Manipulating the function of tumor-associated macrophages by siRNA-loaded lipid nanoparticles for cancer immunotherapy.

The tumor-microenvironment contains large numbers of tumor-associated macrophages (TAMs) which are largely M2 phenotypes and are involved in pro-tumorous functions. Targeting TAMs so as to manipulate them and to modify their functions could be a novel immunotherapy for the treatment of cancer. Such a strategy would involve targeting TAMs with short interfering RNA (siRNA) to modify their functions by silencing certain genes that are responsible for their M2 polarization. In this study, a lipid nanoparticle (LNP) formulation was used to target and deliver siRNA to TAMs. The LNP was mainly composed of a novel, pH-sensitive cationic lipid, referred to as the CL4H6 lipid, which had previously been optimized to target hepatocytes. The optimized siRNA-loaded CL4H6-LNPs were selectively and efficiently taken up and showed strong gene silencing activity in TAMs in a human tumor xenograft model in nude mice. Furthermore, an anti-tumor therapeutic response in the same tumor model was obtained by targeting TAMs using the optimized siRNA-loaded CL4H6-LNPs. The anti-tumor therapeutic response was obtained through the silencing of the signal transducer and activator of transcription 3 (STAT3) and hypoxia inducible factor 1 α (HIF-1α), which resulted in an increase in the level of infiltrated macrophage (CD11b+ cells) into the tumor-microenvironment (TME) as well as a tendency to increase the concentration of M1 macrophages (CD169+ cells). The treatment also resulted in reversing the pro-tumorous functions of TAMs -mainly angiogenesis and tumor cell activation-, as evidenced by a decrease in the related gene expression at the mRNA level. This research has promising clinical and pharmaceutical applications for achieving novel macrophage-based cancer immunotherapy.