Abstract
AbstractRadiolabelled bisphosphonates (BPs) and [18F]NaF (18F-fluoride) are the two types of radiotracers available to image calcium mineral (e.g. bone), yet only [18F]NaF has been widely explored for the non-invasive molecular imaging of extraosseous calcification (EC) using positron emission tomography (PET) imaging. These two radiotracers bind calcium mineral deposits via different mechanisms, with BPs chelating to calcium ions and thus being non-selective, and [18F]NaF being selective for hydroxyapatite (HAp) which is the main component of bone mineral. Considering that the composition of EC has been reported to include a diverse range of non-HAp calcium minerals, we hypothesised that BPs may be more sensitive for imaging EC due to their ability to bind to both HAp and non-HAp deposits. We report a comparison between the 68Ga-labelled BP tracer [68Ga]Ga-THP-Pam and [18F]NaF for PET imaging in a rat model of EC that develops macro- and microcalcifications in several organs. Macrocalcifications were identified using preclinical computed tomography (CT) and microcalcifications were identified using µCT-based 3D X-ray histology (XRH) on isolated organs ex vivo. The morphological and mineral analysis of individual calcified deposits was performed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). PET imaging and ex vivo analysis results demonstrated that while both radiotracers behave similarly for bone imaging, the BP-based radiotracer [68Ga]Ga-THP-Pam was able to detect EC more sensitively in several organs in which the mineral composition departs from that of HAp. Our results strongly suggest that BP-based PET radiotracers such as [68Ga]Ga-THP-Pam may have a particular advantage for the sensitive imaging and early detection of EC by being able to detect a wider array of relevant calcium minerals in vivo than [18F]NaF, and should be evaluated clinically for this purpose.
Funder
Engineering and Physical Sciences Research Council
Wellcome Trust
Publisher
Springer Science and Business Media LLC
Reference52 articles.
1. Russell, R. G. G., Watts, N. B., Ebetino, F. H. & Rogers, M. J. Mechanisms of action of bisphosphonates: Similarities and differences and their potential influence on clinical efficacy. Osteoporos. Int. 19, 733–759. https://doi.org/10.1007/s00198-007-0540-8 (2008).
2. Clarke, B. Normal bone anatomy and physiology. Clin. J. Am. Soc. Nephrol. 3, S131–S139. https://doi.org/10.2215/CJN.04151206 (2008).
3. Cole, L. E., Vargo-Gogola, T. & Roeder, R. K. Targeted delivery to bone and mineral deposits using bisphosphonate ligands. Adv. Drug Del. Rev. 99, 12–27. https://doi.org/10.1016/j.addr.2015.10.005 (2016).
4. Subramanian, G., McAfee, J. G., Blair, R. J., Kallfelz, F. A. & Thomas, F. D. Technetium 99m methylene diphosphonate: A superior agent for skeletal imaging: Comparison with other technetium complexes. J. Nucl. Med. 16, 744–755 (1975).
5. Cook, G. J. R. Imaging with radiolabelled bisphosphonates. Bone 137, 372. https://doi.org/10.1016/j.bone.2020.115372 (2020).