Hydroalcoholic extract of the widely used Mexican plant Justicia spicigera Schltdl. exerts a cytostatic effect on LNCaP prostate cancer cells

Justicia spicigera Schltdl. (Acanthaceae) is a plant used in traditional Mexican medicine to treat several types of cancer. Some studies reported cytotoxic effects of J. spicigera extracts on cancer cell lines, but that the androgen-independent DU-145 prostate cancer cell line resists its cytotoxic action. The aim of the present study was to investigate whether an hydroalcoholic J. spicigera extract (HJsE) exerts antiproliferative and cytotoxic effects on the androgen-dependent stage of prostate cancer, thus contributing to the scientific validation of this plant for prostate cancer treatment. LNCaP cells were treated with HJsE (62.5–4000 μg/ml) for 24–72 h. HJsE reduced the proliferation of LNCaP cells by 62% ± 1.7% (IC50 = 3026 ± 421 μg/ml) without affecting cell viability, assessed by both MTT assay and cell counting based on Trypan blue exclusion assay. Ki-67 immunostaining revealed that HJsE (4000 μg/ml) increased the percentage of cells in the G0 phase (Ki-67-negative; 5.26% ± 0.82%, p < 0.001) and interphase (late G1/S/G2; 4.37% ± 0.82%, p < 0.01), decreased the percentage of cells in the early G1 phase (1.76% ± 0.82%, p < 0.001), and decreased the percentage of cells that progressed to mitosis (7.87% ± 0.82%, p < 0.001). HJsE had low cytotoxicity in LNCaP cells (IC50 > 4000 μg/ml). These results indicate that HJsE affects the proliferation of LNCaP cells through a cytostatic mechanism rather than a cytotoxic mechanism, preventing the progression to mitosis in the cell-cycle. The cytostatic potential of HJsE should be explored in other models of prostate cancer to demonstrate its utility as an alternative strategy for prostate cancer treatment.