Parent Grant Summary and Specific Aims In 2020 there will be ~ 276,480 estimated new cases of invasive breast cancer (BCa) among women in the US, causing an estimated ~ 42,170 deaths. Two common mechanisms for the sustenance of BCa are epigenetic dysfunction and the malfunction of endocrine proteins such as estrogen receptor (ER). The specific focus of the studies proposed in this application is to repurpose deferiprone (Def), an FDA-approved iron chelator, as a template for the discovery of novel histone lysine demethylase (KDM) inhibitors optimized for BCa therapy. Most compounds that have been or are being developed clinically exhibit greater efficacy for a subtype of BCa. In this regard, therapeutic interventions that capitalize on ER signaling malfunctions, a driver of more than 70% of BCas, have enjoyed measured success in BCa therapy and/or chemoprevention. However, despite initial benefits, most patients eventually relapse due to acquired resistance to these drugs. Additionally, there are no targeted treatment options for triple-negative breast cancer (TNBC), a BCa subtype lacking ER, Human Epidermal Growth Factor receptor 2 (HER2), and Progesterone Receptor (PR) which accounts for over 20% of BCa incidence. Therefore, there is an unmet medical need for increasingly selective and potent drugs to treat early and resistant stages of all BCa subtypes. BCa viability, regardless of ER expression status, depends on an extensive network of epigenetic modifiers - histone mark writers, readers and erasers. Bioinformatic and functional analysis have identified specific subfamilies of the amino oxidase and Jumonji family of histone lysine demethylases (KDMs), histone methyltransferases (HMTs) and histone deacetylase (HDACs) as essential in supporting ERα signaling activation. Among these epigenetic modifiers, KDM1, KDM3A, KDM5A, KDM5B and KDM6A are exquisitely wired into ERα signaling and are collectively vital for BCa cell viability. Moreover, studies have implicated KDMs such as KDM6A in other ER-independent epigenetic reprograming which sustains TNBC as well. Unlike ERα signaling, pharmacological inhibition of KDMs has not been clinically validated. Although inhibition of KDM3A, KDM5A, KDM5B and KDM6A caused BCa cells growth arrest in vitro and in vivo, there are however precedents for compensation among KDM paralogs in tumor models generated by selective deletion of a paralog member. We hypothesize that collective inhibition of KDM paralogs implicated in BCa etiology will blunt the possibility of compensation among KDM paralogs that could occur from paralog selective inhibition, resulting in novel selective and potent drugs to treat BCa regardless of the cell ER expression status. The proposed study is designed to test this hypothesis. The specific aims are: 1) Develop Def-based KDM inhibitors with favorable toxicological and pharmacokinetic (PK) properties. 2) Characterize the correlation between intracellular on-target effects and whole cell...