Estrogen receptor-alpha (ER) drives the majority of breast cancers (BC), which are treated with endocrine therapy. ER also remains active in endocrine-resistant disease, a major contributor of BC mortality. ER is a DNA transcription factor that can be “reprogrammed” to less oncogenic genetic loci via activation of the progesterone receptor in endocrine-sensitive disease. Whether ER can be reprogrammed in endocrine-resistant BC is unknown. Moreover, DNA hyper-methylation at specific enhancer loci might impede this treatment strategy in the endocrine-resistant context. To determine the optimal conditions for nuclear receptor-mediated growth inhibition of endocrine-sensitive and endocrine-resistant BC, we performed a medium-throughput, image-based screen of 38 novel or FDA-approved ligands using a panel of ER-positive cell lines that were endocrine-sensitive (n=3) or endocrine-resistant (n=3). We further investigated whether epigenetic remodelling is required for growth inhibition. Two ER-negative lines were included as controls. Each ligand was tested at six 10-fold incremental doses, with or without pre-treatment of the DNA demethylation agent Decitabine. Cell number was quantified and cellular morphology analysed using Hoescht staining. Criteria for defining hits included >25% growth reduction, morphological changes, and EC50 <100nM. Pre-treatment with Decitabine did not enhance growth inhibition by any ligand in most BC cell lines. Twelve ligands were selected for subsequent validation. Four ligands, known to act through the androgen, glucocorticoid or ER-beta receptors, inhibited growth across a broader panel of ER-positive, endocrine-sensitive and –resistant cell lines, with the same or better efficacy than progesterone. In summary, epigenetic remodelling using Decitabine is not required for growth inhibition in endocrine-resistant cell line models. Four novel or FDA-approved ligands significantly reduced growth of endocrine-sensitive and –resistant ER positive BC cells, which will be further tested for ER reprogramming capacity by ChIP-seq in vitro and their ability to reduce growth and reprogram ER in patient-derived xenograft models of BC.