Vitamin K2 sensitizes the efficacy of venetoclax in acute myeloid leukemia by targeting the NOXA-MCL-1 pathway.

Promising outcomes have been reported in elder patients with acute myeloid leukemia (AML) using combined therapy of venetoclax (VEN) and azacytidine (AZA) in recent years. However, approximately one-third of patients appear to be refractory to this therapy. Vitamin K2 (VK2) shows apoptosis-inducing activity in AML cells, and daily oral VK2 (menaquinone-4, GlakayR) has been approved for patients with osteoporosis in Japan. We observed a high response rate to AZA plus VEN therapy, with no 8-week mortality in the newly diagnosed AML patients consuming daily VK2 in our hospital. The median age of the patients was 75.9 years (range 66-84) with high-risk features. Patients received AZA 75 mg/m2 on D1-7, VEN 400 mg on D1-28, and daily VK2 45 mg. The CR/CRi ratio was 94.7% (18/19), with a CR rate of 79%. Complete cytogenetic CR was achieved in 15 of 19 (79%) patients, and MRD negativity in 2 of 15 (13%) evaluable CR patients. Owing to the extremely high response rate in clinical settings, we further attempted to investigate the underlying mechanisms. The combination of VK2 and VEN synergistically induced apoptosis in all five AML cell lines tested. VK2, but not VEN, induced mitochondrial reactive oxygen species (ROS), leading to the transcriptional upregulation of NOXA, followed by MCL-1 repression. ROS scavengers repressed VK2 induced-NOXA expression and led to the cancellation of pronounced apoptosis and the downregulation of MCL-1 by VK2 plus VEN. Additionally, knockdown and knockout of NOXA resulted in abrogation of the MCL-1 repression as well as enhanced cytotoxicity by the two-drug combination, indicating that VK2 suppresses MCL-1 via ROS-mediated NOXA induction. These data suggest that the dual inhibition of BCL-2 by VEN and MCL-1 by VK2 is responsible for the remarkable clinical outcomes in our patients. Therefore, large-scale clinical trials are required.

Evaluation of MCL-1 as a prognostic factor in canine mammary gland tumors.

Myeloid cell leukemia-1 (MCL-1), which belongs to the anti-apoptotic B cell lymphoma-2 family protein, is overexpressed in various cancers and is associated with cell immortality, malignant transformation, chemoresistance, and poor prognosis in humans. However, the significance of MCL-1 in canine mammary gland tumors (MGTs) remains unknown. This study aimed to examine MCL-1 expression in normal canine mammary glands and tumors and to assess its correlation with clinical and histologic variables. In total, 111 samples were examined, including 12 normal mammary gland tissues, 51 benign MGTs, and 48 malignant MGTs. Immunohistochemistry revealed that 53% of benign tumors and 75% of malignant tumors exhibited high MCL-1 expression, whereas only 8% of normal mammary glands exhibited high MCL-1 expression. High MCL-1 expression correlated with tumor malignancy (p < 0.001), large tumor size (> 3 cm) (p = 0.005), high Ki-67 expression (p = 0.046), and metastasis (p = 0.027). Survival curve analysis of dogs with malignant MGTs demonstrated a significant association between high MCL-1 expression and shorter median overall survival (p = 0.027) and progression-free survival (p = 0.014). Our study identified MCL-1 as a prognostic factor and potential therapeutic target in canine MGTs.

Combined inhibition of KRASG12C and mTORC1 kinase is synergistic in non-small cell lung cancer.

Current KRASG12C (OFF) inhibitors that target inactive GDP-bound KRASG12C cause responses in less than half of patients and these responses are not durable. A class of RASG12C (ON) inhibitors that targets active GTP-bound KRASG12C blocks ERK signaling more potently than the inactive-state inhibitors. Sensitivity to either class of agents is strongly correlated with inhibition of mTORC1 activity. We have previously shown that PI3K/mTOR and ERK-signaling pathways converge on key cellular processes and that inhibition of both pathways is required for inhibition of these processes and for significant antitumor activity. We find here that the combination of a KRASG12C inhibitor with a selective mTORC1 kinase inhibitor causes synergistic inhibition of Cyclin D1 expression and cap-dependent translation. Moreover, BIM upregulation by KRASG12C inhibition and inhibition of MCL-1 expression by the mTORC1 inhibitor are both required to induce significant cell death. In vivo, this combination causes deep, durable tumor regressions and is well tolerated. This study suggests that the ERK and PI3K/mTOR pathways each mitigate the effects of inhibition of the other and that combinatorial inhibition is a potential strategy for treating KRASG12C-dependent lung cancer.

