INSULIN-LIKE GROWTH-FACTORS IN CENTRAL-NERVOUS-SYSTEM TUMORS

Insulin-like growth factors (IGFs) appear to play a role in the develo pment of tumors in general and brain tumors in particular. Specific re ceptors for IGFs have been identified in normal human and rat brain, a nd evidence suggests that components of the IGF signal transduction sy stem may play a role in the transformation process. Secretion of IGFs by a variety of human brain tumors has been confirmed, and these growt h factors appear to have an autocrine stimulatory effect on these tumo rs. IGFs circulate in the blood stream bound to at least six distinct binding proteins which may modulate the effects of these growth factor s on target tissues. Sex steroids may also regulate the behavior of ce rtain brain tumors such as meningiomas at least in part through their effects on the expression of IGFs and their binding proteins. Recently , antisense gene technology against certain IGFs or their receptors ha ve resulted in potent antitumor effects in the case of several gliomas , although the mechanism for this remains unclear.