Tannic acid enhances cisplatin effect on cell proliferation and apoptosis of human osteosarcoma cell line (U2OS)

Background The increase in cases of chemoresistance of cisplatin for osteosarcoma treatment has called for the need to establish a new treatment regime. Tannic acid (TA) possesses a potent antiproliferative effect against various cancers. Therefore, this study investigated the effect of TA combined with cisplatin on human osteosarcoma cell lines (U2OS). Methods MTT assay was used to determine the half-maximal inhibitory concentration (IC 50 ), while the combination index (CI) value was utilized to analyze the interaction within each combination. The antiproliferative effect of the treatment was evaluated by trypan blue exclusion assay. The morphological changes of cells were observed under a phase-contrast inverted microscope. The nuclear morphology and percentage of apoptosis cells were evaluated by using the Hoechst 33258 staining and annexin V/PI assay, respectively. Results The U2OS cells showed cytotoxic effect when treated with TA and cisplatin, with IC 50 at 4.47 µg/mL and 16.25 µg/mL, respectively. The TA demonstrated no significant inhibition effect on the normal human fetal osteoblast cells (hFOB 1.19); yet, interestingly, a potent proliferative effect was indicated. Synergistic interaction was triggered when TA was combined with cisplatin at percentage ratios of 90:10 and 85:15. Meanwhile, antagonistic interaction was induced in the combination at percentage ratios of 75:25 and 50:50. On the other hand, a significant antiproliferative effect with prominent morphological alteration was detected in the cells treated with a combination of TA and cisplatin at the percentage ratio of 90:10. Additionally, combination-treated cells demonstrated the highest percentage of apoptosis cells, with distinct chromosomal condensation, nuclear fragmentation, reduction of nuclear volume, and notable apoptotic body. Conclusion Therefore, there is a high potential for the inclusion of TA in the cisplatin-based chemotherapeutic regimen of osteosarcoma. Graphic abstract