A subset of cells within solid tumors become highly enlarged and enter a state of dormancy\n(sustained proliferation arrest) in response to anticancer treatment. Although dormant cancer\ncells might be scored as â??deadâ? in conventional preclinical assays, they remain viable, secrete\ngrowth-promoting factors, and can give rise to progeny with stem cell-like properties. Furthermore,\ncancer cells exhibiting features of apoptosis (e.g., caspase-3 activation) following genotoxic stress\ncan undergo a reversal process called anastasis and survive. Consistent with these observations,\nsingle-cell analysis of adherent cultures (solid tumor-derived cell lines with differing p53 status)\nhas demonstrated that virtually all cellsâ??irrespective of their size and morphologyâ??that remain\nadherent to the culture dish for a long time (weeks) after treatment with anticancer agents exhibit\nthe ability to metabolize 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl- tetrazolium bromide (MTT).\nThe purpose of this commentary is to briefly review these findings and discuss the significance\nof single-cell (versus population averaged) observation methods for assessment of cancer cell viability\nand metabolic activity.
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