Confounding Factors in Targeted Degradation of Short-Lived Proteins.

Targeted protein degradation has recently emerged as a novel option in drug discovery. Natural protein half-life is expected to affect the efficacy of degrading agents, but to what extent it influences target protein degradation has not been systematically explored. Using simple mathematical modeling of protein degradation, we find that the natural half-life of a target protein has a dramatic effect on the level of protein degradation induced by a degrader agent which can pose significant hurdles to screening efforts. Moreover, we show that upon screening for degraders of short-lived proteins, agents that stall protein synthesis, such as GSPT1 degraders and generally cytotoxic compounds, deceptively appear as protein-degrading agents. This is exemplified by the disappearance of short-lived proteins such as MCL1 and MDM2 upon GSPT1 degradation and upon treatment with cytotoxic agents such as doxorubicin. These findings have implications for target selection as well as for the type of control experiments required to conclude that a novel agent works as a bona fide targeted protein degrader.

Modeling the Binding of Anticancer Peptides and Mcl-1.

Mcl-1 (myeloid cell leukemia 1), a member of the Bcl-2 family, is upregulated in various types of cancer. Peptides representing the BH3 (Bcl-2 homology 3) region of pro-apoptotic proteins have been demonstrated to bind the hydrophobic groove of anti-apoptotic Mcl-1, and this interaction is responsible for regulating apoptosis. Structural studies have shown that, while there is high overall structural conservation among the anti-apoptotic Bcl-2 (B-cell lymphoma 2) proteins, differences in the surface groove of these proteins facilitates binding specificity. This binding specificity is crucial for the mechanism of action of the Bcl-2 family in regulating apoptosis. Bim-based peptides bind specifically to the hydrophobic groove of Mcl-1, emphasizing the importance of these interactions in the regulation of cell death. Molecular docking was performed with BH3-like peptides derived from Bim to identify high affinity peptides that bind to Mcl-1 and to understand the molecular mechanism of their interactions. The interactions of three identified peptides, E2gY, E2gI, and XXA1_F3dI, were further evaluated using 250 ns molecular dynamics simulations. Conserved hydrophobic residues of the peptides play an important role in their binding and the structural stability of the complexes. Understanding the molecular basis of interaction of these peptides will assist in the development of more effective Mcl-1 specific inhibitors.

Low BCL-xL expression in triple-negative breast cancer cells favors chemotherapy efficacy, and this effect is limited by cancer-associated fibroblasts.

Triple negative breast cancers (TNBC) present a poor prognosis primarily due to their resistance to chemotherapy. This resistance is known to be associated with elevated expression of certain anti-apoptotic members within the proteins of the BCL-2 family (namely BCL-xL, MCL-1 and BCL-2). These regulate cell death by inhibiting pro-apoptotic protein activation through binding and sequestration and they can be selectively antagonized by BH3 mimetics. Yet the individual influences of BCL-xL, MCL-1, and BCL-2 on the sensitivity of TNBC cells to chemotherapy, and their regulation by cancer-associated fibroblasts (CAFs), major components of the tumor stroma and key contributors to therapy resistance remain to be delineated. Using gene editing or BH3 mimetics to inhibit anti-apoptotic BCL-2 family proteins in TNBC line MDA-MB-231, we show that BCL-xL and MCL-1 promote cancer cell survival through compensatory mechanisms. This cell line shows limited sensitivity to chemotherapy, in line with the clinical resistance observed in TNBC patients. We elucidate that BCL-xL plays a pivotal role in therapy response, as its depletion or pharmacological inhibition heightened chemotherapy effectiveness. Moreover, BCL-xL expression is associated with chemotherapy resistance in patient-derived tumoroids where its pharmacological inhibition enhances ex vivo response to chemotherapy. In a co-culture model of cancer cells and CAFs, we observe that even in a context where BCL-xL reduced expression renders cancer cells more susceptible to chemotherapy, those in contact with CAFs display reduced sensitivity to chemotherapy. Thus CAFs exert a profound pro-survival effect in breast cancer cells, even in a setting highly favoring cell death through combined chemotherapy and absence of the main actor of chemoresistance, BCL-xL.

