Proffered Papers— Young Investigator

REGULATION OF OSTEOSARCOMA (OS) METASTASIS BY IGF-I RECEPTOR SIGNALING: A NOVEL THERAPEUTIC TARGET

Weber K, Tsan R, Doucet M, MacEwen E, Radinsky R (MD Anderson Cancer Center, Houston, TX 77030)

Patients with metastatic OS continue to have a survival of ~20% at five years despite aggressive chemotherapy and multiple thoracotomies. Increased understanding of the biology of OS progression, metastasis, and its resistance to chemotherapy will uncover new molecular targets. OS overexpresses insulin-like growth factor I receptor (IGF-I-R), and recent data suggests that OS progression and metastasis requires a functional IGF-I-R. The purpose of this study was to abolish IGF-I-R activity in highly metastatic OS cells and to test its effects on growth and metastatic properties in vitro and in an orthotopic nude mouse model. Cellular proliferation assays of the human SAOS-2 and metastatic variant SAOS-LM2 OS cells revealed a 40% increase in proliferation subsequent to IGF-I treatment compared to controls. A 30% inhibition of growth was observed following treatment with IGF-BP-3, a negative regulator of IGF-I. A chemoresistance/survival advantage was also observed for SAOS-LM2 OS cells in the presence of IGF-I as shown by reduction in doxorubicin-induced apoptosis from 62% (doxorubicin alone) to 21% (doxorubicin + IGF-I) (p<.05). Enforced expression of a dominant negative truncated IGF-I-R (952-STOP) in these cells resulted in a 50-85% decrease in IGF-I-R autophosphorylation compared to controls following IGF-I treatment. There was also a corresponding decrease in downstream AKT and MAP kinase activity. OS 952-STOP clones had a 30% longer doubling time under anchorage-dependent conditions, and failed to form colonies under anchorage-independent conditions vs. controls. In vivo experiments in an orthotopic nude mouse model are ongoing to test the contribution of IGF-I-R to OS growth, metastasis and response to therapy. Preliminary results show that mice injected with the parental OS cells form lung metastasis, whereas those injected with the dominant negative IGF-I-R transfectant cells do not.