MCL-1 is a clinically targetable vulnerability in breast cancer

Exploring the interplay between triple-negative breast cancer stem cells and tumor microenvironment for effective therapeutic strategies

Triple-negative breast cancer (TNBC) is a highly aggressive and metastatic malignancy with poor treatment outcomes. The interaction between the tumor microenvironment (TME) and breast cancer stem cells (BCSCs) plays an important role in the development of TNBC. Owing to their ability of self-renewal and multidirectional differentiation, BCSCs maintain tumor growth, drive metastatic colonization, and facilitate the development of drug resistance. TME is the main factor regulating the phenotype and metastasis of BCSCs. Immune cells, cancer-related fibroblasts (CAFs), cytokines, mesenchymal cells, endothelial cells, and extracellular matrix within the TME form a complex communication network, exert highly selective pressure on the tumor, and provide a conducive environment for the formation of BCSC niches. Tumor growth and metastasis can be controlled by targeting the TME to eliminate BCSC niches or targeting BCSCs to modify the TME. These approaches may improve the treatment outcomes and possess great application potential in clinical settings. In this review, we summarized the relationship between BCSCs and the progression and drug resistance of TNBC, especially focusing on the interaction between BCSCs and TME. In addition, we discussed therapeutic strategies that target the TME to inhibit or eliminate BCSCs, providing valuable insights into the clinical treatment of TNBC.

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.

Programmed nanocarrier loaded with paclitaxel and dual-siRNA to reverse chemoresistance by synergistic therapy

Paclitaxel (PTX) is commonly used in clinical tumor therapy. However, chemoresistance and the inducement of tumor metastasis severely affect the efficacy of PTX. To develop a treatment strategy to reverse chemoresistance, the co-delivery of PTX and small interfering RNA with nanocarriers were programmed in this study. The carrier we have programmed exhibits excellent safety, stability, and delivery efficiency for co-delivery of siRNA and PTX. After rapid release of siRNA, PTX could be released within 72 h. The siBcl-xL and siMcl-1 inhibited cell migration decreased the mitochondrial membrane potential, and induced the release of reactive oxygen species while synergistically functioning with the antineoplastic effects of PTX. Our strategy reduced IC50 values by 2-5-fold in different cell lines, and the results of flow cytometry confirmed increased apoptosis rates and effectively inhibited cell migration. Synergistic therapy effectively reversed chemoresistance in PTX-resistant breast cancer cells. Similarly, the synergistic administration strategy showed significant sensitizing effects in vivo. Our study demonstrates the combined application of multiple synergistic antitumor administration strategies.

Development of Potent Mcl-1 Inhibitors: Structural Investigations on Macrocycles Originating from a DNA-Encoded Chemical Library Screen

Evasion of apoptosis is critical for the development and growth of tumors. The pro-survival protein myeloid cell leukemia 1 (Mcl-1) is an antiapoptotic member of the Bcl-2 family, associated with tumor aggressiveness, poor survival, and drug resistance. Development of Mcl-1 inhibitors implies blocking of protein-protein interactions, generally requiring a lengthy optimization process of large, complex molecules. Herein, we describe the use of DNA-encoded chemical library synthesis and screening to directly generate complex, yet conformationally privileged macrocyclic hits that serve as Mcl-1 inhibitors. By applying a conceptual combination of conformational analysis and structure-based design in combination with a robust synthetic platform allowing rapid analoging, we optimized in vitro potency of a lead series into the low nanomolar regime. Additionally, we demonstrate fine-tuning of the physicochemical properties of the macrocyclic compounds, resulting in the identification of lead candidates 57/59 with a balanced profile, which are suitable for future development toward therapeutic use.

Cancer Resistance Is Mediated by the Upregulation of Several Anti-Apoptotic Gene Products via the Inducible Nitric Oxide Synthase/Nitric Oxide Pathway: Therapeutic Implications

Significance: Several therapeutic strategies for cancer treatments have been developed with time, and significant milestones have been achieved recently. However, with these novel therapies, not all cancer types respond and in the responding cancer types only a subset is affected. The failure to respond is principally the result that these cancers develop several mechanisms of resistance. Thus, a focus of current research investigations is to unravel the various mechanisms that regulate resistance and identify suitable targets for new therapeutics. Recent Advances: Hence, many human cancer types have been reported to overexpress the inducible nitric oxide synthase (iNOS) and it has been suggested that iNOS/nitric oxide (NO) plays a pivotal role in the regulation of resistance. We have postulated that iNOS overexpression or NO regulates the overexpression of pivotal anti-apoptotic gene products such as B-cell lymphoma 2 (Bcl-2), B-cell lymphoma extra large (Bcl-xL), myeloid cell leukemia-1 (Mcl-1), and survivin. In this report, we describe the various mechanisms, transcriptional, post-transcriptional, and post-translational, by which iNOS/NO regulates the expression of the above anti-apoptotic gene products. Critical Issues: The iNOS/NO-mediated regulation of the four gene products is not the same with both specific and overlapping pathways. Our findings are, in large part, validated by bioinformatic analyses demonstrating, in several cancers, several direct correlations between the expression of iNOS and each of the four examined anti-apoptotic gene products. Future Directions: We have proposed that targeting iNOS may be highly efficient since it will result in the underexpression of multiple anti-apoptotic proteins and shifting the balance toward the proapoptotic gene products and reversal of resistance. Antioxid. Redox Signal. 39, 853-889.

