# EGFR‐STAT3 activation provides a therapeutic rationale for targeting aggressive ETV1‐positive prostate cancer

## TL;DR

This study identifies a new pathway involving ETV1, EGFR, and STAT3 in aggressive prostate cancer, suggesting a potential treatment strategy using existing drugs.

## Contribution

The study reveals a novel ETV1-regulated EGFR–STAT3 oncogenic pathway in ETV1-positive prostate cancer.

## Key findings

- ETV1 forms a positive feedback loop with EGFR, with STAT3 as a downstream effector.
- Combined inhibition of EGFR and STAT3 significantly reduces growth of ETV1-overexpressing prostate cancer cells.
- ERG-overexpressing cells show reduced EGFR–STAT3 activation and lower drug response.

## Abstract

Prostate cancer (PCa) is the fifth leading cause of cancer‐related death. The lack of data linking genomic alterations to targeted treatment strategies has hindered progress in disease management. Genomic rearrangements involving the ETS transcription factors ERG or ETV1 are among the most frequent genetic alterations in PCa; however, their clinical utility remains elusive. Using PCa cells overexpressing ETV1 or ERG, representing early and advanced disease stages, we unveiled a positive feedback loop between ETV1 and EGFR, with STAT3 acting as a downstream effector of ETV1–EGFR signaling. Analysis of external datasets revealed that both EGFR and STAT3 are significantly upregulated in ETV1‐positive PCa, consistent with ChIP‐seq data identifying them as direct ETV1 targets. Accordingly, combined inhibition of EGFR and STAT3 using Erlotinib and TTI‐101, respectively, led to a significant reduction in 2D and 3D cell growth of early and advanced PCa cells overexpressing ETV1. Collectively, our findings highlight EGFR–STAT3 activation as a novel ETV1‐regulated oncogenic pathway, providing a rationale for repurposing EGFR inhibitors in combination with STAT3 inhibitors as a therapeutic strategy for the 8–10% of prostate carcinomas characterized by ETV1 rearrangements/overexpression.

Cotargeting EGFR and STAT3 with Erlotinib and TTI‐101 impairs both 2D and 3D growth of ETV1‐overexpressing prostate cancer cells by disrupting a self‐sustaining ETV1–EGFR positive feedback loop that promotes EGFR and STAT3 expression and phosphorylation (activation). In contrast, ERG‐overexpressing cells show reduced EGFR–STAT3 activation and consequently a lower therapeutic response to Erlotinib and TTI‐101.