High expression of NQO1 is associated with poor prognosis in serous ovarian carcinoma

Abstract

Nad(p)h: quinone oxidoreductase (NQO1) is a flavoprotein that catalyzes two-electron reduction and detoxification of quinones and its derivatives. NQO1 catalyzes reactions that have a protective effect against redox cycling, oxidative stress and neoplasia. High expression of NQO1 is associated with many solid tumors including those affecting the colon, breast and pancreas; however, its role in the progression of ovarian carcinoma is largely undefined. This study aimed to investigate the clinicopathological significance of high NQO1 expression in serous ovarian carcinoma.

Methods: NQO1 protein expression was assessed using immunohistochemical (IHC) staining in 160 patients with serous ovarian carcinoma, 62 patients with ovarian borderline tumors and 53 patients with benign ovarian tumors. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect NQO1 mRNA expression levels. The correlation between high NQO1 expression and clinicopathological features of ovarian carcinoma was evaluated by Chi-square and Fisher's exact test. Overall survival (OS) rates of all of ovarian carcinoma patients were calculated using the Kaplan-Meier method, and univariate and multivariate analyses were performed using the Cox proportional hazards regression model.

Results: NQO1 protein expression in ovarian carcinoma cells was predominantly cytoplasmic. Strong, positive expression of NQO1 protein was observed in 63.8% (102/160) of ovarian carcinomas, which was significantly higher than in borderline serous tumors (32.3%, 20/62) or benign serous tumors (11.3%, 6/53). Importantly, the rate of strong, positive NQO1 expression in borderline serous tumors was also higher than in benign serous tumors. High expression of NQO1 protein was closely associated with higher histological grade, advanced clinical stage and lower OS rates in ovarian carcinomas. Moreover, multivariate analysis indicated that NQO1 was a significant independent prognostic factor, in addition to clinical stage, in patients with ovarian carcinoma.

Conclusions: NQO1 is frequently upregulated in ovarian carcinoma. High expressin of NQO1 protein may be an effective biomarker for poor prognostic evaluation of patients with serous ovarian carcinomas.

Figure 1

IHC staining of NQO1 protein in ovarian tumor samples. (A) Negative expression of NQO1 protein in a benign serous tumor. (B–C) Weak positive expression of NQO1 protein (B) and positive expression (C) in atypical cells of borderline serous tumors. (D) Strong positive expression of NQO1 protein in serous carcinoma cells, in a patient with metastasis. (E) Positive expression of NQO1 protein in a serous carcinoma patient without metastasis. Scattered, strongly positive-staining cancer cells are seen (arrows). (F) Negative expression of NQO1 protein in a serous carcinoma patient without metastasis. Original magnification, A–F: ×200.

Figure 2

qRT-PCR analysis of NQO1 mRNA. Serous carcinoma specimens (n = 19) and benign serous tumors (n = 15) were collected, and NQO1 mRNA levels were assessed by qRT-PCR. Error bars represent the standard deviation of the mean (SD) calculated from three parallel experiments. **P < 0.01.

Figure 3

Kaplan-Meier survival curves illustrating the significance of NQO1 expression in ovarian carcinomas. (A) OS rates of patients with high (solid, n = 92) and low (dashed, n = 68) NQO1 expression. A: Log-rank = 21.699, P = 0.000. (B-C) High NQO1 expression was strongly associated with poor OS in early-stage (solid, n = 37) and late-stage (solid, n = 55). B: Log-rank = 6.527, P = 0.011; C: Log-rank = 4.806, P = 0.028. (D-F) High NQO1 expression was strongly associated with poor OS in G1 (solid, n = 10), G2 (solid, n = 29) and G3 (solid, n = 53). D: Log-rank = 4.359, P = 0.037; E: Log-rank = 7.020, P = 0.008; F: Log-rank = 5.978, P = 0.015).