Metformin‐Mediated Immunosuppressive Microenvironment Remodeling in Combination with Chemotherapy via a Spatial‐Specific Multi‐Responsive Carrier‐Free Self‐Assembled Nanoparticle

Abstract The complex tumor immune pathology requires a precise spatial‐control release of the combination drugs, but most multi‐drug loaded nanoparticles release all drugs simultaneously in the tumor microenvironment (TME), making them difficult to reach the exact action site. To address the spatial specific release of drugs, a carrier‐free self‐assembled multi‐responsive nanodrug delivery system is designed, in which p‐phthalaldehyde (p‐APA) and dithiodipropionic acid are used to connect metformin (MET) and 7‐ethyl‐10‐hydroxycamptothecin (SN38) through a matrix metalloproteinase‐2 (MMP‐2) responsive peptide, and dipyridamole (DIP) is further loaded (MA‐GPLGVRGDK‐SS‐SN38@DIP, MR NPs). The MR NPs first target tumor by enhanced permeability and retention effect, then the highly expressed MMP‐2 at tumor site cleaves GPLGVRGDK, breaking the nanoparticle into three parts—DIP, MA‐GPLG, and VRGDK‐SS‐SN38. DIP automatically binds with platelets in TME, inhibiting their function and restraining tumor metastasis. MA‐GPLG releases MET in response to the acidic TME to reverse the immunosuppressive networks through PD‐L1 downregulation and M2‐like macrophages repolarization. Moreover, VRGDK‐SS‐SN38 binds to the overexpressed integrin α_vβ₃ receptor to achieve tumor cells specific delivery and precise killing. Overall, this study offers an intelligent spatial‐specific multi‐responsive carrier‐free drug delivery system in breast cancer, which releases drug spatial specifically, therefore reverses the tumor immunosuppressive microenvironment and inhibits metastasis.