Low expression of aldehyde dehydrogenase 1A1 (ALDH1A1) is a prognostic marker for poor survival in pancreatic cancer

Abstract

Background: Aldehyde dehydrogenase 1 (ALDH1) has been characterised as a cancer stem cell marker in different types of tumours. Additionally, it plays a pivotal role in gene regulation and endows tumour cells with augmented chemoresistance. Recently, ALDH1A1 has been described as a prognostic marker in a pancreatic cancer tissue microarray. The aim of this study was to reevaluate the expression of ALDH1A1 as a prognostic marker on whole-mount tissue sections.

Methods: Real-time-quantitative-PCR (qRT-PCR) and Western blotting were used to evaluate the expression profile of ALDH1A1 in seven pancreatic cancer cell lines and one non-malignant pancreatic cell line. Immunostaining against ALDH1A1 and Ki-67 was performed on paraffin-embedded samples from 97 patients with pancreatic cancer. The immunohistochemical results were correlated to histopathological and clinical data.

Results: qRT-PCR and Western blotting revealed a different expression pattern of ALDH1A1 in different malignant and non-malignant pancreatic cell lines. Immunohistochemical analysis demonstrated that ALDH1A1 was confined to the cellular cytoplasm and occurred in 72 cases (74%), whereas it was negative in 25 cases (26%). High expression of ALDH1A1 was significantly correlated to an increased proliferation rate (Spearman correlation, p = 0.01). Univariate and multivariate analyses showed that decreased expression of ALDH1A1 is an independent adverse prognostic factor for overall survival.

Conclusions: Immunohistochemical analysis on whole-mount tissue slides revealed that ALDH1A1 is more abundantly expressed in pancreatic cancer than initially reported by a tissue microarray analysis. Moreover, high expression of ALDH1A1 correlated significantly with the proliferation of tumour cells. Intriguingly, this study is the first which identifies low expression of ALDH1A1 as an independent adverse prognostic marker for overall survival in pancreatic cancer.

Figure 1

(A) Gene expression analysis of ALDH1 by qPCR in seven pancreatic cancer cell lines and one non-malignant pancreatic cell line. Fold-change (y-axis) of ALDH1 expression in pancreatic cancer cell lines compared to the non-malignant pancreatic epithelial cell ACBRI, respectively. (B) Western blotting analysis of ALDH1A1 in seven pancreatic cancer cell lines and one non-malignant pancreatic cell line (8). MW α/β-tubulin as loading control. 1: BxPC3, 2: T3M4, 3: MiaPaCa-2, 4: AsPC-1, 5: Colo357, 6: Panc1, 7: SU8686:, 8: ACBRI.

Figure 2

Immunohistochemical analyses of ALDH1 in pancreatic cancer revealed a cytoplasmic expression varying from 0 - 3. Comparing expression of ALDH1 and Ki-67 in corresponding sequential slides resulted in a positive correlation between strong expression of ALDH1 and a high proliferation rate. (A - D): pancreatic tumour samples displaying cytoplasmic expression of 0 (A), 1 (B), 2 (C) and 3 (D). (E - H): corresponding sequential slides with immunohistochemical staining against Ki-67. Original magnification 200×.

Figure 3

Kaplan-Meier curves displaying (A) median overall survival and (B) median recurrence-free survival in 97 patients with pancreatic cancer and ALDH1^negative/low or ALDH1^high expression.

Figure 4

Kaplan-Meier curves displaying (A) median overall survival and (B) median recurrence-free survival in a subgroup analysis of patients having received adjuvant chemotherapy.