Human pancreatic cancer stem cells are sensitive to dual inhibition of IGF-IR and ErbB receptors

Nerea Urtasun, Anna Vidal-Pla, Sandra Pérez-Torras, Adela Mazo

Pancreatic ductal adenocarcinoma is a particularly challenging malignancy characterized by poor responsiveness to conventional chemotherapy. Although this tumor frequently overexpresses or possesses constitutively activated variants of IGF-IR and EGFR/Her-2, clinical trials using inhibitors of these receptors have failed. ErbB receptors have been proposed as one mechanism involved in the resistance to IGF-IR inhibitors. Therefore, combined treatment with inhibitors of both IGF-IR and ErbB receptors would appear to be a good strategy for overcoming the emergence of resistance. Sensitivity of cells to NVP-AEW541 and lapatinib in single or combination treatment was assessed by MTT or WST-8 assays in a panel of human pancreatic cancer cell lines and cancer stem cells. Tumorspheres enriched in cancer stem cells were obtained from cultures growing in non-adherent cell plates. The effects on cell signalling pathways were analyzed by Western blot. We found that combined treatment with the IGF-IR and EGFR/Her-2 inhibitors NVP-AEW541 and lapatinib, respectively, synergistically inhibited pancreatic cancer cell growth. Analysis at molecular level argued in favor of cross-talk between IGF-IR and ErbBs pathways at IRS-1 level and indicated that the synergistic effect is associated with the total abolishment of Akt, Erk and IRS-1 phosphorylation. Moreover, these inhibitors acted synergistically in tumorsphere cultures to eliminate cancer stem cells, in contrast to their resistance to gemcitabine. Taken together, these data indicate that simultaneous blockade of IGF-IR and EGFR/Her-2 using NVP-AEW541 and lapatinib may overcome resistance in pancreatic cancer. Thus, the synergy observed with this combined treatment indicates that it may be possible to maximize patient benefit with the appropriate combination of currently known anticancer agents.