Abstract 4495: Fisetin, a dietary flavonoid, binds to and disrupts microtubule dynamic instability in prostate cancer cells.
Authors: Mukhtar Eiman , Adhami Vaqar M. , Syed Deeba N. , Mukhtar Hasan 
Published: August 2014

Taxanes are the first class of chemotherapy drugs shown to improve survival in advanced prostate cancer (PCa). Taxanes bind β-tubulin and stabilize microtubules, resulting in mitotic arrest and cell death. Therefore, disruption of microtubule function may provide an effective therapy for human PCa, which has been observed in clinical settings using paclitaxel. However, these drugs are associated with severe side effects and are sensitive to resistance mechanisms. Thus, search for novel and non-toxic tubulin targeting agents is urgently needed. We hypothesized that fisetin may offer PCa chemotherapeutic and/or chemopreventive effects by interfering with microtubule assembly, either by inhibiting or enhancing tubulin polymerization. Using an in vitro microtubule polymerization assay, we observed that fisetin enhanced tubulin polymerization whose kinetics paralleled that of paclitaxel. Because acetylation of α-tubulin is considered as a marker of stable microtubule structure, we next tested whether increased acetylated α-tubulin correlates with increased microtubule stability in PC-3 and DU-145 cells. We found that fisetin (20-80 μM) treatment increased α-tubulin acetylation in a dose dependent manner in PC-3 and DU-145 cells. To further investigate the stabilization of the microtubule network in fisetin-treated cells, we evaluated microtubule resistance to cold-induced depolymerization. Immunofluorescence labeling revealed that fisetin-treated PC-3 and DU-145 cells were resistant to cold-induced microtubule depolymerization. To identify microtubule-dependent tumor-specific pathways modulated by fisetin, we determined its effect on MAP2 expression in PC-3 and DU-145 cells. We found increased expression of MAP-2 with fisetin treatment. Stabilization of microtubules resulted in arrest of the cells in the G2/M phase of cell cycle and subsequent cell growth inhibition. Activation of microtubule-stabilizing proteins in PCa cells may inhibit their proliferation and correlate with a delay or inhibition of cell migration. Therefore, we investigated the efficacy of fisetin on the invasion and metastasis of PCa using scratch wound assay. We found that fisetin treatment (20-80 μM) for 24 hours inhibited PC-3 cells migration and invasion, which suggested fisetin as an anti-metastatic agent. As a mechanism for these effects we observed that fisetin increased the expression of nuclear migration protein Nud C in PC-3 and DU-145 cells in a dose dependent manner. Because Nud C protein regulates microtubule dynamics in the cell, the result reveal anti-microtubule effects of fisetin. The data reported here provide the first evidence of the dietary flavonoid fisetin as a microtubule stabilizing agent in PCa. Our observation suggests that fisetin could be used for the treatment of advanced PCa alone or as an adjuvant with other chemotherapy drugs.

Citation Format: Eiman Mukhtar, Vaqar M. Adhami, Deeba N. Syed, Hasan Mukhtar. Fisetin, a dietary flavonoid, binds to and disrupts microtubule dynamic instability in prostate cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4495. doi:10.1158/1538-7445.AM2013-4495