Therapeutic Intervention Using a Smad7-Based Tat Protein to Treat Radiation-Induced Oral Mucositis

Purpose Recent studies reported therapeutic effects of Smad7 on oral mucositis in mice without compromising radiation therapy–induced cancer cell killing in neighboring oral cancer. This study aims to assess whether a Smad7-based biologic can treat oral mucositis in a clinically relevant setting by establishing an oral mucositis model in dogs and analyzing molecular targets. Methods and Materials We created a truncated human Smad7 protein fused with the cell-penetrating Tat tag (Tat-PYC-Smad7). We used intensity modulated radiation therapy to induce oral mucositis in dogs and applied Tat-PYC-Smad7 to the oral mucosa in dose-finding studies after intensity modulated radiation therapy. Clinical outcomes were evaluated. Molecular targets were analyzed in biopsies and serum samples. Results Tat-PYC-Smad7 treatment significantly shortened the duration of grade 3 oral mucositis based on double-blinded Veterinary Radiation Therapy Oncology Group scores and histopathology evaluations. Topically applied Tat-PYC-Smad7 primarily penetrated epithelial cells and was undetectable in serum. NanoString nCounter Canine IO Panel identified that, compared to the vehicle samples, top molecular changes in Tat-PYC-Smad7 treated samples include reductions in inflammation and cell death and increases in cell growth and DNA repair. Consistently, immunostaining shows that Tat-PYC-Smad7 reduced DNA damage and neutrophil infiltration with attenuated TGF-β and NFκB signaling. Furthermore, IL-1β and TNF-α were lower in Tat-PYC-Smad7 treated mucosa and serum samples compared to those in vehicle controls. Conclusions Topical Tat-PYC-Smad7 application demonstrated therapeutic effects on oral mucositis induced by intensity modulated radiation therapy in dogs. The local effects of Tat-PYC-Smad7 targeted molecules involved in oral mucositis pathogenesis as well as reduced systemic inflammatory cytokines.