Anti-tumor and anti-metastasis efficacy of E6201, a MEK1 inhibitor, in preclinical models of triple-negative breast cancer

ADAR1 Regulates Lipid Remodeling through MDM2 to Dictate Ferroptosis Sensitivity

Triple-negative breast cancer (TNBC), lacking expression of estrogen, progesterone, and HER2 receptors, is aggressive and lacks targeted treatment options. An RNA editing enzyme, adenosine deaminase acting on RNA 1 (ADAR1), has been shown to play important roles in TNBC tumorigenesis. We posit that ADAR1 functions as a homeostatic factor protecting TNBC from internal and external pressure, including metabolic stress. We tested the hypothesis that the iron- dependent cell death pathway, ferroptosis, is a ADAR1-protected metabolic vulnerability in TNBC by showing that ADAR1 knockdown sensitizes TNBC cells to GPX4 inhibitors. By performing single-reaction monitoring-based liquid chromatography coupled to mass spectrometry (LC-MS) to measure intracellular lipid contents, we showed that ADAR1 loss increased the abundance of polyunsaturated fatty acid phospholipids (PUFA-PL), of which peroxidation is the primary driver of ferroptosis. Transcriptomic analyses led to the discovery of the proto-oncogene MDM2 contributing to the lipid remodeling in TNBC upon ADAR1 loss. A phenotypic drug screen using a ferroptosis-focused library was performed to identify FDA- approved cobimetinib as a drug-repurposing candidate to synergize with ADAR1 loss to suppress TNBC tumorigenesis. By demonstrating that ADAR1 regulates the metabolic fitness of TNBC through desensitizing ferroptosis, we aim to leverage this metabolic vulnerability to inform basic, pre-clinical, and clinical studies to develop novel therapeutic strategies for TNBC.

Conserved gatekeeper methionine regulates the binding and access of kinase inhibitors to ATP sites of MAP2K1, 4, and 7: Clues for developing selective inhibitors

Mitogen-activated protein kinase kinases (MAP2Ks) 1, 4, and 7 are potential targets for treating various diseases. Here, we solved the crystal structures of MAP2K1 and MAP2K4 complexed with covalent inhibitor 5Z-7-oxozeaenol (5Z7O). The elucidated structures showed that 5Z7O was non-covalently bound to the ATP binding site of MAP2K4, while it covalently attached to cysteine at the DFG-1 position of the deep ATP site of MAP2K1. In contrast, we previously showed that 5Z7O covalently binds to MAP2K7 via another cysteine on the solvent-accessible edge of the ATP site. Structural analyses and molecular dynamics calculations indicated that the configuration and mobility of conserved gatekeeper methionine located at the central ATP site regulated the binding and access of 5Z7O to the ATP site of MAP2Ks. These structural features provide clues for developing highly potent and selective inhibitors against MAP2Ks. Abbreviations: ATP, adenosine triphosphate; FDA, Food and Drug Administration; MAP2Ks, mitogen-activated protein kinase kinases; MD, molecular dynamics; NSCLC, non-small cell lung cancer; 5Z7O, 5Z-7-oxozeaenol; PDB, protein data bank; RMSD, root-mean-square deviation.

Genomic and transcriptomic profiling of inflammatory breast cancer reveals distinct molecular characteristics to non-inflammatory breast cancers

PURPOSE

Inflammatory breast cancer (IBC), a rare and highly aggressive form of breast cancer, accounts for 10% of breast cancer-related deaths. Previous omics studies of IBC have focused solely on one of genomics or transcriptomics and did not discover common differences that could distinguish IBC from non-IBC.

METHODS

Seventeen IBC patients and five non-IBC patients as well as additional thirty-three Asian breast cancer samples from TCGA-BRCA were included for the study. We performed whole-exon sequencing (WES) to investigate different somatic genomic alterations, copy number variants, and large structural variants between IBC and non-IBC. Bulk RNA sequencing (RNA-seq) was performed to examine the differentially expressed genes, pathway enrichment, and gene fusions. WES and RNA-seq data were further investigated in combination to discover genes that were dysregulated in both genomics and transcriptomics.

RESULTS

Copy number variation analysis identified 10 cytobands that showed higher frequency in IBC. Structural variation analysis showed more frequent deletions in IBC. Pathway enrichment and immune infiltration analysis indicated increased immune activation in IBC samples. Gene fusions including CTSC-RAB38 were found to be more common in IBC. We demonstrated more commonly dysregulated RAS pathway in IBC according to both WES and RNA-seq. Inhibitors targeting RAS signaling and its downstream pathways were predicted to possess promising effects in IBC treatment.

