Mylotarg (gemtuzumab ozogamicin) therapy is associated with hepatic venoocclusive disease in patients who have not received stem cell transplantation

Strategies and Advancement in Antibody-Drug Conjugate Optimization for Targeted Cancer Therapeutics

Antibody-drug conjugates utilize the antibody as a delivery vehicle for highly potent cytotoxic molecules with specificity for tumor-associated antigens for cancer therapy. Critical parameters that govern successful antibody-drug conjugate development for clinical use include the selection of the tumor target antigen, the antibody against the target, the cytotoxic molecule, the linker bridging the cytotoxic molecule and the antibody, and the conjugation chemistry used for the attachment of the cytotoxic molecule to the antibody. Advancements in these core antibody-drug conjugate technology are reflected by recent approval of Adectris(®) (anti-CD30-drug conjugate) and Kadcyla(®) (anti-HER2 drug conjugate). The potential approval of an anti-CD22 conjugate and promising new clinical data for anti-CD19 and anti-CD33 conjugates are additional advancements. Enrichment of antibody-drug conjugates with newly developed potent cytotoxic molecules and linkers are also in the pipeline for various tumor targets. However, the complexity of antibody-drug conjugate components, conjugation methods, and off-target toxicities still pose challenges for the strategic design of antibody-drug conjugates to achieve their fullest therapeutic potential. This review will discuss the emergence of clinical antibody-drug conjugates, current trends in optimization strategies, and recent study results for antibody-drug conjugates that have incorporated the latest optimization strategies. Future challenges and perspectives toward making antibody-drug conjugates more amendable for broader disease indications are also discussed.

Hemopexin and haptoglobin: allies against heme toxicity from hemoglobin not contenders

The goal here is to describe our current understanding of heme metabolism and the deleterious effects of "free" heme on immunological processes, endothelial function, systemic inflammation, and various end-organ tissues (e.g., kidney, lung, liver, etc.), with particular attention paid to the role of hemopexin (HPX). Because heme toxicity is the impetus for much of the pathology in sepsis, sickle cell disease (SCD), and other hemolytic conditions, the biological importance and clinical relevance of HPX, the predominant heme binding protein, is reinforced. A perspective on the function of HPX and haptoglobin (Hp) is presented, updating how these two proteins and their respective receptors act simultaneously to protect the body in clinical conditions that entail hemolysis and/or systemic intravascular (IVH) inflammation. Evidence from longitudinal studies in patients supports that HPX plays a Hp-independent role in genetic and non-genetic hemolytic diseases without the need for global Hp depletion. Evidence also supports that HPX has an important role in the prognosis of complex illnesses characterized predominantly by the presence of hemolysis, such as SCD, sepsis, hemolytic-uremic syndrome, and conditions involving IVH and extravascular hemolysis (EVH), such as that generated by extracorporeal circulation during cardiopulmonary bypass (CPB) and from blood transfusions. We propose that quantitating the amounts of plasma heme, HPX, Hb-Hp, heme-HPX, and heme-albumin levels in various disease states may aid in the diagnosis and treatment of the above-mentioned conditions, which is crucial to developing targeted plasma protein supplementation (i.e., "replenishment") therapies for patients with heme toxicity due to HPX depletion.

CD30 as a therapeutic target for lymphoma

Hodgkin's lymphoma (HL) and ALK(+) anaplastic large-cell lymphoma (ALCL) have become highly curable due to the success of modern regimens of chemotherapy and radiotherapy. However, up to one-third of the patients experience relapse or do not respond to first-line therapy, and half of them relapse again after secondary therapy with limited options for further treatment. In the last 15 years, monoclonal antibodies (mAbs) directed to surface receptors became a new and valuable therapeutic option in many hematologic malignancies. Due to its restricted expression on normal activated lymphocytes and its high expression on malignant cells, CD30 represents an attractive target molecule for HL and ALCL therapy. However, unconjugated CD30 mAbs have demonstrated a lack of objective clinical responses in patients with recurrent HL. CD30 exhibits complex signaling pathways, and binding of its natural ligand or anti-CD30 mAbs can induce apoptosis but may also promote proliferation and activation depending on the cellular context. Moreover, CD30 rapidly internalizes after crosslinking, which counteracts efficient recruitment of immunologic effectors but also provides the opportunity to transfer cytotoxic payloads coupled to CD30-specific mAbs into the tumor cells. Several tumor targeting approaches have been studied, including radio-immunoconjugates, immunotoxins, immunoRNases, immunokinases, and antibody drug conjugates (ADCs). In 2011, the ADC brentuximab-vedotin, consisting of the CD30-specific chimeric mAb cAC10 and the potent tubulin toxin monomethyl auristatin E, gained regulatory approval as a well tolerated and highly active drug in patients with refractory and relapsed HL and ALCL. SGN-35 is on the way to being incorporated in the standard management of CD30(+) lymphoma with significant therapeutic impact. This review gives a critical overview about anti-CD30 therapies with unconjugated, engineered, and conjugated mAbs and the therapeutic challenges of treatment of CD30(+) lymphoma.

