Use of gemtuzumab ozogamycin combined with conventional chemotherapy in patients with acute myeloid leukemia

Objective: To analyze the outcome of patients treated with gemtuzumab ozogamycin combined with conventional therapy treated at Hospital Israelita Albert Einstein. Methods: 14 patients who had high risk features (secondary leukemia, unfavorable cytogenetics, and refractory disease) were treated with gemtuzumab ozogamycin combined with conventional therapy and their outcome was analysed by reviewing their medical records. results: Overall response rate was 58%, with 43% achieving complete response, with a median followup of 11 months, event-free survival was 3 months. Eleven patients died, 6 of them due to refractory acute myeloid leukemia. Only four patients presented with grade 3 to 4 toxicities and only one patient had sinusoidal obstruction syndrome after bone marrow transplant. conclusion: gemtuzumab ozogamycin combined with chemotherapy is a feasible treatment regimen in acute myeloid leukemia patients. However, further studies are necessary to clarify which subgroup of patients may benefit from this treatment.


intrODUctiOn
Current treatment of patients with acute myeloid leukemia (AML) involves administering an intensive phase of chemotherapy (induction chemotherapy) with the objective of achieving a state of complete remission (CR) which is a pre-requisite for cure (1,2) .The most traditional induction regimen consists of a combination of cytarabine (ara-C) with anthracyclines, such as daunorubicin or idarubicin (7+3 regimen) (2) .However, in elderly patients with AML (usually defined as > 55-60 years of age), administering an aggressive induction course of chemotherapy can be limited by the presence of comorbidities and poor tolerance (3) .Additionally, elderly patients with AML more commonly present with poor-risk features and a high rate of resistant disease (3) .
for elderly patients with AML are in the range of 40 to 50% only, and long term survival rates are less than 10% (3) .Thus, there is great need for improving therapy in elderly patients with AML.
Gemtuzumab ozogamycin (GO) (Mylotarg ® ; Pfizer, New York, NY) is a monoclonal antibody targeted against the CD33 antigen and coupled with the chemotherapeutic agent calicheamicin (4) .CD33 is a surface molecule which is expressed on the surface of myeloid cells and in myeloid blasts of the majority of patients with AML (4) .The anti-CD33 antibody in GO is coupled with calicheamicin through an acid-sensitive linker.Calicheamicin is a compound from the enediyne class, and it induces cleavage of DNA strands through formation of free radicals (5) .Upon binding to CD33, GO is internalized into a lysosomal vesicle, and the acid pH cleaves the linker and releases calicheamicin from the monoclonal antibody (4) .
Clinical trials have shown that GO has activity in the setting of both relapsed/refractory and untreated AML.Three phase II studies enrolled 142 patients with untreated first relapsed CD33-positive AML (6) .Patients were treated with GO at a dose of 9 mg/m 2 for one or two infusions.The CR rate was 16%, and 13% achieved CR without full recovery of platelet counts (CRp) for an overall response rate (ORR) of 29%.Based on this report, GO was approved as a single agent for therapy of elderly (age ≥ 60 years) patients with relapsed AML (7) .Other reports confirmed activity of GO as a single agent (8)(9)(10)(11)(12)(13)(14) .More recently, clinical trials focused on combination of GO with other agents, including cytarabine, anthracyclines and purine analogues (15,16) .We report the experience of our institution with a combination regimen containing cytarabine and GO for treatment of elderly patients with AML.

MetHODS
The outcomes of 14  treatment Fourteen patients were treated with different combinations of GO and conventional chemotherapeutic agents depending on age, comorbidities and clinical judgment.GO was administered at a dose of 3 mg/m 2 IV, over 2 hours, on treatment days 1, 4 and 7.This fractionated regimen was first published by Taksin et  al., in 2007, and differs from the initial dose schedule of GO approved by the Food and Drug Administration (FDA), in the United States (17) .

response definitions and statistical analysis
Crieria for response and survival endpoints were previously published.Briefly, complete remission (CR) was defined by the presence of less than 5% blasts in the BM with more than 1 x 10 9 /L neutrophils and more than 100,000/mm 3 platelets in the peripheral blood (PB) (18,19) .Patients with CR without platelet recovery met all criteria for CR, except for recovery of platelet counts above 100,000/mm 3 .A relapse was defined by more than 5% blasts in a BM aspirate unrelated to recovery or by the presence of extramedullary disease.Event-free survival (EFS) was calculated from the beginning of treatment until an event.An event was defined as relapse, resistant disease and death.Induction death was defined as death occurring before achievement of CR or confirming resistant disease.Patients without an event were censored at last followup.Disease-free survival (DFS) was calculated from the time of CR until relapse or death in CR.Patients alive in CR were censored at last follow-up.Overall survival (OS) was calculated from the time of diagnosis until death.All patients alive at last follow-up were censored.Cumulative incidence of relapse and death in CR were estimated by the Gray method, taking into account competitive risks (20) .Descriptive statistics were used for baseline covariates.Survival was estimated by the Kaplan-Meier method.

