Seminars in
`Oncology
`
`IPR2017-01768
`
`Editors John W. Yarbro, MD,PhD + Michael J. Mastrangelo, MD
`
`* + . * * : a
`
`O # . - b
`
`a . A ‘ & - a D L 3 7 ‘ 7
`
`HEALTH SCIENCES LIBRA
`UNIVERSITY OF WISCONSIN
`
`OCT 2 3 2000
`
`1305 Linden Drive
`Madison, WI 53706
`
`peee UNDERS COMPANY
`
`A Harcourt Health Sciences Company
`
`Page1 of 20
`
`Horizon Exhibit 2031
`
`Par v. Horizon
`
`Page 1 of 20
`
`Horizon Exhibit 2031
`Par v. Horizon
`IPR2017-01768
`
`

`

`_$
`
`3
`2 soo
`7%
`=S
`“9az
`Ss .
`
`Seminars in
`Oncology
`
`EDITORS
`John W. Yarbro, MD, PhD
`Michael J. Mastrangelo, MD
`
`is published
`Seminars in Oncology (ISSN 0093-7754)
`bimonthly by W.B. Saunders Company, Corporate and
`Edirorial Offices: The Curtis Center, Independence Square
`West, Philadelphia, PA 19106-3399, Accounting and Circu-
`lation Offices: W.B. Saunders Company, 6277 Sea Harbor
`Dr, Orlando, FL 32887-4800. Months of issue are February,
`April, June, August, October, and December. Periodicals
`postage paid at Orlando, FL 32862, and ar additional
`mailing offices.
`POSTMASTER: Sendchange of address to Seminars m
`Oncology, W.B. Saunders Company, Periodicals Depart-
`ment, 6277 Sea Harbor Dr, Orlando, FL 32887-4800.
`Editorial correspondence should be addressed to John W.
`Yarbro, MD, PhD, 2604 Luan Court, Columbia, MO 65203,
`Business correspondence (subscriptions, change of adl-
`dress) should be addressed to the Publisher, W.B. Saunders
`Company, Periodicals Department, 6277 Sea Harbor Dr,
`Orlando, FL 32887-4800.
`including both the old and new
`Change ofaddress notices,
`addresses of the subscriber, should be sent at least one month m
`advance.
`Customer Service; 1-800-654-2452; outside rhe Unired
`States and Canada, (407) 345-4000.
`Yearly subscription rates: United States and possessions:
`individual, $168.00; institution, $243.00; single issue, $52.00.
`All other countries: individual, $265.00; institution, $310.00;
`single issue, $52.00. For all areas outside the United Srates
`and possessions, there is no additional charge for surface
`delivery. For air mail delivery, add $24.00. Student/resident:
`United States and possessions: $92.00; all other countries:
`$265.00. To receive student/resident rate, orders must be
`accompanied by nameofaffiliated institution, dare of term,
`and the signature of program/resideney coordinator on
`institution letterhead. Orders will be billed at individual
`rate until proof of starus is received. Current prices are in
`effect for back volumes and hack issues. Back issues sold in
`conjunction with a subscription are on a prorated basis.
`Current and hack single issues exist in limited quantities
`and are offered for sale subject to availability. 1999 bound
`volume price: $85.00; customers ourside USA, please add
`315,00 for postage. To purchase a 1999 bound volume,
`customer must be a subscriber for 1999, Cumulative Index
`(1980-1989) price: $95.00; customers outside USA, please
`add $2.25 for surface delivery, or $8.00 for air mail delivery.
`Prices are subject to change without notice. Checks should
`be made payable to W.B. Saunders Companyandsent to
`Seminars in Oncology, W.B. Saunders Company, Periodicals
`Department, PO Box 628239, Orlando, FL 32862-8239.
`Copyright © 2000 by W.B. Saunders Company. All rights
`reserved. Nopart of this publication may be reproduced or
`transmitted in any form or by any means nowor hereafter
`known, electronic or mechanical,
`including photocopy,
`recording, or any information storage and retrieval system,
`
`without permission in writing from the publisher. Printed in
`the United States of America.
`Correspondence regarding permission to reprint all or
`part of any article published in this journal should be
`addressed to W.B, Saunders Company, Periodicals Depart-
`ment, Orlando, FL 32887. Telephone number 1-407-345-
`2500.
