Bacterial Proteomic Profile of Early Colonizers on the Acquired Pellicle of Patients with Head and Neck Cancer

Abstract Radiotherapy is the cornerstone of head and neck cancer (HNC) treatment, but it has been frequently associated with changes in the acquired enamel pellicle (AEP), potentially affecting the early stages of dental biofilm formation. Thus, this study aimed to characterize the bacterial proteomic profiles of early colonizers adhering to the AEP in patients with HNC undergoing radiotherapy, with emphasis on radiation-induced changes that may influence oral biofilm development and oral health outcomes. AEP samples were collected from nine patients with HNC before radiotherapy (BRT), during radiotherapy (DRT), and after radiotherapy (ART), as well as from nine orally healthy individuals. Pellicles were obtained 120 min after formation and analyzed by shotgun label-free proteomics using nanoLC-ESI-MS/MS. Protein expression levels were compared between groups using the t test (p < 0.05). AEP showed elevated levels of bacterial proteins predominantly attributed to Actinomyces, mainly associated with DNA binding, chromatin organization, and glucose metabolism. The bacterial proteomic profile shifted markedly DRT, with exclusive detection of proteins involved in carbohydrate transport and metabolism, oxidative stress response, and protein folding, including several ATP-binding cassette transporters and glycolytic enzymes. Proteins related to stress tolerance, transcriptional regulation, and secretion systems were detected ART, many of them associated with bacterial species commonly linked to periodontal diseases, such as Tannerella and Oribacterium. Notably, Cysteine synthase was identified exclusively BRT in all comparisons, suggesting its potential as a biomarker. These findings indicate that radiotherapy induces dynamic changes in the AEP bacterial proteome, potentially favoring dysbiotic biofilm development and increasing susceptibility to oral diseases in patients with HNC.