Enriched in flavonoid compounds, phenol acids, and terpene derivatives, propolis has been shown to regulate apoptosis signaling pathways and alter the expression of microRNAs (miRNAs). In the present study, it has been aimed to examine the effects of Turkish propolis on miRNA levels of breast cancer (MCF-7) cells, and its relationship with cell proliferation and apoptosis. Cytotoxic activity of ethanolic propolis extract (EEP) was evaluated using MTT assay. Mechanisms involved in the cytotoxic action of Turkish propolis in MCF-7 cells were investigated with regard to apoptosis and cell cycle using flow cytometry and western blot. Mitochondrial membrane potential (MMP) were evaluated by spectrofluorometric method. miRNA levels were detected by qRT-PCR method. EEP exhibited selective toxicity against MCF-7 cells compared to normal fibroblast cells. EEP increased the cell cycle arrest at the G₁ phase. EEP elevated the apoptotic cell death through increasing pro-apoptotic protein levels (p21, Bax, p53, p53-Ser46, and p53-Ser15), decreasing MMP and altering the expression levels of specific tumor suppressors (miR-34, miR-15a, and miR-16-5p) and oncogenic (miR-21) miRNAs. These data support that Turkish propolis may be evaluated as a potential natural agent for new anticancer drugs in future.

Breast cancer (BC) is the most common heterogeneous disease in women and one of the leading causes of cancer-related death. Surgery, chemotherapy, radiotherapy, hormone, and targeted therapy are the gold standards for BC treatment. One of the significant challenges during the treatment of BC represents resistance to chemotherapeutics, resistance that severely limits the use and effectiveness of the drugs used for BC treatment. Therefore, it is essential to develop new strategies to improve therapeutic efficacy. Circular RNAs (circRNAs) are a large group of non-coding RNAs that covalently form closed circular loops by joining their 5′, and 3′; ends. Accumulating evidence suggests that circRNAs have a vital role in cancer development, progression, and BC resistance to chemotherapy. The purpose of this review is to discuss the biological properties of circRNAs, and how circRNAs induce resistance to conventional therapeutic anti-cancer drugs used in BC treatment, by emphasizing and summarizing the potential roles of circRNAs in mechanisms of drug resistance, such as drug efflux, apoptosis dysfunction, autophagy, and DNA damage repair. CircRNAs are associated with drug resistance via ATP-binding cassette (ABC) efflux transporters, while some others by inhibition of cell apoptosis, thus leading to resistance to tamoxifen in BC cells. In contrast, others are involved in the promotion of BC cells chemoresistance by doxorubicininduced autophagy. CircRNAs may have clinical significance in regulating or overcoming BC drug resistance and may give directions towards a novel approach to personalized BC treatment. CircRNAs may significantly contribute to the identification of new therapeutic targets for the prevention of BC chemoresistance.

In an attempt to develop potent and selective anticancer agents, some 5‐ or 6‐ and N‐substituted benzoxazol‐2‐carboxamide derivatives were designed, synthesized, and evaluated for their cyclooxygenase inhibitory, antioxidant, and anti‐proliferative activity against MCF‐7 and MDA‐MB‐231 cell lines. Among them 5‐OMe, N‐piperidine substituted (compound 30 ), 5‐OMe, N‐4‐methylpiperidine substituted (compound 31 ) and 5‐Cl, N‐piperidine substituted (compound 34 ) benzoxazole 2‐carboxamide compounds have a moderate inhibitory effect in COX‐1 and COX‐2 enzymes. Anti‐proliferative studies show that compound 30 (IC ₅₀ =5.35 μM) and compound 31 (IC ₅₀ =5.82 μM) have similar activity to reference drug 5‐FU (IC ₅₀ =3.95 μM) on MCF‐7 cell but they have lower toxic effect for healthy WI‐38 cell line. For the MCF‐7 cell line, compounds 30 and 31 show approximately 1.5 times higher selectivity compared to the 5‐FU control. Among the synthesized compounds 30 , 31 , and 34 had the best anti‐proliferative effect and were used to perform flow cytometry and cell cycle analysis on MCF‐7 cell line. To predict the binding modes and pharmacokinetic parameters of all compounds, in silico studies were carried out. These compounds may shed light on cancer treatment and cancer research.