(Arsenic Trioxide) in the Treatment of Myelodysplastic Syndromes

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Opportunities for Trisenoxs (arsenic trioxide) in the treatment of myelodysplastic syndromes A List1, M Beran2, J DiPersio3, J Slack4, N Vey5, CS Rosenfeld6 and P Greenberg7 1Arizona Cancer Centre 3945, University of Arizona, Tucson, AZ, USA; 2The University of Texas M.D. Anderson Cancer Center, Houston, TX, USA; 3Washington University, St. Louis, MO, USA; 4Roswell Park Cancer Institute, Buffalo, NY, USA; 5Institut Paoli- Calmettes, Marseille, France; 6Texas Oncology, Dallas, TX, USA; 7Stanford University School of Medicine, Stanford, CA, USA

Arsenic trioxide (ATO) has a long history of efficacy as an recently that the clinical efficacy and safety of ATO in acute antileukemic agent. However, with the advent of modern promyelocytic leukemia (APL) was established. ATO was therapy, it had been relegated to a historical footnote. In the approved by the Food and Drug Administration (FDA) for this 1990s, investigators in China reported that ATO was safe and s had dramatic efficacy in patients with acute promyelocytic indication (as Trisenox , Cell Therapeutics, Inc., Seattle, WA, leukemia (APL). Preclinical investigations indicate that the USA). ATO’s multiple targets of action suggest that it may have biological targets of this novel drug extend to a variety of broad therapeutic potential, including MDS. Preliminary clinical malignancies other than APL and include induction of apopto- investigations with ATO in MDS have shown promising results, sis, nonterminal differentiation, and suppression of prolifera- and further studies are under way. tion and angiogenesis. The myelodysplastic syndromes (MDSs) present a particular therapeutic challenge. Ineffective hemato- This article provides an overview of the concepts essential to poiesis predominates in patients with low-grade prognostic understanding the rationale for the application of ATO in MDS. scores. The survival of those patients with high-grade disease It reviews the pathobiology of MDS and describes the relevant is compromised by a high risk of leukemia transformation. mechanisms of action of ATO. A brief discussion of the clinical Although a number of therapeutic options have been investi- experience with ATO in APL explains the adverse events that gated, none has emerged as being broadly efficacious and may be anticipated with the clinical use of this agent, most of having an acceptable toxicity profile. No drug has yet received approval by the Food and Drug Administration for this which are predictable and reversible. Present therapy for MDS is indication. Biologic features of MDS, which include accelerated primarily supportive, but the initial results from clinical studies apoptotic potential, limited maturation capacity, and medullary with ATO, described at the conclusion of this report, support the neovascularity, create a strong scientific rationale for the need for additional clinical investigations in MDS. investigation of ATO in MDS. This report describes the history and scientific basis for ATO treatment of hematologic malignancies, enumerates the potential benefits of ATO in MDS, and discusses the direction of ongoing trials of this novel Pathobiologic features of MDS antineoplastic agent. Leukemia (2003) 17, 1499–1507. doi:10.1038/sj.leu.2403021 The principal pathologic feature of MDS is ineffective hemato- Keywords: apoptosis; arsenic trioxide; cellular redox; clinical trials; s poiesis, characterized by dysplastic and incomplete maturation myelodysplastic syndromes; Trisenox and progressive increase in the percentage of myeloblasts. The dissociation between peripheral hematopoietic deficits and medullary hypercellularity is explained in part by accelerated Introduction abnormal proliferative and apoptotic fractions. Proliferative abnormalities may be an intrinsic property of the neoplastic clone or may relate to autocrine or paracrine cytokine The myelodysplastic syndromes (MDSs) represent a varied interaction or microenvironment interaction. In some patients spectrum of hematopoietic stem cell malignancies for which with MDS, progressive expansion of immature myeloid pre- safe and effective therapy is limited. Characterized by ineffec- cursors is stimulated in part by the autocrine and paracrine effect tive hematopoiesis, MDS may evolve to nonpromyelocytic, of the vascular endothelial growth factor (VEGF).2 The presence acute myelogenous leukemia (AML). MDS can arise de novo or of both VEGF and its receptor on MDS cells provides a it may develop secondary to cytotoxic therapy or environmental mechanism for autocrine