Cisplatin is effective against solid tumors including ovarian cancer. However, inherent or acquired cisplatin resistance limits clinical success. We recently demonstrated that a combination of sodium arsenite (NaAsO2) and hyperthermia sensitizes p53-expressing ovarian cancer cells to cisplatin by modulating DNA repair pathway and enhancing platinum accumulation. However, it is not understood how this combination therapy modulates cell cycle following platinum-DNA damage. The goal of the present study was to determine if NaAsO2 and hyperthermia alter cisplatin-induced G2 arrest and cause mitotic arrest and mitotic catastrophe. Human epithelial ovarian cancer cells (A2780 and A2780/CP70) were treated with cisplatin ± 20 μM NaAsO2 at 37 or 39°C for 1 h. Cisplatin ± NaAsO2 at 37 or 39°C caused cells to accumulate in G2/M compartment at 36 h after treatment. Western blot analysis of cyclin A and cyclin B suggested that combined NaAsO2, hyperthermia, and cisplatin induced mitotic arrest. However, we observed < 3% mitotic index and phosphorylation of histone H3 on serine 10 was undetectable. These results did not confirm mitotic arrest. BUBR1 (BUB1B) also was not phosphorylated, suggesting disrupted mitotic checkpoint. Postmitotic cells accumulated in pseudo-G1 as demonstrated by cyclin E stabilization, CDKN1A induction, and hypophosphorylation of retinoblastoma protein. These cells also were positive for Annexin V binding indicating they were apoptotic. In summary, cisplatin plus NaAsO2 and hyperthermia induced pseudo-G1 associated apoptosis in ovarian cancer cells.
Keywords: cisplatin; hyperthermia; ovarian cancer; postmitotic; pseudo-G1; sodium arsenite.