Abstract

Isoliquiritigenin, a natural flavonoid found in licorice, shallots, and bean sprouts, has been demonstrated to inhibit proliferation and to induce apoptosis in a variety of human cancer cells. We attempted to ascertain the underlying mechanism by which isoliquiritigenin induced cell cycle arrest and cytotoxicity in HeLa human cervical cancer cells. Isoliquiritigenin treatment arrested cells in both G2 and M phase. The cells arrested in interphase (G2) showed markers for DNA damage including the formation of γ-H2AX foci and the phosphorylation of ATM and Chk2, whereas the cells arrested in M phase evidenced separate poles and mitotic metaphase-like spindles with partially unaligned chromosomes. The induction of DNA damage and blockade at the metaphase/anaphase transition implied that isoliquiritigenin might function as a topoisomerase II poison, which was further demonstrated via an in vitro topoisomerase II inhibition assay. These results show that isoliquiritigenin inhibits topoiosmerase II activity, and the resultant DNA damage and arrest in mitotic metaphase-like stage contributes to the antiproliferative effects of isoliquiritigenin.

Keywords: Isoliquiritigenin; Topoisomerase II poison; DNA damage; Cell cycle arrest

Article Outline

1. Introduction

2. Materials and methods

2.1. Materials

2.2. Cell culture

2.3. MTT assay

2.4. Flow cytometric analysis

2.5. Confocal microscopy

2.6. Immunoblotting

2.7. In vitro topoiosmerase II assay

2.8. Statistical analysis

3. Results

3.1. Isoliquiritigenin inhibits the proliferation of HeLa cells by arresting cell cycle at G2/M phase

3.2. Isoliquiritigenin induces cell cycle arrest in mitotic metaphase-like stage

3.3. Isoliquiritigenin induces DNA damage

3.4. Isoliquiritigenin activates G2/M checkpoint and triggers DNA damage signaling

3.5. Isoliquiritigenin inhibits the activity of topoisomerase II in vitro

4. Discussion

Conflict of interest Statement

Acknowledgements

References