CONCLUSION

We discovered differences unique in Asian women that could potentially explain IBC etiology and presented RAS signaling pathway as a potential therapeutic target in IBC treatment.

Small Molecule Therapeutics in the Pipeline Targeting for Triple-Negative Breast Cancer: Origin, Challenges, Opportunities, and Mechanisms of Action

Triple-negative breast cancer (TNBC) cells are devoid of estrogen receptors (ERs), progesterone receptor (PRs), and human epidermal growth factor receptor 2 (HER2), and it (TNBC) counts for about 10-15% of all breast cancers. TNBC is highly invasive, having a faster growth rate and a higher risk of metastasis and recurrence. Still, chemotherapy is one of the widely used options for treating TNBC. This study reviewed the histological and molecular characterization of TNBC subtypes, signaling pathways that are aberrantly expressed, and small molecules targeting these pathways, as either single agents or in combination with other therapeutic agents like chemotherapeutics, immunotherapeutics, and antibody-drug conjugates; their mechanisms of action, challenges, and future perspectives were also reviewed. A detailed analytical review was carried out using the literature collected from the SciFinder, PubMed, ScienceDirect, Google Scholar, ACS, Springer, and Wiley databases. Several small molecule inhibitors were found to be therapeutics for treating TNBC. The mechanism of action and the different signaling pathways through which the small molecules exert their effects were studied, including clinical trials, if reported. These small molecule inhibitors include buparlisib, everolimus, vandetanib, apatinib, olaparib, salidroside, etc. Some of the signaling pathways involved in TNBC, including the VEGF, PARP, STAT3, MAPK, EGFR, P13K, and SRC pathways, were discussed. Due to the absence of these biomarkers, drug development for treating TNBC is challenging, with chemotherapy being the main therapeutic agent. However, chemotherapy is associated with chemoresistance and a high toxicity to healthy cells as side effects. Hence, there is a continuous demand for small-molecule inhibitors that specifically target several signaling pathways that are abnormally expressed in TNBC. We attempted to include all the recent developments in this field. Any omission is truly unintentional.

CircZCCHC2 decreases pirarubicin sensitivity and promotes triple-negative breast cancer development via the miR-1200/TPR axis

Triple-negative breast cancer (TNBC) has attracted attention due to its poor prognosis and limited treatment options. The mechanisms underlying the association between circular RNAs (circRNAs) and the occurrence and development of TNBC remain unclear. CircZCCHC2 is observed to be upregulated in TNBC cells, tissues, and plasma exosomes. Knockdown of circZCCHC2 inhibited the proliferation, migration, invasion, and epithelial-mesenchymal transition of TNBC cells in vitro and in vivo. Pirarubicin (THP) treatment downregulated circZCCHC2, and circZCCHC2 affected the sensitivity to THP. CircZCCHC2/miR-1200/translocated promoter region, the nuclear basket protein (TPR) pathway was cascaded and verified. It is demonstrated that circZCCHC2 plays a crucial role in the malignant progression of TNBC via the miR-1200/TPR axis, thereby activating the RAS-RAF-MEK-ERK pathway. The present results indicate that circZCCHC2 has the potential to serve as a novel prognostic biomarker for TNBC.

Development of a cancer metastasis-on-chip assay for high throughput drug screening