Desmethylclomipramine triggers mitochondrial damage and death in TGF-ß-induced mesenchymal type of A549 cells.

Lung cancer is the leading cause of cancer deaths, where the metastasis often causes chemodrug resistance and leads to recurrence after treatment. Desmethylclomipramine (DCMI), a bioactive metabolite of clomipramine, shows the therapeutic efficacy with antidepressive agency as well as potential cytostatic effects on lung cancer cells. Here, we demonstrated that DCMI effectively caused transforming growth factor (TGF)-ß1-mediated mesenchymal type of A549 cells to undergo mitochondrial death via myeloid cell leukemia-1 (Mcl-1) suppression and activation of truncated Bid (tBid). TGF-ß1 induced epithelial mesenchymal transition in A549 cells with the increase of fibronectin and decrease of E-cadherin, the activation of Akt/glycogen synthase kinase-3ß (GSK-ß)/Mcl-1 axis, and the hypo-responsiveness to cisplatin. DCMI initiated a dose-dependent cytotoxicity on TGF-ß1-mediated mesenchymal type of A549 cells through inactivating Akt/GSK-ß/Mcl-1 axis, in which mitochondria instability and caspase-9/3 activation also occurred concurrently. Pharmacological inhibition of caspase-8 and cathepsin B partly reversed tBid expression and mitochondrial damage to further attenuate DCMI-mediated cytotoxicity. Additionally, DCMI presented partial therapeutic effects in treating mesenchymal type of A549 tumor bearing nude mice through an acceleration of cancer cell death. Taken together, DCMI exerts antitumor effects via initiating the mechanisms of Akt/GSK-ß/Mcl-1 inactivation and cathepsin B/caspase-8-regulated mitochondrial death, which suggests its potential role in mesenchymal type of cancer cell therapy.

Gypenosides exert cardioprotective effects by promoting mitophagy and activating PI3K/Akt/GSK-3ß/Mcl-1 signaling.

Background: Gynostemma pentaphyllum (Thunb.) Makino, a well-known edible and medicinal plant, has anti-aging properties and is used to treataging-associated conditions such as diabetes, metabolic syndrome, and cardiovascular diseases. Gypenosides (GYPs) are the primary constituents of G. pentaphyllum. Increasing evidence indicates that GYPs are effective at preserving mitochondrial homeostasis and preventing heart failure (HF). This study aimed to uncover the cardioprotective mechanisms of GYPs related to mitochondrial regulation. Methods: The bioactive components in GYPs and the potential targets in treating HF were obtained and screened using the network pharmacology approach, followed by drug-disease target prediction and enrichment analyses. The pharmacological effects of GYPs in cardioprotection, mitochondrial function, mitochondrial quality control, and underlying mechanisms were further investigated in Doxorubicin (Dox)-stimulated H9c2 cardiomyocytes. Results: A total of 88 bioactive compounds of GYPs and their respective 71 drug-disease targets were identified. The hub targets covered MAPK, EGFR, PI3KCA, and Mcl-1. Enrichment analysis revealed that the pathways primarily contained PI3K/Akt, MAPK, and FoxO signalings, as well as calcium regulation, protein phosphorylation, apoptosis, and mitophagy process. In Dox-stimulated H9c2 rat cardiomyocytes, pretreatment with GYPs increased cell viability, enhanced cellular ATP content, restored basal oxygen consumption rate (OCR), and improved mitochondrial membrane potential (MMP). Furthermore, GYPs improved PINK1/parkin-mediated mitophagy without influencing mitochondrial fission/fusion proteins and the autophagic LC3 levels. Mechanistically, the phosphorylation of PI3K, Akt, GSK-3ß, and the protein level of Mcl-1 was upregulated by GYP treatment. Conclusion: Our findings reveal that GYPs exert cardioprotective effects by rescuing the defective mitophagy, and PI3K/Akt/GSK-3ß/Mcl-1 signaling is potentially involved in this process.

