MCL-1 targeting is an effective approach to overcome venetoclax resistance in high BCL-2-expressing SCLCs with intact BAX.

Fibroblast growth factor receptor inhibitor erdafitinib promotes Mcl-1 degradation and synergistically induces apoptosis with Bcl-xL/Bcl-2 inhibitor in urothelial cancer cells.

Metastatic urothelial cancer is a lethal disease. Although recent advances in immunotherapies and targeted therapy against fibroblast growth factor receptor (FGFR)2/3 mutation (erdafitinib) have improved patient survival, there is still a critical need for novel therapeutic strategies for patients who do not benefit from these treatments. Evasion of apoptosis through amplifying anti-apoptotic Bcl-2 family proteins (Mcl-1, Bcl-xL, Bcl-2) is one mechanism responsible for treatment resistance in urothelial cancers, suggesting that targeting anti-apoptotic proteins may be a possible therapeutic strategy for urothelial cancers. Here, we showed that erdafitinib increased Mcl-1 degradation mainly through previously unknown mechanisms and synergized with a BH3 mimetic drug targeting Bcl-xL/Bcl-2 to induce apoptosis in FGFR wild-type urothelial cancer cells. Strikingly, clinical sequencing data showed amplification of MCL1 or BCL2L1 (encoding Bcl-xL) in subsets of FGFR mutation-negative bladder cancer tissues. In conclusion, these findings suggest that exploiting apoptosis pathways may be a promising treatment strategy for patients with FGFR wild-type metastatic urothelial cancer with Mcl-1 or Bcl-xL overexpression.

A novel aryl-guanidinium derivative, VP79s, targets the signal transducer and activator of transcription 3 signaling pathway, downregulates myeloid cell leukaemia-1 and exhibits preclinical activity against multiple myeloma.

AIMS: We have recently described a novel guanidinium-based compound, VP79s, which induces cytotoxicity in various cancer cell lines. Here, we aim to investigate the activity of VP79s and associated mechanisms of action in multiple myeloma (MM) cells in vitro and ex vivo. MAIN METHODS: The effects of VP79s on cell viability and induction of apoptosis was examined in a panel of drug-sensitive and drug-resistant MM cell lines, as well as ex vivo patient samples and normal donor lymphocytes and platelets. Cell signaling pathways associated with the biological effects of VP79s were analysed by immunoblotting and flow cytometry. Gene expression changes were assessed by quantitative real-time PCR analysis. KEY FINDINGS: VP79s was found to rapidly inhibit both constitutively active and IL-6-induced STAT3 signaling with concurrent downregulation of the IL-6 receptors, CD130 and CD126. VP79s induced a rapid and dose-dependent downregulation of anti-apoptotic Bcl-2 family member, myeloid cell leukaemia-1 (MCL-1). VP79s enhanced bortezomib induced cell death and was also found to overcome bone marrow stromal cell induced drug resistance. VP79s exhibited activity in ex vivo patient samples at concentrations which had no effect on peripheral blood mononuclear cells, lymphocytes and platelets isolated from healthy donors. SIGNIFICANCE: As VP79s resulted in rapid inhibition of the key IL-6/STAT3 signaling pathway and downregulation of MCL-1 expression with subsequent selective anti-myeloma activity, VP79s may be a potential therapeutic agent with a novel mechanism of action in MM cells.

Knockdown of Myeloid Cell Leukemia-1 by MicroRNA-101 Increases Sensitivity of A549 Lung Cancer Cells to Etoposide.

Background: Studies have shown that myeloid cell leukemia-1 (Mcl-1) is the target gene for microRNA -101 (miRNA-101), and decreased levels of miRNA-101 are associated with elevated levels of Mcl-1 and lung cancer survival. The objective of the present study was to investigate the effect of miRNA-101 on the sensitivity of A549 lung cancer cells to etoposide. Methods: The study was conducted during 2018 and 2019 at Arak University of Medical Sciences, Arak, Iran. The effect of miRNA-101 on Mcl-1 expression was assessed using reverse transcription-quantitative polymerase chain reaction 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT), and trypan blue exclusion assays were performed to determine the effect of treatments on cell survival and proliferation, respectively. The interaction between miRNA-101 and etoposide was evaluated using the combination index analysis of Chou-Talalay. Apoptosis was quantified using ELISA cell death assay. ANOVA and Bonferroni's tests were used to determine statistical differences between the groups (P<0.05). GraphPad Prism software (version 6.01) was used for data analysis. Results: The results showed that miRNA-101 clearly inhibited the expression of Mcl-1 and reduced the growth of A549 cells, relative to blank control and negative control miRNA (P<0.05). Transfection of miRNA-101 synergistically enhanced the sensitivity of the A549 cells to etoposide. Apoptosis assay data also showed that miRNA-101 triggered apoptosis and augmented the etoposide-mediated apoptosis. Conclusion: Up-regulation of miRNA-101 inhibited cell survival and proliferation, and sensitized A549 cells to etoposide by suppressing Mcl-1 expression. miRNA-101 replacement therapy can be considered as an effective therapeutic strategy in non-small cell lung cancer.

