How to Manage Acute Promyelocytic Leukemia

HOW TO MANAGEy How to manage acute promyelocytic leukemia

J-Q Mi, J-M Li, Z-X Shen, S-J Chen and Z Chen

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML). The prognosis of APL is changing, from the worst among AML as it used to be, to currently the best. The application of all-trans-retinoic acid (ATRA) to the induction therapy of APL decreases the mortality of newly diagnosed patients, thereby significantly improving the response rate. Therefore, ATRA combined with anthracycline-based chemotherapy has been widely accepted and used as a classic treatment. It has been demonstrated that high doses of cytarabine have a good effect on the prevention of relapse for high-risk patients. However, as the indications of arsenic trioxide (ATO) for APL are being extended from the original relapse treatment to the first-line treatment of de novo APL, we find that the regimen of ATRA, combined with ATO, seems to be a new treatment option because of their targeting mechanisms, milder toxicities and improvements of long-term outcomes; this combination may become a potentially curable treatment modality for APL. We discuss the therapeutic strategies for APL, particularly the novel approaches to newly diagnosed patients and the handling of side effects of treatment and relapse treatment, so as to ensure each newly diagnosed patient of APL the most timely and best treatment.

Leukemia (2012) 26, 1743--1751; doi:10.1038/leu.2012.57 Keywords: acute promyelocytic leukemia (APL); all-trans-retinoic acid (ATRA); arsenic trioxide (ATO)

INTRODUCTION In this review, we introduce the therapeutic strategies of APL, Acute promyelocytic leukemia (APL) is a distinct subtype of acute including the treatment of newly diagnosed and relapsed myeloid leukemia (AML) characterized by its abnormal promye- patients, as well as the ways to deal with the side effects. locytes infiltrating bone marrow and other hematopoietic organs In addition, we show a novel paradigm of translational medicine and its t(15;17) translocation leading to PML--RARa fusion gene. here. The experimental and clinical researches have promoted and There have been tremendous innovations in therapeutic strategies inspired each other, which has led to a revolution in the treatment and substantial improvement in the outcome of patients since the of leukemia. application of all-trans-retinoic acid (ATRA).1 The leukemia cells undergo terminal differentiation under the remission induction of ATRA, in contrast to cytolysis with conventional chemotherapy, LEUKEMOGENESIS OF APL AND MECHANISMS UNDERLYING which ameliorate the coagulopathy, thereby reducing the EFFECT OF ATRA/ATO requirement of blood products and the difficulty of initial More than 98% of APL patients harbor t(15;17) in leukemia cells,7 treatment. This effect has been particularly evident in developing which results in the fusion of RARa on chromosome 17 to PML on countries, due to the limitations of medical resources. At present, chromosome 15.8 The consequence is the generation of the ATRA combined with chemotherapy became the classic treatment PML--RARa fusion gene encoding a chimeric protein. APL has a of APL owing to the significantly improved long-term survival rate. nearly constant incidence with age, suggesting that it arises from The further amelioration of chemotherapy in the past two a single rate-limiting genetic event and PML--RARa is the constant decades, for example, the application of high-dose cytosine genomic abnormality in APL cells.9 Transgenic mice with arabinoside to high-risk patients2,3 and the recognition of the PML--RARa develop a typical APL phenotype.10,11 These findings importance of maintenance therapy,4 has led to further improve- in addition to other evidence have established PML--RARa as the ment of APL survival.5 However, it has always been our dream to key driver of APL leukemogenesis. lower the relapse rate and to reduce side effects through even PML--RARa protein is an abnormal transcriptional factor, more effective therapy targeting APL cells. The use of arsenic retaining N-terminal RBCC (RING, B Boxes and coiled coil) domains trioxide (ATO) in the last two decades, from salvage therapy for of PML and most portions of RARa.12 PML--RARa expression is relapsed cases to the first-line therapy,6 gradually revealed its believed to exert a dominant-negative dual-function on each of its superiority in the treatment of APL, proven by a sizable proportion parental proteins, which are demonstrated to be involved in of patients cured by just a single agent as the compound directly various cellular processes such as myeloid differentiation, apop- targets PML--RARa. Moreover, a great majority of patients tosis and DNA replication and repair.13 Several crucial PML--RARa achieved a 5-year disease-free survival when treated with the features contribute to APL pathogenesis, such as the absolute combination of ATO and ATRA. Therefore, the association of ATO binding with RXRa,14 -- 16 interaction with the chromatin remodel- and ATRA5 is gradually being accepted by all. We have confidence ing complexes17 -- 19 and functional disruption of other key in the hope that it will become a new standard treatment for APL, myeloid transcription factors (that is, PU.1).20 In addition, other although the results of randomised comparisons are still being genetic alterations are present such as mutations in NRAS, awaited. KRAS, FLT3--internal tandem duplication (FLT3--ITD) and point