Application of molecular dynamics-based pharmacophore and machine learning approaches to identify novel Mcl1 inhibitors through drug repurposing and mechanics research.

Myeloid cell leukemia 1 (Mcl1), a critical protein that regulates apoptosis, has been considered as a promising target for antitumor drugs. The conventional pharmacophore screening approach has limitations in conformation sampling and data mining. Here, we offered an innovative solution to identify Mcl1 inhibitors with molecular dynamics-refined pharmacophore and machine learning methods. Considering the safety and druggability of FDA-approved drugs, virtual screening of the database was performed to discover Mcl1 inhibitors, and the hit was subsequently validated via TR-FRET, cytotoxicity, and flow cytometry assays. To reveal the binding characteristics shared by the hit and a typical Mcl1 selective inhibitor, we employed quantum mechanics and molecular mechanics (QM/MM) calculations, umbrella sampling, and metadynamics in this work. The combined studies suggested that fluvastatin had promising cell inhibitory potency and was suitable for further investigation. We believe that this research will shed light on the discovery of novel Mcl1 inhibitors that can be used as a supplemental treatment against leukemia and provide a possible method to improve the accuracy of drug repurposing with limited computational resources while balancing the costs of experimentation well.

Machine learning-assisted SERS approach enables the biochemical discrimination in Bcl-2 and Mcl-1 expressing yeast cells treated with ketoconazole and fluconazole antifungals.

Antifungal medications are important due to their potential application in cancer treatment either on their own or with traditional treatments. The mechanisms that prevent the effects of these medications and restrict their usage in cancer treatment are not completely understood. The evaluation and discrimination of the possible protective effects of the anti-apoptotic members of the Bcl-2 family of proteins, critical regulators of mitochondrial apoptosis, against antifungal drug-induced cell death has still scientific uncertainties that must be considered. Novel, simple, and reliable strategies are highly demanded to identify the biochemical signature of this phenomenon. However, the complex nature of cells poses challenges for the analysis of cellular biochemical changes or classification. In this study, for the first time, we investigated the probable protective activities of Bcl-2 and Mcl-1 proteins against cell damage induced by ketoconazole (KET) and fluconazole (FLU) antifungal drugs in a yeast model through surface-enhanced Raman spectroscopy (SERS) approach. The proposed SERS platform created robust Raman spectra with a high signal-to-noise ratio. The analysis of SERS spectral data via advanced unsupervised and supervised machine learning methods enabled unquestionable differentiation (100 %) in samples and biomolecular identification. Various SERS bands related to lipids and proteins observed in the analyses suggest that the expression of these anti-apoptotic proteins reduces oxidative biomolecule damage induced by the antifungals. Also, cell viability assay, Annexin V-FITC/PI double staining, and total oxidant and antioxidant status analyses were performed to support Raman measurements. We strongly believe that the proposed approach paves the way for the evaluation of various biochemical structures/changes in various cells.

Apoptosis Pathway-Associated Proteins Are Frequently Expressed in Melanoma: A Study of 32 Cases With Focus on Acral Lentiginous Melanoma.

ABSTRACT: Acral lentiginous melanoma (ALM) is an aggressive type of cutaneous melanoma (CM) that arises on palms, soles, and nail units. ALM is rare in White population, but it is relatively more frequent in dark-skinned populations. There is an unmet need to develop new personalized and more effective treatments strategies for ALM. Increased expression of antiapoptotic proteins (ie, BCL2, MCL1) has been shown to contribute to tumorigenesis and therapeutic resistance in multiple tumor types and has been observed in a subset of ALM and mucosal melanoma cell lines in vivo and in vitro. However, little is known about their expression and clinical significance in patients with ALM. Thus, we assessed protein expression of BCL2, MCL1, BIM, and BRAF V600E by immunohistochemistry in 32 melanoma samples from White and Hispanic populations, including ALM and non-ALM (NALM). BCL2, MCL1, and BIM were expressed in both ALM and NALM tumors, and no significant differences in expression of any of these proteins were detected between the groups, in our relatively small cohort. There were no significant associations between protein expression and BRAF V600E status, overall survival, or ethnicity. In summary, ALM and NALM demonstrate frequent expressions of apoptosis-related proteins BCL2, MCL1, and BIM. Our findings suggest that patients with melanoma, including ALM, may be potential candidates for apoptosis-directed therapies.

