RECENT ADVANCES IN POLYPHENOLS NANOCARRIERS AGAINST BREAST CANCER THERAPY FOCUS ON IN VITRO STUDIES: LITERATURE REVIEW

Cancer is considered a severe public health problem worldwide. Among the most incident cases, breast cancer, which affects many women in the entire world, can be mentioned. Currently, there are well-established protocols for the treatment of this type of cancer. However, cancer treatment presents collateral effects that can compromise the patient’s quality of life. Therefore, studies have suggested that plants and fruits rich in polyphenols have antitumor activity, decrease chemotherapy resistance, and reduce side effects caused by chemotherapy. However, most of these compounds have low bioavailability making their potential pharmaco logical challenging. Therefore, the search for carriers that can efficiently protect and transport these bioatives to tumor cells is of great interest. In this sense, nanostructured systems can be included as the delivery of bioactive molecules and drugs. Thus, this study aimed to report the current studies using nanocarriers containing phenolic compounds to evaluate their antitumor effect against breast cancer cells. Data collection included the virtual databases Science Direct and Web of Science using the descriptors: nanoparticles and polyphenols and breast cancer, for experimental articles published from 2015 to September 15, 2020. The search resulted in a total of 1346 articles, of 37 met the inclusion criteria. The studies have demonstrated the efficiency of nanostructures containing polyphenols against cancer cells, suggesting excellent perspectives in the use of nanotechnology combined with bioactive compounds in the treatment of breast cancer.


INTRODUCTION
Breast cancer is the most commonly diagnosed neoplasm worldwide, being the leading cause of cancer death in women. According to estimates by the National Cancer Institute (INCA) the estimated number of incident breast cancer cases in Brazil, for 2020, was 66,280 for each year of the 2020-2022 triennium. The incidence of this pathology comes persistently due to several genetic and environmental factors such as eating habits, physical inactivity, radiation exposure, hormonal therapy, alcohol consumption, cases of cancer in the family, among others (KOLAK et al., 2017). Currently, treatment for breast cancer can be classified as systemic, radical, or conservative. Among the protocols used in treatments includes hormonal or cytotoxic chemotherapy, immunotherapy, surgery, and radiotherapy. However, one of the main problems associated with cancer treatment is the toxic side effect. Most chemotherapeutic agents used cannot differentiate between normal and tumor cells and induce cell death in all cells that present a rapid proliferation (RAMLJAK et al., 2005).
In search of compounds that can be efficient with low or no adverse effects, the pharmaceutical industry is continuously investigating natural products to prevent and treat cancer (SILVA et al., 2019).
Polyphenols are one of the most numerous and widely distributed groups of natural products.
Research on polyphenols in the diet has shown positive results by reducing several chronic diseases, including cancer. Some studies reported antioxidant, anti-inflammatory, and antimicrobial effects (KHAN et al., 2019). Different mechanisms have been suggested to explain the anticancer effects of phenolic compounds, such as, for example, acting as suppressive agents that inhibit the formation and growth of tumors, inhibiting proliferation offering better preventive and therapeutic options. However, the low solubility, rapid metabolism, and low gastrointestinal absorption of polyphenols used in the diet are significant obstacles to their pharmacological potential (KHAN et al., 2019). To overcome the polyphenols bioavailability problem and improve the pharmacokinetics, several methodologies have been proposed for the encapsulation of these compounds, generating more stable forms of delivery. Nanostructures are one of the main options for being a delivery system for bioactive compounds, offering advantages such as protection against degradation, interaction with the biological environment, better absorption, retention time, controlled delivery, among other Disciplinarum Scientia. Série: Naturais e Tecnológicas, Santa Maria, v. 21, n. 3, p. 139-155, 2020. 141 benefits (SANTOS et al., 2019). Through the targeted administration of drugs through nanoformulations, better administration of the tumor site, and better therapeutic responses can reduce side effects.
Besides, there is an increase in cell selectivity reducing the adverse effects caused by conventional chemotherapy, showing that nanotechnology may be able to overcome the limitations of polyphenols, causing promising results in the treatment of cancer (DAVATGARAN-TAGHIPOUR et al., 2017;PEREZ -RUIZ et al., 2018). This study aims to review available data on nanoformulations containing natural polyphenols as chemopreventive and chemotherapeutic agents and discuss anticancer action mechanisms in recent years.

