Interleukin-6 fused to a mutant form of Pseudomonas exotoxin kills
malignant cells from patients with multiple myeloma
RJ Kreitman, CB Siegall, DJ FitzGerald, J Epstein, B Barlogie and I Pastan
Division of Cancer Biology, Diagnosis and Centers, National Cancer
Institute, National Institutes of Health, Bethesda, MD 20892.
IL-6-PE4E is a recombinant protein consisting of interleukin-6 (IL-6) fused
to a mutant form of Pseudomonas exotoxin in which four basic amino acids
are changed to glutamate (PE4E). The chimeric toxin has been previously
shown to specifically kill malignant hepatic, prostatic, epidermoid, and
myeloma cell lines in vitro. To explore the possible clinical utility of
IL-6-PE4E, particularly as an agent for ex vivo purging of marrow for
autologous bone marrow transplantation (ABMT), we tested malignant cells
from patients with multiple myeloma for sensitivity to this chimeric toxin.
Ficoll-purified bone marrow cells were incubated with and without
IL-6-toxin for 2 to 3 days. Eight of the 15 myeloma patients had cells that
were sensitive to IL-6-toxin as measured by a decrease in the level of
protein synthesis. Cells from five patients were very sensitive to
IL-6-PE4E, with 50% inhibition of protein synthesis (ID50) achieved at or
below 6 ng/mL (7 x 10(-11) mol/L). Cells from three additional patients
showed moderate sensitivity, with ID50s between 30 and 140 ng/mL. The
remaining seven samples showed little or no sensitivity, with ID50s greater
than or equal to 400 ng/mL. Normal bone marrow cells or normal BFU-E and
CFU-GM were resistant to the IL-6-toxin even at 1,000 ng/mL. Neither IL-6,
IL- 2-PE4E, nor an enzymatically deficient mutant of IL-6-PE4E was
cytotoxic toward the myeloma cells, indicating that the cytotoxic effect of
IL-6-PE4E required the adenosine diphosphate-ribosylation function as well
as the specific ligand. Our data suggest that IL-6- toxin could be
effective in ex vivo marrow purging in selected multiple myeloma patients
who are candidates for ABMT, and that this toxin should also be
investigated further for in vivo therapy.
Volume 79,
Issue 7,
pp. 1775-1780,
04/01/1992
Copyright © 1992 by The American Society of Hematology