growth stimulation. toxins. Patients may be asymptomatic or present cytopenias (ie Accelerated rates of apoptosis and proliferation are pathologic anemia, neutropenia, or thrombocytopenia). The disease is 1 features of MDS. In the initial stage of the disease, the majority uncommon before age 60, increasing in incidence with age. of myeloid bone marrow elements exist in the early stages of The heterogeneity of MDS and its complex pathophysiology programmed cell death.3 As a result, production of hemato- contribute to its therapeutic challenge. An understanding of the poietic elements is ineffective, potentiated by excessive molecular biology of MDS is limited, but the profile of disease production of tumor necrosis factor-alpha (TNF-a)4 and soluble mechanisms that has been identified provides a rationale for Fas ligand.5,6 In fact, elevated levels of TNF-a correlate with investigational treatment with a number of agents. One of these increased caspase-3 activity in MDS bone marrows, DNA is arsenic trioxide (ATO). Despite the long history of arsenic as a oxidation, and exhaustion of glutathione reserves.7 chemotherapeutic agent for hematologic diseases, it was only As the myelodysplastic clone evolves and the disease progresses, the apoptotic fraction decreases, and less-differen- Correspondence: Dr A List, Arizona Cancer Center 3945, University of Arizona, 1515 N. Campbell Avenue, Tucson, AZ 85724, USA; Fax: +1 tiated bone marrow elements accumulate. This change in 520 626 2415 susceptibility to apoptosis is reflected in the ratio of the Received 24 February 2003; accepted 4 April 2003 proapoptotic protein c-Myc to the antiapoptotic protein Bcl-2, Trisenoxs in the treatment of MDS A List et al 1500 8,9 in a maturation-stage–dependent fashion. Thus, bone marrow a aspirates from patients with early MDS show a significantly Apoptosis Induction in AML + APL [As2O3 x 24H] higher CD34-positive cell pro- vs antiapoptotic Bcl-2–family 80 TUNEL protein ratio than bone marrow from patients with advanced ∗ ∗ ∗ disease.10 For this reason, one principle of recent therapeutic ∗ Control ∗ strategies is the modulation of apoptotic threshold. 60 0.5 µM As O ∗ ∗ ∗ 2 3 ∗ µ 1.0 M As2O3 µ 40 ∗ 2.0 M As2O3 Mechanisms of action of ATO ∗ ∗ ∗ ∗ In vitro analyses of the antitumor efficacy of ATO in various

Apoptotic cells (%) 20 neoplastic cell lines suggest that its effects are not limited to APL and are mediated through several different mechanisms, the 0 most important of which are (a) induction of nonterminal NB4 HEL Meg-01 UT7 M07e HL60 differentiation and apoptosis and (b) suppression of proliferative potential and angiogenesis. ATO thus has the potential to target b Bcl-2 Protein (Western blot ) and interfere with critical pathways involved in tumor growth As2O3 ( M) and survival in a variety of hematologic malignancies, including C 0.5 1.0 2.5 5.0 MDS. UT7

Differentiation Meg-01 Sequential ex vivo analysis of APL cells from patients treated with ATO shows partial induction of surface differentiation antigens.11 The ability of ATO to promote differentiation in APL NB4 ND cells is mediated in part by its ability to target the leukemogenic a fusion protein PML-RAR . This fusion protein, which is HL60 singularly responsible for the pathogenesis of APL, results from the chromosomal translocation t(15;17), fusing the PML gene Figure 2 Dose-dependent suppression of apoptosis (a) and Bcl-2 with the RARa gene. PML-RARa protein acts in a dominant- (b) by ATO in AML cells. Reprinted with permission from Lu et al24 negative fashion to inhibit RARa target gene expression, yielding a maturation block at the promyelocytic stage of myeloid development. At therapeutic concentrations, ATO accelerates 14,17–20 degradation of PML-RARa, thereby releasing the maturation (Figure 1). It covalently crosslinks available sulfhydryl block and promoting differentiation in APL cells.12,13 groups to disrupt mitochondrial membrane potential, leading to In non-APL cells, ATO can modulate gene expression to the release of cytochrome c and activation of caspase 21,22 promote nonterminal differentiation in myeloid leukemic cell effectors. Contributing to this mitochondria-specific effect lines by induction of histone hyperacetylation, activation of the is the ability of ATO to downregulate Bcl-2 protein expression, mitogen-activated protein kinase (MAPk) signaling pathway, which may shift the balance of Bcl-2–family proteins to favor a 17,23,24 and interference with nuclear corepressors and their transcrip- proapoptotic state (Figure 2). In addition to these actions, tion factor partners.14–16 ATO promotes the generation of reactive oxygen species and