Targeting the ELF1/EGFR/ERK positive feedback loop overcomes resistance to androgen receptor inhibition in AR-Vs positive prostate cancer

While anti-androgen therapies have significantly improved survival outcomes for patients with advanced prostate cancer, their efficacy is often limited by the emergence of resistance. This resistance is largely driven by the expression of AR splice variants (AR-Vs). However, therapeutic strategies to effectively target AR-V-mediated castration-resistant PCa remain an unmet clinical need. Here, we report that prolonged exposure of PCa cells expressing both AR-FL and AR-Vs to enzalutamide induces extensive reprogramming of their transcriptomic and proteomic profiles. Notably, in enzalutamide-resistant cells, EGFR expression was upregulated at both the mRNA and protein levels, despite the absence of EGFR mutations. Downstream of EGFR, the extracellular signal-regulated kinase (ERK) pathway was constitutively activated, promoting tumor cell proliferation. Furthermore, protein array analyses of clinical specimens revealed that high EGFR protein levels-but not EGFR mRNA levels-were associated with poor patient prognosis. In addition, we demonstrated that inhibiting EGFR, either through genetic knockdown or pharmacological intervention, significantly sensitized AR-V-mediated enzalutamide-resistant cells to AR-targeted therapy (Enzalutamide or Mithramycin). Mechanistically, our data indicate that ELF1 transcriptionally regulates EGFR and that ERK1/2 interacts with ELF1, suggesting the existence of a positive ELF1/EGFR/ERK feedback loop that sustains resistance. This study elucidates a possible mechanism of resistance to AR inhibition driven by an ELF1/EGFR/ERK feedback loop in AR-Vs positive cells and provides a rationale for combining EGFR inhibitors with AR-targeted therapy as a potential treatment strategy for patients with advanced, enzalutamide-resistant prostate cancer.