`Other correspondence (copyediting, production) should
`be addressed to W.B. Saunders Company, The Curtis
`Center, Independence Square West, Philadelphia, PA 19106-
`3399,
`The appearanceof the code at the bottom ofthefirst page
`ofan article in this journal indicates the copyright owner's
`consent that copies of the article may be made for personal
`or internal use, or for the personal or internal use of specific
`clients, for those registered with the Copyright Clearance
`Center, Inc. (222 Rosewood Drive, Danvers, MA 01923;
`(508) 750-8400; www.copyright.com). This consent is given
`on the condition that the copier pay the stated per-copyfee
`for that article through the Copyright Clearance Center,
`Inc. for copying beyond that permitted by Sections 107 or
`108 of the US Copyright Law. This consent does not extend
`to other kinds of copying, such as copying for general
`distribution, for advertising or promotional purposes,
`for
`creating newcollective works, or for resale. Absence of the
`code indicates that
`the material may not he processed
`through the Copyright Clearance Center, Inc.
`Advertising representative: CunninghamAssociates, 180
`Old Tappan Rd, Old Tappan, NJ 07675, telephone 1-201-
`767-4170; fax 1-201-767-8065.
`Theideas and opinions expressed in Seminars in Oncology
`do not necessarily reflect
`those of the Editor or
`the
`Publisher. Publication of an advertisement or orher produce
`mention in Seminars in Oncology should not be construed as
`an endorsement of the product or the manufacturer's claims.
`Readers are encouraged to contact the manufacturer with
`any questions about
`the features or
`limitations of the
`products mentioned. The Publisher does not assume any
`responsibility for any injury and/or damage to persons or
`property arising out of or related to any use of the material
`contained in this periodical. The reader is advised to check
`the appropriate medical literarure and the product informa-
`tion currently provided by the manufacturer of each drug to
`he administered to verify the dosage,
`the method and
`duration of administration, or contraindications, It is the
`responsibility of the treating physician or other health care
`professional, relying on independent experience and knowl-
`edge of the patient, to determine drug dosages and the best
`treatment for the patient.
`The contents of Seminars in Oncology are included in
`Index Medicus/MEDLINE, Current Contents, Excerpta
`Medica/EMBASE, and BIOSIS.
`
`W.B. Saunders Company
`
`Philadelphia, PA
`
`Page 2 of 20
`
`A Harcourt Health Sciences Company
`
`Page 2 of 20
`
`

`

`Novel Therapeutic Agents for the Treatment
`of Myelodysplastic Syndromes
`
`Bruce D. Cheson, James A. Zwiebel, Janet Dancey, and Anthony Murgo
`
`Few chemotherapy agents have demonstrated activity
`in patients with myelodysplastic syndromes (MDS) and
`supportive management remains the standard ofcare.
`An increasing number of new drugs in development are
`being directed at specific molecular or biological tar-
`gets of these diseases. Topotecan, a topoisomerase |
`inhibitor, has shown single-agent activity and is now
`being combined with other agents,
`including cy-
`tarabine. The aminothiol amifostine induces responses
`in about 30% of patients; however,its role is still being
`clarified. Agents that inhibit histone deacetylase and
`target DNA hypermethylation, thus permitting dere-
`pression of normal genes, include 5-azacytidine, decita-
`bine, phenylbutyrate, and depsipeptide. Arsenic triox-
`ide has demonstrated impressive activity in acute
`promyelocytic leukemia and preclinical data suggest
`the potential for activity in MDS. UCN-0I is a novel
`agent that inhibits protein kinase C and other protein
`kinases important for progression through the G, and
`G, phasesof the cell cycle. Dolastatin-10 has extremely
`potent in vitro activity against a variety of tumor cell
`lines. Since its dose-limiting toxicities include myelosup-
`pression,
`it
`is being studied in acute myelogenous
`leukemia (AML) and MDS. Ras mayplay a role in MDS,
`and activation of this gene and its signaling pathways
`may require farnesylation. Several farnesyl transferase
`inhibitors are now available for study in patients with
`MDS. An increasing body of data suggests a possible
`role for angiogenesis in MDS,and several antiangiogen-
`esis agents are in clinical trials, including thalidomide,
`$U5416, and anti-vascular endothelial growth factor
`(VEGF) antibodies. Development of new drugs and
`regimenswill be facilitated by recently developed stan-
`dardized response criteria. Future clinical trials should
`focus on rational combinations of these agents and
`others with the goal of curing patients with MDS.