the accumulation of intracellular hydrogen peroxide (H2O2). Increased concentrations of H2O2 enhance the permeability of Apoptosis the mitochondrial membrane.21 Glutathione transferase and glutathione peroxidase, enzymes that detoxify cellular reactive ATO induces programmed cell death in varied non-APL cell oxygen species, are inhibited by ATO, leading to the accumula- lines through interaction with a number of cellular targets tion of oxygen-free radicals. Not surprisingly, a deficiency of reduced thiols increases sensitivity to ATO cytotoxicity. For example, the NB4 (APL-derived) cell line exhibits relatively low CD95L levels of reduced glutathione and glutathione peroxidase and Extrinsic Intrinsic 21,25,26 Pathway Pathway expresses constitutively high levels of H2O2. When NB4 cells are incubated with buthionine sulfoximine, a specific CD95 GST FADD/ inhibitor of glutathione synthesis, their sensitivity to ATO- As(GS)3 MORT1 25,26 As2O3 induced apoptosis is increased.

HO H2 The sulfhydryl-rich cytoskeletal proteins are important C-FLIP GPx GSH targets of ATO. By binding to microtubular proteins such as O2- IKK tubulin, ATO disrupts assembly of the mitotic apparatus, Caspase-8 tBid Ascorbic acid which leads to aneuploidy and apoptosis.18 Another target of BCL-2 BCL-X NFκB ATO-induced apoptosis is the ability of arsenic to block activation of nuclear factor-kappa B (NF-kB).27 NF-kB mod- Cytochrome c + APAF-1 ulates the transcription of a variety of cytokines that play 28 Caspase-3 Caspase-9 IAPs a role in maintaining the viability of MDS cells. Additionally, ATO induces activation of the MAPK cascade. c-Jun N-terminal Death Substrates kinase (JNK) is an important member of the MAPK family that Figure 1 Mechanisms of apoptosis induction by ATO. activates transcription factors, nuclear proteins, and other

Leukemia Trisenoxs in the treatment of MDS A List et al 1501 protein kinases, enabling cells to respond to redox-related changes in their environment; JNK may thus be an important As2O3 contributor to the apoptotic activity of ATO.29,30 (–) Leukemia cells IL-6 (+) IL-7 VEGF Growth inhibition IL-10 GM-CSF Arsenic has significant antiproliferative activity relating in part to modulation of cytokine release and interference with cell cycle (–) progression. The relation between cytokine elaboration and the proliferative capacity of diseases such as MDS and AML is complex. Elevated plasma concentrations of cytokines, including TNF-a,31 interleukin (IL)-1b, and transforming growth factor- beta (TGF-b),32 contribute to the ineffective hematopoiesis and Rapidly proliferating endothelial cells hypercellularity of MDS. NF-kB modulates the transcription of a Figure 3 Endothelial cytotoxicity and suppression of leukemia variety of inflammatory cytokines and myeloid gene-regulatory VEGF generation by ATO. Reprinted with permission from Roboz factors, such as C/EBPa, which has been implicated in the et al38 proliferation and survival of normal and malignant hematopoietic progenitors.33 The release of NF-kB from its cytoplasmic The significance of medullary angiogenic response in patients inhibitor permits transcriptional expression of a variety of with MDS has been evaluated by immunohistochemical staining cytokines, including IL-1b and TNF-a.28 IL-1a is believed to for vascular antigens or angiogenic factors such as VEGF. play a major role in stimulating the proliferation of myeloid Analysis of MVD in 81 patients with MDS demonstrated blasts, whereas TNF-a promotes ineffective hematopoiesis by significantly higher neovascular density compared with controls accelerating apoptotic cell death. (Po0.001) (Deliliers GL et al. Leukemia Res, 1999; 23: S24; Cellular response to proliferative signals is driven by the abstract). MVD values were higher in refractory anemia with formation, activation, and subsequent inactivation of cyclins excess blasts in transformation (RAEB-t) and chronic myelomo- and cyclin-dependent kinases. The antiproliferative activity of nocytic leukemia (CMML) and correlated with blast counts, and ATO has been linked to both prolongation of the cell cycle as the levels increased further upon progression to AML. Normal well as arrest of malignant hematopoietic cells in the G and G / 1 2 bone marrows harbor little VEGF, which is generally restricted M phases (Chen G-Q et al. Blood 1998; 92(Suppl. 