FAP-α-Responsive Size-Transformable Lipid Nanoparticles for Stromal Remodeling and Enhanced Drug Penetration in Fibrotic Hepatocellular Carcinoma

Fibrotic tumor microenvironment driven by activated hepatic stellate cells (aHSCs) and cancer-associated fibroblasts poses a formidable challenge to antitumoral drug delivery in hepatocellular carcinoma (HCC) by promoting angiogenesis, immunosuppression, and dense extracellular matrix barrier. Overcoming this fibrosis-associated delivery resistance requires nanotherapeutic systems to not only target the stromal compartment but also adapt their structure within the tumor matrix to improve deep penetration. Herein, we report a fibroblast activation protein-α (FAP-α)-responsive, size-transformable lipid nanoparticle platform with integrated stromal targeting, enzymatic activation, and intracellular delivery capacity for enhanced drug penetration and stromal remodeling in fibrotic HCC. This developed system, denoted as SOR/DOX@GPA-LNP, is co-loaded with sorafenib and doxorubicin and engineered with three key features: (i) a FAP-α-cleavable GPA peptide linker for TME-specific activation, (ii) FAP-α-mediated targeting of aHSCs, and (iii) a PAMAM core-mediated proton sponge activity to facilitate endosomal escape. Physicochemical characterization demonstrates that GPA-LNPs possess uniform size distribution, high colloidal stability, pH-responsive release behavior, and favorable heme- and cyto-compatibility. In vitro studies confirmed their selective aHSC-targeting ability, while in vivo imaging showed enhanced accumulation and retention in nude mice bearing subcutaneous tumors and orthotopic tumor-bearing mice. GPA-LNPs exhibited size reduction (from 170.5 to 146.3 nm) upon exposure to FAP-α, which significantly improved transport in three-dimensional HCC/aHSC spheroid models and increased deeper intratumoral accumulation. This size-transformable property establishes a direct structure-property-function relationship linking FAP-α enzymatic responsiveness with enhanced stromal penetration. Functionally, SOR/DOX@GPA-LNPs simultaneously suppressed aHSC activation, disrupted the fibrotic stromal barrier, and delivered cytotoxic agents to tumor cells. In the orthotopic HCC model, SOR/DOX@GPA-LNPs achieved superior antitumor efficacy, improved stromal remodeling and reduced systemic toxicity compared to nonresponsive counterparts. Overall, this work presents a versatile strategy that couples TME-responsive size adaptability with dual-action payloads, offering a compelling approach to navigate the complexities of fibrotic HCC therapy.