WARNINGS

Mylotarg should be administered under the supervision of physicians experienced in the treatment of acute leukemia and in facilities equipped to monitor and treat leukemia patients.

There are no controlled trials demonstrating efficacy and safety using Mylotarg in combination with other chemotherapeutic agents. Therefore, Mylotarg should only be used as single agent chemotherapy and not in combination chemotherapy regimens outside clinical trials.

Severe myelosuppression occurs when Mylotarg is used at recommended doses.

HYPERSENSITIVITY REACTIONS INCLUDING ANAPHYLAXIS, INFUSION REACTIONS, PULMONARY EVENTS

Mylotarg administration can result in severe hypersensitivity reactions (including anaphylaxis), and other infusion-related reactions which may include severe pulmonary events. Infrequently, hypersensitivity reactions and pulmonary events have been fatal. In most cases, infusion-related symptoms occurred during the infusion or within 24 hours of administration of Mylotarg and resolved. Mylotarg infusion should be interrupted for patients experiencing dyspnea or clinically significant hypotension. Patients should be monitored until signs and symptoms completely resolve. Discontinuation of Mylotarg treatment should be strongly considered for patients who develop anaphylaxis, pulmonary edema, or acute respiratory distress syndrome. Since patients with high peripheral blast counts may be at greater risk for pulmonary events and tumor lysis syndrome, physicians should consider leukoreduction with hydroxyurea or leukapheresis to reduce the peripheral white count to below 30,000/μL prior to administration of Mylotarg. (See WARNINGS.)

HEPATOTOXICITY:

Hepatotoxicity, including severe hepatic veno-occlusive disease (VOD), has been reported in association with the use of Mylotarg as a single agent, as part of a combination chemotherapy regimen, and in patients without a history of liver disease or hematopoietic stem cell transplant (HSCT). Patients who receive Mylotarg either before or after HSCT, patients with underlying hepatic disease or abnormal liver function, and patients receiving Mylotarg in combinations with other chemotherapy are at increased risk for developing VOD, including severe VOD. Death from liver failure and from VOD has been reported in patients who received Mylotarg. Physicians should monitor their patients carefully for symptoms of hepatotoxicity, particularly VOD. These symptoms can include: rapid weight gain, right upper quadrant pain, hepatomegaly, ascites, elevations in bilirubin and/or liver enzymes. However, careful monitoring may not identify all patients at risk or prevent the complications of hepatotoxicity. (See WARNINGS and ADVERSE REACTIONS sections.)

DESCRIPTION

Mylotarg® (gemtuzumab ozogamicin for Injection) is a chemotherapy agent composed of a recombinant humanized IgG4, kappa antibody conjugated with a cytotoxic antitumor antibiotic, calicheamicin, isolated from fermentation of a bacterium, Micromonospora echinospora subsp. calichensis. The antibody portion of Mylotarg binds specifically to the CD33 antigen, a sialic acid-dependent adhesion protein found on the surface of leukemic blasts and immature normal cells of myelomonocytic lineage, but not on normal hematopoietic stem cells.

The anti-CD33 hP67.6 antibody is produced by mammalian cell suspension culture using a myeloma NS0 cell line and is purified under conditions which remove or inactivate viruses. Three separate and independent steps in the hP67.6 antibody purification process achieves retrovirus inactivation and removal. These include low pH treatment, DEAE-Sepharose chromatography, and viral filtration. Mylotarg contains amino acid sequences of which approximately 98.3% are of human origin. The constant region and framework regions contain human sequences while the complementarity-determining regions are derived from a murine antibody (p67.6) that binds CD33. This antibody is linked to N-acetyl-gamma calicheamicin via a bifunctional linker. Gemtuzumab ozogamicin has approximately 50% of the antibody loaded with 4-6 moles calicheamicin per mole of antibody. The remaining 50% of the antibody is not linked to the calicheamicin derivative. Gemtuzumab ozogamicin has a molecular weight of 151 to 153 kDa.

