A bioreducible N-oxide-based probe for photoacoustic imaging of hypoxia

Abstract

Hypoxia occurs when limited oxygen supply impairs physiological functions and is a pathological hallmark of many diseases including cancer and ischemia. Thus, detection of hypoxia can guide treatment planning and serve as a predictor of patient prognosis. Unfortunately, current methods suffer from invasiveness, poor resolution and low specificity. To address these limitations, we present Hypoxia Probe 1 (HyP-1), a hypoxia-responsive agent for photoacoustic imaging. This emerging modality converts safe, non-ionizing light to ultrasound waves, enabling acquisition of high-resolution 3D images in deep tissue. HyP-1 features an N-oxide trigger that is reduced in the absence of oxygen by heme proteins such as CYP450 enzymes. Reduction of HyP-1 produces a spectrally distinct product, facilitating identification via photoacoustic imaging. HyP-1 exhibits selectivity for hypoxic activation in vitro, in living cells, and in multiple disease models in vivo. HyP-1 is also compatible with NIR fluorescence imaging, establishing its versatility as a multimodal imaging agent.

Recent progress in photoacoustic molecular imaging

“…The second strategy seeks to recover the signal contribution from the molecular probes by exploring the temporal changes of the detected signals, assuming that the changes are confined only to the local molecular probes of interest [27, 74–83]. The temporal signal changes can be induced externally ( e.g.…”

“…, light illumination) [36, 74] or internally ( e.g. , chemical cleavage) [75, 76, 83]. For example, several groups (including the authors’) have explored the reversible photoswitching capability of several fluorescent (Dronpa, rsTagRFP) and non-fluorescent (BphP1, AGP1) proteins [36, 74, 84].…”

“…Knox et al reported an NIR agent for PA imaging of tissue hypoxia, which features an N-oxide-based trigger that can undergo facile bioreduction in the absence of oxygen and shifts the optical absorption peak from 670 nm to 760 nm (Fig. 3a) [83]. By taking ratiometric measurement, the hypoxic tissue environment ( e.g ., tumor and ischemia) can be imaged.…”

“…(a) PACT images showing that HyP-1, an NIR hypoxia-response dye, changed its absorption peak from 670 nm to 760 nm five hours after exposure to the hypoxic environment of a breast tumor in a mouse [83]. (b) PACT images of a mouse breast tumor before and 24h after i.v.…”

Photoacoustic Probes for Molecular Detection: Recent Advances and Perspectives

“…f) The PA 770 imaging of the tumor‐bearing and control flank before and 5 h after injection of HyP‐1 (50 µL, 0.3 mg kg −1 ) and g) PA 770 of the ischemic and control leg before and 1 h following injection of HyP‐1 (50 µL, 50 × 10 −6 m ). Reproduced with permission . Copyright 2017, Nature Publishing Group.…”