Evaluation of glycodendron and synthetically modified dextran clearing agents for multistep targeting of radioisotopes for molecular imaging and radioimmunotherapy.
A series of N-acetylgalactosamine-dendrons (NAG-dendrons) and dextrans bearing biotin moieties were compared for their ability to complex with and sequester circulating bispecific antitumor antibody streptavidin fusion protein (scFv4-SA) in vivo, to improve tumor-to-normal tissue concentration ratios for multistep targeted (MST) radioimmunotherapy and diagnosis. Specifically, a total of five NAG-dendrons employing a common synthetic scaffold structure containing 4, 8, 16, or 32 carbohydrate residues and a single biotin moiety were prepared (NAGB), and for comparative purposes, a biotinylated-dextran with an average molecular weight of 500 kD was synthesized from amino-dextran (DEXB). One of the NAGB compounds, CA16, has been investigated in humans; our aim was to determine if other NAGB analogues (e.g., CA8 or CA4) were bioequivalent to CA16 and/or better suited as MST reagents. In vivo studies included dynamic positron-emission tomography (PET) imaging of (124)I-labeled-scFv4-SA clearance and dual-label biodistribution studies following MST directed at subcutaneous (s.c.) human colon adenocarcinoma xenografts in mice. The MST protocol consists of three injections: first, a scFv4-SA specific for an antitumor-associated glycoprotein (TAG-72); second, CA16 or other clearing agent; and third, radiolabeled biotin. We observed using PET imaging of the (124)I-labeled-scFv4-SA clearance that the spatial arrangement of ligands conjugated to NAG (i.e., biotin linked with an extended spacer, referred to herein as long-chain (LC)) can impact the binding to the antibody in circulation and subsequent liver uptake of the NAG-antibody complex. Also, NAGB CA32-LC or CA16-LC can be utilized during MST to achieve comparable tumor-to-blood ratios and absolute tumor uptake seen previously with CA16. Finally, DEXB was equally effective as NAGB CA32-LC at lowering scFv4-SA in circulation, but at the expense of reducing absolute tumor uptake of radiolabeled biotin.
Department of Radiology, ‡Organic Synthesis Core Facility, §Program in Molecular Pharmacology and Chemistry, and ∥Molecular Pharmacology and Therapy Service, Memorial Sloan-Kettering Cancer Center , New York, New York 10065, United States.
Sarah M
SM
Cheal
Barney
B
Yoo
Sarah
S
Boughdad
Blesida
B
Punzalan
Guangbin
G
Yang
Anna
A
Dilhas
Geralda
G
Torchon
Jun
J
Pu
Don B
DB
Axworthy
Pat
P
Zanzonico
Ouathek
O
Ouerfelli
Steven M
SM
Larson
D000818:Animals; D002240:Carbohydrate Sequence; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy*; D056831:Coordination Complexes / Q000737:chemistry / Q000627:therapeutic use; D003911:Dextrans / Q000737:chemistry / Q000627:therapeutic use; D016503:Drug Delivery Systems; D004355:Drug Stability; D064593:Heterografts; D006801:Humans; D051379:Mice; D057054:Molecular Imaging; D015394:Molecular Structure; D049268:Positron-Emission Tomography; D016499:Radioimmunotherapy; D011868:Radioisotopes / Q000737:chemistry*
D056831:Coordination Complexes; D003911:Dextrans; D011868:Radioisotopes