Limonene terpenoid obstructs human bladder cancer cell (T24 cell line) growth by inducing cellular apoptosis, caspase activation, G2/M phase cell cycle arrest and stops cancer metastasis.

Purpose: The primary purpose of the current study was to investigate the antitumor activity of limonene which is a plant monoterpene along with evaluating its effects on cell apoptosis, cell cycle phase distribution, cell migration and invasion.

Methods: The cell proliferation of T24 bladder cancer cells was examined by WTS-1 assay. The apoptotic effects induced by limonene were investigated by a combination of fluorescence microscopy and flow cytometry and then confirmed by western blot assay. The effects of limonene on cell cycle in T24 bladder cancer cells were studied by flow cytometry. The effects on cell migration and invasion were examined by wound healing assay and transwell assay using Matrigel.

Results: The results showed that limonene induced cytotoxic effects and reduced cell viability of T24 human bladder cancer cells showing an IC50 value of 9 μM. Limonene also induced significant apoptosis in bladder cancer cells since it induced significant nuclear fragmentation, chromatin condensation, and splitting of the nucleus, representative of the apoptotic cascade. The apoptotic cell percentage was 1.95, 5.35, 15.61 and 34.71% at limonene concentrations of 0, 9, 18 and 36 µM. Further, the apoptotic effects of limonene were also confirmed by Western blot analysis and the results showed increase in the expression of Bax and caspase-3 and decrease of Bcl-2 expression. Limonene also caused G2/M phase cell cycle arrest as well as suppression of cell migration and invasion.

Conclusions: These results indicate that limonene might be used as a potent anticancer agent against human bladder cancer for which further in depth studies are needed, especially over its toxicological studies.