The Proportion of ALDEFLUOR-Positive Cancer Stem Cells Changes with Cell Culture Density Due to the Expression of Different ALDH Isoforms.
A significant number of discrepancies exist within the literature regarding ALDEFLUOR-positive stem cell populations in cell lines. We hypothesized that these inconsistencies resulted from differences in culture conditions, particularly cell density. We cultured several colon cancer cell lines (N=8) at high and low densities and found a significant decrease in ALDEFLUOR-positive cell populations at high density.
However, we found no changes in the CD166-positive stem cell population, self-renewal, or cell cycle distribution of cells cultured at different densities. Interestingly, when we sorted both ALDEFLUOR positive and negative populations from the different density cultures.
This novel finding suggests that multiple ALDH isoforms contribute to ALDEFLUOR activity in colon cancer stem cells and decreases in ALDEFLUOR-positive stem cells at high cell density are due to decreased expression of multiple ALDH isoforms. Thus, designing therapeutics to target ALDEFLUOR-positive cancer stem cells may require inhibition of multiple ALDH isoforms. With the increased use of the ALDEFLUOR assay to isolate and identify Cancer Stem Cells we noticed different published papers reported different percent ALDEFLUOR positive cells for the same cancer cell lines.
We hypothesized that the variation in ALDEFLUOR results was due to cultures being grown at different densities and that ALDEFLUOR-positive stem cell populations might express different Aldehyde dehydrogenase isoforms dependent on culture density. However, there are a few articles and reviews that acknowledge that gene expression can change with respect to the changing characteristics of stem cells observed at different culture densities.
Cancer Stud Mol Med Open J. 2015; 2(2): 87-95. doi: 10.17140/CSMMOJ-2-113
