Experimental assessment of photodynamic therapy effects on 4NQO-induced rat tongue carcinogenesis: Clinical, morphological, and immunohistochemical analysis.

Abstract

The present study aimed to evaluate the safety of photodynamic therapy (PDT) during oral carcinogenesis using a 4-nitroquinoline 1-oxide (4NQO) rat model, which serves as a surrogate for tobacco-induced oral cancer. Forty male Wistar rats received 4NQO (25 ppm) in drinking water for either 12 or 20 weeks to induce oral lesions. Animals were divided into two groups: Control and PDT. PDT was applied weekly from the beginning of the protocol. A 5-aminolevulinic acid (5-ALA) solution was topically applied to the posterior tongue, followed by laser irradiation guided by fluorescence detection 2 h post-application. Clinical, histopathological, and immunohistochemical (Ki-67) evaluations were performed. Lesions on the posterior dorsum of the tongue manifested in all animals, initially presented as white patches, and over time, progressed to erosive lesions, nodules, and ulcers. Histopathological analysis revealed that epithelial dysplasia predominated at 12 weeks, while squamous cell carcinoma was more frequent at 20 weeks in both groups. No significant differences were observed between the Control and PDT groups concerning clinical appearance or microscopic analysis at either time point. However, Ki-67 expression was significantly lower in the PDT group (p < 0.05), indicating reduced cell proliferation. Cellular proliferation was also downregulated at distant sites, specifically in the anterior tongue, similar to that observed in 4NQO-treated posterior tongue in the PDT group relative to controls at 12 and 20 weeks, suggesting that the antiproliferative effect of PDT extends beyond the irradiated site. Although PDT did not significantly influence lesion progression, it was found to markedly reduce Ki-67 expression levels - even at non-irradiated sites. This observation suggests a potential suppressive effect of PDT on cellular proliferation, which may play a role in modulating tumor growth during the carcinogenesis process.