Remodeling tumor immune microenvironment via targeted blockade of PI3K-γ and CSF-1/CSF-1R pathways in tumor associated macrophages for pancreatic cancer therapy

Immunotherapy has exhibited great potential in cancer treatment. However, for immunosuppressive tumors such as pancreatic cancer, immunotherapy is far from satisfactory. PI3K-γ and colony stimulating factor-1/colony stimulating factor-1 receptor (CSF-1/CSF-1R) pathways are involved in the infiltration and polarization of immunosuppressive cells including M2 tumor associated macrophages (M2 TAMs), causing a suppressive tumor immune microenvironment (TIME) in pancreatic cancer. Herein, a M2 TAM targeting nanomicelle was developed to co-deliver PI3K-γ inhibitor NVP-BEZ 235 and CSF-1R-siRNA for specific TAMs reprogramming and antitumor immune responses activation. M2 TAM targeting peptide M2pep was modified on a mixed micelle, which was potent to co-encapsulate BEZ 235 and CSF-1R siRNA. The formulated nanomicelle increased M2 TAM targeting efficiency both in vitro and in vivo. Compared with single pathway blockade, dual blockade of PI3k-γ and CSF-1R demonstrated enhanced TAM remodeling effects by reducing M2 TAM level and elevating M1 TAM level, and also suppressed tumor infiltration of myeloid-derived suppressor cells (MDSCs). Consequently, the M2 TAM targeting reprogramming system activated antitumor immune responses and achieved enhanced anti-pancreatic tumor effects via PI3K-γ blockade and downregulation of CSF-1R. The M2pep modified nanomicelle provides a promising method for co-delivery of siRNA and small molecule inhibitor to M2 TAM. Dual inhibition of both PI3K-γ and CSF-1R can remodel TIME and activate antitumor immune responses synergistically, providing an alternative approach for pancreatic cancer treatment.