image: GA-OH activates p53 and Caspase 8 and induces apoptosis. (A) SCC19, SCC90 and SCC104 were seeded and treated with vehicle, 0.5 μM and 1 μM Of GA-OH for 24 hours. Activation of p53 was tested by blotting for p53 expression and activation. Caspase 8 activation and apoptosis was tested by blotting for Caspase 8 expression and activation of downstream targets. (B) Various HPV+ and HPV- cell lines were seeded in 96 well plates and treated with 0.75 uM GA-OH. Caspase 3/7 activity was measured after 24 hours. HPV+ cell lines show high levels of Caspase 3/7 activity.
Oncotarget published "A high-content AlphaScreen™ identifies E6-specific small molecule inhibitors as potential therapeutics for HPV+ head and neck squamous cell carcinomas" which reported that the incidence of human papillomavirus-positive head and neck squamous cell carcinoma has increased dramatically over the past decades due to an increase in infection of the oral mucosa by HPV.
The etiology of HPV -HNSCC is linked to expression of the HPV oncoprotein, E6, which influences tumor formation, growth and survival.
E6 effects this oncogenic phenotype in part through inhibitory protein-protein interactions and accelerated degradation of proteins with tumor suppressor properties, such as p53 and caspase 8. Interfering with the binding between E6 and its cellular partners may therefore represent a reasonable pharmacological intervention in HPV tumors.
In this study, the authors probed a small-molecule library using AlphaScreen™ technology to discover novel E6 inhibitors.
Further testing of this analog in a panel of HPV and HPV– cell lines showed good potency and a large window of selectivity as demonstrated by apoptosis induction and significant inhibition of cell growth, cell survival in HPV cells.
Dr. Penelope J. Duerksen-Hughes from The Loma Linda University said, "Head and neck squamous cell carcinomas (HNSCC) are heterogeneous tumors that arise in the upper respiratory tract and are the 6th most common cancer worldwide by incidence."
"Head and neck squamous cell carcinomas (HNSCC) are heterogeneous tumors that arise in the upper respiratory tract and are the 6th most common cancer worldwide by incidence."
In parallel, HPV -HNSCC, which is caused by HPV, has risen dramatically within the same period.
Compared to its HPV- counterpart, HPV -HNSCC carries a more favorable prognosis and is more prevalent in younger and otherwise healthier patients.
HPV oncoproteins, particularly E6, represent a unique and potentially therapeutically favorable strategic approach for targeted HPV -HNSCC treatment.
These findings are corroborated by findings that have shown that the absence of p53 and caspase 8 in HNSCC is correlated with attenuation of sensitivity of HPV -HNSCC to chemotherapy and radiation.
Consistent with this, genetic tools such as CRISPER, TALEN gene knockouts, RNAi and other agents that indirectly knock down E6 mRNA have demonstrated that depleting the protein abundance of E6 leads to anti-proliferative effects and enhances the response of HPV cells to chemotherapy agents and radiation.
The Duerksen-Hughes Research Team concluded in their Oncotarget Research Output, "the evidence we have gathered suggests that GA-OH can serve as a basis for better understanding the mechanism of E6 inhibition, and has the potential for further development to improve potency and drug-likeness. Tools such as computational modelling and medicinal chemistry can utilize this inhibitor as a good starting point for optimization and in understanding important interactions between E6 and its inhibitors."