One of the most well-known, potentially fatal malignancy is breast cancer. Advances in food and lifestyle are contributing to a significant increase in the morbidity of breast cancer (Arving et al. 2014). In the present study, myricetin exhibits powerful cytotoxic attributes against MCF-7 cell line (Fig. 1). As concentration increased, breast cancer cells viability declined. Our results demonstrated that the IC50 dosage (5.06 µg/100 µl) of myricetin succeeded in preventing the cells from proliferating. Moreover, the investigation by Sajedi et al. (2020) indicated that myricetin depicted a significant impact on MCF-7 cell viability. The concentration of myricetin that substantially decreased cell viability was 54µM. This observation implies that myricetin holds promise as a prospective cancer-fighting compound that targets breast cancer cells. The researchers observed that 54 µM of myricetin reduced the cell viability by intrinsic and extrinsic apoptotic pathways (Sajedi et al. 2020).
The cell cycle comprises of G1, S, G2 (interphase), and M Phase (mitosis). According to our findings, inhibition of cell growth with IC50 (5.06 µg/100 µl) at 24 h presented in Fig. 1 was attributed to the induction of apoptotic activity at sub G0/G1 phase. Kumar et al. (2023) employed a unique nano-platform to deliver myricetin by fusing a hydrogel with a cross-linked hydrophilic polymer (CA-Myr-NG) with chitosan/alginate (CA) as the core. With a dosage of 6 µg/ml, 30.92% of treated cells showed apoptosis and cell cycle arrest at the G2/M phase in MCF-7. Our data revealed that percentages of untreated cells with sub G0/G1, G0/G1, S-phase and G2/M phase were determined to be 1.39%, 64.96%, 3.46% and 30.19% respectively; whereas myricetin treated cells were 10.38%, 51.21%, 5.43% and 32.98% respectively (Table 2, Fig. 3). This result confirms that myricetin inhibits cell cycle progression at G0/G1-phase and increases the apoptotic cell concentration in sub G0/G1 phase.
The study using Annexin V-FITC/PI flow cytometry verified that myricetin caused the MCF-7 cells displayed in Fig. 4 to suffer apoptosis. Since, apoptosis is a monitored and highly controlled process, its occurrence during cancer treatment has attracted a lot of attention. (Fulda 2009). Phospholipid PS, a membrane phospholipid, travels from the inner to the outside leaflet of the plasma membrane in apoptotic cells. This change enables fluorescently labelled annexin V to attach to PS, which may be found using flow cytometry. Propidium iodide(PI) is excluded from intact membranes, but damaged or dead cells are penetrable for PI staining. FITC-conjugated annexin V (FITC-annexin V) staining is therefore usually combined with PI (Nagata et al. 2016). Our findings disclosed that treatment with myricetin for 24 h at IC50 concentration (5.06 µg/100 µl), yielded 15.08% of early apoptotic cells while there was no cell death via necrosis (Table 3). These findings clearly show that myricetin causes MCF-7 cells to undergo early apoptosis.
The qRT-PCR approach was used to investigate the molecular pathways involved in myricetin-induced apoptosis. Caspases 9 activation and an increased BAX/BCl-2 ratio are important factors in the intrinsic route of apoptosis that cause cells to die (Vaskivo et al. 2002). In our study, the mRNA expression of caspase 9, caspase 7, and Bcl-2 was upregulated while caspase 3 was downregulated following treatment with myricetin as shown in Fig. 6. A significant element influencing cell sensitivity to apoptosis-inducing stimuli is the ratio of Bcl-2 to Bax proteins. A number of proteins in the bcl-2 family are essential during cell apoptosis. As a result, Bcl-2 expression levels overall have an impact on the development, course, and prognosis of malignancies (Guo et al. 2015). Our research revealed that myricetin increased the activity of caspase 9, caspase 3, and BCl-2, which in turn hindered the proliferation of MCF-7 cells.
A research investigation found that myricetin promoted apoptosis in the human promyeloleukemic cell line HL-60 by upregulating the activities of caspase3 and caspase9, as well as BAX/BCl2 expression (Wang et al. 1999). Different myricetin doses cause breast cancer cell lines to undergo apoptosis, shown by a specific study conducted on MCF-7 cell lines. Moreover, it was discovered that myricetin increased caspase3 activity and activated the production of the Bax protein (Jiao and Zhang 2016). BCl-2 family proteins regulate a pore in the outer mitochondrial membrane, that allows cytochrome c release during mitochondrial death. This pore also facilitates the activation of caspase9 in apoptotic bodies, which later triggers the activation of the apoptotic effector caspases − 3 and − 7, ultimately resulting in cell apoptosis (Iurlaro and Munoz 2016). Research by Li et al. (2022) provides valuable insights into the dynamic regulation of apoptosis-related genes, specifically highlighting the enhanced expression of caspase3 and the attenuated expression of BCl-2 gene and P53 following the administration of myricetin. In line with this, the molecular docking analysis of the current study showed efficient binding of myricetin to BCL-2, inhibiting its anti-apoptotic activity. These findings open avenues for further exploration into the molecular mechanisms governing programmed cell death and offer potential targets for therapeutic interventions in diseases where apoptosis regulation is dysregulated.