PO-022 Benzamide class of HDACi differentially enhance sodium iodide symporter expression in breast cancer

Abstract

IntroductionSodium iodide symporter (hNIS) expression is reported across all subtypes of breast cancer (BC) and is a potential endogenous gene target for radioiodine therapy [PlosOne8(1:e54055, 2012]. Successful clinical application however relies on very high expression of functional NIS in BC cells. We have been exploiting various transcriptional regulation approaches for NIS, of which use of HDAC inhibitors (HDACi) have shown promising amplification of endogenous NIS expression in BC [Scientific Reports6:19341, 2016]. Here, we show that differential induction of NIS expression in BC is possible using Benzamide class of HDACi (bHDACi) with minimal off-target effects on other cell types.Material and methodsThe effect of bHDACi, i.e. CI-994, Chidamide, MS-275 and AR-42, on NIS gene transcription was verified on a panel of human cancer cells by RTPCR. Functional in vitro assessment was done by non-radioactive iodine uptake. I131therapeutic efficacy was measured by clonogenic assay. Promoter binding transcription factor (TF) profiler array was done to identify novel TFs responsible for differential activation in BC cells. Further, in vivo therapeutic efficacy was monitored by bioluminescence imaging (BLI) of ZR-75–1-fl2.tdt orthotopic model.Results and discussionsUsing a non-toxic, low dose of bHDACi(s) treatment on a cancer cell panel, including breast, thyroid, lung, glioma, fibrosarcoma and ovarian, a significant induction of NIS expression (p<0.05) was observed only in BC cells. Observed differences of NIS expression was confirmed by protein expression and functional assessment on BC cells. Further, novel TFs (FOXA1, FOXOF2 etc.) were identified which show differential activation in BC after CI-994 treatment. Only in case of BC cells pre-treated with bHDACi(s), cell survival assay results showed enhanced cell death on exposure to I131. Further, AR-42 drug was tested in vivo which showed similar results. AR-42 pre-treated ZR-75–1 fl2tdt orthotopic tumour showed increased NIS expression. In comparison to untreated and only I131 treated group, a combination treatment of AR-42 with 1mCi I131, BLI imaging showed 20% and 30% signal drop on day1 and day 2 respectively indicating specific radio-ablation effect.ConclusionbHDACi(s) show differentially higher regulation of endogenous NIS with minimal effect on non-breast tissues and thus may potentially benefit NIS-based radioablation therapy trials in BC patients with low/moderate expression of NIS.