Mylotarg is a sterile, white, preservative-free lyophilized powder containing 5 mg of drug conjugate (protein equivalent) in an amber vial. The drug product is light sensitive and must be protected from direct and indirect sunlight and unshielded fluorescent light during the preparation and administration of the infusion. The inactive ingredients are: dextran 40; sucrose; sodium chloride; monobasic and dibasic sodium phosphate.

CLINICAL PHARMACOLOGY

General

Gemtuzumab ozogamicin binds to the CD33 antigen. This antigen is expressed on the surface of leukemic blasts in more than 80% of patients with acute myeloid leukemia (AML). CD33 is also expressed on normal and leukemic myeloid colony-forming cells, including leukemic clonogenic precursors, but it is not expressed on pluripotent hematopoietic stem cells or on nonhematopoietic cells.

Mechanism of Action: Mylotarg is directed against the CD33 antigen expressed by hematopoietic cells. Binding of the anti-CD33 antibody portion of Mylotarg with the CD33 antigen results in the formation of a complex that is internalized. Upon internalization, the calicheamicin derivative is released inside the lysosomes of the myeloid cell. The released calicheamicin derivative binds to DNA in the minor groove resulting in DNA double strand breaks and cell death.

Gemtuzumab ozogamicin is cytotoxic to the CD33 positive HL-60 human leukemia cell line. Gemtuzumab ozogamicin produces significant inhibition of colony formation in cultures of adult leukemic bone marrow cells. The cytotoxic effect on normal myeloid precursors leads to substantial myelosuppression, but this is reversible because pluripotent hematopoietic stem cells are spared. In preclinical animal studies, gemtuzumab ozogamicin demonstrates antitumor effects in the HL-60 human promyelocytic leukemia xenograft tumor in athymic mice.

Human Pharmacokinetics

After administration of the first recommended 9 mg/m2 dose of gemtuzumab ozogamicin, given as a 2 hour infusion, the elimination half lives of total and unconjugated calicheamicin were about 41 and 143 hours, respectively. After the second 9 mg/m2 dose, the half life of total calicheamicin was increased to about 64 hours and the area under the concentration-time curve (AUC) was about twice that in the first dose period. The AUC for the unconjugated calicheamicin increased 30% after the second dose. Age, gender, body surface area (BSA), and weight did not affect the pharmacokinetics of Mylotarg.

Patients, especially patients previously treated with HSCT, have an underlying risk of VOD. The AUC of total calicheamicin was correlated with additional risk of hepatomegaly and the risk of veno-occlusive disease (VOD). There is no evidence that reducing Mylotarg dose will reduce the underlying risk of VOD. Metabolic studies indicate hydrolytic release of the calicheamicin derivative from gemtuzumab ozogamicin. Many metabolites of this derivative were found after in vitro incubation of gemtuzumab ozogamicin in human liver microsomes and cytosol, and in HL-60 promyelocytic leukemia cells. Metabolic studies characterizing the possible isozymes involved in the metabolic pathway of Mylotarg have not been performed.

CLINICAL STUDIES

The efficacy and safety of Mylotarg as a single agent have been eva luated in 277 patients in three single arm open-label studies in patients with CD33 positive AML in first relapse. The studies included 84, 95, and 98 patients. In studies 1 and 2 patients were ≥ 18 years of age with a first remission duration of at least 6 months. In study 3, only patients ≥ 60 were enrolled and their first remission had to have lasted for at least 3 months. Patients with secondary leukemia or white blood cell (WBC) counts ≥ 30,000/μL were excluded. Some patients were leukoreduced with hydroxyurea or leukapheresis to lower WBC counts below 30,000/μL in order to minimize the risk of tumor lysis syndrome. The treatment course included two 9 mg/m2 doses separated by 14 days and a 28-day follow-up after the last dose. Although smaller doses had elicited responses in earlier studies, the 9 mg/m2 was chosen because it would be expected to saturate all CD33 sites regardless of leukemic burden. A total of 157 patients were ≥ 60 years of age and older. The primary endpoint of the three clinical studies was the rate of complete remission (CR), which was defined as

