Wide Variability in the Time Required for Immunotoxins to Kill B Lineage Acute Lymphoblastic Leukemia Cells: Implications for Trial Design.
OBJECTIVE
Recombinant immunotoxins (rITs) targeting CD22 are highly active in hairy cell leukemia, but less so in acute lymphoblastic leukemia (ALL). This study aims to understand the variable activity of an rIT against ALL toward improving responses in clinical application.


METHODS
We determined in vitro activity of rITs by WST-8 assays and the time needed to kill ALL cell lines and patient-derived ALL blasts by flow cytometry. The findings were translated into two systemic ALL xenograft models. Differences in time needed to kill KOPN-8 cells for distinct rITs were addressed biochemically.


RESULTS
In vitro activity (IC50) of anti-CD22 rIT varied 210-fold from 0.02 to 4.6 ng/mL. Activity also varied greatly depending on the time ALL cells were exposed to immunotoxin from < 30 minutes to > 4 days. For KOPN-8, the difference in exposure time was related to intracellular rIT processing. We showed in newly developed ALL xenograft models, where immunotoxins have a short half-life, that the needed exposure time in vitro predicted the responses in vivo By replacing bolus dose with small doses at frequent intervals or with continuous infusion, responses were substantially improved. We confirmed exposure time variability on patient-derived ALL samples and showed a correlation between exposure time needed to reach maximal cytotoxicity in vitro and their clinical response.


CONCLUSIONS
The exposure time needed for rITs targeting CD22 to kill ALL cells varies widely. Our results suggest that ALL patients would have a better response rate to anti-CD22 immunotoxins if treated by continuous infusion rather than by bolus injections. Clin Cancer Res; 22(19); 4913-22. ©2016 AACR.
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland.
Fabian
F
Müller
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland.
Tyler
T
Cunningham
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland.
Xiu Fen
XF
Liu
Children's Center for Cancer and Blood Diseases, Division of Hematology, Oncology and Blood and Marrow Transplantation, Children's Hospital Los Angeles, Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California, Los Angeles, California.
Alan S
AS
Wayne
Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland. pastani@mail.nih.gov.
Ira
I
Pastan
D000818:Animals; D001427:Bacterial Toxins / Q000494:pharmacology*; D045744:Cell Line, Tumor; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000494:pharmacology*; D000922:Immunotoxins / Q000494:pharmacology*; D051379:Mice; D058990:Molecular Targeted Therapy / Q000379:methods*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy*; D012107:Research Design; D051918:Sialic Acid Binding Ig-like Lectin 2 / Q000037:antagonists & inhibitors; D013997:Time Factors; D023041:Xenograft Model Antitumor Assays
D001427:Bacterial Toxins; C497867:CD22 protein, human; D007135:Immunoglobulin Variable Region; D000922:Immunotoxins; C000625804:LMB-11; D051918:Sialic Acid Binding Ig-like Lectin 2