Abstract 3904: Inhibition of the ERK5 pathway as a novel approach to target human chronic myeloid leukemia stem cells

Abstract

Abstract Tyrosine kinase inhibitors (TKi) targeting BCR/ABL are very effective for the treatment of Chronic Myeloid Leukaemia (CML). However, resistance mechanisms or their inefficacy on CML leukaemia stem cells (LSC) may lead to relapse. Therefore, there is urgent need to identify new molecular targets. The Extracellular signal-Regulated Kinase 5 (ERK5) is a Mitogen-Activated Protein Kinase involved in cancer. Our aim was to study a possible role of the ERK5 pathway in CML LSC. Cells used were: human CML cell lines K562 and KCL22 that express constitutively active ERK5; CML patient-derived cells and CD34+ cells from heathy donors (after informed consent had been obtained). Cells were incubated in normoxic (routine) or hypoxic (0.2% O2) primary cultures (LC1) in the presence or the absence of drugs. Day-7 LC1 cells were transferred to drug-free, non-selective normoxic secondary cultures (LC2), to measure LC2 repopulation as a read-out of progenitor/stem cell potential (CRA assay). Compounds: XMD8-92 (ERK5 inhibitor) and BIX02189 (MEK5 inhibitor); imatinib (BCR/ABL inhibitor, IM). We previously showed that stem cell potential of CML LSC is maintained in severe hypoxia. In K562 and KCL22 cells and in primary cells derived from 9 CML patients, the treatment in hypoxic LC1 with XMD8-92 or BIX02189, but not with IM, impaired progenitor/stem cell potential. The same results were obtained by combined treatment of XMD892 with IM. Importantly, XMD8-92 did not affect progenitor/stem cell potential of CD34+ cells from heathy donors. In colony formation ability assays ERK5 inhibition decreased colony formation by human primary CML cells to a higher extent than that by normal human CD34+ hematopoietic cells. Interestingly, in hypoxia, combined treatment XMD8-92/IM decreased the expression of genes relevant for stem cell maintenance such as p21, nanog and c-myc and the expression of CD26, a CML LSC marker. Moreover, combined XMD8- 92/IM maintained low the expression of p27, another gene involved in stem cell maintenance, that is increased by either drug when administered alone. This indicate that the ERK5 pathway inhibitors impaired LSC maintenance of CML cell lines and primary CML cells. Citation Format: Ignazia Tusa, Giulia Cheloni, Nathanael Gray, Antonella Gozzini, Persio Dello Sbarba, Elisabetta Rovida. Inhibition of the ERK5 pathway as a novel approach to target human chronic myeloid leukemia stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3904. doi:10.1158/1538-7445.AM2017-3904