Gemtuzumab ozogamicin (Mylotarg) monotherapy for relapsed AML after hematopoietic stem cell transplant: efficacy and incidence of hepatic veno-occlusive disease

Stepping forward in antibody-drug conjugate development

Antibody-drug conjugates (ADCs) are cancer therapeutic agents comprised of an antibody, a linker and a small-molecule payload. ADCs use the specificity of the antibody to target the toxic payload to tumor cells. After intravenous administration, ADCs enter circulation, distribute to tumor tissues and bind to the tumor surface antigen. The antigen then undergoes endocytosis to internalize the ADC into tumor cells, where it is transported to lysosomes to release the payload. The released toxic payloads can induce apoptosis through DNA damage or microtubule inhibition and can kill surrounding cancer cells through the bystander effect. The first ADC drug was approved by the United States Food and Drug Administration (FDA) in 2000, but the following decade saw no new approved ADC drugs. From 2011 to 2018, four ADC drugs were approved, while in 2019 and 2020 five more ADCs entered the market. This demonstrates an increasing trend for the clinical development of ADCs. This review summarizes the recent clinical research, with a specific focus on how the in vivo processing of ADCs influences their design. We aim to provide comprehensive information about current ADCs to facilitate future development.

Gemtuzumab ozogamicin for the treatment of acute myeloid leukemia in adults

INTRODUCTION

Treatment of acute myeloid leukemia (AML) has changed dramatically in the past ten years with the approval of targeted agents, the first of which was the anti-CD33 antibody-drug conjugate gemtuzumab ozogamicin (GO). Despite withdrawal from the market after accelerated approval, GO was reapproved and now has a well-established role in treating select AML patients. CD33 has proven to be an important target for drug development in AML as evidenced by the improvement in survival with GO treatment.

AREAS COVERED

The review summarizes the development of GO, its mechanism of action, initial studies and approval, withdrawal from the market, and subsequent reapproval after the results of several large randomized studies became available. We also provide an overview of its current role in the treatment landscape of AML.

EXPERT OPINION

Multiple phase 3 trials with GO have established a significant benefit with GO in induction therapy for favorable risk AML. Additional studies support the use of GO in relapsed/refractory AML and APL. Despite the withdrawal of GO from the market after initial approval, GO has proven to improve survival of select AML patients when added to induction chemotherapy and in relapsed disease.

First-in-human, phase I study of PF-06647263, an anti-EFNA4 calicheamicin antibody-drug conjugate, in patients with advanced solid tumors

PF-06647263, a novel antibody-drug conjugate consisting of an anti-EFNA4 antibody linked to a calicheamicin payload, has shown potent antitumor activity in human xenograft tumor models, including triple-negative breast cancer (TNBC). In the dose-escalation part 1 of this multicenter, open-label, phase I study (NCT02078752), successive cohorts of patients (n, 48) with advanced solid tumors and no available standard therapy received PF-06647263 every 3 weeks (Q3W) or every week (QW), following a modified toxicity probability interval (mTPI) method (initial dosing: 0.015 mg/kg Q3W). Primary objective in part 1 was to estimate the maximum tolerated dose (MTD) and select the recommended phase 2 dose (RP2D). In part 2 (dose-expansion cohort), 12 patients with pretreated, metastatic TNBC received PF-06647263 at the RP2D to further evaluate tumor response and overall safety. PF-06647263 QW administration (n, 23) was better tolerated than the Q3W regimen (n, 25) with only 1 DLT reported (thrombocytopenia). The most common AEs with the QW regimen (fatigue, nausea, vomiting, mucosal inflammation, thrombocytopenia, and diarrhea) were mostly mild to moderate in severity. The MTD was not estimated. PF-06647263 exposures increased in a dose-related manner across the doses evaluated. The RP2D was determined to be 0.015 mg/kg QW. Six (10%) patients achieved a confirmed partial response and 22 (36.7%) patients had stable disease. No correlations were observed between tumor responses and EFNA4 expression levels. Study findings showed manageable safety and favorable PK for PF-06647263 administered QW at the RP2D, with preliminary evidence of limited antitumor activity in patients with TNBC and ovarian cancer.

A phase 1 trial of vadastuximab talirine combined with hypomethylating agents in patients with CD33-positive AML

Treatment of acute myeloid leukemia (AML) among the elderly is challenging because of intolerance of intensive therapy and therapy-resistant biology. Hypomethylating agents (HMAs) are commonly used, with suboptimal outcomes. Vadastuximab talirine is a CD33-directed antibody conjugated to pyrrolobenzodiazepine (PBD) dimers. Preclinically, HMAs followed by vadastuximab talirine produced upregulated CD33 expression, increased DNA incorporation by PBD, and enhanced cytotoxicity. A combination cohort in a phase 1 study (NCT01902329) assessed safety, tolerability, and activity of vadastuximab talirine with HMAs. Those eligible had Eastern Cooperative Oncology Group status 0 to 1 and previously untreated CD33-positive AML, and declined intensive therapy. Vadastuximab talirine was administered intravenously at 10 μg/kg on last day of HMA (azacitidine or decitabine) infusion in 4-week cycles. Among 53 patients treated, the median age was 75 years. Patients had adverse (38%) or intermediate (62%) cytogenetic risk. Median treatment duration was 19.3 weeks. No dose-limiting toxicities were reported. The majority of adverse events were a result of myelosuppression, with some causing therapy delays. Thirty- and 60-day mortality rates were 2% and 8%, respectively. The composite remission rate (complete remission [CR] and CR with incomplete blood count recovery) was 70%. Fifty-one percent of remissions were minimal residual disease-negative by flow cytometry. Similarly high remission rates were observed in patients with secondary AML, aged at least 75 years, and with adverse cytogenetic risk. Median relapse-free survival and overall survival were 7.7 and 11.3 months, respectively. Compared with historical data for HMA monotherapy, the combination of vadastuximab talirine with HMAs produced a high remission rate, but was accompanied by increased hematologic toxicity.

