Targeting primary human Ph(+) B-cell precursor leukemia-engrafted SCID mice using radiolabeled anti-CD19 monoclonal antibodies.
The Philadelphia chromosome translocation (Ph(+)) confers a poor prognosis in patients with acute lymphocytic leukemia (ALL). CD19 is highly expressed (CD19(+)) on ALL cells and is an attractive target for antibody-based therapies. CLB-CD19 is an IgG1kappa murine monoclonal antibody (mAb) directed against an epitope on the CD19 antigen.


METHODS
Radiolabeled CLB-CD19 antibody was evaluated for targeting ALL in a severe combined immunodeficient (SCID) mouse model engrafted with primary human leukemia cells. Lodgment of CD19(+) ALL cells in spleen and liver was confirmed using immunohistochemistry analyses. Circulating CD19(+) ALL cells in blood were also detected by flow cytometry.


RESULTS
Antibody was labeled directly with the radiohalogen (125)I and radiometal (111)In via the bifunctional metal ion chelate CHX-A"-diethylenetriaminepentaacetic acid (DTPA) with retention of immunoreactivities. After intravenous injection of radioconjugates, biodistribution studies showed rapid localization of the (111)In-conjugate to leukemia-infiltrated spleen, reaching a maximum (mean +/- SD) of 72.78 +/- 13.67 % injected dose per gram of tissue (%ID/g) by 24 h after injection. In contrast, peak localization of coinjected (125)I-CLB-CD19 occurred by 4 h and was significantly lower (11.41 +/- 12.79 %ID/g) (P < 0.001). Uptake of (111)In-conjugate in the liver containing tumor was also evident but not in other normal tissues. Uptake of radiolabeled CLB-CD19 in tumor-bearing organs was specific, as uptake of radiolabeled isotype-matched antibody control was low. Gamma-camera imaging detected the uptake of (111)In-CHX-A"-DTPA CLB-CD19 in enlarged tumor-bearing spleen of engrafted mice. A single injection of 32 micro g CLB-CD19 mAb had a delayed suppressive effect on the level of circulatory leukemia cells in surviving mice and extended the median survival from 48.5 to 58 d (n = 8; P = 0.03).


CONCLUSIONS
The radiolabeled anti-CD19 antibody showed specific targeting and rapid internalization in ALL cell-engrafted SCID mice and may also be used for selective intracellular delivery of cytotoxic radionuclides with beta-, Auger, or alpha-emissions.
Mitchell
Paul
P
Ludwig Institute For Cancer Research, Melbourne Tumour Biology Branch, Austin and Repatriation Medical Centre, Melbourne, Victoria, Australia.
Lee
Fook-Thean
FT
Hall
Cathrine
C
Rigopoulos
Angela
A
Smyth
Fiona E
FE
Hekman
Anne-Marie
AM
van Schijndel
Gijs M
GM
Powles
Ray
R
Brechbiel
Martin W
MW
Scott
Andrew M
AM
D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000493:pharmacokinetics*; D018941:Antigens, CD19 / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000378:metabolism; D006801:Humans; D007205:Indium Radioisotopes / Q000493:pharmacokinetics; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D007553:Isotope Labeling / Q000379:methods; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D016513:Mice, SCID; D009368:Neoplasm Transplantation; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D011877:Radionuclide Imaging; D011994:Recombinant Proteins / Q000737:chemistry / Q000493:pharmacokinetics; D013154:Spleen / Q000378:metabolism; D013160:Splenic Neoplasms / Q000378:metabolism*; D014018:Tissue Distribution
D000911:Antibodies, Monoclonal; D018941:Antigens, CD19; D014408:Biomarkers, Tumor; D007205:Indium Radioisotopes; D007457:Iodine Radioisotopes; D011994:Recombinant Proteins