1. leukemic blasts absent from the peripheral blood;
2. ≤ 5% blasts in the bone marrow, as measured by morphology studies;
3. hemoglobin (Hgb) ≥ 9 g/dL, platelets ≥ 100,000/μL, absolute neutrophil count (ANC) ≥ 1500/μL; and
4. red cell and platelet-transfusion independence (no red cell transfusions for 2 weeks; no platelet transfusions for 1 week).

In addition to CR, a second response category, CRp, was defined as patients satisfying the definition of CR, including platelet transfusion independence, with the exception of platelet recovery ≥100,000/μL. Remission status was determined at approximately 28 days after the last dose of Mylotarg. This category was added because Mylotarg appears to delay platelet recovery in some patients. Clinical equivalence between CR and CRp responses has not been established. Median time to recovery of platelet counts in patients who achieved a CR or a CRp is summarized in TABLE 4 (see ADVERSE REACTIONS section).

All patients were pre-medicated with acetaminophen 650-1000 mg and diphenhydramine 50 mg to decrease acute infusion-related symptoms. Growth factors and cytokines were not permitted. Use of prophylactic antibiotics was not specified.

Response Rate

The overall response (OR) rate for the three pooled monotherapy studies was 26% (71/277) consisting of 13% (35/277) of patients with CR and 13% (36/277) of patients with CRp. The median time to blast clearance in both CR and CRp patients was 28 days from the first dose of Mylotarg. The median time to remission was 60 days for both CR and CRp. Remission rates are shown in Table 1. Of the 157 patients who were ≥ 60 years old, the overall remission rate (OR = CR + CRp) was 24%. For the patients < 60 years old and all 277 patients the OR rates were 28% and 26%, respectively. Two of the most important determinants of response following relapse are age and duration of first remission. Remission rates by prognostic category are outlined in Table 1.

The overall response rates were similar for females and males: 27% of females and 25% of males achieved remission.

In the studies, 95% of the patients were white and 5% of the patients were non-white.

Survival

Overall survival was measured from date of first dose of gemtuzumab ozogamicin to date of death or data cut-off date (Table 2). Relapse-free survival (duration of remission) for patients in remission was defined as the time period from date of first documentation of maximum response (CR or CRp) to the first date of documentation of relapse (pathology report or complete blood count showing leukemic blast recurrence in peripheral blood or bone marrow), or death, or data cut-off date.

Rates of Remission by Cytogenetic Risk

Patients in all three cytogenetic risk classification groups (poor, intermediate, favorable) responded to gemtuzumab ozogamicin.

Post-Remission Therapy

Twenty-five (25/71, 35%) OR patients (11 CR and 14 CRp patients) went on to hematopoietic stem cell transplantation (HSCT). Fourteen (14) received allogeneic HSCT and 11 received autologous HSCT.

Thirty-five (35/71, 49%) OR patients (17 CR and 18 CRp patients) who responded to treatment with Mylotarg received no additional therapy.

Repeat Courses

Twenty (20) patients have received more than 1 course of Mylotarg in clinical trials. These patients were initially treated with Mylotarg, achieved remission, then subsequently relapsed and then received additional doses of Mylotarg.

Overview of Clinical Data

Available single arm trial data do not provide valid comparisons with various cytotoxic regimens that have been used in relapsed acute myeloid leukemia. Response rates are in the range of rates reported with such regimens only if the CRp responses are included. Nevertheless, treatment with Mylotarg can provide responses, including some of reasonable duration. The data support its use in patients for whom aggressive cytotoxic regimens would be considered unsuitable, such as many patients 60 years of age or older.

