Abstract B17: The small RhoGTPase RhoB as a new potential marker of EGFR-TKI resistance

Abstract

Abstract Introduction: EGFR tyrosine kinase inhibitors (EGFR-TKI) are widely used in metastatic non small cell lung cancer (NSCLC). Nevertheless, the majority of patients with wild type EGFR do not respond to these treatments and, in the selected group with EGFR mutations, we some primary resistance and all the patients will ultimately develop acquired resistance. The small RHO GTPase RhoB is involved in cell proliferation, invasion, apoptosis and can act as a tumor suppressor gene in lung carcinogenesis by controlling survival and invasion through AKT pathway. Furthermore, RhoB participates in the regulation of endocytic trafficking of EGFR. Specifically, activated RhoB is able to delay the transport of internalized EGFR to lysosomes, thus modifying its downstream signaling. The objective of our study is to know if RhoB is a molecular determinant of the response to the EGFR-TKI erlotinib, and if RhoB could be a marker for erlotinib resistance. Material and Method: We used various lung cancer cell lines harboring either wild-type or mautated EGFR and K-Ras. RhoB was either overexpressed by adenovirus transfection or inhibited by interfering RNA (siRNA) in these cells. Cell proliferation after 72h of treatment with erlotinib was measured by a colorimetric assay. In the same way, we performed invasion assays and western-blot analyses of downtsream signaling pathways. Results: (1) RhoB overexpression decreases the sensitivity to erlotinib of cells presenting a wild type or mutated EGFR in a dose-dependent manner whereas the sensitivity to erlotinib of cells bearing KRas mutation was not affected by RhoB overexpression. (2) Erlotinib-induced inhibition of cellular invasion is impaired by overexpression of RhoB in wild type or mutated EGFR cell lines. (3) The phosphorylation of Akt (and not of ERK) is inhibited by erlotinib and is restored upon overexpression of RhoB invasion. Conclusions: Our results suggest that RhoB is involved in the sensitivity to erlotinib in wild-type K-Ras cells harboring either mutated or wild-type EGFR. RhoB is able to block erlotinib-induced inhibition of cell proliferation and invasion mainly through AKT pathway modulation. We plan to extend our in vitro findings in a cohort of patients treated with erlotinib.