Effective treatment of acute promyelocytic leukemia with all-trans-retinoic acid, arsenic trioxide, and gemtuzumab ozogamicin

Retinoic acid and arsenic trioxide for acute promyelocytic leukemia

BACKGROUND

All-trans retinoic acid (ATRA) with chemotherapy is the standard of care for acute promyelocytic leukemia (APL), resulting in cure rates exceeding 80%. Pilot studies of treatment with arsenic trioxide with or without ATRA have shown high efficacy and reduced hematologic toxicity.

METHODS

We conducted a phase 3, multicenter trial comparing ATRA plus chemotherapy with ATRA plus arsenic trioxide in patients with APL classified as low-to-intermediate risk (white-cell count, ≤10×10(9) per liter). Patients were randomly assigned to receive either ATRA plus arsenic trioxide for induction and consolidation therapy or standard ATRA-idarubicin induction therapy followed by three cycles of consolidation therapy with ATRA plus chemotherapy and maintenance therapy with low-dose chemotherapy and ATRA. The study was designed as a noninferiority trial to show that the difference between the rates of event-free survival at 2 years in the two groups was not greater than 5%.

RESULTS

Complete remission was achieved in all 77 patients in the ATRA-arsenic trioxide group who could be evaluated (100%) and in 75 of 79 patients in the ATRA-chemotherapy group (95%) (P=0.12). The median follow-up was 34.4 months. Two-year event-free survival rates were 97% in the ATRA-arsenic trioxide group and 86% in the ATRA-chemotherapy group (95% confidence interval for the difference, 2 to 22 percentage points; P<0.001 for noninferiority and P=0.02 for superiority of ATRA-arsenic trioxide). Overall survival was also better with ATRA-arsenic trioxide (P=0.02). As compared with ATRA-chemotherapy, ATRA-arsenic trioxide was associated with less hematologic toxicity and fewer infections but with more hepatic toxicity.

CONCLUSIONS

ATRA plus arsenic trioxide is at least not inferior and may be superior to ATRA plus chemotherapy in the treatment of patients with low-to-intermediate-risk APL. (Funded by Associazione Italiana contro le Leucemie and others; ClinicalTrials.gov number, NCT00482833.).

Outcomes in patients with relapsed or refractory acute promyelocytic leukemia treated with or without autologous or allogeneic hematopoietic stem cell transplantation

BACKGROUND

Outcomes in patients with acute promyelocytic leukemia (APL) have improved; however, a significant number of patients still relapse despite receiving all-trans-retinoic acid (ATRA) and arsenic-based therapies.

PATIENTS AND METHODS

Outcomes of patients with relapsed APL who were treated at our institution (1980-2010) and who received HCT were compared with those who received chemotherapy (CT) only.

RESULTS

Among 40 patients, 24 received HCT (autologous [auto] HCT, 7; allogeneic [allo] HCT, 14; both, 3); 16 received CT only. The median age at diagnosis was 36 years (range, 13-50 years), 31 years (range, 16-58 years), and 44 years (range, 24-79 years) for the auto-HCT, allo-HCT, and CT groups, respectively. Ten (100%) patients who received auto-HCT and 12 (71%) who received allo-HCT were in complete remission at the time of the HCT. The median follow-ups in the auto-HCT, allo-HCT, and CT groups were 74 months (range, 26-135 months), 118 months (range, 28-284 months), and 122 months (range, 32-216 months), respectively. Transplantation-related mortality (1 year) after auto-HCT and allo-HCT were 10% and 29%, respectively. The 7-year event-free survival after auto-HCT and allo-HCT was 68.6% and 40.6%, respectively (P = .45). The 7-year overall survival was 85.7%, 49.4%, and 40% in the auto-HCT, allo-HCT, and CT groups, respectively (P = .48).

CONCLUSION

Both auto-HCT and allo-HCT are associated with durable remission and prolonged survival. All 3 strategies (auto-HCT, allo-HCT, CT) were found to be feasible in the relapsed APL setting and result in long-term disease control in selected patients. In this retrospective analysis, overall survival for patients who received HCT was not significantly better than patients who received CT only, but a trend toward better outcomes was seen in patients who underwent auto-HCT, although not statistically significant.

Current strategies in immunotherapy for acute myeloid leukemia

The prognosis of acute myeloid leukemia, particularly when associated with adverse chromosomal or molecular aberrations, is poor due to a high relapse rate after induction chemotherapy. Postremission therapy for elimination of minimal residual disease remains a major challenge. Allogeneic hematopoietic stem cell transplantation has proven to provide a potent antileukemic effect. Novel strategies are needed for patients ineligible for this treatment. Here current immunotherapeutic concepts in acute myeloid leukemia in a nonallogeneic hematopoietic stem cell transplantation setting are reviewed. Data gathered with different monoclonal antibodies are discussed. Adoptive transfer of NK and T cells is reviewed, including evolving data on T-cell engineering. Results of systemic cytokine administration and of therapeutic vaccinations with peptides, modified leukemic cells and dendritic cells are presented. One particular focus of this review is the integration of currently running clinical trials. Recent immunotherapeutic studies have been encouraging and further interesting results are to be expected.

