Restriction of cisplatin induction of acute apoptosis to a subpopulation of cells in a three-dimensional carcinoma culture model

Cisplatin is a clinically important chemotherapeutical agent used to treat epithelial malignancies. High concentrations (20-100 mu M) of cisplatin have been used in numerous studies to induce apoptosis of carcinoma tells grown in monolayer culture over 24-48 hr. These conditions may not be relevant to 3-D tumor tissue in vivo and the importance of apoptosis for tumor response is controversial. We here studied the effects of cisplatin on a 3-D colon carcinoma in vitro model (multicellular spheroids). Cisplatin at a dose of 40 mu M induced active caspase-3 preferentially in the peripheral 30 mu m, cell layer of spheroids, mainly during late stages (72-96 hr). The p53 response to cisplatin was also largely confined to peripheral cell layers. Despite the use of a high cisplatin concentration, a significant fraction of the cells in the spheroids survived treatment. A high proportion of surviving cells stained positive for beta-galactosidase, a marker of premature senescence. Cells growth-arrested by cisplatin treatment showed a higher spontaneous cell death rate than untreated proliferating cells. We propose that acute apoptosis is of minor significance for the overall response of carcinoma cells to cisplatin treatment. (C) 2009 UICC