INDICATIONS AND USAGE

Mylotarg is indicated for the treatment of patients with CD33 positive acute myeloid leukemia in first relapse who are 60 years of age or older and who are not considered candidates for other cytotoxic chemotherapy. The safety and efficacy of Mylotarg in patients with poor performance status and organ dysfunction has not been established.

The effectiveness of Mylotarg is based on OR rates (see CLINICAL STUDIES section). There are no controlled trials demonstrating a clinical benefit, such as improvement in disease-related symptoms or increased survival, compared to any other treatment.

CONTRAINDICATIONS

Mylotarg is contraindicated in patients with a known hypersensitivity to gemtuzumab ozogamicin or any of its components: anti-CD33 antibody (hP67.6), calicheamicin derivatives, or inactive ingredients.

WARNINGS

Mylotarg should be administered under the supervision of physicians experienced in the treatment of acute leukemia and in facilities equipped to monitor and treat leukemia patients.

There are no controlled trials demonstrating efficacy and safety using Mylotarg in combination with other chemotherapeutic agents. Therefore, Mylotarg should only be used as single agent chemotherapy and not in combination chemotherapy regimens outside clinical trials.

Myelosuppression: Severe myelosuppression will occur in all patients given the recommended dose of this agent. Careful hematologic monitoring is required. Systemic infections should be treated.

Hypersensitivity Reactions Including Anaphylaxis, Infusion Reactions, Pulmonary Events: Mylotarg administration can result in severe hypersensitivity reactions (including anaphylaxis), and other infusion-related reactions which may include severe pulmonary events. Infrequently, hypersensitivity reactions and pulmonary events have been fatal. In most cases, infusion-related symptoms occurred during the infusion or within 24 hours of administration of Mylotarg and resolved.

Mylotarg infusion should be interrupted for patients experiencing dyspnea or clinically significant hypotension. Patients should be monitored until signs and symptoms completely resolve. Discontinuation of further Mylotarg treatment should be strongly considered for patients who develop anaphylaxis, pulmonary edema, or acute respiratory distress syndrome. Since patients with high peripheral blast counts may be at greater risk for such reactions, physicians should consider leukoreduction with hydroxyurea or leukapheresis to reduce the peripheral white count to below 30,000/μL prior to administration of Mylotarg.

Infusion Reactions: Mylotarg can produce a post-infusion symptom complex of fever and chills, and less commonly hypotension and dyspnea that may occur during the first 24 hours after administration. Grade 3 or 4 non-hematologic infusion-related adverse events included chills, fever, hypotension, hypertension, hyperglycemia, hypoxia, and dyspnea. Most patients received the following prophylactic medications before administration: diphenhydramine 50 mg po and acetaminophen 650-1000 mg po; thereafter, two additional doses of acetaminophen 650-1000 mg po, one every 4 hours as needed. Vital signs should be monitored during infusion and for the four hours following infusion.

In clinical studies, these symptoms generally occurred after the end of the 2-hour intravenous infusion and resolved after 2 to 4 hours with a supportive therapy of acetaminophen, diphenhydramine, and IV fluids. Fewer infusion-related events were observed after the second dose.

Pulmonary Events: Severe pulmonary events leading to death have been reported infrequently with the use of Mylotarg in the postmarketing setting. Signs, symptoms and clinical findings include dyspnea, pulmonary infiltrates, pleural effusions, non-cardiogenic pulmonary edema, pulmonary insufficiency and hypoxia, and acute respiratory distress syndrome. These events occur as sequelae of infusion reactions; patients with WBC counts ≥ 30,000/μL may be at increased risk. (See Infusion Reactions section of WARNINGS.) Physicians should consider leukoreduction with hydroxyurea or leukapheresis to reduce the peripheral white count to below 30,000/μL prior to administration of Mylotarg. Patients with symptomatic intrinsic lung disease may also be at greater risk of severe pulmonary reactions.

