Development of NIR-II Photoacoustic Probes Tailored for Deep-Tissue Sensing of Nitric Oxide

Abstract

Photoacoustic (PA) imaging has emerged as a reliable in vivo technique for diverse biomedical applications ranging from disease screening to analyte sensing. Most contemporary PA imaging agents employ NIR-I light (650−900 nm) to generate an ultrasound signal; however, there is significant interference from endogenous biomolecules such as hemoglobin that are PA active in this window. Transitioning to longer excitation wavelengths (i.e., NIR-II) reduces the background and facilitates the detection of low abundance targets (e.g., nitric oxide, NO). In this study, we employed a two-phase tuning approach to develop APNO-1080, a NIR-II NO-responsive probe for deep-tissue PA imaging. First, we performed Hammett and Brønsted analyses to identify a highly reactive and selective aniline-based trigger that reacts with NO via N-nitrosation chemistry. Next, we screened a panel of NIR-II platforms to identify chemical structures that have a low propensity to aggregate since this can diminish the PA signal. In a head-tohead comparison with a NIR-I analogue, APNO-1080 was 17.7-fold more sensitive in an in vitro tissue phantom assay. To evaluate the deep-tissue imaging capabilities of APNO-1080 in vivo, we performed PA imaging in an orthotopic breast cancer model and a heterotopic lung cancer model. Relative to control mice not bearing tumors, the normalized turn-on response was 1.3 ± 0.12 and 1.65 ± 0.07, respectively.

Recent Progress of Cyanine Fluorophores for NIR‐II Sensing and Imaging

“…In 2021, employing a two‐phase tuning approach, Chan group developed a NO‐responsive NIR‐II probe APNO‐1080. Applying APNO‐1080, they achieved the deep‐tissue NO imaging in an orthotopic breast cancer model and a heterotopic lung cancer model for the first time [55] …”

Targeted contrast agents and activatable probes for photoacoustic imaging of cancer

“…To this end, we developed APNO-1080, a NIR-II PA probe for NO, by employing a two-phase tuning approach. 262 First, we identified a new aniline-based trigger by varying the electronics of the substituent at the para position. Second, we installed the optimized trigger onto a panel of five NIR-II absorbing cyanine dyes (Fig.…”

Fluorescent Chemosensors for Ion and Molecule Recognition: The Next Chapter

“…Another approach capable of achieving enhanced tissue penetration depth is photoacoustic (PA) imaging, where optical excitation is coupled with acoustic detection (light in, sound out), thereby enabling high resolution and deep tissue imaging at centimetre depths (Knox and Chan, 2018;Cheng et al, 2020;Ren et al, 2020;Chen et al, 2021;Lucero et al, 2021). PA probes that can be activated by specific biological species are of particular interest as they have the potential to complement other clinically used diagnostic systems (i.e., Ultrasound) for disease diagnosis.…”

“…PA probes that can be activated by specific biological species are of particular interest as they have the potential to complement other clinically used diagnostic systems (i.e., Ultrasound) for disease diagnosis. Within this arena, the Chan group has developed nitric oxide (NO) triggered probes for acoustogenic imaging (Lucero et al, 2021). For example APNO-5 (7), could be used for the ratiometric imaging of endogenous NO in vivo (BALB/c mice) in a murine lipopolysaccharide-induced inflammation model (Reinhardt et al, 2018).…”