KRIBB11 Induces Apoptosis in A172 Glioblastoma Cells via MULE-Dependent Degradation of MCL-1.

KRIBB11, an HSF1 inhibitor, was shown to sensitize various types of cancer cells to treatment with several anticancer drugs. However, the exclusive effects of KRIBB11 in preventing the growth of glioblastoma cells and the related mechanisms have not been elucidated yet. Herein, we aimed to examine the potential of KRIBB11 as an anticancer agent for glioblastoma. Using MTT and colony formation assays and Western blotting for c-PARP, we demonstrated that KRIBB11 substantially inhibits the growth of A172 glioma cells by inducing apoptosis. At the molecular level, KRIBB11 decreased anti-apoptotic protein MCL-1 levels, which was attributable to the increase in MULE ubiquitin ligase levels. However, the constitutive activity of HSF1 in A172 cells was not influenced by the exclusive treatment with KRIBB11. Additionally, based on cycloheximide chase assay, we found that KRIBB11 markedly retarded the degradation of MULE. In conclusion, stabilization of MULE upon KRIBB11 treatment is apparently an essential step for degradation of MCL-1 and the subsequent induction of apoptosis in A172 cells. Our results have expanded the knowledge on molecular pathways controlled by KRIBB11 and could be potentially effective for developing an inhibitory therapeutic strategy for glioblastoma.

Phragmunis a suppresses glioblastoma through the regulation of MCL1-FBXW7 by blocking ELK1-SRF complex-dependent transcription.

Glioblastoma (GBM) is a highly aggressive brain tumor. During screening work, we found a new compound named phragmunis A (PGA), which is derived from the fruitbody of Trogia venenata, exhibits a potential cytotoxic effect on patient-derived recurrent GBM cells and temozolomide (TMZ)-resistant cell lines. The present study was designed to investigate the potential molecular mechanism of the anti-glioma effects of PGA in vitro and in vivo. Studies investigating the mechanism revealed that PGA diminished the binding efficiency of ETS family of transcription factor (ELK1) and Serum response factor (SRF), and suppressed ELK1-SRF complex-dependent transcription, which decreased the transcriptional levels of downstream genes Early growth response protein 1 (EGR1)-Polycomb ring finger (BMI1), thus inducing the imbalanced regulation between Myeloid cell leukaemia-1 (MCL1) and F-Box and WD repeat domain containing 7 (FBXW7). Finally, orthotopic xenograft models were established to confirm the anti-glioma effect of PGA on tumour growth. We showed, for the first time, that the cytotoxic effects of PGA occurred by inducing MCL1 inhibition and FBXW7 activation by blocking ELK1-SRF complex-dependent transcription. The blockage of ELK1-mediated transcription resulted in the suppression of EGR1-BMI1, which led to the upregulation of FBXW7 expression and downregulation of MCL1. These findings suggested that PGA could be a therapeutic drug candidate for the treatment of recurrent GBM by targeting the ELK1-SRF complex.

Dendrobium nobile Lindl. polysaccharides reduce cerebral ischemia/reperfusion injury in mice by increasing myeloid cell leukemia 1 via the downregulation of miR-134.

