Characterization of 64Cu-DOTA-Conatumumab: A PET Tracer for In Vivo Imaging of Death Receptor 5

Journal of Nuclear Medicine

Art Hewig¹  Terry Sharp¹  Dah-Ren Hwang¹  Aviv Hagooly¹  Jeffrey L. Evelhoch¹  Qing Chen¹  Thomas Arroll¹  Greg Friberg¹  Tadahiko Kohno¹  Raffaella Rossin¹  Michael J. Welch¹  Brian Gliniak¹  Paula Kaplan-Lefko¹  Robert Radinsky¹ 

关键词: conatumumab;    death receptor 5;    PET;    tracer;    ⁶⁴Cu;   

DOI  :  10.2967/jnumed.110.086157

学科分类：医学（综合）

来源: Society of Nuclear Medicine

【 摘 要 】

Conatumumab is a fully human monoclonal antibody that binds to and activates human death receptor 5 (DR5; also known as TRAIL receptor 2). The purpose of this study was to characterize 64Cu-labeled conatumumab as a PET tracer for imaging DR5 in tumors. Methods: DOTA-conatumumab was synthesized by incubating conatumumab with 2,2′,2″-(10-(2-(2,5-dioxopyrrolidin-1-yloxy)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (DOTA-NHS). The absolute numbers of DOTA molecules per conatumumab molecules were determined by matrix-assisted laser desorption ionization mass spectrometry and electrospray ionization quadrupole time-of-flight mass spectrometry. 64Cu-DOTA-conatumumab was prepared by incubating 64CuCl2 (33–222 MBq) with DOTA-conatumumab at 37°C for 1 h. Binding of conatumumab and DOTA-conatumumab to Fc-coupled human DR5 (huTR2-Fc) was tested in a kinetic analysis assay, and the biologic activity of copper-DOTA-conatumumab was measured using a caspase-3/7 luminescent assay. In vivo evaluation of DOTA-conatumumab and copper-DOTA-conatumumab was done in severe combined immunodeficiency mice bearing Colo205 xenografts: tissue uptake was determined with biodistribution studies, and small-animal PET and autoradiography were used to determine the uptake of 64Cu-DOTA conatumumab into tumors and other tissues. Results: DOTA-conatumumab was prepared with an average of 5 DOTA molecules per conatumumab molecule. The in vitro median effective concentration required to induce a 50% effect of DOTA-conatumumab and conatumumab from the assay were 389 and 320 pM, respectively. The median effective dose (±SD) of DOTA-conatumumab and conatumumab via the caspase assay was 135 ± 31 and 128 ± 30 pM, respectively. In female CB17 severe combined immunodeficiency mice bearing Colo205 xenografts, DOTA-conatumumab and conatumumab inhibited tumor growth to the same extent. Small-animal PET studies showed tumor uptake at 24 h after injection of the tracer, with a mean standardized uptake value of 3.16 (n = 2). Tumor uptake was decreased by the coadministration of 400 μg of unlabeled conatumumab (mean standardized uptake value, 1.55; n = 2), suggesting saturable uptake. Tissue uptake determined by biodistribution studies was in agreement with the small-animal PET findings. Conclusion: These results suggest that 64Cu-DOTA-conatumumab is a potential PET tracer for imaging DR5 in tumors and may be useful for measuring on-target occupancy by conatumumab.

【 授权许可】

Unknown