Redox-responsive micellar-like nanoparticles can overcome intrinsic multi-drug resistance in tumour spheroids of triple negative breast cancer†

Abstract

Triple negative breast cancer (TNBC) is one of the most difficult subtypes of breast cancer to treat, due to its aggressiveness, high heterogeneity and lack of targeted therapies. Efforts have been made to elucidate the mechanisms by which TNBC cells become drug-resistant, aiming to identify new molecular targets for the development of effective treatments. Here, we have generated a TNBC 3D multi-cellular spheroid model using MDA-MB-231 cells and assessed the efficacy of drug delivery formulations based on docetaxel (DTX)-loaded micellar-like nanoparticles (MLNP) compared with free DTX. We assessed the viability and the induction of apoptosis in the treated spheroids using established apoptosis and necrosis biomarkers: annexin-V, PI, Sytox and caspase 3 and 7 activity by flow cytometry. Given the efficacy results of the MLNPs and free DTX, the expression of selected genes related to resistance in breast cancer cells was assessed by RT-qPCR (real-time polymerase chain reaction) as well as western blot and immunofluorescence of the drug resistance protein (ABCG2/BCRP) in both 3D and 2D cell culture models of MDA-MB-231 cells. The results from these assays indicate that the TNBC 3D multi-cellular spheroids exhibit an intrinsic multi-drug resistance (MDR) through the up-regulation of ABCG2/BCRP gene and protein, compared to monolayers of the same cell line. Moreover, the results also demonstrate that the MLNPs had the best efficacy against TNBC 3D spheroids whereas the free drug was less efficacious. This suggests that the MLNPs were able to overcome the MDR of the TNBC 3D cell culture model when compared to free DTX.