Antibody-based therapy of acute myeloid leukemia with gemtuzumab ozogamicin

Antibodies have created high expectations for effective yet tolerated therapeutics in acute myeloid leukemia (AML). Hitherto the most exploited target is CD33, a myeloid differentiation antigen found on AML blasts in most patients and, perhaps, leukemic stem cells in some. Treatment efforts have focused on conjugated antibodies, particularly gemtuzumab ozogamicin (GO), an anti-CD33 antibody carrying a toxic calicheamicin-g 1 derivative that, after intracellular hydrolytic release, induces DNA strand breaks, apoptosis, and cell death. Serving as paradigm for this strategy, GO was the first anti-cancer immunoconjugate to obtain regulatory approval in the U.S. While efficacious as monotherapy in acute promyelocytic leukemia (APL), GO alone induces remissions in less than 25-35% of non-APL AML patients. However, emerging data from well controlled trials now indicate that GO improves survival for many non-APL AML patients, supporting the conclusion that CD33 is a clinically relevant target for some disease subsets. It is thus unfortunate that GO has become unavailable in many parts of the world, and the drug's usefulness should be reconsidered and selected patients granted access to this immunoconjugate.

Efficacy and resistance of gemtuzumab ozogamicin for acute myeloid leukemia

Seventy to 80 % of patients with acute myeloid leukemia (AML) achieve complete remission following intensive chemotherapy, but more than 50 % of patients in remission subsequently relapse, which is often associated with clinical drug resistance. Therapy based on monoclonal antibodies (mAbs) has been developed to increase the selectivity of cytotoxic agents by conjugating them with a mAb. Gemtuzumab ozogamicin (GO) is a conjugate of a cytotoxic agent, a calicheamicin derivative, linked to a recombinant humanized mAb directed against the CD33 antigen, which is expressed on leukemia cells from more than 90 % of patients with AML. This conjugated mAb was introduced following promising results from phase I and II studies. However, the initial phase III study did not confirm the efficacy of GO in combination with conventional chemotherapies. Several subsequent phase III studies have shown the efficacy of GO in favorable and intermediate risk AML. Several resistance mechanisms against GO have been reported. Multidrug resistant (MDR) P-glycoprotein (P-gp), a trans-membrane glycoprotein that pumps out many anti-leukemic agents from cells, also affects GO. For this reasons, GO has been used in combination with MDR modifiers, such as cyclosporine, and in cases without P-gp. Several investigators have reported successful results of the use of GO in acute promyelocytic leukemia (APL). GO has also been described as effective in cases relapsed after treatment with all-trans retinoic acid (ATRA), arsenic acid and conventional chemotherapeutic agents. The efficacy of GO will be studied mainly in a favorable risk of AML, such as core binding factor leukemia and APL. In addition, suitable combinations with other chemotherapies and administration schedules should be discussed.

New Strategies to Direct Therapeutic Targeting of PML to Treat Cancers

The tumor suppressor function of the promyelocytic leukemia (PML) protein was first identified as a result of its dysregulation in acute promyelocytic leukemia, however, its importance is now emerging far beyond hematological neoplasms, to an extensive range of malignancies, including solid tumors. In response to stress signals, PML coordinates the regulation of numerous proteins, which activate fundamental cellular processes that suppress tumorigenesis. Importantly, PML itself is the subject of specific post-translational modifications, including ubiquitination, phosphorylation, acetylation, and SUMOylation, which in turn control PML activity and stability and ultimately dictate cellular fate. Improved understanding of the regulation of this key tumor suppressor is uncovering potential opportunities for therapeutic intervention. Targeting the key negative regulators of PML in cancer cells such as casein kinase 2, big MAP kinase 1, and E6-associated protein, with specific inhibitors that are becoming available, provides unique and exciting avenues for restoring tumor suppression through the induction of apoptosis and senescence. These approaches could be combined with DNA damaging drugs and cytokines that are known to activate PML. Depending on the cellular context, reactivation or enhancement of tumor suppressive PML functions, or targeted elimination of aberrantly functioning PML, may provide clinical benefit.

Acute promyelocytic leukemia: progress far and wide

In this issue of Blood, Rego and colleagues describe the exciting accomplishments of the International Consortium on Acute Promyelocytic Leukemia (IC-APL), an initiative of the International Members Committee of the American Society of Hematology (ASH).(1) The purpose of this initiative is to create a network of institutions in developing countries that will work in partnership with cooperative groups in the United States and Europe in order to close the gap in quality of care and outcomes in acute promyelocytic leukemia (APL) between developed and developing countries.

Gemtuzumab ozogamicin in acute myeloid leukemia: a remarkable saga about an active drug

Despite living in an era of unprecedented progress in the understanding of the genetic and molecular biology of acute myeloid leukemia (AML), this has not translated into significant advances in therapy. Never before have so many potential targets been studied. Yet most have not advanced beyond the phase 1 and, occasionally, phase 2 studies. The few ongoing phase 3 studies seem unlikely to have more than a marginal benefit, if at all. Thus, it is not surprising that in past few decades almost no new drugs for AML have received regulatory approval. In 2000, gemtuzumab ozogamicin (GO) was granted accelerated approval by the US Food and Drug Administration based on promising phase 2 data in relapsed older adults with AML. GO held promise as a new agent that also could be efficacious in newly diagnosed AML with acceptable toxicity. Several phase 3 studies were designed to test GO in this setting. The results of a randomized study by the Southwest Oncology Group led in 2010 to the voluntary withdrawal of this agent when improved efficacy could not be demonstrated and toxicity appeared excessive. Since then, 4 randomized studies have been completed that, in aggregate, strongly support the efficacy of this agent in newly diagnosed AML with acceptable toxicity. There is a very plausible explanation for this discrepancy, making a compelling case for reapproval of GO in AML.