MATERIALS AND METHODS
This study is a systematic literature review. The search for work publications happened from January to September 2020 through the electronic databases: Science Direct and Web of Science. The descriptors used for this review were: nanoparticles and polyphenols, and breast cancer, with articles published from 2015 to September 15, 2020. The inclusion criteria used to select the items were: article-type publications with texts in the English language. The exclusion criteria were publications whose central theme did not match the research, literature review studies, book chapters, and other works that did not correspond to experimental studies.

RESULTS AND DISCUSSIONS
According to the chemical structure, polyphenols are classifi ed into fl avonoids, phenolic acids, stilbenes, lignans, curcuminoids, and tannins, as illustrated by some examples in the fi gure below (MOJZER et al., 2016) (Figure 2). Many of these compounds have been found in the literature as a primary or adjuvant asset with chemotherapy drugs evaluating their cytotoxic potential in vitro studies against diff erent lines of breast cancer cells (AVTANSKI, PORETSKY, 2018). Despite its numerous advantages, most phenolic compounds have limitations on bioavailability.
This study showed particles of approximately 150 nm. To assess the uptake of nanoparticles in vitro, cells were incubated for 5 minutes, 2 hours, 6 hours, and 24 hours and in the cell growth evaluation, it was observed that all pomegranate nanoparticles inhibited the growth of ifere cells in a significantly higher than the free extract in both cell lines. This corroborates the studies by Khorrami, Zarepour, Zarrabi (2019) and Badawi et al. (2018). They produced nanoparticles loaded with pomegranate extract showing more significant cell proliferation inhibition when compared to the free form, in addition to acting selectively against breast ifere cells.
Pirzadeh-Naeeni et al. (2020) used ellagic acid, the main antitumor compound of pomegranate loaded in schizophyllan and chitin nanoparticles, to investigate its effectiveness in the treatment of MCF-7 cells. The iferentete activity indicated that during the first three hours, the actions of eliminating free ellagic acid and nanoparticles containing ellagic acid increased the iferentete activity to 77% and 70%, respectively. Cell viability assessment showed significant antiproliferation effects on MCF-7 cells, which improved at higher concentrations. These studies may suggest that nanoparticles using polyphenols iferent in pomegranate represent a method of choice for further investigations regarding breast ifere treatment using nanocarriers.
One of the most commonly found polyphenols in the literature in the treatment of breast ifere is curcumin. Extracted from the rhizome of Curcuma longa, it has been widely used in medicine due to its antitumor, iferentete, anti-inflammatory, healing, and antibacterial benefits (BANIK et al., 2017).
Despite many advantages in the medical field, curcumin has low bioavailability when administered freely. This is one of the main reasons this bioactive compound needs a carrier capable of protecting and delivering it effectively, as is the case with nanostructures. Because it has a hydrophobic characteristic, curcumin is nanoencapsulated mainly in lipid nanoparticles and liposomes (FENG et al., 2017) (Table 2).   (Table 3).

