Biological evaluation of avidin-based tumor pretargeting with DOTA-Triazole-Biotin constructed via versatile Cu(I) catalyzed click chemistry

Abstract

Background: The biotin-avidin interaction remains a gold standard for the two-step pretargeting approach to image tumor sites. We aim to develop two-step pretargeting systems utilizing ^99mTc labeled biotin functionalized macrocyclic chelating agents synthesized using the highly efficient Cu(I) catalyzed azide–alkyne cycloaddition for potential radioimaging applications.

Methods: A facile synthesis of DOTA-Triazole-Biotin, radiocomplexation with ^99mTc and the pretargeting protocol is described. The synthesis features Cu(I) catalyzed click conjugation between biotinylated azide and propynyl functionalized DO3A. ^99mTc radiolabeling was performed to detect the accumulation of avidin as the pretargeting agent. Cytotoxicity was determined using the trypan blue exclusion assay, macrocolony, and MTT assay. Cell uptake studies were performed using radiolabeled DOTA-Triazole-Biotin and compared with avidin treated cells for 2 h. Tumor imaging was performed in U-87MG cell line implanted tumor bearing nude mice and uptake of the radiotracer was estimated.

Results: All compounds have been successfully characterized by NMR and MS spectroscopy. More than 96% radiolabeling efficiency was obtained and the radioconjugate exhibited sufficient stability under physiological conditions.

Conclusion: To summarize, a new candidate for avidin based two-step pretargeting of tumors has been synthesized and evaluated for potential imaging and diagnostic applications. The chelate possesses high stability under physiological conditions, exhibits effective interaction with its avidin target, and low nonspecific retention in vivo.

Keywords::

• Tumor/nontumor ratio
• dipolar cycloaddition
• tetrazacyclododecane
• receptor binding
• tumor imaging

Acknowledgements

We are grateful to Dr. R. P. Tripathi, Institute of Nuclear Medicine and Allied Sciences, University of Delhi, for providing excellent research facilities.

Declaration of Interest

The work was supported by Defence Research and Development Organization, Ministry of Defence, under R&D project INM-311.