Title : Targeting oral squamous cell carcinoma with thienopyrimidines

Oral squamous cell carcinoma (OSCC) is among the most aggressive and lethal cancers of the head and neck, often diagnosed at an advanced stage and marked by treatment resistance. In search of selective anticancer agents, we evaluated a series of 2-substituted 4-amino-thieno[2,3-d]pyrimidines—originally synthesized as DPP-4 inhibitors—for their cytotoxic potential against oral cancer.

The compounds (1–7) were tested against SCC-9 and HSC-3 human oral cancer cell lines, and HaCaT normal keratinocytes, using the MTT assay. Selectivity index (SI) was calculated to assess discrimination between malignant and non-malignant cells. Additionally, FACS analyses, colony forming assay, cell migration and cytoskeleton staining were performed.

Compound 6 showed the highest selectivity toward both SCC-9 (SI = 22.3) and HSC-3 (SI = 6.4), indicating strong anticancer potential. Compound 4 also exhibited notable selectivity for SCC-9 (SI = 12.8). Compound 5 displayed moderate selectivity, comparable to doxorubicin. In contrast, compounds 1 and 2 showed low SI values (<3), while compounds 3 and 7 demonstrated moderate selectivity.

These findings support the further development of compound 6, and potentially compound 4, as promising leads for selective oral cancer therapeutics, particularly due to their ability to discriminate between malignant and non-malignant cells. Further studies are underway to elucidate their mechanism of action and optimize anticancer potency.

Acknowledgments: This study was partially supported by the following grants: COST Action CA21140 INTERCEPTOR, KP-06-COST/30. Bulgarian Ministry of Education and Science for support: Scientific Infrastructure on Cell Technologies in Biomedicine (SICTB) D01-361/2023 and National Center for Biomedical Photonics D01-352/2023, part of the Bulgarian National Roadmap for Scientific Infrastructures 2020–2027. A.N. thanks the Bulgarian Ministry of Education and Science, National Research Program “Young scientists and postdoctoral students-2”, Module “Young scientists”, for financial support on her project entitled “Interaction of conventional cytostatics with selected plant extracts on breast cancer models”.

Prof. Biliana Nikolova is an expert in biomedical biophysics, specializing in the effects of electric fields on biological systems. She holds a Ph.D. in Biophysics from the Bulgarian Academy of Sciences and is based at the Institute of Biophysics and Biomedical Engineering (IBPhBME), where she heads the Department of Electroinduced and Adhesive Properties. Her research combines biophysical techniques—such as patch clamp, FACS, and fluorescence microscopy—with nanomedicine, electrotherapy, and biopolymer pharmacology, focusing on anticancer applications and tissue engineering. Prof. Nikolova’s work bridges basic science and translational research, contributing significantly to the fields of medical biophysics and bioengineering.