Breast cancer is the most common cause of cancer-related death in women worldwide. Multidrug resistance (MDR) has been a large hurdle in reducing BC death rates. The drug resistance mechanisms include increased drug efflux, enhanced DNA repair, senescence escape, epigenetic alterations, tumor heterogeneity, tumor microenvironment (TME), and the epithelial-to-mesenchymal transition (EMT), which make it challenging to overcome. This review aims to explain the mechanisms of resistance in BC further, identify viable drug targets, and elucidate how those targets relate to the progression of BC and drug resistance.

Background: High-grade serous ovarian cancer (OvCa) is the most common type of epithelial OvCa. It is usually diagnosed in advanced stages, leaving a woman’s chance of survival below 50%. Despite traditional chemotherapeutic therapies, there is often a high recurrence rate following initial treatments. Hence, a targeted drug delivery system is needed to attack the cancer cells and induce apoptosis, overcome acquired drug resistance, and protect normal cells from cytotoxicity. The present study shows that targeting folate receptor alpha (FRα) through planetary ball milling (PBM) nanoparticles (NPs) induces apoptosis in OvCa cells. Results: Human tissue microarrays (TMAs) show overexpression of FRα in Stage IV OvCa tissues compared to matched normal tissues. They provide a focus for a targeted delivery system. We formulated PBM nanoparticles encapsulated with paclitaxel (PTX) or fisetin (Fis) and conjugated with folic acid (FA). The cytotoxic effect of these PBM NPs reduced the concentration of the toxic chemotherapy drug PTX by five-fold. The combined treatment of PTX-FA NPs and Fis-FA NPs inhibited cell proliferation and induced apoptosis more extensively than the individual drugs alone. Apoptosis of OvCa cells, determined by flow cytometry, showed an increase from 14.4 to 80.4% (OVCAR3 cells) and from 2.69 to 90.0% (CAOV3 cells) in the number of apoptotic cells. Also, expressions of the pro-apoptotic markers, BAK and active caspase-3, were increased after PTX-FA + Fis-FA PBM NP treatment. In addition to looking at targeted treatment effects on apoptosis, drug resistance was investigated. Drug resistance in OvCa cells was reversed by ABCG2, an ABC-transporter marker. Conclusions: Our study shows that PTX-FA and Fis-FA PBM NPs directly target platinum-resistant OvCa cells, induce cytotoxic/apoptotic effects, and reverse multi-drug resistance (MDR). These findings allow us to create new clinical applications using PTX-FA and Fis-FA combination nanoparticles to treat drug-resistant cancers.

Background/Objectives: This study aimed to further enhance the properties of paclitaxel (PTX) and honokiol (HNK) through encapsulation in planetary ball-milled nanoparticles (PBM NPs) and specific targeting of breast cancer (BrCa) cells via MUC1 targeting using an aptamer (S2.2) coating. Methods: Tissue microarray (TMA) analysis was utilized to measure MUC1 expression in stages 1, 2, 3, and 4 BrCa tissue samples. Pharmacokinetic simulations were performed to explore the potential advantages of using PTX and HNK in combination while targeting MUC1 for BrCa treatment. To investigate the efficacy of the PBM NPs for MUC1 targeting, we synthesized the aptamer-conjugated PTX and HNK PBM NPs (PTX-S2.2-PBM NPs, HNK-S2.2-PBM NPs) using N-hydroxysuccinimide (NHS) coupling. Dynamic light scattering (DLS), Fourier-transform infrared (FTIR), and high-performance liquid chromatography (HPLC) were utilized to characterize the NPs. MTT and live/dead cell assays were used to evaluate the cytotoxicity of the NPs. Results: TMA sample analysis confirmed the upregulation of MUC1 in BrCa tissues, which increased with the stage of BrCa. DLS analysis revealed that the PTX-S2.2 and HNK-S2.2 NPs have a desirable size (83.4 nm and 163 nm, respectively) and zeta potential (−9.74 mV and −7.16 mV, respectively), which are suitable for systemic circulation and improved therapeutic outcomes. FTIR and HPLC analysis suggest proper conjugation was achieved, and an encapsulation efficiency of PTXS2.2 and HNKS2.2 NPs at 77% and 84%, respectively, was achieved. Cell viability assays demonstrated that PTX-S2.2-PBM and HNK-S2.2-PBM NPs exhibit cytotoxicity comparable to or greater than free PTX and HNK, respectively. Conclusions: These findings support the belief that using PTX-S2.2 and HNK-S2.2 PBM NPs could be a promising treatment option for BrCa.