Molecular Insight into Thiopurine Resistance: Transcriptomic Signature in Lymphoblastoid Cell Lines

Despite significant improvements in acute lymphoblastic leukemia (ALL) treatment, long-term survival is still challenging. 6-mercaptopurine (6-MP), a thiopurine agent part of maintenance therapy, is of particular importance for determining clinical outcome and preventing relapse. Genetic inheritance in thiopurine metabolism plays a major role in interindividual clinical response variability to thiopurine. However, thiopurine resistance remains mostly unexplained. Using lymphoblastoid cell lines (LCLs) selected for their extreme resistant phenotype to thiopurine drugs, we performed a genome-wide expression profiling in order to highlight underlying mechanisms of thiopurine resistance. We established a transcriptomic signature of 32 genes predicting thiopurine resistance, including GTPBP4, a GTP-binding protein which is a p53 interactor. Besides, among the differentially expressed genes between resistant and sensitive cell lines, gene ontology analysis highlights the involvement of RNA processes and cell cycle in thiopurine resistance. A comprehensive pathway analysis revealed the overexpression of the ATM/p53/p21 pathway, which is activated in response to DNA damage and resulting in a cell cycle arrest. Furthermore, an increased expression of TNFRSF10D, a p53 target gene, or CCNG2, a negative regulator of cell cycle, could result in a cell cycle arrest and have associated with resistance. Finally, ARHGDIA under-expression in resistant cell lines could constitute a novel molecular mechanism contributing to thiopurine resistance in relation thiopurine pharmacodynamics, based on Rac1 inhibition and apoptosis. Our study represents a step toward the knowledge of underlying molecular mechanisms contributing to thiopurine resistance and potential therapeutic targets in the field of personalized medicine. Transcriptomic analysis of thiopurine-resistant LCLs (n=5) compared to thiopurine-sensitive LCLs (n=6); t test for each gene after RMA process.