Inhibitory effect of miR342 on the progression of triple-negative breast cancer cells in vitro and in the mice model

Introduction

Breast cancer is the most common cancer in women worldwide, and the triple-negative subtype is the most invasive, with limited therapeutic options. Since miRNAs are involved in many cellular processes, they harbor great value for cancer treatment. Therefore, in this study, we have investigated the anti-proliferative and anti-invasive roles of miR342 in 4T1 triple-negative cells in vitro and also studied the effect of this miRNA on tumor progression and the expression of its target genes in vivo.

Methods

4T1 cells were transduced with conditioned media of miR342-transfected Hek-LentiX cells. MTT and clonogenic assays were used to assess the viability and colony-forming ability of 4T1 cells. Apoptosis and invasion rates were respectively evaluated by annexin/7-AAD and wound healing assays. At last, in vivo tumor progression was evaluated using H&E staining, real-time PCR, and immunohistochemistry.

Results

The viability of transduced-4T1 cells reduced significantly 48 hours after cell seeding and colony forming ability of these cells reduced to 50% of the control group. Also, miR342 imposed apoptotic and anti-invasive influence on these cells in vitro. A 30-day follow-up of the breast tumor in the mice model certified significant growth suppression along with reduced mitotic index and tumor grade in the treatment group. Moreover, decreased expression of Bcl2l1, Mcl1, and ID4, as miR342 target genes, was observed, accompanied by reduced expression of VEGF and Bcl2/Bax ratio at the protein level.

Conclusion

To conclude, our data support the idea that miR342 might be a potential therapeutic target for the treatment of triple-negative breast cancer (TNBC).

Dual-Targeted Therapy in HER2-Overexpressing Breast Cancer with Trastuzumab and Novel Cholesterol-Based Nioplexes Silencing Mcl-1

The challenge in HER2-overexpressing breast cancer therapy lies in creating an effective target therapy to overcome treatment resistance. Monoclonal antibodies and target gene silencing by siRNA are two potential strategies that have been widely developed for treating HER2-positive breast cancer. The siRNA delivery system is a crucial factor that influences siRNA therapy's success. In this study, lipid-based nanoparticles (cationic niosomes) composed of different cholesterol-based cationic lipids were formulated and characterized for delivering siRNA into HER2-overexpressing breast cancer cells. Niosomes containing a trimethylammonium headgroup showed the highest siRNA delivery efficiency with low toxicity. The myeloid cell leukemia-1 (Mcl-1) siRNA nioplex treatment significantly decreased mRNA expression and breast cancer cell growth. Dual-targeted therapy, consisting of treatment with an Mcl-1 siRNA nioplex and trastuzumab (TZ) solution, noticeably promoted cell-growth inhibition and apoptosis. The synergistic effect of dual therapy was also demonstrated by computer modeling software (CompuSyn version 1.0). These findings suggest that the developed cationic niosomes were effective nanocarriers for siRNA delivery in breast cancer cells. Furthermore, the Mcl-1 nioplex/TZ dual treatment establishes a synergistic outcome that may have the potential to treat HER2-overexpressing breast cancer.

MCL1 Inhibition Overcomes the Aggressiveness Features of Triple-Negative Breast Cancer MDA-MB-231 Cells

Triple-Negative Breast Cancer (TNBC) is a particularly aggressive subtype among breast cancers (BCs), characterized by anoikis resistance, high invasiveness, and metastatic potential as well as Epithelial-Mesenchymal Transition (EMT) and stemness features. In the last few years, our research focused on the function of MCL1, an antiapoptotic protein frequently deregulated in TNBC. Here, we demonstrate that MCL1 inhibition by A-1210477, a specific BH3-mimetic, promotes anoikis/apoptosis in the MDA-MB-231 cell line, as shown via an increase in proapoptotic markers and caspase activation. Our evidence also shows A-1210477 effects on Focal Adhesions (FAs) impairing the integrin trim and survival signaling pathways, such as FAK, AKT, ERK, NF-κB, and GSK3β-inducing anoikis, thus suggesting a putative role of MCL1 in regulation of FA dynamics. Interestingly, in accordance with these results, we observed a reduction in migratory and invasiveness capabilities as confirmed by a decrease in metalloproteinases (MMPs) levels following A-1210477 treatment. Moreover, MCL1 inhibition promotes a reduction in EMT characteristics as demonstrated by the downregulation of Vimentin, MUC1, DNMT1, and a surprising re-expression of E-Cadherin, suggesting a possible mesenchymal-like phenotype reversion. In addition, we also observed the downregulation of stemness makers such as OCT3/4, SOX2, NANOG, as well as CD133, EpCAM, and CD49f. Our findings support the idea that MCL1 inhibition in MDA-MB-231 could be crucial to reduce anoikis resistance, aggressiveness, and metastatic potential and to minimize EMT and stemness features that distinguish TNBC.

