Prostate cancer (PCa) contains small population of cancer stem cells (CSCs) that contribute to its initiation and progression. Development of specific markers for identification of the CSCs may lead to new diagnostic strategies of PCa. Increased aldehyde dehydrogenase 1A1 (ALDH1A1) activity has been found in stem cell populations of leukemia and some solid tumors. The goal of the study was to investigate the stem cell-related function and clinical significance of the ALDH1A1 in human PCa. Aldefluor assay was used to isolate ALDH1A1+ cells from PCa cell lines. Stem cell characteristics of the ALDH1A1+ cells were then investigated by in vitro and in vivo approaches. ALDH1A1 expression by immunohistochemestry in 18 normal prostate and 163 PCa tissues was also analyzed. The ALDH1A1+ PCa cells displayed high clonogenic and tumorigenic capacities, and serially reinitiated transplantable tumors that resembled histopathologic characteristics and heterogeneity of the parental PCa cells in mice. Immunohistochemical analysis of human prostate tissues showed that ALDH1A1+ cells were sparse and limited to the basal component in normal prostates. In tumor specimens, however, increased ALDH1A1 immunopositivity was found not only in secretory type cancer epithelial cells, but also in neuroendocrine tumor populations. Furthermore, the high ALDH1A1 expression in PCa was positively correlated with Gleason score (P=0.01) and pathologic stage (P=0.01), and inversely associated with overall survival and cancer-specific survival of the patients (P=0.00093, P=0.00017). ALDH1A1 could be a prostate CSC-related marker. Measuring its expression might provide a potential approach to study tumorigenesis of PCa and predict outcome of the disease.

Aldehyde dehydrogenase 1 A1 (ALDH1A1) has recently been suggested as a marker for cancer stem or stem-like cancer cells of some human malignancies. The purpose of this study was to investigate the stem cell-related function and clinical significance of the ALDH1A1 in bladder urothelial cell carcinoma. Aldefluor assay was used to isolate ALDH1A1+ cells from bladder cancer cells. Stem cell characteristics of the ALDH1A1+ cells were then investigated by in vitro and in vivo approaches. Immunohistochemistry (IHC) was performed for evaluating ALDH1A1 expression on 22 normal bladder tissues and 216 bladder tumor specimens of different stage and grade. The ALDH1A1+ cancer cells displayed higher in vitro tumorigenicity compared with isogenic ALDH1A1− cells. The ALDH1A1+ cancer cells could generate xenograft tumors that resembled histopathologic characteristics and heterogeneity of the parental cells. High ALDH1A1 expression was found in 26% (56 of 216) human bladder tumor specimens, and significantly related to advanced pathological stage, high histological grade, recurrence and progression, and metastasis of bladder urothelial cell carcinomas (all P < 0.05). Furthermore, ALDH1A1 expression was inversely associated with cancer-specific and overall survivals of the patients (P = 0.027 and P = 0.030, respectively). Therefore, ALDH1A1+ cell population could be enriched in tumor-initiating cells. ALDH1A1 may serve as a useful marker for monitoring the progression of bladder tumor and identifying bladder cancer patients with poor prognosis who might benefit from adjuvant and effective treatments.