High ABCG4 Expression Is Associated with Poor Prognosis in Non-Small-Cell Lung Cancer Patients Treated with Cisplatin-Based Chemotherapy

<div><p>ATP-binding cassette (ABC) transporters are associated with poor response to chemotherapy, and confer a poor prognosis in various malignancies. However, the association between the expression of the ABC sub-family G member 4 (ABCG4) and prognosis in patients with non-small-cell lung cancer (NSCLC) remains unclear. NSCLC tissue samples (n = 140) and normal lung tissue samples (n = 90) were resected from patients with stage II to IV NSCLC between May 2004 and May 2009. ABCG4 mRNA and protein expressions were detected by RT-PCR, western blot, and immunohistochemistry. Patients received four cycles of cisplatin-based post-surgery chemotherapy and were followed up until May 31^st, 2014. ABCG4 positivity rate was higher in NSCLC than in normal lung tissues (48.6% <i>vs</i>. 0%, <i>P</i><0.001) and ABCG4 expression was significantly associated with poor differentiation, higher tumor node metastasis (TNM) stage, and adenocarcinoma histological type (all <i>P</i><0.001). Univariate (HR = 2.284, 95%CI: 1.570–3.324, <i>P</i><0.001) and multivariate (HR = 2.236, 95%CI: 1.505–3.321, <i>P</i><0.001) analyses showed that ABCG4 expression was an independent factor associated with a poor prognosis in NSCLC. Patients with ABCG4-positive NSCLC had shorter median survival than ABCG4-negative NSCLC (20.1 <i>vs</i>. 43.2 months, <i>P</i><0.001). The prognostic significance of ABCG4 expression was apparent in stages III and IV NSCLC. In conclusion, high ABCG4 expression was associated with a poor prognosis in patients with NSCLC treated with cisplatin-based chemotherapy.</p></div

Correlation between ABCG4 expression status and prognosis of NSCLC patients treated with cisplatin-based chemotherapy.

<p>(A) Kaplan-Meier curves were plotted to determine cumulative survival rate of NSCLC patients based on ABCG4 expression (negative <i>vs</i>. positive). (B) Kaplan-Meier curves were plotted to determine cumulative survival rate of NSCLC patients based on tumor node metastasis (TNM) stage (II <i>vs</i>. III <i>vs</i>. IV). (C) Kaplan-Meier curves were plotted to determine cumulative survival rate of NSCLC patients based on differentiation (poorly <i>vs</i>. moderately/well). (D) Kaplan-Meier curves were plotted to determine cumulative survival rate of NSCLC patients with TNM stage II based on ABCG4 expression (negative <i>vs</i>. positive). (E) Kaplan-Meier curves were plotted to determine cumulative survival rate of NSCLC patients with TNM stage III based on ABCG4 expression (negative <i>vs</i>. positive). (F) Kaplan-Meier curves were plotted to determine cumulative survival rate of NSCLC patients with TNM stage IV based on ABCG4 expression (negative <i>vs</i>. positive). Negative:-; Positive: +, ++ and +++.</p

ABCG4 protein expression in NSCLC and normal lung tissues was detected by immunohistochemistry.

<p>(A) Normal lung tissue; (B) Negative (-) staining of ABCG4 in NSCLC tissue; (C) Weakly positive (+) staining of ABCG4 in NSCLC tissue; (D) Moderately positive (++) staining of ABCG4 in NSCLC tissue; (E) Strongly positive (+++) staining of ABCG4 in NSCLC tissue; (F) Immunohistochemistry showing ABCG4-negative staining in NSCLC tissues (++) using ABCG4 blocking peptide. Magnification: 200×.</p

ATP-binding cassette sub-family G member 4 (ABCG4) mRNA expression was detected in non-small-cell lung cancer (NSCLC) (n = 14) and normal lung (n = 2) tissues by reverse transcription-polymerase chain reaction (RT-PCR).

<p>β-actin was used as an internal reference. M: marker. (<b>A)</b> Lane 1: positive control (A549-ABCG4). Lanes 2–3: normal lung tissues (NORM) (n = 2); <b>(B)</b> NSCLC tissues (NSCLC) (n = 14, lanes 1–14).</p