Abstract 4049: Preclinical pharmacology profile of GTX-0196: A novel, potent and highly selective dihydroorotate dehydrogenase (DHODH) inhibitor for the treatment of hematologic malignancies

Dihydroorotate dehydrogenase (DHODH) is a key enzyme in the de novo pyrimidine synthesis [Löffler et al., 1997]. Initial clinical studies with the DHODH inhibitor brequinar in solid tumors showed limited efficacy due to dose limiting adverse effects [Peters et al, 2018]. Recently, there is renewed interest in the use of more potent and selective DHODH inhibitors for the treatment of myeloid and lymphoid malignancies [Sykes et al, 2016].

Here we report the identification of the novel potent and highly selective DHODH inhibitor GTX-0196, with excellent physicochemical properties. GTX-0196 exhibited a biochemical IC50 of 3.7 nM in a DHODH biochemical assay and an antiproliferative IC50 of 1.1 nM in the MOLM-13 cell line, with brequinar showing IC50 values of 6.9 and 50 nM, respectively. The activity in the MOLM-13 proliferation assay was uridine-dependent, indicating absence of general toxicity of the compound and confirming DHODH-mediated efficacy.

Profiling of GTX-0196 in the BioPrint panel (Eurofins/CEREP, at 10 µM), showed <50% inhibition for all 133 target proteins tested (GPCR’s, NR´s, kinases and other enzymes), illustrating the high selectivity for DHODH (> 2000-fold selectivity versus other targets tested). Furthermore, no inhibition was observed in a human CYP panel (1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4, at 30 µM) and in a panel of transporters (at 10 µM). High metabolic stability in human liver microsomes and hepatocytes was observed with t½ > 6h and 10h, respectively.

Compared to an earlier lead compound, GTX-0196 demonstrated enhanced potency and metabolic stability (particularly in preclinical species). Potent and efficacious inhibition of proliferation through DHODH was confirmed in a large number of solid tumor and hematologic malignancy cell lines, illustrating the broad potential use of this chemical series. Furthermore, tumor growth inhibition was observed in the MOLM-13 xenograft mouse model.

Due to its favorable properties, GTX-0196 has progressed towards IND-enabling studies. In parallel, we are exploring mono and combination therapy opportunities in hematological malignancies as well as combination therapy opportunities in solid tumors to investigate the full therapeutic potential in oncology for this optimized DHODH inhibitor.

Löffler et al. Mol. Cell. Biochem. 1997Peters GJ et al, Nucleosides, Nucleotides and Nucleic Acids 2018Sykes DB et al. Cell 2016

Citation Format: Allard Kaptein, Sonia Lain, Diede Brunen, Edward van Wezel, Tjeerd Barf. Preclinical pharmacology profile of GTX-0196: A novel, potent and highly selective dihydroorotate dehydrogenase (DHODH) inhibitor for the treatment of hematologic malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4049.

Optimization of Tetrahydroindazoles as Inhibitors of Human Dihydroorotate Dehydrogenase and Evaluation of Their Activity and In Vitro Metabolic Stability

Human dihydroorotate dehydrogenase (DHODH), an enzyme in the de novo pyrimidine synthesis pathway, is a target for the treatment of rheumatoid arthritis and multiple sclerosis and is re-emerging as an attractive target for cancer therapy. Here we describe the optimization of recently identified tetrahydroindazoles (HZ) as DHODH inhibitors. Several of the HZ analogues synthesized in this study are highly potent inhibitors of DHODH in an enzymatic assay, while also inhibiting cancer cell growth and viability and activating p53-dependent transcription factor activity in a reporter cell assay. Furthermore, we demonstrate the specificity of the compounds toward the de novo pyrimidine synthesis pathway through supplementation with an excess of uridine. We also show that induction of the DNA damage marker γ-H2AX after DHODH inhibition is preventable by cotreatment with the pan-caspase inhibitor Z-VAD-FMK. Additional solubility and in vitro metabolic stability profiling revealed compound 51 as a favorable candidate for preclinical efficacy studies.

Functional characterization of novel germline TP53 variants in Swedish families

Pathogenic germline TP53 variants predispose to a wide range of early onset cancers, often recognized as the Li-Fraumeni syndrome (LFS). They are also identified in 1% of families with hereditary breast cancer (HrBC) that do not fulfill the criteria for LFS. In this study, we present a total of 24 different TP53 variants identified in 31 Swedish families with LFS or HrBC. Ten of these variants, nine exonic and one splice, have previously not been described as germline pathogenic variants. The nine exonic variants were functionally characterized and demonstrated partial transactivation activity compared to wild-type p53. Some show nuclear localization similar to wild-type p53 while others possess cytoplasmic or perinuclear localization. The four frameshift variants (W91Gfs*32, L111 Wfs*12, S227 Lfs*20 and S240Kfs*25) had negligible, while F134 L and T231del had low level of p53 activity. The L111 Wfs*12 and T231del variants are also deficient for induction of apoptosis. The missense variant R110C retain p53 effects and the nonsense E349* shows at least partial transcription factor activity but has reduced ability to trigger apoptosis. This is the first functional characterization of novel germline TP53 pathogenic or likely pathogenic variants in the Swedish cohort as an attempt to understand its association with LFS and HrBC, respectively.

Constitutive activation of WASp in X-linked neutropenia renders neutrophils hyperactive

Congenital neutropenia is characterized by low absolute neutrophil numbers in blood, leading to recurrent bacterial infections, and patients often require life-long granulocyte CSF (G-CSF) support. X-linked neutropenia (XLN) is caused by gain-of-function mutations in the actin regulator Wiskott-Aldrich syndrome protein (WASp). To understand the pathophysiology in XLN and the role of WASp in neutrophils, we here examined XLN patients and 2 XLN mouse models. XLN patients had reduced myelopoiesis and extremely low blood neutrophil number. However, their neutrophils had a hyperactive phenotype and were present in normal numbers in XLN patient saliva. Murine XLN neutrophils were hyperactivated, with increased actin dynamics and migration into tissues. We provide molecular evidence that the hyperactivity of XLN neutrophils is caused by WASp in a constitutively open conformation due to contingent phosphorylation of the critical tyrosine-293 and plasma membrane localization. This renders WASp activity less dependent on regulation by PI3K. Our data show that the amplitude of WASp activity inside a cell could be enhanced by cell-surface receptor signaling even in the context in which WASp is already in an active conformation. Moreover, these data categorize XLN as an atypical congenital neutropenia in which constitutive activation of WASp in tissue neutrophils compensates for reduced myelopoiesis.

cMyc-p53 feedback mechanism regulates the dynamics of T lymphocytes in the immune response

Activation and proliferation of T cells are tightly regulated during the immune response. We show here that kinetics of proliferation of PHA activated T cells follows the expression of cMyc. Expression of p53 is also elevated and remains high several days after activation. To investigate the role of p53 in activated T cells, its expression was further elevated with nultin-3 treatment, a small molecule that dissociates the E3 ubiquitin protein ligase MDM2 from p53. Concomitantly, cMyc expression and proliferation decreased. At the other end of the cMyc-p53 axis, inhibition of cMyc with 10058-F4 led to down regulation of p53, likely through the lower level of cMyc induced p14ARF, which is also known to dissociate the p53-MDM2 complex. Both compounds induced cell cycle arrest and apoptosis. We conclude that the feedback regulation between cMyc and p53 is important for the T cell homeostasis. We also show that the two compounds modulating p53 and cMyc levels inhibited proliferation without abolishing the cytotoxic function, thus demonstrating the dichotomy between proliferation and cytotoxicity in activated T cells.

Proceedings of the Frontiers of Retrovirology Conference 2016

Oral presentations

Session 1: Entry & uncoating

O1 Host cell polo-like kinases (PLKs) promote early prototype foamy virus (PFV) replication

Irena Zurnic, Sylvia Hütter, Ute Lehmann, Nicole Stanke, Juliane Reh, Tobias Kern, Fabian Lindel, Gesche Gerresheim, Martin Hamann, Erik Müllers, Paul Lesbats, Peter Cherepanov, Erik Serrao, Alan Engelman, Dirk Lindemann

O2 A novel entry/uncoating assay reveals the presence of at least two species of viral capsids during synchronized HIV-1 infection

Claire Da Silva Santos, Kevin Tartour, Andrea Cimarelli

O3 Dynamics of nuclear envelope association and nuclear import of HIV-1 complexes

Rya Burdick, Jianbo Chen, Jaya Sastri, Wei-Shau Hu, Vinay Pathak

O4 Human papillomavirus protein E4 potently enhances the susceptibility to HIV infection

Oliver T. Keppler

Session 2: Reverse transcription & integration

O5 Structure and function of HIV-1 integrase post translational modifications

Karine Pradeau, Sylvia Eiler, Nicolas Levy, Sarah Lennon, Sarah Cianferani, Stéphane Emiliani, Marc Ruff

O6 Regulation of retroviral integration by RNA polymerase II associated factors and chromatin structure

Vincent Parissi

Session 3: Transcription and latency

O7 A novel single-cell analysis pipeline to identify specific biomarkers of HIV permissiveness

Sylvie Rato, Antonio Rausell, Miguel Munoz, Amalio Telenti, Angela Ciuffi

O8 A capsid-dependent integration program linking T cell activation to HIV-1 gene expression

Alexander Zhyvoloup, Anat Melamed, Ian Anderson, Delphine Planas, Janos Kriston-Vizi, Robin Ketteler, Chen-Hsuin Lee, Andy Merritt, Petronela Ancuta, Charles Bangham, Ariberto Fassati

O9 Characterisation of new RNA polymerase III and RNA polymerase II transcriptional promoters in the Bovine Leukemia Virus genome

Anthony Rodari, Benoit Van Driessche, Mathilde Galais, Nadége Delacourt, Sylvain Fauquenoy, Caroline Vanhulle, Anna Kula, Arsène Burny, Olivier Rohr, Carine Van Lint

O10 Tissue-specific dendritic cells differentially modulate latent HIV-1 reservoirs

Thijs van Montfort, Renee van der Sluis, Dave Speijer, Ben Berkhout

Session 4: RNA trafficking & packaging

O11 A novel cis-acting element affecting HIV replication

Bo Meng, Andrzej Rutkowski, Neil Berry, Lars Dölken, Andrew Lever

O12 Tolerance of HIV’s late gene expression towards stepwise codon adaptation

Thomas Schuster, Benedikt Asbach, Ralf Wagner

Session 5: Assembly & release

O13 Importance of the tax-inducible actin-bundling protein fascin for transmission of human T cell leukemia virus Type 1 (HTLV-1)

Christine Gross, Veit Wiesmann, Martina Kalmer, Thomas Wittenberg, Jan Gettemans, Andrea K. Thoma-Kress

O14 Lentiviral nef proteins antagonize TIM-mediated inhibition of viral release

Minghua Li, Eric O. Freed, Shan-Lu Liu

Session 6: Pathogenesis & evolution

O15 SEVI and semen prolong the half-life of HIV-1

Janis Müller, Jan Münch

O16 CD169⁺ macrophages mediate retrovirus trans-infection of permissive lymphocytes to establish infection in vivo

Xaver Sewald, Pradeep Uchil, Mark Ladinsky, Jagadish Beloor, Ruoxi Pi, Christin Herrmann, Nasim Motamedi, Thomas Murooka, Michael Brehm, Dale Greiner, Thorsten Mempel, Pamela Bjorkman, Priti Kumar, Walther Mothes

O17 Efficient replication of a vpu containing SIVagm construct in African Green Monkeys requires an HIV-1 nef gene

Simone Joas, Erica Parrish, Clement Wesley Gnanadurai, Edina Lump, Christina M. Stürzel, Nicholas F. Parrish, Ulrike Sauermann, Katharina Töpfer, Tina Schultheiss, Steven Bosinger, Guido Silvestri, Cristian Apetrei, Nicholas Huot, Michaela Müller-Trutwin, Daniel Sauter, Beatrice H. Hahn, Christiane Stahl-Hennig, Frank Kirchhoff

O18 Reprogramming initiates mobilization of endogenous mutagenic LINE-1, Alu and SVA retrotransposons in human induced pluripotent stem cells with consequences for host gene expression

Gerald Schumann, Sabine Jung-Klawitter, Nina V. Fuchs, Kyle R. Upton, Martin Muñoz-Lopez, Ruchi Shukla, Jichang Wang, Marta Garcia-Canadas, Cesar Lopez-Ruiz, Daniel J. Gerhardt, Attila Sebe, Ivana Grabundzija, Patricia Gerdes, Sylvia Merkert, Andres Pulgarin, Anja Bock, Ulrike Held, Anett Witthuhn, Alexandra Haase, Ernst J. Wolvetang, Ulrich Martin, Zoltán Ivics, Zsuzsanna Izsvák, J. Garcia-Perez, Geoffrey J. Faulkner

O19 NF-κB activation induces expression of human endogenous retrovirus and particle production

Tara Hurst, Aris Katzourakis, Gkikas Magiorkinis

Session 7a and b: Innate sensing & intrinsic immunity

O20 Identification of the phosphatase acting on T592 in SAMHD1 during M/G₁ transition

Kerstin Schott, Rita Derua, Janna Seifried, Andreas Reuter, Heike Schmitz, Christiane Tondera, Alberto Brandariz-Nuñez, Felipe Diaz-Griffero, Veerle Janssens, Renate König

O21 Vpx overcomes a SAMHD1-independent block to HIV reverse transcription that is specific to resting CD4 T cells

Hanna-Mari Baldauf, Lena Stegmann, Sarah-Marie Schwarz, Maud Trotard, Margarethe Martin, Gina Lenzi, Manja Burggraf, Xiaoyu Pan, Oliver I. Fregoso, Efrem S. Lim, Libin Abraham, Elina Erikson, Laura Nguyen, Ina Ambiel, Frank Rutsch, Renate König, Baek Kim, Michael Emerman, Oliver T. Fackler, Oliver T. Keppler

O22 The role of SAMHD1 in antiviral restriction and immune sensing in the mouse

Sabine Wittmann, Rayk Behrendt, Bianca Volkmann, Kristin Eissmann, Thomas Gramberg

O23 T cells expressing reduced restriction factors are preferentially infected in therapy naïve HIV-1 patients

Sebastian Bolduan, Herwig Koppensteiner, Stefanie Regensburg, Ruth Brack-Werner, Rika Draenert, Michael Schindler

O24 cGAS-mediated innate immunity spreads through HIV-1 env-induced membrane fusion sites from infected to uninfected primary HIV-1 target cells

Aurélie Ducroux, Shuting Xu, Aparna Ponnurangam, Sergej Franz, Angelina Malassa, Ellen Ewald, Christine Goffinet

O25 Perturbation of innate RNA and DNA sensing by human T cell leukemia virus type 1 oncoproteins

Sin-Yee Fung, Ching-Ping Chan, Chun-Kit Yuen, Kin-Hang Kok, Chin-Ping Chan, Dong-Yan Jin

O26 Induction and anti-viral activity of Interferon α subtypes in HIV-1 infection

Ulf Dittmer

O27 Vpu-mediated counteraction of tetherin is a major determinant of HIV-1 interferon resistance

Dorota Kmiec, Shilpa Iyer, Christina Stürzel, Daniel Sauter, Beatrice Hahn, Frank Kirchhoff

O28 DNA repair protein Rad18 restricts HIV-1 and LINE-1 life cycle

Yasuo Ariumi, Mariko Yasuda-Inoue, Koudai Kawano, Satoshi Tateishi, Priscilla Turelli

O29 Natural mutations in IFITM3 allow escape from post-translational regulation and toggle antiviral specificity

Alex Compton, Nicolas Roy, Françoise Porrot, Anne Billet, Nicoletta Casartelli, Jacob Yount, Chen Liang, Oliver Schwartz

Session 8: Adaptive immunity & immune evasion

O30 Observing evolution in HIV-1 infection: phylogenetics and mutant selection windows to infer the influence of the autologous antibody response on the viral quasispecies

Carsten Magnus, Lucia Reh, Penny Moore, Therese Uhr, Jacqueline Weber, Lynn Morris, Alexandra Trkola

O31 Dose and subtype specific analyses of the anti-HIV effects of IFN-alpha family members

Rashel V. Grindberg, Erika Schlaepfer, Gideon Schreiber, Viviana Simon, Roberto F. Speck

Session 9: Novel antiviral strategies

O32 LEDGIN-mediated inhibition of the integrase-LEDGF/p75 interaction reduces reactivation of residual latent HIV

Zeger Debyser, Lenard Vranckx, Jonas Demeulemeester, Suha Saleh, Eric Verdin, Anna Cereseto, Frauke Christ, Rik Gijsbers

O33 NKG2D-mediated clearance of reactivated viral reservoirs by natural killer cells

O34 Inhibition of HIV reactivation in brain cells by AAV-mediated delivery of CRISPR/Cas9

O35 CRISPR-Cas9 as antiviral: potent HIV-1 inhibition, but rapid virus escape and the subsequent design of escape-proof antiviral strategies

Ben Berkhout, Gang Wang, Na Zhao, Atze T. Das

Session 10: Recent advances in HIV vaccine development

O36 Priming with a potent HIV-1 DNA vaccine frames the quality of T cell and antibody responses prior to a poxvirus and protein boost

Benedikt Asbach, Josef Köstler, Beatriz Perdiguero, Mariano Esteban, Bertram L. Jacobs, David C. Montefiori, Celia C. LaBranche, Nicole L. Yates, Georgia D. Tomaras, Guido Ferrari, Kathryn E. Foulds, Mario Roederer, Gary Landucci, Donald N. Forthal, Michael S. Seaman, Natalie Hawkins, Steven G. Self, Sanjay Phogat, James Tartaglia, Susan W. Barnett, Brian Burke, Anthony D. Cristillo, Song Ding, Jonathan L. Heeney, Giuseppe Pantaleo, Ralf Wagner

O37 Passive immunisation with a neutralising antibody against HIV-1 Env prevents infection of the first cells in a mucosal challenge rhesus monkey model

