Figure 1

Topotecan and paclitaxel upregulate MHC-I and Fas on ID8 cells and exert their cytotoxic effects in a phase-specific manner. (A) Cytotoxic effects of paclitaxel, gemcitabine, topotecan, carboplatin or control sodium azide on ID8 tumor cells. ID8 cells were incubated with the chemotherapeutic agents for 6 hours. Survival fraction 42 hours later versus concentration (IC₅₀ is used as unit) is shown. Curves are sigmoidal and for the same time of exposure (6 hours) they plateau at a level that depends on the cell cycle specificity. For topotecan and paclitaxel the plateau level is > 30% and > 20% respectively, indicating significant phase specificity. For carboplatin and gemcitabine the sigmoidal curve plateaus at a level < 2.5%. The sigmoidal curves represent the fit of the obtained data to a logistic regression dose response curve. The killing curve of sodium azide (chemical, no interfering with the cell cycle) was used as a negative control. (B) Upregulation of MHC-I and Fas on viable ID8 cells treated with topotecan (left) or paclitaxel (right). Cells were exposed to the drugs for 6 hours, washed and incubated in drug free media for 42 hours before harvesting and staining with MHC-I and Fas antibodies. Isotype control (Red); untreated (Blue); Drug concentration inducing approximately 50% killing (IC₅₀; Green); Drug concentration corresponding to the plateau of the dose response curve (10 fold IC₅₀; Brown). All the histograms depict Annexin-V negative (non apoptotic) cells. (C) Dot plot diagrams depicting the upregulation of MHCI and Fas in non-apoptotic tumor cells exposed to Topotecan (upper) and Paclitaxel (lower) at IC₅₀ or 10 fold IC₅₀ for 6 hours 2 days before. (D) Growth curve of sorted MHC-I positive ID8cells following treatment with topotecan, paclitaxel and carboplatin, as indicated. Error bars represent interquartile range (25-75%).