Abstract A60: Activation of compensatory receptor tyrosine kinases after the acquisition of resistance to anti-Her2 therapies

Background: Acquired resistance to therapy is a main obstacle in the success of cancer treatment. In HER2+ breast cancer (BC) patient survival has raised considerably after the introduction of the anti-target therapies Trastuzumab and Lapatinib. However, a considerable number of patients develop resistance to anti-HER2 therapies by HER2-related and unrelated mechanisms. Cancer cells displaying HER2 overexpression initially rely on the oncogenic addiction for HER2-controlled survival signaling pathways. However, the fact that some tumors resistant to anti-HER2 therapies still present HER2 amplification suggest the activation of compensatory pathways for the control of cell survival. Objectives: We aimed to identify compensatory survival pathways activated after the acquisition of resistance to Trastuzumab and Lapatinib that could be therapeutically targeted to overcome resistance to anti-HER2 therapies. We focus our efforts in identifying activated RTKs given that they are easily targetable proteins. Experimental Procedures: To identify compensatory pathways related to tumor escape to anti-HER2 therapies we developed an in vitro model of drug resistance by continuous exposure of the MDA-MB-453, BT474, and SKBR3 cell lines to increased concentrations of Trastuzumab or Lapatinib for over 6 months. Activated RTKs were identified by a phosphoproteome array, and their role in cell survival in cell lines resistant to anti-HER2 therapies was validated by siRNA and chemical inhibition experiments. Results: The resistant phenotype of the cell lines was confirmed by determining cell proliferation and apoptosis upon drug treatment. Moreover, the resistant cell lines displayed the more aggressive biological behavior in vitro and in vivo, as evidenced by the increased clonogenic ability and their tumorigenicity in immmunosupressed mice. We did not observed changes in the copy number of 17q12 (HER2) or 7p12 (EGFR) by FISH or in the mRNA levels by qPCR in any of the resistant cell lines, although there was a significant increase in the protein levels as determined by immunohistochemistry. By phosphoproteome array we identified the activation of several RTKs. The INGENUITY pathway analysis of the receptors identified indicated a main relevance for the processes related to cell signaling and cell cycle, cellular growth and proliferation, and more interestingly with axonal guidance signaling and human embryonic stem cell pluripotency. To confirm the involvement of those receptors in the activation of compensatory pathways in Trastuzumab and Lapatinib resistant cell lines, we performed a chemical screening. We further validated the involvement of several receptors in cell survival by siRNA. Conclusion: Several compensatory pathways for cell survival are activated after the acquisition of resistance to Trastuzumab and Lapatinib. The inhibition of such pathways could be used a new therapeutic approach for the treatment of resistant tumors, or to avoid the development of resistant cells. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A60. Citation Format: Patricia Fernandez Nogueira, Anke Bill, Inga Rye, Domiziana Costamagna, Hege Russnes, Pedro Gascón, Alex Gaither, Vanessa Almendro. Activation of compensatory receptor tyrosine kinases after the acquisition of resistance to anti-Her2 therapies. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A60.