Christiane Stahl-Hennig, Viktoria Stab, Armin Ensser, Ulrike Sauermann, Bettina Tippler, Dennis Burton, Matthias Tenbusch, Klaus Überla

O38 HIV antibody Fc-glycoforms drive B cell affinity maturation

Galit Alter, Giuseppe Lofano, Anne-Sophie Dugast, Viraj Kulkarni, Todd Suscovich

Poster presentations

Topic 1: Entry & uncoating

P1 Dynein light chain is required for murine leukemia virus infection

Tatiana Opazo, Felipe Barraza, Diego Herrera, Andrea Garces, Tomas Schwenke, Diego Tapia, Jorge Cancino, Gloria Arriagada

P2 Peptide paratope mimics of the broadly neutralising HIV-1 antibody b12

Christina Haußner, Dominik Damm, Anette Rohrhofer, Barbara Schmidt, Jutta Eichler

P3 Investigating cellular pathways involved in the transmission of HIV-1 between dendritic cells and T cells using RNAi screening techniques

Rebecca Midgley, James Wheeldon, Vincent Piguet

P4 Co-receptor tropism in HIV-1, HIV-2 monotypic and dual infections

Priyanka Khopkar, Megha Rohamare, Smita Kulkarni

P5 Characterisation of the role of CIB1 and CIB2 as HIV-1 helper factors

Ana Godinho-Santos, Allan Hance, Joao Goncalves, Fabrizio Mammano

P6 Buffering deleterious polymorphisms in the highly constrained C2 region of HIV-1 envelope by the flexible V3 domain

Romain Gasser, Meriem Hamoudi, Martina Pellicciotta, Zhicheng Zhou, Clara Visdeloup, Philippe Colin, Martine Braibant, Bernard Lagane, Matteo Negroni

P7 Entry inhibition of HERV-K(HML-2) by an Env-IgG fusion protein

Jula Wamara, Norbert Bannert

Topic 2: Reverse transcription & integration

P8 The R263K/H51Y resistance substitutions in HIV integrase decreases levels of integrated HIV DNA over time

Thibault Mesplede, Nathan Osman, Kaitlin Anstett, Jiaming Calvin Liang, Hanh Thi Pham, Mark Wainberg

P9 The Retrovirus Integration Database (RID)

Wei Shao, Jigui Shan, Mary Kearney, Xiaolin Wu, Frank Maldarelli, John Mellors, Brian Luke, John Coffin, Stephen Hughes

P10 The small molecule 3G11 inhibits HIV-1 reverse transcription

Thomas Fricke, Silvana Opp, Caitlin Shepard, Dmitri Ivanov, Baek Kim, Jose Valle-Casuso, Felipe Diaz-Griffero

P11 Dual and opposite regulation of HIV-1 integration by hRAD51: impact on therapeutical approaches using homologous DNA repair modulators

Vincent Parissi

P12 A flexible motif essential for integration by HIV-1 integrase

Marine Kanja, Pierre Cappy, Matteo Negroni, Daniela Lener

P13 Interaction between HIV-1 integrase and the host protein Ku70: identification of the binding site and study of the influence on integrase-proteasome interplay

Ekaterina Knyazhanskaya, Andrey Anisenko, Timofey Zatsepin, Marina Gottikh

P14 Normalisation based method for deep sequencing of somatic retroelement integrations in human genome

Alexander Komkov, Anastasia Minervina, Gaiaz Nugmanov, Vadim Nazarov, Konstantin Khodosevich, Ilgar Mamedov, Yuri Lebedev

Topic 3: Transcription and latency

P15 BCA2/RABRING7 restricts HIV-1 transcription by preventing the nuclear translocation of NF-κB

Marta Colomer-Lluch, Ruth Serra-Moreno

P16 MATR3 post-transcriptional regulation of HIV-1 transcription during latency

Ambra Sarracino, Anna Kula, Lavina Gharu, Alexander Pasternak, Carine Van Lint, Alessandro Marcello

P17 HIV-1 tat intersects the SUMO pathway to regulate HIV-1 promoter activity

Ann Marie McCartin, Anurag Kulkarni, Valentin Le Douce, Virginie Gautier

P18 Conservation in HIV-1 Vpr guides tertiary gRNA folding and alternative splicing

Ann Baeyens, Evelien Naessens, Anouk Van Nuffel, Karin Weening, Anne-Marie Reilly, Eva Claeys, Wim Trypsteen, Linos Vandekerckhove, Sven Eyckerman, Kris Gevaert, Bruno Verhasselt

P19 The majority of reactivatable latent HIV are genetically distinct

Hoi Ping Mok, Nicholas Norton, Axel Fun, Jack Hirst, Mark Wills, Andrew Lever

P20 Do mutations in the tat exonic splice enhancer contribute to HIV-1 latency?

Nicholas Norton, Hoi Ping Mok, Jack Hirst, Andrew Lever

P21 Culture-to-Ct: A fast and direct RT-qPCR HIV gene reactivation screening method using primary T cell culture

Valentin Le Douce, Ann Marie McCartin, Virginie Gautier

P22 A novel approach to define populations of early silenced proviruses

Dalibor Miklik, Filip Senigl, Jiri Hejnar

Topic 4: RNA trafficking & packaging

P23 Functional analysis of the structure and conformation of HIV-1 genome RNA DIS

Jun-ichi Sakuragi, Sayuri Sakuragi, Masaru Yokoyama, Tatsuo Shioda, Hironori Sato

P24 Regulation of foamy viral env splicing controls gag and pol expression

Jochen Bodem, Rebecca Moschall, Sarah Denk, Steffen Erkelenz, Christian Schenk, Heiner Schaal

Topic 5: Assembly & release

P25 Transfer of HTLV-1 p8 to target T cells depends on VASP: a novel interaction partner of p8

Norbert Donhauser, Ellen Socher, Sebastian Millen, Heinrich Sticht, Andrea K. Thoma-Kress

P26 COL4A1 and COL4A2 are novel HTLV-1 tax targets with a putative role in virus transmission

Christine Gross, Sebastian Millen, Melanie Mann, Klaus Überla, Andrea K. Thoma-Kress

P27 The C terminus of foamy virus gag protein is required for particle formation, and virus budding: starting assembly at the C terminus?

Guochao Wei, Matthew J. Betts, Yang Liu, Timo Kehl, Robert B. Russell, Martin Löchelt

P28 Generation of an antigen-capture ELISA and analysis of Rec and Staufen-1 effects on HERV-K(HML-2) virus particle production

Oliver Hohn, Saeed Mostafa, Kirsten Hanke, Stephen Norley, Norbert Bannert

P29 Antagonism of BST-2/tetherin is a conserved function of primary HIV-2 Env glycoproteins

Chia-Yen Chen, Masashi Shingai, Pedro Borrego, Nuno Taveira, Klaus Strebel

P30 Mutations in the packaging signal region of the HIV-1 genome cause a late domain mutant phenotype

Chris Hellmund, Bo Meng, Andrew Lever

P31 p6 regulates membrane association of HIV-1 gag

Melanie Friedrich, Friedrich Hahn, Christian Setz, Pia Rauch, Kirsten Fraedrich, Alina Matthaei, Petra Henklein, Maximilian Traxdorf, Torgils Fossen, Ulrich Schubert

Topic 6: Pathogenesis & evolution

P32 Molecular and structural basis of protein evolution during viral adaptation

Aya Khwaja, Meytal Galilee, Akram Alian

P33 HIV-1 enhancement and neutralisation by soluble gp120 and its role for the selection of the R5-tropic “best fit”

Birco Schwalbe, Heiko Hauser, Michael Schreiber

P34 An insertion of seven amino acids in the Env cytoplasmic tail of Human Immunodeficiency Virus type 2 (HIV-2) selected during disease progression enhances viral replication

François Dufrasne, Mara Lucchetti, Patrick Goubau, Jean Ruelle

P35 Cell-associated HIV-1 unspliced to multiply spliced RNA ratio at 12 weeks ART correlates with markers of immune activation and apoptosis and predicts the CD4 T-cell count at 96 weeks ART

Mirte Scherpenisse, Ben Berkhout, Alexander Pasternak

P36 Faster progression in non-B subtype HIV-1-infected patients than Korean subclade of subtype B is accompanied by higher variation and no induction of gross deletion in non-B nef gene by Korean red ginseng treatment

Young-Keol Cho, Jungeun Kim, Daeun Jeong

P37 Aberrant expression of ERVWE1 endogenous retrovirus and overexpression of TET dioxygenases are characteristic features of seminoma

Katerina Trejbalova, Martina Benesova, Dana Kucerova, Zdenka Vernerova, Rachel Amouroux, Petra Hajkova, Jiri Hejnar

P38 Life history of the oldest lentivirus: characterisation of ELVgv integrations and the TRIM5 selection pattern in dermoptera

Daniel Elleder, Tomas Hron, Helena Farkasova, Abinash Padhi, Jan Paces

P39 Characterisation of a highly divergent endogenous retrovirus in the equine germ line

