Abstract A58: Bcr-Abl independent activation of Erk1/2 in an imatinib resistant cell line
Authors: Silva Danielle Cardoso da , Moreira Miguel A. , Maia Raquel C. , Vasconcelos Flavia C. 
Published: May 2019

Abstract
Tyrosine kinase inhibitor (TKI)-based therapy has dramatically enhanced chronic myeloid leukemia (LMC) panorama of treatment response, disease progression, and overall survival. In spite of its effectiveness and the development of more potent TKIs, resistance to treatment is still an issue. The recurrence of patients whose resistance is unrelated to BCR-ABL mutations points out to the importance of studying other resistance mechanisms. In this context, our group developed an imatinib (IM)-resistant cell line named K-IM through culturing K562 cells in gradually increasing IM concentrations. Since this cell line harbors no BCR-ABL kinase domain mutation, it is a perfect model for the study of Bcr-Abl unrelated resistance mechanisms. K-IM cells displayed an increase in BCR-ABL mRNA levels, but neither an increase in Bcr-Abl activity nor an impaired inhibition by IM was observed. Since ABC transporters are determinants for the multidrug resistance phenotype, P-glycoprotein (Pgp) expression as well as Pgp and breast cancer resistance protein activity was evaluated; however, K-IM cells showed neither Pgp expression nor transporter activity. Another important mechanism is the deregulation of apoptosis pathways and the inhibitor of apoptosis proteins XIAP and survivin have been extensively studied as putative targets for cancer treatment. K-IM cells presented mRNA levels of XIAP similar to its parental cell line K562 and higher mRNA levels of survivin. Protein analysis confirmed an increase in survivin expression, suggesting that this protein could contribute to the cell line's resistance. The search for signaling pathways that could promote survivin overexpression led to the observation of higher phosphorylation levels of Erk 1/2 that persisted even during Bcr-Abl inhibition in the resistant cell line K-IM. This suggests that the MAPK/Erk signaling pathway participates in a Bcr-Abl-independent resistance mechanism. There was a reduction in survivin levels after IM treatment, indicating its regulation is dependent on Bcr-Abl and not MAPK/Erk. One of the proteins that could evoke MAPK/Erk activation is the Shp2 phosphatase that interacts with adaptor proteins leading to Ras activation. However, IM treatment also impaired Shp2 phosphorylation, suggesting it is not the responsible mechanism for MAPK/Erk activation. Our data suggest that different resistance mechanisms that promote resistance may occur simultaneously and that K-IM cell line is an intriguing model for the study of resistance mechanisms and putative drug targets.
Citation Format: Danielle Cardoso da Silva, Miguel A. Moreira, Raquel C. Maia, Flavia C. Vasconcelos. Bcr-Abl independent activation of Erk1/2 in an imatinib resistant cell line [abstract]. In: Proceedings of the AACR International Conference held in cooperation with the Latin American Cooperative Oncology Group (LACOG) on Translational Cancer Medicine; May 4-6, 2017; São Paulo, Brazil. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(1_Suppl):Abstract nr A58.