Interferon-γ Promotes Antibody-mediated Fratricide of Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) is characterized by the proliferation of immature myeloid lineage blasts. Due to its heterogeneity and to the high rate of acquired drug resistance and relapse, new treatment strategies are needed. Here, we demonstrate that IFNγ promotes AML blasts to act as effector cells within the context of antibody therapy. Treatment with IFNγ drove AML blasts toward a more differentiated state, wherein they showed increased expression of the M1-related markers HLA-DR and CD86, as well as of FcγRI, which mediates effector responses to therapeutic antibodies. Importantly, IFNγ was able to up-regulate CD38, the target of the therapeutic antibody daratumumab. Because the antigen (CD38) and effector receptor (FcγRI) were both simultaneously up-regulated on the AML blasts, we tested whether IFNγ treatment of the AML cell lines THP-1 and MV4-11 could stimulate them to target one another after the addition of daratumumab. Results showed that IFNγ significantly increased daratumumab-mediated cytotoxicity, as measured both by ⁵¹Cr release and lactate dehydrogenase release assays. We also found that the combination of IFNγ and activation of FcγR led to the release of granzyme B by AML cells. Finally, using a murine NSG model of subcutaneous AML, we found that treatment with IFNγ plus daratumumab significantly attenuated tumor growth. Taken together, these studies show a novel mechanism of daratumumab-mediated killing and a possible new therapeutic strategy for AML.

Thromboembolism in Cancer Patients: Pathogenesis and Treatment

In this review we summarize the causes of cancer related thrombosis as well as modern treatment approaches. Malignancy as a risk factor for thromboembolism is becoming increasingly recognized by clinicians caring for these patients. The probability of thrombosis occurring in an individual patient is dependent on several factors, including accompanying medical problems, the type of cancer, the clinical stage, performance status, and the treatment modalities employed. Thrombophilia with a history of thromboembolism is important as well. The overall risk of thrombosis is sevenfold that of noncancer patients. Though much has been learned about the pathogenesis of cancer-related thrombosis, we are in fact just beginning to understand the cross-talk between cancer cells and their related microenvironment, and such investigations are likely to increase our knowledge of cancer-related thrombosis mechanisms. Research in these areas may also suggest new strategies for cancer prevention, metastasis suppression, and new treatments. Drugs used in cancer therapy are increasingly recognized to directly contribute to the thrombotic tendency. Few studies provide data on the optimal management of cancer patients with thrombosis. It has been learned that retreating with the same drug can be very hazardous. In general the approach to prevention of thrombosis is the same as for noncancer patients, recognizing that specific cancer types and stage can place a patient in a high-risk category. Initial coumadin therapy fails in a significant number of patients with cancer. Recognition of the cancer patients at highest risk for coumadin failure is challenging. Low-molecular-weight heparins appear to be more effective in such situations where coumadin is likely to fail or has failed, but these drugs are thought to be costlier. Newer agents such as Factor Xa inhibitors and TF inhibitors are currently under investigation and may be found useful in the management of cancer-related thrombosis.

Results from the first decade of research conducted by the Research on Adverse Drug Events and Reports (RADAR) project

INTRODUCTION

In 1998, a multidisciplinary team of investigators initiated the Research on Adverse Drug events And Reports (RADAR) project, a post-marketing surveillance effort that systematically investigates and disseminates information describing serious and previously unrecognized serious adverse drug and device reactions (sADRs).

OBJECTIVE

Herein, we describe the findings, dissemination efforts, and lessons learned from the first decade of the RADAR project.

METHODS

After identifying serious and unexpected clinical events suitable for further investigation, RADAR collaborators derived case information from physician queries, published and unpublished clinical trials, case reports, US FDA databases and manufacturer sales figures.

STUDY SELECTION

All major RADAR publications from 1998 to the present are included in this analysis.

DATA EXTRACTION

For each RADAR publication, data were abstracted on data source, correlative basic science findings, dissemination and resultant safety information.

RESULTS

RADAR investigators reported 43 serious ADRs. Data sources included case reports (17 sADRs), registries (5 sADRs), referral centers (8 sADRs) and clinical trial reports (13 sADRs). Correlative basic science findings were reported for ten sADRs. Thirty-seven sADRS were described as published case reports (5 sADRs) or published case-series (32 sADRs). Related safety information was disseminated as warnings or boxed warnings in the package insert (17 sADRs) and/or 'Dear Healthcare Professional' letters (14 sADRs).

CONCLUSION

An independent National Institutes of Health-funded post-marketing surveillance programme can supplement existing regulatory and pharmaceutical manufacturer-supported drug safety initiatives.

Incidence of sinusoidal obstruction syndrome following Mylotarg (gemtuzumab ozogamicin): a prospective observational study of 482 patients in routine clinical practice

The purpose of this prospective observational study was to determine the incidence of hepatic sinusoidal obstruction syndrome (SOS), following gemtuzumab ozogamicin (GO) therapy in routine clinical practice. Patients receiving GO for acute myeloid leukemia (AML) were eligible. Assessments were requested to be performed weekly for 6 weeks after the start of GO therapy or 4 weeks after the last dose (whichever was later), and after 6 months. The primary outcome variable was the incidence of SOS as judged by a panel of independent experts. A total of 512 patients were enrolled at 54 US centers and 482 were evaluable. The incidence of SOS in this study population was 9.1 % (44/482; 95 % confidence interval 6.9-12.0 %). Of the 44 patients classified as having SOS, 8 were mild, 17 moderate, and 19 severe; 33 died within 6 months (20 of disease progression and 13 of SOS and multiorgan failure). Most (68 %) patients in the study died within 6 months; most of these deaths (73 %) were due to progression of AML. Serious adverse events occurred in 85 % of patients, most (81 %) due to AML, febrile neutropenia, pyrexia, and sepsis. GO administered in routine clinical practice carries an overall 9.1 % risk of SOS and a 2.7 % risk of death from SOS and multiorgan failure. No risk factors were identified for the development of SOS.

Multiple isolated extramedullary relapse of acute promyelocytic leukemia after allogeneic hematopoietic stem cell transplant: a case report and review of literature

Isolated extramedullary disease (EMD) is uncommon, especially in acute promyelocytic leukemia (APL) after allogeneic hematopoietic stem cell transplantation (HSCT). We review the literature and present a 32 year old woman with APL who developed multiple EMDs after allogeneic HSCT within the calvarium, and later found to have various isolated lesions including femur, humerus and thoraco lumbar vertebrae. She was treated with local radiotherapy (XRT) to EMD lesions, all-trans retinoic acid, arsenic trioxide and donor lymphocyte infusion at different time points in her clinical course, without success. Out of reported cases in clinical setting as ours, average onset of isolated EMD is 25 months and median survival 14 months. Effective treatment of isolated EMD after HSCT is not yet clear, but ATO in combination with local XRT, tamibarotene and second HSCT have shown good results in some reported cases, but accumulation of more cases is needed to elucidate optimal therapy in such setting.

What is the impact, present and future, of novel targeted agents in acute lymphoblastic leukemia?

