Thymol inhibits oral squamous cell carcinoma growth via mitochondria-mediated apoptosis

• Main Authors: De La Chapa, J.J (Author), Gonzales, C.B (Author), Lee, D.R (Author), Singha, P.K (Author)
• Format: Article
• Language: English
• Published: Blackwell Publishing Ltd 2018
• Subjects: acetylcysteine; agonists; animal; animal experiment; animal model; Animals; antineoplastic agent; Antineoplastic Agents, Phytogenic; antiproliferative activity; apoptosis; Apoptosis; Article; CAL-27 cell line; calcium; calcium transport; cancer inhibition; Carcinoma, Squamous Cell; Cell Line, Tumor; cell viability assay; clonogenic assay; controlled study; cytotoxicity; drug effect; female; HeLa cell line; HeLa Cells; histopathology; human; human cell; Humans; in vitro study; in vivo study; inflammatory infiltrate; ionomycin; listerine; membrane potential; Membrane Potential, Mitochondrial; Mice; Mitochondria; mitochondrial dysfunction; mitochondrial membrane potential; mitochondrion; mouse; mouth squamous cell carcinoma; MTS assay; n (4 isopropylphenyl) 2 (1,2,3,6 tetrahydro 1,3 dimethyl 2,6 dioxo 7h purin 7 yl)acetamide; nonhuman; oral squamous cell carcinoma; pathology; phytotherapy; Phytotherapy; priority journal; squamous cell carcinoma; study; thymol; Thymol; Tongue Neoplasms; tongue tumor; transient receptor potential channel; transient receptor potential channel A1; TRPA1; TRPA1 Cation Channel; tumor cell line; tumor volume; tumor xenograft; TUNEL assay; Western blotting
• Online Access: View Fulltext in Publisher

 Background: Thymol is a transient receptor potential ankyrin subtype 1 channel, (TRPA1) agonist found in thyme and oregano. Thymol has antioxidant, anti-inflammatory, and antimicrobial properties; thus, thymol is added to many commercially available products including Listerine mouthwash. Thymol is also cytotoxic to HL-60 (acute promyelocytic leukemia) cells in vitro. Therefore, we evaluated the effects of thymol against oral squamous cell carcinoma (OSCC) and its anticancer mechanism-of-action. Methods: The antiproliferative effects of thymol in OSCC Cal27 cells were determined by MTS assays. Antitumor effects were evaluated in Cal27- and HeLa-derived mouse xenografts. Calcium imaging, mitochondrial transmembrane potential (ΔΨm) studies, and Western blot analysis of cleaved PARP (c-PARP) evaluated thymol's mechanism-of-action. Results: Thymol had significant, long-lasting antiproliferative effects in vitro. In vivo, thymol displayed significant antitumor effects in Cal27-derived tumors. Thymol's anticancer effects were confirmed in HeLa-derived xenografts demonstrating that thymol effects are not tumor-type specific. Calcium imaging verified calcium influx in Cal27 cells that were reversed with the TRPA1 antagonist, HC030031. However, no calcium influx was seen in HeLa cells indicating that TRP channels do not regulate thymol cytotoxicity. This was confirmed using cell viability assays in which pre-treatment with HC030031 had no effect on thymol cytotoxicity. Instead, ΔΨm studies revealed that thymol induces significant ΔΨm depolarization and apoptosis. Conclusion: Our findings provide the first evidence of thymol's novel antitumor effects against OSCC in vivo, which do not rely on TRPA1 activity. Instead, we show that thymol induces mitochondrial dysfunction and apoptosis and may be efficacious against multiple cancers. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd