Synergistic Antitumor Interaction of Risedronate Sodium and Standard Anticancer Agents in Canine (D-17) and Human Osteosarcoma (U-2 OS) Cell Lines

The study discusses in vitro cytotoxicity of a combination of cytostatic drugs (doxorubicin, cisplatin, carboplatin, etoposide) and risedronate sodium against canine and human osteosarcoma (D-17 and U-2 OS). Standard protocols were used for the preparation of cell cultures and evaluation of their viability and apoptosis. MTT assay assessed the culture viability and EC50, while the apoptotic effect of the drugs was checked with a TUNEL assay. Doxorubicin alone showed the strongest cytotoxicity against D-17 (0.056 &plusmn: 0.019 &micro:g/mL) and U-2 OS (0.051 &plusmn: 0.003 &micro:g/mL), while the lowest cytotoxicity was observed for carboplatin (D-17, 6.45 &plusmn: 0.2 &micro:g/mL and U2-OS, 27.5 &plusmn: 2.3 &micro:g/mL). Risedronate sodium at 100, 10 and 1 &micro:g/mL lowered viability in OS cell lines by 53.38 &plusmn: 1.46 and 49.56 &plusmn: 0.7%, 97.08 &plusmn: 3.32 and 74.92 &plusmn: 4.01%, and 102.67 &plusmn: 3.56 and 94.56 &plusmn: 3.52%, respectively. In all analyzed drug combinations, risedronate sodium significantly (* p &lt: 0.05) increased the cytotoxicity against tested osteosarcoma cell lines. The decrease in cell viability caused by the studied compound combinations was weaker in canine than in human cell cultures. A combination of doxorubicin (all concentrations), cisplatin (1 &micro:g/mL) and etoposide (1 &micro:g/mL) with 100 &micro:g/mL of risedronate sodium significantly improved the cytotoxicity of the drugs against canine and human osteosarcoma. Administration of carboplatin (1 &micro:g/mL) and risedronate sodium (100 &micro:g/mL), compared to carboplatin per se, produced no significant differences in cytotoxicity against the D-17 cell culture but significantly enhanced cytotoxicity in the U-2 OS line. The strongest apoptosis in both lines was detected for 0.01 &micro:g/mL doxorubicin combined with 100 &micro:g/mL risedronate sodium or 1 &micro:g/mL cisplatin and 100 &micro:g/mL risedronate sodium. In all combinations, the tested compounds revealed a synergistic mechanism of action.