Targeted and immuno-biology driven treatment strategies for triple-negative breast cancer: current knowledge and future perspectives

TRAF6 promotes chemoresistance to paclitaxel of triple negative breast cancer via regulating PKM2-mediated glycolysis

Ample evidence reveals that glycolysis is crucial to tumor progression; however, the underlying mechanism of its drug resistance is still worth being further explored. TRAF6, an E3 ubiquitin ligase, is well recognized to overexpress in various types of cancer, which predicts a poor prognosis. In our study, we discovered that TRAF6 was expressed more significantly in the case of triple-negative breast cancer (TNBC) than in other of breast cancers, promoting chemoresistance to paclitaxel; that inhibited TRAF6 expression in the chemoresistant TNBC (TNBC-CR) cells enhanced the sensitivity by decreasing glucose uptake and lactate production; that TRAF6 regulated glycolysis and facilitated chemoresistance via binding directly to PKM2; and that overexpressing PKM2 in the TNBC-CR cells with TRAF6 knocked down regained significantly TRAF6-dependent drug resistance and glycolysis. Additionally, we verified that TRAF6 could facilitate PKM2-mediated glycolysis and chemoresistance in animal models and clinical tumor tissues. Thus, we identified the novel function of TRAF6 to promote glycolysis and drug resistance in TNBC with the regulation of PKM2, which could provide a potential molecular target for TNBC treatment.

Molecular Classification, Treatment, and Genetic Biomarkers in Triple-Negative Breast Cancer: A Review

Breast cancer is the most common malignancy and the second most common cause of cancer-related mortality in women. Triple-negative breast cancers do not express estrogen receptors, progesterone receptors, or human epidermal growth factor receptor 2 and have a higher recurrence rate, greater metastatic potential, and lower overall survival rate than those of other breast cancers. Treatment of triple-negative breast cancer is challenging; molecular-targeted therapies are largely ineffective and there is no standard treatment. In this review, we evaluate current attempts to classify triple-negative breast cancers based on their molecular features. We also describe promising treatment methods with different advantages and discuss genetic biomarkers and other prediction tools. Accurate molecular classification of triple-negative breast cancers is critical for patient risk categorization, treatment decisions, and surveillance. This review offers new ideas for more effective treatment of triple-negative breast cancer and identifies novel targets for drug development.

Lovastatin Inhibits EMT and Metastasis of Triple-Negative Breast Cancer Stem Cells Through Dysregulation of Cytoskeleton-Associated Proteins

Triple-negative breast cancer (TNBC) is more aggressive and has poorer prognosis compared to other subtypes of breast cancer. Epithelial-to-mesenchymal transition (EMT) is a process in which epithelial cells transform into mesenchymal-like cells capable of migration, invasion, and metastasis. Recently, we have demonstrated that lovastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor and a lipid-lowering drug, could inhibit stemness properties of cancer stem cells (CSCs) derived from TNBC cell in vitro and in vivo. This study is aimed at investigating whether lovastatin inhibits TNBC CSCs by inhibiting EMT and suppressing metastasis and the mechanism involved. In the present study, we found that lovastatin dysregulated lysine succinylation of cytoskeleton-associated proteins in CSCs derived from TNBC MDA-MB-231 cell. Lovastatin inhibited EMT as demonstrated by down-regulation of the protein levels of Vimentin and Twist in MDA-MB-231 CSCs in vitro and vivo and by reversal of TGF-β1-induced morphological change in MCF10A cells. Lovastatin also inhibited the migration of MDA-MB-231 CSCs. The disruption of cytoskeleton in TNBC CSCs by lovastatin was demonstrated by the reduction of the number of pseudopodia and the relocation of F-actin cytoskeleton. Combination of lovastatin with doxorubicin synergistically inhibited liver metastasis of MDA-MB-231 CSCs. Bioinformatics analysis revealed that higher expression levels of cytoskeleton-associated genes were characteristic of TNBC and predicted survival outcomes in breast cancer patients. These data suggested that lovastatin could inhibit the EMT and metastasis of TNBC CSCs in vitro and in vivo through dysregulation of cytoskeleton-associated proteins.