Novel markers of MCL1 inhibitor sensitivity in triple-negative breast cancer cells.

Triple-negative breast cancer (TNBC) is an aggressive breast cancer sub-type with limited treatment options and poor prognosis. Currently, standard treatments for TNBC include surgery, chemotherapy, and anti-PDL1 therapy. These therapies have limited efficacy in advanced stages. Myeloid-cell leukemia 1 (MCL1) is an anti-apoptotic BCL2 family protein. High expression of MCL1 contributes to chemotherapy resistance and is associated with a worse prognosis in TNBC. MCL1 inhibitors are in clinical trials for TNBC, but response rates to these inhibitors can vary and predictive markers are lacking. Currently, we identified a 4-member (AXL, ETS1, IL6, EFEMP1) gene signature (GS) that predicts MCL1 inhibitor sensitivity in TNBC cells. Factors encoded by these genes regulate signaling pathways to promote MCL1 inhibitor resistance. Small molecule inhibitors of the GS factors can overcome resistance and sensitize otherwise resistant TNBC cells to MCL1 inhibitor treatment. These findings offer insights into potential therapeutic strategies and tumor stratification for MCL1 inhibitor use in TNBC.

Targeting MCL1-driven anti-apoptotic pathways overcomes blast progression after hypomethylating agent failure in chronic myelomonocytic leukemia.

RAS pathway mutations, which are present in 30% of patients with chronic myelomonocytic leukemia (CMML) at diagnosis, confer a high risk of resistance to and progression after hypomethylating agent (HMA) therapy, the current standard of care for the disease. Here, using single-cell, multi-omics technologies, we seek to dissect the biological mechanisms underlying the initiation and progression of RAS pathway-mutated CMML. We identify that RAS pathway mutations induce transcriptional reprogramming of hematopoietic stem and progenitor cells (HSPCs) and downstream monocytic populations in response to cell-intrinsic and -extrinsic inflammatory signaling that also impair the functions of immune cells. HSPCs expand at disease progression after therapy with HMA or the BCL2 inhibitor venetoclax and rely on the NF-κB pathway effector MCL1 to maintain survival. Our study has implications for the development of therapies to improve the survival of patients with RAS pathway-mutated CMML.

Combining Mefloquine with an Mcl-1 Inhibitor as a Novel Therapeutic Strategy for the Treatment of Nasopharyngeal Carcinoma.

Considering the established pharmacokinetics and toxicity profiles, drug repurposing has emerged as an alternative therapeutic approach for treating cancer. Mefloquine has previously demonstrated inhibitory effects on multiple cancer types. This study aims to explore the impact of mefloquine on nasopharyngeal carcinoma (NPC). We found that mefloquine, at pharmacologically achievable concentrations, displayed anti-NPC activity while sparing normal counterparts. Mefloquine inhibits proliferation and induces death by reducing the levels of Cyclin A2, Bcl-2, and Bcl-xL. Intriguingly, we observed an increase in the levels of the anti-apoptotic protein Mcl-1. Mefloquine exerts its effects on NPC cells by inducing lysosomal-mediated ROS production, and the heightened expression of Mcl-1 is a consequence of ROS generation in mefloquine-treated NPC cells. The combination of an Mcl-1 inhibitor with mefloquine synergistically inhibits NPC growth in mice without causing substantial toxicity. These findings demonstrate the effectiveness and limited toxicity of mefloquine as a monotherapy and in combination with an Mcl-1 inhibitor. Our research underscores the promise of the mefloquine and Mcl-1 inhibitor combination as a potential treatment for NPC. Additionally, the elevation of Mcl-1 is a compensatory response in cells exposed to oxidative stress, offering a potential target to overcome resistance induced by pro-oxidant therapies.