`Semin Oncol 27:560-577. This is a US government work.
`There are no restrictions on its use.
`
`HE MYELODYSPLASTIC syndromes (MDS)
`are a heterogeneous group of hematopoietic
`disorders characterized by pancytopenia, generally
`in thesetting of a hypercellular bone marrow. MDS
`
`
`
`From the Cancer Therapy Evaluation Program (CTEP), Divi
`son of Cancer Treatment and Diagnosis, National Cancer Institute ,
`Bethesda, MD.
`Address reprine requests to Bruce D, Cheson, MD, National
`CumcerInstitute, Executive Plaza North-Room741, Bethesda, MD
`20892.
`This is a US government work. There are no restrictions on its
`se,
`0093-7754/00/2704-0001 $0,00/0
`doi: 10.1053/sone.2000,969|
`
`560
`
`Page 3 of 20
`
`have historically been referred to as oligoblastic
`leukemia, refractory anemia, smoldering acute leu-
`kemia, or preleukemia.
`In 1982,
`the French-
`American-British (FAB) group presentedaclassifi-
`cation, modified in 1985, which currently is the
`most widely used.'? The FAB group separated
`MDSintofive categories: refractory anemia (RA),
`RA with ringed sideroblasts (RARS), RA with
`excess blasts (RAEB), and RAEB in transforma-
`tion (RAEB-T). The distinction between RAEB-T
`and acute myelogenous leukemia (AML) is based
`onhistopathology, notclinicalfeatures. Asaresult,
`patients with MDS mayexhibit a clinical picture
`consistent with AML withrapidly increasing num-
`bers of blasts, but without the requisite number to
`fulfill
`the criteria for
`the diagnosis of AML
`Recently, a World Health Organization (WHO)
`steering committee proposed changes to the MDS
`subtypes with the major modifications including
`reclassifying chronic myelomonocytic leukemia
`(CMML)
`as
`a myeloproliferative disorder and
`decreasing the thresholdfor diagnosing AML from
`30%blasts to 20%.* This system may eventually
`replace the FAB.
`Thelikelihood of transformation to AMLvaries by
`FAB subtype**: approximately 10%to 20%for RA or
`RARS, 20%to 30%for CMML, 40% to 50%for
`RAEB,and 60%to 75%for RAEB-T. Nevertheless,
`the MDSare uniformlyfatal, even without progression
`to AML, because of infection andbleeding.'®
`Over the years, a numberofscoring and prognos-
`tic systems have been publishedtofacilitate com-
`parisons among reports of various treatments for
`MDS. Recently, the International Prognostic Scor-
`ing System (IPSS) has been widely adopted."
`Factors taken into consideration included bone
`marrowblasts, cytogenetics, and cytopenias. Groups
`were identified with relative risks for transforma-
`tion to AML and overall survival. Patients in the
`good cytogenetics group were those with a normal
`karyotype; poor risk included patients with com-
`plex abnormalities or with an involved chromo-
`some 7; intermediate-risk patients consisted ofall
`others (Table 1).
`There are no curative therapies other than stem
`cell transplantation, which is an optionfor onlya
`subset of patients. Therefore, numerous therapies
`
`Seminars in Oncology, Vol 27, No $ (October), 2000; pp 560-577
`
`Page 3 of 20
`
`

`

`NEW THERAPEUTIC AGENTS FOR MDS
`
`56/
`
`
`
`Table |. International Prognostic Scoring System for the Myelodysplastic Syndromes
`
`Prognostic Variable
`
`Bone marrow blasts (%)
`Karyotype
`Cytopenias (no. oflineages)
`
`Score
`
`0
`Lo
`[.5
`2.0
`
`<5
`Good
`Intermediate
`
`ol
`
`Poor
`
`11-20
`
`21-30
`
`NOTE.Thetotal of the values for each prognostic variable is used to place patients in | of 4 risk groups: low,intermediate-|, intermediate-2, and
`high. These risk groups havesignificantly different outcomes.
