MMP-responsive multiwalled carbon nanotubes enable tumor-selective drug delivery with altered intracellular...

Doxorubicin (DOX) is a widely used chemotherapeutic agent, but its clinical efficacy is limited by multidrug resistance (MDR), poor tumor penetration, and off-target toxicity. To address these challenges, we developed matrix metalloproteinase (MMP)-responsive multiwalled carbon nanotubes (MWCNTs) for tumor-targeted DOX delivery. The MWCNT formulation exhibited MMP-responsive cellular uptake, cell permeability, tissue penetration, and enhanced cytotoxicity of loaded DOX in cancer cells, a transwell model, and tumor spheroids. Mechanistic studies revealed that these CNTs entered cells primarily via clathrin-mediated endocytosis. Acidic endosomal conditions promoted lipid redistribution and membrane destabilization of endolysosomes, facilitating efficient endosomal escape and strong colocalization with the endoplasmic reticulum (ER). This intracellular trafficking pathway bypassed drug efflux mechanisms and prolonged intracellular drug retention in MDR cancer cells. In a mouse breast tumor model, MMP-responsive MWCNTs resulted in approximately 5-fold higher blood DOX levels and 2-fold greater tumor DOX accumulation than free DOX at the end of the treatment regimen. Improved pharmacokinetics and tumor specificity enhanced DOX's tumor inhibitory effects and increased tumor cell apoptosis. Importantly, the MMP-responsive MWCNTs significantly reduced DOX's off-target toxicity, as evidenced by approximately 2-fold lower cardiac DOX accumulation, reduced cardiomyocyte apoptosis, and preservation of white blood cell counts. Overall, this MMP-responsive CNT-based nanoplatform offers a promising strategy to enhance tumor targeting and retention, overcome MDR, and improve the therapeutic index of DOX.