Evaluation of a Mucoadhesive Fenretinide Patch for Oral Cancer Chemoprevention

Systemic administration of vitamin A-like compounds, e.g., fenretinide, has been extensively evaluated in oral cancer chemoprevention trials.  These previous trials were largely inefficacious due to dose-limiting toxicities and sub-therapeutic chemopreventive levels. A viable alternative is local delivery which provides therapeutic levels in target tissues without deleterious systemic effects. Objectives: Determine pharmacokinetic parameters of mucoadhesive fenretinide patches placed on rabbit buccal mucosa and assess local tissue effects.  Methods: Fenretinide and blank-control patches were placed on right/left buccal mucosa, respectively, in 8 rabbits (30-minutes q.d., 10-days).  Pre-/post-application sera and post-study oral mucosal specimens were obtained for fenretinide/metabolite quantification (LC-MS/MS) and determination of chemoprevention-relevant parameters (proliferation-Ki67, differentiation-transglutaminase1 (TGase1), apoptosis-TUNEL, bioactivation-UGT1A1). Concurrent studies assessed human oral mucosal enzymatic profiles (n=8) and fenretinide’s growth modulatory effects on cultured human oral keratinocytes.  Mann-Whitney and paired t-test statistics were used. Results: Fenretinide patches delivered highest levels at the patch-mucosal interface, therapeutically-relevant levels to oral mucosa (Mean±SEM:5.59±0.44μM, n=8, p<0.001: fenretinide-treated vs. blank-treated), and undetectable sera levels. No clinical or histologic deleterious effects occurred.   Relative to rabbit-matched blank-treated mucosa, oral tissues containing 0.1-5μM fenretinide (n=6) exhibited increased intraepithelial TGase1 levels (Mean±SEM:+32.8±2.96%) and negligible effects on Ki-67 indices (Mean±SEM:-1.0±0.05%). Tissues containing >5μM (n=2) demonstrated substantially decreased TGase1 levels (Mean±SEM:-29.2±1.8%) and marked reduction of Ki-67 indices (Mean±SEM:-5.6±0.3%).  All fenretinide-treated specimens showed significant intraepithelial increases of TUNEL indices (p<0.01, greatest in tissues >5μM) and significantly increased levels of UGT1A1 expression (p<0.01, greatest in tissues <5μM).  Substantial inter-donor variations in fenretinide-metabolizing enzymes (CYP3A4, UGT1A1) were observed in human oral mucosa.  Fenretinide-treatment of keratinocytes (0-5μM) revealed optimal increases of TGase1 and involucrin at 1μM. Cell proliferation and apoptosis studies are ongoing.  Conclusion: Patch-delivered fenretinide recapitulates the favorable growth modulation previously only observed in cultured cells. This delivery strategy provides a means to clinically re-introduce an effective epithelial-relevant oral cancer chemopreventive.  [F30DE020992, R01CA129609]