Cell growth analysis and nucleotide excision repair modulation in breast cancer cells submitted to a protocol using doxorubicin and paclitaxel.

Introduction: One of the most used regimens to treat breast cancer is the dose-dense ACT protocol, a combination of anthracycline doxorubicin (DOX) with cyclophosphamide and paclitaxel (PCTX). However, many tumors show resistance to the protocols applied. It is known that the nucleotide excision repair (NER) pathway acts by removing the DOX-generated lesions, and this, together with other DNA repair pathways, can modulate the response to treatment.

Aims: To evaluate the in vitro growth profile of breast cancer cells (MCF7), and the modulation of DNA repair genes, submitted to a protocol using DOX and PCTX in a similar regimen to what is used in clinical practice.

Main Methods: MCF7 cells were treated with repeated cycles of DOX and PCTX and followed-up during and after each of the treatments. The population doubling of the remaining cells was calculated during the complete protocol and DNA repair gene expression was evaluated at different time-points.

Key Findings: An increase in all NER genes analyzed after the DOX treatment was observed, but not after the PCTX treatment. MRE11was overexpressed at all evaluated time-points. There was a resumption of NER genes overexpression profile when cells were maintained for follow-up and retook their growth pattern, indicating that DNA repair pathways can modulate their expression during the chemotherapy exposure.