A novel inhibitory BAK antibody enables assessment of non-activated BAK in cancer cells.

BAX and BAK are pro-apoptotic members of the BCL2 family that are required to permeabilize the mitochondrial outer membrane. The proteins can adopt a non-activated monomeric conformation, or an activated conformation in which the exposed BH3 domain facilitates binding either to a prosurvival protein or to another activated BAK or BAX protein to promote pore formation. Certain cancer cells are proposed to have high levels of activated BAK sequestered by MCL1 or BCLXL, thus priming these cells to undergo apoptosis in response to BH3 mimetic compounds that target MCL1 or BCLXL. Here we report the first antibody, 14G6, that is specific for the non-activated BAK conformer. A crystal structure of 14G6 Fab bound to BAK revealed a binding site encompassing both the α1 helix and α5-α6 hinge regions of BAK, two sites involved in the unfolding of BAK during its activation. In mitochondrial experiments, 14G6 inhibited BAK unfolding triggered by three diverse BAK activators, supporting crucial roles for both α1 dissociation and separation of the core (α2-α5) and latch (α6-α9) regions in BAK activation. 14G6 bound the majority of BAK in several leukaemia cell lines, and binding decreased following treatment with BH3 mimetics, indicating only minor levels of constitutively activated BAK in those cells. In summary, 14G6 provides a new means of assessing BAK status in response to anti-cancer treatments.

Hexafluoropropylene oxide trimer acid (HFPO-TA) exerts cytotoxic effects on leydig cells via the ER stress/JNK/ß-trcp/mcl-1 axis.

Hexafluoropropylene oxide trimer acid (HFPO-TA) is an alternative to perfluorooctanoic acid (PFOA) and is widely used in various industries. The effects of HFPO-TA on the male reproductive system and the underlying mechanisms are still not fully understood. In this study, TM3 mouse Leydig cells were used as the main model to evaluate the cytotoxicity of HFPO-TA in vitro. HFPO-TA inhibited the viability and expression of multiple biomarkers of Leydig cells. HFPO-TA also induced Leydig cell apoptosis in a caspase-dependent manner. Moreover, HFPO-TA induced the ubiquitination and degradation of Mcl-1 in a ß-TrCP-dependent manner. Further investigations showed that HFPO-TA treatment led to the upregulation of ROS, which activated the ER stress/JNK/ß-TrCP axis in Leydig cells. Overall, our study provides novel insights into the cytotoxic effects of HFPO-TA on the male reproductive system.

TCEB3 initiates ovarian cancer apoptosis by mediating ubiquitination and degradation of MCL-1.

Platinum resistance remains a major contributor to the poor prognosis of ovarian cancer. Anti-apoptotic protein myeloid cell leukemia-1 (MCL-1) has emerged as a promising target for overcoming drug resistance, but different cancer cells utilize distinct protein degradation pathways to alter MCL-1 level. We systematically investigated E3 ligases to identify novel candidates that mediate platinum resistance in ovarian cancer. Transcription Elongation Factor B (TCEB3) has been identified as a novel E3 ligase recognition subunit that targets MCL-1 in the cytoplasm during platinum treatment other than its traditional function of targeting the Pol II in the nuclear compartment. TCEB3 expression is downregulated in platinum-resistant cell lines and this low expression is associated with poor prognosis. The ubiquitination of MCL-1 induced by TCEB3 leads to cell death in ovarian cancer. Moreover, platinum treatment increased the cytoplasm proportion of TCEB3, and the cytoplasm localization of TCEB3 is important for its targeting of MCL-1. This study emphasizes the dual function of TCEB3 in homeostasis maintenance and in cell fate determination under different conditions, and provides a new insight into drug resistance in ovarian cancer.

ONC212 enhances YM155 cytotoxicity by triggering SLC35F2 expression and NOXA-dependent MCL1 degradation in acute myeloid leukemia cells.

