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Breast cancer is the most prevalent cancer in women. Despite improvements in treatment, the rate of breast cancer-related deaths is still high, and this issue needs further, accurate investigations. Although several treatment options are available, none of them are efficient for complete remission, particularly in advanced stages of the disease. It is known that cancerous cells have dysregulated apoptosis-related pathways, by which they can remain alive for a long time, expand freely, and escape from apoptosis-inducing drugs or antitumor immune responses. Therefore, modulation of apoptosis resistance in cancer cells may be an efficient strategy to overcome current problems faced in the development of immunotherapeutic approaches for the treatment of breast cancer. The inhibitors of apoptosis protein (IAPs) are important targets for cancer therapy because it has been shown that these molecules are overexpressed and highly active in various cancer cells and suppress apoptosis process in malignant cells by blockage of caspase proteins. There is evidence of Smac mimetics efficacy as a single agent; however, recent studies have indicated the efficacy of current anticancer immunotherapeutic approaches when combined with Smac mimetics, which are potent inhibitors of IAPs and synthesized mimicking Smac/Diablo molecules. In this review, we are going to discuss the efficacy of treatment of breast cancer by Smac mimetics alone or in combination with other therapeutics. K E Y W O R D S apoptosis, breast cancer, Smac mimetic, treatment 1 | INTRODUCTION Because of the high prevalence of the breast cancer among women, it is considered one of the main public healthrelated problems worldwide. There are several risk factors forbreast cancer, such as obesity, alcohol consumption, ionizing radiation, lack of physical exercise, early age menstruation, and family history. 1 Inheritance of genes such as BRCA1 and BRCA2 is another risk factor that affects about 5% to 10% of the subjects. More than 20 breast cancer subtypes have been J Cell Biochem. 2019;120:9300-9314. wileyonlinelibrary.com/journal/jcb 9300 |

There is an interconnected network between S1P/sphingosine‐1‐phosphate receptor 1 (S1PR1), IL‐6/glycoprotein 130 (GP130), and signal transducer and activator of transcription 3 (STAT3) signaling pathways in the tumor microenvironment, which leads to cancer progression. S1P/S1PR1 and IL‐6/GP130 signaling pathways phosphorylate and activate STAT3, and it then induces the expression of S1PR1 and interleukin‐6 (IL‐6) in a positive feedback loop leading to cancer progression. We hypothesized that blockade of this amplification loop can suppress the growth and development of cancer cells. Therefore, we silenced STAT3 upstream molecules including the S1PR1 and GP130 molecules in cancer cells using small interfering RNA (siRNA)‐loaded alginate‐conjugated trimethyl chitosan (ATMC) nanoparticles (NPs). The generated NPs had competent properties including the appropriate size, zeta potential, polydispersity index, morphology, high uptake of siRNA, high rate of capacity, high stability, and low toxicity. We evaluated the effects of siRNA loaded ATMC NPs on tumor hallmarks of three murine‐derived cancer cell lines, including 4T1 (breast cancer), B16‐F10 (melanoma), and CT26 (colon cancer). The results confirmed the tumor‐suppressive effects of combinational targeting of S1PR1 and GP130. Moreover, combination therapy could potently suppress tumor growth as assessed by the chick chorioallantoic membrane assay. In this study, we targeted this positive feedback loop for the first time and applied this novel combination therapy, which provides a promising approach for cancer treatment. The development of a potent nanocarrier system with ATMC for this combination was also another aspect of this study, which should be further investigated in cancer animal models in further studies.

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