Pb1822: inhibition of the dna damage response: a possible new route in acute myeloblastic leukemia treatment

Topic: 3. Acute myeloid leukemia - Biology & Translational Research Background: DNA integrity is threatened by endogenous and exogenous factors that can induce DNA damage. Therefore, cells have developed mechanisms to protect the integrity of the genome and repair damaged DNA, called the DNA damage response (DDR). The DDR includes sensor proteins (e.g. PARP1/2), signaling mediators and transducers, and effector molecules (e.g. CHK1/2). Increased DNA damage and altered DDR mechanisms are critical features of genetic instability that are potentially implicated in the pathogenesis of acute myeloblastic leukemia (AML). AML is a clonal stem cell and hematopoietic progenitor cell disease characterized by an arrest in myeloid differentiation and increased proliferation. Aims: The aim of the study was to evaluate the therapeutic potential of DDR inhibition in AML using in vitro models. Methods: To this end, AML cell lines (HEL, HL-60, K-562, KG-1, LAMA-84 and NB-4) were incubated in the absence or presence of increasing concentrations of two DDR inhibitors, CCT245737 (CHK1 inhibitor) and niraparib (PARP1/2 inhibitor). Cell density and viability were assessed by trypan blue assay during 72h. Cell cycle was assessed by flow cytometry using propidium iodide/RNAse labeling. Cell death was determined by flow cytometry using annexin V/7-AAD staining and by light microscopy (May-Grünwald-Giemsa staining). The results were analyzed statistically, considering a significance level of 95%. Results: CCT245737 and niraparib reduced cell proliferation and viability in a dose-, time- and cell-line-dependent manner. KG-1 cells (IC50 of 47 μM at 48 hours) were the most sensitive to CHK1 inhibition while LAMA-84 cells (IC50 of 78 μM at 48 hours) were the most resistant. The most sensitive cell line to niraparib was NB-4 (IC50 of 20 μM at 48 hours) and the most resistant was KG-1 (IC50 of 68 μM at 48 hours). Both inhibitors led to an increase in the percentage of cells in late apoptosis, confirmed by morphological evaluation. A cytostatic effect by blocking the cell cycle in G0/G1 phase was also detected. Summary/Conclusion In conclusion, AML cell lines have different sensitivities to CCT245737 and niraparib. KG-1 and NB-4 cells appear to be the most sensitive while LAMA-84 and KG-1 cells appear to be the most resistant to CHK1 and PARP1/2 inhibition, respectively. Thus, this work may help to identify new therapeutic approaches that can improve the treatment of AML patients. Keywords: Targeted therapy, Apoptosis, DNA repair, Acute myeloid leukemia