NIR Bioluminescence Probe Enables Discovery of Diet-Induced Modulation of the Tumor Microenvironment via Nitric Oxide

Abstract

Nitric oxide (NO) plays a critical role in acute and\nchronic inflammation. NO’s contributions to cancer are of particular interest\ndue to its context-dependent bioactivities. For example, immune cells initially\nproduce cytotoxic quantities of NO in response to the nascent tumor. However,\nit is believed that this fades over time and reaches a concentration that\nsupports the tumor microenvironment (TME). These complex dynamics are further\ncomplicated by other factors, such as diet and oxygenation, making it\nchallenging to establish a complete picture of NO’s impact on tumor progression.\nAlthough many activity-based sensing (ABS) probes for NO have been developed,\nonly a small fraction have been employed in vivo and fewer yet are\npractical in cancer models where the NO concentration is < 200 nM. To overcome\nthis outstanding challenge, we have developed BL660-NO, the first ABS\nprobe for NIR bioluminescence imaging of NO in cancer. Owing to the low intrinsic\nbackground, high sensitivity, and deep tissue imaging capabilities of our\ndesign, BL660-NO was successfully employed to visualize endogenous NO\nin cellular systems, a human liver metastasis model, and a murine breast cancer\nmodel. Importantly,\nits exceptional performance facilitated the design of a dietary study to examine\nthe impact of NO on the TME by varying the intake of fat. BL660-NO provides\nthe first direct molecular evidence that intratumoral NO becomes elevated in mice\nfed a high-fat diet who became obese with larger tumors compared to control\nanimals on a low-fat diet. These results indicate that an inflammatory diet can\nincrease NO production via recruitment of macrophages and overexpression of iNOS which\nin turn can drive tumor progression.