The role of Paraoxonase 2 (PON2) in resistance of oral squamous cell carcinoma against radio- and chemotherapy

• Applicant: Dr. Maximilian Krüger
• Subject Area: Dentistry, Oral Surgery
• Term: from 2013 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 240969075

Squamous cell carcinoma of the head and neck is the seventh most common cancer worldwide. Despite the interdisciplinary treatment by surgery, chemo- and radiotherapy the five year survival rate ranges only at a poor level of 50%. Induction of programmed cell death (apoptosis) is a key mechanism of the adjuvant radio- and chemotherapy. Unfortunately, carcinomas often present an altered protein expression with upregulation of antiapoptotic proteins to undergo therapeutic induced apoptosis. So for today a valid prediction about an individual therapy success is not possible. Recent studies of our own group showed for cells of the vascular system a protective effect against ROS (reactive oxygen species) by the endogenous enzyme Paraoxonase2 (PON2), which localizes mainly to nucleus, endoplasmatic reticulum (ER) and mitochondria. The enzyme is further involved in an ER stress pathway known as unfolded protein response (UPR) with critical influence on survival or induction of apoptosis. In vascular cells PON-2 diminishes overwhelming ROS levels in mitochondria and prevents thereby cytochrome c release, caspase activation and mitochondrial induced apoptosis. Since irradiation and treatment with cisplatin typically induces elevated levels of ROS and subsequent oxidative damage in nucleus, mitochondria and ER, PON2 could also protect oral squamous cell carcinoma against therapeutic induced apoptosis.Elevated PON2 expression was shown for tumors of bladder, endometrium, liver and kidney while its expression in oral squamous cell carcinoma has not been analyzed yet. In tumor cell lines of lung and leukemia temporary PON2 knock down led to spontaneous apoptosis, while PON2 knock-out mice are survivable. This accents the role of PON2 expression in survival of tumor cells: Elevated PON2 levels could be an advantage for tumor cells under adjuvant therapy.Based on the hypothesis PON2 protects oral squamous cell carcinoma against radio- and cisplatin induced apoptosis, PON2 expression in oral squamous cell carcinoma cell lines PCI-13, PCI-52, SCC-4, SCC-68 and human oral keratinocytes will be analyzed on RNA- and protein-level basal, after irradiation and after treatment with cisplatin. Further, analysis of subcellular localization of PON2 will be performed using immune fluorescence staining. After temporary PON2 knock down by siRNA treatment its potential protective effect against radio- and cisplatin-induced apoptosis induction will be analyzed using FACS and activity measurement of caspase 3/7. The in vivo expression of PON2 will be analyzed on protein level by specimen of tumor and healthy mucosa from 20 patients treated in our department for oral carcinoma.

• DFG Programme: Research Grants
• Participating Persons: Professor Dr. Bilal Al-Nawas; Privatdozent Dr. Sven Horke; Privatdozent Dr. Maximilian Moergel