Enhancement of Histone Deacetylase Inhibitor Sensitivity in Combination with Cyclin-Dependent Kinase Inhibition for the Treatment of Oral Squamous Cell Carcinoma.

Background/aims: Previous research has indicated that the currently available histone deacetylase inhibitors (HDACis) are not effective as monotherapies against oral squamous cell carcinoma (OSCC). However, HDACis act synergistically with other therapeutic agents to exert significant antitumor activities. Thus, a strategy to develop chemotherapeutic agents by combining several active groups based on histone deacetylase (HDAC) into a single molecule as a conjugate that modulates multiple cellular pathways may be useful for the treatment of OSCC.

Methods: The novel inhibitor Roxyl-ZR was prepared by organic synthesis and its anticancer effects on OSCC were investigated by cell metabolism (n=5), colony formation (n=3), cell cycle (n=3), cell apoptosis (n=3), wound healing (n=3), transwell migration (n=3), and 5-bromo-2'-deoxyuridine staining (n=3) assays in vitro and in in vivo xenograft mice models (4 mice/group for subcutaneous xenograft and 3 mice/group for orthotopic xenograft ). The abundance of Ki67, Bcl-2, and p-STAT3 was detected by immunohistochemistry staining (n=4). Apoptotic cells in the tumor tissues of mice were detected by terminal deoxynucleotidyl transferase dUTP nickend labeling assay (n=3). The abundance of related proteins levels were evaluated by western blot (n=3). E-cadherin expression was detected by an immunofluorescence assay (n=3).

Results: Compared with the approved HDACi, conjugated Roxyl-ZR exhibited significantly higher antitumor effects in OSCC cells. Roxyl-ZR suppressed OSCC cell proliferation by inducing the reduction of S phase and inducing caspase-dependent apoptosis by down-regulating Bcl-2 expression. Moreover, Roxyl-ZR attenuated the epithelial-mesenchymal transition, which is closely associated with migration and invasion. In addition, Roxyl-ZR inhibited OSCC xenograft mice models and showed low toxicity. The mechanism underlying the Roxyl-ZR-enhanced sensitivity to HDACi may be attributed to the inhibition of key regulators of JAK1-STAT3 signaling pathway.

Conclusion: HDAC-cyclin-dependent kinase conjugates represent a novel approach to the development of OSCC treatment. Our findings may open a new avenue for the development of novel inhibitors for the treatment of OSCC.