A new tandem peptide modified liposomal doxorubicin for tumor "ecological therapy"

The tumor microenvironment (TME) acts as an ecosystem that includes not only tumor cells, but also stromal cells such as cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). In addition, the abnormal extracellular environment (ECM), of which the mechanical forces are regulated by fibronectin (Fn) and collagen I, orchestrates tumorigenesis and progression by directly promoting invasion and cellular transformation of the ecosystem. Herein, we develop a novel peptide-modified liposome incorporated into doxorubicin (FnBPA5-AAN-Dox) as an ecological therapy system, which targets not only the cellular compartment but also non-cellular components of breast cancer. FnBPA5 is a Fn-binding peptide showing high affinity with relaxed Fn and collagen I in the ECM as well as α-SMA-expressing CAFs. However, the fast clearance by Fn-excreting organs such as the liver and spleen limits the accumulation of FnBPA5-Dox in the TME. The AAN peptide, which targets legumain overexpressed in the TAMs, could extend the circulation time and improve the therapeutic response as well as modulate the tumor immune microenvironment (TMIE). Given twice at an equivalent dose of 5 mg kg^-1 intravenously, the multi-in-one 'ecological therapy' applied AAN-FnBPA5-Dox showed excellent antitumor efficacy in 4T1 breast cancer mice, and the tumor growth inhibition (TGI) is up to 98.20% compared with saline. Immunofluorescence, flow cytometry and reverse transcription polymerase chain reaction (RT-PCR) results revealed that the dramatic improvement in antitumor efficacy can be attributed to the multifunctional targets of the drug delivery system.