GHRH Antagonists JMR-132 and JV-1-38 Abolish HER Receptor Transactivation in Prostate Cancer
Background
Advanced prostate cancer often involves dysregulated growth signaling, with human epidermal growth factor receptor (HER) family members like EGFR and HER2 playing critical roles in mitogenic pathways. Current therapies face challenges in effectively targeting these pathways, especially in androgen-independent disease. Growth hormone-releasing hormone (GHRH) and its receptors (GHRH-R) are increasingly implicated in tumorigenesis, suggesting a potential cross-talk with HER signaling that could offer novel therapeutic avenues. Understanding this interaction is crucial for developing more effective treatments for aggressive prostate cancer.
Study Design
Researchers investigated the interplay between GHRH and HER receptors in human androgen-independent PC3 prostate cancer cells in vitro and in nude mice xenografts. They evaluated the stimulatory effects of GHRH on HER signaling and the antagonistic effects of GHRH analogues, JMR-132 and JV-1-38. Time-course studies assessed EGFR and HER2 expression. In vivo, the impact of GHRH antagonist JV-1-38 on tumor growth and EGFR/HER2 expression was examined in PC3 xenografts. Key assays included mRNA and protein level analysis for EGFR, HER2, and phosphorylated Src levels.
Results
Time-course studies revealed that GHRH stimulated both the expression of EGFR and HER2 in PC3 cells. The GHRH antagonists, JMR-132 and JV-1-38, effectively abrogated this stimulatory response to GHRH in vitro. GHRH was found to induce a rapid, ligand-independent activation of EGFR and HER2, mediated by cAMP/PKA and Src family signaling pathways. Additionally, a slower, ligand-dependent activation of EGFR and HER2 was observed, involving an extracellular pathway with a significant role for ADAM. Preliminary data also indicated that EGF increased mRNA levels for GHRH and GHRH-R. In vivo, treatment with GHRH antagonist JV-1-38 led to: a substantial reduction in tumor growth, which was associated with a significant decrease in both mRNA and protein levels of EGFR and HER2 within the tumors. Furthermore, JV-1-38 significantly decreased phosphorylated Src levels, confirming its impact on key signaling nodes.
Key Findings
- GHRH stimulated EGFR and HER2 expression in PC3 prostate cancer cells.
- GHRH antagonists JMR-132 and JV-1-38 abolished GHRH-induced EGFR/HER2 activation in vitro.
- GHRH activated EGFR and HER2 via ligand-independent (cAMP/PKA, Src) and ligand-dependent (ADAM) pathways.
- In vivo, JV-1-38 substantially reduced tumor growth in PC3 xenografts.
- Tumor inhibition by JV-1-38 was linked to reduced EGFR and HER2 mRNA/protein levels and decreased phosphorylated Src.
Why It Matters
This research highlights a critical cross-talk between GHRH-R and HER signaling pathways in advanced prostate cancer, suggesting that targeting GHRH-R could be a viable therapeutic strategy. Combining GHRH antagonists with agents targeting HER family members could offer a more potent and comprehensive approach to treating human advanced prostate cancer. For peptide users and clinicians, this opens the door to exploring GHRH antagonists, such as JMR-132 or JV-1-38, as potential adjunctive therapies. While currently preclinical, these findings provide a strong mechanistic basis for future clinical trials, potentially leading to novel combination protocols that overcome resistance or enhance efficacy in aggressive forms of the disease.
ghrh-antagonist
prostate-cancer
egfr
her2
tumor-growth
preclinical-animal