Exploiting androgen receptor agonism as a treatment strategy in estrogen receptor-positive metastatic breast cancer

The androgen receptor (AR) is expressed in 75% of estrogen receptor-positive (ER+) breast cancers (BC). Selective AR modulators (SARMs), like EP0062, present a promising therapeutic strategy for ER + BC, particularly in patients who cannot tolerate endocrine therapy (ET) or whose tumors have developed resistance. We aimed to study the antitumor activity of EP0062 in ER+ patient-derived xenograft (PDX) models. EP0062 displayed comparable antitumor efficacy to selective ER degraders (SERDs), including in PDXs with ESR1 , PIK3CA , or PTEN mutations. Tumors sensitive to SARMs were enriched in GATA3 mutations. EP0062 treatment induced AR-target genes across all models tested. A transcriptional signature associated with SARM sensitivity was identified, primarily driven by proliferation-related processes, consistent with a significant decrease in S-phase cell cycle proteins upon treatment in EP0062-sensitive models. In some EP0062-resistant tumors, the combination with palbociclib enhanced the antitumor effect of EP0062, suggesting a potential strategy for metastatic patients with acquired ET resistance.