Abstract 3763: Ribonucleotide reductase subunit M2 plays important role in cisplatin resistance of cancer cells
Authors: Rahman Mohammad Aminur , Amin A.R.M. R. , Peng Xianghong , Zhang Jun , Chen Zhuo G. , Shin Dong M. 
Published: May 2015

Abstract
Background: Cisplatin is widely used as a cancer therapeutic for many types of cancers. It mediates the formation of DNA adducts which impair DNA replication and transcription, and consequently induces cell death when there is no prompt DNA repair. However, resistance to cisplatin continues to be the major hurdle to its optimal effect in cancer therapy. Ribonucleotide reductase subunit M2 (RRM2), an essential regulator of balanced deoxyribonucleotides (dNTPs), is critical for DNA replication and repair, and hence cell survival. It has been shown that overexpression of RRM2 is associated with resistance to chemotherapeutic agents including cisplatin. However, the exact mechanism needs to be further deciphered.
Methods: We generated cisplatin-resistant H1299-ptR cells from the H1299 (non-small cell lung cancer) cell line for this study, and also employed KB-8-5 and KB-CP 0.5 cells, previously derived from the KB-3-1 (head and neck cancer) cell line. RRM2 expression level was compared between resistant vs. parental cell lines. In addition, the impact on cisplatin resistance was mechanistically pursued by using RRM2 silencing.
Results: Based on EC50, we found that KB-8-5 and KB-CP 0.5 cell lines were 4- and 36-fold more resistant to cisplatin compared to their parental cell line KB-3-1, respectively. Similarly, H1299-ptR was 12-fold more resistant than its parental H1299 cell line. Interestingly, in all resistant cell lines, RRM2 expression level was found to be 2- to 4-fold higher than in the parental counterparts. Silencing of RRM2 in resistant cell lines induced cell apoptosis, along with enhanced DNA damage, which manifested as an elevated level of histone γ-H2AX. In KB-CP 0.5 cells, RRM2 knockdown resulted in increased level of p53 (∼60% apoptosis) and reduced activation of ATR-Chk1, indicating that inhibition of ssDNA damage repair system is attributable to cellular apoptosis. Strikingly, the ATR-Chk1 signaling pathway was found to be hyperactive in cisplatin resistant cells. Taken together, these findings suggest that RRM2 plays an active role in the development of cisplatin resistance through its action in the DNA repair system.
Conclusions: Increased expression of RRM2 may induce drug-resistance potential in cancer cells, whereas RRM2 suppression reverses drug resistance and decreases proliferation. This study suggests that targeting RRM2 can be an effective approach to overcome drug resistance and potently induce apoptosis. (This work is supported by grants from NIH U01CA151802, P50CA128613).
Citation Format: Mohammad Aminur Rahman, A.R.M. R. Amin, Xianghong Peng, Jun Zhang, Zhuo G. Chen, Dong M. Shin. Ribonucleotide reductase subunit M2 plays important role in cisplatin resistance of cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3763. doi:10.1158/1538-7445.AM2014-3763