State Key Laboratory for Medical Genomics and Department of Hematology, Shanghai Institute of Hematology, Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. Correspondence: Dr J-Q Mi or Dr Z Chen, State Key Laboratory for Medical Genomics and Department of Hematology, Shanghai Institute of Hematology, Rui Jin Hospital, Shanghai Jiao Tong University School of Medicine, 197 Rui Jin Er Road, Shanghai 200025, China. E-mail: [email protected] (J-QM) or [email protected] (ZC) Received 24 August 2011; revised 20 February 2012; accepted 21 February 2012; accepted article preview online 16 March 2012; advance online publication, 30 March 2012 APL and its treatment J-Q Mi et al 1744 mutations of FLT3--tyrosine kinase domain (FLT3--TKD) as well as intermediate risk (WBC count o10 Â 109/l, platelet count Jak1,21 -- 23 which favor APL progression in patients. p40 Â 109/l) and high risk (WBC count X10 Â 109/l).39 Although The critical role of PML--RARa in APL leukemogenesis has also it is reported from time to time that CD56 expression in patients suggested itself as a potential target for APL treatment. Indeed, with APL may be an independent factor predicting poor PML--RARa represents the direct pharmaceutical target of two prognosis, further confirmation is needed.40,41 effective agents for APL, ATRA and ATO (Figure 1a). Arsenic binds We agree with the views of Sanz et al.42 that three simultaneous to the RBCC domain of PML moiety,24,25 whereas ATRA targets the actions should be done when a diagnosis of APL is suspected: the RARa moiety of PML--RARa. Both the agents can induce the start of ATRA therapy before confirmation of the diagnosis; degradation of PML--RARa,26 -- 29 which probably accounts for institution of supportive measures; and rapid confirmation of their curable effects. genetic diagnosis. As Tallman et al.5 mentioned, bleeding is the Leukemia-initiating cells (LICs) are a rare subpopulation in the most dangerous complication and represents a major cause of bulk of leukemia, which are pluripotent, self-renewing and early death (ED) for the newly diagnosed APL patients. When APL mitotically quiescent, and responsible for the development, is highly suspected with clinical symptoms such as peripheral progression and maintenance of leukemia.30 The non-cycling blood smear and bone marrow morphology, it’s not necessary to status and inherent or acquired drug-resistant feature of LICs wait for the confirmation by cytogenetic or molecular studies. make them insensitive to conventional chemotherapy, that could Immediate application of ATRA would be a wise choice, so that the explain the later relapse of leukemia. Although nearly all the APL biological signs of APL coagulopathy could be improved rapidly, patients could obtain complete remission using ATRA or ATO as a decreasing the risk of severe bleeding. For the high-risk patients single agent, most single ATRA-treated cases would relapse, with hyperleukocytosis (for example, WBC410 Â 109/l), once the contrarily to the situation of ATO, which could cure a sizable diagnosis is confirmed, chemotherapy should be initiated as soon portion (around 65%) of the patients,31 -- 33 suggesting that ATO as possible (immediately or be delayed for up to 1 day) to prevent targets the LICs in APL (Figure 1b). More recently, the targeted serious APL differentiation syndrome (DS). clearance of LICs by arsenic treatment has been reported in Supportive measures are particularly important in the first few mouse models.34,35 Besides PML--RARa, a number of proteins days after the beginning of APL treatment, especially for those have been described to have an important role in the counteracting the coagulopathy. Although severe bleedings can maintenance of LICs phenotype, many of which, indeed, have be significantly controlled with the use of ATRA, we still encounter been shown to be targeted by arsenic, including PML,35 Gli2(ref. 36) a small number of patients being on the verge of death when they and NFkB.37 However, ATRA has been reported to exert a dual come to seek treatment, with chief complaints being serious effect on LICs: induction of differentiation in the more mature bleedings.43 It must be emphasized that every positive effort blast population and induction of proliferation and/or self-renewal should be made, both in detection and in treatment. The of the LICs.38 Studies have shown that ex vivo treatment with ATRA determination of blood count, fibrinogen level, prothrombin time decreases APL LICs frequency.34 However, secondary transplant and partial thromboplastin time should be performed at least recipients still develop APL,34 suggesting that ATRA cannot twice a day. Appropriate measures should be taken, such as completely eradicate LICs. In vitro analysis of Sca1 þ /lin-- murine transfusions of fibrinogen, fresh frozen plasma and platelet hematopoietic stem cells transduced with PML--RARa has further concentrates, to maintain the platelet count at 30 Â 109/l or more shown that ATRA does not abrogate their stem cell capacity and and fibrinogen level at 1.5 g/l or more. In the circumstances of further induces proliferation of LICs.38 coagulopathy, the use of heparin has been basically abandoned, except in major deep vein thrombosis, which is very rare. It should be noted that lumbar puncture is not allowed until the INITIAL APPROACH FOR SUSPECTED APL coagulopathy is fully resolved in order to prevent iatrogenic In addition to common symptoms of leukemia, such as fever, bleeding, even for high-risk patients (such as patients with infection and anemia, APL is also characterized by a severe life- hyperleukocytosis). In addition, the newly diagnosed APL patients threatening coagulopathy resulting from disseminated intravas- often present pancytopenia, and some of them develop cular coagulation and/or fibrinolysis. Therefore, there are some agranulocytosis leading to serious infection. For this reason, it is difficulties in the treatment of this disease. It is found that essential to begin the anti-infectious therapy in a timely and leukocyte and platelet counts are important parameters to predict appropriate manner. the prognosis of patients. According to Sanz score, patients can be Currently there are several common methods to establish the divided into three groups: low risk of relapse (white blood diagnosis, among which the fastest and the best is the reverse cell (WBC) count o10 Â 109/l, platelet count440 Â 109/l), transcriptase PCR for the PML--RARa fusion transcript. It requires a

