LSM4214 Lecture 10_Advances of HDAC Inhibitors in Cancer Therapeutics PDF

LSM4214: Cancer Pharmacology Advances of HDAC Inhibitors in Cancer Therapeutics Dr Alan Prem Kumar Department of Pharmacology and NUS Center for Cancer Research Yong Loo Lin School of Medicine National University of Singapore E-mail: [email protected] In eukaryotes, DNA...

LSM4214: Cancer Pharmacology Advances of HDAC Inhibitors in Cancer Therapeutics Dr Alan Prem Kumar Department of Pharmacology and NUS Center for Cancer Research Yong Loo Lin School of Medicine National University of Singapore E-mail: [email protected] In eukaryotes, DNA is packaged by histones into nucleosomes which are composed of 147 base pairs of DNA and core histone proteins H2A, H2B, H3 and H4. 2 Activation of target genes requires chromatin remodelling and histone modifications. L9: Advances of HDAC Inhibitors in cancer therapeutics 3 HATs and HDACs Participate in Regulation of Gene Expression Histone Deacetylases HDACs Acetylation regulates gene expression HAT transcription activation complex HDAC transcription repression complex L9: Advances of HDAC Inhibitors in cancer therapeutics 4 Histone Acetyltransferases Activation of target genes by hormones requires chromatin remodeling and histone modifications. In eukaryotes, DNA is packaged by histones into nucleosomes which are composed of 147 base pairs of DNA and core histone proteins H2A, H2B, H3 and H4. The histone acetyltransferases (HAT) and histone deacetylases (HDAC) regulate acetylation and deacetylation of the conserved lysine residues present in the amino terminal tails of all four core histones. B-type HATs have a housekeeping role in the cell, acetylating newly synthesized free histones in the cytoplasm for transport into the nucleus. The A-type HATs, on the other hand, acetylate nucleosomal histone within chromatin in the nucleus, and are thereby linked to transcriptional regulation.  HDAC classification Class I Class II Class IV Class III HDAC1 HDAC4 HDAC 11 Sir 2 HDAC2 HDAC5 HDAC3 HDAC6 HDAC8 HDAC7 Zn²⁺dependent HDAC9 HDAC10 NAD⁺dependent L9: Advances of HDAC Inhibitors in cancer 6 therapeutics  The acetylation status of histones regulates Histone access of transcription factors to DNA and influences levels of gene expression. Deacetylases in Histone deacetylase (HDAC) activity diminishes acetylation of histones, causing compaction of the DNA/histone complex. Cancer Several work has identified at least 18 human HDACs, with varying function, localization, and substrates. Histone Deacetylases in Cancer 8 L9: Advances of HDAC Inhibitors in cancer therapeutics Chromatin remodeling and gene regulation Aberrant HDAC activity is a hallmark of several cancers HDAC hyperactivity can lead to gene silencing HDAC inhibition is a focus of pharmaceutical anticancer R&D L9: Advances of HDAC Inhibitors in cancer 9 therapeutics HDACs Impact Cancer Biology gene expression oncoprotein stability cell migration protein catabolism cell cycle control 10 HDACs Impact Cancer Biology L9: Advances of HDAC Inhibitors in cancer therapeutics 11  Introduction to HDACi Dimethyl sulfoxide (DMSO) Terminal differentiation of murine erythroleukemia cells Interest in Histone Deacetylase (HDAC) inhibitors Chromatin remodeling SAHA made it!! (to mimic DMSO) Treat rare cancer cutaneous T-cell lymphoma (CTCL) Antitumor action of compounds undergoing clinical trials L9: Advances of HDAC Inhibitors in cancer 12 therapeutics  Class of compounds that interfere with the function of histone deacetylase Class of HDAC 4 classes of HDAC inhibitors inhibitors A short-chain fatty acid Hydroxamic acid Cyclic tetrapeptides Benzamides L9: Advances of HDAC Inhibitors in cancer therapeutics 13  Phenylbutyrate (urea cycle disorders) The short One of the first HDAC inhibitors to be tested in patients chain fatty Valporic acid (anticonvulsant) a histone