Objective To investigate the effects of isocorydine (ICD) on the proliferation and radiosensitivity of cervical cancer SiHa cells and determine the underlying mechanism.

Methods Different concentrations (25, 50, 100, and 200 μmol/L) of ICD were used to treat cervical cancer SiHa cells (ICD treatment group). Normal cultured SiHa cells without ICD treatment were set as the normal control (NC) group. The 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to detect cell proliferation. Cell clone formation experiment was conducted to determine the radiation sensitization effect of ICD on cells. Western blot analysis was employed to detect phosphorylated histone H2AX (γ-H2AX), phosphorylated phosphatidylinositol 3-kinase (p-PI3K), and phosphorylated protein kinase B (p-Akt) expression. Real-time quantitative PCR (qRT-PCR) was used to detect the expression of microRNA-129-5p (miR-129-5p). SiHa cells were transfected with miR-NC and miR-129-5p, and the roles of transfection of miR-129-5p on cell proliferation, radiosensitivity, cyclinD1, and γ-H2AX protein expression were observed. Anti-miR-NC and anti-miR-129-5p were transfected into SiHa cells, which were then treated with ICD to evaluate the effects on ICD-induced cell proliferation, radiosensitivity, and PI3K/Akt signaling pathway. Data between two groups were compared by independent sample t test.

Results The MTT assay showed that the 25, 50, 100, and 200 μmol/L ICD treatment groups exhibited significant increase in the proliferation inhibition rate ((10.26±1.03)%, (22.16±2.21)%, (44.09±4.41)%, (70.88±7.09)%) of SiHa cells compared with the NC group ((0.05±0.01)%), and the differences were statistically significant (t=29.736−30.013, all P<0.05). The cell clone formation, Western blot, and qRT-PCR analyses showed that the 100 μmol/L ICD treatment group had increased radiosensitivity to different doses of X-rays (t=19.135−44.478, all P<0.05), increased γ-H2AX protein expression (t=15.041, P<0.05) and miR-129-5p expression (t=19.682, P<0.05), and decreased expression of p-PI3K and p-Akt protein compared with the NC group (t=14.897, 15.429; both P<0.05). Transfected (highly expressed) miR-129-5p considerably increased the proliferation inhibition rate ((75.06±7.51)% vs. (1.04±0.10)%; t=29.566, P<0.05), radiosensitivity to different doses of X-rays (t=13.239−37.015, all P<0.05), and γ-H2AX protein expression (t=17.076, P<0.05) of SiHa cells and evidently decreased the expression of the cyclinD1 protein (t=17.393, P<0.05) compared with transfected miR-NC. The transfection of anti-miR-129-5p (low expression of miR-129-5p) reversed the inhibitory effect of ICD on SiHa cell proliferation and PI3K/Akt signaling pathway and reversed its ability to enhance cell radiosensitivity compared with the transfection of anti-miR-NC, and the differences were statistically significant (t=13.370−28.252, all P<0.05).

Conclusion ICD inhibits the proliferation of cervical cancer SiHa cells and enhances radiosensitivity by up-regulating the expression of miR-129-5p and the PI3K/Akt signaling pathway.