Abstract 3384: High ALDH activity is associated with high tumorigenicity in prostate cancer

OBJECTIVE: Tumor initiation and progression might be driven by rare populations of cells endowed with stem-properties, and therefore defined as cancer stem cells (CSC). High Aldehyde dehydrogenase (ALDH) activity has been suggested to selectively identify CSC in several tumor types including breast cancer, and, possibly, prostate cancer (PCA). In this study, we investigated presence and potential CSC characteristics of cells with high ALDH activity (ALDH bright) in PCA cell lines, fresh surgical specimens, and primary cultures. MATERIALS AND METHODS: PC3, Du145, VCaP, and LNCaP PCA cell lines were evaluated. Surgical specimens, including Benign Prostate Hyperplasia (BPH) and PCA, were used directly for gene expression studies. Surgical samples were also enzymatically digested for functional analysis and the establishment of primary cultures. ALDH activity was tested using ALDEFLUOR® technology. Cells were sorted from individual cell lines by flow cytometry and evaluated for CSC properties, including spheroid formation ability, clonogenicity, stemness-related gene expression, ALDH specific isoforms expression, and tumorigenicity upon injection in NOD/SCID mice. RESULTS: PCA cell lines and primary cultures displayed heterogeneous ALDH activity and expression of specific ALDH isoforms. Despite a higher expression of Oct4A and Klf4 stemness associated genes, ALDH bright cells isolated from Du145 and PC3 did not show improved spheroid formation or clonogenic capacity, as compared to their dim counterparts. Interestingly, however, ALDH bright cells were associated with a significantly higher tumorigenic capacity in vivo as compared to ALDH low cells. Nevertheless, ALDH bright cells lost their higher tumorigenic capacity following serial “in vivo” passages. Most importantly, a well defined ALDH bright population could also be detected in cells isolated from PCA specimens (n>20). ALDH activity was consistent with a strong expression of several ALDH specific isoforms in PCA tissues. Notably, a significant increase of defined ALDH isoforms such as ALDH1A3 (p=0.001) was detectable in tissues obtained from patients with PCA as compared to BPH or normal specimens. CONCLUSIONS: ALDH bright subsets can be detected in cells isolated from fresh PCA tissue samples, PCA cell lines and primary cultures. These populations appear to be associated with increased “in vivo” tumorigenicity rather than enhanced “in vitro” stem properties in the cell lines investigated. Importantly, expression of ALDH specific isoforms appears to be increased in clinical PCA as compared to BPH and “normal” samples, thereby suggesting a putative role of ALDH in PCA tumorigenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3384. doi:1538-7445.AM2012-3384