Henan Zhu, Robert Gifford, Pablo Murcia

P40 The emergence of pandemic retroviral infection in small ruminants

Maria Luisa Carrozza, Anna-Maria Niewiadomska, Maurizio Mazzei, Mounir Abi-Said, Joseph Hughes, Stéphane Hué, Robert Gifford

P41 Near full-length genome (NFLG) Characterisation of HIV-1 subtype B identified in South Africa

Adetayo Obasa, Graeme Jacobs, Susan Engelbrecht

P42 Acquisition of Vpu-mediated tetherin antagonism by an HIV-1 group O strain

Katharina Mack, Kathrin Starz, Daniel Sauter, Matthias Geyer, Frederic Bibollet-Ruche, Christina Stürzel, Marie Leoz, Jean Christophe Plantier, Beatrice H. Hahn, Frank Kirchhoff

P43 The human endogenous retrovirus type K is involved in cancer stem cell markers expression and in human melanoma malignancy

Ayele Argaw-Denboba, Emanuela Balestrieri, Annalucia Serafino, Ilaria Bucci, Chiara Cipriani, Corrado Spadafora, Paolo Sinibaldi-Vallebona, Claudia Matteucci

P44 Natural infection of Indian non-human primates by unique lentiviruses

S. Nandi Jayashree, Ujjwal Neogi, Anil K. Chhangani, Shravan Sing Rathore, Bajrang R. J. Mathur

P45 Free cervical cancer screening among HIV-positive women receiving antiretroviral treatment in Nigeria

Adeyemi Abati

P46 Molecular evolutionary status of feline immunodeficiency virus in Turkey

B. Taylan Koç, Tuba Çiğdem Oğuzoğlu

Topic 7: Innate sensing & intrinsic immunity

P47 Cell-to-cell contact with HTLV-1-infected T cells reduces dendritic cell immune functions and contributes to infection in trans.

Takatoshi Shimauchi, Stephan Caucheteux, Jocelyn Turpin, Katja Finsterbusch, Charles Bangham, Yoshiki Tokura, Vincent Piguet

P48 Deciphering the mechanisms of HIV-1 exacerbation induced by Mycobacterium tuberculosis in monocytes/macrophages

Shanti Souriant, Luciana Balboa, Karine Pingris, Denise Kviatcowsky, Brigitte Raynaud-Messina, Céline Cougoule, Ingrid Mercier, Marcelo Kuroda, Pablo González-Montaner, Sandra Inwentarz, Eduardo Jose Moraña, Maria del Carmen Sasiain, Olivier Neyrolles, Isabelle Maridonneau-Parini, Geanncarlo Lugo-Villarino, Christel Vérollet

P49 The SAMHD1-mediated inhibition of LINE-1 retroelements is regulated by phosphorylation

Alexandra Herrmann, Sabine Wittmann, Caitlin Shepard, Dominique Thomas, Nerea Ferreirós Bouzas, Baek Kim, Thomas Gramberg

P50 Activities of nuclear envelope protein SUN2 in HIV infection

Xavier Lahaye, Anvita Bhargava, Takeshi Satoh, Matteo Gentili, Silvia Cerboni, Aymeric Silvin, Cécile Conrad, Hakim Ahmed-Belkacem, Elisa C. Rodriguez, Jean-François Guichou, Nathalie Bosquet, Matthieu Piel, Roger Le Grand, Megan King, Jean-Michel Pawlotsky, Nicolas Manel

P51 Activation of TLR7/8 with a small molecule agonist induces a novel restriction to HIV-1 infection of monocytes

Henning Hofmann, Benedicte Vanwalscappel, Nicolin Bloch, Nathaniel Landau

P52 Steady state between the DNA polymerase and Rnase H domain activities of reverse transcriptases determines the sensitivity of retroviruses to inhibition by APOBEC3 proteins

Stanislav Indik, Benedikt Hagen

P53 HIV restriction in mature dendritic cells is related to p21 induction and p21-mediated control of the dNTP pool and SAMHD1 activity.

José Carlos Valle-Casuso, Awatef Allouch, Annie David, Françoise Barré-Sinoussi, Michaela Müller-Trutwin, Monsef Benkirane, Gianfranco Pancino, Asier Saez-Cirion

P54 IFITM protens restrict HIV-1 protein synthesis

Wing-Yiu Lee, Chen Liang, Richard Sloan

P55 Characterisation and functional analysis of the novel restriction factor Serinc5

Bianca Schulte, Silvana Opp, Felipe Diaz-Griffero

P56 piRNA sequences are common in Human Endogenous Retroviral Sequences (HERVs): An antiretroviral restriction mechanism?

Jonas Blomberg, Luana Vargiu, Patricia Rodriguez-Tomé, Enzo Tramontano, Göran Sperber

P57 Ferroportin restricts HIV-1 infection in sickle cell disease

Namita Kumari, Tatiana Ammosova, Sharmeen Diaz, Patricia Oneal, Sergei Nekhai

P58 APOBEC3G modulates the response to antiretroviral drugs in humanized mice

Audrey Fahrny, Gustavo Gers-Huber, Annette Audigé, Roberto F. Speck, Anitha Jayaprakash, Ravi Sachidanandam, Matt Hernandez, Marsha Dillon-White, Viviana Simon

P59 High-throughput epigenetic analysis of evolutionarily young endogenous retrovirus presents in the mule deer (Odocoileus hemionus) genome

Tomas Hron, Helena Farkasova, Daniel Elleder

P60 Characterisation of the expression of novel endogenous retroviruses and immune interactions in a macaque model

Neil Berry, Emmanuel Maze, Claire Ham, Neil Almond, Greg Towers, Robert Belshaw

P61 HIV-1 restriction by orthologs of SERINC3 and SERINC5

Patrícia de Sousa-Pereira, Joana Abrantes, Massimo Pizzato, Pedro J. Esteves, Oliver T. Fackler, Oliver T. Keppler, Hanna-Mari Baldauf

P62 TRIM19/PML restricts HIV infection in a cell type-dependent manner

Bianca Volkmann, Tanja Kahle, Kristin Eissmann, Alexandra Herrmann, Sven Schmitt, Sabine Wittmann, Laura Merkel, Nina Reuter, Thomas Stamminger, Thomas Gramberg

P63 Recent invasion of the mule deer genome by a retrovirus

Helena Farkasova, Tomas Hron, Daniel Elleder

P64 Does the antiviral protein SAMHD1 influence mitochondrial function?

Ilaria Dalla Rosa, Kate Bishop, Antonella Spinazzola, Harriet Groom

P65 cGAMP transfers intercellularly via HIV-1 Env-mediated cell–cell fusion sites and triggers an innate immune response in primary target cells

Shuting Xu, Aurélie Ducroux, Aparna Ponnurangam, Sergej Franz, Gabrielle Vieyres, Mathias Müsken, Thomas Zillinger, Angelina Malassa, Ellen Ewald, Veit Hornung, Winfried Barchet, Susanne Häussler, Thomas Pietschmann, Christine Goffinet

P66 Pre-infection transcript levels of FAM26F in PBMCS inform about overall plasma viral load in acute and postacute phase after SIV-infection

Ulrike Sauermann, Aneela Javed, Nicole Leuchte, Gabriela Salinas, Lennart Opitz, Christiane Stahl-Hennig, Sieghart Sopper

P67 Sequence-function analysis of three T cell receptors targeting the HIV-1 p17 epitope SLYNTVATL

Christiane Mummert, Christian Hofmann, Angela G. Hückelhoven, Silke Bergmann, Sandra M. Müller-Schmucker, Ellen G. Harrer, Jan Dörrie, Niels Schaft, Thomas Harrer

P68 An immunodominant region of the envelope glycoprotein of small ruminant lentiviruses may function as decoy antigen

Laure Cardinaux, M.-L. Zahno, H.-R. Vogt, R. Zanoni, G. Bertoni

P69 Impact of immune activation, immune exhaustion, broadly neutralising antibodies and viral reservoirs on disease progression in HIV-infected children

Maximilian Muenchhoff, Philip Goulder, Oliver Keppler

Topic 9: Novel antiviral strategies

P70 Identification of natural compounds as new antiviral products by bioassay-guided fractionation

Alexandra Herrmann, Stephanie Rebensburg, Markus Helfer, Michael Schindler, Ruth Brack-Werner

P71 The PPARG antagonism disconnects the HIV replication and effector functions in Th17 cells

Yuwei Zhang, Huicheng Chen, Delphine Planas, Annie Bernier, Annie Gosselin, Jean-Pierre Routy, Petronela Ancuta

P72 Characterisation of a multiresistant subtype AG reverse transcriptase: AZT resistance, sensitivity to RNase H inhibitors and inhibitor binding

Birgitta Wöhrl, Anna Schneider, Angela Corona, Imke Spöring, Mareike Jordan, Bernd Buchholz, Elias Maccioni, Roberto Di Santo, Jochen Bodem, Enzo Tramontano, Kristian Schweimer

P73 Insigths into the acetylation pattern of HDAC inhibitors and their potential role in HIV therapy