Focal Adhesion Kinase Fine Tunes Multifaced Signals toward Breast Cancer Progression

Breast cancer represents the most common diagnosed malignancy and the main leading cause of tumor-related death among women worldwide. Therefore, several efforts have been made in order to identify valuable molecular biomarkers for the prognosis and prediction of therapeutic responses in breast tumor patients. In this context, emerging discoveries have indicated that focal adhesion kinase (FAK), a non-receptor tyrosine kinase, might represent a promising target involved in breast tumorigenesis. Of note, high FAK expression and activity have been tightly correlated with a poor clinical outcome and metastatic features in several tumors, including breast cancer. Recently, a role for the integrin-FAK signaling in mechanotransduction has been suggested and the function of FAK within the breast tumor microenvironment has been ascertained toward tumor angiogenesis and vascular permeability. FAK has been also involved in cancer stem cells (CSCs)-mediated initiation, maintenance and therapeutic responses of breast tumors. In addition, the potential of FAK to elicit breast tumor-promoting effects has been even associated with the capability to modulate immune responses. On the basis of these findings, several agents targeting FAK have been exploited in diverse preclinical tumor models. Here, we recapitulate the multifaceted action exerted by FAK and its prognostic significance in breast cancer. Moreover, we highlight the recent clinical evidence regarding the usefulness of FAK inhibitors in the treatment of breast tumors.

Disseminated Tumor Cells and Dormancy in Breast Cancer Progression

Hematogenous dissemination of single cancer cells is a common phenomenon in patients with solid tumors. These cells may experience different fates: most will die during the process; some will grow into metastasis and some will persist in secondary homing sites for many years in a state referred to as dormancy. The mechanisms of this state are still not clear; single cancer cells can survive either by completely withdrawing from the cell cycle or by continuing to proliferate at a slow rate that is counterbalanced by cell death. Another hypothesis assumes that at least some of dormant tumor cells feature stem cell-like characteristics that may contribute to their extremely long half-lives and enhance chemotherapy resistance. Breast cancer is particularly known for prolonged periods of clinical freedom of disease (sometimes up to 20-30 years), followed by a distant relapse. In this chapter, we explore the relationship between the clinical phenomenon of tumor dormancy and the disseminated tumor cells and discuss the potential implications for treatment.

Atezolizumab for use in PD-L1-positive unresectable, locally advanced or metastatic triple-negative breast cancer

Since the US FDA-approval of the first immune checkpoint inhibitor, anticytotoxic T-lymphocyte antigen-4 monoclonal antibody ipilimumab, for metastatic melanoma on 28 March 2011, another six agents have been granted use among a multitude of tumors, including renal cell cancer, Hodgkin lymphoma, urothelial carcinoma and non-small-cell lung cancer. The first anti-programmed cell death ligand-1 monoclonal antibody to receive the FDA approval, atezolizumab (Tecentriq^®), has yielded promising results among international Phase III trials in triple-negative breast cancer and small-cell lung cancer, expanding the field of cancer immunotherapies. Herein, we review the pharmacodynamic and pharmacokinetic properties of atezolizumab, its safety and efficacy data from early clinical trials and summarize data from Phase III IMpassion130 trial, prompting FDA and EMA approval of atezolizumab in metastatic triple-negative breast cancer. Finally, implications for clinical use and ongoing research will be briefly discussed.

Positive correlation between programmed death ligand-1 and p53 in triple-negative breast cancer

Purpose

Tumors with high mutation load tend to have a stronger immune response in some tumors. The correlation between expression of programmed death ligand-1 (PD-L1), a biomarker of immune response in tumors, and p53, accepted as the most frequently mutated gene in many cancers, in triple-negative breast cancer (TNBC) has not been fully investigated in cancer patients.

Materials and methods

132 cases of TNBC and 32 cases of non-TNBC paraffin-embedded tissue sections were selected to detect the expression of PD-L1 and p53 by immunohistochemistry, and results were correlated with clinical data and survival outcomes. The staining of PD-L1 in tumor cells (TCs) and tumor-associated immune cells (TAICs) was assessed separately.

Results

Strong positive correlations were observed between expression of p53 and PD-L1 both in TCs (r=0.338, P=0.000) and TAICs (r=0.186, P=0.033). The same positive correlation was found in the expression of PD-L1 in TCs and TAICs (r=0.764, P=0.000). Like p53 (P=0.024), positive rate of PD-L1 in TCs was significantly higher in TNBC than in non-TNBC (P=0.02). PD-L1 and p53 in TCs staining were significantly associated with histological grade, tumor size and Ki67 index (P<0.05). PD-L1 in TCs staining was also associated with lymphatic metastasis status (P=0.000). However, PD-L1 in TAICs was only related to histological grade in statistically (P=0.012). Kaplan–Meier survival analysis showed that positive groups of p53, PD-L1 in TCs and TAICs had a worse overall survival and a worse progression-free survival as compared with the negative groups, but marginal significance was found only in overall survival of PD-L1 in TCs and TAICs, and progression-free survival of PD-L1 in TAICs (P=0.074, 0.097, 0.068, respectively).

Conclusion

Our findings suggest that positive correlation between p53 and PD-L1 in TNBC and the higher expression rates are closely correlated with some key prognostic factors and worse survival outcomes. These findings would lay the foundation for further study on the relationship of p53 and PD-L1 and the combination of mutated p53 inhibitors and PD-1/PD-L1 antibodies in TNBC.