A calcium-sensor for NMR/MRI based diagnostic imaging using hyperpolarized xenon

Conventional diagnostic imaging reveals changes in morphology or organ functions that ­occur at a later stage than impacts visible at the molecular level. It is thus of high relevance to focus on early responses in molecular imaging to understand the biochemical pathways of ­diseases and effects of substances. Notably, magnetic resonance imaging (MRI) and the ­nuclear ­magnetic resonance (NMR) are potent modalities in biomedical imaging. However, conventional NMR/MRI which detects the water proton signal in biological samples ­suffers from intrinsically low sensitivity. The present new technology combines highly sensitive ­hyperpolarized xenon ­biosensors for NMR/MRI to non-invasively sense the critical second messenger calcium with high sensitivity.

This technology provides a calcium-sensor for NMR and MRI, based on spectral changes of the NMR signature of temporarily encapsulated hyperpolarized ¹²⁹Xenon caused by calcium-dependent changes of the local environment of a xenon-binding molecule coupled to calcium-binding proteins or peptides. A xenon-binding cage-like molecule such as cryptophane is conjugated to a peptide such as RS20 that binds to an EF hand protein such as calmodulin in a calcium-dependent manner. When hyperpolarized ¹²⁹xenon interacts with the cryptophane cage, its NMR signal exhibits a different chemical shift and/or switches Hyper-CEST efficiency when the peptide is bound to calmodulin as opposed to the unbound state; calcium binding and in vivo signaling can thus be read out via the chemical shift and/or changes in the Hyper-CEST effect. Since the ¹²⁹xenon is not bound covalently to the cage, the sensor can be delivered in advance, independently of the hyperpolarization lifetime, giving a significant advantage compared to compounds containing ¹³C or ¹⁵N that have short decay rates.

• in vitro, in vivo and ex vivo detection of calcium changes via NMR and MRI & Hyper-CEST
• in particular for diagnosing and/or monitoring treatment of diseases in which calcium uptake, storage, utilization or excretion is affected (e.g. endrocinological, gastrointestinal, inflammatory or bone-related diseases)

Proof of concept.