Epidemiological and experimental studies have identified
hyperinsulinemia as an important risk factor for
breast cancer induction and for the poor prognosis in
breast cancer patients with
obesity and
type 2 diabetes. Recently it was demonstrated that both the
insulin receptor (IR) and the IGF-IR mediate
hyperinsulinemia's mitogenic effect in several
breast cancer models. Although IGF-IR has been intensively investigated, and anti-IGF-IR
therapies are now in advanced clinical trials, the role of the IR in mediating
hyperinsulinemia's mitogenic effect remains to be clarified. Here we aimed to explore the potential of IR inhibition compared to dual IR/IGF-IR blockade on
breast tumor growth. To initiate
breast tumors, we inoculated the mammary
carcinoma Mvt-1 cell line into the inguinal mammary fat pad of the hyperinsulinemic MKR female mice, and to study the role of IR, we treated the mice bearing
tumors with the recently reported high-affinity IR antagonist-S961, in addition to the well-documented IGF-IR inhibitor
picropodophyllin (PPP). Although reducing IR activation, with resultant severe
hyperglycemia and
hyperinsulinemia, S961-treated mice had significantly larger
tumors compared to the vehicle-treated group. This effect maybe secondary to the severe
hyperinsulinemia mediated via the
IGF-1 receptor. In contrast, PPP by partially inhibiting both IR and IGF-IR activity reduced
tumor growth rate with only mild metabolic consequences. We conclude that targeting (even partially) both IR and IGF-IRs impairs
hyperinsulinemia's effects in
breast tumor development while simultaneously sparing the metabolic abnormalities observed when targeting IR alone with virtual complete inhibition.