The absence of a standard of care for adults with acute lymphoblastic leukemia (ALL), the inadequate outcome of all adult regimens, and the lack of improvement in treatment outcomes over the past decades suggest a critical need for new approaches to treating adults with this disease. Several new strategies are now being considered, including the use of novel targeted agents alone and in combination with other chemotherapeutic drugs. This paper discusses several of these approaches and their impact on overall outcome.

Gemtuzumab ozogamicin as postconsolidation therapy does not prevent relapse in children with AML: results from NOPHO-AML 2004

There are no data on the role of postconsolidation therapy with gemtuzumab ozogamicin (GO; Mylotarg) in children with acute myeloid leukemia (AML). The NOPHO-AML 2004 protocol studied postconsolidation randomization to GO or no further therapy. GO was administered at 5 mg/m(2) and repeated after 3 weeks. We randomized 120 patients; 59 to receive GO. Survival was analyzed on an intention-to-treat basis. The median follow-up for patients who were alive was 4.2 years. Children who received GO showed modest elevation of transaminase and bilirubin without signs of veno-occlusive disease. Severe neutropenia followed 95% and febrile neutropenia 40% of the GO courses. Only a moderate decline in platelet count and a minor decrease in hemoglobin occurred. Relapse occurred in 24 and 25 of those randomized to GO or no further therapy. The median time to relapse was 16 months versus 10 months (nonsignificant). The 5-year event-free survival and overall survival was 55% versus 51% and 74% versus 80% in those randomized to receive GO or no further therapy, respectively. Results were similar in all subgroups. In conclusion, GO therapy postconsolidation as given in this trial was well tolerated, showed a nonsignificant delay in time to relapse, but did not change the rate of relapse or survival (clinicaltrials.gov identifier NCT00476541).

Role of tumor vascular architecture in drug delivery

Tumor targeted drug delivery has the potential to improve cancer care by reducing non-target toxicities and increasing the efficacy of a drug. Tumor targeted delivery of a drug from the systemic circulation, however, requires a thorough understanding of tumor pathophysiology. A growing or receding (under the impact of therapy) tumor represents a dynamic environment with changes in its angiogenic status, cell mass, and extracellular matrix composition. An appreciation of the salient characteristics of tumor vascular architecture and the unique biochemical markers that may be used for targeting drug therapy is important to overcome barriers to tumor drug therapy and to facilitate targeted drug delivery. This review discusses the unique aspects of tumor vascular architecture that need to be overcome or exploited for tumor targeted drug delivery.

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 follow-up 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 beneft from this treatment.

Efficacy of fractionated gemtuzumab ozogamicin combined with cytarabine in advanced childhood myeloid leukaemia

Gemtuzumab ozogamicin (GO) monotherapy is reported to yield a 20-30% response rate in advanced acute myeloid leukaemia (AML). This study examined the efficacy and tolerability of GO combined with cytarabine (GOCYT) in children with refractory/relapsed CD33(+) AML. Seventeen children received GO 3 mg/m(2) on days 1, 4 and 7 plus cytarabine 100 mg/m(2)/d for 7 d on a compassionate-use basis. Seven patients then received GO-based consolidation. At the outset of GOCYT, two patients were refractory; eight patients were in refractory first relapse; six patients had relapsed after stem cell transplantation (SCT); and one patient [del(5q) therapy-related AML (t-AML)] had not yet been treated. Mean follow-up was 17 months (8-33 months). Ten responses were obtained after GOCYT induction, including complete remission (CR) or CR without complete recovery of platelets (CRp) in six patients (35%). The responses improved in three children who received GOCYT consolidation, increasing the CR + CRp rate to 53%. SCT was subsequently performed in eight responders. Grade 3-4 adverse events consisted of haematological disorders (n = 17, 100%) and documented infections (n = 5, 29%). No cases of sinusoidal obstructive syndrome occurred. Three patients were alive at the cut-off date for this analysis, all of whom had responded to GOCYT. GOCYT combination therapy yielded a high response rate (53%) and showed acceptable toxicity in heavily pretreated children with refractory/relapsed AML. These results warrant a larger prospective study.

Gemtuzumab-ozogamicin in combination with fludarabine, cytarabine, idarubicin (FLAI-GO) as induction therapy in CD33-positive AML patients younger than 65 years

INTRODUCTION

The addition of gemtuzumab-ozogamicin (GO) to an induction regimen including synergistic drugs, such as intermediate dose of cytarabine (Ara-C), idarubicin and fludarabine (FLAI), could reduce treatment failure in acute myeloid leukemia (AML) patients. Nevertheless, the role and safety of this antibody target-therapy in first-line chemotherapy in patients younger than 65 years has not yet been defined.

PATIENTS AND METHODS

The primary goal of this prospective phase II pilot study was to evaluate the efficacy and the safety profile of FLAI plus GO as induction regimen. Thirty consecutive AML patients were included. All patients were younger than 65 with a median age of 53 years and CD33 expression exceeded 20% in all cases. The M/F ratio was 16/14 and 21/30 (70%) of patients were poor-risk at diagnosis. The induction regimen (FLAI-GO) included fludarabine (30mg/m(2)) and Ara-C (2g/m(2)) on days 1-5, idarubicin (10mg/m(2)) on days 1, 3, and 5 and GO (3mg/m(2)) on day 6. Hematopoietic stem cell transplant (HSCT) was planned for all high risk AML patients in first complete remission (CR) after consolidation with intermediate doses of Ara-C and idarubicin (IDAC-IDA). Cytogenetic, multidrug-resistance phenotype, FLT3 mutation status, and WT1 quantitative expression analyses were performed at diagnosis in all patients. WT1 expression and cytogenetic (in positive cases) analyses were performed after induction to detect and follow minimal residual disease.

RESULTS

Patients were evaluated for response rate, treatment-related adverse events, overall survival and relapse free survival. After induction with FLAI-GO, CR rate was 90% (26 of 29 evaluable pts); one patient achieved partial remission and two were resistant. There was only one case of death during induction (DDI). After FLAI-GO, the mean value of WT1 dropped from 4200+/-2777 copies/10(4)ABL to 192+/-399 copies/10(4)ABL. The toxicity of FLAI-GO was acceptable; 57% of patients experienced transient and reversible GO infusion-related adverse events (especially fever and chills), but no cases of veno-occlusive disease occurred during CHT or after HSCT. After a median follow-up of 16 months (range 2-25), 24/30 (80%) patients are alive (24/24 in CR). The probability of 1-year OS and RFS was 90 and 85%, respectively. Allogeneic and autologus HSCT was performed in 19 (63%) and 4 (13%) patients, respectively.

