Multilevel Assessment of a Carbosilane Dendrimer−siRNA Nanoplatform: Cellular Compatibility, Blood−Brain Barrier Model Integrity, and Murine Model Biodistribution

Abstract The tight regulation of bidirectional solute flux between the systemic circulation and neural tissue by the blood−brain barrier (BBB) remains a principal obstacle to effective pharmacotherapy of the central nervous system. In this study, we evaluate the biocompatibility and biodistribution of a novel third-generation PEGylated carbosilane dendrimer (G3Si PEG6000) and its siRNA dendriplex with an APOE4-directed siRNA relevant to late-onset Alzheimer’s disease using a tiered, upstream strategy that progresses from BBB-relevant monocultures to a capillary-weighted BBB model and in vivo/ex vivo biodistribution in mice, in accordance with current recommendations for nanomaterial testing. In endothelial cells, pericytes, and astrocytes, mitochondrial/redox profiling (MTT, DCF-ROS, and JC-1 ΔΨm) defined tolerated exposure ranges. Complexation with siRNA consistently attenuated apparent cytotoxicity across cell types, yet both free and complexed formulations elicited modest ROS and dose-dependent ΔΨm depolarization, indicating persistent mitochondrial stress. In the BBB model, responses were concentration- and formulation-dependent: 10 µM free dendrimers produced sustained impedance and nuclear confluence loss with sheet-like detachment, whereas the 0.1−2.5 µM free dendrimer and the dendriplex induced transient, recoverable perturbations or increases in impedance and proliferation. In vivo, whole-body IVIS imaging demonstrated prolonged systemic exposure for the dendriplex and an ex vivo kidney-dominant, liver-secondary distribution; no robust dendriplex signal was detected in brain fluorescence by planar NIR-I IVIS under the applied acquisition conditions. Collectively, these data indicate that siRNA complexation broadens the functional window at the BBB model with partially recoverable barrier effects and improved systemic exposure, while not substantially reducing mitochondrial or oxidative stress responses. The results provide a mechanistically informed basis for dose optimization and efficacy testing of this dendrimer−siRNA platform in CNS indications and for advancing this platform in further investigations targeting Alzheimer's disease.