Christian Schölz, Brian Weinert, Sebastian Wagner, Petra Beli, Yasuyuki Miyake, Jun Qi, Lars Jensen, Werner Streicher, Anna McCarthy, Nicholas Westwood, Sonia Lain, Jürgen Cox, Patrick Matthias, Matthias Mann, James Bradner, Chunaram Choudhary

P74 HPV-derived and seminal amyloid peptides enhance HIV-1 infection and impair the efficacy of broadly neutralising antibodies and antiretroviral drugs

Marcel Stern, Oliver T. Keppler

P75 D(−)lentiginosine inhibits both proliferation and virus expression in cells infected by HTLV-1 in vitro

Elena Valletta, Caterina Frezza, Claudia Matteucci, Francesca Marino-Merlo, Sandro Grelli, Anna Lucia Serafino, Antonio Mastino, Beatrice Macchi

P76 HIV-1 resistance analyses of the Cape Winelands districts, South Africa

Sello Mikasi, Graeme Jacobs, Susan Engelbrecht

Topic 10: Recent advances in HIV vaccine development

P77 Induction of complex retrovirus antigen-specific immune responses by adenovirus-based vectors depends on the order of vector administration

Meike Kaulfuß, Sonja Windmann, Wibke Bayer

P78 Direct impact of structural properties of HIV-1 Env on the regulation of the humoral immune response

Rebecca Heß, Michael Storcksdieck gen. Bonsmann, Viktoria Stab, Carsten Kirschning, Bernd Lepenies, Matthias Tenbusch, Klaus Überla

P79 Lentiviral virus-like particles mediate gerenration of T-follicular helper cells in vitro

Anne Kolenbrander, Klaus Überla, Vladimir Temchura

P80 Recruitment of HIV-1 Vpr to DNA damage sites and protection of proviral DNA from nuclease activity

Kenta Iijima, Junya Kobayashi, Yukihito Ishizaka

SIRT1 activation by a c-MYC oncogenic network promotes the maintenance and drug resistance of human FLT3-ITD acute myeloid leukemia stem cells

The FLT3-ITD mutation is frequently observed in acute myeloid leukemia (AML) and is associated with poor prognosis. In such patients, FLT3 tyrosine kinase inhibitors (TKIs) are only partially effective and do not eliminate the leukemia stem cells (LSCs) that are assumed to be the source of treatment failure. Here, we show that the NAD-dependent SIRT1 deacetylase is selectively overexpressed in primary human FLT3-ITD AML LSCs. This SIRT1 overexpression is related to enhanced expression of the USP22 deubiquitinase induced by c-MYC, leading to reduced SIRT1 ubiquitination and enhanced stability. Inhibition of SIRT1 expression or activity reduced the growth of FLT3-ITD AML LSCs and significantly enhanced TKI-mediated killing of the cells. Therefore, these results identify a c-MYC-related network that enhances SIRT1 protein expression in human FLT3-ITD AML LSCs and contributes to their maintenance. Inhibition of this oncogenic network could be an attractive approach for targeting FLT3-ITD AML LSCs to improve treatment outcomes.

SIRT1 and SIRT2 inhibition impairs pediatric soft tissue sarcoma growth

Sirtuins are NAD+ dependent deacetylases and/or ADP-ribosyl transferases active on histone and non-histone substrates. The first sirtuin was discovered as a transcriptional repressor of the mating-type-loci (Silent Information Regulator sir2) in the budding yeast, where it was shown to extend yeast lifespan. Seven mammalian sirtuins (SIRT1-7) have been now identified with distinct subcellular localization, enzymatic activities and substrates. These enzymes regulate cellular processes such as metabolism, cell survival, differentiation, DNA repair and they are implicated in the pathogenesis of solid tumors and leukemias. The purpose of the present study was to investigate the role of sirtuin expression, activity and inhibition in the survival of pediatric sarcoma cell lines.We have analyzed the expression of SIRT1 and SIRT2 in a series of pediatric sarcoma tumor cell lines and normal cells, and we have evaluated the activity of the sirtuin inhibitor and p53 activator tenovin-6 (Tv6) in synovial sarcoma and rhabdomyosarcoma cell lines. We show that SIRT1 is overexpressed in synovial sarcoma biopsies and cell lines in comparison with normal mesenchymal cells. Tv6 induced apoptosis as well as impaired autophagy flux. Using siRNA to knock down SIRT1 and SIRT2, we show that the expression of both proteins is crucial for the survival of rhabdomyosarcoma cells and that the loss of SIRT1 expression results in a decreased LC3II expression. Our results show that SIRT1 and SIRT2 expressions are crucial for the survival of synovial sarcomas and rhabdomyosarcomas, and demonstrate that the pharmacological inhibition of sirtuins impairs the autophagy process and induces tumor cell death.

Molecular mechanisms of nutlin-3 involve acetylation of p53, histones and heat shock proteins in acute myeloid leukemia

BACKGROUND

The small-molecule MDM2 antagonist nutlin-3 has proved to be an effective p53 activating therapeutic compound in several preclinical cancer models, including acute myeloid leukemia (AML). We and others have previously reported a vigorous acetylation of the p53 protein by nutlin-treatment. In this study we aimed to investigate the functional role of this p53 acetylation in nutlin-sensitivity, and further to explore if nutlin-induced protein acetylation in general could indicate novel targets for the enhancement of nutlin-based therapy.

RESULTS

Nutlin-3 was found to enhance the acetylation of p53 in the human AML cell line MOLM-13 (wild type TP53) and in TP53 null cells transfected with wild type p53 cDNA. Stable isotope labeling with amino acids in cell culture (SILAC) in combination with immunoprecipitation using an anti-acetyl-lysine antibody and mass spectrometry analysis identified increased levels of acetylated Histone H2B, Hsp27 and Hsp90 in MOLM-13 cells after nutlin-treatment, accompanied by downregulation of total levels of Hsp27 and Hsp90. Intracellular levels of heat shock proteins Hsp27, Hsp40, Hsp60, Hsp70 and Hsp90α were correlated to nutlin-sensitivity for primary AML cells (n = 40), and AML patient samples with low sensitivity to nutlin-3 tended to express higher levels of heat shock proteins than more responsive samples. Combination therapy of nutlin-3 and Hsp90 inhibitor geldanamycin demonstrated synergistic induction of apoptosis in AML cell lines and primary AML cells. Finally, TP53 null cells transfected with a p53 acetylation defective mutant demonstrated decreased heat shock protein acetylation and sensitivity to nutlin-3 compared to wild type p53 expressing cells.

CONCLUSIONS

Altogether, our results demonstrate that nutlin-3 induces acetylation of p53, histones and heat shock proteins, and indicate that p53 acetylation status and the levels of heat shock proteins may participate in modulation of nutlin-3 sensitivity in AML.

p53-Based cyclotherapy: exploiting the 'guardian of the genome' to protect normal cells from cytotoxic therapy

Side effects of chemotherapy are a major impediment in the treatment of cancer. Cyclotherapy is an emerging therapeutic strategy for protecting normal cells from the side effects of chemotherapy. Low, non-genotoxic doses of known p53 activators can be used to induce p53-dependent cell cycle arrest in normal cells bearing wild-type p53. This cytostatic effect of p53 can protect normal cells from the toxicity of S- or M-phase poisons. Here, we have reviewed existing cyclotherapy regimens using two well-known p53 activators, nutlin-3 and actinomycin D. We have highlighted an exemplar clinical perspective for cyclotherapy in breast cancer. The recent development of novel stapled peptides as activators of p53 without the corresponding cytotoxicity holds great promise for cyclotherapy to enhance the therapeutic window of existing chemotherapy drugs.

Dysregulation of autophagy in chronic lymphocytic leukemia with the small-molecule Sirtuin inhibitor Tenovin-6

Tenovin-6 (Tnv-6) is a bioactive small molecule with anti-neoplastic activity. Inhibition of the Sirtuin class of protein deacetylases with activation of p53 function is associated with the pro-apoptotic effects of Tnv-6 in many tumors. Here, we demonstrate that in chronic lymphocytic leukemia (CLL) cells, Tnv-6 causes non-genotoxic cytotoxicity, without adversely affecting human clonogenic hematopoietic progenitors in vitro, or murine hematopoiesis. Mechanistically, exposure of CLL cells to Tnv-6 did not induce cellular apoptosis or p53-pathway activity. Transcriptomic profiling identified a gene program influenced by Tnv-6 that included autophagy-lysosomal pathway genes. The dysregulation of autophagy was confirmed by changes in cellular ultrastructure and increases in the autophagy-regulatory proteins LC3 (LC3-II) and p62/Sequestosome. Adding bafilomycin-A1, an autophagy inhibitor to Tnv-6 containing cultures did not cause synergistic accumulation of LC3-II, suggesting inhibition of late-stage autophagy by Tnv-6. Thus, in CLL, the cytotoxic effects of Tnv-6 result from dysregulation of protective autophagy pathways.

p53 contributes to T cell homeostasis through the induction of pro-apoptotic SAP

Lack of functional SAP protein, due to gene deletion or mutation, is the cause of X-linked lymphoproliferative disease (XLP), characterized by functionally impaired T and NK cells and a high risk of lymphoma development. We have demonstrated earlier that SAP has a pro-apoptotic function in T and B cells. Deficiency of this function might contribute to the pathogenesis of XLP. We have also shown that SAP is a target of p53 in B cell lines. In the present study, we show that activated primary T cells express p53, which induces SAP expression. p53 is functional as a transcription factor in activated T cells and induces the expression of p21, PUMA and MDM2. PARP cleavage in the late phase of activation indicates that T cells expressing high levels of SAP undergo apoptosis. Modifying p53 levels using Nutlin-3, which specifically dissociates the MDM2-p53 interaction, was sufficient to upregulate SAP expression, indicating that SAP is a target of p53 in T cells. We also demonstrated p53's role as a transcription factor for SAP in activated T cells by ChIP assays. Our result suggests that p53 contributes to T cell homeostasis through the induction of the pro-apoptotic SAP. A high level of SAP is necessary for the activation-induced cell death that is pivotal in termination of the T cell response.

