Inhibition of SENP5 by Cucurbitacin B Suppresses Cell Growth and Promotes Apoptosis in Osteosarcoma Cells

Purpose: To investigate the effect of cucurbitacin B on the expression of SUMO-specific proteases (SENP5).
Methods: Effect of cucurbitacin B (10-50 mg/mL) on viability of U2OS and Saos-2 cells was determined in a plate reader by recording absorbance at 570 nm. In Western blot analysis, bicinconinic acid (BCA) method was used to determine protein concentration. Flow cytometry was employed to measure DNA content.
Results: Cucurbitacin B treatment inhibits the expression of SENP5 in U2OS and Saos-2 osteosarcoma cells in a dose- and time-dependent manner. Significant inhibition (p = 0.005) of SENP5 expression was observed at 50 mg/ml from day 10, reaching a maximum on day 20. It also induced a significant decrease (p = 0.005) in mRNA and protein levels of SENP5. The decrease in mRNA and protein levels of SENP5 led to decrease in proliferation of U2OS and Saos-2 cells. The 48 h cell cultures containing 50 mg of cucurbitacin B caused induction of apoptosis in 54.72 ± 5.42 % of the total cell population in U2OS cells. Similarly, in Saos-2 cells, exposure to 50 mg/mL cucurbitacin B increased apoptotic rate from 9.86 ± 8.89 % for 10 mg/mL to 48.54 ± 14.5 % with 50 mg/mL of cucurbitacin B.
Conclusion: Cucurbitacin B is a potential therapeutic strategy for the treatment of aggressive malignancy in osteosarcoma.

Keywords
Cucurbitacin B; Osteosarcoma; SUMO-specific proteases; Cell proliferation; Apoptosis; Malignancy