Factors affecting topotecan-induced programmed cell death: adhesion protects cells from apoptosis and impairs cleavage of poly(ADP-ribose)polymerase.

We have evaluated the influence of anchorage status together with endogenous levels of bcl-2 family members on the ability of the topoisomerase I inhibitor, topotecan (TPT), to induce programmed cell death (PCD) in human colon, breast, lymphoid, and cervical cancer cell lines. As part of this study, we assessed the use of measuring poly(ADP-ribose) polymerase (PARP) cleavage by Western blot, as an index of apoptosis, relative to measuring chromatin condensation by acridine orange analysis. Our results show a strong correlation between both assays, indicating that PARP cleavage is an accurate method to examine PCD. We have encountered a strong association between cell attachment and sensitivity to TPT-induced PCD. Cells growing attached to flasks appear to be relatively more resistant than suspension-growing cells in spite of endogenous bcl-2, bax, or bcl-x levels. Furthermore, we demonstrate that interference with attachment status alters the sensitivity of cells to TPT-induced PCD. Although cell attachment to ProNectin F confers protection against TPT-induced chromatin condensation and cleavage of PARP, cell detachment by poly(2-hydroxyethyl methacrylate) stimulates TPT-induced PCD and PARP cleavage.