NSC606985 at nanomolar concentrations induces apoptosis in NB4 cells. (A) Chemical structure of NSC606985 (adapted from Rapisarda et al20 ; image reproduced with permission from the American Association for Cancer Research). (B) NB4 cells were treated with NSC606985 for 24 and 48 hours at the indicated concentrations, and growth-inhibiting percentages (left) and viability (right) were measured by trypan-blue exclusion assay. Each column represents the mean + SD of triplicates in an independent experiment. (C) NB4 cells treated with or without 25 nM NSC606985 for the indicated times were collected onto slides by cytospin, stained with Wright stain, and examined under an Olympus BX60 microscope equipped with a 100 ×/1.3 objective lens (Olympus, Tokyo, Japan). Images were acquired through a SPOT RT camera and SPOT software (Diagnostic Instruments, Sterling Heights, MI). Open arrowheads indicate apoptotic cells, and filled arrowheads point to secondary necrotic cells. (D-E) NB4 cells were treated with 25 nM NSC606985 for the indicated times, and analyses of nuclear DNA content distribution (D), DNA fragmentation (E),and annexin-V assay (F) were performed as described in “Patients, materials, and methods.” The arrow-pointed numbers in panel D represent the percentage of apoptotic cells, and the values are the mean of triplicates. The numbers in panel F represent the percentage of annexin-V+/PI- (lower right quadrant) and annexin-V+/PI+ (upper right quadrant) cells. All experiments were repeated 5 times with similar results.
