Abstract 2598: siRNA silencing of survivin enhances activity of mitomycin C in human bladder RT4 xenografts
Authors: Minjain Cui, M. Guillaume Wientjes, Jessie L.-S. Au, Michael O'Donnell, Kevin Loughlin, Ze Lu
Journal: Cancer Research (2014)

Abstract For intravesical therapy of nonmuscle-invading bladder cancer, maximizing the mitomycin (MMC) exposure by pharmacokinetic interventions yielded 43% 5-year recurrence-free survival (Au et al., JNCI, 2001). Further improvement requires enhancing chemosensitivity, such as silencing of survivin, an inhibitor of apoptosis and indicator of bladder cancer aggressiveness and recurrence. Survivin is induced by chemotherapy, and its in vitro knockdown by si/shRNA enhances sensitivity to chemotherapy including MMC. As the utility of siRNA has been impeded by lack of activity in vivo, we developed a siRNA carrier that enhances its intracellular bioavailability and in vivo transfection. This carrier uses a fusogenic lipid to destabilize the endosomal membrane plus paclitaxel to perturb the endosomal siRNA transport (PPCat). The present study investigated if survivin siRNA-loaded PPCat (PPCat-siSurvivin) produces in vivo survivin knockdown and enhances MMC activity in human bladder RT4 tumors. Table shows the results. In vitro studies showed that MMC at 50% cytotoxic concentration induced survivin expression, which was reversed by PPCat-siSurvivin. A separate experiment evaluated if a modified PPCat-siSurvivin (i.e., PCat, without paclitaxel) enhanced the MMC activity; the results showed (a) lower clonogenicity for the combination compared to either agents (p&amp;lt;0.05, n=3 experiments), and (b) PCat comprising non-target siRNA had no effects. Taken together, these data indicate the enhanced activity was due to survivin knockdown and not the paclitaxel contained in PPCat. In mice bearing subcutaneous RT4 tumors, single agent MMC delayed tumor growth, with the residual tumors showing higher survivin expression. PPCat-siSurvivin significantly enhanced the MMC activity, which appeared to correlate with reduced survivin level. As single agent PPCat-siSurvivin was inactive in vivo, the enhanced activity for the combination indicates synergy. Supported in part by R43TR000356 and RO1CA158300, DHHS. GroupIn VitroIn VivoSurvivin expression (3 experiments, 3 samples each)Time for 50% size increase, Median (Range), daysRelative survivin protein levelmRNAProteinControl1.00 ± 0.101.00 ± 0.098 (8-12, n=4)1.00 (0.94-1.06, n=2)PPCat-NT siRNA Control1.08 ± 0.050.99 ± 0.2512 (8-12, n=4)Not donePPCat-siSurvivin0.82 ± 0.02*0.58 ± 0.10*12 (8-12, n=4)Not doneMMC1.47 ±0.34*1.52 ± 0.08*37 (23-44, n=8)*2.60 (2.56-2.72, n=2)MMC + PPCat-NT siRNA1.53 ± 0.24*1.33 ± 0.06*Not doneNot doneMMC + PPCat-siSurvivin1.13 ± 0.17**0.90 ± 0.04**44 (37-58, n=8)***1.06 (0.94-1.18, n=2)* p&amp;lt;0.05 vs. control groups. ** p&amp;lt;0.05 vs. MMC and MMC+PPCat-NT siRNA, but not different from the two control groups. *** p&amp;lt;0.05 vs. all other groups. Citation Format: Minjain Cui, M. Guillaume Wientjes, Jessie L.-S. Au, Michael O'Donnell, Kevin Loughlin, Ze Lu. siRNA silencing of survivin enhances activity of mitomycin C in human bladder RT4 xenografts. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2598. doi:10.1158/1538-7445.AM2014-2598