Background: Development of radioresistance in oral squamous cell carcinoma (OSCC) remains a significant problem in cancer treatment, contributing to the lack of improvement in survival trends in recent decades. Effective strategies to overcome radioresistance are necessary to improve the therapeutic outcomes of radiotherapy in OSCC patients. Methods: Cells and xenograft tumors were irradiated using the Small Animal Radiation Research Platform. AKT inhibitor capivasertib (AZD5363) was encapsulated into cathepsin B-responsible nanoparticles (NPs) for tumor-specific delivery. Cell viability was measured by alamarBlue, cell growth was determined by colony formation and 3D culture, and apoptosis was assessed by flow cytometry with the staining of Fluorescein isothiocyanate (FITC) Annexin V and PI. An orthotopic tongue tumor model was used to evaluate the in vivo therapeutic effects. The molecular changes induced by the treatments were assessed by Western blotting and immunohistochemistry. Results: We show that upregulation of AKT signaling is the critical mechanism for radioresistance in OSCC cells, and AKT inactivation by a selective and potent AKT inhibitor capivasertib results in radiosensitivity. Moreover, relative to irradiation (IR) alone, IR combined with the delivery of capivasertib in association with tumor-seeking NPs greatly enhanced tumor cell repression in 3D cell cultures and OSCC tumor shrinkage in an orthotopic mouse model. Conclusions: These data indicate that capivasertib is a potent agent that sensitizes radioresistant OSCC cells to IR and is a promising strategy to overcome failure of radiotherapy in OSCC patients.

For patients with head and neck cancer whose tumors are HPV negative HPV(-), current therapy does not lead to significant longevity and most succumb to loco-regional recurrence of the primary tumor. We discovered that HPV(-) head and neck squamous cell carcinoma (HNSCC) highly expressed ATPase family AAA-domain containing protein 3A (ATAD3A). ATAD3A is the mitochondrial protein which has been demonstrated as an oncogene in breast and lung cancer; however, nothing has been reported regarding its role in HNSCC. Using the HPV(-) HNSCC cell line HN12 as a cell model, we show here that knockout of ATAD3A expression by CRISPR-CAS9 in HNSCC cells leads to reduced cell proliferation and decreased the ability of colony formation and anchorageindependent growth in soft agar. Importantly, ATAD3A loss also significantly suppressed HNSCC cells to grow in 3D culture. Together, these findings suggest the potential oncogenic role of ATAD3A in HNSCC cells, and implicate that ATAD3A represents a promising target for better treatment of patients with HPV(-) HNSCC.