Peroxynitrite Production Induced by LPS and X-ray Treatment Enhances Cellular Incorporation of Porphyrin in Mouse RAW264 Macrophages

Photodynamic therapy (PDT) is a minimally invasive cancer therapy that combines the accumulation of photosensitizers such as porphyrins in cancer cells with laser irradiation. I have previously reported that mitochondrially derived reactive oxygen species (ROS) regulate the expression of a porphyrin transporter, heme carrier protein 1 (HCP1), and increase porphyrin accumulation in cancer cells. Tumors that contain activated macrophages, referred to as tumor-associated macrophages (TAMs), have been reported to have increased malignancy. TAMs produce nitric oxide (NO), via the expression of inducible NO synthase (iNOS), and the highly reactive nitrogen species, peroxynitrite, which is produced by the reaction of NO with superoxide. Here, I examined the relationship between peroxynitrite, HCP1 expression, and intracellular porphyrin uptake in the murine macrophage cell line RAW264. RAW264 cells were activated by lipopolysaccharide (LPS) treatment which resulted in increased iNOS expression and NO production. Additional X-ray irradiation resulted in the generation of ROS and the subsequent generation of peroxynitrite. Importantly, LPS and X-ray co-treatment significantly enhanced HCP1 expression and porphyrin accumulation in cells, suggesting that the peroxynitrite upregulates the porphyrin transporter, HCP1. Therefore, TAMs may be effectively targeted with PDT, and tumor progression may be suppressed in general by agents that target the activation of macrophages.