Cholesterol-Modulated, pH Charge-Reversible Rhodamine-Cored Dendrimers for Transcytosis-Mediated Deep Tumor Delivery

Abstract

Deep and uniform drug penetration into solid tumors remains a critical challenge in nanomedicine, as conventional nanocarriers relying on the enhanced permeability and retention (EPR) effect are largely confined to perivascular regions. While cellular transcytosis offers a promising active transport route to overcome this barrier, reconciling prolonged blood circulation with efficient transcytosis remains difficult due to conflicting surface chemistry requirements. Here, we report a series of well-defined rhodamine-cored poly(l-lysine) dendrimers (Rh-PLL-Gx, x = 1–8) with monodisperse size and generation-tunable fluorescence, providing a robust platform for systematic evaluation. We develop a pH-responsive charge-reversal strategy by capping surface amines with dimethylmaleic anhydride (DMMA) after introducing varying cholesterol content (0, 0.5, and 3 mol %) to establish a hydrophobicity gradient. At physiological pH, DMMA confers moderate negative surface charge that minimizes nonspecific interactions and prolongs systemic circulation. In the acidic tumor microenvironment, rapid charge reversal restores positive surface charge, enabling adsorption-mediated cellular uptake and transcytosis. Increased hydrophobicity via cholesterol modification further enhances cellular internalization, transcellular transport, and deep tumor penetration. These findings establish a clear hydrophobicity-transcytosis relationship and offer valuable design guidance for engineering nanocarriers with improved tumor delivery efficiency.