PS1006 INHIBITORS OF HOXA9 LEUKEMOGENIC TRANSCRIPTION FACTOR ARE EFFICIENT ON HUMAN AML CELL MODELS BUT NOT ON NORMAL HUMAN BONE MARROW CD34+ HEMATOPOIETIC CELLS

Abstract

Background:The HOXA9 protein is a transcription factor associated with normal hematopoiesis and which expression on hematopoietic stem cells and progenitor cells decreases in the course of blood cell differentiation. The expression of HOXA9 is however maintained at high level in several subtypes of acute myeloid leukemia (AML) such as mll‐rearranged leukemias, NPM1‐mutated AMLs and AML presenting MYST3‐CREBP, NUP98‐NSD1 or RUNX/EVI1 translocations. The over‐expression of HOXA9 in these AML subtypes is associated with the maintenance of cell proliferation and the blockade of cell differentiation. It is well known that HOXA9 exerts its leukemic potential through DNA interaction and, therefore, we selected direct inhibitors of HOXA9/DNA interaction to block its activity and evaluate them on a murine leukemia cell model (Depauw et al., 2019).Aims:In order to go further, we aim at evaluating them on human AML cell models expressing or not HOXA9 and on normal human CD34+ hematopoietic cells to address any potential effect of our inhibitors on normal hematopoiesis.Methods:The expression level of HOXA9 was quantified by qRT‐PCR on a series of human AML cell lines. The sensitivity of those cell lines regarding two selected inhibitors was seen addressed using global cell survival analysis using MTS reaction. Methylcellulose clonogenic assays were performed on a series of human AML cell lines and on normal human bone marrow CD34+ hematopoietic cells. Knock‐down of HOXA9 expression was performed as a control using lentiviral delivery of HOXA9‐specific or control shRNAs.Results:A strong correlation between HOXA9 expression and the sensitivity to two of our inhibitors was evidenced in a series of 14 human AML cell lines with linear determination coefficients of R of ∼0.75 and ∼0.8.Clonogenic assays evidenced a decrease in the number and size of the colony forming units of treated related to untreated AML cell models. The relevance of HOXA9 expression in the clonogenicity is addressed by use of lentivirally transduced shHOXA9 in some of the AML cell models. By contrast, no difference were observed on either the number, the size and the differentiation subtypes of the colonies obtained from treated versus untreated normal human CD34+ hematopoietic cells.Summary/Conclusion:In conclusion, we selected inhibitors of HOXA9/DNA interaction that alter cell proliferation and clonogenic activity in a series of HOXA9‐positive AML cell models but that do not affect the progenitor cell number from normal bone marrow CD34+ cells.