The role of insulin-like growth factor I and its receptor in cell growth, transformation, apoptosis, and chemoresistance in solid tumors

Insulin-like growth factor I(IGF-I) exerts pleiotropic effects on mammalian cells via stimulation of its receptor (IGF-IR), a receptor tyrosine kinase . In vivo, IGF-I acts both as a local tissue growth factor and as a circula ting hormone. In oncological research, IGF-I has received increased attenti on as the activated IGF-I/IGF-IR system displays mitogeneic, transforming, and antiapoptotic properties in various cell types by stimulating distinct intracellular signaling pathways. Recent data suggest that the anti-apoptot ic effect of IGF-I may mediate decreased sensitivity to chemotherapeutic dr ugs in vitro and in vivo. Thus, targeting the IGF-I/IGF-IR system could ser ve as an approach to overcome clinical drug resistance in certain tumors.