Cu-64-Labeled Phosphonate Cross-Bridged Chelator Conjugates of c(RGDyK) for PET/CT Imaging of Osteolytic Bone Metastases

Ocak M., Beaino W., White A., Zeng D., CAI Z., ANDERSON C. J.

CANCER BIOTHERAPY AND RADIOPHARMACEUTICALS, vol.33, no.2, pp.74-83, 2018 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 33 Issue: 2
  • Publication Date: 2018
  • Doi Number: 10.1089/cbr.2017.2419
  • Journal Name: CANCER BIOTHERAPY AND RADIOPHARMACEUTICALS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.74-83
  • Keywords: osteoclast, v3 integrin, click chemistry, copper-64, RADIOLABELED RGD PEPTIDES, ALPHA(V)BETA(3) INTEGRIN, BIOLOGICAL EVALUATION, MACROCYCLIC CHELATORS, COPPER RADIONUCLIDES, VITRONECTIN RECEPTOR, IN-VIVO, RESORPTION, OSTEOCLAST, EXPRESSION
  • Istanbul University Affiliated: Yes

Abstract

Objective: The goal of this research was to evaluate c(RGDyK) conjugated to phosphonate-based cross-bridged chelators using Cu-free click chemistry in the 4T1 mouse mammary tumor bone metastasis model in comparison with Cu-64-CB-TE2A-c(RGDyK), which previously showed selective binding to integrin v3 on osteoclasts. Experimental: Two phosphonate-based cross-bridged chelators (CB-TE1A1P and CB-TE1K1P) were conjugated to c(RGDyK) through bio-orthogonal strain-promoted alkyne-azide cycloaddition. In vitro and in vivo evaluation of the Cu-64-labeled TE1A1P-DBCO-c(RGDyK) (AP-c(RGDyK)), TE1K1P-PEG4-DBCO-c(RGDyK) (KP-c(RGDyK)), and CB-TE2A-c(RGDyK) were compared in the 4T1 mouse model of bone metastasis. The affinities of the unconjugated and chelator-c(RGDyK) analogs for v3 integrin were determined using a competitive-binding assay. For in vivo evaluation, BALB/c mice were injected with 1x10(5) 4T1/Luc cells in the left ventricle. Formation of metastases was monitored by bioluminescence imaging (BLI) followed by small-animal PET/CT 2 h postinjection of radiotracers. Results: The chelator-peptide conjugates showed similar affinity to integrin v3, in the low nM range. PET imaging demonstrated a higher uptake in bones having metastases for all Cu-64-labeled c(RGDyK) analogs compared with bones in nontumor-bearing mice. The correlation between uptake of Cu-64-AP-c(RGDyK) and Cu-64-KP-c(RGDyK) in bones with metastases based on PET/CT imaging, and osteoclast number based on histomorphometry, was improved over the previously investigated Cu-64-CB-TE2A-c(RGDyK). Conclusion: These data suggest that the phosphonate chelator conjugates of c(RDGyK) peptides are promising PET tracers suitable for imaging tumor-associated osteoclasts in bone metastases.