Metallic nanoparticles as anticancer agents in Breast Cancer from molecular features to biological effects

Despite advances, breast cancer remains a major global health challenge, constrained by current systemic therapies that struggle with non-selective toxicity, drug resistance, and the complexity of the tumor microenvironment. This dissertation addresses these limitations by developing two complementary nanomedicine strategies: one focused on innovative cellular drug delivery, and the other on exploiting subtype-specific metabolic vulnerabilities. Part I: ECFC-Mediated Nanothermoradiotherapy with Gold Nanorods (AuNRs) The first part of this study investigates the use of Endothelial Colony-Forming Cells (ECFCs) as "Trojan Horses" to deliver gold nanorods (AuNRs) to carry out synergistic cancer theranostics. ECFCs had substantially enhanced uptake and intracellular clustering of AuNRs compared to breast cancer cells (MCF-7, MDA-MB-231). This new intracellular structure led to a 100- to 200-fold increase in the PAI signal and improved photothermal conversion efficiency, rendering ECFC-AuNRs promising biohybrid agents for application in diagnostics and therapy. Functionally, AuNRs-loaded ECFCs demonstrated anti-tumoral activity in 3D breast cancer spheroids by suppressing proliferation and EMT markers. Besides, we explored ECFC- mediated nanothermoradiotherapy by capitalizing on the tumor-tropic homing capability of ECFCs to deliver AuNRs into cancer cells. With NIR irradiation, mild hyperthermia (~43 °C) initiated by the plasmonic nanoparticles sensitized cells to low-dose radiation (2Gy). The HT + RT treatment elicited a synergistic cytotoxicity, evident by increased DNA damage (γH2AX, COMET assay) and strong suppression of the autophagic survival pathway (reduced LC3 I/II, Beclin-1/p62, and lysosomal activity). Together, these results confer a biohybrid ECFC-AuNRs platform with capacity to enhance imaging contrast, enable targeted photothermal ablation, and augment radiosensitization, thus opening the door to image-guided precision theranostics in breast cancer. Part II: Silver Nanoparticle (AgNP) Cytotoxicity and Metabolic Vulnerabilities The second part of this thesis reviews the mechanisms of cytotoxicity induced by Silver Nanoparticles (AgNPs) in two metabolically distinct breast cancer subtypes: MDA-MB-231 (glycolytic, triple-negative) and BT474 (OXPHOS-dependent, HER2+). AgNPs triggered ROS-mediated oxidative stress, leading to apoptosis and clonogenic loss, with BT474 cells exhibiting higher sensitivity than the more resistant MDA-MB-231 line. A key finding is the identification of a metabolic phenotype-dependent susceptibility. In BT474 cells, AgNPs caused acute mitochondrial damage and an ineffective antioxidant response (NRF2/PRDX1 induction), accompanied by a compensatory shift toward glycolysis, which paradoxically increased vulnerability to glucose deprivation. Conversely, MDA-MB-231 cells displayed an adaptive OXPHOS and lipid oxidation upregulation (increased OCR, ATP production and β-oxidation). This differential response was partly regulated by the TXNIP-GLUT1 axis and P38 MAPK activation, linking redox stress to metabolic reprogramming and intrinsic apoptosis. Overall, this study proposes an integrated model of AgNPs-mediated cytotoxicity that exploits redox and metabolic vulnerabilities in breast cancer subtypes, highlighting AgNPs as selective cytotoxic agents and advancing the concept of metabolism-informed precision nanotherapy.