FIG. 1.

MitoTam associates with mitochondria and efficiently kills breast cancer cells. (A) Structures of tamoxifen and tamoxifen tagged with the TPP⁺ group (MitoTam). (B) MCF7 cells were preloaded with MitoTracker Far Red, exposed to FITC-labeled MitoTam (5 μM), and inspected by time-lapse confocal microscopy for the times shown. The last panel presents the magnified and color-balanced view of the region highlighted at 40-min time point. Size bar = 5 μm. (C) MCF7 cells were exposed to tamoxifen and MitoTam at the concentrations (μM) and time points shown, and cell death was evaluated using the Annexin V-FITC/PI method using flow cytometry. (D) MCF7 and MDA-MB-231 cells were exposed to MitoTam for 24 h at the concentrations shown and cell death was evaluated by Annexin V/PI. (E) MCF7, MDA-MB-453, and SKBR3 cells were exposed to MitoTam for 20 h at the concentrations shown and cell death was evaluated by Annexin V/PI staining. (F) MCF7 cells were exposed to MitoTam, Tam-DPPO, and tamoxifen or (G) MitoTam and C11-TPP for 24 h and cell death was evaluated by Annexin V/PI staining. (H) Parental and tamoxifen-resistant MCF7 cells (MCF7 and TAM-R cells, respectively) were exposed to tamoxifen, (I) MitoTam, or (J) Tam-DPPO for 24 h at the concentrations shown and cell death was evaluated by Annexin V/PI staining. Images in (B) are representative of three independent experiments; data in all other panels are mean values (n ≥ 3) ± SEM. The symbol, *, indicates statistically significant difference (p < 0.05). TPP⁺, triphenylphosphonium; Tam-DPPO, Diphenylphosphine oxide tamoxifen. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars