A Fluorescent Activatable AND‐Gate Chemokine CCL2 Enables In Vivo Detection of Metastasis‐Associated Macrophages

Abstract

We report the novel chemical design of fluorescent activatable chemokines as highly specific functional probes for imaging subpopulations of immune cells in live tumours. Activatable chemokines behave as AND‐gates since they emit only after receptor binding and intracellular activation, showing enhanced selectivity over existing agents. We have applied this strategy to produce mCCL2‐MAF as the first probe for in vivo detection of metastasis‐associated macrophages in a preclinical model of lung metastasis. This strategy will accelerate the preparation of new chemokine‐based probes for imaging immune cell function in tumours.

Near-Infrared Fluorescent Probes for the Detection of Cancer-Associated Proteases

“…The conjugation of activatable fluorophores to small soluble proteins has been also described as an effective approach to improve not only target selectivity but also the biodistribution of fluorophores in vivo . 14 Furthermore, the compatibility of NIR activatable probes with several imaging modalities—from preclinical in vivo imaging to fluorescence-guided surgery—demonstrates their utility for multiple applications, expanding from drug discovery and mechanistic biological studies to more clinically relevant assays. Among these, the design of NIR optoacoustic probes for protease sensing is particularly interesting, 89 given the increased penetration depth of optoacoustic imaging and several clinical studies demonstrating its use for noninvasive imaging in humans.…”

Smart probes for optical imaging of T cells and screening of anti-cancer immunotherapies

“…For instance, our group has demonstrated that the combination of small proteins ( e.g. , chemokines) with pH or protease-activatable fluorophores 128 can be used to target defined subpopulations of immune cells that could not be monitored with a single optical reporter. 129 …”

“…On the other hand, the main shortcoming of transgenic mouse models is their limited translatability to optical imaging in humans, which has encouraged the chemical development of molecular imaging agents that can similarly target subpopulations of immune cells. For instance, our group has demonstrated that the combination of small proteins (e.g., chemokines) with pH or proteaseactivatable fluorophores 128 can be used to target defined subpopulations of immune cells that could not be monitored with a single optical reporter. 129…”

Fluorescent amino acids as versatile building blocks for chemical biology

“…Peptides are excellent scaffolds for biological studies, as they can be used to monitor highly specific molecular interactions with a broad range of biomolecules. Fluorescent peptides have traditionally been synthesized by coupling fluorophores to reactive groups (initially to amines, carboxylic acids and thiols 82 , but now also to imidazoles 83 or phenols 84 ) on the side chains of amino acids or in conveniently placed spacers. However, in some cases, this synthetic approach can alter the native conformation of the peptide or its biological properties (such as functional activity, binding affinity and/or subcellular localization) 85 .…”