Abstract: Background and purpose: One of the reasons why cancer cells are resistant to chemotherapy is the existence of cancer stem cells. The purpose of this study was to investigate the chemoresistance of CD44⁺/CD24⁺ Siha cells to cisplatin and its mechanisms. Methods: Siha cells were cultivated in vitro. The CD44⁺/CD24⁺ Siha cells were sorted out by fluorescence activated cell sorter (FACS) and in vitro proliferation was detected by MTT assay after treatment with the different concentrations of cisplatin. The cell apoptosis rate was detected by flow cytometry after 10 μg/mL cisplatin acted on CD44⁺/CD24⁺ Siha cells for 24, 48 and 72 h. The relative mRNA and protein expressions of Bcl-2, Oct-4 and ABCG2 were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot, respectively. Results: The survival rates of CD44⁺/CD24⁺ Siha cells treated with different concentrations of cisplatin (0.1, 1, 5, 10, 15 and 20 μg/mL) were higher than those of their parental Siha cells [(88.42±1.51)% vs (92.87±1.5)%, (79.94±1.05)% vs (84.72±1.09)%, (69.78±0.81)% vs (75.13±2.86)%, (58.97±0.70)% vs (65.79±2.71)%, (49.60±0.88)% vs (52.10±0.52)%, (45.13±0.69)% vs (48.84±1.02)%, P<0.05]. Compared with their parental Siha cells, the apoptosis rates of CD44⁺/CD24⁺ Siha cells were lower after 10 μg/mL of cisplatin acting on them for 24, 48 and 72 h, respectively [(3.05±0.16)% vs (5.17±0.27)%, (17.94±2.02)% vs (32.60±4.28)% and (40.14±3.01)% vs (56.62±5.32)%, P<0.05]. The results from both qRT-PCR and Western blot indicated that Oct-4, ABCG2 and Bcl-2 were highly expressed on CD44⁺/CD24⁺ Siha cells. A significant difference was found in Oct-4, ABCG2 and Bcl-2 expression between CD44⁺/CD24⁺ Siha cells and their parental cells (P=0.015<0.05). Conclusion: CD44⁺/CD24⁺ Siha cells could be resistant to apoptosis induced by cisplatin and expressed high levels of cancer stem cell markers such as Oct-4 and ABCG2. This study lays the basis for useful isolation and further targeted therapy of cervical cancer stem cells.

Key words: Cervical cancer, Cancer stem cells, CD44⁺, CD24⁺, Cisplatin, Drug resistance, Apoptosis