Emerging new approaches for the treatment of acute promyelocytic leukemia

The introduction of all-trans retinoic acid (ATRA) in the late 1980s combined with anthracycline-based chemotherapy has revolutionized the prognosis of acute promyelocytic leukemia (APL) with more than 90% complete response rates and cure rates of approximately 80%. The subsequent advent of arsenic trioxide (ATO) in 1990s and progress in the treatment of APL have changed its course from a highly fatal to a highly curable disease. Despite the dramatic improvement in clinical outcome of APL, treatment failure still occurs due most often to early death. Relapse has become increasingly less frequent, most commonly occurring in patients with high-risk disease. A major focus of research for the past decade has been to develop risk-adapted and rationally targeted nonchemotherapy treatment strategies to reduce treatment-related morbidity and mortality to low- and intermediate-risk or older patients while targeting more intensive or alternative therapy to those patients at most risk of relapse. In this review, emerging new approaches to APL treatment with special emhasis on strategies to reduce early deaths, risk-adapted therapy during induction, consolidation and maintenance, as well as an overview of current and future clinical trials in APL will be discussed.

All-trans retinoic acid and late relapses in acute promyelocytic leukemia: very long-term follow-up of the North American Intergroup Study I0129

We report a long-term follow-up (median 11.8 years) of the First North American Intergroup Study. 379 patients were randomized to induction with ATRA or to chemotherapy. All complete responders (CR) received consolidation chemotherapy, then randomized to 1 year ATRA or observation. 245 patients received ATRA sometime during the study: 195 (80%) achieved a CR. Nine (4.6%) relapsed late (>3 years from CR), the last occurred after 4.6 years; 7 of them were still alive after 5.5-15 years. In APL patients, late relapses are uncommon, and those who sustain CR >5 years can be considered cured.

All-trans retinoic acid in the treatment of pediatric acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a rare form of acute myeloid leukemia with specific epidemiological, pathogenetic and clinical features. Its frequency varies widely among nations, with a decreased incidence among 'Nordic' origin populations. The molecular hallmark of the disease is the presence of a balanced reciprocal translocation resulting in the PML/RAR-α gene fusion, which represents the target of the all-trans retinoic acid (ATRA) therapy. The introduction of ATRA in conjunction with anthracyclines marked a turning point in the treatment of APL, previously associated with a significant morbidity and mortality. Nowadays the standard front-line therapy for pediatric APL includes ATRA in every phase of the treatment, resulting in a complete remission rate of 90-95%. Here we provide an overview of the role of ATRA in the treatment of pediatric APL, summarizing the most relevant clinical results of recent decades and investigating future therapeutic perspectives for children with APL.

Treatment breakthroughs for the management of acute myeloid leukemia

SUMMARY Although there has been substantial improvement in the survival of younger patients with acute myeloid leukemia (AML) since the 1970s, over the past two decades subsequent gains have been modest. Survival rates in older patients with AML remain dismal and have seen minimal change since the advent of modern induction chemotherapy. However, over the past decade, there has been a dramatic increase in the development of new therapies that have promising potential to further improve survival in both older and younger patients with AML. In this review, we will examine recent and ongoing breakthroughs in genetic discovery and gene profiling, intensification of induction chemotherapy, the development of novel agents, the management of older adults and allogeneic hematopoietic cell transplantation. We will also discuss exciting advances in the management of acute promyelocytic leukemia; a disease that is now imminently curable.

Acute promyelocytic leukemia: a population-based study on incidence and survival in the United States, 1975-2008

BACKGROUND

With the introduction of all-trans retinoic acid and arsenic trioxide, the management of acute promyelocytic leukemia (APL) has changed dramatically. We performed a population-based study of APL in the United States to determine its incidence and relative survival (RS) during a 34-year period.

METHODS

We identified 1397 patients diagnosed with APL between 1975 and 2008 in the Surveillance, Epidemiology, and End Results database. Patients were categorized into 4 age groups and 3 calendar periods. As a comparison, we also reviewed the outcome of APL patients treated at our institution during approximately the same time interval.

RESULTS

The incidences of APL increased with time period and patient age. Short- and long-term RS improved with each calendar period, with the greatest improvement occurring between 1991 and 1999; 5-year RS rates were 0.18 for patients diagnosed in 1975-1990, 0.52 in 1991-1999, and 0.64 in 2000-2008. Age was an important predictor of survival. For example, the 5-year RS rate in patients diagnosed in 2000-2008 was 0.38 for patients aged ≥ 60 years and 0.73 and 0.75 for patients aged <20 years and 20-39 years, respectively. Similar treads of improvements in the survival were observed in APL patients treated at our institution.

CONCLUSIONS

The incidence of APL has increased, especially in the last decade. Clinical outcome improved remarkably in patients with APL diagnosed from 1991 to 1999, mainly because of the increased use of all-trans retinoic acid.

Can we improve outcomes in patients with acute myelogenous leukemia? Incorporating HDAC inhibitors into front-line therapy

There is a need for improvements on the results of current therapies for patients with acute myelogenous leukemia (AML). A number of strategies are being used to achieve this goal. Here we present data that indicate that the addition of a histone deacetylase (HDAC) inhibitor, such as vorinostat, to idarubicin and cytarabine results in a very high response rate and can be safely administered to patients with leukemia. These results form the bases of the next SWOG front-line trial in AML. Here, we present the rationale for such combination and the studies that led to the support of this concept including both in vitro models and initial phase 1 trials.

Usefulness of CD11a and CD18 in flow cytometric immunophenotypic analysis for diagnosis of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is an aggressive disease that requires prompt diagnosis and therapy. Flow cytometry immunophenotyping can serve as a screening test for APL before the results of cytogenetic or molecular testing for t(15;17)(q22;q21)/PML-RARα are often dimly expressed or absent in APL. We used flow cytometry immunophenotyping with an antibody panel including CD11a and CD18 to assess 36 APL and 33 other AML cases. HLA-DR, CD11a, and CD18 were absent in 81% of APL and 12% of other AML cases (specificity, 88%). By further including combinations of HLA-DR-, CD2+, and either CD11a- or CD18-, we identified 92% of APL cases with 85% specificity. These data compare favorably with the combination of HLA-DR-, CD34-, and CD117+ for APL diagnosis, which had a sensitivity of 64% in this study.

