Inhibition of IGF-I receptor signaling in combination with rapamycin or temsirolimus increases MYC-N phosphorylation

Background: It has been previously shown that blockade of the type 1 insulin-like growth factor receptor (IGF1R) signaling combined with mTOR inhibition decreased neuroblastoma proliferation in vitro. MYC-N inactivation occurs through phosphorylation by downstream elements of the IGF1R signaling pathway. It was hypothesized that inhibition of IGF1R signaling would increase the inactivation of MYC-N. Materials and Methods: BE-2(c) and IMR-32 neuroblastoma cell lines were treated with varying concentrations of αIR3, rapamycin and temsirolimus either alone or in combination and the expression of MYC-N and phosphorylated MYC-N proteins were evaluated by Western blotting. The number of apoptotic cells was evaluated through cleaved caspase-3 expression. Results: IGF1R signaling blockade in combination with mTOR inhibition decreased MYC-N protein expression, increased MYC-N phosphorylation and significantly increased cleaved caspase-3 expression in treated cells. Conclusion: The combination of rapamycin or temsirolimus with αIR3 decreases MYC-N expression, increases MYC-N phosphorylation and induces apoptosis in vitro which may have clinical relevance to children with neuroblastoma.