Gemcitabine and carboplatin demonstrate synergistic cytotoxicity in cervical cancer cells by inhibiting DNA synthesis and increasing cell apoptosis

Guixiu Jin,^1,3 Jing Zhao,² Hongyan Qi,² Meng Lou,² Xia Liu,² Yu Qu,³ Lingjun Zhao,³ Weifeng Zhang,³ Jimin Shao,² Huizhen Zhong<sup>3

1</sup>School of Medicine, Ningbo University, Ningbo, ²Department of Pathology and Pathophysiology, Zhejiang University School of Medicine, Hangzhou, ³Department of Gynecological Oncology, Ningbo Women and Children's Hospital, Ningbo, People's Republic of China


Background: The present study aims to investigate the subunit expression and enzyme activity of ribonucleotide reductase in cervical cancer patients, and detect the combined effect of the ribonucleotide reductase inhibitor gemcitabine and the chemotherapeutic agent carboplatin on cervical cancer cell lines.
Methods: Using real-time polymerase chain reaction, Western blotting, and cytidine 5'-diphosphate reduction assays, we tested the expression and activity of ribonucleotide reductase in cervical cancer patients. The antitumor activity of gemcitabine and/or carboplatin treatments to Siha and Caski human cervical cancer cell lines were assessed by Cell Counting Kit-8 viability assay, EdU incorporation assay, immunofluorescence assay, flow cytometry assay, and Western blotting methods. Additionally, synergistic efficacy was quantitatively analyzed using a combination index based on the Chou-Talalay method.
Results: The mRNA levels of three ribonucleotide reductase subunits were all upregulated in the cervical cancer tissues compared with normal tissues (P<0.0001). Consistently, the protein expression and enzyme activity of ribonucleotide reductase were also increased in the cervical cancer tissues. Interestingly, gemcitabine inhibited DNA synthesis and carboplatin induced DNA damage. Further, the combined drug regime had a significant synergistic effect on inhibiting cervical cancer cell viability (log₁₀[combination index] <0) via enhanced DNA damage and cell apoptosis.
Conclusion: The expression and activity of ribonucleotide reductase was increased in cervical cancer. Our study demonstrated the synergistic cytotoxicity of gemcitabine and carboplatin, through inhibiting DNA synthesis and increasing cell apoptosis in cervical cancer cell lines. This evidence might provide a rational clue of their combined application to improve cervical cancer treatment.

Keywords: cervical cancer, ribonucleotide reductase, gemcitabine, carboplatin