reSUltS
Clinical features are summarized in table 1. Median age was 69 years (range 33 to 83 years).Fourteen patients received treatment with GO combined with conventional chemotherapeutic agents.Six patients (UPI# 1,3,4,5,6,7) received GO combined with standard dose cytarabine (100 mg/m 2 IV, by continuous infusion, for 7 days).One patient (UPI#2) received GO combined with low-dose cytarabine (10 mg/m 2 IV, for 10 days), since the patient was in the Intensive Care Unit receiving treatment for a pulmonary infection when treatment started.Median age of these patients was Perini GF, Santos FPS, Esteves I, Nascimento CMB, Rodrigues M, Assis RA, Helman R, Kutner JM, Ribeiro AAF, Hamerschlak N 75 years (range 64 to 83 years), and four patients had a performance status (PS) of 3 to 4. The remaining seven patients received GO combined with chemotherapy for relapsed AML.Median number of prior therapies was 2 (range 1-3).Two patients (UPI#8 and #9) received GO with intermediate-dose of cytarabine (600 mg/m 2 IV for 5 days) and UPIN#9 also received mitoxantrone (10 mg/ m 2 IV for 2 days).One patient (UPIN#11) received GO combined with high-dose cytarabine (3 g/m 2 IV, twice daily, for 5 days) and mitoxantrone (10 mg/m 2 IV, for 3 days).The other four patients received fractionated GO combined with cytarabine and mitoxantrone as per the MIDAM protocol (cytarabine 1 g/m 2 IV, twice daily, for 5 days; mitoxantrone 12 mg/m 2 IV, once daily, for 3 days).Five patients received an allogeneic stem cell transplantation (SCT), on average 2 months after GO chemotherapy (range 1 to 5 months).Source of stem cells were double cord bloods (CB) in three cases and a matched unrelated donor (MUD) in two cases.At time of SCT, two patients had active disease, and three patients were in CR.
Overall, the rate of CR was 43%; two patients achieved CRp for an overall response rate (ORR) of 58%.Refractory disease and induction death ocurred in 21% of patients each.Median time to CR was 29 days (range 22 to 38 days).Among the seven patients who received GO combined with ara-C for initial induction therapy, the ORR was 43% (2 CRs + 1 CRp), one patient had resistant disease and three patients (43%) died before response could be assessed.The ORR for GO combined with chemotherapy used as salvage was 71% (4 CRs + 1 CRp); two patients had refractory leukemia.A CR was obtained in two of three patients who presented with poor-risk cytogenetics; among the remaining nine patients with intermediate-risk karyotype, the ORR was 67%.
Median follow-up of surviving patients was 11 months.Survival estimates are presented on figures 1 to 3. Eleven patients have either died of or relapsed, for a median EFS of 3 months (95%CI: 0-6.6 months).Eleven patients (79%) died, six of them (54%) due to refractory AML and the remainder due to treatmentrelated toxicity (three deaths were due to GO and chemotherapy).The median OS was 4 months (95% CI 0-9.5 months).For the eight patients who had a response, median DFS was 10 months (95%CI: 2.6-17.3months).Among the three survivors at the time of this report, two received consolidation with an allogeneic double CB transplant at the time of CR.The cumulative incidence of relapse for responding patients was 42.5% (95%CI: 6.9-75.9%)at 1 year, and the cumulative incidence of death in CR at 1 year was 21% (95%CI 0.4%-44.4%).As expected, myelosuppressive toxicity was paramount, with universal incidence of grade 3 to 4 neutropenia and thrombocytopenia.In patients who achieved CR, median time to neutrophil recovery (ANC ≥ 1,000/mm 3 for, at least, 2 consecutive days) was 23 days (range 18 to 29 days), and median time to platelet recovery was 35 days (range 22 to 66 days).Grade 3 to 4 hepatic toxicity was observed in three patients, one with grade 3 elevation in bilirubin and grade 4 elevation in gamma-GT and alkaline phosphatase, and two with grade 3 elevation in gamma-GT.No patient developed sinusoidal obstruction syndrome (SOS) while on therapy with GO, but one patient developed SOS post allogeneic MUD SCT two months post-GO.
Chart 1 shows the treatment and outcome of the patients.

DiScUSSiOn
In our experience, GO combined with chemotherapy proved to be feasible regimen, with a low incidence of grade 3 to 4 toxicities.Yet, long term results confirm the need for improving consolidation treatment and maintaining response after achievement of CR.It is still controversial whether treatment with GO has any benefits in the therapy of patients with AML.Recently, Pfizer has withdrawn GO from the market, due to disappointing results observed in a phase III trial (21) .In this study, the addition of GO to induction therapy or as post-consolidation therapy did not improve the CR rate, relapse-free survival (RFS), post-consolidation DFS, or OS, but was associated with a significantly higher risk of fatal induction adverse events.
It is well known that AML is an heterogeneous disease with distinct subtypes identified by morphological, chromosomal and genetic abnormalities (22) .Distinct subtypes of AML may respond differently to a particular drug or chemotherapy regimen.It is also well-known, for instance, that core-binding factor abnormalities, NPM1 mutations (and possible Ras mutations also), may identify subgroups of patients with AML who respond better to high dose cytarabine in consolidation, while the same regimen is supposedly poorly effective in patients with high-risk chromosomal abnormalities (23)(24)(25) .It is thus important to further discern which subgroup of patients can benefit from GO.A recent published study analyzed patients enrolled in a phase III trial of the MRC, focusing on this issue.In this study, patients with CBF AML (favorable-risk karyotype) showed significantly better results with the association of GO (3 mg/m 2 ) during induction chemotherapy (26) .The same results were observed in a preliminary analysis of the other phase III trial mentioned above (21) .It has been postulated that GO may overcome the negative impact of KIT mutations in patients with CBF AML.In the MRC clinical trial, GO did not improve the outcome of patients with high-risk karyotype AML, which further suggests that new treatment options are urgently needed for this subgroup of patients.

cOnclUSiOn
Combining GO with conventional chemotherapy had a modest efficacy in our cohort of patients.We believe that GO is a compound which may benefit selected patients with AML.New trials are necessary to evaluate the role of GO in patients with favorable-risk karyotype AML.

table 1 .
Baseline characteristics at time of treatment * Information on karyotype was available for 12 patients only.MDS: myelodysplastic syndrome; WBC: white blood cell count; Hb: hemoglobin; LDHL: lactate dehydrogenase.