Hepatotoxicity: Hepatotoxicity, including severe VOD, has been reported in association with the use of Mylotarg as a single agent, as part of a combination chemotherapy regimen, and in patients without a history of liver disease or HSCT. Patients who receive Mylotarg either before or after HSCT, patients with underlying hepatic disease or abnormal liver function, and patients receiving Mylotarg in combinations with other chemotherapy may be at increased risk for developing VOD, including severe VOD. Patients who had received HSCT before Mylotarg were at a higher risk of VOD (22%) than patients who had not been transplanted (1%). Patients who had received HSCT following Mylotarg were at a higher risk of VOD (15%) than patients who had not been transplanted (1%). Death from liver failure and from VOD has been reported in patients who received Mylotarg. Physicians should monitor their patients carefully for symptoms of hepatotoxicity, particularly VOD. These symptoms can include: rapid weight gain, right upper quadrant pain, hepatomegaly, ascites, elevations in bilirubin and/or liver enzymes. However, careful monitoring may not identify all patients at risk or prevent the complications of hepatotoxicity. (See ADVERSE REACTIONS section.)

Use in Patients with Hepatic Impairment: Mylotarg has not been studied in patients with bilirubin > 2 mg/dL. Extra caution should be exercised when administering Mylotarg in patients with hepatic impairment (see ADVERSE REACTIONS section).

Tumor Lysis Syndrome (TLS): TLS may be a consequence of leukemia treatment with any chemotherapeutic agent including Mylotarg. Renal failure secondary to TLS has been reported in association with the use of Mylotarg. Appropriate measures, (e.g. hydration and allopurinol), must be taken to prevent hyperuricemia. Physicians should consider leukoreduction with hydroxyurea or leukapheresis to reduce the peripheral white blood count to < 30,000/μL prior to administration of Mylotarg (see CLINICAL STUDIES section).

Pregnancy: Mylotarg may cause fetal harm when administered to a pregnant woman. Daily treatment of pregnant rats with gemtuzumab ozogamicin during organogenesis caused dose-related decreases in fetal weight in association with dose-related decreases in fetal skeletal ossification beginning at 0.025 mg/kg/day. Doses of 0.060 mg/kg/day (approximately 0.04 times the recommended human single dose on a mg/m2 basis) produced increased embryo-fetal mortality (increased numbers of resorptions and decreased numbers of live fetuses per litter). Gross external, visceral, and skeletal alterations at the 0.060 mg/kg/day dose level included digital malformations (ectrodactyly, brachydactyly) in one or both hind feet, absence of the aortic arch, wavy ribs, anomalies of the long bones in the forelimb(s) (short/thick humerus, misshapen radius and ulna, and short/thick ulna), misshapen scapula, absence of vertebral centrum, and fused sternebrae. This dose was also associated with maternal toxicity (decreased weight gain, decreased food consumption). There are no adequate and well-controlled studies in pregnant women. If Mylotarg is used in pregnancy, or if the patient becomes pregnant while taking it, the patient should be apprised of the potential hazard to the fetus. Women of childbearing potential should be advised to avoid becoming pregnant while receiving treatment with Mylotarg.

PRECAUTIONS

DO NOT ADMINISTER AS AN INTRAVENOUS PUSH OR BOLUS

General

Treatment by Experienced Physicians: Mylotarg should be administered under the supervision of physicians experienced in the treatment of acute leukemia and in facilities equipped to monitor and treat leukemia patients.

Laboratory Monitoring: Electrolytes, tests of hepatic function, complete blood counts (CBCs) and platelet counts should be monitored during Mylotarg therapy.

Drug Interactions: There have been no formal drug-interaction studies performed with Mylotarg. The potential for drug-drug interaction with drugs affected by cytochrome P450 enzymes may not be ruled out.

Laboratory Test Interactions: Mylotarg is not known to interfere with any routine diagnostic tests.

