Metformin-Induced Stromal Depletion to Enhance the Penetration of Gemcitabine-Loaded Magnetic Nanoparticles for Pancreatic Cancer Targeted Therapy.

Pancreatic ductal adenocarcinoma, as one of the most aggressive cancers, is characterized by rich desmoplastic stroma that forms a physical barrier for anticancer drugs. To address this issue, we herein report a two-step sequential delivery strategy for targeted therapy of pancreatic cancer with gemcitabine (GEM). In this sequential strategy, metformin (MET) was first administrated to disrupt the dense stroma, based on the fact that MET downregulated the expression of fibrogenic cytokine TGF-β to suppress the activity of pancreatic stellate cells (PSCs), through the 5'-adenosine monophosphate-activated protein kinase pathway of PANC-1 pancreatic cancer cells. In consequence, the PSC-mediated desmoplastic reactions generating α-smooth muscle actin and collagen were inhibited, which promoted the delivery of GEM and pH (low) insertion peptide (pHLIP) comodified magnetic nanoparticles (denoted as GEM-MNP-pHLIP). In addition, pHLIP largely increased the binding affinity of the nanodrug to PANC-1 cells. The targeted delivery and effective accumulation of MET/GEM-MNP-pHLIP in vivo were confirmed by magnetic resonance imaging enhanced by the underlying magnetic nanoparticles. The tumor growth inhibition of the sequential MET and GEM-MNP-pHLIP treatment were investigated on both subcutaneous and orthotopic tumor mice models. A remarkably improved therapeutic efficacy, for example, up to 91.2% growth inhibition ratio over 30 d of treatment, well-exemplified the novel cascade treatment for pancreatic cancer and the innovative use of MET.