Proteasome Inhibitor-Loaded Micelles Enhance Antitumor Activity Through Macrophage Reprogramming by NF-κB Inhibition

Macrophage reprogramming toward a tumor-attacking phenotype is a promising treatment strategy, yet such strategies are scarce and it is not clear how to combine them with cytotoxic therapies that are often used to treat solid tumors. Here, we evaluate whether a micelle-encapsulated proteasome inhibitor, that is, the peptide aldehyde drug MG132, which is cytotoxic to cancer cells, can reprogram macrophages to attack the tumor. Through in vitro studies, we demonstrated that the proteasome inhibition reduces nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling-a known promoter of tumor-supporting macrophages and chemoresistance-in both cancer cells and macrophages. In in vivo studies, we showed that, although free MG132 did not affect the macrophage phenotype in tumors even at its maximum tolerated dose, the micellar formulation of MG132 safely achieved simultaneous cancer cell killing and macrophage reprogramming, thereby enhancing the antitumor efficacy in a syngeneic, orthotopic breast cancer model.