Metastasis is the cause of most triple-negative breast cancer deaths, yet anti-metastatic therapeutics remain limited. To develop new therapeutics to prevent metastasis, pathophysiologically relevant assays that recapitulate tumor microenvironment is essential for disease modeling and drug discovery. Here, we have developed a microfluidic metastasis-on-chip assay of the early stages of cancer metastasis integrated with the triple-negative breast cancer cell line (MDA-MB-231), stromal fibroblasts and a perfused microvessel. High-content imaging with automated quantification methods was optimized to assess the tumor cell invasion and intravasation within the model. Cell invasion and intravasation were enhanced when fibroblasts co-cultured with a breast cancer cell line (MDA-MB-231). However, the non-invasive breast cancer cell line, MCF7, remained non-invasive in our model, even in the presence of fibroblasts. High-content screening of a targeted anti-cancer therapy drug library was conducted to evaluate the drug response sensitivity of the optimized model. Through this screening, we identified 30 compounds that reduced the tumor intravasation by 60% compared to controls. Multi-parametric phenotypic analysis was applied by combining the data from the metastasis-on-chip, cell proliferation and 2D cell migration screens, revealing that the drug library was clustered into eight distinct groups with similar drug responses. Notably, MEK inhibitors were enriched in cluster cell invasion and intravasation. In contrast, drugs with molecular targets: ABL, KIT, PDGF, SRC, and VEGFR were enriched in the drug clusters showing a strong effect on tumor cell intravasation with less impact on cell invasion or cell proliferation, of which, Imatinib, a multi-kinase inhibitor targeting BCR-ABL/PDGFR/KIT. Further experimental analysis showed that Imatinib enhanced endothelial barrier stability as measured by trans-endothelial electrical resistance and significantly reduced the trans-endothelial invasion activity of tumor cells. Our findings demonstrate the potential of our metastasis-on-chip assay as a powerful tool for studying cancer metastasis biology, drug discovery aims, and assessing drug responses, offering prospects for personalized anti-metastatic therapies for triple-negative breast cancer patients.

Three generations of mTOR kinase inhibitors in the activation of the apoptosis process in melanoma cells

Many signaling pathways are involved in the mammalian target of rapamycin (mTOR), and this serine/threonine kinase regulates the most important cellular processes such as cell proliferation, autophagy, and apoptosis. The subject of this research was the effect of protein kinase inhibitors involved in the AKT, MEK, and mTOR kinase signaling pathways on the expression of pro-survival proteins, activity of caspase-3, proliferation, and induction of apoptosis in melanoma cells. The following inhibitors were used: protein kinase inhibitors such as AKT-MK-2206, MEK-AS-703026, mTOR-everolimus and Torkinib, as well as dual PI3K and mTOR inhibitor-BEZ-235 and Omipalisib, and mTOR1/2-OSI-027 inhibitor in single-mode and their combinations with MEK1/2 kinase inhibitor AS-703026. The obtained results confirm the synergistic effect of nanomolar concentrations of mTOR inhibitors, especially the dual PI3K and mTOR inhibitors (Omipalisib, BEZ-235) in combination with the MAP kinase inhibitor (AS-703026) in the activation of caspase 3, induction of apoptosis, and inhibition of proliferation in melanoma cell lines. Our previous and current studies confirm the importance of the mTOR signal transduction pathway in the neoplastic transformation process. Melanoma is a case of a very heterogeneous neoplasm, which causes great difficulties in treating this neoplasm in an advanced stage, and the standard approach to this topic does not bring the expected results. There is a need for research on the search for new therapeutic strategies aimed at particular groups of patients. Effect of three generations of mTOR kinase inhibitors on caspase-3 activity, apoptosis and proliferation in melanoma cell lines.

Non-fused imidazole-biphenyl analogs repress triple-negative breast cancer growth by mainly stabilizing the c-MYC G-quadruplex via a multi-site binding mode

As oncogene c-MYC is abnormally expressed during TNBC pathogenesis, stabilizing its promoter G-quadruplex (G4), which may thus inhibit c-MYC expression and promote DNA damage, may be a potential anti-TNBC strategy. However, large quantities of potential G4-forming sites exist in the human genome, which represents a potential drug selectivity problem. In order to achieve better recognition for c-MYC G4, we herein presented a new approach of designing small-molecule ligands by linking tandem aromatic rings with the c-MYC G4 selective binding motifs. Thus, a series of non-fused, conformation-tunable imidazole-biphenyl analogs were designed and synthesized. Among them, the optimal ligand appeared more effective on stabilizing c-MYC G4 than other types of G4s possibly through an adaptive, multi-site binding mode involved of end-stacking, groove-binding and loop-interacting. Then, the optimal ligand exerted good inhibitory activity on c-MYC expression and induced remarkable DNA damage, leading to the occurrence of G2/M phase arrest, apoptosis and autophagy. Furthermore, the optimal ligand exhibited potent antitumor effects in a TNBC xenograft tumor model. To sum up, this work offers new insights for the development of selective c-MYC G4 ligands against TNBC.

