Two growth hormone-releasing hormone receptor antagonists (MIA-602 and MIA-690) selectively triggered cell death in retinoblastoma cancer cells without harming other retinal cells, exploiting the cancer cells' unique overexpression of GHRH receptors.
Selective cancer cell killing with no retinal cell damageGHRH receptor antagonists triggered apoptosis specifically in retinoblastoma cells while causing no harm to retinal pigmented epithelial cells — a critical distinction for preserving vision during cancer treatment.
What the researchers found
The GHRH receptor (GHRH-R) was found to be highly expressed in retinoblastoma cells but not in other retinal cells, providing a selective target. Two GHRH-R antagonists, MIA-602 and MIA-690, induced specific apoptosis in retinoblastoma cells without triggering cell death in retinal pigmented epithelial cells.
Gene expression profiling revealed that GHRH-R antagonists downregulated cell proliferation genes while upregulating apoptotic genes in the cancer cells. The mechanism exploits the fact that retinoblastoma arises from cone precursor cells with high MDM2 levels that suppress p53-mediated apoptosis — the GHRH-R antagonists appear to restore these suppressed cell death pathways.
Why it matters
Retinoblastoma primarily affects young children, and current treatments (chemotherapy, cryotherapy, laser therapy, and sometimes eye removal) can have devastating consequences for a child's vision and quality of life. A targeted therapy that kills only cancer cells while preserving healthy retinal tissue could transform treatment outcomes, potentially saving both the eye and vision in children with this disease.
How the study worked
Researchers first characterized GHRH receptor expression across retinoblastoma cell lines and other retinal cell types. They then treated both cancer and normal retinal cells with two GHRH-R antagonists (MIA-602, MIA-690) and measured apoptosis. Gene expression profiling was performed to identify the molecular pathways regulated by the antagonists, revealing changes in proliferation and apoptosis-related gene networks.
What this study cannot tell us
This is an in vitro (cell culture) study that has not been validated in animal models or human patients. The selectivity demonstrated between retinoblastoma cells and retinal pigmented epithelial cells may not fully represent the complexity of the eye in vivo, where other cell types and the tumor microenvironment could affect drug behavior. Dosing, delivery to the eye, and potential systemic effects of GHRH-R antagonism were not addressed.
How to read the evidence
This is an in vitro (cell culture) study published in PNAS by a research team including Nobel laureate Andrew Schally. While the selectivity findings are compelling, the lack of in vivo data means the therapeutic potential remains to be validated in animal models and eventually clinical trials.
When this study was published
Published in 2016, this study introduced a novel therapeutic concept for retinoblastoma. Subsequent research has continued to explore GHRH-R antagonists in various cancer types, though clinical translation for retinoblastoma specifically may still be in early stages.
The bigger picture
GHRH receptor antagonists have been explored as anticancer agents in several tumor types, but this is among the first demonstrations of their potential in retinoblastoma — and the selectivity shown here is remarkable. Published in PNAS, the study builds on the broader concept that peptide hormone receptor expression can differ dramatically between cancer and normal cells, creating therapeutic windows for receptor-targeted peptide drugs. The work by Andrew Schally's group (a Nobel laureate in peptide hormone research) adds significant credibility to this approach.
Questions still open
- Can GHRH-R antagonists be delivered directly into the eye to treat retinoblastoma while minimizing systemic effects on growth hormone regulation?
- Would these antagonists be effective against retinoblastoma in animal models, where the tumor microenvironment and drug delivery challenges are more realistic?
- Could GHRH-R expression levels in retinoblastoma serve as a biomarker to predict which patients would respond best to this targeted therapy?
Common questions
What is retinoblastoma and why is it hard to treat?
What is GHRH and why do retinoblastoma cells have more of its receptor?
Read the original research
Antagonists of growth hormone-releasing hormone receptor induce apoptosis specifically in retinoblastoma cells.
Proceedings of the National Academy of Sciences of the United States of America, 113(50), 14396-14401
Citation
Chu, Wai Kit; Law, Ka Sin; Chan, Sun On; Yam, Jason Cheuk Sing; Chen, Li Jia; Zhang, Hao; Cheung, Herman S; Block, Norman L; Schally, Andrew V; Pang, Chi Pui. (2016). Antagonists of growth hormone-releasing hormone receptor induce apoptosis specifically in retinoblastoma cells.. Proceedings of the National Academy of Sciences of the United States of America, 113(50), 14396-14401.