The Individual Effects of Cyclin-Dependent Kinase Inhibitors on Head and Neck Cancer Cells-A Systematic Analysis

Simple Summary This study examined the therapeutic potential of a combined therapy approach, based on clinical approved drugs (5-FU, Cisplatin, cetuximab) and cyclin-dependent kinase inhibitors (CDKi, dinaciclib, palbociclib, THZ1). We identified individual effects on head and neck squamous cell carcinoma cells, including induction of apoptosis/necrosis, and senescence as well as reduced invasiveness. Besides, we describe the relevance of the sequential timing of each combination partner to achieve synergistic effects. Another interesting finding of our study is the upregulation of immunologically relevant molecules on the tumor cell surface under certain CDKi-drug combinations. Here, dinaciclib and palboclicb had highest impact on immunogenicity, which even exceeded effects of the standard drugs. Finally, a therapeutic in vivo approach partially confirmed cell line-based results. Here, effective tumor growth control was seen when cisplatin was combined with dinaciclib. However, antitumoral effects were highly individual and nicely confirm the heterogeneity of this tumor entity. Cyclin-dependent kinase inhibitors (CDKi ' s) display cytotoxic activity against different malignancies, including head and neck squamous cell carcinomas (HNSCC). By coordinating the DNA damage response, these substances may be combined with cytostatics to enhance cytotoxicity. Here, we investigated the influence of different CDKi ' s (palbociclib, dinaciclib, THZ1) on two HNSCC cell lines in monotherapy and combination therapy with clinically-approved drugs (5-FU, Cisplatin, cetuximab). Apoptosis/necrosis, cell cycle, invasiveness, senescence, radiation-induced gamma-H2AX DNA double-strand breaks, and effects on the actin filament were studied. Furthermore, the potential to increase tumor immunogenicity was assessed by analyzing Calreticulin translocation and immune relevant surface markers. Finally, an in vivo mouse model was used to analyze the effect of dinaciclib and Cisplatin combination therapy. Dinaciclib, palbociclib, and THZ1 displayed anti-neoplastic activity after low-dose treatment, while the two latter substances slightly enhanced radiosensitivity. Dinaciclib decelerated wound healing, decreased invasiveness, and induced MHC-I, accompanied by high amounts of surface-bound Calreticulin. Numbers of early and late apoptotic cells increased initially (24 h), while necrosis dominated afterward. Antitumoral effects of the selective CDKi palbociclib were weaker, but combinations with 5-FU potentiated effects of the monotherapy. Additionally, CDKi and CDKi/chemotherapy combinations induced MHC I, indicative of enhanced immunogenicity. The in vivo studies revealed a cell line-specific response with best tumor growth control in the combination approach. Global acting CDKi's should be further investigated as targeting agents for HNSCC, either individually or in combination with selected drugs. The ability of dinaciclib to increase the immunogenicity of tumor cells renders this substance a particularly interesting candidate for immune-based oncological treatment regimens.