OBJECTIVE: The traditional Chinese medicine, Dendrobium nobile Lindl. polysaccharides (DNLP), reportedly has neuroprotective effects. However, its effects following ischemic stroke remain unclear. This study aimed to explore the role and mechanism of DNLP in experimental models of inflammation and apoptosis. METHODS: Inflammation and apoptosis were induced by in vivo ischemia/reperfusion and by in vitro oxygen glucose deprivation/reperfusion (OGD/R). In the in vivo model, immediately after the induction of cerebral ischemia, 50, 100, and 200 mg/kg DNLP were injected intraperitoneally. We subsequently detected indicators of neuronal damage. RESULTS: Treatment with Dendrobium nobile Lindl. polysaccharide significantly reduced cerebral ischemic injury. After in vivo and in vitro middle cerebral artery occlusion/reperfusion or OGD/R-induced hypoxia injury, miR-134 expression in neurons was significantly increased. Altering the expression of miR-134 induced changes in myeloid cell leukemia 1 (MCL-1), one of its target proteins. In addition, DNLP significantly downregulated the in vivo and in vitro expression of miR-134 after ischemic injury, and influenced inflammation and apoptotic proteins by altering the level of MCL-1 protein. DNLP also had a protective effect on neurons damaged by OGD/R, which could improve cell survival rates and inhibit lactate dehydrogenase release as well as apoptosis. CONCLUSIONS: DNLP may protect the brain and neurons from hypoxic damage in mice with ischemic stroke by activating MCL-1 and downregulating miR-134, providing a new therapeutic target for ischemic stroke.

Pharmacological targeting of MCL-1 promotes mitophagy and improves disease pathologies in an Alzheimer's disease mouse model.

There is increasing evidence that inducing neuronal mitophagy can be used as a therapeutic intervention for Alzheimer's disease. Here, we screen a library of 2024 FDA-approved drugs or drug candidates, revealing UMI-77 as an unexpected mitophagy activator. UMI-77 is an established BH3-mimetic for MCL-1 and was developed to induce apoptosis in cancer cells. We found that at sub-lethal doses, UMI-77 potently induces mitophagy, independent of apoptosis. Our mechanistic studies discovered that MCL-1 is a mitophagy receptor and directly binds to LC3A. Finally, we found that UMI-77 can induce mitophagy in vivo and that it effectively reverses molecular and behavioral phenotypes in the APP/PS1 mouse model of Alzheimer's disease. Our findings shed light on the mechanisms of mitophagy, reveal that MCL-1 is a mitophagy receptor that can be targeted to induce mitophagy, and identify MCL-1 as a drug target for therapeutic intervention in Alzheimer's disease.

Identification of BCL-XL as highly active survival factor and promising therapeutic target in colorectal cancer.

Since metastatic colorectal cancer (CRC) is a leading cause of cancer-related death, therapeutic approaches overcoming primary and acquired therapy resistance are an urgent medical need. In this study, the efficacy and toxicity of high-affinity inhibitors targeting antiapoptotic BCL-2 proteins (BCL-2, BCL-XL, and MCL-1) were evaluated. By RNA sequencing analysis of a pan-cancer cohort comprising >1500 patients and subsequent prediction of protein activity, BCL-XL was identified as the only antiapoptotic BCL-2 protein that is overactivated in CRC. Consistently, pharmacologic and genetic inhibition of BCL-XL induced apoptosis in human CRC cell lines. In a combined treatment approach, targeting BCL-XL augmented the efficacy of chemotherapy in vitro, in a murine CRC model, and in human ex vivo derived CRC tissue cultures. Collectively, these data show that targeting of BCL-XL is efficient and safe in preclinical CRC models, observations that pave the way for clinical translation.

Sequential combinations of chemotherapeutic agents with BH3 mimetics to treat rhabdomyosarcoma and avoid resistance.

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in childhood and adolescence. Refractory/relapsed RMS patients present a bad prognosis that combined with the lack of specific biomarkers impairs the development of new therapies. Here, we utilize dynamic BH3 profiling (DBP), a functional predictive biomarker that measures net changes in mitochondrial apoptotic signaling, to identify anti-apoptotic adaptations upon treatment. We employ this information to guide the use of BH3 mimetics to specifically inhibit BCL-2 pro-survival proteins, defeat resistance and avoid relapse. Indeed, we found that BH3 mimetics that selectively target anti-apoptotic BCL-xL and MCL-1, synergistically enhance the effect of clinically used chemotherapeutic agents vincristine and doxorubicin in RMS cells. We validated this strategy in vivo using a RMS patient-derived xenograft model and observed a reduction in tumor growth with a tendency to stabilization with the sequential combination of vincristine and the MCL-1 inhibitor S63845. We identified the molecular mechanism by which RMS cells acquire resistance to vincristine: an enhanced binding of BID and BAK to MCL-1 after drug exposure, which is suppressed by subsequently adding S63845. Our findings validate the use of DBP as a functional assay to predict treatment effectiveness in RMS and provide a rationale for combining BH3 mimetics with chemotherapeutic agents to avoid tumor resistance, improve treatment efficiency, and decrease undesired secondary effects.

Dual targeting of BCL2 and MCL1 rescues myeloma cells resistant to BCL2 and MCL1 inhibitors associated with the formation of BAX/BAK hetero-complexes.

