Analysis of cell death in carcinoma-derived cell lines. Representative image of holoclone and paraclone colonies of 5PT cell line before (A) and 24 hours after (B) UVB irradiation showing greater loss of cells from the paraclone colony (59.7 ± 8.7% cells remaining, compared to 89.3 ± 10.7% cells remaining in holoclones, p < 0.01). Annexin V of H357 colonies showed higher numbers of apoptotic cells in paraclones (C), while BrdU staining showed similar proliferation rates in both holoclones and paraclones (D, E). Quantification of Annexin V in Ca1 cell line exposed to UVB (F) and NCZ (G) showed dose-related increases of apoptosis for CD44low cells, but markedly lower responses for CD44high cell populations. Representative FACS plots (H, I), showing significantly lower levels of apoptosis among CD44high cells than in CD44low cells (p < 0.01). Apoptosis in the MCF7 breast cell line before and after exposure to 10mj UVB and 10 ng/ml TNF assayed by staining for DilC1(5) and PI (J), showing significantly lower apoptosis in CD44high cells (p < 0.01). Exposure of CaLH3 cell line to very high doses of NCZ (250 ng/ml) showed similar pattern of response as obtained at lower doses of drugs (K). Fewer CD44high cells of Ca1 cell line were found dead (floating) 4 days after inducing of apoptosis when compared with CD44low cells, indicating their increased resistance long term after treatment (L). The recovery of cells after exposure to apoptosis-inducing drugs was significantly higher in CD44high cells compared to CD44low cells of the Ca1 cell line (M, N).