Delivery of drugs by biomimetic nanocarriers to enhance the outcome of breast cancer photodynamic therapy

Despite the development, over the past decades, of many diagnostic and therapeutic treatment approaches, breast cancer (BC) still represents a leading health concern among women. In this scenario, combination therapy has established itself as a cornerstone for BC treatment. Targeting different pathways, can decrease the incidence of cancer cell resistance and diminish off-target toxicity by lowering the dose needed for every single drug. Among the approved therapies that could be combined, photodynamic therapy (PDT) has drawn interest as a potential adjuvant of traditional BC treatments. Additionally, recent findings demonstrated that BC spread and recurrence could be linked to breast cancer stem cells (BCSCs). Therefore, another strategy for the treatment of BC may involve the development of selective BCSCs targeting molecules, either alone or in combination with traditional therapies. Even though numerous drug combinations have been found, their use is still far from the clinic due to increased toxicity associated with the off-target accumulation of therapeutic agents. Having realized this inherent problem, the accumulation of the combined drugs in the target tumour tissue could be significantly improved by encapsulation in nanocarrier, such as nanoparticles (NPs). In this PhD thesis, we investigated the combination of PDT with a chemotherapeutic or a specific anti-CSC drug by using the advantages of nanocarriers as delivery vehicles and the use of cell-coated biomimetic NPs, to propose new solutions for BC-targeted PDT. Due to the excellent biocompatibility, keratin was selected for the co-delivery of the anti-CSC-specific drug salinomycin (SAL) and the PDT photosensitizer (PS) chlorin e6 (Ce6) to eradicate both differentiated and BCSCs. The in vitro studies performed in MCF-7 and MDA-MB-231 demonstrated the capacity of the combination of drugs to completely kill differentiated cells, showing a synergic effect of the two drugs when encapsulated in NPs. Moreover, SAL/Ce6@kVEs tested on CSC-enriched mammospheres showed the capability of reducing stemness potential and directly eradicating BCSCs. Importantly, preliminary in vivo results demonstrated that the encapsulation of SAL in kNPs is not affecting its capacity to inhibit the Wnt/β-catenin signalling pathways, one of SAL anti-CSC mechanisms. The potentiality of a combination of PDT treatment with chemotherapy for the eradication of BC was tested also using tumour microenvironment (TME)-responsive NPs formed by a dimeric prodrug of paclitaxel (PTX) (PTX2S) in the presence of the PS pheophorbide A (PheoA) (PheoA≅PTX2S). These NPs aimed to achieve both a stimuli-controlled release of the drugs in the TME and a synergic effect between therapies. Indeed, the results showed that PheoA≅PTX2S NPs quickly disassemble upon exposure to TME-mimicked GSH and ROS concentration, resulting in the release of PTX and PheoA. The in vitro results of combination therapy demonstrated the possibility to obtain a 30-fold dose reduction of PTX and a 3-fold dose reduction of PheoA, despite the limited synergic effect observed in MDA-MB-231 cell lines. The last strategy we investigated was using biomimetic cell membrane-coated NPs to encapsulate the PS meso-tetraphenylchlorin disulfonate (TPCS2a). The coating with mesenchymal stem cell-derived plasma membranes (mMSC) can impart the system features of the specific cell of origin such as immune escape properties, prolonged circulation time and tumour-homing abilities. Indeed, the results demonstrated a significant reduction of uptake by macrophages with respect to the uncoated counterpart. The in vitro experiments, performed on MDA-MB-231 and MCF-7 cells, showed the selectivity of the system for BC cells, as compared to non-tumorigenic MCF 10A cells, and a dose-dependent decrease of the cell viability, following irradiation with red light, in both cell monolayers and spheroids, administering the PS in the nanomolar range.