deacetylase inhibitor (HDACI), in vitro acids induces differentiation of promyelocyte leukemia cell and proliferation arrest and apoptosis of various leukemia cell lines. L9: Advances of HDAC Inhibitors in cancer therapeutics 14  Hydroxamic acid First compound to be identified as HDAC inhibitors suberoyl anilide hydroxamic acid (SAHA) helped define the model pharmacophore for HDAC inhibitors L9: Advances of HDAC Inhibitors in cancer therapeutics 15  Trichostatin A (TSA) (antifugal) Hydroxamic acid Reversible inhibitor of Histone deacetylase Induce cell cycle arrest at G1, apoptosis, and cellular differentiation Has some uses as anti- cancer drug L9: Advances of HDAC Inhibitors in cancer therapeutics 16  Cyclic tetrapeptides Apicidin Depsipeptide Trapoxin Ethyl Modulate ketone the component expression of genes L9: Advances of HDAC Inhibitors in cancer 17 therapeutics  Benzamides Two drugs undergoing clinical trial – MS-275 A substance that is being studied in the treatment of cancers of the blood Mice experiment and result – CI-994 (epilepsy) Mechanism of antitumor activity unclear Causes accumulation of acetylated histones although is not able to inhibit HDAC activity in a direct fashion L9: Advances of HDAC Inhibitors in cancer 18 therapeutics  A common finding in cancer cells is high level Histone expression of HDAC isoenzymes and a Deacetylase corresponding hypoacetylation of histones. An attractive model for the antitumor action of Inhibitors in HDAC inhibitors is that the increase in histone acetylation leads to the activation of Cancer Therapy transcription of a few genes of which the expression causes the inhibition of tumor growth. In vitro and in vivo, HDAC inhibitors cause cell cycle arrest and differentiation of many tumor types. HDAC mediated deacetylation alters the transcriptional activity of nuclear transcription factors, including p53, E2F, c-Myc, nuclear factor B (NF-B), hypoxia-inducible factor 1 (HIF-1), as well as Estrogen Receptor and Androgen Receptor complexes. Histone Deacetylase Inhibitors in Cancer Therapy BCR-ABL, epidermal growth factor receptor, human epidermal growth factor receptor 2/neu, FLT3, Akt, and c-Raf  Prolonged expression of misfolded proteins triggers ER stress Histone Deacetylase Inhibitors in Cancer Therapy 21  The peroxisome proliferator-activated receptors How Do PPARs (PPARs) comprise an important subfamily of the nuclear hormone receptor (NHR) superfamily. The name PPAR derives from the initial cloning of Work at the one isoform as a target of various xenobiotic compounds that were observed to induce proliferation of peroxisomes in the liver. This protein Molecular Level? was called the peroxisome proliferator-activated receptor, now known as PPARα. The group of PPARs was expanded to include PPAR and PPAR (also referred to as PPAR, NUC1, and FAAR).  N-terminal region that contains a potential trans- How Do PPARs activation function known as AF-1, followed by a DNA binding domain that includes two zinc fingers. At the carboxyl terminus is a dimerization and ligand Work at the binding domain that molecular modeling reveals to be a large hydrophobic pocket and which contains a key, ligand dependent trans-activation function called AF-2. Molecular Level? PPARs bind to cognate DNA elements called PPAR response elements (PPREs) in the 5-flanking region of target genes.  PPARs, like other NHRs, form protein- How Do PPARs protein interactions with a variety of nuclear proteins known as coactivators Work at the and corepressors, which mediate contact between the PPAR-RXR heterodimer, chromatin, and the basal Molecular Level? transcriptional machinery and which promote activation and repression of gene expression.  