Molecular Probes for Imaging of Hypoxia in the Retina

Abstract

Hypoxia has been associated with retinal diseases which lead the causes of irreversible vision loss, including diabetic retinopathy, retinopathy of prematurity, and age-related macular degeneration. Therefore, technologies for imaging hypoxia in the retina are needed for early disease detection, monitoring of disease progression, and assessment of therapeutic responses in the patient. Toward this goal, we developed two hypoxia-sensitive imaging agents based on nitroimidazoles which are capable of accumulating in hypoxic cells in vivo. 2-nitroimidazole or Pimonidazole was conjugated to fluorescent dyes to yield the imaging agents HYPOX-1 and HYPOX-2. Imaging agents were characterized in cell culture and animal models of retinal vascular diseases which exhibit hypoxia. Both HYPOX-1 and -2 were capable of detecting hypoxia in cell culture models with >10:1 signal-to-noise ratios without acute toxicity. Furthermore, intraocular administration of contrast agents in mouse models of retinal hypoxia enabled ex vivo detection of hypoxic tissue. These imaging agents are a promising step toward translation of hypoxia-sensitive molecular imaging agents in preclinical animal models and patients.

Evidence for an enduring ischaemic penumbra following central retinal artery occlusion, with implications for fibrinolytic therapy

“…The tracer localises to both penumbra and infarct in the brain, for example, and its tissue kinetics are too slow for rapidly evolving pathologies such as penumbra-to-umbra conversion (Takasawa et al, 2008;Alawneh et al, 2014). Nevertheless, a fluorescein-conjugated nitroimidazole probe has recently been developed for potential ophthalmic use, and shows promise in the rodent oxygen-induced retinopathy model (Evans et al, 2014). This augurs well, especially given the durability of the ischaemic penumbra in the mature retina.…”

Imaging of Hypoxia in Retinal Vascular Disease

“…In preliminary studies, fluorescein isothiocyanate (FITC) was conjugated to a 2-nitroimidazole containing reagent to create the HYPOX-1 probe, and also to pimonidazole to create HYPOX-2. Both HYPOX-1 and HYPOX-2 formed adducts leading to accumulation in a variety of hypoxic retinal cells and allowed for imaging with excellent signal-to-noise ratio in vitro [120]. Furthermore, these imaging agents were capable of detecting hypoxic areas ex vivo in the retinas oxygen induced retinopathy (OIR) mice with no apparent toxicity [120].…”

“…Both HYPOX-1 and HYPOX-2 formed adducts leading to accumulation in a variety of hypoxic retinal cells and allowed for imaging with excellent signal-to-noise ratio in vitro [120]. Furthermore, these imaging agents were capable of detecting hypoxic areas ex vivo in the retinas oxygen induced retinopathy (OIR) mice with no apparent toxicity [120]. Following the success of these fluorescent imaging agents, a new probe, HYPOX-3, was developed in order to create an "on-off" imaging agent for hypoxia [121].…”

Novel Retinal Imaging Technologies

“…Real time imaging with SO was able to quickly quantify RGC death. Evans et al, [40] discovered HY-POX-1 and HYPOX-2 are a promising step toward translation of hypoxia-sensitive molecular imaging agents in preclinical animal models and patients. Dearling et al, [41] reviewed the use of molecular imaging to measure in vivo distribution of nanoparticles, and summerized that nanoparticles are an important and promising target for developing the application of molecular imaging.…”