Optimizing radiolabeled engineered anti-p185HER2 antibody fragments for in vivo imaging.
We have recently described the in vivo properties of an iodinated anti-p185HER2 engineered antibody fragment [minibody (scFv-C(H)3)2; 80 kDa], made from the internalizing 10H8 monoclonal antibody. Although the 10H8 minibody showed excellent binding to the target in vitro, only modest tumor uptake [5.6 +/- 1.7% injected dose per gram (ID/g) of tissue] was achieved in nude mice bearing MCF7/HER2 breast cancer tumors. Here, in an attempt to improve targeting, the 10H8 minibody was conjugated to 1,4,7,10-tetraazacyclododecane-N, N', N'', N'''-tetraacetic acid (DOTA), radiometal labeled, and evaluated in vivo. The tumor uptake of 111In-DOTA 10H8 minibody was 5.7 +/- 0.1% ID/g, similar to the radioiodinated 10H8 minibody. However, in addition to the expected liver clearance, the kidneys had unexpectedly high activity (34.0 +/- 4.0% ID/g). A minibody derived from a second anti-p185(HER2) antibody (trastuzumab; hu4D5v8) was also made. Tumor uptakes, evaluated by quantitative microPET using 64Cu-DOTA hu4D5v8 minibody, were 4.2 +/- 0.5% ID/g. Furthermore, in non-tumor-bearing mice, 111In-DOTA hu4D5v8 minibody exhibited similar elevated uptake in the kidneys (28.4 +/- 6.5% ID/g). Immunohistochemical staining of kidneys from non-tumor-bearing mice showed strong specific staining of the proximal tubules, and Western blot analysis of kidney lysate confirmed the presence of cross-reactive antigen. To further improve tumor uptake and normal tissue distribution, a larger hu4D5v8 fragment [(scFv-C(H)2-C(H)3)2; 105 kDa] was made, engineered to exhibit rapid clearance kinetics. This fragment, when evaluated by microPET, exhibited improved tumor targeting (12.2 +/- 2.4% ID/g) and reduced kidney uptake (13.1 +/- 1.5% ID/g). Thus, by manipulating the size and format of anti-p185(HER2) antibody fragments, the kidney activity was reduced and high or low expression of p185HER2 in xenografts could be distinguished by microPET imaging.
Olafsen
Tove
T
Crump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at University of California at Los Angeles, 90095, USA. tolafsen@mednet.ucla.edu
Kenanova
Vania E
VE
Sundaresan
Gobalakrishnan
G
Anderson
Anne-Line
AL
Crow
Desiree
D
Yazaki
Paul J
PJ
Li
Lin
L
Press
Michael F
MF
Gambhir
Sanjiv S
SS
Williams
Lawrence E
LE
Wong
Jeffrey Y C
JY
Raubitschek
Andrew A
AA
Shively
John E
JE
Wu
Anna M
AM
D000818:Animals; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000276:immunology / Q000378:metabolism; D002272:Carcinoembryonic Antigen / Q000276:immunology; D003301:Copper Radioisotopes / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D018796:Immunoconjugates / Q000737:chemistry / Q000493:pharmacokinetics*; D007128:Immunoglobulin Fragments / Q000737:chemistry / Q000378:metabolism*; D007205:Indium Radioisotopes / Q000737:chemistry / Q000493:pharmacokinetics; D007668:Kidney / Q000000981:diagnostic imaging / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000276:immunology / Q000378:metabolism; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000493:pharmacokinetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D014018:Tissue Distribution
D002272:Carcinoembryonic Antigen; D003301:Copper Radioisotopes; D018796:Immunoconjugates; D007128:Immunoglobulin Fragments; D007205:Indium Radioisotopes; D019275:Radiopharmaceuticals; D018719:Erb-b2 Receptor Tyrosine Kinases