CONCLUSIONS

These preliminary results suggest that FLAI-GO is an effective and well tolerated induction regimen for CD33 positive AML patients younger than 65 years, with a high complete response rate, favourable safety profile, low DDI. These results encourage the testing of this regimen in a multicenter prospective trial.

Monoclonal antibodies as targeted therapy in hematologic malignancies in older adults

BACKGROUND

Biological agents are proving to be increasingly useful and exciting additions to the antineoplastic armamentarium, but many clinicians are unfamiliar with the properties of these types of agents.

OBJECTIVES

This review focuses on monoclonal antibodies (MAbs) that are used in the treatment of hematologic malignancies. Our goal was to provide the reader with information on trials that led to US Food and Drug Administration (FDA) approval of commonly used MAbs in hematologic malignancies, including their mechanisms of action and pharmacokinetics, with specific emphasis on use in elderly patients; we also present data on toxicities and precautions to be aware of when administering these drugs.

METHODS

Materials for this review were gathered based on a computerized literature search (English-language articles only) using the PubMed database covering the period January 1998 to December 2005. Search terms used included the following: elderly, monoclonal antibodies, and neoplasms.

RESULTS

Alemtuzumab is a recombinant DNA-derived, humanized MAb directed against the CD52 B-cell antigen. It is indicated for the treatment of B-cell chronic lymphocytic leukemia (CLL) in patients who have been treated with alkylating agents and who have failed to respond to fludarabine therapy. Gemtuzumab ozogamicin is an MAb conjugated with a cytotoxic antitumor antibiotic, calicheamicin. It has been approved for use in patients with CD33-positive acute myeloid leukemia (AML) in first relapse who are aged > or =60 years and who are not considered candidates for other cytotoxic chemotherapy. Rituximab, one of the first MAbs approved by the FDA for use in human cancers, is an antibody directed against the CD20 antigen found on the surface of normal and malignant B lymphocytes. It is extensively used in the treatment of B-cell malignancies, such as CLL, and non-Hodgkin's lymphomas (NHLs), such as follicular lymphoma and diffuse large B-cell lymphoma.

CONCLUSIONS

It is noteworthy that while there have been a number of studies using these agents in the younger population, there continues to be a paucity of clinical trials targeting the elderly patient in particular; this continues to be an area of research interest. More clinical studies of these agents--conducted specifically in elderly patients with CLL, NHL, AML, and other hematologic malignancies--are needed.

Gemtuzumab ozogamicin, cytosine arabinoside, G-CSF combination (G-AraMy) in the treatment of elderly patients with poor-prognosis acute myeloid leukemia

BACKGROUND

Gemtuzumab ozogamicin (GO) is effective as single agent in the treatment of acute myeloid leukemia (AML). We evaluated efficacy and safety of a chemotherapy including growth factors, cytarabine, and GO (G-AraMy) in the treatment of poor-prognosis AML in elderly patients.

PATIENTS AND METHODS

In three Italian hematology departments from September 2003 to September 2006, 53 elderly patients [median age 69 years (range 65-77)] with untreated or primary refractory/relapsed AML were enrolled on the combination G-AraMy administered according to two consecutive schedules (G-AraMy1 and G-AraMy2), with intensified consolidation in the second. Twenty-three of 53 patients had a secondary acute myeloid leukemia (sAML).

RESULTS

The overall response rate was 57%. The most common adverse event was myelosuppression. Seven patients died in induction (13%). No differences for response rate and toxicity profile were observed between untreated and primary resistant/relapsed patients, de novo AML and sAML, and in the two treatment trials. Median disease-free survival and overall survival were 8 months (range 2-23+) and 9 months (range 2-24+).

CONCLUSIONS

G-AraMy therapy may be considered an useful treatment approach for poor-risk elderly AML patients, with a complete remission rate comparable to literature data with reduced side-effects, also in a poor-prognosis population.

Gemtuzumab therapy for isolated extramedullary AML relapse following allogeneic stem-cell transplant

BACKGROUND

A 19-year-old male with primary refractory acute myeloid leukemia received salvage therapy with mitoxantrone and cytarabine combination. He received consolidation therapy 3 months later with a matched-unrelated-donor stem-cell transplant. The disease relapsed in the bone marrow (BM) 9 months after the initial stem-cell transplant, and was successfully treated by repeat transplant from the same donor. Ten months following repeat transplant, the patient presented with an increasing number of extramedullary sites of biopsy-proven disease relapse (i.e. cranial and peripheral nerves, tongue, abdominal wall and chest wall). Repeated biopsy of the BM and chimera study showed no morphologic evidence of leukemic infiltrate with 100% donor-cell population.

INVESTIGATIONS

Physical examination, complete blood count, BM biopsy, flow cytometry, cytogenetic analysis, chimera study, tongue biopsy, abdominal-wall biopsy, cytology and immunohistochemistry, CT scan of the chest, abdomen and pelvis, MRI of the brain, and cerebrospinal fluid analysis.

DIAGNOSIS

Isolated extramedullary relapse of acute myeloid leukemia after stem-cell transplant.

MANAGEMENT

Primary leukemia treatment with idarubicin, cytarabine, etoposide, dexamethasone, tioguanine on protocol and salvage therapy with mitoxantrone and cytarabine combination for primary refractory disease. A matched-unrelated-donor stem-cell transplant for consolidation and donor-lymphocyte infusions were performed, followed by repeat unrelated-donor transplant for leukemia relapse in the marrow, radiation therapy and gemtuzumab ozogamicin for multiple sites of extramedullary leukemia relapse.

Cancer chemotherapy II: atypical hepatic injuries

Although chemotherapy generally is accompanied by regular testing for liver enzyme abnormalities, atypical reactions may occur that escape ordinary detection, because hepatocyte injury is not the primary event. The presence of fatty liver, mitochondrial changes, and even biliary abnormalities can be associated with normal or nearly normal liver enzyme levels. This article discusses unique aspects of liver damage associated with cancer chemotherapy. These unique reactions merit special attention and a special vigilance from clinicians.

