Molecular imaging of fibrosis using a novel collagen-binding peptide labelled with 99mTc on SPECT/CT

Abstract

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 couplingTc. Labelling efficiency of Tc-CBP1495 was 95.06 ± 1.08 %. The physico-chemical properties, tracer kinetics and biodistribution ofTc-CBP1495 were carried out, and showed that the peptide stably chelated Tc in vitro and in vivo. SPECT/CT imaging withTc-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, andTc-labelled CBP1495 may be a promising radiotracer for the molecular imaging of fibrosis.

Molecular Probes for Imaging Fibrosis and Fibrogenesis

“…[75] The efficacy of probe 99m Tc-CBP1495 ( Figure 6B)w as evaluated in rat modelso fb leomycin-induced pulmonary fibrosis and CCl 4 -induced liver fibrosis. [73] The authors demonstrated al inear correlation between hydroxyproline contenta nd ex vivo 99m Tc -CBP1495 uptake. However,p robe 99m Tc-CBP1495 has as hort circulationt ime, which limits its accumulation in target tissues.…”

“…[72] Another collagen-binding peptidel abeled with 99m Tc wasr eported recently. [73] Peptide CBP1495i sapeptide domain from pro-MMP-2, [74] which is ap recursor of the enzyme MMP-2 that interacts with type Ic ollagen. [75] The efficacy of probe 99m Tc-CBP1495 ( Figure 6B)w as evaluated in rat modelso fb leomycin-induced pulmonary fibrosis and CCl 4 -induced liver fibrosis.…”

“…[72] B) Structure of the collagen-binding SPECT probe 99m Tc -CBP1495 derivedf rom ap eptidedomain from pro-MMP-2. [73] C) Structures of the collagen-binding PET probes 64 Cu-CBP7, [77] Al 18 F-CBP9, [79] Al 18 F-CBP10, [79] and 68 Ga-CBP8. [80] 64 Cu-CBP11 [77] and 68 Ga-CBP12 [80] are the nonbindingi somers of 64 Cu-CBP7 and 68 Ga-CBP8, respectively,i nw hich one l-cysteine was replaced by d-cysteine.…”

Molecular imaging of fibrosis: recent advances and future directions

“…Several other molecular probes allow for noninvasive collagen detection using SPECT or PET imaging techniques (45,(47)(48)(49). Collagelin is a high-affinity collagen probe identified from a screen focused on the platelet glycoprotein VI binding site on collagens I and III (47).…”

Imaging the Cardiac Extracellular Matrix

“…2.4) [33, 47]. In lung and liver models, other peptide-based probes accumulate in fibrotic tissue ([14, 78], p. 201). There have been few other probes demonstrated in the literature, but a recent review has highlighted potential targets for collagen probes [72].…”