Synthesis and biological characterisation of sirtuin inhibitors based on the tenovins

The tenovins are small molecule inhibitors of the NAD(+)-dependent family of protein deacetylases known as the sirtuins. There remains considerable interest in inhibitors of this enzyme family due to possible applications in both cancer and neurodegenerative disease therapy. Through the synthesis of novel tenovin analogues, further insights into the structural requirements for activity against the sirtuins in vitro are provided. In addition, the activity of one of the analogues in cells led to an improved understanding of the function of SirT1 in cells.

Evaluation of an Actinomycin D/VX-680 aurora kinase inhibitor combination in p53-based cyclotherapy

p53-Based cyclotherapy is proving to be a promising approach to palliate undesired effects of chemotherapy in patients with tumours carrying p53 mutations. For example, pre-treatment of cell cultures with Nutlin-3, a highly-selective inhibitor of the p53-mdm2 interaction, has been successfully used as a cytostatic agent to protect normal cells, but not p53-defective cells, from subsequent treatment with mitotic poisons or S-phase specific drugs. Here we sought to evaluate whether low doses of Actinomycin D (LDActD), a clinically-approved drug and potent p53 activator, could substitute Nutlin-3 in p53-based cyclotherapy. We found that pre-treatment with LDActD before adding the aurora kinase inhibitor VX-680 protects normal fibroblasts from polyploidy and nuclear morphology abnormalities induced by VX-680. However, and although to a lower extent than normal fibroblasts, tumour cell lines bearing p53 mutations were also protected by LDActD (but not Nutlin-3) from VX-680-induced polyploidy. We also report that a difference between the response of p53 wild-type cells and p53-defective cells to the LDActD/VX-680 sequential combination is that only the former fail to enter S-phase and therefore accumulate in G1/G0. We propose that drugs that incorporate into DNA during S-phase may perform better as second drugs than mitotic poisons in cyclotherapy approaches using LDActD as a cytostatic agent.

Evaluation of an Actinomycin D/VX-680 aurora kinase inhibitor combination in p53-based cyclotherapy

p53-Based cyclotherapy is proving to be a promising approach to palliate undesired effects of chemotherapy in patients with tumours carrying p53 mutations. For example, pre-treatment of cell cultures with Nutlin-3, a highly-selective inhibitor of the p53-mdm2 interaction, has been successfully used as a cytostatic agent to protect normal cells, but not p53-defective cells, from subsequent treatment with mitotic poisons or S-phase specific drugs. Here we sought to evaluate whether low doses of Actinomycin D (LDActD), a clinically-approved drug and potent p53 activator, could substitute Nutlin-3 in p53-based cyclotherapy. We found that pre-treatment with LDActD before adding the aurora kinase inhibitor VX-680 protects normal fibroblasts from polyploidy and nuclear morphology abnormalities induced by VX-680. However, and although to a lower extent than normal fibroblasts, tumour cell lines bearing p53 mutations were also protected by LDActD (but not Nutlin-3) from VX-680-induced polyploidy. We also report that a difference between the response of p53 wild-type cells and p53-defective cells to the LDActD/VX-680 sequential combination is that only the former fail to enter S-phase and therefore accumulate in G1/G0. We propose that drugs that incorporate into DNA during S-phase may perform better as second drugs than mitotic poisons in cyclotherapy approaches using LDActD as a cytostatic agent.

p53-based cancer therapy

Inactivation of p53 functions is an almost universal feature of human cancer cells. This has spurred a tremendous effort to develop p53 based cancer therapies. Gene therapy using wild-type p53, delivered by adenovirus vectors, is now in widespread use in China. Other biologic approaches include the development of oncolytic viruses designed to replicate and kill only p53 defective cells and also the development of siRNA and antisense RNA's that activate p53 by inhibiting the function of the negative regulators Mdm2, MdmX, and HPV E6. The altered processing of p53 that occurs in tumor cells can elicit T-cell and B-cell responses to p53 that could be effective in eliminating cancer cells and p53 based vaccines are now in clinical trial. A number of small molecules that directly or indirectly activate the p53 response have also reached the clinic, of which the most advanced are the p53 mdm2 interaction inhibitors. Increased understanding of the p53 response is also allowing the development of powerful drug combinations that may increase the selectivity and safety of chemotherapy, by selective protection of normal cells and tissues.

Awakening guardian angels: drugging the p53 pathway

Currently, around 11 million people are living with a tumour that contains an inactivating mutation of TP53 (the human gene that encodes p53) and another 11 million have tumours in which the p53 pathway is partially abrogated through the inactivation of other signalling or effector components. The p53 pathway is therefore a prime target for new cancer drug development, and several original approaches to drug discovery that could have wide applications to drug development are being used. In one approach, molecules that activate p53 by blocking protein-protein interactions with MDM2 are in early clinical development. Remarkable progress has also been made in the development of p53-binding molecules that can rescue the function of certain p53 mutants. Finally, cell-based assays are being used to discover compounds that exploit the p53 pathway by either seeking targets and compounds that show synthetic lethality with TP53 mutations or by looking for non-genotoxic activators of the p53 response.

Leptomycin B induces apoptosis in cells containing the whole HPV 16 genome

Cervical cancer is a major cause of death in women worldwide and is strongly associated with human papillomavirus (HPV) infection. Integration of HPV is thought to be a key step in malignant progression, and is associated with loss of regulation of the viral E6 and E7 oncogenes. Leptomycin B (LMB), a nuclear export inhibitor, has previously been shown to induce apoptosis in primary keratinocytes transduced with the HPV 16 E7 or E6/E7 genes, but not in normal cells. We show here that LMB can also induce apoptosis in derivatives of the W12 cell line that contain either episomal or integrated HPV 16. Cells transduced with HPV 16 E7 or E6/E7, and the episomal and integrated W12 derivatives showed distinct temporal expression patterns of the apoptotic markers activated caspase-3 and M30. The expression of both markers occurred later in the episomal derivatives than in either transduced cells or W12 derivatives containing integrated HPV. These findings suggest that, although LMB can induce apoptosis in keratinocytes containing episomal or integrated HPV 16, genome status is likely to influence the response of HPV-associated anogenital lesions to LMB treatment.

Ribosomal protein S3: A multi-functional protein that interacts with both p53 and MDM2 through its KH domain

The p53 protein responds to cellular stress and regulates genes involved in cell cycle, apoptosis, and DNA repair. Under normal conditions, p53 levels are kept low through MDM2-mediated ubiquitination and proteosomal degradation. In search for novel proteins that participate in this regulatory loop, we performed an MDM2 peptide pull-down assay and mass spectrometry to screen for potential interacting partners of MDM2. We identified ribosomal protein S3 (RPS3), whose interaction with MDM2, and notably p53, was further established by His and GST pull-down assays, fluorescence resonance energy transfer and an in situ proximity ligation assay. Additionally, in cells exposed to oxidative stress, p53 levels increased slightly over 24h, whereas MDM2 levels declined after 6h exposure, but rose over the next 18h of exposure. Conversely, in cells exposed to oxidative stress and harboring siRNA to knockdown RPS3 expression, decreased p53 levels and loss of the E3 ubiquitin ligase domain possessed by MDM2 were observed. DNA pull-down assays using a 7,8-dihydro-8-oxoguanine duplex oligonucleotide as a substrate found that RPS3 acted as a scaffold for the additional binding of MDM2 and p53, suggesting that RPS3 interacts with important proteins involved in maintaining genomic integrity.

Novel cambinol analogs as sirtuin inhibitors: synthesis, biological evaluation, and rationalization of activity

The tenovins and cambinol are two classes of sirtuin inhibitor that exhibit antitumor activity in preclinical models. This report describes modifications to the core structure of cambinol, in particular by incorporation of substituents at the N1-position, which lead to increased potency and modified selectivity. These improvements have been rationalized using molecular modeling techniques. The expected functional selectivity in cells was also observed for both a SIRT1 and a SIRT2 selective analog.