O O H3C CH3 CH3 CH3 O OH As As ATO ATRA O CH3 ATO ATRA

Binding Binding APL cells PML RBCC RARα

Partial LIC Ternimal differentiation Apoptosis clearance differentiation

Figure 1. Molecular mechanisms of ATO and ATRA for APL. (a) Synergistically targeted therapy of ATO and ATRA in APL. Arsenic binds to PML moiety of PML--RARa while ATRA binds through its RARa moiety, both of which initiate the degradation of PML--RARa in a proteasome- dependent way. (b) ATO facilitates the clearance of LIC of APL.

Leukemia (2012) 1743 -- 1751 & 2012 Macmillan Publishers Limited APL and its treatment J-Q Mi et al 1745 small sample, is easy to perform, even in case of low WBCs, and its Introduction of ATO and ATRA/ATO combination therapy positive result directly indicates that the ATRA treatment should Chinese groups were able to report on the first controlled study be effective.44 At the same time, we conduct karyotyping with pure ATO to deal with both relapsed and newly diagnosed routinely. Although this procedure costs more time and energy, APL patients.6,29,58 Of note, the response rate was as high as 85% it remains a classic diagnostic tool. Especially, in patients lacking among cases relapsed after previous ATRA and chemotherapy the typical PML--RARa fusion gene, other rare molecular subtypes treatment. In line with these successful therapeutic practices, could be identified by karyotyping, and subsequent reverse several working groups administered a single agent of ATO as transcriptase PCR analysis, such as PLZF--RARa resulted from first-line therapy, which turned out to be a good attempt and the t(11;17) (q23; q21),45 NuMA--RARa from t(11;17) (q13; q21)46 and effect was much better as compared with ATRA alone,59 -- 62 NPM1--RARa from t(5;17) (q35; q21).47 Florescence in situ suggesting that ATO could target the leukemia stem cells in an hybridization analysis has a role in the diagnosis with its unique APL setting. sensitivity and specificity, although it has limitations in probes. Several lines of evidence prompted us to consider a possible Florescence in situ hybridization remains currently the quickest new strategy in APL by combining ATRA and ATO for newly method in some countries to confirm the diagnosis. Anti-PML diagnosed patients. First, there is no obvious cross-resistance monoclonal antibody testing is a relatively effective screening between ATRA and ATO.29,58 Second, combination of the two method with many advantages, such as specificity, quickness and agents allows a significantly prolonged survival or even disease easy performance, but it is not yet widely used clinically.48 eradication in APL animals.63,64 Third, the two compounds target PML--RARa and modulate key networks involved in apoptosis/ differentiation via distinct but related pathways.24,65,66 Mechan- istically, the combined use of ATO with ATRA has brought about a INDUCTION THERAPY conceptual revolution of synergistic targeting of leukemia and ATRA plus chemotherapy thus impacts the conventional chemotherapy-based treatment. Given that the efficacy of chemotherapy alone on APL was Nevertheless, the possible additional side effects due to the far from perfect, although some reports were surprisingly good, combined use of the two agents likewise raised some concerns. the search for a more effective therapy had been a long-time We therefore carefully examined this aspect while conducting desire. A group from the Shanghai Institute of Hematology animal experiments and while analyzing the transcriptome and (SIH) revealed in the 1980s that ATRA could induce the cell proteome analysis data. No obvious enhancement of side effects differentiation of leukemic promyelocytes and could thus greatly or further activation of stress pathways was detected. On the basis improve the response rate of de novo APL. The complete of these facts, we decided to initiate the new clinical trial of remission (CR) rates are usually 87 to 94% using a classical dosage combination therapy in 2000. Indeed, we found61 that the ATRA/ of 45 mg/m2/day for 4 to 6 weeks.49 However, within 6 months of ATO combination for remission (with maintenance) therapy of APL remission, 8 out of the 24 patients in the first reported series brought much better results than either of the two drugs used relapsed while even higher relapse rates were reported