Pediatric acute myelogenous leukemia cells express IL-6 receptors and are sensitive to a recombinant IL6-Pseudomonas exotoxin

Abstract

We have studied IL-6 receptor (IL-6R) expression on AML cells from 15 pediatric patients by immunocytochemistry/flow cytometry, reverse-transcription polymerase chain reaction, and Scatchard analysis. High-affinity IL-6R were detected on leukemic cells from 12 (80%) patients. Binding sites per cell ranged from 140 to 3580 (median 920; mean 1240), with dissociation constants of 0.26 to 0.71 nM. We therefore assessed the in vitro sensitivity of IL-6R ؉ AML cells to treatment with a recombinant IL6-Pseudomonas exotoxin fusion protein (IL6-PE 4E ), using the XTT cytotoxicity assay. Leukemic cells from eight patients had ID 50 values (concentration of IL6-PE 4E producing a 50% decrease in cell viability) of Ͻ1000 ng/ml (median, 87 ng/ml; mean, 262 ng/ml). Sensitivity to IL6-PE 4E correlated significantly with receptor number. Normal bone marrow mononuclear cells had undetectable IL6-R expression (Ͻ20 receptors/cell) and were relatively resistant to IL6-PE 4E . To test the efficacy of IL6-PE 4E for ex vivo purging in an autologous stem cell transplantation setting, we incubated primary IL-6R ؉ AML cells with 10 3 ng/ml IL6-PE 4E for 24 h, followed by inoculation into SCID mice. Mice receiving treated cells showed no leukemic engraftment, while all mice receiving untreated or control-treated cells developed leukemia with a median presymptomatic interval of 55 days. In recipients of IL6-PE 4E treated cells, no evidence of occult leukemia was detected by PCR analysis of blood and bone marrow cells at 185 days postinoculation. These data suggest that IL-6R are expressed on leukemic cells from a substantial percentage of pediatric AML patients. Furthermore, leukemic cells expressing high numbers of IL6-R may be sensitive to IL6-PE 4E in an ex vivo purging protocol.

Growth factor receptor profile of CD34+ cells in AML and B‐lineage ALL and in their normal bone marrow counterparts

“…This could explain the high numbers of positive samples (90%) in our study, as only CD34 + cases were included. IL-6Ra was found on the leukaemic cells of 80% of children with AML (35). G-CSFR was detected with a radiolabelled cytokine on 14/14 AML samples (36).…”

PARC/CCL18 Is a Plasma CC Chemokine with Increased Levels in Childhood Acute Lymphoblastic Leukemia

“…Furthermore, it was demonstrated that AML cells produce soluble IL-6 receptor, which might explain the reduced serum levels of biologically active IL-6 detected in our study. 42,43 Since tumor cells are often a good cellular source of chemokines, 44 it was verified whether leukocytic cell lines produce PARC in response to various endogenous or exogenous stimuli. It was found that THP-1, HL60, Sup-T1, and MT4 cells did not secrete a detectable amount of PARC after stimulation with the cytokines IL-1, IL-4, IL-10, or IFN-␥, nor after induction with virus, dsRNA, endotoxin, enterotoxin, phorbol ester, or lectin.…”

Targeting Receptors on Cancer Cells with Protein Toxins

“…This chimeric toxin was potently cytotoxicity against a variety of different tumor cell lines displaying IL6Rs including multiple myeloma, prostate, hepatoma and carcinoma [139]. In two studies of pediatric cancer, IL6-PE was cytotoxic for freshly isolated (IL6R-expressing) patient cells diagnosed with either Acute Myelogenous Leukemia or Acute Lymphoblastic Leukemia [140,141]. The killing was roughly proportional to the number of receptors per cell.…”