`
`have been andare being investigated to improve
`the outlook for these patients. Drugs selected for
`study in MDS have typically been those with
`significant activity in AML. Thus, cytarabine has
`been most widely evaluated, dating back more
`than 30 years when Ellison et all? first reported
`complete remissions with doses of cytarabine as
`low as 10 mg/m2/d. Response rates were clearly
`dose-dependent, which encouraged the develop-
`ment of higher dose regimens. Subsequently, anec-
`dotal reports and small series were published in
`which cytarabine at 10% to 20% of the standard
`dose administered either subcutaneously or by
`continuous intravenous infusion appeared to be
`effective in the treatment ofAML and MDS.-2
`Additional studies and a randomized phaseIII rrial
`failed to support a majorrole for this therapy.23-2°
`Anthracyclines and related compounds have
`had beenstudied as single agents only to a limited
`extent."°"7 In a study in which hydroxyurea and
`etoposide were compared in patients with CMML,
`response rates and survival were not impressive
`with either agent, but favored the former.?8 Other
`drugs that have been evaluated include 6-thiogua-
`nine and homoharringtonine, but both showed
`limited activity.2°7°
`
`NEW AGENTS
`
`Several agents with unique mechanisms ofactiv-
`ity are currently or will soon be evaluated in
`clinical trials for patients with MDS.
`
`Topoisomerase I Inhibitors
`
`Topotecan is a topoisomerase | inhibitor whose
`activity in acute leukemia led to its testing in
`MDs.Theinitial report included 47 patients with
`RAEB, RAEB-T, or CMML.?! They were a poor-
`risk group, as demonstrated by the fact that the
`median age was 66 years, 70% exhibited cytoge-
`netic abnormalities, and more than half were
`
`Page4 of 20
`
`thrombocytopenic before topotecan therapy. Topo-
`tecan was delivered at a dose of 2 mg/m? as a
`continuous 24-hour infusion for 5 days. Treatment
`resulted in 28% complete remissions and an addi-
`tional 13%of patients who experienced significant
`hematologic improvement. All eight patients with
`cytogenetic abnormalities before treatment and
`who achieved a complete remission became cytoge-
`netically normal once in complete remission. The
`median remission duration was 7.5 months with
`38% of patients still alive 1 year following treat
`ment. Whether chronic oral topotecanis effective
`is undergoing evaluation.
`The sameinvestigators have shown that combi-
`nation of topotecan and cytarabine is extremely
`active in patients with MDS.Beran et al” reported
`on 86 patients with MDS and CMML, most of
`whom (66%) were previously untreated, bur who
`were considered high risk based on age or cytoge-
`netic abnormalities. Topotecan was administered
`at a dose of 1.25 mg/m? by continuous infusion
`daily for 5 days, and cytarabine at
`1 g/m* by a
`2-hour
`infusion daily for
`5 days. A complete
`remission was attained in 56% of patients, with 7%
`treatment-related deaths and a median survival of
`60 weeks.*? Preliminary results have been pub-
`lished of aggressive combination of topotecan,
`fludarabine, cytarabine, and granulocyte colony-
`stimulating factor (G-CSF); there were 50% com-
`plete remissions and 40% partial remissions, and
`the regimen appeared tobe well tolerated.*3
`
`Amifostine
`Amifostine (Ethyol; Alza Pharmaceuticals, Palo
`Alto, CA) is a phosphorylated aminothiol that
`protects bone marrowprogenitors and other nor-
`mal
`tissues from the toxicities associated with
`chemotherapy or radiation therapy. It was devel-
`oped by the Walter Reed Army Medical Institute
`
`Page 4 of 20
`
`

`

`562
`
`CHESON ET AL
`
`(thus, the military code name WR-2721) during
`the Cold Waraspart ofa classified research project
`to identify an agent that would protect military
`personnel from radiation in the event of nuclear
`war. Amifostine was found toafford greater protec-
`tion against radiation than more than 4,000 other
`compoundsscreened. Nevertheless, the Army ter-
`minated development of this compound in 1988
`because of its poor oral bioavailability and the
`prohibitive nausea, vomiting, diarrhea, and abdomi-
`nal cramps with the oral formulation.
`Further research was encouraged by the observa-
`tion that amifostine stimulates hematopoiesis in
`both animal models and in vitro studies, and thatit
`enhances the formation of hematopoietic progeni-
`tors from MDS bone marrow. In the initial phase
`I/II study,*4 the drug was administered at doses of
`100, 200, or 400 mg/m? three times per week or 740
`mg/m? weekly for 3 weeks. These investigators
`treated 18 patients at a median age of 73 years.