Multiple myeloma is a plasma cell malignancy that escapes from apoptosis by heterogeneously over-expressing anti-apoptotic BCL2 proteins. Myeloma cells with a t(11;14) translocation present a particular vulnerability to BCL2 inhibition while a majority of myeloma cells relies on MCL1 for survival. The present study aimed to determine whether the combination of BCL2 and MCL1 inhibitors at low doses could be of benefit for myeloma cells beyond the single selective inhibition of BCL2 or MCL1. We identified that half of patients were not efficiently targeted neither by BCL2 inhibitor nor MCL1 inhibitor. Seventy percent of these myeloma samples, either from patients at diagnosis or relapse, presented a marked increase of apoptosis upon low dose combination of both inhibitors. Interestingly, primary cells from a patient in progression under venetoclax treatment were not sensitive ex vivo to neither venetoclax nor to MCL1 inhibitor, whereas the combination of both efficiently induced cell death. This finding suggests that the combination could overcome venetoclax resistance. The efficacy of the combination was also confirmed in U266 xenograft model resistant to BCL2 and MCL1 inhibitors. Mechanistically, we demonstrated that the combination of both inhibitors favors apoptosis in a BAX/BAK dependent manner. We showed that activated BAX was readily increased upon the inhibitor combination leading to the formation of BAK/BAX hetero-complexes. We found that BCLXL remains a major resistant factor of cell death induced by this combination. The present study supports a rational for the clinical use of venetoclax/S63845 combination in myeloma patients with the potential to elicit significant clinical activity when both single inhibitors would not be effective but also to overcome developed in vivo venetoclax resistance.

Formononetin inhibits tumor growth by suppression of EGFR-Akt-Mcl-1 axis in non-small cell lung cancer.

BACKGROUND: Epidermal growth factor receptor (EGFR) activating mutations play crucial roles in the tumorigenesis of human non-small cell lung cancer (NSCLC). The mechanism regarding how EGFR signaling regulates myeloid cell leukemia sequence 1 (Mcl-1) protein stability and ubiquitination remains undefined. METHODS: MTS assay was used for natural product library screening. The effect of formononetin (Formo) on NSCLC cells was determined by MTS assay and soft agar assay. Molecular modeling was performed to analyze the potential different binding modes between Formo and EGFR WT or mutants. Mcl-1 protein level and the inhibitory effect of Formo on EGFR signaling were examined by immunoblot, in vitro kinase assay, in vitro pulldown and ATP competition assays, co-immunoprecipitation assay, ubiquitination analysis, in vivo xenograft model, and immunohistochemical staining. RESULTS: Formo was identified as an EGFR inhibitor by a 98 commercially available natural product screening. Formo suppresses WT and mutant EGFR kinases activity in vitro, ex vivo, and in vivo. Molecular modeling indicates that Formo docks into the ATP-binding pocket of both WT and mutant EGFR. Formo inhibits EGFR-Akt signaling, which in turn activates GSK3ß and promotes Mcl-1 phosphorylation in NSCLC cells. Treatment with Formo enhances the interaction between Mcl-1 and SCFFbw7, which eventually promotes Mcl-1 ubiquitination and degradation. Depletion of either GSK3ß or SCFFbw7 compromised Formo-induced Mcl-1 downregulation. Finally, Formo inhibits the in vivo tumor growth in a xenograft mouse model. CONCLUSION: This study highlights the importance of promoting ubiquitination-dependent Mcl-1 turnover might be an alternative strategy to enhance the anti-tumor efficacy of EGFR-TKI.

MCL1 inhibition is effective against a subset of small-cell lung cancer with high MCL1 and low BCL-XL expression.

There have been few advances in the treatment of small-cell lung cancer (SCLC) because of the lack of targets. MCL1, a member of the anti-apoptotic BCL-2 family, may be a treatment target in several cancers, including SCLC. However, whether the expression profile of the anti-apoptotic BCL-2 family affects MCL1 inhibition strategy is unknown. A tissue microarray (TMA) was created from consecutive patients who were diagnosed with SCLC and had previously undergone surgery at Kyoto University Hospital (Kyoto, Japan) between 2001 and 2017. We used S63845, a MCL1 inhibitor, to assess the cytotoxic capacity in SCLC cell lines including a patient-derived cell line in vitro and in vivo. The combination of S63845 with navitoclax, a double BCL-XL/BCL-2 inhibitor, was also employed to examine the comprehensive inhibition of the anti-apoptotic BCL-2 family. Immunohistochemistry of a TMA from patients with surgically resected SCLC demonstrated high MCL1 expression with low BCL-XL and BCL-2 to be the most common expression profile. S63845 was effective in high MCL1- and low BCL-XL-expressing SCLC cell lines. S63845 induced BAK-dependent apoptosis in vitro, and the anti-tumor efficacy was confirmed in an in vivo model. Although knockdown of BCL-XL and BCL-2 improved the cytotoxic activity of S63845 and its combination with navitoclax increased the anti-tumor cytotoxicity, the therapeutic range of S63845 with navitoclax was narrow in in vivo studies. Our study suggests MCL1 inhibition therapy be applied for high MCL1- and low BCL-XL-expressing SCLC patients.