elsewhere, alone in terms of the quality of CR and the status of the disease- indicating that ATRA monotherapy still led to a relatively high free survival. According to data from the SIH, Kaplan--Meier recurrence rate.1,50,51 Several working groups worldwide con- estimates that the 5-year EFS and OS in a group of 85 newly firmed that ATRA, followed by chemotherapy, was superior to diagnosed APL patients were 89.2% and 91.7%, respectively, chemotherapy alone.52,53 Consequently, European APL group demonstrating the high efficacy of ATRA/ATO treatment for newly compared the efficacy of two regimens, which were ATRA plus diagnosed APL.67 Recent literature supports our data in that the chemotherapy and sequential ATRA followed by chemotherapy, CR rate and EFS were relatively higher in the working groups using respectively. It was found that the former regimen gave out a ATO/ATRA combination 68,69 compared with the groups using ATO lower recurrence rate than the latter, with 2-year event-free alone.59,60,62 GIMEMA group carried out a randomized phase III survival (EFS) rates of 84 and 77%.54 ATRA plus chemotherapy study to compare ATO þ ATRA versus standard ATRA þ anthracy- (anthracyclines alone or with cytarabine (Ara-C)) has since been cline-based chemotherapy (AIDA regimen) for newly diagnosed considered as the classic approach, in which the use of non high-risk APL. We are eagerly anticipating their results. anthracyclines is mainly involved with daunorubicin and Idarubi- Mathews et al.70 suggested that mutant FLT3 was not an adverse cin. Their effects were believed to be basically the same,5 except indicator of poor prognosis for APL with ATO-based therapy, for a slight advantage of Idarubicin reported by a small number of which was supported by our group.67 literature, especially for the younger patients.55 Currently, we do At present, our induction therapy program is as follows61,67 2 not find significant effects of Ara-C for the low-risk patients (WBC (Figure 2): 25 mg/m ATRA orally per day, and 0.16 mg/kg As2O3 count p10 Â 109/l). In a joint analysis of results from a LPA 99 i.v. per day until documentation of CR. The reason for us to reduce trial Programa para el Estudio de la Terapeutica en Hemopatia the initial dose of 45 mg/m2 ATRA, which was once our own Maligna (PETHEMA group), where patients received no Ara-C in recommendation, to 25 mg/m2 is to avoid ATRA toxicity; we addition to ATRA, a high cumulative dose of idarubicin, and showed that this relatively low-dose ATRA achieved the same mitoxantrone and an APL 2000 trial (French--Belgian--Swiss APL therapeutic effects as the conventional dosage,28 although the group), where patients received Ara-C in addition to ATRA and a standard dose of 45 mg/m2 is still used in many other medical lower cumulative dose of daunorubicin, 3-year survival was similar centers worldwide. When the patient’s WBC is more than in patients with a WBC count less than 10 Â 109/l; although, 3-year 10 Â 109/l, we use hydroxyurea 20--40 mg/kg daily at first, which cumulative incidence of relapse was significantly lower in the LPA can be effective in some patients, then 3 days after, switch to IA 99 trial: 4.2 versus 14.3% (P ¼ 0.03).4 However, for high-risk (WBC regimen if the WBC count keeps rising. count410 Â 109/l) patients, large doses of Ara-C could act Our novel strategy in APL therapy has thus broken away from better.2,4,56 the conventional chemotherapy-based approaches to remission Although ATRA plus chemotherapy gained great effects, there induction of leukemia, and it has translated the targeted killing are still problems such as relapse, severe side effects of effect of ATO on APL cells proven in experimental studies into chemotherapy and so on. The 5-year relapse-free survival and clinical practice efficiently. In addition, our program has also overall survival (OS) from SIH were only around 34.0 and 52%.57 demonstrated its economic advantages, especially as compared That’s why we were trying to find other alternative clinical with high-dose chemotherapy. Currently in China, the daily cost of approaches. The aim was to further improve the cure rate. In this ATO (provided by Yida Pharmaceutical Company of the Harbin context, the appearance of ATO gives us new hope. Medical University, Harbin, China) is 30 US dollars, whereas the