1, part 1): to megakaryocytes.39 However, intense expression is identified 638a; abstract).19,34,35 Upon exposure to ATO, concentrations in areas of abnormal localization of immature precursors and of cyclin-dependent kinase 6, cdc2, and cyclin A decrease.34 myelomonocytic precursors in patients with MDS. Immunohis- Cell cycle arrest is followed by upregulation of p21 mRNA and tochemical studies that demonstrate expression of both VEGF protein, an event associated with proliferation arrest. Ultimately, and its receptor in neoplastic myelomonocytic cells suggest that by blocking cytokine-induced activation of NF-kB and its in the majority of patients, VEGF may have both autocrine and inhibitory activity on cyclin-dependent kinase activity, ATO paracrine stimulatory capacity. Administration of a neutralizing has significant potential to modulate cellular proliferation in antibody to VEGF inhibits leukemia colony-forming capacity MDS.28 while promoting committed progenitor formation in patient CMML and RAEB-t specimens. These findings suggest that ATO’s ability to inhibit VEGF elaboration and target the vascular Angiogenesis inhibition endothelial cells may have practical significance in patients with MDS. Endothelial cells are an important source of hematopoietic growth factors that support the growth of benign and malignant tumors. Recently, medullary neoangiogenesis has been demon- Clinical experience with ATO in hematologic malignancies strated to be a consistent pathologic feature in hematologic malignancies.36 Both microvascular density (MVD), a marker of ATO in APL in situ angiogenesis, and the concentration of VEGF are increased in the bone marrow of patients with hematologic The activity of arsenic in hematologic malignancies has been malignancies, including acute and chronic leukemias, multiple recognized since 1878, when administration of Fowler’s myeloma, non-Hodgkin’s malignant lymphomas, and MDS.36 In solution was noted to lower white blood cell counts in two a number of these conditions, increased angiogenic activity has normal individuals and in one patient with ‘leukocythemia’.40 been linked to an adverse prognosis. Arsenic became a primary antileukemic intervention until it was In human xenograft models, single-dose administration of replaced by radiation therapy, although in the 1930s it was ATO has been shown to induce apoptosis of endothelial cells in again employed in the treatment of patients with chronic new blood vessels, producing ischemic necrosis while sparing myelogenous leukemia (CML). With the introduction of modern normal tissues.37 This effect appears to be both dose and time chemotherapy, the use of arsenic as a treatment for leukemia dependent. New blood vessels act to stimulate the growth of was all but abandoned.41 hematologic tumors by broadening the reservoir for release of Reports emanating from China in the 1990s describing the cytokines from activated endothelial cells. These cytokines may successful treatment of newly diagnosed and relapsed APL function in both an autocrine and paracrine fashion. ATO patients using ATO regenerated interest in this compound. ATO therapy may interrupt a paracrine positive-feedback loop, induced high rates of complete remission ranging from 52 to promoting tumor growth. It is notable that ATO inhibits 93% in the study patients.42–44 These results were confirmed by production of VEGF in a leukemic cell line (Figure 3).38 two trials conducted in the United States. In a pilot study

Leukemia Trisenoxs in the treatment of MDS A List et al 1502 performed at the Memorial Sloan-Kettering Cancer Center,11 12 The safety profile of Trisenoxs is unlike that of traditional patients with APL who had relapsed after extensive prior therapy chemotherapeutic agents employed in the treatment of with all-trans retinoic acid (ATRA) and cytotoxic agents received leukemia in that Trisenoxs does not induce myelosuppression treatment with 0.06 to 0.2 mg/kg/day of ATO (cumulative doses, or cause alopecia, and the drug can be administered on an 160–515 mg). ATO treatment eliminated all visible leukemic outpatient basis. blasts and promyelocytes from the bone marrow and resulted in 11 of the 12 patients (92%) achieving complete remission. The s duration of therapy in the responding patients ranged from 12 to Pharmacokinetics of Trisenox (as total arsenic) 39 days. Eight of the 11 patients (73%) achieving complete remission also achieved molecular conversion (negative test for Specific pharmacokinetic features of total assayable arsenic PML-RARa) following two cycles of treatment. Additionally, in suggest that less frequent dosing regimens can be developed, vitro analysis of APL cells from treated patients showed particularly for malignancies other than APL, which favor incomplete differentiation accompanied by increased apoptotic patient convenience. After the oral administration of 60 mg/kg cell death. of tetra-arsenic tetra-sulfide (As4S4) to seven patients