Molecular and cellular pharmacology SIRT1 inhibition in pancreatic cancer models: Contrasting effects in vitro and in vivo Chern Ein Oon a,b,n , Carina Strell a , Keng Yoon Yeong b , Arne Östman a , Jai Prakash a,c,n Q1 a Department of Oncology & Pathology, Cancer Center Karolinska, Karolinska Institutet, 171 76 Stockholm, Sweden b Institute for Research in Molecular Medicine, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia c Targeted Therapeutics, Department of Biomaterials Science and Technology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Zuidhorst building, ZH254, 7500AE Enschede, The Netherlands article info Article history: Received 4 August 2014 Received in revised form 25 March 2015 Accepted 25 March 2015 Keywords: Pancreatic cancer EX527 SIRT1 Sirtuin Gemcitabine Tumour resistance Chemical compounds studied in this article: 6-Chloro-2,3,4,9-tetrahydro-1H-Carbazole- 1-carboxamide (EX527) (PubChem CID: 5113032) abstract Gemcitabine remains the standard treatment for pancreatic cancer, although most patients acquire resistance to the therapy. Up-regulated in pancreatic cancer, SIRT1 is involved in tumorigenesis and drug resistance. However the mechanism through which SIRT1 regulates drug sensitivity in cancer cells is mainly unknown. We hypothesise that inhibiting SIRT1 activity may increase sensitivity of pancreatic cancer cells to gemcitabine treatment through the regulation of apototic cell death, cell cycle, epithelial- mesenschymal-transition (EMT) and senescence. We demonstrate that gemcitabine or 6-Chloro-2,3,4,9- tetrahydro-1 H-Carbazole-1-carboxamide (EX527) SIRT1 inhibitor reduces PANC-1 cell proliferation in vitro. EX527 enhanced sensitivity of PANC-1 cells to gemcitabine treatment through increased apoptosis. However, EX527 displayed no beneficial effect either as a monotreatment or in combination with gemcitabine in the modulation of cell cycle progression. Combination treatment did not reverse the two phenomena known to affect drug sensitivity, namely EMT and senescence, which are both induced by gemcitabine. Unexpectedly, EX527 promoted PANC-1 xenograft tumour growth in SCID mice compared to control group. Dual tX527 and gemcitabine displayed no synergistic effect compared to gemcitabine alone. The study reveals that SIRT1 is involved in chemoresistance and that inhibiting SIRT1 activity with EX527 sensitised PANC-1 cells to gemcitabine treatment in vitro. Sensitisation of cells is shown to be mainly through induction of micronuclei formation as a result of DNA damage and apoptosis in vitro. However, the absence of positive combinatorial effects in vivo indicates possible effects on cells of the tumor microenvironment and suggests caution regarding the clinical relevance of tissue culture findings with EX527. & 2015 Published by Elsevier B.V. 1. Introduction Pancreatic cancer is one of the most aggressive malignancies. Gemcitabine is an analogue of deoxycytidine and a pyrimidine antimetabolite which remains the cornerstone for pancreatic cancer patients as first-line therapy. Nevertheless, many patients develop resistance to existing therapeutic regimes, hence under- standing the mechanisms involved in mediating chemoresistance in pancreatic cancer could pave way for novel therapies. The tumour spectrum of epigenetic and genetic alterations may be accountable for poor patient prognosis and survival rate. Sirtuin 1 (SIRT1) is the mammalian ortholog of the yeast silent information regulator 2 (SIR2) which has been described as being upregulated in many cancer types including pancreatic cancer (Ashraf et al., 2006; Huffman et al., 2007; Zhao et al., 2011). Modulation of SIRT1 has been proposed in cancer therapy (Ota et al., 2006) although its biological function is further complicated by its paradox as either a tumor suppressor or tumor promoter depending on cancer types (Roth and Chen, 2013). SIRT1 over- expression has been demonstrated to reduce intestinal (Firestein et al., 2008) and liver (Herranz et al., 2010) tumour formation in mice models, suggesting that SIRT1 may suppress tumour forma- tion. Nevertheless, SIRT1 has been implicated in tumorigenesis and drug resistance through deacetylation of p53 (Vaziri et al., 2001), PTEN (Ikenoue et al., 2008), nuclear factor-kappaB (Yeung 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ejphar European Journal of Pharmacology http://dx.doi.org/10.1016/j.ejphar.2015.03.064 0014-2999/& 2015 Published by Elsevier B.V. n Corresponding author at: Institute for Research in Molecular Medicine, Uni- versiti Sains Malaysia, 11800 Penang, Malaysia. Tel.: þ604 6534879. n Corresponding author at: Targeted Therapeutics, Department of Biomaterials, Science and Technology, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, Zuidhorst building, ZH254, 7500AE Enschede, The Netherlands. Tel.: þ31534893096. E-mail addresses: chern.oon@usm.my (C.E. Oon), j.prakash@utwente.nl (J. Prakash). Please cite this article as: Oon, C.E., et al., SIRT1 inhibition in pancreatic cancer models: Contrasting effects in vitro and in vivo. Eur J Pharmacol (2015), http://dx.doi.org/10.1016/j.ejphar.2015.03.064i European Journal of Pharmacology ∎ (∎∎∎∎) ∎∎∎–∎∎∎