Target Identification of 22-(4-Pyridinecarbonyl) Jorunnamycin A, a Tetrahydroisoquinoline Derivative from the Sponge Xestospongia sp., in Mediating Non-Small-Cell Lung Cancer Cell Apoptosis

A dysregulation of the cell-death mechanism contributes to poor prognosis in lung cancer. New potent chemotherapeutic agents targeting apoptosis-deregulating molecules have been discovered. In this study, 22-(4-pyridinecarbonyl) jorunnamycin A (22-(4'py)-JA), a synthetic derivative of bistetrahydroisoquinolinequinone from the Thai blue sponge, was semisynthesized by the Steglich esterification method, and its pharmacological mechanism in non-small-cell lung cancer (NSCLC) was elucidated by a network pharmacology approach. All predicted targets of 22-(4'py)-JA and genes related to NSCLC were retrieved from drug-target and gene databases. A total of 78 core targets were identified, and their associations were analyzed by STRING and Cytoscape. Gene ontology and KEGG pathway enrichment analyses revealed that molecules in mitogen-activated protein kinase (MAPK) signaling were potential targets of 22-(4'py)-JA in the induction of NSCLC apoptosis. In silico molecular docking analysis displayed a possible interaction of ERK1/2 and MEK1 with 22-(4'py)-JA. In vitro anticancer activity showed that 22-(4'py)-JA has strong cytotoxic and apoptosis-inducing effects in H460, H292 and A549 NSCLC cells. Furthermore, immunoblotting confirmed that 22-(4'py)-JA induced apoptotic cell death in an ERK/MEK/Bcl-2-dependent manner. The present study demonstrated that 22-(4'py)-JA exhibited a potent anticancer effect that could be further developed for clinical application and showed that network pharmacology approaches are a powerful tool to illustrate the molecular pathways of new drugs or compounds.

B7 homolog 3 induces lung metastasis of breast cancer through Raf/MEK/ERK axis

PURPOSE

The essential action of B7 homolog 3 (B7-H3) in different diseases and cancers has been documented. We here focused on its role in breast cancer through the Raf/MEK/ERK axis regarding lung metastasis.

METHODS

Expression pattern of B7-H3 was determined in breast cancer tissues and cells with its correlation with prognosis analyzed. Then, through transfection of lentivirus vector expressing B7-H3-shRNA, overexpression vector of B7-H3 (B7-H3-LV), U0126 (small molecule inhibitor of MEK), or PD98059 (small molecule inhibitor of ERK), the in vitro and in vivo effects of B7-H3 in breast cancer cell biological processes, and lung metastasis were analyzed in relation to the Raf/MEK/ERK axis.

RESULTS

We discovered elevated B7-H3 in breast cancer and its elevation associated with poor prognosis. B7-H3 promoted the malignant properties of breast cancer cells, accompanied with increased N-cadherin and vimentin and reduced E-cadherin. Additionally, overexpression of B7-H3 accelerated the lung metastasis in breast cancer in vivo. All the above promoting action of B7-H3 was achieved through activation of the Raf/MEK/ERK signaling pathway.

CONCLUSION

Taken together, B7-H3 can promote lung metastasis in breast cancer through activation of the Raf/MEK/ERK axis.

Inhibitors of PD-1/PD-L1 and ERK1/2 impede the proliferation of receptor positive and triple-negative breast cancer cell lines

PURPOSE

Triple-negative breast cancer (TNBC) is characterized by an unfavorable prognosis and missing systemic therapeutic approaches beside chemotherapy. Targeting the immune checkpoint PD-1/PD-L1 showed promising results in breast cancer and especially in TNBC. The extracellular signal-regulated kinase 1/2 (ERK1/2) is an important driver of carcinogenesis. Here, the effect of combined PD-1/PD-L1 and ERK1/2 inhibitor treatment is investigated of cell growth and intracellular impact of breast cancer cell lines.

METHODS

The IC50 values of each inhibitor and the effect of combined treatment were determined in three TNBC cell lines of different subtypes and one non-TNBC cell line. Phospho-specific antibodies were used in western blot analyses to investigate an effect on ERK1/2 activation. Expressions of immune modulatory and cell cycle-associated genes were examined by quantitative reverse transcription PCR.

RESULTS

Both inhibitors PD-1/PD-L1 and ERK1/2 impeded the proliferation of TNBC to a higher extent than of non-TNBC. By combined treatment, cell lines were inhibited either synergistically or additively. ERK1/2 and S6 phosphorylation were reduced and expressions of c-Fos and FosL were diminished after ERK1/2 inhibitor as single and combined treatment. Between genes involved in immune modulation, IL-8 was upregulated in TNBC cells after combined treatment.