The role of Gemtuzumab Ozogamicin in the treatment of acute myeloid leukemia patients

Gemtuzumab Ozogamicin (GO) is an antibody-targeted chemotherapy agent consisting of the humanized murine CD33 antibody (clone P67.6) to which the calicheamicin-g1 derivative is attached via a hydrolysable bifunctional linker. GO is able to induce apoptosis in vitro in CD33-expressing cells and it has been approved in USA and in Europe as monotherapy for the treatment of elderly patients (older than 60 years) with relapsed acute myeloid leukemia (AML). GO administered as a single agent has resulted in overall response rates of about 30% in previously relapsed adults AML patients (including also with incomplete platelet recovery). Preliminary data indicate a potential role for GO also as a component of induction or consolidation regimens in adults and children. As for adverse events, veno-occlusive syndrome characterizes its tolerability profile, but GO is comparatively well tolerated by most patients.

Applying Mechanisms of Chemical Toxicity to Predict Drug Safety

Toxicology can no longer be used only as a science that reacts to problems but must be more proactive in predicting potential human safety issues with new drug candidates. Success in this area must be based on an understanding of the mechanisms of toxicity. This review summarizes and extends some of the concepts of an American Chemical Society ProSpectives meeting on the title subject held in June 2006. One important area is the discernment of the exact nature of the most common problems in drug toxicity. Knowledge of chemical structure alerts and relevant biological pathways are important. Biological activation to reactive products and off-target pharmacology are considered to be major contexts of drug toxicity, although defining exactly what the contributions are is not trivial. Some newer approaches to screening for both have been developed. A goal in predictive toxicology is the use of in vitro methods and database development to make predictions concerning potential modes of toxicity and to stratify drug candidates for further development. Such predictions are desirable for several economic and other reasons but are certainly not routine yet. However, progress has been made using several approaches. Some examples of the application of studies of wide-scale biological responses are now available, with incorporation into development paradigms.

Prophylactic low-dose heparin or prostaglandin E1 may prevent severe veno-occlusive disease of the liver after allogeneic hematopoietic stem cell transplantation in Korean children

Studies investigating the effect of prophylactic drugs on hepatic veno-occlusive disease (VOD) development are rare in children that have undergone allogeneic hematopoietic stem cell transplantation (HSCT). This study examined risk factors for VOD, the effect of prophylactic low-dose heparin or lipo-prostaglandin E1 (lipo-PGE1) and the survival rate at day +100 in children undergoing allogeneic HSCT. Eighty five children underwent HSCT between June 1997 and September 2004. Patients were diagnosed and classified as having mild, moderate or severe VOD according to Seattle clinical criteria. Among 85 patients, 25 (29%) developed VOD. VOD occurred more frequently in patients receiving busulfan-based conditioning (24/65, 37%) than in those receiving TBI-based (1/10, 10%) or other (0/10, 0%) regimens (p<0.05). The incidence of VOD was lower in patients with non-malignant disease compared to those with malignant disease (p<0.05). Survival at day +100 for non-VOD patients was better than that for VOD patients (92% vs. 76%, p<0.05). No patients receiving prophylactic heparin or lipo-PGE1 were found to develop severe VOD, whereas 5 of 35 patients not receiving such prophylaxis developed severe VOD. Given severe VOD is associated with a high mortality rate, this study indicates that prophylactic heparin or lipo-PGE1 may decrease mortality in children undergoing HSCT.

Gemtuzumab ozogamicin-associated sinusoidal obstructive syndrome (SOS): an overview from the research on adverse drug events and reports (RADAR) project

Gemtuzumab ozogamicin (GO) was approved for marketing in 2000 by the United States Food and Drug Administration (FDA) for older patients with relapsed acute myeloid leukemia (AML). Four months later, 14 phase II clinical trial participants who received novel GO-containing combination chemotherapy regimens developed an unexpected hepatic toxicity termed sinusoidal obstructive syndrome (SOS) or hepatic veno-occlusive disease (VOD). Investigators associated with the Research on Adverse Drug Events and Reports (RADAR) project reviewed safety reports for GO included in reports of clinical trials and observational studies, interim reports from an FDA mandated Prospective Observational Registry, and the Food and Drug Administration's Adverse Event Reporting System. Medline searches provided incidence estimates of GO-associated SOS and comparative rates of SOS without GO. SOS is characterized by hyperbilirubinemia, painful hepatomegaly, ascites, and sudden weight gain developing at a median of 10 days following GO administration for patients who did not undergo an allogeneic SCT procedure and 13 days following an allogeneic SCT for patients who had previously received GO. Among adult AML patients who received GO in clinical trials, SOS incidence was 3% at doses < or =6 mg/m(2) if administered as monotherapy or in combination with non-hepatotoxic agents versus 28% if administered with thioguanine and 15% when administered as monotherapy at a dose of 9 mg/m(2). Observational studies identified SOS rates between 15% and 40% if an SCT is performed within 3 months of GO administration. The FDA mandated Prospective Observational Registry of patients who receive care at 60 medical centers has identified GO-associated SOS rates of 14% if an SCT is performed and 9% otherwise. Caution is advised when administering GO in routine clinical practice, particularly if administered with other hepatotoxic agents, at doses and schedules more intensive than those approved by the FDA, or within 3 months of a SCT procedure.

Efficacy and tolerability of gemtuzumab ozogamicin (anti-CD33 monoclonal antibody, CMA-676, Mylotarg) in children with relapsed/refractory myeloid leukemia

BACKGROUND

Gemtuzumab ozogamicin (GO) is a cytotoxic anti-CD33 monoclonal antibody that has given promising preliminary results in adult myeloid CD33+ AML. We conducted a retrospective multicenter study of 12 children treated with GO on a compassionate basis (median age 5.5 y). Three patients (2 MDS/AML, 1 JMML) were refractory to first-line treatment, 8 patients with de novo AML were in refractory first relapse, and one patient with de novo AML was in 2nd relapse after stem cell transplantation (SCT). CD33 expression exceeded 20% in all cases.

METHODS

GO was administered alone, at a unit dose of 3-9 mg/m2, once (3 patients), twice (3 patients), three (5 patients) or five times (1 patient). Mean follow-up was 128 days (8-585 d).

RESULTS

There were three complete responses (25%) leading to further curative treatment (SCT). Treatment failed in the other nine patients, and only one patient was alive at the end of follow-up. NCI-CTC grade III/IV adverse events comprised hematological toxicity (n = 12), hypertransaminasemia (n = 2), allergy and hyperbilirubinemia (1 case each). There was only one major adverse event (grade IV allergy). No case of sinusoidal obstruction syndrome occurred.

CONCLUSION

These results warrant a prospective trial of GO in a larger population of children with AML.

