Interleukin-12 and interleukin-18 induce indoleamine 2,3-dioxygenase (IDO) activity in human osteosarcoma cell lines independently from interferon-gamma.
OBJECTIVE
In this study we evaluated the ability of inducing activation of the enzyme indoleamine 2,3-dioxygenase (IDO) for the development of a new adjuvant therapy of osteosarcomas. The pathway that has described in the literature states that IDO activity is elevated by IFN-gamma. This mechanism is important because the increased IDO activation induces an intracellular degradation of the essential amino acid tryptophan and thereby activates apoptosis in human osteosarcoma cells.


METHODS
Four different well-established human osteosarcoma cell lines (MNNG/HOS, KHOS-240, HOS and MG-63) were investigated in vitro. Several cytokines were tested for their ability to induce IDO activity. However special emphasis was placed to evaluate the synergistic effects of Interleukin-12 (IL-12) in combination with Interleukin-18 (IL-18). In the first series of experiments IDO induction was investigated by direct application of the cytokines IFN-gamma, TNF-alpha, IL-12 and IL-18 in different concentrations. Secondly, the increase of IDO expression from osteosarcoma cell lines was analysed in the presence of activated lymphocytes with or without cytokine application.


RESULTS
Our results demonstrated that the combined application of IL-12 and IL-18 enhanced IDO activity in the human osteosarcoma cell lines HOS and MG-63, in the presence of activated lymphocytes. In the absence of activated lymphocytes, no significant enhancement could be detected. In all our experiments the increase in IDO expression was only partly inhibited by blocking INF-gamma.


CONCLUSIONS
The presented study demonstrates that IL-12 and IL-18, or even more a combined application of both cytokines, induce IDO expression besides the known pathway via IFN-gamma. These mechanisms have been shown herein for the first time in human osteosacoma cell lines. Since IDO expression could still be shown after complete blocking of IFN-gamma, we conclude that at least a second pathway is responsible for inducing IDO activity. This is in contrast to the present knowledge about IDO activation.
Liebau
Christian
C
Department of Orthopaedic Surgery, Ernst-Moritz-Arndt-University of Greifswald, Germany.
Baltzer
Axel W A
AW
Schmidt
Sebastian
S
Roesel
Christian
C
Karreman
Christiaan
C
Prisack
Johannes Bernd
JB
Bojar
Hans
H
Merk
Harry
H
D001859:Bone Neoplasms / Q000201:enzymology*; D018920:Coculture Techniques; D003470:Culture Media; D004357:Drug Synergism; D004790:Enzyme Induction / Q000187:drug effects; D006801:Humans; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D007371:Interferon-gamma / Q000494:pharmacology*; D018664:Interleukin-12 / Q000494:pharmacology*; D020382:Interleukin-18 / Q000494:pharmacology*; D008213:Lymphocyte Activation; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects; D012516:Osteosarcoma / Q000201:enzymology*; D011994:Recombinant Proteins / Q000494:pharmacology; D014366:Tryptophan Oxygenase / Q000096:biosynthesis* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D003470:Culture Media; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D020382:Interleukin-18; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D018664:Interleukin-12; D007371:Interferon-gamma; D014366:Tryptophan Oxygenase