Abstract A300: Increased potency of the novel taxane cabazitaxel as compared with the parent compound docetaxel in MCF7 breast cancer cells.
Authors: Azarenko Olga , Smiyun Gregoriy , Wilson Leslie , Jordan Mary Ann 
Published: August 2014

Abstract
Cabazitaxel (CAB), a novel semisynthetic microtubule-targeting taxane, is approved for the treatment of metastatic hormone-refractory prostate cancer. It is effective against tumor cell lines and animal tumor models resistant to taxanes. To compare antitumor mechanisms of action of CAB and its parent compound docetaxel (DOC), we examined the effects of both drugs on MCF7 breast adenocarcinoma cells stably expressing eGFP-alpha-tubulin. Using a 72 h sulforhodamine B assay, we found that both CAB and DOC potently inhibit cell proliferation by arresting cells in mitotic metaphase (IC50= 0.67 nM and 2.5 nM, respectively). Half-maximal mitotic arrest at 24 h occurred at 1.5 nM CAB and 2 nM DOC, and maximal mitotic arrest at 24 h was 56% at all concentrations between 30 nM and 1 uM of either drug. However, interestingly, cell cycle analysis by flow cytometry revealed that CAB arrested cells in G2/M significantly more potently than DOC after 48-72 h drug incubation. For example, after 72 h incubation with 10 or 100 nM CAB or DOC, CAB induced 93% G2/M arrest whereas DOC induced only 60% G2/M arrest. Arrested mitotic spindles showed similar abnormal organization characterized by uncongressed chromosomes and multipolar spindles without noticeable changes in interphase microtubules after 24 h incubation with 2 nM of either drug. Aneuploidy was common. Using quantitative time lapse fluorescence video microscopy, we found that both CAB and DOC suppressed microtubule dynamic instability in interphase MCF7-eGFP-alpha-tubulin cells in time- and concentration-dependent manners. At 24 h, 2 nM CAB and 2 nM DOC strongly reduced the microtubule shortening rate by 59% and 50%, respectively; the growing rate by 33 and 19%, respectively; and the overall dynamicity by 83% and 65%, respectively. Importantly, 2 nM CAB suppressed the catastrophe frequency whereas DOC had no effect on it. CAB more strongly induced time- and concentration-dependent apoptosis; at 72 h, CAB and DOC (1 nM) induced 36% and 14% apoptosis, respectively. Using radiolabeled 14C-CAB and 14C-DOC, we determined that 50 nM CAB was taken up by the cells significantly more rapidly than 50 nM DOC. CAB attained an intracellular concentration of 25 μM (a 500-fold increase) within 2 h, whereas 50 nM DOC required 10 h to attain the same intracellular concentration. The results indicate that both CAB and DOC exert potent antimitotic effects through a common mechanism involving suppression of microtubule dynamic instability. However, CAB suppresses microtubule dynamic instability, arrests mitosis, and inhibits cell proliferation more potently than DOC, in part due to significantly more rapid uptake into MCF7 cells. Supported by a grant from Sanofi-Aventis, France.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A300.
Citation Format: Olga Azarenko, Gregoriy Smiyun, Leslie Wilson, Mary Ann Jordan. Increased potency of the novel taxane cabazitaxel as compared with the parent compound docetaxel in MCF7 breast cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A300.