ATR inhibitor camonsertib (RP-3500) suppresses early-stage erythroblasts by mediating ferroptosis

Background: Ataxia telangiectasia mutated and Rad3-related kinase (ATR) mediates cellular response to replication stress DNA damage. Camonsertib is a potent selective ATR inhibitor with strong pre-clinical efficacy, promising clinical activity (NCT04497116) but results in rapid monocytopenia leading dose limiting anemia potentially implicating disturbance iron homeostasis. Pre-clinically, dosing 3 days on/4 off mitigates without compromising allowing reticulocyte regeneration between doses. High requirements are uniquely essential for heme synthesis during erythropoiesis, specifically increasing erythroblast vulnerability iron-dependent reactive oxygen species (ROS) potential iron-mediated oxidative We thus explore mechanisms of induction RP-3500. Methods Results: In mice, early bone marrow depletion noted 24 hours post camonsertib treatment. This reversible after 2–4 vitro, human CD34+ cell differentiation erythroblasts, we show that ROS concentration highest early-stage erythroblasts does not correlate the degree apoptosis. Next, demonstrate altered expression iron-related genes erythroblasts: mRNA ferritin (FTH FTL), PCBP1, NCOA4, TFR2a increases TFRC decreases confirming reliance on trafficking erythropoiesis. When treated camonsertib, proliferation decreased dependent manner. Specifically proportion decrease, while NCOA4 increase FTH cells decrease; all consistent enhanced ferroptosis. Erythropoietin (EPO) supplementation alter proliferation, differentiation, apoptosis, or levels cells. Finally, addition ferristatin-1, intended block ferroptosis, ROS, prevents dose-dependent decrease culture. first evidence treatment suppresses erythropoiesis via ferroptosis erythroblasts. Conclusions: These camonsertib-induced reversible. characteristic may their susceptibility inhibition, mediated by increased Although supplemental EPO alleviate erythroid intermittent allows recovery, minimizing maintaining efficacy. Ongoing mechanistic studies will be discussed context supportive therapeutic strategies minimize induced anemia. Conflict interest: Ownership: GBF, LL, SF, SJM, MK, AJF AR employees Repare Therapeutics, shareholders have stock options. Corporate-sponsored Research: RH YZG receive sponsored research funding from Therapeutics.