ATRA plus arsenic gets another "A" in APL

In this issue of Blood, Iland et al report that the addition of arsenic trioxide during induction and consolidation can substantially reduce the amount of chemotherapy and the duration of consolidation to achieve excellent outcomes in patients with newly diagnosed acute promyelocytic leukemia (APL; see figure).

Molecular basis for the diagnosis and treatment of acute promyelocytic leukemia

Acute promyelocytic leukemia is characterized by gene rearrangements that always involve the retinoic acid receptor alpha on chromosome 15. In the majority of patients t(15;17) is detected, which generates the promyelocytic leukemia gene/retinoic acid receptor alpha rearrangement. This rearrangement interacts with several proteins, including the native promyelocytic leukemia gene, thus causing its delocalization from the nuclear bodies, impairing its function. The immunofluorescence staining technique using the anti-PML antibody may be used to provide a rapid diagnosis and to immediately start therapy using all-trans retinoic acid. The experience of the International Consortium on Acute Promyelocytic Leukemia has demonstrated that early mortality was significantly reduced by adopting the immunofluorescence technique. All-trans retinoic acid combined with chemotherapy is the standard therapy; this promotes complete remission rates greater than 90% and cure rates of nearly 80%. However, early mortality is still an important limitation and hematologists must be aware of the importance of treating newly diagnosed acute promyelocytic leukemia as a medical emergency.

Long-term outcome and prognostic factors of elderly patients with acute promyelocytic leukemia

Studies focused on elderly acute promyelocytic leukemia (APL) are relatively limited. To evaluate prognostic impact in elderly APL, we compared the long-term outcome of elderly APL patients (60-70 years) with younger patients (15-59 years) treated with all-trans retinoic acid combined with anthracycline and cytarabine in the Japan Adult Leukemia Study Group (JALSG) APL97 study. Of 283 evaluable patients, 46 (16.3%) were elderly who had more frequent lower platelet (P = 0.04), lower albumin (P = 0.006) and performance status 3 (P = 0.02), higher induction death rate due to differentiation syndrome (P = 0.03), and non-relapse mortality (NRM) during consolidation therapy (P = 0.001). Overall survival was significantly inferior in elderly patients (P = 0.005), but disease-free survival and cumulative incidence of relapse were not. Better therapeutic approaches should be considered to reduce NRM during induction and consolidation therapy in elderly APL. This study was registered at http://www.umin.ac.jp/ctrj/ under C000000206.

All-trans-retinoic acid, idarubicin, and IV arsenic trioxide as initial therapy in acute promyelocytic leukemia (APML4)

The treatment of acute promyelocytic leukemia has improved considerably after recognition of the effectiveness of all-trans-retinoic acid (ATRA), anthracycline-based chemotherapy, and arsenic trioxide (ATO). Here we report the use of all 3 agents in combination in an APML4 phase 2 protocol. For induction, ATO was superimposed on an ATRA and idarubicin backbone, with scheduling designed to exploit antileukemic synergy while minimizing cardiotoxicity and the severity of differentiation syndrome. Consolidation comprised 2 cycles of ATRA and ATO without chemotherapy, followed by 2 years of maintenance with ATRA, oral methotrexate, and 6-mercaptopurine. Of 124 evaluable patients, there were 4 (3.2%) early deaths, 118 (95%) hematologic complete remissions, and all 112 patients who commenced consolidation attained molecular complete remission. The 2-year rate for freedom from relapse is 97.5%, failure-free survival 88.1%, and overall survival 93.2%. These outcomes were not influenced by FLT3 mutation status, whereas failure-free survival was correlated with Sanz risk stratification (P[trend] = .03). Compared with our previously reported ATRA/idarubicin-based protocol (APML3), APML4 patients had statistically significantly improved freedom from relapse (P = .006) and failure-free survival (P = .01). In conclusion, the use of ATO in both induction and consolidation achieved excellent outcomes despite a substantial reduction in anthracycline exposure. This trial was registered at the Australian New Zealand Clinical Trials Registry (www.anzctr.org.au) as ACTRN12605000070639.

The arsenic-based cure of acute promyelocytic leukemia promotes cytoplasmic sequestration of PML and PML/RARA through inhibition of PML body recycling

Arsenic in the form of arsenic trioxide (ATO) is used as a therapeutic drug for treatment of acute promyelocytic leukemia (APL). The mechanism by which this agent cures this disease was previously shown to involve direct interactions between ATO and the promyelocytic leukemia protein (PML), as well as accelerated degradation of the APL-associated fusion oncoprotein PML/retinoic acid receptor α (RARA). Here we investigated the fate of PML-generated nuclear structures called PML bodies in ATO-treated cells. We found that ATO inhibits formation of progeny PML bodies while it stabilizes cytoplasmic precursor compartments, referred to as cytoplasmic assemblies of PML and nucleoporins (CyPNs), after cell division. This block in PML body recycling is readily detected at pharmacologic relevant ATO concentrations (0.02-0.5μM) that do not cause detectable cell-cycle defects, and it does not require modification of PML by SUMOylation. In addition, PML and PML/RARA carrying mutations previously identified in ATO-resistant APL patients are impeded in their ability to become sequestered within CyPNs. Thus, ATO may inhibit nuclear activities of PML and PML/RARA in postmitotic cells through CyPN-dependent cytoplasmic sequestration.