The role of gemtuzumab ozogamicin in acute leukaemia therapy

Gemtuzumab ozogamicin (GO) is an immunoconjugate that binds to CD33 on the surface of acute myeloid leukaemia (AML) blasts and, after internalisation, releases a cytotoxic drug, calicheamicin. GO is approved by the US Food and Drug Administration for the treatment of CD33-positive AML at first relapse in patients 60 years and older who are not candidates for other cytotoxic therapy. GO as a single agent has low antileukaemic activity. When given to patients meeting the criteria noted above, it produces a complete response (CR) rate of only 12%, with another 12% achieving CR with inadequate platelet recovery (CRp). The median survival of patients treated with GO monotherapy is 11.2 months. GO therapy at 9 mg/m(2) is complicated with hepatic veno-occlusive disease in 5-10% of patients, particularly prior to or following stem cell transplantation. GO at lower doses combined with chemotherapy as induction or postremission therapy is promising, however, and phase III trials are ongoing. GO is probably most active in acute promyelocytic leukaemia (APL). It is used for induction regimens in high-risk APL and for the elimination of minimal residual APL. Case reports suggest that GO also has activity in CD33-positive acute lymphoblastic leukaemia. In conclusion, single agent GO can induce responses in patients with CD33-positive AML in first recurrence. The future of GO is its use in combination with other cytotoxic agents. Ongoing clinical trials may better define the role of GO combinations, particularly in untreated AML.

Hepatotoxicity of Chemotherapy

The selection of an antineoplastic regimen for an oncology patient is based first on the availability of effective drugs and then on a balancing of potential treatment-related toxicities with the patient's clinical condition and associated comorbidities. Liver function abnormalities are commonly observed in this patient population and identifying their etiology is often difficult. Immunosuppression, paraneoplastic phenomena, infectious diseases, metastases, and poly-pharmacy may cloud the picture. While criteria for standardizing liver injury have been established, dose modifications often rely on empiric clinical judgment. Therefore, a comprehensive understanding of hepatotoxic manifestations for the most common chemotherapeutic agents is essential. We herein review the hepatotoxicity of commonly used antineoplastic agents and regimens.

Review article: updates in the pathogenesis and therapy of hepatic sinusoidal obstruction syndrome

Hepatic sinusoidal obstruction syndrome is frequently linked to high-dose chemotherapy/total-body irradiation in recipients of haematopoietic stem cell transplantation, long-term use of azathioprine after organ transplantation and other chemotherapeutic agents. The incidence of hepatic sinusoidal obstruction syndrome varies from 0% to 70%, and is decreasing. Disease risk is higher in patients with malignancies, hepatitis C virus infection, those who present late, when norethisterone is used to prevent menstruation, and when broad-spectrum antibiotics and antifungals are used during and after the conditioning therapy. Hepatic sinusoidal obstruction syndrome presents with tender hepatomegaly, hyperbilirubinaemia and ascites, and diagnosis is mainly clinical (Seattle and Baltimore Criteria). Imaging excludes biliary obstruction and malignancy, but cannot establish accurate diagnosis. Hepatic sinusoidal obstruction syndrome may be prevented by avoiding the highest risk regimens, using non-myelo-ablative regimens, and reducing total-body irradiation dose. Treatment is largely symptomatic and supportive, because 70-80% of patients recover spontaneously. Tissue plasminogen activator plus heparin improves outcome in <30% of cases. Defibrotide, a polydeoxyribonucleotide, is showing encouraging results. Transjugular intrahepatic porto-systemic shunt relieves ascites, but does not improve outcome. Liver transplantation may be an option in the absence of malignancy. Prognosis is variable and depends on disease severity, aetiology and associated conditions. Death is most commonly caused by renal or cardiopulmonary failure.

Preliminary Results of the Safety of Immunotherapy with Gemtuzumab Ozogamicin following Reduced Intensity Allogeneic Stem Cell Transplant in Children with CD33+ Acute Myeloid Leukemia

PURPOSE

Myeloablative allogeneic stem cell transplantation (SCT) has been successful in the treatment of childhood acute myeloid leukemia (AML), but may be associated with significant toxicity and recurrent disease. Reduced-intensity allogeneic SCT may offer a less toxic approach to patients with AML. Targeted immunotherapy with gemtuzumab ozogamicin has been shown to be safe, well tolerated in children, and, as a single agent, gemtuzumab ozogamicin has induced responses in 30% of patients with recurrent CD33+ AML. There are no safety data with gemtuzumab ozogamicin post allogeneic SCT in children. Therefore, we explored the feasibility and toxicity of targeted immunotherapy following reduced-intensity allogeneic SCT in children with CD33+ AML.

EXPERIMENTAL DESIGN

Eight patients with CD33+ AML received a reduced-intensity allogeneic SCT following fludarabine 30 mg/m2 for 6 days and busulfan 3.2 mg/kg (<4 years, 4 mg/kg/d) for 2 days. Donor sources included six 6/6 HLA-matched related peripheral blood stem cells, one 6/6 sibling cord blood, and one 4/6 unrelated cord blood.

RESULTS

Day 30 and day 60 donor chimerisms in seven of eight evaluable patients were 96 +/- 2% (n = 7) and 94 +/- 3% (n = 6), respectively. Five of six patients (too early for one patient) received two doses of gemtuzumab ozogamicin and one patient received only one dose. After each dose, all patients developed grade 4 neutropenia, with recovery on median days 16 and 13, respectively, after dose 1 and dose 2. Grade 4 thrombocytopenia was only observed in 2 of 11 gemtuzumab ozogamicin courses. No patients have developed dose-limiting toxicity secondary to gemtuzumab ozogamicin.

CONCLUSIONS

The administration of gemtuzumab ozogamicin post reduced-intensity allogeneic SCT in children with average risk AML is feasible and well tolerated with minimal toxicity. The maximal tolerated dose has yet to be determined for gemtuzumab ozogamicin post reduced-intensity allogeneic SCT in children with CD33+ AML. Additional studies in a larger group of patients will be required to adequately assess the safety of this approach.

Outcomes of transplantation with partial T-cell depletion of matched or mismatched unrelated or partially matched related donor bone marrow in children and adolescents with leukemias

Graft-versus-host disease (GVHD) remains a major barrier to successful hematopoietic stem cell transplant for patients who lack a matched related donor. Partial T-cell depletion (TCD) of the graft may decrease the risk of severe GVHD with unrelated donors (URD) and partially matched related donors (PMRD) while retaining an antileukemic effect. We analyzed our experience using URD and PMRD for pediatric patients with leukemias from 1990 to 2001. A subgroup of 'matched' URD donor pairs was retrospectively analyzed for high-resolution class I. Partial TCD was accomplished with monoclonal antibody T10B9 or OKT3 and complement. There were 76 URD (45% matched) and 28 PMRD recipients. Event-free survival (EFS) was 38.3%, and overall survival (OS) 45.1% at 3 years. On multivariate analysis, there was no difference in survival based upon marrow source, but nonrelapse mortality was higher with the use of PMRD. Relapse occurred in 6% of ALL patients, and 22.8% of AML/MDS patients. Grades III-IV GVHD was observed in only 6.7% of patients. Partial TCD allows use of matched or mismatched URD, or PMRD with little mortality from GVHD, durable engraftment, and no increase in relapse risk.