Characterization, chemical optimization and anti-tumour activity of a tubulin poison identified by a p53-based phenotypic screen

A robust p53 cell-based assay that exploits p53's function as a transcription factor was used to screen a small molecule library and identify bioactive small molecules with potential antitumor activity. Unexpectedly, the majority of the highest ranking hit compounds from this screen arrest cells in mitosis and most of them impair polymerization of tubulin in cells and in vitro. One of these novel compounds, JJ78:1, was subjected to structure-activity relationship studies and optimized leading to the identification of JJ78:12. This molecule is significantly more potent than the original hit JJ78:1, as it is active in cells at two-digit nanomolar concentrations and shows clear antitumor activity in a mouse xenograft model as a single agent. The effects of nocodazole, a well established tubulin poison, and JJ78:12 on p53 levels are remarkably similar, supporting that tubulin depolymerization is the main mechanism by which JJ78:12 treatment leads to p53 activation in cells. In summary, these results identify JJ78:12 as a potential cancer therapeutic, demonstrate that screening for activators of p53 in a cell-based assay is an effective way to identify inhibitors of mitosis progression and highlights p53's sensitivity to alterations during mitosis.

p53 as a therapeutic target

Since the discovery of p53, a vast wealth of knowledge on its function and regulation has been accumulated. It is known that it is a key tumour suppressor and that its function is lost in many types of cancers, either by mutation or by excessive negative regulation. Recently, several discoveries have re-energised P53 as a therapeutic target as it has been shown that reintroduction of functional p53 into tumours has a therapeutic benefit. These encouraging results clearly justify the search for small molecules that diminish negative regulation of P53 in tumour cells, where P53 is not mutated as well as compounds that reactivate mutant P53. Important findings have been made to deal with both situations. Additionally, some of the small molecules identified may also help reduce the side effects of commonly used cancer therapeutics. These studies are still in their infancy and require further therapeutic validation, but the future appears bright for finally harnessing p53's tumour suppressing ability.

Discovery, in vivo activity, and mechanism of action of a small-molecule p53 activator

We have carried out a cell-based screen aimed at discovering small molecules that activate p53 and have the potential to decrease tumor growth. Here, we describe one of our hit compounds, tenovin-1, along with a more water-soluble analog, tenovin-6. Via a yeast genetic screen, biochemical assays, and target validation studies in mammalian cells, we show that tenovins act through inhibition of the protein-deacetylating activities of SirT1 and SirT2, two important members of the sirtuin family. Tenovins are active on mammalian cells at one-digit micromolar concentrations and decrease tumor growth in vivo as single agents. This underscores the utility of these compounds as biological tools for the study of sirtuin function as well as their potential therapeutic interest.

The Accuracy of Reporting of General Anaesthesia for Childbirth: A Validation Study

Administrative population health data, such as hospital discharge data, are a potentially valuable resource for determining anaesthesia and analgesia use in childbirth at a population level. However, the reliability of general anaesthesia reporting is unknown. This study aimed to determine the accuracy of the reporting of peripartum general anaesthesia in single and linked population health data. Data from a statewide validation study of 1200 women provided the gold standard for delivery and postpartum general anaesthesia use. The validation data were merged with both the hospital discharge and birth databases. As both of these datasets collect information on general anaesthesia, it could be reported in one, both or neither database. Among the 1184 records available for review, 7.7% of women had a general anaesthetic during the birth admission, of which 6.2% were for delivery and 1.5% were for a postpartum procedure. Reporting sensitivities ranged from 26% to 97% and specificities 94% to 100%. Identifying general anaesthesia from either the birth or hospital data improved general anaesthesia ascertainment. Limiting analysis to caesarean sections resulted in very accurate identification of general anaesthesia for delivery(sensitivity 97.0%, specificity 99.8%) while limiting to vaginal births was moderately accurate for identifying postpartum general anaesthesia (sensitivity 73.2%, specificity 99.8%). General anaesthesia for delivery is reported with a high level of accuracy in birth and linked birth-hospital data, but not in hospital discharge data alone. Population health data are a reliable source for examining general anaesthesia for delivery.

Selective induction of apoptosis by leptomycin B in keratinocytes expressing HPV oncogenes

Human papillomavirus (HPV) infection is strongly associated with the development of anogenital neoplasia, particularly cervical cancer. It has been estimated that 99.7% of all cervical carcinomas are attributable to infection with HPV, and types 16 and 18 account for the vast majority of such cases. Both of these 'high risk' HPV types encode the oncoproteins E6 and E7, which exert multiple effects on many proteins involved in cell-cycle regulation, including p53. The nuclear export protein inhibitor leptomycin B (LMB) has been shown to cause the nuclear sequestration of p53 in cervical carcinoma cells. We demonstrate that LMB induces apoptosis selectively at nanomolar concentrations in primary human keratinocytes (PHKs) expressing HPV oncogenes. Both monolayer and organotypic raft cultures of transduced PHKs were highly susceptible to treatment with LMB. By contrast, although LMB stimulated p53 accumulation in normal PHKs, no significant induction of apoptosis was detected on Western blots or immunostained monolayer/raft cells, or following pulsed exposure to the drug. Furthermore, topical application of microM concentrations of LMB to mouse skin was non-toxic. These data suggest that the topical application of LMB to HPV-infected intra-epithelial lesions may represent a specific and effective therapeutic strategy against HPV-associated anogenital neoplasia.

Pilot screening programme for small molecule activators of p53

Activation of the p53 tumour suppressor is predicted to have therapeutically beneficial effects. Many current anti-cancer therapies activate the p53 response via DNA damage. Non-genotoxic activation of the p53 pathway would open the way to long-term and possibly prophylactic treatments. We have established a simple protocol to screen small compound libraries for activators of p53-dependent transcription, and to select and characterise the most interesting hits, which include non-genotoxic activators. These compounds or their derivatives are of potential clinical interest. This approach may also lead to the identification of novel p53-activating compound families and possibly to the description of novel molecular pathways regulating p53 activity.

P53 abnormalities and outcomes in colorectal cancer: a systematic review

We performed a systematic review of studies that investigated the effect of abnormalities of the tumour suppressor gene p53 upon prognosis in patients with colorectal cancer. The methods used to assess p53 status were immunohistochemistry (IHC), indicating abnormal accumulation of p53, and sequence analysis, indicating presence of p53 mutations (mut). We identified 168 reports, with 241 comparisons of relevant end points and survival data on 18 766 patients. We found evidence of both publication bias and heterogeneity of results. Our analysis was hampered by variability in both the assessment of p53 status and the reporting of results. We used a trim and fill method to correct for publication bias and minimised heterogeneity by using well-defined clinical subgroups for the assessment of outcomes. Overall, patients with abnormal p53 were at increased risk of death: relative risk (RR) with IHC 1.32 (95% confidence interval (c.i.) 1.23–1.42) and with mutation analysis 1.31 (95% c.i. 1.19–1.45). The adverse impact of abnormal p53 was greater in patients with lower baseline risk of dying: good prognosis RR (mut) 1.63 (95% c.i. 1.40–1.90) and poor prognosis RR (mut) 1.04 (95% c.i. 0.91–1.19). We found no effect of abnormal p53 on outcome in patients treated with chemotherapy. Abnormal p53 was associated with failure of response to radiotherapy in patients with rectal cancer: RR (mut) 1.49 (95% c.i. 1.25–1.77).

Oligomerization of the human ARF tumor suppressor and its response to oxidative stress

The tumor suppressor ARF plays an important role as an inhibitor of the Mdm2-mediated degradation of p53. Here we demonstrate that human ARF (p14ARF) can form homo-oligomers. The stability of the oligomers is favored by oxidizing agents in a reversible fashion and involves all three cysteine residues in p14ARF. Furthermore, the effect of p14ARF in clonogenic assays is moderately but reproducibly increased by the mutation of its cysteine residues. We also observed that altering the amino terminus of p14ARF resulted in the appearance of remarkably stable oligomers. This indicates that the amino terminus of p14ARF interferes with the ability of the protein to form multimeric complexes. These observations suggest that p14ARF activity may be linked to its oligomerization status and sensitive to the redox status of the cell.

Improving cancer therapy by non-genotoxic activation of p53

Inactivation of p53 function is a common event in cancer. Approximately 50% of human tumours express mutant p53 and there is evidence that in others, including many childhood tumours, p53 function is impaired in other ways. These defects in p53 function may be due to the alteration of cellular factors that modulate p53 or to the expression of viral oncoproteins. Radiotherapy and many of the chemotherapeutic drugs currently used in cancer treatment are potent activators of p53. However, most of these therapies have a serious drawback, and that is the long-term consequences of their DNA damaging effects. Here, we review the discoveries in p53 research that are most significant to the development of new therapies based on the induction of the transcriptional activity of p53 in a non-genotoxic way and discuss the situations in which this type of approach may be most beneficial.

