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Aldehyde dehydrogenase (ALDH) activity has been implicated in multiple biological and biochemical pathways and has been used to identify potential cancer stem cells. Our main hypothesis is that ALDH activity may be a lung cancer stem cell marker. Using flow cytometry,we sorted cells with bright (ALDH(br)) and dim (ALDH(lo)) ALDH activity found in H522 lung cancer cell line. We used in vitro proliferation and colony assays as well as a xenograft animal model to test our hypothesis. Cytogenetic analysis demonstrated that the ALDH(br) cells are indeed a different clone,but when left in normal culture conditions will give rise to ALDH(lo) cells. Furthermore,the ALDH(br) cells grow slower,have low clonal efficiency,and give rise to morphologically distinct colonies. The ability to form primary xenografts in NOD/SCID mice by ALDH(br) and ALDH(lo) cells was tested by injecting single cell suspension under the skin in each flank of same animal. Tumor size was calculated weekly. ALDH1A1 and ALDH3A1 immunohistochemistry (IHC) was performed on excised tumors. These tumors were also used to re-establish cell suspension,measure ALDH activity,and re-injection for secondary and tertiary transplants. The results indicate that both cell types can form tumors but the ones from ALDH(br) cells grew much slower in primary recipient mice. Histologically,there was no significant difference in the expression of ALDH in primary tumors originating from ALDH(br) or ALDH(lo) cells. Secondary and tertiary xenografts originating from ALDH(br) grew faster and bigger than those formed by ALDH(lo) cells. In conclusion,ALDH(br) cells may have some of the traditional features of stem cells in terms of being mostly dormant and slow to divide,but require support of other cells (ALDH(lo)) to sustain tumor growth. These observations and the known role of ALDH in drug resistance may have significant therapeutic implications in the treatment of lung cancer. View Publication

Aldehyde dehydrogenase (ALDH) activity is used to define normal hematopoietic stem cell (HSC),but its link to leukemic stem cells (LSC) in acute myeloid leukemia (AML) is currently unknown. We hypothesize that ALDH activity in AML might be correlated with the presence of LSC. Fifty-eight bone marrow (BM) samples were collected from AML (n=43),acute lymphoblastic leukemia (ALL) (n=8) and normal cases (n=7). In 14 AML cases,a high SSC(lo)ALDH(br) cell population was identified (ALDH(+)AML) (median: 14.89%,range: 5.65-48.01%),with the majority of the SSC(lo)ALDH(br) cells coexpressing CD34(+). In another 29 cases,there was undetectable (n=23) or rare (textless or =5%) (n=6) SSC(lo)ALDH(br) population (ALDH(-)AML). Among other clinicopathologic variables,ALDH(+)AML was significantly associated with adverse cytogenetic abnormalities. CD34(+) BM cells from ALDH(+)AML engrafted significantly better in NOD/SCID mice (ALDH(+)AML: injected bone 21.11+/-9.07%; uninjected bone 1.52+/-0.75% vs ALDH(-)AML: injected bone 1.77+/-1.66% (P=0.05); uninjected bone 0.23+/-0.23% (P=0.03)) with the engrafting cells showing molecular and cytogenetic aberrations identical to the original clones. Normal BM contained a small SSC(lo)ALDH(br) population (median: 2.92%,range: 0.92-5.79%),but none of the ALL cases showed this fraction. In conclusion,SSC(lo)ALDH(br) cells in ALDH(+)AML might denote primitive LSC and confer an inferior prognosis in patients. View Publication

Aldehyde dehydrogenase (ALDH) is a candidate marker for lung cancer cells with stem cell-like properties. Immunohistochemical staining of a large panel of primary non-small cell lung cancer (NSCLC) samples for ALDH1A1,ALDH3A1,and CD133 revealed a significant correlation between ALDH1A1 (but not ALDH3A1 or CD133) expression and poor prognosis in patients including those with stage I and N0 disease. Flow cytometric analysis of a panel of lung cancer cell lines and patient tumors revealed that most NSCLCs contain a subpopulation of cells with elevated ALDH activity,and that this activity is associated with ALDH1A1 expression. Isolated ALDH(+) lung cancer cells were observed to be highly tumorigenic and clonogenic as well as capable of self-renewal compared with their ALDH(-) counterparts. Expression analysis of sorted cells revealed elevated Notch pathway transcript expression in ALDH(+) cells. Suppression of the Notch pathway by treatment with either a γ-secretase inhibitor or stable expression of shRNA against NOTCH3 resulted in a significant decrease in ALDH(+) lung cancer cells,commensurate with a reduction in tumor cell proliferation and clonogenicity. Taken together,these findings indicate that ALDH selects for a subpopulation of self-renewing NSCLC stem-like cells with increased tumorigenic potential,that NSCLCs harboring tumor cells with ALDH1A1 expression have inferior prognosis,and that ALDH1A1 and CD133 identify different tumor subpopulations. Therapeutic targeting of the Notch pathway reduces this ALDH(+) component,implicating Notch signaling in lung cancer stem cell maintenance. View Publication

