First Comparison Study of the In Vitro and In Vivo Properties of a Randomly and Site-Specifically Conjugated SPECT/NIRF Monomolecular Multimodal Imaging Probe (MOMIP) Based on an aza-BODIPY Fluorophore

Among all approaches in molecular imaging, the combination of near-infrared fluorescence imaging (NIRF) with radioisotopic imaging (PET or SPECT) allows one to benefit from the advantages of each of the imaging techniques, which are very complementary and of comparable sensitivity. To this end, the construction of monomolecular multimodal probes (MOMIP) has made it possible to combine the two imaging modalities within the same molecule, thus limiting the number of bioconjugation sites and yielding more homogeneous conjugates compared with those prepared through sequential conjugation. However, in order to optimize the bioconjugation strategy and, at the same time, the pharmacokinetic and biodistribution properties of the resulting imaging agent, a site-specific approach may be preferred. To further investigate this hypothesis, random and glycan-based site-specific bioconjugation approaches were compared thanks to a SPECT/NIRF bimodal probe based on an aza-BODIPY fluorophore. The overall experiments conducted in vitro and in vivo on HER2-expressing tumors demonstrated a clear superiority of the site-specific approach to improve affinity, specificity, and biodistribution of the bioconjugates.

Automated summary

The combination of near-infrared fluorescence imaging (NIRF) with radioisotopic imaging (PET or SPECT) allows for the advantages of each technique to be utilized, resulting in complementary and equally sensitive imaging. Monomolecular multimodal probes (MOMIP) have been developed to combine both imaging modalities within a single molecule, reducing the number of bioconjugation sites and producing more uniform conjugates. In order to optimize the bioconjugation strategy and the pharmacokinetic and biodistribution properties of the imaging agent, a site-specific approach may be preferred. Comparisons between random and glycan-based site-specific bioconjugation approaches using a SPECT/NIRF bimodal probe showed that the site-specific approach significantly improved affinity, specificity, and biodistribution of the bioconjugates, as evidenced by in vitro and in vivo experiments on HER2-expressing tumors.