Sensitization of prostate cancer DU-145 cells to docetaxel-induced apoptosis as determined by histone-DNA ELISA after 0, 6, 12, 24 and 48 h treatment with docetaxel (1.9 nM) alone, or the combination of docetaxel and d-limonene (0.2 mM). (A) Increased apoptotic response as evidenced from higher enrichment factors in combination treatment group relative to docetaxel-treated group. Data are mean ± SE (n = 3). *P < 0.05 compared with corresponding control. (B) DU-145 cells were pretreated with 10 mM NAC for 2 h and either left alone or exposed to 1.9 nM docetaxel alone or in combination with 0.2 mM d-limonene for 12 h. NAC pretreatment protected against docetaxel and docetaxel plus d-limonene-induced apoptosis in DU-145 cells. Data are mean ± SE (n = 3). *Significantly different between the indicated groups (P < 0.05). (C) M30 antibody stained (a) control cells, (b) docetaxel plus d-limonene-treated cells for 6 h, (c) 12 h, (d) 24 h, (e) 48 h, and (f) docetaxel-treated cells for 48 h for assessing caspases activation as measured by intense staining of fluorescein. DOC, docetaxel; D-L, d-limonene; NAC, N-acetylcystein.