with APL, A subsequent multicenter study of 40 APL patients in either absorption was rapid, with total arsenic being detectable in first or later relapse established ATO as a highly effective plasma within 30 min after administration.47 Following either therapy for patients who failed treatment with ATRA.45 Of the oral or intravenous administration, arsenic metabolism involves 40 patients, 34 (85%) achieved complete remission; 91% of reduction and methylation, predominantly in the liver, and these achieved cytogenetic remission. Molecular conversion subsequent excretion of As3+ and methylated metabolites into (loss of the PML-RARa transcript, as assessed by reverse trans- the urine (urinary excretion half-life of total arsenic is 3–5 days). criptase polymerase chain reaction assay) occurred in 86% of Other routes of excretion include feces, lung, sweat, milk, hair, evaluable patients who achieved clinical complete remission. and skin. On the basis of these data, the FDA granted marketing Preliminary analysis of the pharmacokinetics of daily par- approval for ATO (commercially available in the United States enteral ATO was studied in patients with various hematologic as Trisenoxs, Cell Therapeutics, Inc., Seattle, WA, USA) in malignancies and solid tumors (Soignet SL et al. Cancer Res, September 2000 for the induction of remission and consolida- 2000; 41: 543; abstract). Arsenic Cmax values ranged from 25 to tion in patients with t(15;17)-positive APL who are refractory to, 215 ng/ml (0.3–2.9 mM) in plasma and from 34 to 183 ng/ml 48 or have relapsed from, retinoid and anthracycline chemother- (0.45–2.4 mM) in red blood cells. Total arsenic appears to be apy. The drug is administered intravenously over 1–2 h in a freely exchangeable between plasma and tissue compartments dosage of 0.15 mg/kg/day for induction and consolidation. such as red blood cells, exhibiting comparable elimination Median follow-up of the American trial patients has been 2 curves for the two compartments. The half-life of total arsenic years. Survival estimates for patients treated in first or is greater than 90 h and the volume of distribution at steady subsequent relapse in the two trials combined are 77% for state is large (4400 l), suggesting extensive tissue/protein overall survival and 58% for relapse-free survival.46 binding. On the basis of these pharmacokinetic data and the known covalent interaction with protein sulfhydryl groups, Trisenoxs may be administered via a loading dose, followed s Safety profile of Trisenox in APL by less frequent maintenance dosing.48 Identification of the major active species of Trisenoxs and the characterization of The 52 APL patients treated in the pilot and multicenter studies the methylated metabolites with validated assays represent showed that while most patients will experience some drug- the principal goals of current pharmacologic investigations. related toxicity, the effects are reversible and diminish with Several studies are currently under way to evaluate the III subsequent cycles of treatment. Generally, the adverse effects pharmacokinetics of arsenous acid, As (OH)3, the monomethyl 11 V do not lead to interruption of therapy. and dimethyl metabolites (methylarsonic acid, As OCH3(OH)2, V Common adverse events included gastrointestinal symptoms and dimethylarsinic acid, As O(CH3)2OH), and arsenic acid, of nausea and emesis (generally responsive to conventional AsO(OH)3. antiemetics), fatigue, edema, hyperglycemia, dyspnea, cough, rash or pruritus, headaches, and dizziness. The most significant serious adverse events associated with Trisenoxs therapy in APL Current treatment for MDS patients included the APL differentiation syndrome (30%), hyperleukocytosis (50%; seen almost exclusively during induc- Current and investigational treatment approaches for MDS tion), and QT prolongation (31%; absolute QT X500 ms in 3 are directed at ameliorating cytopenias, improving overall patients). One patient with an absolute QT X500 ms experi- quality of life, and lengthening survival by decreasing the enced an asymptomatic run of torsades de pointes that resolved risk of progression to AML. Several classification systems for spontaneously. Postmarketing safety data have recorded no MDS, based on hematologic findings, clinical presentation, cardiac deaths due to ATO-related arrhythmia (Paradise C et al. and prognosis, have been constructed for these heterogeneous Blood 2001; 98: 205b; abstract). However, since Trisenoxs can disorders to aid in the selection of appropriate treatment prolong the QT interval and potentially lead to complete heart that is tailored to the risks associated with the individual’s block and/or torsades de pointes, it should not be coadminis- disease. tered with other drugs that are known to prolong QT intervals, nor should it be administered in patients with a history of QT abnormalities. Patients should be carefully monitored for Classification systems electrolyte abnormalities that may additively affect the QT interval. All of the serious adverse events known to occur with In 1976, the French–American–British (FAB) Cooperative Trisenoxs therapy in APL are manageable with proper Group established diagnostic criteria for dysmyelopoietic monitoring and timely intervention as needed. syndromes that were often confused with acute leukemia.39

