Abstract 7186: In vitro evaluation of myelosuppressive effects of ATRi tuvusertib and ATMi lartesertib (M4076), alone and in combination

Abstract Introduction: In cancer therapy, combinations of drugs interfering with different molecular pathways enhance efficacy and reduce resistance development, but may also increase the risk of toxicity. DNA damage repair inhibitors (DDRi) induce on- and off-target adverse events including hematological and gastro-intestinal toxicities1, which impact the therapeutic window. We evaluated the hematopoietic effect of ATRi tuvusertib and ATMi lartesertib, alone and in combination, on erythroid, megakaryocytic and myeloid bone marrow cell lineages. Methods: Mobilized peripheral blood CD34+ cells were plated in 96-well plates in specific media cultures allowing growth and differentiation of all three lineages. The cells were cultured for a total of 7 (neutrophils and platelets) to 10 (erythroids) days in the absence of drugs to generate maturing populations. Various concentrations of tuvusertib and lartesertib were incubated in cell media and assessed using LC/MS methods to ensure they remained chemically stable for the duration of the experiments. After in vitro differentiation, the lineages were cultured in the continuous presence of various concentrations of tuvusertib (0. 003 to 3 µM) and/or lartesertib (0. 01 to 10 µM) encompassing an unbound plasma concentration range evaluated in phase 1 studies of these agents and their combination. Cells were evaluated in triplicate by flow cytometry on day 3 and 7 of drug exposure for neutrophils (CD34, CD38, CD33, CD15), megakaryocytes and platelets (CD41, CD42b), and erythroid cells (CD71, CD235a). In another set of experiments, to simulate a "drug holiday", cells were exposed to tuvusertib, lartesertib and their combination for 24 h, washed out and further cultured as described above before evaluation. Results: Tuvusertib and lartesertib were stable in the specific media cultures up to day 7 of drug exposure. Continuous treatment with tuvusertib as a single agent inhibited the hematopoietic cells of all lineages more profoundly than lartesertib as monotherapy. Effects were consistently more pronounced after 7 days than 3 days of drug exposure. Continuous treatment of a combination of tuvusertib and lartesertib inhibited hematopoietic cells of all lineages. Treatment for 24 h followed by wash-out demonstrated a lesser effect compared to continuous treatment. Conclusion: The phenotypic and functional changes induced by tuvusertib and lartesertib on in vitro cultures of erythroid, myeloid, and megakaryocytic cells are consistent with clinical observations in monotherapy studies, suggesting these models may be used to better understand and predict the hematological effects of monotherapies and combinations in the clinic. In vitro washout experiments may help support the concept of intermittent clinical regimens and warrant further investigation. 1. Martorana, et al. Cancers (Basel) 2022;14 (4): 953 Citation Format: Jatinder Kaur Mukker, Rohan Kulkarni, Yongzhao Huang, Emer Clarke, Ioannis Gounaris, Anup Zutshi, Karthik Venkatakrishnan, Anna Tafuri. In vitro evaluation of myelosuppressive effects of ATRi tuvusertib and ATMi lartesertib (M4076), alone and in combination abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 7186.