title: Activity of deacetylase inhibitor panobinostat (LBH589) in cutaneous T-cell lymphoma models: Defining molecular mechanisms of resistance.
abstract: Panobinostat (LBH589) is a highly potent deacetylase inhibitor that has demonstrated clinical efficacy in patients with advanced cutaneous T-cell lymphoma (CTCL). To gain a better understanding of the compound activity in this tumor type, we investigated the cellular and molecular effects of panobinostat using both in vitro and in vivo models of CTCL. All 4 tested CTCL cell lines exhibited very high sensitivity to panobinostat-induced growth inhibition. However, only 2 of 4 lines exhibited significant response to the cytotoxic activity of panobinostat. In a CTCL xenograft mouse tumor model, panobinostat treatment resulted in complete tumor regression. The difference in cell sensitivity to panobinostat-induced death enabled us to further investigate potential mechanisms responsible for tumor sensitivity or resistance. In CTCL cell lines that were insensitive to panobinostat-induced apoptosis, constitutively activated NF-kappaB and high levels of Bcl-2 were observed. Inhibition of Bcl-2 sensitized cells to the cytotoxic activity of panobinostat. Conversely, knockdown of Bax diminished the CTCL cell sensitivity. Interestingly, panobinostat could induce cytotoxicity in vorinostat-resistant CTCL cells by downregulating phosphorylated STAT3 and STAT5 proteins. These studies suggest distinct mechanisms responsible for resistance to different deacetylase inhibitors. We show that the intrinsic apoptotic signaling plays an essential role in mediating panobinostat anticancer activity. Moreover, cancer cell sensitivity to panobinostat treatment may be further improved by combination with inhibition of anti-apoptotic factors. These data provide preclinical support that panobinostat, as a single agent or in combination with other anticancer agents, is a promising therapy for CTCL.
authors.affiliation: Novartis Institutes for Biomedical Research, Oncology Drug Discovery, Cambridge, MA.
authors.forename: Wenlin
authors.initials: W
authors.lastname: Shao
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Growney
authors.forename: Yun
authors.initials: Y
authors.lastname: Feng
authors.forename: Gregory
authors.initials: G
authors.lastname: O'Connor
authors.forename: Minying
authors.initials: M
authors.lastname: Pu
authors.forename: Wenjing
authors.initials: W
authors.lastname: Zhu
authors.forename: Yung-Mae
authors.initials: YM
authors.lastname: Yao
authors.forename: Paul
authors.initials: P
authors.lastname: Kwon
authors.forename: Stephen
authors.initials: S
authors.lastname: Fawell
authors.forename: Peter
authors.initials: P
authors.lastname: Atadja
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D005260:Female; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology / Q000627:therapeutic use*; D007211:Indoles; D016410:Lymphoma, T-Cell, Cutaneous / Q000188:drug therapy*; D051379:Mice; D016513:Mice, SCID; D000077767:Panobinostat; D034622:RNA Interference; D012878:Skin Neoplasms / Q000188:drug therapy*; D023041:Xenograft Model Antitumor Assays; D051028:bcl-2-Associated X Protein / Q000235:genetics
chemical_list: D000970:Antineoplastic Agents; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D007211:Indoles; D051028:bcl-2-Associated X Protein; D000077767:Panobinostat