Effect of chemotherapy on topoisomerase (TOP) expression and activity in colon carcinoma cells

Background: Aim of this study was the evaluation of TOP expression and activity in human cancer cell lines after administration of anti-tumour drugs. Methods: A lymphocytic cell line (Jurkat) and two colon Adenocarcinoma cells lines (LOVO and HT-29) were treated with 1–10 mcM 5-fluorouracile, oxaliplatin, methotrexate and gemcitabine, either as single agents or in combination. Cells were harvested at baseline and at +2h, +3h, +6h and +24h from the beginning of treatment. After RNA extraction, expression of TOP1, TOP2A, TOP 2B was measured by quantitative real-time RT-PCR and correlated with enzymatic activity. Moreover, the cytotoxic effect of the drugs was evaluated on cell lines by MTT assay. Wherever TOP was evaluated by an enzymatic assay. Results: All tested drugs induced TOP1, TOP2A, TOP2B expression at 2–3 h of incubation, with mRNA values ranging from 107% to 910% of baseline levels. TOP expression returned to baseline values at +6h of incubation. Among the different drugs, gemcitabine, oxaliplatin and the combination of 5-fluorouracile + oxaliplatin or methotrexate were the most effective topoisomerase inductors. The increase of mRNA levels corresponded to an increased topoisomerase activity in vitro. Conclusions: Evaluation of cytotoxic activity in vitro showed the schedule including an inductor of TOP (e.g. gemcitabine) followed after +3 h by TOP1 (topotecan) or TOP 2A (etoposide) inhibitors had a synergistic effect, at variance with other sequential administrations of the 2 drugs. In conclusion, anti-tumor drugs acting on DNA replication or cell metabolism induce TOP1, TOP 2A, TOP2B after 2–3 h. Sequential administration of these anticancer drugs with TOP inhibitors show synergistic activity in vitro.