Provocative pearls in diagnosing and treating acute promyelocytic leukemia

The introduction of all-trans retinoic acid (ATRA) into routine clinical practice changed the outcome of acute promyelocytic leukemia (APL) from the most fatal to the most curable subtype of acute myeloid leukemia (AML). Patients who do not survive generally succumb within the first 30 days after presentation or diagnosis, often from intracranial or pulmonary hemorrhage caused by the characteristic coagulopathy associated with this disease. For the majority of patients who avoid hemorrhagic complications, the goals of decreasing the side effects of diagnosis and treatment-including pain, inpatient hospital days, and late sequelae of cytotoxic chemotherapy-have emerged as paramount. Here, we discuss novel and provocative observations regarding diagnostic and treatment strategies for APL that are likely to emerge as standards of care in the next 5 years, and that may improve the rate of early hemorrhagic death and decrease diagnosis- and treatment-related morbidity.

What happened to anti-CD33 therapy for acute myeloid leukemia?

CD33, a 67-kDa glycoprotein expressed on the majority of myeloid leukemia cells as well as on normal myeloid and monocytic precursors, has been an attractive target for monoclonal antibody (mAb)-based therapy of acute myeloid leukemia (AML). Lintuzumab, an unconjugated, humanized anti-CD33 mAb, has modest single-agent activity against AML but failed to improve patient outcomes in two randomized trials when combined with conventional chemotherapy. Gemtuzumab ozogamicin, an anti-CD33 mAb conjugated to the antitumor antibiotic calicheamicin, improved survival in a subset of AML patients when combined with standard chemotherapy, but safety concerns led to US marketing withdrawal. The activity of these agents confirms that CD33 remains a viable therapeutic target for AML. Strategies to improve the results of mAb-based therapies for AML include antibody engineering to enhance effector function, use of alternative drugs and chemical linkers to develop safer and more effective drug conjugates, and radioimmunotherapeutic approaches.

Arsenic trioxide for management of acute promyelocytic leukemia: current evidence on its role in front-line therapy and recurrent disease

INTRODUCTION

Acute promyelocytic leukemia (APL), the most rapidly fatal leukemia only two decades ago, has been converted into the most frequently curable leukemia by the advent of all-trans retinoic acid (ATRA) and its combination with anthracycline-based chemotherapy. More recently, arsenic trioxide (ATO) has been shown to be the most effective single agent in this disease and has been approved for the treatment of relapsed patients both in the United States and Europe. Moreover, ATO has been included in the design of several front-line studies, with the aim to reduce therapy-related toxicity while maintaining the potential of cure.

AREAS COVERED

First, this review briefly discusses the mechanisms of action and the toxicity profile of ATO. Furthermore, the reported experience on the use of ATO as single agent or in combinatorial schemes both in relapsed and in newly diagnosed patients with APL is critically reviewed. Finally, the use of this agent in special subsets of patients unfit to receive conventional chemotherapy is discussed, along with its potential role in maintenance therapy.

EXPERT OPINION

While the role of ATO as single agent or in combination with ATRA is well established and recommended by the European LeukemiaNet guidelines as a first option for relapsed patients, the role of the drug in newly diagnosed patients is still uncertain and based only on evidence levels mostly originating from non-randomized trials. The results of ongoing randomized studies should better define the role of ATO in front-line therapy.

How to manage acute promyelocytic leukemia

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.

Upfront maintenance therapy with arsenic trioxide in acute promyelocytic leukemia provides no benefit for non-t(15;17) subtype

AIMS

The optimal maintenance therapy for patients with acute promyelocytic leukemia (APL) who achieved complete remission (CR) and complete consolidation chemotherapy is still controversial. Whether the use of arsenic trioxide (ATO) alone or along with all-trans retinoic acid (ATRA) improves overall survival (OS) or disease-free survival (DFS) is still debated.

METHODS

A retrospective reivew was conducted of 20 patients diagnosed with APL according to the French - American - British system. After achieving CR and receiving consolidation chemotherapy, nine patients were given maintenance therapy for 1 year (ATRA 45 mg/m(2) /day p.o., mercaptopurine 60 mg/m(2) /day p.o. and ATO 0.15 mg/kg/day × 5 days/week for six cycles in five patients; ATRA 45 mg/m(2) /d p.o. alternating with ATO 0.15 mg/kg/day × 5 days/week in 1 patient; ATRA only in three patients).

RESULTS

In all patients the rates of CR, 3-year OS and 5-year OS were 75, 71 and 57%, respectively. For patients treated with ATO maintenance, the rates were 100% for both 5-year OS and 5-year DFS. Four of six patients on ATO maintenance had grade 1 or grade 2 adverse events. Excluding the two patients who died from intracerebral hemorrhage within 4 days after diagnosis, these rates were 85, 82 and 78%, respectively.

CONCLUSION

Upfront ATO maintenance therapy for one year is safe and appears to be effective, with the benefits restricted to patients with APL with t(15;17) translocation. Larger studies will be required to confirm this observation.

Role of minimal residual disease monitoring in acute promyelocytic leukemia treated with arsenic trioxide in frontline therapy

Data on minimal residual disease (MRD) monitoring in acute promyelocytic leukemia (APL) are available only in the context of conventional all-trans retinoic acid plus chemotherapy regimens. It is recognized that the kinetics of leukemia clearance is different with the use of arsenic trioxide (ATO) in the treatment of APL. We undertook a prospective peripheral blood RT-PCR-based MRD monitoring study on patients with APL treated with a single agent ATO regimen. A total of 151 patients were enrolled in this study. A positive RT-PCR reading at the end of induction therapy was significantly associated on a multivariate analysis with an increased risk of relapse (relative risk = 4.9; P = .034). None of the good risk patients who were RT-PCR negative at the end of induction relapsed. The majority of the relapses (91%) happened within 3 years of completion of treatment. After achievement of molecular remission, the current MRD monitoring strategy was able to predict relapse in 60% of cases with an overall sensitivity and specificity of 60% and 93.2%, respectively. High-risk group patients and those that remain RT-PCR positive at the end of induction are likely to benefit from serial MRD monitoring by RT-PCR for a period of 3 years from completion of therapy.