Recent efforts in our study of cancer stem cells (CSC) in hepatocellular carcinoma (HCC) have led to the identification of CD133 as a prominent HCC CSC marker. Findings were based on experiments done on cell lines and xenograft tumors where expression of CD133 was detected at levels as high as 65%. Based on the CSC theory,CSCs are believed to represent only a minority number of the tumor mass. This is indicative that our previously characterized CD133(+) HCC CSC population is still heterogeneous,consisting of perhaps subsets of cells with differing tumorigenic potential. We hypothesized that it is possible to further enrich the CSC population by means of additional differentially expressed markers. Using a two-dimensional PAGE approach,we compared protein profiles between CD133(+) and CD133(-) subpopulations isolated from Huh7 and PLC8024 and identified aldehyde dehydrogenase 1A1 as one of the proteins that are preferentially expressed in the CD133(+) subfraction. Analysis of the expression of several different ALDH isoforms and ALDH enzymatic activity in liver cell lines found ALDH to be positively correlated with CD133 expression. Dual-color flow cytometry analysis found the majority of ALDH(+) to be CD133(+),yet not all CD133(+) HCC cells were ALDH(+). Subsequent studies on purified subpopulations found CD133(+)ALDH(+) cells to be significantly more tumorigenic than their CD133(-)ALDH(+) or CD133(-)ALDH(-) counterparts,both in vitro and in vivo. These data,combined with those from our previous work,reveal the existence of a hierarchical organization in HCC bearing tumorigenic potential in the order of CD133(+)ALDH(+) textgreater CD133(+)ALDH(-) textgreater CD133(-)ALDH(-). ALDH,expressed along CD133,can more specifically characterize the tumorigenic liver CSC population. View Publication

Markers that reliably identify cancer stem cells (CSC) in ovarian cancer could assist prognosis and improve strategies for therapy. CD133 is a reported marker of ovarian CSC. Aldehyde dehydrogenase (ALDH) activity is a reported CSC marker in several solid tumors,but it has not been studied in ovarian CSC. Here we report that dual positivity of CD133 and ALDH defines a compelling marker set in ovarian CSC. All human ovarian tumors and cell lines displayed ALDH activity. ALDH(+) cells isolated from ovarian cancer cell lines were chemoresistant and preferentially grew tumors,compared with ALDH(-) cells,validating ALDH as a marker of ovarian CSC in cell lines. Notably,as few as 1,000 ALDH(+) cells isolated directly from CD133(-) human ovarian tumors were sufficient to generate tumors in immunocompromised mice,whereas 50,000 ALDH(-) cells were unable to initiate tumors. Using ALDH in combination with CD133 to analyze ovarian cancer cell lines,we observed even greater growth in the ALDH(+)CD133(+) cells compared with ALDH(+)CD133(-) cells,suggesting a further enrichment of ovarian CSC in ALDH(+)CD133(+) cells. Strikingly,as few as 11 ALDH(+)CD133(+) cells isolated directly from human tumors were sufficient to initiate tumors in mice. Like other CSC,ovarian CSC exhibited increased angiogenic capacity compared with bulk tumor cells. Finally,the presence of ALDH(+)CD133(+) cells in debulked primary tumor specimens correlated with reduced disease-free and overall survival in ovarian cancer patients. Taken together,our findings define ALDH and CD133 as a functionally significant set of markers to identify ovarian CSCs. View Publication

To investigate whether aldehyde dehydrogenase-1 (ALDH-1) in human lung cancer can be used as a sorting marker for stem cells in targeted therapies against human lung cancer. Spheres were induced by incubating cancer cells in a serum-free medium and formed with epidermal growth factor and fibroblast growth factor-10 (FGF10). Spheroid cells were combined with flow cytometry using the Aldefluor reagent to separate the SSCloALDEbr (ALDH-1-positive) cells. Cancer stem cells (CSCs) were characterized by their proliferation,colony formation,and tumorigenesis in nude mice and using phenotypic analysis. Float-growing spheres (pulmospheres") were developed after SPC-A1 cells were cultured in a serum-free medium. The resultant sphere-forming cells included ALDH-1-positive cells as high as 15.13%. ALDH-1-positive CSCs have high proliferative ability View Publication

