Biodistribution and planar gamma camera imaging of 123I- and 131I-labeled F(ab′)2 and Fab fragments of monoclonal antibody 14C5 in nude mice bearing an A549 lung tumor

Detection of antigen 14C5, involved in substrate adhesion and highly expressed on the membrane of many carcinomas, including lung cancer, provides important diagnostic information that can influence patient management. The aim of this study was to evaluate the biodistribution and planar gamma camera imaging characteristics of radioiodinated F(ab')2 and Fab fragments of monoclonal antibody (rnAb) 14C5 in tumor-bearing mice. Methods: F(ab)2 and Fab 14C5 fragments were radioiodinated using the Iodo-Gen method. In vitro stability, binding specificity and affinity of 125 I-labeled 14C5 fragments were studied in A549 lung carcinoma cells. Biodistribution, blood clearance and tumor-targeting characteristics of 131 I-labeled 14C5 fragments and intact mAb 14C5 were studied in Swiss nu/nu mice bearing A549 lung carcinoma tumors. Planar gamma imaging illustrated the potential use of these 123 I-labeled 14C5 fragments for radiommumodetection (RID). Results: Saturation binding experiments showed highest affinity for 125 I-labeled F(ab)2 fragments (K-d=0.37 +/- 0.10 nmol/L) and lowest affinity for 125 I-labeled Fab fragments (K-d=2.25 +/- 0.44 nmol/L). Blood clearance studies showed that the alpha half-life (t(1)/(2)alpha) value for Fab, F(ab)2 and mAb 14C5 was 14.9, 21 and 118 min, respectively. The beta half-life t(1)/(2)beta value for Fab, F(ab')2 and mAb 14C5 was 439, 627 and 4067 min, respectively. (131I)-Fab fragments showed highest tumor uptake 3 It after injection (2.4 +/- 0.8 %ID/g), I-131-labeled F(ab)2 showed highest tumor uptake 6 h after injection (4.7 +/- 0.7 %ID/g) and for I-131-labeled mAb highest tumor uptake was observed at 24 h (10.7 2.3 %ID/g). In planar gamma imaging, both labeled fragments gave better tumor-to-background contrast than I-123-mAb 14C5. Conclusion: Fab and F(ab)2 fragments derived from intact mAb 14C5 have significant potential for diagnostic and therapeutic applications and may provide new tools in mAb-based radiopharmaceuticals for targeting non-small cell lung cancer. (c) 2007 Elsevier Inc. All rights reserved.