Administration of mylotarg 4 days after beginning of a chemotherapy including intermediate-dose aracytin and mitoxantrone (MIDAM regimen) produces a high rate of complete hematologic remission in patients with CD33+ primary resistant or relapsed acute myeloid leukemia

We have used the dose of 9 mg/m(2) of mylotarg 4 days after the beginning of a chemotherapy including intermediate-dose aracytin and mitoxantrone (MIDAM) in 17 patients with refractory (n=4) or relapsed (n=13) AML. Thirteen patients (76%) achieved CR (n=12) or partial CR (n=1). All four refractory patients and all four patients with poor risk cytogenetic achieved CR or CRp. Although the dose of mylotarg given in combination with chemotherapy was not reduced, the toxicity profile was acceptable (1VOD/17 patients). The MIDAM protocol appears to be highly effective especially in patients with poor risk cytogenetic and/or refractory disease.

Tumour-targeted chemotherapy with immunoconjugates of calicheamicin

Antibody-targeted chemotherapy is a therapeutic strategy in cancer therapy that involves a monoclonal antibody specific for a tumour-associated antigen, covalently linked via a suitable linker to a potent cytotoxic agent. Tumour-targeted delivery of a cytotoxic agent in the form of an immunoconjugate is expected to improve its antitumour activity and safety. Calicheamicin is a cytotoxic natural product isolated from Micromonospora echinospora that is at least 1000-fold more potent than conventional cytotoxic chemotherapeutics. Calicheamicin binds DNA in the minor groove and causes double-strand DNA breaks, leading to cell death. Immunoconjugates of calicheamicin targeted against tumour-associated antigens exhibit tumour-specific cytotoxic effects and cause regression of established human tumour xenografts in nude mice. Gemtuzumab ozogamicin is the first clinically validated cytotoxic immunoconjugate in which a humanised anti-CD33 antibody is linked to a derivative of calicheamicin. Gemtuzumab ozogamicin is indicated for the treatment of elderly patients with relapsed acute myeloid leukaemia. A similar conjugate, inotuzumab ozogamicin, is being evaluated at present in Phase I clinical trials in patients with non-Hodgkin's lymphoma. A number of tumour-targeted immunoconjugates of calicheamicin are being explored preclinically at present for their therapeutic applications.

CD33-directed therapy with gemtuzumab ozogamicin in acute myeloid leukemia: progress in understanding cytotoxicity and potential mechanisms of drug resistance

CD33 is expressed on the malignant blast cells in most cases of acute myeloid leukemia (AML) but not on normal hematopoietic pluripotent stem cells. Antibody-based therapies for AML have, therefore, focused on CD33 as a suitable tumor-associated target antigen. The most promising results have been obtained with gemtuzumab ozogamicin (GO, Mylotarg), a humanized IgG(4) anti-CD33 monoclonal antibody joined to a calicheamicin-gamma(1) derivative. Engagement of CD33 by GO results in immunoconjugate internalization and hydrolytic release of the toxic calicheamicin moiety, which, in turn, causes DNA damage and cell death. Since 2000, when GO was approved for clinical use, treatment trials and pilot studies have revealed potential expanded applications along with additional limitations. At the same time, correlative biological and in vitro functional studies have further characterized CD33 expression patterns in AML, the significance of CD33-antibody interactions, pathways involved in GO-induced cytotoxicity and potential drug resistance mechanisms. This review summarizes the recent data addressing mechanisms of GO action and discusses their relevance with regard to clinical applications and the limitations of using experimental model systems to mimic in vivo conditions. As the first drug conjugate approved for clinical use, GO serves as an important paradigm for other immunoconjugates against internalizing tumor antigens.

Gemtuzumab ozogamicin (MylotargTM) is infrequently associated with sinusoidal obstructive syndrome/veno-occlusive disease

BACKGROUND

Gemtuzumab ozogamicin (GO) is approved for the treatment of older adults with acute myeloid leukemia in first relapse. Several reports have suggested an association between GO administration and hepatic veno-occlusive disease (VOD), which has recently been termed sinusoidal obstructive syndrome (SOS). However, the majority of these studies were done in patients who had undergone high-dose therapy with stem cell transplantation or when GO was administered in combination with other cytotoxic chemotherapy.

PATIENTS AND METHODS

We performed a retrospective review of all patients treated at our institution with single-agent GO, either as initial therapy or in the relapsed and refractory setting. All patients were planned to receive GO 9 mg/m2 in two doses, 14 days apart. We reviewed liver function tests before and after administration and analyzed hepatic injuries in the context of patients' other comorbid conditions. Patients were classified as experiencing liver toxicity if their liver function(s) abnormality lasted for > 7 days, as documented by repeated serum studies.

RESULTS

Forty-seven patients were analyzed. Response rate (27.2%) and median duration of response (6 months) were comparable to other reports. All patients were assessable for liver toxicity, of which 23 (48%) had elevation of at least one of their liver function tests (alanine aminotransferase, aspartate aminotransferase, total bilirubin or alkaline phosphatase). Elevations in liver function test(s) were noted at a median of 14 days (range 7-175 days). Eight patients had other comorbid conditions that could explain their liver abnormality, making the incidence of direct GO-induced liver injury 31%. However, only one patient had radiographic and clinical evidence suggesting SOSVOD.

CONCLUSIONS

When administered using the recommended dose and schedule, GO has little association with VODSOS if given as a single agent. In this retrospective review, the incidence of GO-related SOSVOD is as low as 2%.