`FAB rypes included RA (seven patients), RARS
`(n = 5), RAEB (n = 4), and RAEB-T (n = 2),
`Seventeen patients were anemic, 15 of whom were
`transfusion-dependent; 12 had an absolute neutro-
`phil countless than 1,000/yL and 14 were thrombo-
`cytopenic. Hematologic improvement was ob-
`served in 83% with the three-times-a-week
`schedules, including either an increase in neutro-
`phils or a reduction in red blood cell transfusion
`requirements, More than 40%of patients hada rise
`in their plateler counts. However, there was accel-
`eration to AMLin several patients with RAEB-T.
`Although 61% of patients had clonal cytogenetic
`abnormalities before therapy,
`the abnormalities
`persisted even in patients with a hematologic
`response. No data regarding duration of response
`were provided, although responses were reported to
`persist during continuation therapy.
`List et al® reported the results of a subsequent
`multicenter trial of amifostine in 117 patients, 104
`of whom were evaluable at the time of presenta-
`tion. A neutrophil response occurred in 10 (33%)
`of 30 patients, and was considered major in nine
`and minor in the other. A red blood cell response
`was evaluable in 66 patients, and a major response
`occurred in seven, with three experiencing a minor
`response. A major improvementin platelet count
`was seen in seven of 27 patients, with a minor
`response in three others, and 21% of patients had
`an increase in the reticulocyte count. A decrease in
`myeloblasts and sideroblasts occurred in 28%and
`
`Page 5 of 20
`
`31%, respectively. The overall response rate was
`30%, which is significantly lower than in the
`previous trial. Adverse events that were moderate
`or severe included fatigue (14%, 18%), nausea
`(19%, 36%), and vomiting (14%, 27%).
`In a
`smaller series,*° a single or multilineage response
`was noted in five of
`12 patients (58%). The
`absolute neutrophil count increased in 25%(by
`102 ta 1,560/nL), platelets in 50% (by 24,000 ta
`49,000/pL), reticulocytes in 25%(1.9% to 20%),
`and hemoglobin in 16%(5.3 to 5.6 g/dL).
`In other reports, results with this agent were
`disappointing.*"* Hofmann et al’* described 32
`patients with RA/RARS (n = 26) and RAEB/
`RAEB-T (n = 15) treated at a dose of 200 mg/m?
`three times per week followedby a 2-weekinterval,
`for four courses. Limited benefit was observed even
`in patients with low- or intermediate-risk disease
`hy the IPSS.
`The role of amifostine in MDS is still being
`clarified. Nevertheless, combinations of amifostine
`with other agents such as 5-azacytidine are being
`evaluated.
`
`Agents That Target Transcription
`Recent developments in understanding the mo-
`lecular basis
`for
`transcriptional
`repression and
`activation have presented new possibilities for
`cancer therapy. Two mechanismsofgenesilencing,
`promoter hypermethylation andhistone deacetyla-
`tion, appear
`to be interrelated. The utility of
`targeting DNA hypermethylation and histone
`deacetylation is being explored clinically. Agents
`shown to inhibit histone deacetylase in vitro
`include sodium phenylbutyrate, depsipeptide, hy-
`brid polar compounds,*” and MS-27-275.Hypo-
`methylating agents include 5-azacytidine and5-aza-
`2-deoxycytidine. The exploration of these agents
`in the clinic, either alone or in combination with
`retinoids, demethylation agents, and chemothera-
`peutic agents,
`is a novel and promising area of
`cancer therapeutics.
`5-Azacytidine and
`Hypomethylating agents.