Arsenic compounds: revived ancient remedies in the fight against human malignancies

Arsenic, the 20th most abundant element in the earth crust, is one of the oldest drugs in the world. It was used in the 18th century in treating hematopoietic malignancies, discarded in 1950s in favor of chemotherapeutic agents (busulphan and others), and was revived in the 1970s due to its dramatic efficacy on acute promyelocytic leukemia (APL) driven by the t(15;17) translocation-generated PML-RARα fusion. Arsenic represents the most potent single agent for APL, and achieves a five-year overall survival of 90% in APL patients when combined with all-trans retinoic acid (ATRA) and chemotherapy (daunorubicin and cytarabine), turning this disease from highly fatal to highly curable. Arsenic triggers sumoylation/ubiquitination and proteasomal degradation of PML-RARα via directly binding to the C3HC4 zinc finger motif in the RBCC domain of the PML moiety and induction of its homodimerization/multimerization and interaction with the SUMO E2 conjugase Ubc9. Because of its multiplicity of targets and complex mechanisms of action, arsenic is widely tested in combination with other agents in a variety of malignancies. Other arsenic containing recipes including oral formulations and organic arsenicals are being developed and tested, and progress in these areas will definitely expand the use of arsenicals in other malignant diseases.

Antibody-drug conjugates of calicheamicin derivative: gemtuzumab ozogamicin and inotuzumab ozogamicin

Antibody-drug conjugates (ADC) are an attractive approach for the treatment of acute myeloid leukemia and non-Hodgkin lymphomas, which in most cases, are inherently sensitive to cytotoxic agents. CD33 and CD22 are specific markers of myeloid leukemias and B-cell malignancies, respectively. These endocytic receptors are ideal for an ADC strategy because they can effectively carry the cytotoxic payload into the cell. Gemtuzumab ozogamicin (GO, Mylotarg) and inotuzumab ozogamicin consist of a derivative of calicheamicin (a potent DNA-binding cytotoxic antibiotic) linked to a humanized monoclonal IgG4 antibody directed against CD33 or CD22, respectively. Both of these ADCs have a target-mediated pharmacokinetic disposition. GO was the first drug to prove the ADC concept in the clinic, specifically in phase II studies that included substantial proportions of older patients with relapsed acute myeloid leukemia. In contrast, in phase III studies, it has thus far failed to show clinical benefit in first-line treatment in combination with standard chemotherapy. Inotuzumab ozogamicin has shown remarkable clinical activity in relapsed/refractory B-cell non-Hodgkin lymphoma, and it has started phase III evaluation. The safety profile of these ADCs includes reversible myelosuppression (especially neutropenia and thrombocytopenia), elevated hepatic transaminases, and hyperbilirubinemia. There have been postmarketing reports of hepatotoxicity, especially veno-occlusive disease, associated with GO. The incidence is ~2%, but patients who undergo hematopoietic stem cell transplantation have an increased risk. As we steadily move toward the goal of personalized medicine, these kinds of agents will provide a unique opportunity to treat selected patient subpopulations based on the expression of their specific tumor targets.

Results of the APML3 trial incorporating all-trans-retinoic acid and idarubicin in both induction and consolidation as initial therapy for patients with acute promyelocytic leukemia

BACKGROUND

Initial therapy for patients with acute promyelocytic leukemia most often involves the combination of all-trans-retinoic acid with anthracycline-based chemotherapy. The role of non-anthracycline drugs in induction and consolidation is less well-established and varies widely between different cooperative group protocols.

DESIGN AND METHODS

In an attempt to minimize relapse and maximize survival for patients with newly diagnosed acute promyelocytic leukemia, the Australasian Leukaemia and Lymphoma Group utilized all-trans-retinoic acid and idarubicin as anti-leukemic therapy for both induction and consolidation. The protocol (known as APML3) was subsequently amended to incorporate maintenance with all-trans-retinoic acid, methotrexate and 6-mercaptopurine.

RESULTS

Eight (8%) of 101 patients died within 30 days, and 91 (90%) achieved complete remission. With a median estimated potential follow-up of 4.6 years, 4-year overall survival was 84%, and 71% of the patients remained in remission at 4 years. The cumulative incidence of all relapses was 28.1%, with 15 of the 25 relapses initially identified as an isolated molecular relapse. Both FLT3 mutations (internal tandem duplications and codon 835/836 kinase domain mutations) and increased white cell count at diagnosis were associated with inferior overall survival, but in multivariate analyses only FLT3 mutations remained significant (hazard ratio 6.647, P=0.005). Maintenance therapy was significantly associated with improved remission duration (hazard ratio 0.281, P<0.001) and disease-free survival (hazard ratio 0.290, P<0.001).

CONCLUSIONS

The combination of all-trans-retinoic acid and just two cycles of idarubicin followed by triple maintenance produced durable remissions in most patients, but patients with high-risk disease, especially those with FLT3 mutations, require additional agents or alternative treatment approaches. The significant reduction in relapse seen after the addition of maintenance to the protocol supports a role for maintenance in the context of relatively low chemotherapy exposure during consolidation. (actr.org.au identifier: ACTRN12607000410459).

