Abstract 682: Identification of HSP90 inhibitor sensitizers through pooled RNA interference screen

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Key words: HSF1, cancer cells, HSP90 inhibitor, Melanoma, HCC, DEDD2. The molecular chaperone heat shock protein 90 ( HSP90) facilitates the appropriate folding of various oncogenic proteins and is necessary for the survival of some cancer cells. HSP90is therefore an attractive drug target, but the efficacy of HSP90 inhibitormay be limited by HSP90inhibition induced feedback mechanisms. To identify genes that modulate the efficacy of HSP90inhibition on tumor cell growth, we performed a large-scale RNA interference (RNAi) genetic screenwith a collection of short hairpin RNA (shRNA) vectors targeting 1,000 human genes in A375. A barcoding technique was used to identify genes whose suppression caused resistance or sensitivity to two separate concentrations of NVP-AUY922. 163 and 360 shRNA constructs were significantly depleted form either low- or high-dose NVP-AUY922treated samples (FDR<=0.15). Among those shRNA hits, 84 hits (including 81 genes) were common shRNA hits as shown in Venn diagramand sensitizing genes or rescuing genes were also shown. Among of these shRNA hits, HSF1and heat shock protein 90 alpha, class B member 1( HSP90AB1) knockdown scored as the most top sensitizers to HSP90inhibition in A375 cells, and are known to regulate the cell response to heat shock conditions, which may reflect the potential feedback mechanism of HSP90inhibition. Taking together, HSF1is identified as a sensitizer of HSP90 inhibitorthrough pooled shRNA screening. A striking combinational effect was observed when HSF1knockdown plus with HSP90 inhibitorstreatment in various cancer cell lines: A375, A2058 and HCT116 and tumor mouse models. Interestingly, HSF1is highly expressed in hepatocellular carcinoma (HCC) patient samples and HCC is sensitive to combinational treatment, indicating a potential indication for the combinational treatment. To understand the mechanism of the combinational effect, we identified that a HSF1-target gene DEDD2 is involved in attenuating the effect of HSP90 inhibitors. Thus, the transcriptional activities of HSF1induced by HSP90 inhibitorsprovide a feedback mechanism of limiting the HSP90inhibitor's activity, and targeting HSF1may provide a new avenue to enhance HSP90 inhibitorsactivity in human cancers. Citation Format: Yaoyu Chen, Jinyun Chen, Alice Loo, Margaret Mclaughlin, Raymond Pagliarini, Wenlai Zhou. Identification of HSP90 inhibitorsensitizers through pooled RNA interference screen. [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 682. doi:10.1158/1538-7445.AM2014-682