Small-Animal PET of Tumor Angiogenesis Using a 76Br-Labeled Human Recombinant Antibody Fragment to the ED-B Domain of Fibronectin

Abstract

The aim of this study was to image the extra domain B (ED-B) of fibronectin, an angiogenesis-related target, in solid tumors using small-animal PET. Toward this aim, an ED-B fibronectin-binding human antibody derivative (L19-SIP) was labeled with 76 Br via an enzymatic approach. Biodistribution and imaging studies were performed in human teratoma-bearing mice for up to 48 h after injection. Methods: L19-SIP was labeled with 76 Br using bromoperoxidase/H 2 O 2 . The stability of the labeled antibody was tested both in vitro and in vivo. Biodistribution and small-animal imaging studies (PET and CT) were performed in F9-bearing 129/ sv mice (n 5 3 or 4). Results: The enzymatic radiobromination approach afforded the labeled antibody in high yield (.55%) under mild reaction conditions. 76 Br-L19-SIP stability in mouse serum proved to be similar to that of the 125 I-labeled analog (.80% of intact material at 48 h after injection). Fast and specific in vivo targeting was obtained in tumors and other organs expressing ED-B fibronectin (i.e., ovaries and uterus). However, slow renal clearance and persistent activity predominately in blood and stomach suggests partial 76 Br-L19-SIP debromination in vivo. This debromination was confirmed in a metabolism study in normal mice. The F9 tumors were clearly imaged by small-animal PET at each considered time point, starting at 5 h up to 48 h after injection. Conclusion: 76 Br-L19-SIP specifically accumulated at the target site, enabling detailed small-animal PET of tumor neovasculature. Therefore, targeting the angiogenesis-associated expression of ED-B fibronectin can be a valuable tool for tumor detection using molecular imaging with PET.

Biodegradable dendritic positron-emitting nanoprobes for the noninvasive imaging of angiogenesis

“…In contrast, previous studies of mice administered 76 Br-radiolabeled antibodies noted the complete debromination of the bromotyrosine residues within 24 h p.i. and high stomach uptake of radioactivity as early as 4 h p.i (21). Therefore, as we anticipated during the design of the dendritic nanoprobe, burying the 76 Br-tyrosine within the core of the structure, protected by a layer of PEO chains, slows down the in vivo enzymatic dehalogenation.…”

Immuno-PET Quantitation of de2-7 Epidermal Growth Factor Receptor Expression in Glioma Using 124I-IMP-R4–Labeled Antibody ch806

“…Although several studies have been published regarding immuno-PET using short-lived (t 1/2 , 1-2 h) positron emitters such as 18 F-FDG (20) or 68 Ga (21)(22)(23), these are suitable only for antibody fragments or smaller antibody constructs because of their short t 1/2 . Although the medium-lived (t 1/2 , 12-16 h) isotopes such as 64 Cu (24)(25)(26)(27), 86 Y (28,29), and 76 Br (30,31) have been used to label both intact antibodies and partial antibody constructs, the most favorable isotopes for labeling whole antibodies are long-lived isotopes such as 124 I or 89 Zr (3,4,32). Both 124 I (33,34) and 89 Zr (32,(35)(36)(37)(38) have been conjugated to mAbs in preclinical (1,3,32,(35)(36)(37) and clinical studies (33,34,37,38).…”

Radretumab Radioimmunotherapy in Patients with Brain Metastasis: A 124I-L19SIP Dosimetric PET Study

“…The 124 I-L19SIP product seems to be more stable than other radiohalogens, such as 76 Br-L19SIP (46), and it displays a lower accumulation in critical organs (liver, spleen, and kidney) compared with radiometals (32). The identical chemical nature of the radioisotope used for immuno-PET ( 124 I) and for therapy ( 131 I) facilitates the determination of meaningful provisional therapeutic dosimetries.…”