Acute myeloid leukemia stem cells and CD33-targeted immunotherapy

Although the identification of cancer stem cells as therapeutic targets is now actively being pursued in many human malignancies, the leukemic stem cells in acute myeloid leukemia (AML) are a paradigm of such a strategy. Heterogeneity of these cells was suggested by clonal analyses indicating the existence of both leukemias resulting from transformed multipotent CD33(-) stem cells as well others arising from, or predominantly involving, committed CD33(+) myeloid precursors. The latter leukemias, which may be associated with an intrinsically better prognosis, offer a particularly attractive target for stem cell-directed therapies. Targeting the CD33 differentiation antigen with gemtuzumab ozogamicin was the first attempt of such an approach. Emerging clinical data indicate that gemtuzumab ozogamicin is efficacious not only for acute promyelocytic leukemia but, in combination with conventional chemotherapy, also for other favorable- and intermediate-risk AMLs, providing the first proof-of-principle evidence for the validity of this strategy. Herein, we review studies on the nature of stem cells in AML, discuss clinical data on the effectiveness of CD33-directed therapy, and consider the mechanistic basis for success and failure in various AML subsets.

Current treatment strategy of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML). The prognosis of APL has changed from the worst among the AMLs to currently the best. The application of all-trans retinoic acid (ATRA) in the induction therapy of APL decreases the high mortality of newly diagnosed patients, thereby significantly improving the response rate. ATRA combined with anthracycline-based chemotherapy is the current standard treatment, and for high-risk patients, high doses cytarabine have a beneficial effect on relapse prevention. In recent years, the indications of arsenic trioxide (ATO) therapy for APL have been extended from the salvage therapy for relapse patients to the first-line treatment of de novo APL. The introduction of both ATRA and ATO represents great achievements in translational medicine. In this review article, we discuss the therapeutic strategies for this disease, including the initial approaches to newly diagnosed patients, prevention, and treatment of side effects and relapse to ensure the best and timely treatment for each newly diagnosed APL patient.

Newly diagnosed acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) represents a medical emergency with a high rate of early mortality. As a consequence, as soon as the diagnosis is suspected based upon cytologic criteria, it is necessary to start all- trans retinoic acid (ATRA) treatment without delay. For patients with newly diagnosed APL, induction therapy with ATRA plus anthracycline based chemotherapy is recommended. At present the combination of arsenic trioxide plus ATRA should be considered for patients who are not candidates for anthracycline-based therapy. For pediatric and adult patients with APL aged < 60 years who achieve a CR with induction, I recommend 3 intensive courses of consolidation chemotherapy associated to ATRA, targeted on the basis of the risk group at diagnosis. In patients treated with a very intensive consolidation chemotherapy maintenance treatment can be omitted. However If a maintenance treatment has to be adopted I suggest the use of intermittent ATRA for 15 days every 3 months for a period of 2 years, rather than ATRA associated to chemotherapy. Moreover, taking into account the medical literature, a reduced dosage of ATRA ( 25 mg/m(2)) in pediatric patients and a consolidation chemotherapy of reduced intensity in elderly patients is recommended. Furthermore, in order to maximize survival, careful attention should be reserved to the coagulopathy and to the appearance of the differentiation syndrome. Finally, PCR for the PML/RARA fusion gene on a bone marrow specimen every three months for two years, and then every six months for additional three years are needed during the follow-up.

Oral arsenic trioxide–based maintenance regimens for first complete remission of acute promyelocytic leukemia: a 10-year follow-up study

Seventy-six patients with acute promyelocytic leukemia (APL) in first complete remission after induction and consolidation by daunorubicin and cytosine arabinoside received oral arsenic trioxide (As2O3)-based maintenance. Three regimens were used: oral As2O3 (10 mg/day, regimen A, n = 20), oral As2O3 plus all-trans retinoic acid (ATRA, 45 mg/m2 per day, regimen AA, n = 19), and oral As2O3 plus ATRA plus ascorbic acid (1000 mg/day, regimen AAA, n = 37), each given for 2 weeks every 2 months for 2 years. Patients receiving A, AA, and AAA maintenance did not differ significantly in clinicopathologic features and risk factors. Headache, dyspepsia, reversible liver function derangement, and herpes zoster reactivation were adverse effects observed during maintenance. QTc prolongation and arrhythmias were not encountered. At a median follow-up of 24 months (range, 1-115 months), there were 8 relapses. The 3-year leukemia-free-survival, event-free-survival, and overall-survival were 87.7%, 83.7%, and 90.6%, respectively. Adverse prognostic factors included male gender for leukemia-free-survival, and unrelated cancers for overall survival. Age, presentation WBC count and platelet count, and the type of oral As2O3 maintenance regimens had no impact on survivals. Prolonged oral As2O3 maintenance was feasible and safe and resulted in favorable outcomes when used with a simple induction and consolidation regimen compared with other protocols composed of multiple chemotherapeutic agents.