Ramadass et al. (2015) produced liposomes as co-delivery of epigallocatechin gallate and
paclitaxel, a chemotherapeutic ifere used in breast ifere treatment ifere to inhibit target metalloproteinases. It has already been shown that MMP-2 and MMP-9 metalloproteinases are entirely expressed in cancerous tissues, and this has drawn a ifere attention due to their implications for tumor invasion and metastasis. Therefore, there are reports that epigallocatechin 3-gallate (EGCG) reduces the iferentet of MMP-2 and MMP-9. The cell viability showed high inhibition of metalloproteinases in the treatment with liposomes, with the activity of MMP-2 and MMP-9 being reduced by about 80% compared to the control. This study corroborates with that carried out by Narayanan et al. (2015). They also investigated EGCG and Paclitaxel's combination as na inhibitor of multiple signaling, focusing on the NF-kB pathway. It was encapsulated in a PLGA-casein nanoparticle targeted at breast ifere cell line MDA-MB-231 that sensitized paclitaxel-resistant breast ifere cells, inducing their apoptosis and inhibiting the activation of NF-κB by regulating the genes associated with angiogenesis and tumor metastasis.
In another study, Mukherjee et al. (2015) produced gold nanoparticles conjugated to EGCG and nanoparticles with green ifere assess toxicity against MCF-7 breast ifere cells. The nanoparticles showed toxic effects on MCF-7 cells, while they did not show any cytotoxic effects on the mice's hepatocytes used as controls. Besides, they limited the activation of NFr-B by almost 50% and triggered the onset of apoptosis. It also iferente significant cell uptake and good results in iferentete activity in vitro. It was observed that (-) -epicatechin showed no effect during 72 h of incubation. In contrast, NPs-EC-CLT generated the most significant inhibition of cell proliferation in all breast ifere cell lines and did not show cytotoxic effects to healthy cells, demonstrating that these nanoparticles have na inhibitory effect on human breast ifere cell line, in addition to presenting cell selectivity.
Resveratrol is a polyphenol that is iferen the class of stybenes. This compound has attracted attention due to its potential health benefits. It is widely found in plants such as grapes, plums, and peanuts (WANG et al., 2017;SUN et al., 2019). Its iferente, anti-inflammatory, iferentete, anti-aging, blood-sugar-lowering, and beneficial cardiovascular effects have been reported in many in vitro studies.

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The cell viability test demonstrated a cytotoxic effect against MCF-7 cells of 88% at 100 µg/mL-1 just as the iferentete evaluation by the DPPH method proved to be quite iferente, suggesting a useful alternative as a future treatment. Aghapour et al. (2018) prepared quercetin nanoparticles to evaluate their effect on the MCF-7 strain cells. The nanoparticles had na average size of 84 nm. When performing the MTT test with iferente formulation concentrations, a higher inhibition (87%) was observed in the 72h period in a dose-dependent manner. Besides, the nano-quercetin inhibitor's antiproliferative effect measured the progression of the cell cycle from phase G1 to phase S and apoptotic cell death in MCF-7 cells.
Finally, it can be observed that several phenolic compounds present in different fruits and plants cytotoxicity against breast cancer cells in the in vitro treatments performed, showing greater effectiveness when nanostructured in comparison with free compounds, resulting in the nanoencapsulated compounds having greater protection when exposed to external factors of degradation. In addition, some studies reported here brought results in which they point out that the nanostructures had an action on the modulation of gene and protein expression, suggesting a better targeting of the nanostructures in the treatment of cancer. However, it is necessary to carry out further studies using different experimental models that can ensure their effectiveness.

CONCLUSION
The present study reported the current research carried out regarding nanocarriers' production containing polyphenols in isolation or association with drugs for the treatment and prevention of breast cancer. Most of the polyphenols found in the studies have limitations in their bioavailability to the organism when included in the diet. In recent years, nanotechnology has gained significant prominence for developing carriers that can safely forward drugs and bioactive compounds, maintaining their chemical properties. We brought here different nanostructures for this purpose. Those that present significant results focus on liposomes and lipid nanoparticles associated with chemotherapy drugs and phenolic compounds to treat breast cancer cells in vitro studies. As well, curcumin and catechins were the most evident polyphenols in the studies, presenting satisfactory results. The studies, including nanotechnology for breast cancer treatment reported here, are of great interest to complement future research.