Immunophenotyping as a guide for targeted therapy

Immunophenotyping of acute and chronic leukaemias has revealed many lineage- and differentiation-specific antigens. It has now become possible to classify leukaemias according to their unique antigenic expression pattern. Among many lineage- and differentiation-specific antigens, disease-specific antigens are increasingly recognized because of their specific prognostic or therapeutic relevance. Expression of the multidrug resistance proteins of the ABC transporter family is associated with a poor response to treatment and a grave clinical prognosis. Recently, attempts to reverse refractory disease by using P-glycoprotein inhibitors have been performed in acute myeloid leukaemia, so far without evidence of clinical benefit. Other new leads to use antigen expression as a way of designing tumour-specific therapy have resulted in imatinib and Flt3 inhibitors which target tyrosine kinases in the leukaemic cell. Clinical trials are underway to investigate the effect of these new agents. The development of an antibody-calicheamycin complex directed against the myeloid-specific antigen CD33 has shown clinical activity in patients with relapsed acute myeloid leukaemia. The further development of these approaches is discussed.

Emerging antibody-targeted therapy in leukemia and lymphoma: current concepts and clinical implications

The success of immune-mediated therapies has encouraged studies on passive and active immunotherapy in leukemia and lymphoma. This review outlines the impact of increasing insights from basic immunology studies on the potentiation of effective immune responses and the identification of new antigens as targets for antibody (Ab)-targeted therapies. The principles of treatment in leukemia and lymphoma based on current knowledge on the classification of hematologic malignancies are reviewed, and discussed in the context of a rationale to implement new Ab-targeted immunotherapeutic approaches. An update is provided on the use of Ab-targeted therapies in clinical trials with emphasis on new emerging strategies to further expand the successful field of immunotherapy in leukemia and lymphoma.

Homing and mobilization of hematopoietic stem cells and hematopoietic cancer cells are mirror image processes, utilizing similar signaling pathways and occurring concurrently: circulating cancer cells constitute an ideal target for concurrent treatment with chemotherapy and antilineage-specific antibodies

Adhesion molecules and stromal cell-derived factor-1 (SDF-1)/CXCR4 signaling play key role in homing and mobilization of hematopoietic progenitor (HPC) and hematopoietic cancer clonogenic cells (HCC). High expression of VLA-4 is required for homing of HPC and HCC, whereas downregulation of these molecules is required for successful mobilization of HPC and HCC. Upregulation and activation of the SDF-1/CXCR4 signaling is required for homing of HPC and HCC, whereas disruption of the SDF-1 signaling is required for mobilization of HPC and HCC. Hence, mobilizations of HPC and HCC occur concurrently. It is proposed that drug resistance evolves as a result of repeated cycles of chemotherapy. Following each cycle of chemotherapy, HCC lose adhesion molecules and SDF-1 signaling. Surviving cells, released from tumor sites, circulate until re-expression of adhesion molecules and CXCR4 occurs, then homing to stroma of distal tissues occurs. Cytokines secreted by cells in the new microenvironment induce proliferation and drug resistance of HCC. This process is amplified in each cycle of chemotherapy resulting in disease progression. A novel model for treatment is proposed in which circulating HCC are the target for clinical intervention, and concurrent treatment with chemotherapy and antilineage-specific antibodies will result in abrogation of the 'vicious cycle' of conventional anticancer therapy.

Probable veno-occlusive disease after treatment with gemtuzumab ozogamicin in a patient with acute myeloid leukemia and a history of liver transplantation for familial hemochromatosis

A 69-yr-old male with a history of familial hemochromatosis and status after liver transplantation was found to have severe thrombocytopenia (platelet count of 8000/microL). He was also anemic and was diagnosed with acute myeloid leukemia (AML) after a bone marrow biopsy. He was started on gemtuzumab ozogamicin (Mylotarg) and developed hepatic and multiorgan failure consistent with veno-occlusive disease within 2 wk. He did not have a history of hematopoietic stem cell transplantation, which is usually the case in AML patients who develop veno-occlusive disease of the liver after treatment with Mylotarg.

Gemtuzumab ozogamicin in the treatment of acute myeloid leukemia

Gemtuzumab ozogamicin (GO) is a chemotherapeutic agent that consists of a humanized anti-CD33 antibody (hP67.6) linked to N-acetyl-gamma calicheamicin 1,2-dimethyl hydrazine dichloride, a potent enediyne antitumor antibiotic. GO was approved conditionally by the Federal Drug Administration in May 2000 as single-agent therapy for first recurrence of acute myeloid leukemia (AML) in a subset of older patients. Data on studies in AML with GO-based regimens have been reported rapidly in addition to new observations on the target antigen, CD33. These data indicate promising new areas of investigation with GO, including its application as maintenance therapy in patients with AML and as an induction and/or maintenance agent in patients with acute promyelocytic leukemia;, and they also have highlighted challenges in the development of GO, particularly its association with hepatic venoocclusive disease. In vitro data on the mechanism of action of GO may be particularly helpful in the design of future clinical studies.

Acute myeloid leukemia

In this chapter, Drs. Keating and Willman review recent advances in our understanding of the pathophysiology of acute myeloid leukemia (AML) and allied conditions, including the advanced myelodysplastic syndromes (MDS), while Drs. Goldstone, Avivi, Giles, and Kantarjian focus on therapeutic data with an emphasis on current patient care and future research studies. In Section I, Dr. Armand Keating reviews the role of the hematopoietic microenvironment in the initiation and progression of leukemia. He also discusses recent data on the stromal, or nonhematopoietic, marrow mesenchymal cell population and its possible role in AML. In Section II, Drs. Anthony Goldstone and Irit Avivi review the current role of stem cell transplantation as therapy for AML and MDS. They focus on data generated on recent Medical Research Council studies and promising investigation approaches. In Section III, Dr. Cheryl Willman reviews the current role of molecular genetics and gene expression analysis as tools to assist in AML disease classification systems, modeling of gene expression profiles associated with response or resistance to various interventions, and identifying novel therapeutic targets. In Section IV, Drs. Hagop Kantarjian and Francis Giles review some promising agents and strategies under investigation in the therapy of AML and MDS with an emphasis on novel delivery systems for cytotoxic therapy and on targeted biologic agents.

New developments in antibody therapy for acute myeloid leukemia

In the past three decades, improvements in the treatment of acute myeloid leukemia (AML) have increased survival in patients younger than 55 years without significant survival impact in older individuals. Unfortunately, many patients, regardless of age at diagnosis, will eventually die from their disease. Advances in the development of targeted therapies have proven beneficial in chronic myeloid leukemia and lymphoma. Gemtuzumab ozogamicin (GO; Mylotarg, Wyeth-Ayerst, St Davids, PA), a monoclonal antibody conjugated to calicheamicin, targets the CD33 antigen found on the surface of more than 80% of AML leukemic blasts. GO is approved for relapsed disease in patients older than 60 years, but is being evaluated in combination with chemotherapy, in the setting of hematopoietic stem cell transplant, and in high-risk myelodysplasia.