Synergism between arsenite and proteasome inhibitor MG132 over cell death in myeloid leukaemic cells U937 and the induction of low levels of intracellular superoxide anion

Increased oxygen species production has often been cited as a mechanism determining synergism on cell death and growth inhibition effects of arsenic-combined drugs. However the net effect of drug combination may not be easily anticipated solely from available knowledge of drug-induced death mechanisms. We evaluated the combined effect of sodium arsenite with the proteasome inhibitor MG132, and the anti-leukaemic agent CAPE, on growth-inhibition and cell death effect in acute myeloid leukaemic cells U937 and Burkitt's lymphoma-derived Raji cells, by the Chou-Talalay method. In addition we explored the association of cytotoxic effect of drugs with changes in intracellular superoxide anion (O₂⁻) levels. Our results showed that combined arsenite+MG132 produced low levels of O₂⁻ at 6h and 24h after exposure and were synergic on cell death induction in U937 cells over the whole dose range, although the combination was antagonistic on growth inhibition effect. Exposure to a constant non-cytotoxic dose of 80μM hydrogen peroxide together with arsenite+MG132 changed synergism on cell death to antagonism at all effect levels while increasing O₂⁻ levels. Arsenite+hydrogen peroxide also resulted in antagonism with increased O₂⁻ levels in U937 cells. In Raji cells, arsenite+MG132 also produced low levels of O₂⁻ at 6h and 24h but resulted in antagonism on cell death and growth inhibition. By contrast, the combination arsenite+CAPE showed high levels of O₂⁻ production at 6h and 24 h post exposure but resulted in antagonism over cell death and growth inhibition effects in U937 and Raji cells. We conclude that synergism between arsenite and MG132 in U937 cells is negatively associated to O₂⁻ levels at early time points after exposure.

The differentiation syndrome in patients with acute promyelocytic leukemia: experience of the pethema group and review of the literature

Differentiation syndrome (DS), formerly known as retinoic acid syndrome, is the main life-threatening complication of therapy with differentiating agents (all-trans retinoic acid [ATRA] or arsenic trioxide [ATO]) in patients with acute promyelocytic leukemia (APL). The differentiation of leukemic blasts and promyelocytes induced by ATRA and/or ATO may lead to cellular migration, endothelial activation, and release of interleukins and vascular factors responsible of tissue damage. Roughly one quarter of patients with APL undergoing induction therapy will develop the DS, characterized by unexplained fever, acute respiratory distress with interstitial pulmonary infiltrates, and/or a vascular capillary leak syndrome leading to acute renal failure. Although the development of the DS, particularly of the severe form, is still associated with a significant increase in morbidity and mortality during induction, the early administration of high-dose dexamethasone at the onset of the first symptoms seems likely to have dramatically reduced the mortality rate of this complication. In this article, we will review the clinical features, incidence, prognostic factors, management, and outcome of the DS reported in the scientific literature. We will make focus in the experience of the three consecutive Programa Español de Tratamientos en Hematología trials (PETHEMA LPA96, LPA99, and LPA2005), in which more than one thousand patients were treated with ATRA plus idarubicin for induction.

Treatment of acute promyelocytic leukemia with single-agent arsenic trioxide

It is well recognized that arsenic trioxide (ATO) is an efficacious agent for the treatment of acute promyelocytic leukemia (APL). Use of single agent ATO in the treatment of APL leads to remissions which are durable in the majority. ATO is probably the most effective single agent in the treatment of APL and there have been very few reports of primary resistance. It has been used both as a single agent and in combination with other conventional drugs to treat APL. Use of ATO is the accepted standard of care in the management of relapsed APL, where it is often used effectively as a bridge to a stem cell transplant. However, its role in newly diagnosed APL remains controversial. ATO probably has multiple mechanisms of action. Better understanding of its mechanisms of action/s is likely to lead to more rationale use of this agent or its derivatives either alone or in combination with other drugs. There is limited data on the kinetics of leukemia clearance and normal haematopoietic recovery after the administration of single agent ATO for the treatment of APL, preliminary data suggests that it is likely to be different from conventional therapy. There have been a number of concerns of the potential short and long term toxicity of this agent. Most such concerns arise from the toxicity profile noted in people exposed to long term arsenic exposure in the environment. With the therapeutic doses and schedules of administration of ATO in the treatment of malignancies the overall toxicity profile has been favorable. In a resource constrained environments the use of a single agent ATO based regimen is a realistic and acceptable option to treat almost all patients. In the developed world it has the potential in combination with other agents to improve the clinical outcome with reduction of dose intensity of chemotherapy and remains an option for patients who would not tolerate conventional therapy. In this review we focus on the use of single agent ATO for the treatment of APL and summarize our experience and review the literature.

Therapy-related acute promyelocytic leukemia: observations relating to APL pathogenesis and therapy

Therapy-related acute promyelocytic leukemia (t-APL) is a well-recognized form of APL for which the underlying etiology has been well characterized. The pathogenesis of de novo (dn-APL) remains unknown; but epidemiologic studies have consistently identified increased body mass index (BMI), younger age, and ethnicity as possible risk factors. We analyzed demographics, clinical features, and treatment responses in a contemporary series of 64 patients treated with all-trans-retinoic acid and anthracycline-based therapy to assess for differences in these two etiologically distinct patient groups. Compared with patients with t-APL (n = 11), those with dn-APL (n = 53) had a greater median BMI (31.33 vs. 28.48), incidence of obesity (60.4% vs. 27.3%) (P = 0.04), and history of hyperlipidemia (45.3% vs. 18.2%) (P = 0.01). Fewer t-APL than dn-APL patients achieved complete remission at 63.6% vs. 92.5% respectively (P = 0.008). This was the result of a higher induction mortality rate of 36.4% vs. 7.5% respectively (P = 0.008). No cases of leukemic resistance were seen in either group. Overall survival (OS) was inferior in t-APL compared with dn-APL at 51% vs. 84%, respectively (P < 0.005), primarily as a result of higher induction mortality. Relapse occurred in nine patients (16.1%) overall, but no relapses occurred in the t-APL cohort. Our observations provide further support for the hypothesis that abnormalities in lipid homeostasis may in some way be of pathogenic importance in dn-APL. Therapy-related APL is sensitive to standard therapy with no cases of resistance or relapse seen. The inferior OS of the t-APL was due to induction mortality, possibly reflecting prior therapy.