CONCLUSION

In conclusion, combination of PD-1/PD-L1 and ERK1/2 inhibitors showed favorable effects for a new therapy strategy, with better results in TNBC cell lines than in non-TNBC cells. The effects have to be validated in models that can reflect the interaction between immune and tumor cells like the situation in the tumor micro-environment.

Small-Molecule Drug Discovery in Triple Negative Breast Cancer: Current Situation and Future Directions

Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, but an effective targeted therapy has not been well-established so far. Considering the lack of effective targets, where do we go next in the current TNBC drug development? A promising intervention for TNBC might lie in de novo small-molecule drugs that precisely target different molecular characteristics of TNBC. However, an ideal single-target drug discovery still faces a huge challenge. Alternatively, other new emerging strategies, such as dual-target drug, drug repurposing, and combination strategies, may provide new insight into the improvement of TNBC therapeutics. In this review, we focus on summarizing the current situation of a series of candidate small-molecule drugs in TNBC therapy, including single-target drugs, dual-target drugs, as well as drug repurposing and combination strategies that will together shed new light on the future directions targeting TNBC vulnerabilities with small-molecule drugs for future therapeutic purposes.

Imbalance of Molecular Module of TINCR-miR-761 Promotes the Metastatic Potential of Early Triple Negative Breast Cancer and Partially Offsets the Anti-Tumor Activity of Luteolin

Background

Triple negative breast cancer (TNBC) poses a great threat to patient prognosis. LncRNA-miRNA is a molecular module formed by a long non-coding RNA (LncRNA) and a microRNA (miRNA) that mediates the metastatic potential of tumours such as TNBC, and luteolin (LU) is a natural compound with anti-TNBC activity.

Objective

We aim to explore the regulatory mechanism of terminal differentiation-induced non-coding RNA (TINCR)-miR-761 molecular module in early TNBC, as well as its influence on anti-tumor activity of LU.

Methods

The serum was collected from TNBC patients in early stage to detect the expression of TINCR and miR-761 using RT-PCR. Transwell method was applied for the determination of cell migration and invasion, Western blot for epithelial–mesenchymal transition (EMT), flow cytometry (FCM) for cell apoptosis, and dual luciferase reporter and RNA pull-down experiment for the verification of the targeted relationship between TINCR and miR-761.

Results

Both TINCR and miR-761 were up-regulated in the serum of patients with early TNBC and the area under the curve (AUC) of the two for distinguishing TNBC from BC was not less than 0.850. In the cell function tests, down-regulation of TINCR or miR-761 notably suppressed the metastatic potentials (cell migration, invasion and EMT) of TNBC cells were remarkably inhibited, while up-regulation of TINCR or miR-761 notably promoted the metastatic potentials. We also confirmed that TINCR acts as the molecular sponge of miR-761, and has positive regulation on it. Besides, LU can significantly down-regulate TINCR and miR-761, and partially offset the anti-TNBC activity of LU when they were abnormally up-regulated, which was mainly reflected in the decrease of anti-proliferation and pro-apoptotic ability of LU against TNBC.

Conclusion

There is an imbalance of TINCR-miR-761 molecular module in early TNBC, which may be a potential new therapeutic target of TNBC.

Proteomic analysis of circulating extracellular vesicles identifies potential markers of breast cancer progression, recurrence, and response

Proteomic profiling of circulating small extracellular vesicles (sEVs) represents a promising, noninvasive approach for early detection and therapeutic monitoring of breast cancer (BC). We describe a relatively low-cost, fast, and reliable method to isolate sEVs from plasma of BC patients and analyze their protein content by semiquantitative proteomics. sEV-enriched fractions were isolated from plasma of healthy controls and BC patients at different disease stages before and after surgery. Proteomic analysis of sEV-enriched fractions using reverse phase protein array revealed a signature of seven proteins that differentiated BC patients from healthy individuals, of which FAK and fibronectin displayed high diagnostic accuracy. The size of sEVs was significantly reduced in advanced disease stage, concomitant with a stage-specific protein signature. Furthermore, we observed protein-based distinct clusters of healthy controls, chemotherapy-treated and untreated postsurgery samples, as well as a predictor of high risk of cancer relapse, suggesting that the applied methods warrant development for advanced diagnostics.