& 2012 Macmillan Publishers Limited Leukemia (2012) 1743 -- 1751 APL and its treatment J-Q Mi et al 1746 from high-dose Ara-C, which could thereby increase the risk of serious infections. Our recommendation is (Figure 2) three courses of consolidation therapy: Each course includes three consecutive regimens, that is, DA regimen (daunorubicin, 45 mg/m2 per day for 3 days; Ara-C, 100 mg/m2 per day for 7 days), Ara-C ‘pulse’ regimen (Ara-C, 1.5--2.5g/m2 per day for 3 days) and HA regimen (homoharringtonine, 2--3 mg/m2 per day for 3 days; Ara-C, 100 mg/m2 per day for 7 days). In the countries where homoharringtonine is unavailable, we recommend application of MA regimen (Mitox- antrone 6--10 mg/m2 per day for 3 days, Ara-C 100 mg/m2 per day for 7 days). This program can be said to be a supplement to the remission induction program mentioned above, for few chemotherapy is given in our remission induction regimen. However, in consideration of the toxicities of high-dose Ara-C, we just select the middle dosage. In contrast, the remission induction regimen of the North American work group only consists of ATRA and conventional Figure 2. Shanghai APL trial. DA, DNR+Ara-C; DNR, Daunorubicin; chemotherapy, which explains why this group aptly adds ATO in HA, HH+Ara-C; HH, Homoharringtonine; HU, Hydroxyurea; 6-MP, the consolidation therapy. According to the recent data of this 6-Mercaptopurine; MTX, Methotrexate. important trial (Leukemia Intergroup Study C9710), the addition of ATO is an important improvement to the treatment strategy since the 3-year EFS reached 80%,76 which is consistent with our point of view that the treatment of APL should target both PML and ATRA (provided by Shanghai Rui Jin Hospital pharmacies, RARa to fulfill a maximum efficacy. In this study, both of the two Shanghai, China) costs no more than 20 US dollars for each randomized groups were given the same induction therapy (ATRA, course (4--6 weeks) of treatment. Ara-C and daunorubicin). For the consolidation regimen, the trial group received two 25-day courses of ATO consolidation immediately after induction, while the control group received two Introduction of other arsenic compounds for APL therapy 71 courses of consolidation therapy with ATRA plus daunorubicin. A It was reported by Lu et al. that, instead of the first-line i.v. ATO very significant advantage in 3-year EFS and DFS (80% and 90%, treatment, oral tetra-arsenic tetra-sulfide (As4S4) also yielded good respectively) was shown in the ATO group compared with the responses in APL patients. The randomized and controlled clinic control group, although the results of the control group were trial, led by Peking University Institute of Hematology and SIH, slightly unsatisfactory. The administration of ATO allows us to investigating ATO or As4S4 combined with ATRA for the newly generate further thinking: For the consolidation, can ATO replace diagnosed APL, is being conducted in many hospitals in China. all or part of the conventional chemotherapy? And, when is the This clinical trial is scheduled to include 250 patients randomized best time to use ATO? Future research will tell us the answers to to ATRA þ ATO or ATRA þ As4S4 group. Currently, the these questions of great interest. enrollment is nearing completion. The preliminary results No matter which consolidation therapy used, patients must suggested As4S4 yielded a similar CR and 2-year EFS rate as the reach a molecular remission (MR) (PCR negativity of PML--RARa in ATO did. However, the side effects seemed fewer and the patients the marrow) before commencement of maintenance therapy. If needed much less hospitalization time (Huang XJ et al., personal not yet met, the prognosis of the patient will be poor, and salvage communication). We expect good results, for the oral As4S4 therapy should be considered. If MR is obtained after salvage, (provided by Tian Kang Pharmaceutical Company, Anhui, China) is autologous hematopoietic stem-cell transplantation (HSCT) is more conveniently used, and also cheaper. suggested, but if the fusion gene transcripts are persistently positive, allogeneic HSCT should be recommended. CONSOLIDATION THERAPY Although consensus has not yet been reached on the details of MAINTENANCE THERAPY specific consolidation therapy, it has been widely accepted that at The importance of ATRA plus chemotherapy maintenance was least 2--3 times of anthracycline-based chemotherapy should be addressed by both the North American Intergroup Study I0129 given to the low-risk and intermediate-risk patients.5,49 However, and the European APL Group.53,54 Ten years later, the European there is no conclusion whether or not the administration of ATRA APL Group re-analyzed this issue. It was shown that the 10-year is really an advantage for the consolidation therapy, although relapse rate was the lowest (13.4%) in the ATRA plus chemother- some investigators reported that the relapse rate of APL was apy maintenance group, as compared with that of chemotherapy reduced in their results as compared with the historical alone, ATRA alone as maintenance and no maintenance groups, control.72,73 which were 23.4%, 33% and 43.2%, respectively. The differences of In 2006, the European APL Group reported2 a randomized relapse rates were more significant in the patients with initial WBC study of 340 patients. For the high-risk patients (WBC410 Â 109/l), count higher than 5 Â 109/l, which was 20.6% with combined it was shown that adding Ara-C to anthracyclines was superior to (ATRA plus chemotherapy) maintenance and 68.4% with no high-dose anthracyclines used as single agents, especially in maintenance. However, the Japan Adult Leukemia Study Group reducing relapse rate. In 2009, the same working group3 (JALSG) found little difference with or without maintenance. One compared the results of APL93 trial and APL2000 trial and explanation to this situation could be that the JALSG trial only confirmed that high-dose Ara-C could significantly lower the compared no maintenance versus six courses of intensified cumulative incidence of relapse and ameliorate survival in high- maintenance chemotherapy rather than ATRA maintenance.77 risk patients, which was supported by both German AML Although ATRA plus chemotherapy was originally considered to Cooperative Group74 and PETHEMA Group.75 However, one should be the best solution of maintenance therapy, with our in-depth pay attention to the severe bone marrow suppression resulting in vitro study on the mechanisms of ATRA and ATO, a better

