Abstract 2151: Inhibition of WIP1/PPM1D phosphatase by GSK2830371 potentiates the growth inhibitory and cytotoxic activity of MDM2 antagonists (nutlin-3, RG7388 and HDM201) in cutaneous melanoma cells
Authors: Wu Chiao-En , Esfandiari Arman , Ho Yi-Hsuan , Shepherd Colin , Mahdi Ahmed Khairallah , Aptullahoglu Erhan , Chang John Wen-Cheng , Lovat Penny , Lunec John 
Published: July 2017

Abstract
Cutaneous melanoma is the most serious skin malignancy. The current study aimed to investigate the WIP1 inhibitor GSK2830371 and MDM2-p53 antagonists (nutlin-3, RG7388 and HDM201) alone and in combination treatment in cutaneous melanoma cell lines and explored the mechanistic basis of these responses in relation to the genotype and induced gene expression profile of the cells. A panel of three p53WT (A375, WM35, C8161) and three p53MUT (WM164, WM35-R5R1, CHL-1) melanoma cell lines were used. GSK2830371 (≤10 μM) alone had no growth-inhibitory or cytotoxic effects on the cells, measured by sulforhodamine B (SRB) and clonogenic assays. In combination treatment GSK2830371 significantly potentiated the growth-inhibitory and clonogenic cell killing effects of MDM2 inhibitors in p53WT but not p53MUT melanoma cells, indicating the potentiation worked in a p53-dependent manner (Table). Western blotting demonstrated GSK2830371 increased p53 stabilization through Ser15 phosphorylation and consequent Lys382 acetylation when it was combined with MDM2 inhibitors. These changes were ATM-mediated, shown by reversal with the ATM inhibitor (KU55933). Furthermore, GSK2830371 was demonstrated to slow down p53 degradation when de-novo protein synthesis was inhibited by cycloheximide. In qRT-PCR, nutlin-3 or RG7388 induced p53 transcriptional target genes (CDKN1A, MDM2, BAX, FAS, PUMA, TNFBSF10B, TP53INP1) and GSK2830371 enhanced the induction in p53WT but not p53MUT cells. In conclusion, GSK2830371, a WIP1 inhibitor, at doses with no growth-inhibitory activity alone, potentiated the growth-inhibitory and cytotoxic activity of MDM2 inhibitors, by increasing phosphorylation, acetylation, and stabilization of p53 in cutaneous melanoma cells in a functional p53-dependent manner. Further studies in vivo are warranted to investigate the efficacy of this combination treatment.
GI50 by sulforhodamine B (SRB) and LC50 by clonogenic assays in p53WT melanoma cellsCell linesGI50 (Mean + SEM)A375WM35C8161GSK2830371-+-+-+Nutlin-3 (µM)5.1 + 0.61.5 + 0.48.3 + 1.55.3 + 1.41.7 + 0.31.0 + 0.5p value0.0120.0100.049RG7388 (nM)228 + 3962 + 2377 + 58169 + 5746 + 015 + 5p value0.0250.0280.009HDM201 (nM)167 + 2541 + 9165 + 9877 + 5981 + 1149 + 10p value0.00460.1048&lt; 0.001LC50 (Mean + SEM)A375WM35C8161GSK2830371-+-+-+Nutlin-3 (µM)2.0 + 0.90.8 + 0.50.5 + 0.10.4 + 0.10.9 + 0.20.4 + 0.1p value0.0400.07140.003RG7388 (nM)166 + 9554 + 37186 + 7868 + 2350 + 2221 + 10p value0.0060.0700.026HDM201 (nM)198 + 7015 + 411 + 38 + 3139 + 8519 + 5p value&lt;0.0010.10620.010
Citation Format: Chiao-En Wu, Arman Esfandiari, Yi-Hsuan Ho, Colin Shepherd, Ahmed Khairallah Mahdi, Erhan Aptullahoglu, John Wen-Cheng Chang, Penny Lovat, John Lunec. Inhibition of WIP1/PPM1D phosphatase by GSK2830371 potentiates the growth inhibitory and cytotoxic activity of MDM2 antagonists (nutlin-3, RG7388 and HDM201) in cutaneous melanoma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2151. doi:10.1158/1538-7445.AM2017-2151