`5-aza-2-'deoxycytidine are pyrimidine analogs that
`have been extensively evaluated in patients with
`MDS. These compounds are metabolized intracel-
`lularly to triphosphates and subsequently incorpo-
`rated into newly synthesized DNA, where they
`directly inhibit DNA synthesis and inhibit
`the
`activity of DNA methyltransterase,
`the enzyme
`required for 5'-cytosine methylation of cytosine-
`
`Page 5 of 20
`
`

`

`NEW THERAPELITIC AGENTS FOR MDS
`
`563
`
`guanosine (CpG) dinucleotides.4!*? As a result,
`cytosine methylation is blocked in newlyrepli-
`cated DNA, but net
`in the DNA ofresting or
`nondividing cells. Inhibition of methylation by
`5-azacytidine and decitabine is associated with
`transcription of genes previously silenced by meth-
`ylation of promoter region CpG-rich islands, and
`with cellular phenotypic changes; these effects can
`occur at concentrations that are too low to inhibit
`DNA synthesis directly or to cause substantial
`cytotoxicity.!49 The potential application of
`5-azacytidine and decitabine as inhibitors of DNA
`methylation and inducers ofcell differentiation of
`normal and neoplastic hematopoietic progenitor
`cells is an area ofactive investigation.7349-4%
`5-Azacytidine initially demonstrated activity in
`AML,*} but with considerable toxicity at doses
`required for response. Since the drug also induces
`in vitro cellular differentiation in association with
`hypomethylation of DNA,
`it was of interest for
`study in MDS. Chitambaret al®4 used a relatively
`low dose (10 to 35 mg/m24/d for 14 days) to treat 13
`patients,
`three of whom achieved a partial re-
`sponse. Cancer and Leukemia Group B (CALGB)
`investigators’? conducted a phaseII trial of 5-aza-
`cytidine at 75 mg/m2/d by continuous infusionfor 7
`days every 28 days in 48 patients with MDS and
`noted 11% complete remissions and 25%partial
`remissions. Major toxicities included nausea and
`vomiting; one patient died of neutropenic sepsis.
`Subcutaneous administration resulted in. slightly
`lower
`response rates—7% complete remissions,
`17% partial remissions, and 14% with trilineage
`improvement, but less than a partial
`response.>®
`These findings are similar to those achieved with
`low-dose cytarabine.
`The CALGB recently reported the preliminary
`results of a phase LI randomized trial of 5-azacyti-
`dine versus observationin 191 patients with MDS.7
`Thepatients were stratified by FAB subtype (19%
`RA, 4% RARS, 42% RAEB, 21% RAEB-T, 6%
`CMML); patients with RA or RARS had,
`in
`addition, symptomatic cytopenias. 5-Azacytidine
`was administered subcutaneously at a dose of 75
`mg/m2/d for 7 days every 4 weeks for four cycles.
`Patients on the observation arm could receive
`5-azacytidine upon progression. Hematologic re-
`sponses were significantly higher in patients ran-
`domized to receive 5-azacytidine compared with
`observation (P < .0001): 63%(6% complete re-
`sponse, 10% partial response, and 47%improve-
`
`Page6 of 20
`
`ment) versus 7%(all improvement, no complete or
`partial responses), The median time to leukemic
`transformation or death was 22 monthsfor patients
`on the treatment arm, compared with 12 months
`for
`the patients randomized to observation
`(P = .0034). The 12- and 24-month overall sur-
`vival rate was higher in patients randomized to
`receive azacytidine (70% and 41%versus 62%and
`25%, respectively), as was the median survival
`time (18 versus 14 months), but the differences
`were not yet signiticant. Treatment with 5-azacyti-
`dine was associated with subjective improvement
`in quality of life as measured byfatigue, dyspnea,
`physical functioning, positive affect, and psycho-
`logic distress.** Whether 5-azacytidine improves
`overall survival or reduces transformation toleuke-
`mia will require additional follow-up evaluation.
`5-Aza-2'deoxycytidine (decitabine) is another
`hypomethylating agent with potent in vitro activ-
`ity. In earlier studies, decitabine administered as an
`intermittent intravenous infusion achieved brief
`responses in a small series of patients with MDS;
`however, the majority experiencedlife-threatening
`neutropenia and/or
`thrombocytopenia.” Wijer-
`mans et al® reviewed the experience with chis
`agent in MDSand founda 54%response rate of 29
`elderly patients, although there were 17% toxic
`deaths. This drug is under development for MDS
`both in Europe and the United States.4°
`Histone deacetylation and DNA hypermethylation,
`Retinoids, other hormone receptors, and the Myc/
`Mad/Max network of growth regulators exert their
`effects on gene expression by interacting with
`nuclear corepressor complexes that are present on
`the DNA of promoter regions.°4° Gene silencing
`occurs with the recruitment ofhistone deacetylases
`and the formation of a nuclear corepressor-histone
`deacetylase complex (NCHDC). Histone deacety-
`lase catalyzes the removal of acetyl groups from
`histone proteins, inducing a conformation change
`thatresults in an environment unfavorable to gene
`transcription. A NCHDC has been found to play
`an importantrole in acute promyelocytic leukemia
`(APL), where the NCHDCisrecruited by bath the
`PML-RARa and PLZF-RARa fusion proteins,
`which form as a consequence of chromosomal
`translocations t(15;17) and t(11;17),
`respec-
`tively.6**? A NCHDCis also recruited by ETO, a
`component of the fusion product resulting from
`the t($;21) chromosomal translocation in AML."
