Molecular imaging of fibrosis using a novel collagen-binding peptide labelled with Tc on SPECT/CT.

Fibrosis, closely related to chronic various diseases, is a pathological process characterised by the accumulation of collagen (largely collagen type I). Non-invasive methods are necessary for the diagnosis and follow-up of fibrosis. This study aimed to develop a collagen-targeted probe for the molecular imaging of fibrosis. We identified CPKESCNLFVLKD (CBP1495) as an original collagen-binding peptide using isothermal titration calorimetry and enzyme-linked immunosorbent assay. CBP1495 effectively bound to collagen type I (K  = 861 nM) and (GPO) (K  = 633 nM), a collagen mimetic peptide. Western blot and histochemistry validated CBP1495 targeting collagen in vitro and ex vivo. (Gly-(D)-Ala-Gly-Gly) was introduced to CBP1495 for coupling Tc. Labelling efficiency of Tc-CBP1495 was 95.06 ± 1.08 %. The physico-chemical properties, tracer kinetics and biodistribution of Tc-CBP1495 were carried out, and showed that the peptide stably chelated Tc in vitro and in vivo. SPECT/CT imaging with Tc-CBP1495 was performed in rat fibrosis models, and revealed that Tc-CBP1495 significantly accumulated in fibrotic lungs or livers of rats. Finally, Tc-CBP1495 uptake and hydroxyproline (Hyp), a specific amino acid of collagen, were quantitatively analysed. The results demonstrated that Tc-CBP1495 uptake was positvely correlated with Hyp content in lungs (P < 0.0001, r  = 0.8266) or livers (P < 0.0001, r  = 0.7581). Therefore, CBP1495 is a novel collagen-binding peptide, and Tc-labelled CBP1495 may be a promising radiotracer for the molecular imaging of fibrosis.