Thyroid cancer (TC) is the most common endocrine
malignancy.
Thyroidectomy and
radiotherapy are common treatment modalities for patients with undifferentiated TC (UTC), and
sorafenib is usually recommended to prevent a recurrence. However, malignant cells may evade
chemotherapy-induced apoptosis, and combination
therapy was developed to achieve better outcomes. This study investigated whether
eugenol in combination with
sorafenib was more effective than either substance individually in triggering apoptosis in the UTC. The IC50 of
sorafenib and
eugenol was determined in a UTC cell line (8305C) by MTT assay, and their synergistic effect in combination
therapy was investigated. Flow cytometry was used to evaluate the rate of apoptosis in treated cells. To confirm that cell death occurred through apoptosis, immunoblotting was used to determine the relative cleavage of
caspase-8 and
caspase-9. The IC50 of
sorafenib was 20 µM, and that of
eugenol was 2100 µM. The
sorafenib-
eugenol combination (1:105) showed synergistic effects at concentrations equal to or less than their IC50. The rate of apoptosis induction was higher in cells treated with
eugenol or the
eugenol-
sorafenib combination compared to
sorafenib-treated cells. The relative intensity of cleaved/un cleaved forms of
caspase-8 increased in
eugenol-treated cells compared to
sorafenib-treated cells.Sorafenib and
eugenol at concentrations equal to or less than their IC50 had a synergistic effect in 8305C cells. The most potent apoptotic effect was achieved with
sorafenib and
eugenol at their IC50. Lower doses of
sorafenib could be used with
eugenol to improve its efficacy while reducing its side effects.