Macropinocytosis of nab-paclitaxel drives macrophage activation in pancreatic cancer

Abstract

Pancreatic cancer is a devastating disease that is largely refractory to currently available treatment strategies. Therapeutic resistance is partially attributed to the dense stromal reaction of PDAC tumors that includes a pervasive infiltration of immunosuppressive (M2) macrophages. Nab-paclitaxel (trade name Abraxane) is a nanoparticle albumin-bound formulation of paclitaxel that, in combination with gemcitabine, is currently the first line treatment for pancreatic cancer. Here, we show that macrophages internalized nab-paclitaxel via macropinocytosis. The macropinocytic uptake of nab-paclitaxel induced macrophage immunostimulatory (M1) cytokine expression and synergized with IFNγ to promote inducible nitric oxide synthase (iNOS) expression in a TLR4-dependent manner. Nab-paclitaxel was internalized by tumor-associated macrophages in vivo, and therapeutic doses of nab-paclitaxel alone, and in combination with gemcitabine, increased the MHCII⁺CD80⁺CD86⁺ M1 macrophage population. These data revealed an unanticipated role for nab-paclitaxel in macrophage activation and rationalize its potential use to target immune evasion in pancreatic cancer.