Leukemia (2012) 1743 -- 1751 & 2012 Macmillan Publishers Limited APL and its treatment J-Q Mi et al 1747 understanding has been obtained on the importance of the emphasizes ECG monitoring and maintenance of electrolyte combined use of various drugs with different therapeutic targets. within normal ranges, for example, the serum potassium above Thus, for the maintenance treatment, we have been optimizing 4.0 mEq/l and serum magnesium above 1.8 mg/dl. In patients the idea of ATO/ATRA combined with chemotherapy. On the basis whose absolute QT interval value is longer than 500 ms, ATO of a previous report,61 our maintenance therapy currently consists should be withheld or discontinued if necessary.81 -- 83 of five cycles of sequential use of ATRA, ATO and low-dose The total dose of ATO is 1600--1800 mg in our entire treatment chemotherapy (Figure 2): ATRA, 25 mg/m2 per day for 30 days; regimen. We believe that this dosage is safe, as no patient As2O3, 0.16 mg/kg per day for 30 days; 6-mercaptopurine, 100 mg/ discontinued the treatment because of the toxicity of ATO. At the day for 30 days or 15--40 mg of methotrexate once a week for 4 same time, arsenic concentrations in the urine of patients who weeks. Notably, the 5-year relapse-free survival and OS of our had ceased maintenance treatment for 2 years were below the patients who achieved CR were 94.8% and 97.4%, respectively.67 safety limits recommended by government agencies in several Although it was usually a common practice to avoid CNS countries or regions, whereas arsenic levels in plasma, nails and prophylaxis for patients without hyperleukocytosis, among whom hair were only slightly higher than those found in healthy the risk of CNS relapse is extremely low,42 we still recommend 4--6 controls.67 times of CNS prophylaxis, methotrexate (10--15 mg), dexamethasone (5 mg) (or Prednisolone 40 mg) and Ara-C (40--50 mg), during maintenance therapy, in considering that the first site of MANAGEMENT OF RELAPSE relapse was exclusively the CNS in all of the total four relapses out The determination of minimal residual disease is especially of our recent series of 80 patients achieving complete remission, important to the patients in remission. The first sign of recurrence and most of the relapsed patients exhibited no hyperleukocytosis is usually indicated by the PCR detection of PML--RARa transcripts initially.67 Nevertheless, for the patients with high WBC counts, the in bone marrow. The vast majority of patients relapse in the first 3 CNS prophylaxis should be carried out for at least 6--8 times. years after the end of treatment;84 however, there are also individuals who only relapse in the extramedullary sites (such as the CNS). APL DS A number of international clinical trials, such as the APL study of DS is a common life-threatening complication in the ATRA or ATO German AML Cooperative Group (GMLCG) including HD ARAC-C, treatment, with a frequency being around 25% both in US and in the APL2000 trial of European APL Group and ours, have shown Europe.53,78 The common clinical symptoms were dyspnea with that the CR rate of APL is more than 90%,1,4,74 the 10-year relapse interstitial pulmonary infiltrates, peripheral edema, unexplained free survival was similar in GMLCG (75.5%) as that of European APL fever, weight gain, hypotension and acute renal failure.79 When Group (76.3%), but there are still about 25% of patients who suffer these happen, early use of chemotherapy and high dose of from relapse.85 For the APL patients in relapse, the treatment dexamethasone can decrease the mortality down to 1% or strategy is remission re-induction and remission consolidation.5,49 lower.42 ATO is considered to be the first-line treatment of relapsed APL It has been described that prophylactic treatment of APL DS by without previous exposure to the compound, which could allow a prednisolone can reduce the incidence of DS significantly,80 but it remission rate of re-induction to more than 80%.86 In a multi- is risky to use the steroids routinely as prophylaxis. We echo Dr center clinical study in the US, 40 relapsed APL patients were Tallman’s view: ‘caution should be exercised, because the given ATO as remission induction, and 34 (85%) of them achieved administration of corticosteroids to neutropenic patients may CR. With subsequent ATO treatment or HSCT, the 18-month OS predispose them to infection, such as sepsis, or fungal infection’.5 and relapse-free survival were 66% and 56%, respectively.81 Therefore, only in the treatment of patients with hyperleukocy- Alimoghaddam et al.87 have also conducted similar research in tosis (at least WBC430 Â 109/l) at diagnosis, sometimes accom- which 31 patients who relapsed from ATRA plus chemotherapy panied by coagulopathy, should dexamethasone be given were reinduced to remission and consolidated by a single agent of preventively at a dose of 10 mg twice daily. Moreover, when ATO. After a median time of 32 months of follow-up, it was found dealing with DS, corticosteroids can also participate in hemostasis. that 10 (41.6%) patients relapsed in the 24 CR2 patients. The Troubled by the serious DS, since the late 1990s, at SIH, ATRA 2-year DFS and OS were 54.6% and 81.1%, respectively. This report has been used at an oral dose of 25 mg/m2 per day as a routine from Iran reminds us that, although the single agent of ATO is treatment for APL patients, after a study showing that lower doses quite effective on remission induction, the recurrence rate after of ATRA had the same therapeutic effect as the conventional CR2 induced by ATO is not low. Thus, post-remission therapy is dosage but with fewer side effects, including DS.28,61 In the past essential for the prognosis of patients. two decades, the frequency of DS in our patients has been very Once CR2 is achieved, the treatment strategy after induction low,67 with the exception of a few patients presenting hyperleu- therapy remains controversial. The options include continued kocytosis at the diagnosis of the disease. administration of ATO, ATRA combined with chemotherapy and/or ATO, and HSCT.49,88 Thirugnanam et al.89 treated 37 patients with relapsed APL. Of these patients, 33 attained MR with ATO-based SIDE EFFECTS OF ATO induction therapy (including three types of regimens, that is, ATO ATO proves to be quite safe. When compared with anthracyclines, alone, ATO plus ATRA, ATO plus ATRA plus anthracycline). Among bone marrow myelosuppression due to ATO appears to be minor. them, 14 patients chose autologous stem cell transplantation as The common adverse effects are mainly grade I--II hepatotoxicity, subsequent treatment, and the remaining 19 were given a single gastrointestinal reactions, neurotoxicity and very rarely, grade III-- agent of ATO or ATO combined with ATRA. The 5-year EFS of these IV hepatotoxicity, which are usually reversible.59,60 Thus, in clinical two groups of patients were 83.33% and 34.45% (P ¼ 0.01), practice, we recommend administration of some therapeutic respectively, as calculated with the Kaplan--Meier method. In agents (for example, Diammonium Glycyrrizinate, a drug based on the study of Ferrara et al.,90 of the six patients who underwent the Traditional Chinese Medicine; Polyene Phosphatidylcholine) to autologous stem cell transplantation after achieving MR after prevent liver damage. relapse, five survived and remained in MR for a long term, and Another important potential adverse event related to ATO is only one died of primary disease after recurrence. In 2007, the manifested by prolongation of the QT interval on the ECG, which European Group for Blood and Marrow Transplantation compared may lead to torsade de pointes, a life-threatening ventri- the follow-up data of 625 patients treated by HSCT and found that cular arrhythmia. Proper management of patients given ATO there was no significant difference in leukemia-free survival

