Capsazepine-Analogs Induce Apoptosis of OSCC Independent of TRPV1 Interactions

Objectives: Head and neck squamous cell carcinoma (HNSCC) is the 6th most common cancer world-wide whose incidence is ever-increasing. The majority of these tumors are found in the oral cavity (OSCC) with a five-year survival rate of 40% for patients with advanced disease. Our previous studies developed novel capsazepine (CPZ) analogs (CIDD24, CIDD99, CIDD111) with significant anti-tumor effects in OSCC xenografts that surpassed the parent compound, CPZ. CIDD99 was the most potent followed by CIDD24 and CIDD111. Objectives: To further delineate the mechanism(s)-of-action of these novel compounds.
Methods: Methods: Mitochondrial membrane potential assays and Mito-Tracker red staining were used to further analyze the effects on mitochondrial function. Western blot analysis of cleaved Parp (cParp) was used to assess induction of apoptosis. To determine the potential role of TRPV1 and reactive oxygen species (ROS) as potential regulators of OSCC proliferation, MTS assays were performed to evaluate the anti-proliferative efficacy in the presence of the TRPV1 antagonist CPZ and the anti-oxidant N-acetyl-cysteine (NAC).
Results: Results: We found all three compounds to be efficacious against a panel of cancer types indicating a universal mechanism-of-action. Our previous calcium imaging studies confirmed that CIDD24 activates TRPV1. Thus TRPV1 could not be ruled out as a potential regulator of CIDD24 efficacy. However, pre-treatment with CPZ had no influence on CIDD24 anti-proliferative effects nor on CIDD99 and CIDD111 indicating that TRPV1 does not regulate OSCC proliferation. In addition, NAC reversed the anti-proliferative effects of these compounds supporting our hypothesis that ROS induction mediates the anti-tumor properties of these analogs. This was further supported by dose-dependent mitochondrial depolarization and corresponding induction of cParp in response to these treatments
Conclusions: Conclusion: CPZ analogs are highly efficacious in treating OSCC due to their superior induction of mitochondrial dysfunction and apoptosis. Furthermore, TRPV1 activity does not mediate the actions of CIDD24, CIDD99, or CIDD111.