`Moreover,
`inhibitors of histone deacetylase have
`
`Page 6 of 20
`
`

`

`564
`
`CHESON ET AL
`
`been found to overcome transcriptional repression
`and to potentiate retinoid-induced differentiation
`of APL and AML cells.**6 A clinical test of this
`observation was performed in a patient with APL
`who had become refractory to both chemotherapy
`and all-trans retinoic acid (ATRA). Administra-
`tion of both ATRA and a histone deacetylase
`inhibitor, sodium phenylbutyrate (see below), re-
`sulted in a complete remission. The clinical re-
`sponse was associated with acetylation of histone
`proteins in the leukemiccells.”
`While methylation of CpG islands in gene
`promoter regions has long been known to be
`associated with gene silencing,
`it was not known
`how such DNA hypermethylation exerts its effect
`on gene transcription. Recent studies have shed
`light on both the role of DNA hypermethylation
`in the inactivation of tumor suppressor genes, as
`well as the mechanism of transcriptional repres-
`sion, Examples of genes associated with CpG
`hypermethylation include, among others, RB in
`retinoblastoma, VHL (the von Hippel-Lindaugene)
`in renal carcinoma, pl6INK4A and pl5INK4A
`(cyclin-dependent kinase inhibitors) in solid tu-
`mors andin hematologic malignancies, and hMLH!
`(a DNA mismatch repair gene) in colon cancer.’!
`The mechanism of gene silencing by DNA hyper-
`methylation now appears to involve the recruit-
`ment of a NCHDC by the methyl-CpG-binding
`protein, MeCP2.'27? In fact, the combined admin-
`istration of a demethylating agent and a histone
`deacetylase inhibitor has been shown to synergize
`in reactivating genes that were silenced in cancer
`cells.” This finding not only links the processes of
`DNA hypermethylation and histone deacetyla-
`tion, but also presents therapeutic targets for
`agents that are relatively nontoxic, or used at
`nontoxic doses.
`
`Phenylbutyrate
`Phenylbutyrate (PB) is a low-molecular-weight
`phenyl-fatry acid that been usedclinically to treat
`hyperammonemia in children with inborn errors of
`urea synthesis.It also been shown to enhance
`fetal hemoglobin production in some patients with
`hemoglobinopathies.”” A number of mechanisms
`have been proposed for the antitumoreffect ofPB,
`including (1) elimination of glutamine necessary
`for nucleic acid and protein synthesis in rapidly
`growing normal and tumor cells’?78; (2) inhibition
`ofthe mevalonate pathwayof cholesterol synthesis
`
`Page7 of 20
`
`leadingto interference of post-translational process-
`ing of proteins, modification of lipid metabolism,
`inhibition of protein isoprenylation, and regula-
`tion of gene expression through DNA hypomethyl-
`ation”?*°. (3) activation of a peroxisome prolifera-
`toractivated receptor by PB, a transcriptional
`factor regulating lipid metabolismand cell growth*!;
`and (4)
`regulation of gene expression through
`histone hyperacetylation via inhibition of nuclear
`histone deacetylases.*? “4
`PB has been shown to induce differentiation,
`tumor cytostasis, and reversion of malignant pheno-
`type in several
`in vitro models.***? PB, as a
`histone deacetylase inhibitor, may have synergistic
`activity with ATRAin the treatment of APL.O67°"
`The PML-RAR fusion protein was shown to re-
`cruit a transcriptional corepressor complex that
`includes a histone deacetylase. ATRA alone could
`partially dissociate the complex, allowing in-
`creased transcription, but butyrate (or other inhibi-
`tors of histone deacetylases) in combination with
`ATRA was able to completely abrogate the inhibi-
`tion of transcription. In light of these observations,
`an APL patient who experienced multiple relapses
`after ATRA treatment was treated with PB in
`combination with ATRA under compassionate
`release, and achieved a complete remission.”
