Pb2478: asciminib induces erythropoiesis in chronic myeloid leukemia cells through differentiation and not by selection

Topic: 23. Hematopoiesis, stem cells and microenvironment Background: Tyrosine Kinase Inhibitors (TKIs) are shown to be effective in suppressing BCR-ABL1 expression and have been widely used in clinical settings. However, the application of TKIs in erythroid induction has remained a less explored area due to dose-limiting toxicities. In this study, we used asciminib, an allosteric inhibitor which specifically targets the ABL myristate pocket (STAMP), to evaluate its effectiveness in K562 cells for erythroid induction. Aims: To determine whether asciminib/ imatinib induces K562 cells to undergo differentiation or are the cells being specifically selected due to drug pressure. Methods: The K562 cells were sorted into three different populations based on their CD235a and CD71 expressions, where CD235a+/CD71+ is denoted as Q2, CD235a-/CD71- is denoted as Q3, and CD235a-/CD71+ is denoted as Q4. These sorted populations were subsequently cultured over a 6-day period in RPMI and EPO-based differentiation media in the absence and presence of TKIs (i.e.: 200nM imatinib and 10nM asciminib). CD235a and CD71 surface marker expressions were analyzed on the 6th day by flow cytometry to determine whether the erythroid induction is due to differentiation or by selection. Results: Asciminib was observed to drive erythroid induction through differentiation, as not only did the Q3 and Q4 populations survived the drug pressure but were also observed to be following their parental differentiation profile (i.e.: the transition from Q3 or Q4 to Q2) in both RPMI and EPO-based differentiation media. The EPO-based differentiation media gave survival advantage to the cells. The Q4 population contributed to ~50% of the parental populations` distribution and as indicated in the data, the Q4 population was less susceptible to asciminib; therefore, asciminib treated cells showed differentiation at earlier time points when compared to the imatinib treated cells. Summary/Conclusion: Our study demonstrates a novel application of asciminib in the erythroid differentiation of K562 cells. Asciminib promoted the erythroid-specific surface maker expression (CD235a/CD71). The data presented in this study may provide a basis for developing novel differentiation therapy for treating CML patients.Keywords: Erythroid lineage, Erythropoieisis, Erythroid differentiation