Leukemia Trisenoxs in the treatment of MDS A List et al 1503 These definitions were subsequently incorporated into the ATRA has been used alone and in combination with interfer- FAB classification schema formalized 6 years later.49,50 on-a, erythropoietin, or G-CSF in this setting with limited The more recent World Health Organization (WHO) classifica- success.64–66 Recently, data from a randomized, controlled trial tion for MDS was derived through modifications in the of 5-azacytidine, a DNA methyltransferase inhibitor, in patients original FAB system.47,50 The FAB and WHO classifications with symptomatic MDS showed that this agent could induce are currently the primary morphologic classification systems significant clinical benefit, as compared with the control for MDS. subjects who received only supportive care (response rate, 60 vs 5% for controls; Po0.001).63–68 Treatment with 5-azacytidine also prolonged the time to progression to acute leukemia or Prognostic determination death (median time to progression, 21 vs 13 months for controls; P ¼ 0.007), and it was associated with a decrease in the In the FAB classification, prognostic discrimination is provided probability of leukemia transformation during the course of by the number of type I myeloblasts.51 By definition, the best study treatment (15 vs 38% for controls; P ¼ 0.001). Quality of prognosis is the category of o5% myeloblasts, represented by life assessments were also improved in patients treated with 5- patients with refractory anemia (RA) and refractory anemia with azacytidine, including physical function, symptoms, and psy- ring sideroblasts (RARS). Categories such as refractory anemia chological state. Although these results are encouraging, this with excess blasts (RAEB), with 5–20% myeloblasts, and RAEB-t, agent has not as yet gained FDA approval for this indication. with 21–30% myeloblasts, signify progressively worse prog- noses. Patients in these categories have an incrementally higher probability of transformation to AML.52 The diagnosis of CMML Cytokine and anticytokine therapy: Interventions for MDS imparts an intermediate to poor prognosis. A separate prognostic are intended to limit proinflammatory cytokine production or scoring system has been proposed for CMML because of its action by interfering with signaling pathways or cytokine half- 69,70 significantly heterogeneous presentation and clinical course.53 life. Cytokines such as TNF-a, IL-1b, and TGF-a, produced 71,72 The International Prognostic Scoring System (IPSS) is a more in paracrine fashion, are targets of these interventions. Since recently developed classification system that has demonstrated autoimmune suppression of hematopoiesis may contribute to reliability for predicting survival and risk of leukemia transfor- the genesis of hypoplastic MDS, immunosuppressive agents mation.54,55 Published in 1997, it is the result of a global such as antithymocyte globulin or cyclosporine have been 73,74 analysis of survival data in patients with MDS who were either applied with encouraging results. untreated or had received low-intensity therapy. The IPSS Conversely, certain recombinant cytokines (IL-11, IL-3, IL-6) utilizes three features in its classification: the percentage of and the recombinant human hematopoietic growth factor bone marrow myeloblasts, the cytogenetic pattern, and the thrombopoietin also have the potential to decrease symptoms 56–62 number of cytopenias. These three factors allow patients to be and improve quality of life. categorized into one of four groups segregated by survival and risk for evolution to acute leukemia. These groups are designated as low (median survival, 5.7 years), intermediate-1 Chemotherapy and stem cell transplantation: Chemo- (3.5 years), intermediate-2 (1.2 years), and high risk (0.4 years). therapy and stem cell transplantation have been applied in The prognostic validity of the IPSS is improved with incorpora- suitable candidates with intermediate-risk or