Synergistic anticancer activity of Juniperus indica Bertol extract plus 5-fluorouracil against oral squamous cell carcinoma in vitro

Purpose: To investigate the potential effect and underlying mechanism of Juniperus indica Bertol extract (JIB) in combination with 5-fluorouracil (5-FU) for the treatment of oral squamous cell carcinoma (OSCC). Methods: The OECM-1, and OSCC cells were exposed to JIB and/or 5-FU for 24–72 h, and subsequently, cell viability, cell cycle distribution, caspase activity, apoptotic cells, and protein expression were determined using the (3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide; MTT) assay. Flow cytometry, fluorometric caspase activity assay kit, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay and western blotting were carried out. Results: The combination of JIB and 5-FU significantly inhibited the growth of OECM-1 cells compared to JIB or 5-FU alone (p < 0.05). After treatment with JIB plus 5-FU, the cell cycle was significantly impeded by downregulating levels of CKD2/cyclin A and CDK4/cyclin D1 (p < 0.05). Furthermore, the combination treatment triggered apoptosis through activation of caspases and the regulation of Bax/caspase 9/caspase 3. In particular, JIB significantly suppressed the regrowth of 5-FU-treated cells and diminished the development of 5-FU resistance during OSCC treatment (p < 0.05) Conclusion: Juniperus indica Bertol extract (JIB) in combination with 5-FU synergistically inhibits cell proliferation, alters cell cycle distribution, and triggers apoptosis compared to single drug. There is need to further explore the potential use of JIB-based combination therapies to improve the clinical application of 5-FU in OSCC.