Selective BH3-mimetics targeting BCL-2, BCL-XL or MCL-1 induce severe mitochondrial perturbations.

Induction of apoptosis by selective BH3-mimetics is currently investigated as a novel strategy for cancer treatment. Here, we report that selective BH3-mimetics induce apoptosis in a variety of hematological malignancies. Apoptosis is accompanied by severe mitochondrial toxicities upstream of caspase activation. Specifically, the selective BH3-mimetics ABT-199, A-1331852 and S63845, which target BCL-2, BCL-XL and MCL-1, respectively, induce comparable ultrastructural changes including mitochondrial swelling, a decrease of mitochondrial matrix density and severe loss of cristae structure. These shared effects on mitochondrial morphology indicate a similar function of these anti-apoptotic BCL-2 proteins in maintaining mitochondrial integrity and function.

miR-146a down-regulation alleviates H2O2-induced cytotoxicity of PC12 cells by regulating MCL1/JAK/STAT pathway : miR-146a down-regulation relieves H2O2-induced PC12 cells cytotoxicity by MCL1/JAK/STAT.

Oxidative stress and miRNAs have been confirmed to play an important role in neurological diseases. The study aimed to explore the underlying effect and mechanisms of miR-146a in H2O2-induced injury of PC12 cells. Here, PC12 cells were stimulated with 200 µM of H2O2 to construct oxidative injury model. Cell injury was evaluated on the basis of the changes in cell viability, migration, invasion, apoptosis, and DNA damage. Results revealed that miR-146a expression was up-regulated in H2O2-induced PC12 cells. Functional analysis showed that down-regulation of miR-146a alleviated H2O2-induced cytotoxicity in PC12 cells. Dual-luciferase reporter and western blot assay verified that MCL1 was a direct target gene of miR-146a. Moreover, anti-miR-146a-mediated suppression on cell cytotoxicity was abated following MCL1 knockdown in H2O2-induced PC12 cells. Furthermore, MCL1 activated JAK/STAT signaling pathway and MCL1 overexpression attenuated H2O2-induced cytotoxicity in PC12 cells by JAK/STAT signaling pathway. In conclusion, this study suggested that suppression of miR-146a abated H2O2-induced cytotoxicity in PC12 cells via regulating MCL1/JAK/STAT pathway.

Curcumin induces apoptosis and inhibits proliferation in infantile hemangioma endothelial cells via downregulation of MCL-1 and HIF-1α.

BACKGROUND: Curcumin has been used as an alternative medicine for the treatment of infantile hemangiomas (IHs); however, the mechanism underlying the effectiveness of curcumin in IHs remains largely unclear. METHODS: In this study, we isolated primary human hemangioma endothelial cells (HemECs) from fresh surgical specimens of 3 patients. We treated HemECs by curcumin and investigated the alterations in proliferative and apoptotic signaling pathways with cell counting kit-8, flow cytometry, western blotting, immunofluorescence, and real-time polymerase chain reaction. RESULTS AND CONCLUSION: We found that curcumin potently inhibited proliferation in HemECs, achieving low-micromolar IC50 (the half maximal inhibitory concentration) value. We also observed that treatment with curcumin induced apoptosis in HemECs, as evidenced by positively Annexin-V-FITC staining, caspase-3 activation, and cleavage of poly(adenosine diphosphate-ribose) polymerase (PARP) in the treated cells. Moreover, we showed that curcumin suppressed the expression of antiapoptotic protein myeloid cell leukemia-1 (MCL-1), hypoxia-inducible factor 1α (HIF-1α), and vascular endothelial growth factor (VEGF).Altogether, our study suggests that the effectiveness of curcumin in IHs may be associated with its potent antiproliferative and apoptotic activities in HemECs.