high-risk IPSS tion of patient age. This system has provided practitioners with scores. Cytosine arabinoside is the most widely studied reproducible and clinically useful prognostic information to chemotherapy agent for MDS, administered in low- or high- guide them in the choice of therapeutic interventions. dose regimens. With low-dose cytosine arabinoside, only 10% of patients achieve complete remission, and neutropenic infections are common. This treatment does not appear to 75,76 Supportive care prolong survival or decrease the evolution to AML. Other agents employed as monotherapy include topotecan and Although therapeutic goals for patients with MDS vary with the decitabine. The rate of complete remission with topotecan is risk posed by the disease, supportive care is the mainstay of approximately 30%, and repeated courses of decitabine have been reported to produce major cytogenetic responses in 17% current MDS therapy. Patients are transfused with packed red 75,77 blood cells and platelets to improve anemia-related signs and of patients. Aggressive antileukemic therapy and salvage- type AML regimens have also been employed with limited symptoms and to decrease the risk of thrombocytopenic 78,79 hemorrhage. Antibiotics should be administered promptly to success. patients with suspected manifestations of bacterial infection. Allogeneic bone marrow transplantation is curative in patients Hematopoietic growth factors (granulocyte–macrophage col- with higher-risk MDS. Unfortunately, although age considera- ony-stimulating factor [GM-CSF], G-CSF, erythropoietin), alone tion has been broadened, many patients with MDS are too old to or in combination, have the potential to decrease symptoms qualify or lack a matched donor. In addition, transplantation- and improve quality of life.56–62 Amifostine, a cytoprotective related morbidity, mortality, and relapse rates remain high. sulfhydryl compound with antioxidant and in vitro hematopoietic stimulatory activity, has been employed with limited success.63 Treatment of MDS with Trisenoxs

To date, few of the investigational agents applied in MDS have Investigational treatments for MDS emerged as singularly efficacious and safe, and none has received FDA approval for an MDS indication. Continued Differentiating agents: Differentiating agents have been research into alternative therapeutic options for this disease is administered to MDS patients in an attempt to overcome therefore of primary importance. The broad mechanistic targets the maturation disturbance in bone marrow progenitors. of Trisenoxs and its established efficacy and safety profile in

Leukemia Trisenoxs in the treatment of MDS A List et al 1504 APL make it an attractive candidate for the treatment of patients higher-risk (intermediate-2 or high IPSS category). The primary with MDS. efficacy end point for the low-risk cohort is estimation of the Both in vitro studies and preliminary clinical evaluations have proportion of patients experiencing major hematologic im- demonstrated evidence for ATO activity in MDS. In mono- provement; for the high-risk cohort, the end point is the nuclear cells harvested from the peripheral blood or bone proportion of patients with partial or complete response. marrow of 14 patients with advanced MDS, micromolar Secondary end points include safety and quality of life. To date, concentrations of ATO induced apoptosis in 7 of 11 cases.80 20 patients have been enrolled (Table 1), all with evaluable Administration of GM-CSF increased the sensitivity of the data. Thus far, three of the 20 (15%) patients (all high-risk) have neoplastic cells to ATO-induced apoptosis. experienced erythroid hematologic improvement and transfu- In a dose-ranging study of Trisenoxs in patients with various sion independence (unpublished data, Cell Therapeutics, Inc.; types of advanced hematologic cancers, Trisenoxs treatment Singer J et al. European Hematology Association Annual produced stable disease in one patient with MDS (Soignet SL Meeting, 2002). Hematologic improvement has occurred in et al. Cancer Res, 2000; 41: 543; abstract). In another individual three of the nine (33%) high-risk patients (unpublished data, Cell case, treatment with ATO yielded a complete hematologic Therapeutics, Inc.). remission (Dutcher JP et al. Blood 2000; 96: 260b; abstract). The second trial, the European multicenter trial, evaluates an This patient was a 56-year-old woman with RAEB-t and normal alternative schedule employing a loading dose of 0.30 mg/kg/ cytogenetics, who was pancytopenic and was red blood cell and day for 5 days followed by a maintenance treatment of 0.25 mg/ platelet transfusion