New Immunotoxins Targeting CD123, a Stem Cell Antigen on Acute Myeloid Leukemia Cells

Abstract

The specific alpha subunit of the interleukin-3 receptor (IL-3Ralpha, CD123) is strongly expressed in various leukemic blasts and leukemic stem cells and seems to be an excellent target for the therapy of leukemias. In this study, immunotoxins were developed to target CD123 only, which bypasses the dependence on other subunits to form intact IL-3R. Three anti-CD123 hybridomas (26292, 32701, and 32716) were selected on the basis of their affinity for CD123. Total RNAs were extracted from the 3 anti-CD123 hybridomas and used to clone the fragment of variable region (Fvs). The Fvs were assembled into single chain Fvs and fused to a 38-kd fragment of Pseudomonas exotoxin A to make recombinant immunotoxins. 26292(Fv)-PE38 was found to have the highest cytotoxic activity on the CD123 expressing leukemia cell line TF-1. It bound the cells with a kd of 3.5 nM. Another immunotoxin, 32716(Fv)-PE38, belonging to a different epitope group, had a similar binding ability but was less active, demonstrating the role of epitope selection in immunotoxin action. The cytotoxic activity of 26292(Fv)-PE38 was increased from 200 to about 40 ng/mL by mutating the REDLK sequence at the C terminus to KDEL. 26292(Fv)-PE38-KDEL was specifically cytotoxic to several CD123 expressing cell lines (TF-1, Molm-13, and Molm-14) with good CD123 expression but not to ML-1 or U937 with low or absent expression. In conclusion, 26292(Fv)-PE38-KDEL shows good cytotoxic activity against CD123 expressing cell lines, and merits further development for the possible treatment of acute myeloid leukemia and other CD123 expressing malignancies.

Engineering botulinum neurotoxin to extend therapeutic intervention

“…The successful delivery of LC/E(K 224 D) into cells to inhibit IL-8 and mucin secretion supports a role for LC/E(K 224 D) as a research tool and also shows the potential for therapy to regulate human hypersecretion diseases such as asthma and inf lammatory diseases. The therapeutic specificity of LC/ E(K 224 D) would be based upon the receptor binding component, as described for toxin chimeras, such as diphtheria toxin A fragment-IL2 (29) and Exotoxin A fragment-IgG variable region fragment (30). In conclusion, the current study shows proof of principle for altered substrate specificity to extend the application of BoNTs beyond neurological inflictions.…”

Targeted therapy aimed at cancer stem cells: Wilms’ tumor as an example

“…This discovery was followed by several efforts aimed at targeting the hematopoietic cancer stem cell markers, such as CD44 and CD123 in AML [64][65][66][67][68]. Further studies have since been performed by targeting CSCs in several solid tumors such as pancreatic, breast, prostate and colon cancers, melanoma, glioma, hepatocellular carcinoma, and others.…”

FCRL1 on chronic lymphocytic leukemia, hairy cell leukemia, and B-cell non-Hodgkin lymphoma as a target of immunotoxins

“…This strategy has been successfully used to target antigens on plasma membrane such as CD22, CD25, CD30, CD123, and mesothelin. [13][14][15][16][17] Several immunotoxins have undergone clinical evaluation. 13,[17][18][19] The most successful of these is BL22 that targets CD22 on B-cell malignancies and has produced a very high complete remission rate in chemotherapy-resistant relapsed HCL.…”