# Polymeric Nanoparticles--Tools in a Drug Delivery System in Selected Cancer Therapies
## 5 Polymeric Nanoparticles in Breast and Ovarian Therapy

Table 3: Polymeric nanoparticles as drug delivery systems for colorectal cancer therapy. The problem of chemotherapy for treatment of breast and ovarian cancer is the non-selective mechanism of action of the platinum-based or cytostatic drugs concerned [61]. In addition, the drugs applied in therapy are poorly soluble, and also, in some cases, cell resistance to the drug may occur [67]. Multidrug resistance (MDR) is an increasingly common phenomenon in cancer therapy that complicates the treatment process [68]. The development of chemoresistance in tumor cells occurs either after treatment with cytostatic drugs or, surprisingly, in patients not treated with chemotherapeutic agents. In addition, the use of one type of drug may lead to the development of resistance not only to the drug used, but also to other subtypes [68]. This occurrence is one of the most challenging obstacles for sufficient treatment for both types of cancers. Therefore, there are increasing reports on the development of new formulations using polymeric nanoparticles in targeted drug delivery aimed at cancer cells [68]. A poly(D,L-lactide-_co_-glycolide) nanoparticle functionalized with 0.2 mg folic acid and loaded with 10 mg docetaxel was investigated by the team of [PERSON] et al. [69]. In their study on breast cancer cell lines with overexpression of the folic acid receptor alpha (FR\(\alpha\)), they found that the use of the polymeric carrier overcomes the chemopre effective effect. Additionally, increases in the cytotoxicity of docetaxel towards breast cancer cells, compared to the use of DTX in its native form, were observed [68,69]. This indicates that the polymeric nanocarriers have a significant effect on both distribution and selectivity, as well as reducing toxic effects on normal cells [68,69]. Currently, Abraxane(r), an albumin-based nanoparticle loaded with 5 mg paclitaxel, is used for the treatment of metastatic breast cancer [61]. It should be noted here that it is commonly referred to as a polymeric nanoparticle, even though it should actually be classified as a nanoconjugate due to its physicochemical properties and structure. However, for relevance and illustration, several applications of nanoconjugates based on albumin-bound nanoparticles are also included in this review. However, the two terms should not be mixed up. In addition, cancer stem cells (CSCs) also play an important role in the development of MDR, which is also the reason for cancer recurrence [68,70]. The major factor behind this process is an increase in the expression of selected ATP-binding cassette efflux transporters, which contributes to a greater pumping of the medicinal substance out of the cell, leading to a reduced cellular response to the chemotherapeutic agent [68,70]. However, this process can be abolished in some cases by using coadministration of cytostatic drugs with chemosensitizers [68]. In a study by [PERSON] et al. [71] using solvent-based methods, mPEG-D,L-PLA nanoparticles loaded with docetaxel and resveratrol were obtained simultaneously. The study, conducted on MCF-7 breast cancer lines and in vivo, observed that the coadministration of these two substances increased the cytotoxic effect and abolished the MDR effect in tumor cells. This suggests that reducing the effect of resistance to chemotherapeutics can be achieved by combining drugs that exhibit synergistic effects, causing MDR to be eliminated in cancer cells [71]. The use of polymeric magnetic nanoparticles in the treatment of breast cancer also seems interesting, because it reduces the elimination of drug-loaded NPs by the reticuloendothelial system [72]. The team of [PERSON] et al. [72] conducted a study to evaluate the potential of using PLGA NPs loaded with methotrexate (MTX)-functionalized magnetico against the SK-BR-3 line. The results of the study showed similar cytotoxicity to MTX. In addition, based on the accumulation of particles at the target site, they concluded that such a combination could reduce the side effects of MTX [72].