dependent. She was treated with ATO kg twice a week for 15 weeks. The European multicenter trial 20 mg/day administered intravenously (32 doses), including a 3- utilizes the same efficacy end points as the US trial and will also day treatment break. At 8 months after completing ATO evaluate the effect of Trisenoxs on tumor cell apoptosis. In all, treatment, the patient remained in hematologic remission, 41 patients have been enrolled in the study and data are showing a normal white blood cell count and differential and available for 21 patients. Median age is 66 years. Seven patients a normal hematocrit. Her platelet levels were mildly decreased, are in the low-risk group (low or intermediate-1 IPSS category) at 90 000/ml. Bone marrow biopsies done at the completion of and 14 patients are in the high-risk group (IPSS intermediate-2 or the course of ATO demonstrated improved maturation of the high-IPSS category). Of the 21 patients, 15 were transfusion myeloid, megakaryocytic, and erythroid lineages. dependent. Treatment was well tolerated and was administered Such preliminary data provided justification to explore further on an outpatient basis in all cases. Analysis of response in the the therapeutic role of Trisenoxs in MDS in larger clinical patients who had received at least 8 weeks of ATO (n ¼ 16 studies. patients) showed that two of six patients in the low-risk group had hematologic improvements in erythrocytes (HI-E), including

s one patient who achieved transfusion independence. In the Current and proposed clinical trials of Trisenox in MDS high-risk group (n ¼ 10), two patients had HI-E and three patients had stable disease, while three progressed to AML. Trisenoxs is currently being studied in MDS patients in two s Evaluation of apoptosis in CD34+ cells shows an increase of Phase II multicenter trials. The end points of the Trisenox MDS annexin-V expression after 8 weeks of treatment. Despite the trials are those that have been proposed by the International small number of patients and the limited follow-up currently Working Group to standardize criteria for drug response. The available, these results clearly show that ATO has clinical response criteria are based on drug-related alterations in the activity in MDS. natural history of the disease and alleviation of MDS-related Preliminary results from both trials provide evidence for the 81 complications, translating to an improved quality of life. drug’s activity in patients with advanced, transfusion-dependent MDS. The drug has been well tolerated, an important consideration in the elderly patients who comprise most of the Ongoing trials population of individuals with MDS. The study design of the current trials is an open-label, two-stage design in adults representing all FAB MDS subtypes.82 In the United States Central Trial, patients receive Trisenoxs 0.25 mg/ Future trials kg/day for ﬁve consecutive days of weeks 1 and 2 of a 28-day cycle. Patients are stratiﬁed by IPSS criteria into two study Additional trials of Trisenoxs in MDS have been initiated. These cohorts: lower-risk (low or intermediate-1 IPSS category) and trials are being designed to evaluate Trisenoxs as monotherapy

Table 1 Preliminary ﬁndings in a Phase II clinical study of Trisenoxs in patients with MDS Low risk High risk Evaluable patients 11 9 Median cycles administered, n (range) 4 (2–6) 4 (1–9) Partial response 1 0 Improveda 03 Stable disease 6 0 Disease progression 3 1 Off study before disease assessment 1 5 Hematologic response 1 major (erythroid; transfusion independent) 1 minor (erythroid; transfusion independent) 1 major (erythroid; transfusion independent) 1 major platelet response aMono- or bilineage response or X50% decrease in transfusion requirement from baseline.

Leukemia Trisenoxs in the treatment of MDS A List et al 1505 and in combination with other agents (eg hematopoietic growth precursors and leukemia progenitor formation in myelodysplastic factors and thalidomide) that either have independent activity in syndromes. Blood 2001; 97: 1427–1434. the disease or enhance the antitumor activity of Trisenoxs. 3 Raza A, Gezer S, Mundle S, Gao X-Z, Alvi S, Borok R et al. Some of these studies investigate alternative dosing schedules, Apoptosis in bone marrow biopsy samples involving stromal and hematopoietic cells in 50 patients with myelodysplastic syn- similar to the European multicenter trial. s dromes. Blood 1995; 86: 268–276. Before the patient selection criteria for Trisenox therapy can 4 Greenberg PL. Apoptosis and its role in the myelodysplastic be established, further data are needed from current trials. 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