Pretargeted radioimmunotherapy of mesothelin-expressing cancer using a tetravalent single-chain Fv-streptavidin fusion protein.
Mesothelin is a glycoprotein that is overexpressed in several human tumors, including mesotheliomas and ovarian cancers, and has been identified as a potential target for therapy. We evaluated the biodistribution and tumor-targeting ability of an antimesothelin tetravalent single-chain Fv-streptavidin fusion protein (SS1scFvSA) in mice.


METHODS
SS1scFvSA was labeled with 125I or 111In for evaluation of internalization in vitro and for optimization of its biodistribution. The A431-K5 mesothelin transfected cell line was used as the target. We used a 3-step pretargeting approach consisting of injections of (i) SS1scFvSA, followed 20 h later by (ii) a synthetic clearing agent, and (iii) 4 h later, radiolabeled (111In, 88Y/90Y, or 177Lu) 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA)-biotin. To optimize the tumor uptake, the effect of the specific activity of 111In-DOTA-biotin was evaluated.


RESULTS
Approximately 60% of SS1sc FvSA internalized within 6 h. The optimal dose of SS1scFvSA for pretargeting was 600 microg. Decreasing the specific activity of DOTA-biotin by administering 0.1-5 microg of DOTA-biotin resulted in tumor uptake decreasing from 31.8 to 5.5 %ID/g (percentage injected dose per gram) at 2 h. Pretargeted therapy of A431-K5 tumor with 90Y doses of 11.1-32.4 MBq resulted in a dose-dependent tumor response. With 32.4 MBq, 86% of mice survived tumor free for 110 d. All nontreated mice died, with a median survival of 16 d.


CONCLUSIONS
SS1scFvSA localized in the mesothelin-expressing tumor, resulting in a high accumulation of radiolabeled DOTA-biotin. The specific activity of DOTA-biotin had a significant effect on its tumor uptake. Therapeutic tumor doses were obtained without dose-limiting toxicity.
Nuclear Medicine Department, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, Maryland 20892, USA.
Noriko
N
Sato
Raffit
R
Hassan
Donald B
DB
Axworthy
Karen J
KJ
Wong
Sarah
S
Yu
Louis J
LJ
Theodore
Yukang
Y
Lin
Luke
L
Park
Martin W
MW
Brechbiel
Ira
I
Pastan
Chang H
CH
Paik
Jorge A
JA
Carrasquillo
D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D016503:Drug Delivery Systems / Q000379:methods; D005260:Female; D058851:GPI-Linked Proteins; D006801:Humans; D007128:Immunoglobulin Fragments / Q000378:metabolism / Q000627:therapeutic use; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D000090204:Mesothelin; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009928:Organ Specificity; D016499:Radioimmunotherapy / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics / Q000627:therapeutic use*; D011993:Recombinant Fusion Proteins / Q000493:pharmacokinetics / Q000627:therapeutic use; D019809:Streptavidin / Q000493:pharmacokinetics / Q000627:therapeutic use*; D016019:Survival Analysis; D014018:Tissue Distribution; D016896:Treatment Outcome
D058851:GPI-Linked Proteins; D007128:Immunoglobulin Fragments; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins; C000715528:Msln protein, mouse; D019275:Radiopharmaceuticals; D011993:Recombinant Fusion Proteins; D019809:Streptavidin; D000090204:Mesothelin