& 2012 Macmillan Publishers Limited Leukemia (2012) 1743 -- 1751 APL and its treatment J-Q Mi et al 1748 between the autologous group and the allogeneic group,91 with a has recently attracted attention again from investigators.33,95,96 lower transplant-related mortality and a higher relapse incidence Park et al.97 reported 1400 cases of APL from 1992 to 2007, the overall in the autologous group. We therefore recommend that, for ED rate was 17.3%, and only a modest change in ED was observed patients with relapsed APL, once MR is achieved by ATO-based over time. Lehmann et al.98 reported 105 cases of APL patients therapy, the autologous stem cell transplantation should be among whom the frequency of ED (within 30 days) actually conducted, whereas for those who can not achieve MR, allogeneic reached 29%, a rate significantly higher than those in non-APL stem cell transplantation could be the choice. AML, especially evident in the elderly (460 years) population. As an anti-CD33 monoclonal antibody, gemtuzumab ozogami- For those EDs, 41% died from hemorrhagic complications, most of cin (GO) was approved by the US FDA in 2000 for the single-agent which were CNS bleeding. Therefore, early diagnosis, and proper treatment of elder patients with relapsed APL. The recommended handling of hemorrhagic diathesis is proven to be especially dose was 9 mg/m2 i.v. (given on days 1 and 15). As the CD33 important.98 Thus, for the novo APL patients, the treatment should antigen is often expressed on the surface of APL cells, the be further optimized. Our aim is to deliver the most timely and administration of GO could increase the MR rate. Lo-Coco et al.92 best treatment to each newly diagnosed APL patient, that is, to gave GO to 16 molecularly relapsed patients, 14 patients mobilize our entire human and material resources if necessary, responded, with a median MR time of 15 months for 7 of them, including emergency room, intensive care unit, multi-disciplinary with the other 7 patients relapsing soon after. Among the relapsed team of physicians and nurses, to ensure the maximum saving of patients, two continued GO treatment and both achieved MR lives at the onset of disease. More importantly, as Park et al.97 again. It was demonstrated that a single agent of GO exerts mentioned, there is a clear need to provide the knowledge significant effects on the APL patients with molecular relapse. As necessary to recognize APL as a medical emergency that requires to the combination therapy, Aribi had conducted relevant specific and simultaneous actions, including a prompt initiation of research88 in which the re-remission rate was 100% with ATRA, aggressive supportive care to counteract the coagulopathy combination treatment of ATO, ATRA and GO. However, because and transfer to experienced medical centers when the disease is of the limited sample size (n ¼ 8), these data need to be further first suspected. investigated. For those high-risk patients, we are further looking for better treatment; will it be the median-dose or high-dose chemotherapy, or ATO, or even a combination of both? The answer is to be given CNS RELAPSE in the future series of clinical trials. However, for those low-risk As the prognosis of APL patients is getting much better, the issue patients, ATO þ ATRA combined with less chemotherapy may be a of CNS relapse is becoming increasingly important and we believe more appropriate choice. In our 85 cases of APL patients,67 none an overall treatment strategy of APL seems unreasonable without of them developed therapy-related myelodysplastic syndrome- intrathecal prophylaxis. At present, the relapse rate is more than acute myelogenous leukemia or other malignancies. The possible 1% in a 5-year follow-up, especially in patients with initial WBC explanation may be the absence of VP-16 in our protocol, and also greater than 10 Â 109/l, in which the recurrence rate could exceed may be the relatively lower intensity of chemotherapy. In the 5%.49,93 Once a CNS relapse is recognized, we recommend reports of working groups with more intensive chemotherapy, for intrathecal therapy with methotrexate (10--15 mg), dexametha- example, in the GIMEMA group using VP-16, the incidence of MDS sone (5 mg) (or Prednisolone 40 mg) and Ara-C (40--50 mg) 2--3 or AML after APL treatment was 6.5%, whereas in the studies of times per week until complete clearance of blasts in the European APL group which omitted the application of VP16 that cerebrospinal fluid. At the same time, systemic medication, incidence was 0.97%.99,100 including ATO and ATRA, should be started. However, simulta- The cheaper prices of ATRA and ATO (provided by the Chinese neous chemotherapy is not recommended because of its pharmaceutical manufacturers) make them widely used in China. myeloablative effect resulting in a rapid decline in platelets count, In some other developing countries like India and Iran ATO is also which may lead to the unavailability of lumbar puncture. available, however, these two drugs are more expensive on Subsequently, at least 6--8 intrathecal therapiess are to be international markets, especially ATO. Thus, they are often more performed as consolidation. Owing to unfortunately repeated accessible in the richer North America and Western countries, yet lumbar punctures, each of them should be carried out cautiously. lack affordability to the APL patients from many other countries. The chemotherapy drugs should be injected after confirmation of For this reason, we regret that such a good treatment is difficult to the successfulness of the procedure, thereby reducing the be widely spread because of economic reasons. To a certain iatrogenic possibilities of paralysis resulted from multiple in- extent, there is an absence in the fairness of health care for those trathecal therapies. For consolidation chemotherapy, regimens patients in poor countries. Currently, the As4S4 developed with high CNS penetration (for example, high-dose Ara-C) independently in China is similar to the ATO in terms of efficacy, could be given, and allogeneic or autologous transplants and its oral administration makes it more conveniently used. After including appropriate craniospinal irradiation should be under further clarifying its efficacy, in consideration of its relatively lower consideration. price, we will encourage the Chinese companies to provide it to the world when possible at a reasonably low cost, to make sure that each patient receives treatment of an equally high quality. FUTURE PERSPECTIVES However, arsenic is not a panacea, and there are still relapses It has been 27 years since 1985, when the world’s first patient after ATO. Recently, a Japanese working group demonstrated from received ATRA in Shanghai. APL has experienced the conversion a study of two cases of relapsed patients that the mechanism for from the most lethal to the most curable acute leukemia. The ways ATO-resistance may be missense mutations in PML--RARa coding of treatment have also turned from the original single chemother- sequence, resulting in amino-acid substitutions of A216V and apy to comprehensive treatment, which consists of not only L218P in the PML B2 motif of the RBCC domain.101 On the other chemotherapy, but particularly targeting therapy of ATRA and hand, we recently found DNMT3A mutations in a relapsed ATO and salvage therapy of autologous or allogeneic HSCT, patient.102 These results have prompted us to further identify as well. the mechanisms of drug resistance in future work, so that the Although good prognosis has been demonstrated in APL as subset of patients who may develop resistance could be screened compared with other leukemia, how to further improve the cure out earlier in the treatment, and specific therapeutic strategies can rate is always a question worth thinking about. ED, the term be given from the very beginning, to finally alter the prognosis of proposed 20 years ago when ATRA had not been widely used,94 these patients.