Molecular subtypes and precision treatment of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype. Despite the progress made in precision treatment of cancer patients, targeted treatment is still at its early stage in TNBC, and chemotherapy remains the standard treatment. With the advances in next generation sequencing technology, genomic and transcriptomic analyses have provided deeper insight into the inter-tumoral heterogeneity of TNBC. Much effort has been made to classify TNBCs into different molecular subtypes according to genetic aberrations and expression signatures and to uncover novel treatment targets. In this review, we summarized the current knowledge regarding the molecular classification of TNBC and explore the future paradigm for using molecular classification to guide the development of precision treatment and clinical practice.

The Fluoro-Thiazolylhydrazone Compound TSC-3C Inhibits Triple Negative Breast Cancer (TNBC) Cell Line Activity by Promoting Apoptosis, Regulating the MAPK Pathway and Inducing Mitochondrial Dysfunction

Triple negative breast cancer (TNBC) is the most aggressive cancer in women, and despite improved treatments, it remains a major cause of morbidity and mortality. We and others have demonstrated that different hybrid compounds targeting PARP/MAPK or other pathways to inhibit cancer progression may lead to promising therapeutic results. We introduced fluorine to alter the physical properties of the compounds. TSC-3C was one of the generated compounds. Upon treatment with TSC-3C, MDA-MB-231 cell proliferation, invasion, and migration were inhibited. TSC-3C induced MDA-MB-231 cell mitochondrial dysfunction and apoptosis, which may be caused by reducing the level of phosphorylated p44/42 MAPK (ERK1/2) and increasing the level of p-JNK. The present study may help to elucidate the role of the MAPK pathway in the development of breast cancer and may promote further research on halogenated heterocyclic compounds for the treatment of breast cancer.

Protein phosphatase 2A activation as a therapeutic strategy for managing MYC-driven cancers

The tumor suppressor protein phosphatase 2A (PP2A) is a serine/threonine phosphatase whose activity is inhibited in most human cancers. One of the best-characterized PP2A substrates is MYC proto-oncogene basic helix-loop-helix transcription factor (MYC), whose overexpression is commonly associated with aggressive forms of this disease. PP2A directly dephosphorylates MYC, resulting in its degradation. To explore the therapeutic potential of direct PP2A activation in a diverse set of MYC-driven cancers, here we used biochemical assays, recombinant cell lines, gene expression analyses, and immunohistochemistry to evaluate a series of first-in-class small-molecule activators of PP2A (SMAPs) in Burkitt lymphoma, KRAS-driven non-small cell lung cancer, and triple-negative breast cancer. In all tested models of MYC-driven cancer, the SMAP treatment rapidly and persistently inhibited MYC expression through proteasome-mediated degradation, inhibition of MYC transcriptional activity, decreased cancer cell proliferation, and tumor growth inhibition. Importantly, we generated a series of cell lines expressing PP2A-dependent phosphodegron variants of MYC and demonstrated that the antitumorigenic activity of SMAPs depends on MYC degradation. Collectively, the findings presented here indicate a pharmacologically tractable approach to drive MYC degradation by using SMAPs for the management of a broad range of MYC-driven cancers.

Combined MEK inhibition and tumor-associated macrophages depletion suppresses tumor growth in a triple-negative breast cancer mouse model

Tumor-associated macrophages (TAMs) are closely related to poor prognosis in triple-negative breast cancer (TNBC). Thus, gaining insight into how TAMs support cancer progression could contribute to effective therapies. We utilized the 4 T1 murine TNBC cell line and murine bone marrow-derived macrophages to assess TAM-mediated pro-proliferative effects in vivo and in vitro. Further, Transcriptional analysis was performed to identify pathways activated in TAM-stimulated 4 T1 cells. We also explored the therapeutic efficacy of combining a mitogen-activated protein kinase kinase (MEK) inhibitor with TAM-targeted therapy using a TNBC mouse model. We found that the presence of TAMs was significantly associated with proliferating cancer cells in a TNBC mouse model. Moreover, RNA sequencing analysis showed that TAMs could enhance mitogen-activated protein kinase (MAPK) pathway activation in 4 T1 cells compared to that in control cells. Further, the depletion of TAMs by clodronate liposomes significantly reduced MAPK pathway activation in vivo. In addition, the blockade of MAPK signaling by a MEK inhibitor repressed TAM-mediated cancer cell proliferation. Most importantly, MEK inhibition combined with macrophage depletion significantly suppressed tumor growth and increased T lymphocyte infiltration in a TNBC model. Our study suggests the possibility that TAM-induced MAPK pathway activation promotes cancer cell proliferation. Thus, MEK inhibition combined with macrophage depletion might represent an effective treatment for TNBC.