Chemoprevention of Oral Squamous Cell Carcinoma: Extending Therapeutic Parameters of Fenretinide.

摘要

Oral squamous cell carcinoma (OSCC) represents the primary cancer of the oral cavity and poses a worldwide health problem. OSCC arises from malignant transformation of clinically detectable premalignant epithelial lesions known as oral intraepithelial neoplasia (OIN). OIN's visible nature and clinical accessibility render this process a prime target for local chemopreventive strategies. OIN chemoprevention is a patient-centric, optimal strategy to prevent OSCC's co-morbidities and mortality. The membrane-associated protein, focal adhesion kinase (FAK), modulates cell-extracellular matrix interactions and also conveys pro-survival and proliferative signals. Notably, increased intraepithelial FAK levels accompany transformation of premalignant oral intraepithelial neoplasia (OIN) to OSCC. The cancer chemopreventive and synthetic vitamin A-derivative, fenretinide, has demonstrated protein-binding capacities e.g. mTOR and retinol binding protein interactions. These studies assessed potential fenretinide-FAK drug protein interactions and functional consequences on cellular growth regulation and motility. Molecular modeling studies demonstrated fenretinide has ~200-fold greater binding affinity relative to the natural ligand (ATP) at FAK's kinase domain. Fenretinide also shows intermediate binding at FAK's FERM domain and interacts at the ATP-binding site of the closest FAK analogue, Pyk2. Fenretinide significantly suppressed proliferation via induction of apoptosis and G2/M cell cycle blockade. Fenretinide-treated cells also demonstrated F-actin disruption, significant inhibition of both directed migration and invasion of a synthetic basement membrane, and decreased phosphorylation of growth-promoting kinases. A commercially available FAK inhibitor did not suppress cell invasion. Notably, while FAK's FERM domain directs cell invasion, FAK inhibitors target the kinase domain. In addition, FAK-specific siRNA treated cells showed an intermediate cell migration capacity; data which suggest co-contribution of the established migrating-enhancing Pyk2. Our data imply that fenretinide is uniquely capable of disrupting FAK's and Pyk2's pro-survival and mobility-enhancing effects and further extend fenretinide's chemopreventive contributions beyond induction of apoptosis and differentiation. Intra-/inter-tumor heterogeneity of oral squamous cell carcinoma (OSCC) poses a conundrum to conventional therapeutic management, which assumes the presence of therapeutic targets within OSCC precursor lesions or tumors. Notably, cetuximab, a FDA-approved EGFR-targeting monoclonal antibody for locally advanced HNSCC, has encountered chemoresistance, lowering its clinical efficacy; OSCC cells activate compensatory signaling pathways to ensure continual proliferation and survival. Personalized tumor profiling, therefore, enables identification of aberrant molecular and biochemical phenotypes and customization of therapeutic strategy to fit individual patient's OSCC profiles. Characterization of specific tumorigenic signaling pathways and cytokine secretion profiles revealed significant heterogeneity among recently isolated OSCC cell lines (JSCC-1, JSCC-2, and JSCC-3), leading to varied response to specific inhibition of key tumorigenic pathways (e.g. EGFR and STAT3); Afatinib, specific EGFR inhibitor, was able to inhibit STAT3 phosphorylation in JSCC-3 but not in JSCC-1 and JSCC-2. Notably, STAT3 inhibition-refractory cells lines were responsive to fenretinide, a vitamin A-derived chemopreventive. Previous studies have demonstrated fenretinide's capacity to modulate cellular phosphorylation status toward anti-tumorigenic phenotypes. Fenretinide combined with specific small molecule inhibitors (i.e. afatinib and vargatef) were able to prevent activation of targeted tumorigenic pathway as well as redundant signaling. Our data demonstrated that fenretinide is capable of regulating key tumorigenic pathways both as a single agent and an adjunct drug.