Radiolabeled 111In-FGF-2 Is Suitable for In Vitro/Ex Vivo Evaluations and In Vivo Imaging

Fibroblast growth factor-2 (FGF-2) is a potent modulator of cell growth and regulation, with improper FGF-2 signaling being involved in impaired responses to injury or even cancer. Therefore, the exploitation of FGF-2 as a therapeutic drives the prerequisite for effective insight into drug disposition kinetics. In this article, we present an In-111-radiolabeled FGF-2 derivative for noninvasive imaging in small animals deploying single photon emission tomography (SPECT). In-111-FGF-2 is equally well suitable for in vitro and ex vivo investigations as I-125-FGF-2. Furthermore, FGF-2 permits the performance of in vivo imaging, for example for the analysis of FGF-2 containing pharmaceutical formulations in developmental or preclinical stages. In-111-FGF-2 had affinity for the low-molecular-weight heparin enoxaparin identical to that of unlabeled FGF-2 (K-d: 0.6 +/- 0.07,mu M and 0.33 +/- 0.03 mu M, respectively) as assessed by isothermal titration calorimetry. The binding of In-111-FGF-2 to heparan sulfate proteoglycans (HPSGs) and the biological activity were comparable to those of unlabeled FGF-2, with EC50 values of 12 +/- 2 pM and 25 +/- 6 pM, respectively. In vivo biodistribution in healthy nude mice indicated a predominant accumulation of In-111-FGF-2 in filtering organs and minor uptake in the retina and the salivary and pituitary glands, which was confirmed by SPECT imaging. Therefore, In-111-FGF-2 is a valid tracer for future noninvasive animal imaging of FGF-2 in pharmaceutical development.