Targeting the differential addiction to anti-apoptotic BCL-2 family for cancer therapy.

BCL-2 family proteins are central regulators of mitochondrial apoptosis and validated anti-cancer targets. Using small cell lung cancer (SCLC) as a model, we demonstrated the presence of differential addiction of cancer cells to anti-apoptotic BCL-2, BCL-XL or MCL-1, which correlated with the respective protein expression ratio. ABT-263 (navitoclax), a BCL-2/BCL-XL inhibitor, prevented BCL-XL from sequestering activator BH3-only molecules (BH3s) and BAX but not BAK. Consequently, ABT-263 failed to kill BCL-XL-addicted cells with low activator BH3s and BCL-XL overabundance conferred resistance to ABT-263. High-throughput screening identified anthracyclines including doxorubicin and CDK9 inhibitors including dinaciclib that synergized with ABT-263 through downregulation of MCL-1. As doxorubicin and dinaciclib also reduced BCL-XL, the combinations of BCL-2 inhibitor ABT-199 (venetoclax) with doxorubicin or dinaciclib provided effective therapeutic strategies for SCLC. Altogether, our study highlights the need for mechanism-guided targeting of anti-apoptotic BCL-2 proteins to effectively activate the mitochondrial cell death programme to kill cancer cells.

Knockdown of the FoxM1 enhances the sensitivity of gastric cancer cells to cisplatin by targeting Mcl-1.

Resistance to chemotherapy is a main obstacle for effective treatment of gastric cancer, the mechanism of which is still poorly understood. Forkhead box M1 (FoxM1) plays an important role in chemo-resistance of various tumors. This study aimed to explore whether FoxM1 mediated resistance of the gastric cancer cell line SGC7901 to the chemotherapy agent cisplatin (DDP). In the study, we detected FoxM1 and Mcl-1 expression via real time-PCR and western blot and demonstrated that FoxM1 is overexpressed in cisplatin-resistance GC cells and Mcl-1 expression is regulated by FoxM1. We examined SGC7901/DDP cell viability by MTT assay, which revealed that suppression of the FoxM1/Mcl-1 pathway impaired cell viability and thus increased sensitivity to cisplatin in gastric cancer cells. Taken together, the study implied that the FoxM1/Mcl-1 pathway may overcome cispaltin resistance of gastric cancer and provide a new therapeutic target for the treatment of gastric cancer.

Inhibition of MARCH5 ubiquitin ligase abrogates MCL1-dependent resistance to BH3 mimetics via NOXA.

BH3 mimetic compounds induce tumor cell death through targeted inhibition of anti-apoptotic BCL2 proteins. Resistance to one such compound, ABT-737, is due to increased levels of anti-apoptotic MCL1. Using chemical and genetic approaches, we show that resistance to ABT-737 is abrogated by inhibition of the mitochondrial RING E3 ligase, MARCH5. Mechanistically, this is due to increased expression of pro-apoptotic BCL2 family member, NOXA, and is associated with MARCH5 regulation of MCL1 ubiquitylation and stability in a NOXA-dependent manner. MARCH5 expression contributed to an 8-gene signature that correlates with sensitivity to the preclinical BH3 mimetic, navitoclax. Furthermore, we observed a synthetic lethal interaction between MCL1 and MARCH5 in MCL1-dependent breast cancer cells. Our data uncover a novel level at which the BCL2 family is regulated; furthermore, they suggest targeting MARCH5-dependent signaling will be an effective strategy for treatment of BH3 mimetic-resistant tumors, even in the presence of high MCL1.

Tyrosine kinase inhibitor tyrphostin AG490 triggers both apoptosis and autophagy by reducing HSF1 and Mcl-1 in PEL cells.

PEL cells relay on the constitutive activation of STAT3 for their survival, thus its inhibition by AG490 leads to apoptotic cell death. In this study, we found that the cytotoxic activity of AG490 correlated with the reduction of HSP70 and its master regulator HSF1 that, based on knocking-down experiments, was found to play a pro-survival role in PEL cells. To counteract the pro-death effect mediated by HSF1/HSP70 down-regulation, AG490 induced a complete autophagy, whose inhibition potentiated its cytotoxic effect against PEL cells. AG490 as well as HSF1 siRNA reduced the expression of Mcl-1, a Bcl-2 family member that negatively regulates apoptosis and autophagy. These results suggest that STAT3 inhibition, by down-regulating the expression of HSF1/HSP70, reduces Mcl-1 and leads to both apoptosis and autophagy induction in PEL cells.