Scoparone induces both apoptosis and ferroptosis via multiple mechanisms in non-small-cell lung cancer cells

The present study investigated the anti-tumour effects of scoparone, also known as 6,7-dimethoxycoumarin, in non-small-cell-lung cancer (NSCLC) cells. It was discovered that scoparone inhibited the proliferation and induced cell death of NSCLC cells. Scoparone induced both apoptosis and ferroptosis in NSCLC cells. Mechanically, scoparone treatment led to the FBW7-mediated ubiquitination and downregulation of Mcl-1. Moreover, scopaone induced Bax activation in a reactive oxygen species (ROS)-dependent manner. Interestingly, scoparone also triggered ferroptosis, a novel form of cell death, as evidenced by upregulation of lipid peroxidation, ROS, and iron levels. The mechanism investigation showed that scoparone activated the ROS/JNK/SP1/ACSL4 axis to trigger ferroptosis in NSCLC cells. Overall, our data suggest that scoparone is a promising agent for the treatment of NSCLC.

Breast cancer sub-types display heterogeneity in gene amplification and mRNA expression of the anti-apoptotic members of BCL2 family

BACKGROUND

Progress in therapies and improved outcomes in recent decades have followed a better understanding of breast cancers pathogenesis and their heterogeneity but new treatments are needed especially for metastatic disease which remains incurable. Inhibition of apoptosis is a hallmark characteristic of cancer and can be targeted for therapy.

METHODS

The five anti-apoptotic members of the BCL2 family are at the core of apoptosis execution and are involved in apoptosis evasion of transformed cells. Genetic lesions as well as mRNA regulation of these members in breast cancer and its sub-types and implications for survival outcomes were investigated using data from various publicly available databases.

RESULTS

Genes encoding for anti-apoptotic BCL2 proteins are rarely mutated in breast cancer and copy number alterations are observed only in MCL1 gene which is amplified in a minority of breast cancer ranging from 1.6% to 18.7% in breast cancers. Over-expression of BCL2, BCL-X and MCL1 is observed in luminal A cancers, while cases of luminal B and basal breast cancers display mRNA up-regulation of BCL-X and MCL1, respectively. Basal cancers possess also more frequently than other sub-sets MCL1 amplifications. Survival outcomes are not significantly different in cancers with higher expression of anti-apoptotic BCL2 mRNAs.

CONCLUSION

Therapeutic targeting of the apoptotic process in breast cancer sub-types will be improved by a detailed understanding of the core players in the process, including anti-apoptotic BCL2 family proteins. A sub-set of breast cancers harbor amplifications of MCL1 and dysregulations of expression of most family members that could affect the sensitivity to their inhibition by altering the cell's apoptotic threshold.

Pleiotropic Roles of a KEAP1-Associated Deubiquitinase, OTUD1

Protein ubiquitination, which is catalyzed by ubiquitin-activating enzymes, ubiquitin-conjugating enzymes, and ubiquitin ligases, is a crucial post-translational modification to regulate numerous cellular functions in a spatio-temporal-specific manner. The human genome encodes ~100 deubiquitinating enzymes (DUBs), which antagonistically regulate the ubiquitin system. OTUD1, an ovarian tumor protease (OTU) family DUB, has an N-terminal-disordered alanine-, proline-, glycine-rich region (APGR), a catalytic OTU domain, and a ubiquitin-interacting motif (UIM). OTUD1 preferentially hydrolyzes lysine-63-linked ubiquitin chains in vitro; however, recent studies indicate that OTUD1 cleaves various ubiquitin linkages, and is involved in the regulation of multiple cellular functions. Thus, OTUD1 predominantly functions as a tumor suppressor by targeting p53, SMAD7, PTEN, AKT, IREB2, YAP, MCL1, and AIF. Furthermore, OTUD1 regulates antiviral signaling, innate and acquired immune responses, and cell death pathways. Similar to Nrf2, OTUD1 contains a KEAP1-binding ETGE motif in its APGR and regulates the reactive oxygen species (ROS)-mediated oxidative stress response and cell death. Importantly, in addition to its association with various cancers, including multiple myeloma, OTUD1 is involved in acute graft-versus-host disease and autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and ulcerative colitis. Thus, OTUD1 is an important DUB as a therapeutic target for a variety of diseases.