`
`Depsipeptide
`Depsipeptide (NSC 630176) is a bicyclic pep-
`tide originallyisolated from Chromobacterium viola-
`ceum, strain 968, by Fujisawa Pharmaceutical Co
`(Osaka, Japan). In the original observations, depsi-
`peptide selectively decreased the mRNA expres-
`sion of the c-myc oncogene and inhibited the
`growth of the Ha-ras—transformed NIH3T3 clonal
`cell
`line, Ras-1, bur had no effect on Ha-ras
`mRNA expression.”! It did not affect DNA synthe-
`sis, but caused cell cycle arrest at Gy/G,. Recently,
`it has been shown to be a histone deacetylase
`inhibitor.”
`incubation of
`Byrd et al demonstrated that
`chronic lymphocytic leukemia cells with depsipep-
`tide resulted in an alteration in apoptosis-associ-
`ated proteins: an increase in Bax with no changein
`Bel-2, and a decrease in p27 expression.”
`In collaboration with Fujisawa Pharmaceutical
`Co, the National Cancer Institute (NCI) is cur-
`rently sponsoring two phase [ trials of depsipeptide
`administered as a 4-hour intravenous infusion. In
`one trial, a once-weekly infusion schedule (days 1,
`
`Page 7 of 20
`
`

`

`NEW THERAPEUTIC AGENTS FOR MDS
`
`565
`
`8, and 15 every 28 days) is used, while the other
`trial evaluates a twice-weekly (days 1 and 5 every
`21 days) schedule.
`
`MS-27-275
`
`MS-27-275 is a benzamide derivative thar was
`synthesized by Mitsui Pharmaceuticals (Tokyo,
`Japan) in a search for novel antitumor agents.*°
`The compound was foundto have histone deacety-
`lase activity in vitro at micromolar concentrations.
`In addition, when administered orally, MS-27-275
`inhibited the growth of a number of tumor xeno-
`grafts. The NCI,
`in collaboration with Mitsui
`Pharmaceuticals, plans to sponsor phase| trials of
`this agent in the near future.
`
`Hybrid Polar Compounds
`Hexamethylene bisacetamide (HMBA) was the
`first of the class of hybrid polar compounds to be
`evaluated as an antitumor agent
`in MDS and
`AML. The limited clinical activity that was ob-
`served was attributed to the inability to achieve
`the plasma concentrations that were required to
`induce differentiation in cells in vitro and to
`dose-limiting thrombocytopenia.** Subsequently,
`Richon et al” described compounds structurally
`related to HMBA, but which exhibited 3-log
`greater potency in inducing terminal differentia-
`tion and apoptosis in transformed cell lines.
`In
`addition, these compoundspossess histone deacety-
`lase inhibitory activity at micromolar concentra-
`tions. Recently, one such compound, M-carboxy-
`cinnamic acid bishydroxamide (CBHA), was found
`to induce apoptosis in human neuroblastoma, and
`the effect was associated with CD95/CD95 ligand
`expression by the tumor cells. These agents
`should be entering into early clinical trials in the
`nearfuture.
`
`Arsenic Trioxide
`
`Arsenic was used as a medicinal 2,400 years ago
`in the time of the ancient Greeks and Romans.
`Paul Ehrlich used organic arsenicals for the treat-
`ment of syphilis. Arsenicals are still included as
`ingredients
`in folk remedies of some cultures,
`particularly in China and other parts of Asia.
`Arsenic was widely used totreat syphilis before the
`advent of penicillin, and the organic arsenical
`melarsoprol
`is a recognized treatment
`for
`the
`meningoencephalitic stage of African trypanoso-
`miasis.”° Fowler's solution (1% arsenic trioxide in
`
`Page 8 of 20
`
`potassium bicarbonate), formulated in the 18th
`century to treat a varietyof infectious and neoplas-
`tic disorders, was reported by US physicians in the
`1930s to be useful
`in the treatment of chronic
`myelogenous leukemia (CML), and more recently
`by hematologists in China to treat various forms of
`leukemia, including CML.”
`Recent interest in the development ofarsenic
`trioxide as an anticancer agent emanates from
`reports by Chinese investigators”®” of its efficacy
`in the treatment of APL. These favorable results in
`APL were confirmed in the United States by
`investigators at Memorial Sloan-Kettering Cancer
`Center (MSKCC),!
`Preclinical studies have shown that human APL
`cells are very sensitive to the growth-inhibitory
`and cytotoxic effects of arsenic trioxide.!°!!°2 Sen-
`sitivity to arsenic trioxide in vitro has also been
`demonstrated ag