Crosstalk between EGFR and IGF1R mediated by polymorphisms in the EGFR promoter as a mechanism for resistance to IGF1R directed therapy in osteosarcoma

Osteosarcoma is the most common primary malignant tumor of bone, with a pea incidence in the second decade of life. New therapies are needed to improve survival especially among patients with recurrent or metastatic disease. Insulin growth factor-I (IGF-I) is essential for growth in osteosarcoma. Several of the fully humanized monoclonal antibodies targeting the IGF-I receptor (IGF-IR) currently in clinical trials have clear evidence of growth inhibition in osteosarocoma tumor lines. However, some osteosarcoma lines remain resistant to IGF signal inhibition. Preliminary data presented using a fully humanized monoclonal anti-IGF-IR antibody, indicates that osteosarcoma tumors may employ salvage signaling through the epidermal growth factor receptor (EGFR) and mitogen-activated protein kinase (MAPK) pathways to permit growth in the presence of IGF-IR inhibition. In fact, preliminary data presented in this proposal demonstrate that single nucleotide polymorphism in the EGFR promoter predicts induction of EGFR in response to IGF1 R inhibiton. The hypothesis evaluated in Specific Aim 1 is that the activity of the EGFR pr6moter in osteosarcoma is influenced by the sequence of the Sp1 binding site of the EGFR promoter leading to differential activation of EGFR in response to IGF1R inhibition. Specifically, plasmid constructs representing the different -216 sequences of the EGFR promoter driving a luciferase reporter will be transiently transfected into osteosarcoma cells and human fibroblasts. Promoter activity in response to an antibody blocking IGF1R activity and IGF1R RNA interference (RNAi) will be measured.

The hypothesis evaluated in Specific Aim 2 is that the genotype at -216 of the EGFR promoter will serve a biomarker for response to IGF1 R inhibition. Peripheral blood mononuclear cells will be harvested from volunteer donors and EGFR expression evaluated in response to an antibody blocking IGF1 R activity and IGF1 R RNAi. Results will be correlated with genotyping of buccal mucosal cells.