Abstract A021: Bone marrow mesenchymal stem cells tune autophagic circuitry of chronic myeloid leukemia cells in response to imatinib treatment
Authors: Mukherjee Devdeep , Das Joyjyoti , Chakrabarti Prantar , Maiti Tapas Kumar 
Published: August 2018

Abstract
Chronic myeloid leukemia (CML) is a stem cell disorder with the characteristic presence of chromosomal translocation resulting in the formation of Bcr-Abl protein tyrosine kinase. Within bone marrow, leukemia stem cells (LSCs) share a niche with mesenchymal stem cells (MSCs). Therefore, there exists a strong signalling traffic between MSC and LSC that may direct therapeutic outcome of the CML patients. Imatinib is commonly used as the first line of therapy for CML. However, therapeutic resistance appears to be a major challenge for treatment of CML. Autophagy is one of the key phenomena that may direct cells towards survival or death. However, current understanding on the regulation of autophagy in CML cells by bone marrow niche cells is limited. Therefore, the present study is focused on the regulation of imatinib-induced autophagy in CML cells by MSCs. Here, we cocultured bone marrow-derived MSCs with chronic myeloid leukemia cells, K562 to understand the signaling axis that controls autophagy and subsequent apoptosis of CML cells. We studied K562 cell viability and proliferation by MTT and CFSE assay. For autophagy determination, we performed Western blot analysis and live cell confocal microscopy with K562 cells transfected with ptfLC3 plasmid (the microtubule-associated protein 1 light chain 3, LC3 protein fused to mRFP and EGFP plasmid). Results revealed that there was a reduction in the viability of K562 cells when cocultured with MSC for 48 h. Further reduction in the viability was observed when cells were exposed to 5 µM imatinib for 48 h. The presence of MSCs caused ~2-fold higher accumulation of the lipidated form of LC3 (LC3BII) in K562 cells as compared to control. In addition, imatinib treatment resulted in ~10-fold higher accumulation of LC3BII in K562 cells. Interestingly, as compared to imatinib-treated K562 cells, ~2-fold lower autophagic flux was observed when imatinib was administered to K562 cells in the presence of MSCs. However, enhanced expression of pro-apoptotic protein Bcl-xl was observed. Involvements of ATG5 and Beclin-1 were also detected. This was also microscopically confirmed in K562 cells using mRFP and GFP tagged plasmid. In conclusion, all these studies suggest that bone marrow MSCs play a pivotal role in regulating imatinib-induced autophagy in CML cells. This might provide an important clue to effectively formulate a therapeutic strategy involving MSCs to eliminate imatinib-resistant CML cells from bone marrow niche.
Citation Format: Devdeep Mukherjee, Joyjyoti Das, Prantar Chakrabarti, Tapas Kumar Maiti. Bone marrow mesenchymal stem cells tune autophagic circuitry of chronic myeloid leukemia cells in response to imatinib treatment [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A021.