Patients with chronic ulcerative colitis are at increased risk of developing colorectal cancer. Although current hypotheses suggest that sporadic colorectal cancer is due to inability to control cancer stem cells,the cancer stem cell hypothesis has not yet been validated in colitis-associated cancer. Furthermore,the identification of the colitis to cancer transition is challenging. We recently showed that epithelial cells with the increased expression of aldehyde dehydrogenase in sporadic colon cancer correlate closely with tumor-initiating ability. We sought to determine whether ALDH can be used as a marker to isolate tumor-initiating populations from patients with chronic ulcerative colitis. We used fluorescence-activated cell sorting to identify precursor colon cancer stem cells from colitis patients and report both their transition to cancerous stem cells in xenografting studies as well as their ability to generate spheres in vitro. Similar to sporadic colon cancer,these colitis-derived tumors were capable of propagation as sphere cultures. However,unlike the origins of sporadic colon cancer,the primary colitic tissues did not express any histologic evidence of dysplasia. To elucidate a potential mechanism for our findings,we compared the stroma of these different environments and determined that at least one paracrine factor is up-regulated in the inflammatory and malignant stroma compared with resting,normal stroma. These data link colitis and cancer identifying potential tumor-initiating cells from colitic patients,suggesting that sphere and/or xenograft formation will be useful to survey colitic patients at risk of developing cancer. View Publication

Recent evidence suggests that enhanced aldehyde dehydrogenase (ALDH) activity is a hallmark of cancer stem cells (CSC) measurable by the aldefluor assay. ALDH1A1,one of 19 ALDH isoforms expressed in humans,was generally believed to be responsible for the ALDH activity of CSCs. More recently,experiments with murine hematopoietic stem cells,murine progenitor pancreatic cells,and human breast CSCs indicate that other ALDH isoforms,particularly ALDH1A3,significantly contribute to aldefluor positivity,which may be tissue and cancer specific. Therefore,potential prognostic application involving the use of CSC prevalence in tumor tissue to predict patient outcome requires the identification and quantification of specific ALDH isoforms. Herein we review the suggested roles of ALDH in CSC biology and the immunohistological studies testing the potential application of ALDH isoforms as novel cancer prognostic indicators. View Publication

The cancer stem cell (CSC) theory has been proposed to explain the tumor heterogeneity and carcinogenesis process. Recent studies indicate that aldehyde dehydrogenase (ALDH) activity represents a promising CSC marker. Here,we aimed to determine whether human adenoid cystic carcinoma (AdCC) also follows CSC model by exploring the CSC properties of AdCC cells expressing high level of ALDH activity. Utilizing in-vivo series transplantation assays,we found ALDH(high) AdCC cells were capable of self-renewal and of generating tumors that recapitulate the heterogeneity of the parental tumor. Utilizing in-vitro assay,we found only ALDH(high) AdCC cells have tumorsphere-forming ability in anchorage-independent cultures. Finally,we showed ALDH(high) AdCC cells possess highly invasive capability and are responsible for mediating metastasis. These findings suggest the existence of a developmental hierarchy within human AdCC and further elucidation of the unique survival mechanism of AdCC derived CSC population may provide novel therapeutic strategies to treat AdCC. View Publication

Application of stem cell biology to breast cancer research has been limited by the lack of simple methods for identification and isolation of normal and malignant stem cells. Utilizing in vitro and in vivo experimental systems,we show that normal and cancer human mammary epithelial cells with increased aldehyde dehydrogenase activity (ALDH) have stem/progenitor properties. These cells contain the subpopulation of normal breast epithelium with the broadest lineage differentiation potential and greatest growth capacity in a xenotransplant model. In breast carcinomas,high ALDH activity identifies the tumorigenic cell fraction,capable of self-renewal and of generating tumors that recapitulate the heterogeneity of the parental tumor. In a series of 577 breast carcinomas,expression of ALDH1 detected by immunostaining correlated with poor prognosis. These findings offer an important new tool for the study of normal and malignant breast stem cells and facilitate the clinical application of stem cell concepts. View Publication

Prostate cancer (PCa) contains a small population of cancer stem cells (CSCs) that contribute to its initiation and progression. The 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 the stem cell populations of leukemia and some solid tumors. The aim 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. The ALDH1A1 expression was also analyzed by immunohistochemistry in 18 normal prostate and 163 PCa tissues. The ALDH1A1(+) PCa cells showed 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. However,in tumor specimens,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 and 0.00017,respectively). 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. View Publication