Expression of an IGF‐I receptor dominant negative mutant induces apoptosis, inhibits tumorigenesis and enhances chemosensitivity in Ewing's sarcoma cells

IGF‐IR plays an essential role in the establishment and maintenance of the transformed phenotype of ES cells and interference with the IGF‐IR pathways causes reversal of the malignant potential of this neoplasm. In this report, we stably transfected a dominant negative IGF‐IR expression plasmid in an ES cell line to determine the effectiveness of this strategy against the in vitro and in vivo growth of ES cells. DXR sensitivity of TC‐71 cells expressing dominant negative mutants of IGF‐IR was also examined. The mutated IGF‐IR that we used carries a mutation in the ATP‐binding domain of the intracellular β subunit, while the extracellular, ligand‐binding α subunit remains unchanged. Cells carrying the dominant mutant IGF‐IR had a marked decrease in proliferation, a significant increase in anoikis‐induced apoptosis and a severely reduced ability to form colonies in soft agar. In vivo, when cells carrying dominant negative IGF‐IR were injected into nude mice, the tumor formation and metastatic abilities of ES cells were reduced and survival increased. Furthermore, transfected clones showed significantly higher sensitivity to DXR, a major drug in the treatment of ES. These results indicate that the IGF/IGF‐IR stimulation of ES cells may be inhibited by expression of mutated IGF‐IR on their surfaces and that this strategy may be considered a possible alternative to impair this important target of ES cells, whose therapeutic potential was further confirmed. © 2002 Wiley‐Liss, Inc.