Differences in the ubiquitination of p53 by Mdm2 and the HPV protein E6

The human papillomavirus (HPV) protein E6 can promote the ubiquitination of the p53 tumour suppressor in vitro, providing an explanation for the ability of E6 to induce p53 degradation in vivo and contribute to the potential tumorigenic effect of the virus. Instead, in non-infected cells, p53 levels are primarily destabilised by the ubiquitin E3 ligase activity of the Mdm2 protein. Here we have compared the effects of E6 and Mdm2 on p53 ubiquitination in vivo. We show that whereas in the presence of Mdm2 proteasome inhibitors induce the accumulation of ubiquitinated forms of p53, this does not occur in the presence of E6. Accordingly, we confirm that the effect of E6 and p53 is independent of the six C-terminal lysine residues in p53, which have previously been described to play an important role for effective ubiquitination and degradation of 53 mediated by Mdm2. We also show that other yet unidentified residues in p53 are also susceptible to ubiquitination. These results indicate that E6 does not induce ubiquitination of p53 in the same way as Mdm2 in order to promote its degradation, suggesting important differences between the Mdm2 and E6 effects on p53 degradation.

Therapeutic exploitation of the p53 pathway

Analysis of the gene encoding p53 could serve to evaluate the effectiveness of a cancer treatment. Mutations in this gene occur in half of all human cancers, and regulation of the protein is defective in a variety of others. Novel strategies that exploit our knowledge of the function and regulation of p53 are being actively investigated. Strategies directed at treating tumours that have p53 mutations include gene therapy, viruses that only replicate in p53 deficient cells, and the search for small molecules that reactivate mutant p53. Potentiating the function of p53 in a non-genotoxic way in tumours that express wildtype protein can be achieved by inhibiting the expression and function of Mdm2 or viral oncoproteins.

Phosphorylation of the protein kinase mutated in Peutz-Jeghers cancer syndrome, LKB1/STK11, at Ser431 by p90(RSK) and cAMP-dependent protein kinase, but not its farnesylation at Cys(433), is essential for LKB1 to suppress cell vrowth

Peutz-Jeghers syndrome is an inherited cancer syndrome that results in a greatly increased risk of developing tumors in those affected. The causative gene is a protein kinase termed LKB1, predicted to function as a tumor suppressor. The mechanism by which LKB1 is regulated in cells is not known. Here, we demonstrate that stimulation of Rat-2 or embryonic stem cells with activators of ERK1/2 or of cAMP-dependent protein kinase induced phosphorylation of endogenously expressed LKB1 at Ser(431). We present pharmacological and genetic evidence that p90(RSK) mediated this phosphorylation in response to agonists that activate ERK1/2 and that cAMP-dependent protein kinase mediated this phosphorylation in response to agonists that activate adenylate cyclase. Ser(431) of LKB1 lies adjacent to a putative prenylation motif, and we demonstrate that full-length LKB1 expressed in 293 cells was prenylated by addition of a farnesyl group to Cys(433). Our data suggest that phosphorylation of LKB1 at Ser(431) does not affect farnesylation and that farnesylation does not affect phosphorylation at Ser(431). Phosphorylation of LKB1 at Ser(431) did not alter the activity of LKB1 to phosphorylate itself or the tumor suppressor protein p53 or alter the amount of LKB1 associated with cell membranes. The reintroduction of wild-type LKB1 into a cancer cell line that lacks LKB1 suppressed growth, but mutants of LKB1 in which Ser(431) was mutated to Ala to prevent phosphorylation of LKB1 were ineffective in inhibiting growth. In contrast, a mutant of LKB1 that cannot be prenylated was still able to suppress the growth of cells.

Multiple C-terminal lysine residues target p53 for ubiquitin-proteasome-mediated degradation

In normal cells, p53 is maintained at a low level by ubiquitin-mediated proteolysis, but after genotoxic insult this process is inhibited and p53 levels rise dramatically. Ubiquitination of p53 requires the ubiquitin-activating enzyme Ubc5 as a ubiquitin conjugation enzyme and Mdm2, which acts as a ubiquitin protein ligase. In addition to the N-terminal region, which is required for interaction with Mdm2, the C-terminal domain of p53 modulates the susceptibility of p53 to Mdm2-mediated degradation. To analyze the role of the C-terminal domain in p53 ubiquitination, we have generated p53 molecules containing single and multiple lysine-to-arginine changes between residues 370 and 386. Although wild-type (WT) and mutant molecules show similar subcellular distributions, the mutants display a higher transcriptional activity than WT p53. Simultaneous mutation of lysine residues 370, 372, 373, 381, 382, and 386 to arginine residues (6KR p53 mutant) generates a p53 molecule with potent transcriptional activity that is resistant to Mdm2-induced degradation and is refractory to Mdm2-mediated ubiquitination. In contrast to WT p53, transcriptional activity directed by the 6KR p53 mutant fails to be negatively regulated by Mdm2. Those differences are also manifest in HeLa cells which express the human papillomavirus E6 protein, suggesting that p53 C-terminal lysine residues are also implicated in E6-AP-mediated ubiquitination. These data suggest that p53 C-terminal lysine residues are the main sites of ubiquitin ligation, which target p53 for proteasome-mediated degradation.

Activation of p53 in cervical carcinoma cells by small molecules

In over 90% of cervical cancers and cancer-derived cell lines, the p53 tumor suppressor pathway is disrupted by human papillomavirus (HPV). The HPV E6 protein promotes the degradation of p53 and thus inhibits the stabilization and activation of p53 that would normally occur in response to HPV E7 oncogene expression. Restoration of p53 function in these cells by blocking this pathway should promote a selective therapeutic affect. Here we show that treatment with the small molecule nuclear export inhibitor, leptomycin B, and actinomycin D leads to the accumulation of transcriptionally active p53 in the nucleus of HeLa, CaSki, and SiHa cells. Northern blot analyses showed that both actinomycin D and leptomycin B reduced the amount of HPV E6-E7 mRNA whereas combined treatment with the drugs showed almost complete disappearance of the viral mRNA. The combined treatment activated p53-dependant transcription, and increases in both p21(WAF1/CIP1) and Hdm2 mRNA were seen. The combined treatment resulted in apoptotic death in the cells, as evidenced by nuclear fragmentation and PARP-cleavage indicative of caspase 3 activity. These effects were greatly reduced by expressing a dominant negative p53 protein. The present study shows that small molecules can reactivate p53 in cervical carcinoma cells, and this reactivation is associated with an extensive biological response, including the induction of the apoptotic death of the cells.

SUMO-1 modification activates the transcriptional response of p53

The p53 tumour suppressor protein is regulated by ubiquitin-mediated proteasomal degradation. In normal cells p53 is constitutively ubiquitylated by the Mdm2 ubiquitin ligase. When the p53 response is activated by stress signals p53 levels rise due to inhibition of this degradative pathway. Here we show that p53 is modified by the small ubiquitin-like protein SUMO-1 at a single site, K386, in the C-terminus of the protein. Modification in vitro requires only SUMO-1, the SUMO-1 activating enzyme and ubc9. SUMO-1 and ubiquitin modification do not compete for the same lysine acceptor sites in p53. Overexpression of SUMO-1 activates the transcriptional activity of wild-type p53, but not K386R p53 where the SUMO-1 acceptor site has been mutated. The SUMO-1 modification pathway therefore acts as a potential regulator of the p53 response and may represent a novel target for the development of therapeutically useful modulators of the p53 response.

Cell-cycle arrest and inhibition of Cdk4 activity by small peptides based on the carboxy-terminal domain of p21WAF1

BACKGROUND

A common event in the development of human neoplasia is the inactivation of a damage-inducible cell-cycle checkpoint pathway regulated by p53. One approach to the restoration of this pathway is to mimic the activity of key downstream effectors. The cyclin-dependent kinase (Cdk) inhibitor p21(WAF1) is one such molecule, as it is a major mediator of the p53-dependent growth-arrest pathway, and can, by itself, mediate growth suppression. The primary function of the p21(WAF1) protein appears to be the inhibition of G1 cyclin-Cdk complexes. Thus, if we can identify the region(s) of p21(WAF1) that contain its inhibitor activity they may provide a template from which to develop novel anti-proliferative drugs for use in tumours with a defective p53 pathway.

RESULTS

We report on the discovery of small synthetic peptides based on the sequence of p21(WAF1) that bind to and inhibit cyclin D1-Cdk4. The peptides and the full-length protein are inhibitory at similar concentrations. A 20 amino-acid peptide based on the carboxy-terminal domain of p21(WAF1) inhibits Cdk4 activity with a concentration for half-maximal inhibition (l0.5) of 46 nM, and it is only four-fold less active than the full-length protein. The length of the peptide has been minimized and key hydrophobic residues forming the inhibitory domain have been defined. When introduced into cells, both a 20 amino-acid and truncated eight amino-acid peptide blocked phosphorylation of the retinoblastoma protein (pRb) and induced a potent G1/S growth arrest. These data support a physiological role for the carboxyl terminus of p21(WAF1) in the inhibition of Cdk4 activity.

CONCLUSIONS

We have discovered that a small peptide is sufficient to mimic p21(WAF1) function and inhibit the activity of a critical G1 cyclin-Cdk complex, preventing pRb phosphorylation and producing a G1 cell-cycle arrest in tissue culture cell systems. This makes cyclin D1-Cdk4 a realistic and exciting target for the design of novel synthetic compounds that can act as anti-proliferative agents in human cells.