Background

Excision repair cross complementation group 1 (ERCC1) protein encoded by ERCC1 gene is a key player in nucleotide excision repair (NER), and our previous work and others have demonstrated that this protein is also expressed in breast cancer [29].

Patients with lower DNA repair capacity are more chemosensitive than those who carry a proficient DNA repair system. In early, it was shown that elevated DNA repair capacity is associated with drug resistance in lung cancer cell lines [30], and it was suggested that modulation of DNA repair mechanisms, such as the incorporation of specific DNA repair inhibitors in therapeutic regimens. Although low expression of ERCC1 is related to carcinogenesis, high expression could enhance the NER, leading to rapid repair of the damaged tumor DNA after chemotherapy, a plausible mechanism of multi-drug resistance in many cancers [31]. Thus, we processed a serial studies about ERCC1 in breast cancer and look for novel anti-cancer strategies to avoid drug resistance and improve treatment outcomes.

EMD is a chemical compound of the anthraquinone family mainly derived from the root of Rheum palmatum, a widely used herb in traditional Chinese medicine, with a variety of anti-bacteria, anti-tumor and anti-constipation properties. Studies at the cellular level have shown that EMD affects cell proliferation by inhibiting DNA synthesis, prolonging the cell cycle duration, and suppressing mitosis. In our study, when the two breast cancer cells were exposed to 0~120 μg/ml of EMD, the IC50 was 100 ± 0.35 μg/ml for MCF-7 and 79 ± 0.28 μg/ml for MCF-7/Adr. At 20μg/ml EMD, cell viability was over 85% for both MCF-7 and MCF-7/Adr. Therefore, we selected 10μg/ml EMD at which no cell growth inhibition was observed as the starting dose for the reversal test. Our results showed that in MCF-7/Adr cells, EMD could reduce the ADM-resistance by 2.86 folds, and the DDP resistance was reduced by 1.79 folds. These results confirm that EMD is a highly effective drug-resistance reversal agent with low toxicity.

High expression of NER repairing ability enhancement is considered as one of the mechanisms of tumor drug resistance [32, 33]. In this study, two concentrations of emodin, 20μg/mL and 10μg/mL, were used to deal with low toxicity concentration MCF-7/Adr cell line, in 2, 4, 6 and10 days and the expression of ERCC1 protein was examined by Western blotting. The results showed higher levels of ERCC1 protein expression in MCF-7/Adr cell lines than in MCF-7 ones, but after emodin treatment, the ERCC1 protein levels decreased further and is significantly time-dependent and possibly dose-dependent as greater inhibitory effect was observed in the concentration of 20μg/ml. Given that only two concentration were studied, it may still have a certain concentration range to explore further the true dose-effect relationship.

Many new anti-cancer agents is being developed in recent years, but many studies have now focused on the reversal of chemoresistance in tumor in order to maximize the treatment capacity of existing chemotherapeutic agents. Some medicinal herbs may hold great potential in this field. This in vitro study found that EMD can significantly reverse the multi-drug resistance and reduce ERCC1 expression in breast cancer cells. Further studies are warranted to explore how ERCC1 plays role in reversing drug resistance and more pre-clinical evidence is necessary before the use emodin will be studied in clinical trials.

Conclusions

In this in vitro study, we noticed that ERCC1 expression might be associated with drug resistance and that emodin might play a possible role of reversing drug resistance. This is a preliminary finding which needs further investigation to explore the use of emodin in breast cancer treatment. However, we must emphasize that with recent advances of molecular biology, breast cancer was categorized into many different molecular subtypes which might possess different characteristics from carcinogenesis to metastasis. Therefore, the study of a single biomarker might be further complicated. Nevertheless, we believe further studies on ERCC1 expression in breast cancer and emodin in facilitating the reversal of drug resistance are warranted.