Carcinogenesis, Mutagenesis, Impairment of Fertility: No long-term studies in animals have been performed to eva luate the carcinogenic potential of Mylotarg. Gemtuzumab ozogamicin was clastogenic in the mouse in vivo micronucleus test. This positive result is consistent with the known ability of calicheamicin to cause double-stranded breaks in DNA. Gemtuzumab ozogamicin adversely affected male, but not female, fertility in rats. Following daily administration of gemtuzumab ozogamicin to male rats for 28 days at doses of 0.02 to 0.16 mg/kg/day (approximately 0.01 to 0.11 times the human dose on a mg/m2 basis) gemtuzumab ozogamicin caused: decreased fertility rates, epididymal sperm counts, and sperm motility; increased incidence of sperm abnormalities; and microscopic evidence of decreased spermatogonia and spermatocyte count. These findings did not resolve following a 9-week recovery period.

Pregnancy Category D: See WARNINGS section.

Nursing Mothers: It is not known if Mylotarg is excreted in human milk. Because many drugs, including immunoglobulins, are excreted in human milk, and because of the potential for serious adverse reactions in nursing infants from Mylotarg, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use: The safety and effectiveness of Mylotarg in pediatric patients have not been established.

Use in Patients with Renal Impairment: Patients with renal impairment were not studied.

ADVERSE REACTIONS

Mylotarg has been administered to 277 patients with relapsed AML at 9 mg/m2. Mylotarg was generally given as two intravenous infusions separated by 14 days.

Acute Infusion-Related Events (Table 3)

Fever and chills were commonly reported despite prophylactic treatment with acetaminophen and antihistamines (see WARNINGS section). Generally, these symptoms occurred at the end of the 2 hour infusion and resolved after 2 to 4 hours with supportive therapy including acetaminophen, diphenhydramine, and intravenous fluids. These events all occurred on the same day as gemtuzumab ozogamicin infusion. Fewer infusion-related events were observed after the second dose. Methylprednisolone given prior to Mylotarg infusion may ameliorate infusion-related symptoms.

Antibody Formation: Antibodies to gemtuzumab ozogamicin were not detected in any of the 277 patients, including the 20 patients who received more than 1 course of study drug, in the Phase 2 clinical studies. Two patients in a Phase 1 study developed antibody titers against the calicheamicin/calicheamicin-linker portion of gemtuzumab ozogamicin after three doses. One patient experienced transient fever, hypotension and dyspnea; the other patient had no clinical symptoms. No patient developed antibody responses to the hP67.6 antibody portion of Mylotarg.

Myelosuppression: Severe myelosuppression is the major toxicity associated with Mylotarg.

Neutropenia: During the treatment phase, 267/272 (98%) patients experienced Grade 3 or Grade 4 neutropenia. For all patients, the median times to ANC recovery at 500/μL for the CR and CRp patients were 40.0 and 43.0 days, respectively.

Anemia, Thrombocytopenia: During the treatment phase, 143/276 (52%) patients experienced Grade 3 or Grade 4 anemia and 272/276 (99%) patients experienced Grade 3 or Grade 4 thrombocytopenia. A summary of the platelet recovery for responding patients is provided in Table 4.

Infection: During the treatment phase, 84/277 (30%) patients experienced Grade 3 or Grade 4 infections, including opportunistic infections. The most frequent Grade 3 or Grade 4 infection-related treatment-emergent adverse events (TEAEs) were sepsis (17%), pneumonia (8%), shock (4%), infection (3%), stomatitis (2%), and herpes simplex (2%).

Bleeding: During the treatment phase, 36/277 (13%) patients experienced Grade 3 or Grade 4 bleeding. The most common bleeding events for all patients were epistaxis (3%), cerebral hemorrhage (2%), intracranial hemorrhage (1%), melena (1%), petechiae (1%), hematuria (1%), and disseminated intravascular coagulation (1%).

A greater proportion of NR patients (15%) experienced NCI grade 3 or 4 bleeding events compared with OR patients (7%). Among CR patients, 1 grade 3 bleeding event, epistaxis, was experienced. Bleeding events occurred in 1/35 CR patients and 4/36 CRp patients.