PPAR ligands encompass wide range of structurally PPAR ligands diverse compounds, natural and synthetic. Natural ones include long chain polyunsaturated fatty acids and derivatives (eicosanoids, prostaglandins, like 15-deoxy-Δ12,14- prostaglandin J2 (15D-PGJ2)). The thiazolidinedione drugs are used for the treatment of type II diabetes and specifically target PPAR.  PPAR Regulatory Mechanisms (b) (d) (a) (c) (a) Positive and negative regulators of the PPARγ gene transcription. (b) The regulation of PPARγ levels by Rb and E2F. (c) The mechanism of ligand-dependent PPARγ activation. (d) The regulation of PPARγ activity by MEK and Erk kinases: MEK1 activates Erk-1/2, which phosphorylates PPARγ and targets it to proteasomes; in addition, MEK1 binds PPARγ in the nucleus and exports it to the cytoplasm. MEK5 can serve as coactivator for the PPARγ.  PPAR Regulatory Mechanisms L9: Advances of HDAC Inhibitors in cancer 27 therapeutics  Prostaglandins are a family of chemicals that are produced by the cells of the body and have several important functions. What are NSAIDs and They promote inflammation, pain, and fever; support the blood clotting function of how do they platelets; and protect the lining of the stomach from the damaging effects of acid. work? Prostaglandins are produced within the body's cells by the enzyme cyclooxygenase (COX).  There are two COX enzymes, COX-1 and COX-2. Both enzymes produce prostaglandins that promote inflammation, pain, and fever. What are COX-1 is a constitutively expressed enzyme with a "house-keeping" NSAIDs and role in regulating many normal physiological processes. One of these is in the stomach lining, how do they where prostaglandins serve a protective role, preventing the stomach mucosa from being work? eroded by its own acid. Most NSAIDs act as non-selective inhibitors of the both COX-1 and COX-2. L9: Advances of HDAC Inhibitors in cancer therapeutics 29  COX-2 is known to produce prostaglandins that Cyclooxygenase- regulate tumor-associated angiogenesis, 2 (COX-2) and modulate the immune system, regulate cell migration/invasion, and inhibit apoptosis, all of Cancer which promote cancer progression. Byproducts of the COX-2 pathway, such as malondialdehyde, directly form DNA adducts resulting in mutations that could initiate carcinogenesis. One of the major prostaglandin products of the COX- 2 pathway in the gastrointestinal tumor microenvironment is PGE2. PGs produced by COX-1 from epithelial and stromal cells in the subepithelial tissue of the colon are thought to maintain mucosal homeostasis.  Cyclooxygenase-2 (COX-2) and Cancer However, COX-2–derived PGE2 has been shown to be proinflammatory, mediating the progression of diseases such as arthritis and cancer A steady-state level of PGE2 is maintained in the tumor microenvironment by (a) a biosynthetic pathway, including PG synthases mPGES and cPGES, which converts PGH2 into PGE2, and (b) a catabolic pathway involving 15-hydroxyprostaglandin dehydrogenase (15-PGDH), which degrades PGE2 to an inactive 15-keto PGE2 metabolite. Loss of 15-PGDH expression correlates with tumor formation. Restoration of 15-PGDH expression strongly inhibited growth of colon cancer xenografts, suggesting that 15-PGDH may have a tumor-suppressor function. L9: Advances of HDAC Inhibitors in cancer 31 therapeutics Potential chemopreve ntive targets downstream of COX-2  Brief Summary: HATs and HDACs and Cellular Functions L9: Advances of HDAC Inhibitors in cancer therapeutics 33  Future Further clinical studies are needed to define the optimal dosage and duration of therapy with HDAC inhibitors in the fight against cancer. Additionally, more work is needed to understand the molecular basis of the HDAC inhibitors selectivity in the alteration of gene transcription, and in chromatin dynamics during malignant transformation. Lastly, the resistance of normal cells to HDAC inhibition by these agents is also needed to be studied further. L9: Advances of HDAC Inhibitors in cancer therapeutics 34 Thank you for your attention!