Leukemia (2012) 1743 -- 1751 & 2012 Macmillan Publishers Limited APL and its treatment J-Q Mi et al 1749 It should be particularly emphasized that where ATO or 15 Zeisig BB, Kwok C, Zelent A, Shankaranarayanan P, Gronemeyer H, Dong S et al. conventional ATRA is ineffective, either given alone or combined, Recruitment of RXR by homotetrameric RARalpha fusion proteins is essential for other different therapeutic strategies, such as liposomal ATRA, can transformation. Cancer Cell 2007; 12:36--51. be tried under permitting conditions. Douer et al.103 reported that 16 Kamashev D, Vitoux D, De The H. PML-RARA-RXR oligomers mediate retinoid and liposomal ATRA was effective in inducing CR in newly diagnosed rexinoid/cAMP cross-talk in acute promyelocytic leukemia cell differentiation. J Exp Med 2004; 199: 1163 -- 1174. and relapsed patients, and it can induce MRs without chemother- 17 Villa R, Pasini D, Gutierrez A, Morey L, Occhionorelli M, Vire E et al. Role of the apy in some patients, especially in the low-risk cases. However, polycomb repressive complex 2 in acute promyelocytic leukemia. Cancer Cell this drug is currently unavailable commercially, and we are 2007; 11: 513 -- 525. 104 looking forward to more and better results. 18 Boukarabila H, Saurin AJ, Batsche E, Mossadegh N, van Lohuizen M, Otte AP et al. How to improve the quality of life of patients without affecting The PRC1 Polycomb group complex interacts with PLZF/RARA to mediate treatment efficacy? It is also an issue we are often thinking about. leukemic transformation. Genes Dev 2009; 23: 1195 -- 1206. Oral ATRA, oral arsenics and even oral chemotherapy drugs have 19 Pietersen AM, van Lohuizen M. Stem cell regulation by polycomb repressors: given rise to our expectations. We believe that the successful postponing commitment. Curr Opin Cell Biol 2008; 20: 201 -- 207. model of APL can also shed light on the therapy of other acute 20 Wang K, Wang P, Shi J, Zhu X, He M, Jia X et al. PML/RARalpha targets promoter regions containing PU.1 consensus and RARE half sites in acute promyelocytic leukemias, and even solid tumors, thereby improving the efficacy leukemia. Cancer Cell 2010; 17: 186 -- 197. of our anti-tumor therapy in various fields. 21 Chan IT, Kutok JL, Williams IR, Cohen S, Moore S, Shigematsu H et al. Oncogenic K-ras cooperates with PML-RAR alpha to induce an acute promyelocytic leukemia-like disease. Blood 2006; 108: 1708 -- 1715. CONFLICT OF INTEREST 22 Akagi T, Shih LY, Kato M, Kawamata N, Yamamoto G, Sanada M et al. Hidden The authors declare no conflict of interest. abnormalities and novel classification of t(15;17) acute promyelocytic leukemia (APL) based on genomic alterations. Blood 2009; 113: 1741 -- 1748. 23 Rampal RK, Levine RL. 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