Although the anticancer activity of ONC212 has been reported, the precise mechanism underlying its apoptotic effects remains unclear. In this study, we investigated the apoptotic mechanism of ONC212 in acute myeloid leukemia (AML) cells. ONC212 induces apoptosis, MCL1 downregulation, and mitochondrial depolarization in AML U937 cells. Ectopic MCL1 expression alleviates mitochondria-mediated apoptosis in ONC212-treated U937 cells. ONC212 triggers AKT phosphorylation, inducing NOX4-dependent ROS production and promoting HuR transcription. HuR-mediated ATF4 mRNA stabilization stimulates NOXA and SLC35F2 expression; ONC212-induced upregulation of NOXA leads to MCL1 degradation. The synergistic effect of ONC212 on YM155 cytotoxicity was dependent on increased SLC35F2 expression. In addition, YM155 feedback facilitated the activation of the ONC212-induced signaling pathway. A similar mechanism explains ONC212- and ONC212/YM155-induced AML HL-60 cell death. The continuous treatment of U937 cells with the benzene metabolite hydroquinone (HQ) generated U937/HQ cells, exhibiting enhanced responsiveness to the cytotoxic effects of ONC212. In U937/HQ cells, ONC212 triggered apoptosis through NOXA-mediated MCL1 downregulation, enhancing YM155 cytotoxicity. Collectively, our data suggested that ONC212 upregulated SLC35F2 expression and triggered NOXA-mediated MCL1 degradation in U937, U937/HQ, and HL-60 cells by activating the AKT/NOX4/HuR/ATF4 pathway. The ONC212-induced signaling pathway showed anti-AML activity and enhanced YM155 cytotoxicity.

Targeting Myeloid Leukemia-1 in Cancer Therapy: Advances and Directions.

As a tripartite cell death switch, B-cell lymphoma protein 2 (Bcl-2) family members precisely regulate the endogenous apoptosis pathway in response to various cell signal stresses through protein-protein interactions. Myeloid leukemia-1 (Mcl-1), a key anti-apoptotic Bcl-2 family member, is positioned downstream in the endogenous apoptotic pathway and plays a central role in regulating mitochondrial function. Mcl-1 is highly expressed in a variety of hematological malignancies and solid tumors, contributing to tumorigenesis, poor prognosis, and chemoresistance, making it an attractive target for cancer treatment. This Perspective aims to discuss the mechanism by which Mcl-1 regulates apoptosis and non-apoptotic functions in cancer cells and to outline the discovery and optimization process of potent Mcl-1 modulators. In addition, we summarize the structural characteristics of potent inhibitors that bind to Mcl-1 through multiple co-crystal structures and analyze the cardiotoxicity caused by current Mcl-1 inhibitors, providing prospects for rational targeting of Mcl-1.

Homoharringtonine enhances cytarabine-induced apoptosis in acute myeloid leukaemia by regulating the p38 MAPK/H2AX/Mcl-1 axis.

Acute myeloid leukaemia (AML) is a fatal haematopoietic malignancy and is treated with the conventional combination of cytarabine (Ara-C) and daunorubicin (Dau). The survival rate of AML patients is lower due to the cardiotoxicity of daunorubicin. Clinically, homoharringtonine (HHT) plus Ara-C has been reported to be equally effective as Dau plus Ara-C in some types of AML patients with less toxic effects. We utilized the clinical use of homoharringtonine in combination with Ara-C to test its combination mechanism. We found that the insensitivity of AML cells to cytarabine-induced apoptosis is associated with increased Mcl-1 stability and p38 inactivation. HHT downregulates Mcl-1, phosphorylates H2AX and induces apoptosis by activating p38 MAPK. Inactivation of p38 through inhibitors and siRNA blocks apoptosis, H2AX phosphorylation and Mcl-1 reduction. HHT enhances Ara-C activation of the p38 MAPK signalling pathway, overcoming Ara-C tolerance to cell apoptosis by regulating the p38/H2AX/Mcl-1 axis. The optimal ratio of HHT to Ara-C for synergistic lethality in AML cells is 1:4 (M/M). HHT synergistically induces apoptosis in combination with Ara-C in vitro and prolongs the survival of xenografts. We provide a new mechanism for AML treatment by regulating the p38 MAPK/H2AX/Mcl-1 axis to improve cytarabine therapy.