Advanced targeted therapies in cancer: Drug nanocarriers, the future of chemotherapy

Cancer is the second worldwide cause of death, exceeded only by cardiovascular diseases. It is characterized by uncontrolled cell proliferation and an absence of cell death that, except for hematological cancers, generates an abnormal cell mass or tumor. This primary tumor grows thanks to new vascularization and, in time, acquires metastatic potential and spreads to other body sites, which causes metastasis and finally death. Cancer is caused by damage or mutations in the genetic material of the cells due to environmental or inherited factors. While surgery and radiotherapy are the primary treatment used for local and non-metastatic cancers, anti-cancer drugs (chemotherapy, hormone and biological therapies) are the choice currently used in metastatic cancers. Chemotherapy is based on the inhibition of the division of rapidly growing cells, which is a characteristic of the cancerous cells, but unfortunately, it also affects normal cells with fast proliferation rates, such as the hair follicles, bone marrow and gastrointestinal tract cells, generating the characteristic side effects of chemotherapy. The indiscriminate destruction of normal cells, the toxicity of conventional chemotherapeutic drugs, as well as the development of multidrug resistance, support the need to find new effective targeted treatments based on the changes in the molecular biology of the tumor cells. These novel targeted therapies, of increasing interest as evidenced by FDA-approved targeted cancer drugs in recent years, block biologic transduction pathways and/or specific cancer proteins to induce the death of cancer cells by means of apoptosis and stimulation of the immune system, or specifically deliver chemotherapeutic agents to cancer cells, minimizing the undesirable side effects. Although targeted therapies can be achieved directly by altering specific cell signaling by means of monoclonal antibodies or small molecules inhibitors, this review focuses on indirect targeted approaches that mainly deliver chemotherapeutic agents to molecular targets overexpressed on the surface of tumor cells. In particular, we offer a detailed description of different cytotoxic drug carriers, such as liposomes, carbon nanotubes, dendrimers, polymeric micelles, polymeric conjugates and polymeric nanoparticles, in passive and active targeted cancer therapy, by enhancing the permeability and retention or by the functionalization of the surface of the carriers, respectively, emphasizing those that have received FDA approval or are part of the most important clinical studies up to date. These drug carriers not only transport the chemotherapeutic agents to tumors, avoiding normal tissues and reducing toxicity in the rest of the body, but also protect cytotoxic drugs from degradation, increase the half-life, payload and solubility of cytotoxic agents and reduce renal clearance. Despite the many advantages of all the anticancer drug carriers analyzed, only a few of them have reached the FDA approval, in particular, two polymer-protein conjugates, five liposomal formulations and one polymeric nanoparticle are available in the market, in contrast to the sixteen FDA approval of monoclonal antibodies. However, there are numerous clinical trials in progress of polymer-protein and polymer-drug conjugates, liposomal formulations, including immunoliposomes, polymeric micelles and polymeric nanoparticles. Regarding carbon nanotubes or dendrimers, there are no FDA approvals or clinical trials in process up to date due to their unresolved toxicity. Moreover, we analyze in detail the more promising and advanced preclinical studies of the particular case of polymeric nanoparticles as carriers of different cytotoxic agents to active and passive tumor targeting published in the last 5 years, since they have a huge potential in cancer therapy, being one of the most widely studied nano-platforms in this field in the last years. The interest that these formulations have recently achieved is stressed by the fact that 90% of the papers based on cancer therapeutics with polymeric nanoparticles have been published in the last 6 years (PubMed search).

Mylotarg has potent anti-leukaemic effect: a systematic review and meta-analysis of anti-CD33 antibody treatment in acute myeloid leukaemia

Conventional chemotherapy is ineffective in the majority of patients with acute myeloid leukaemia (AML), and monoclonal antibodies recognising CD33 expressed on myeloid progenitors (e.g. gemtuzumab ozogamicin (GO)) have been reported to improve outcome in patients with AML. Reports of excess toxicity have resulted in GO's licence being withdrawn. As a result, the role of these agents remains unclear. A systematic review and meta-analysis included studies of patients with AML who had entered a randomised control trial (RCT), where one arm included anti-CD33 antibody therapy. Fixed effect meta-analysis was used, involving calculation of observed minus expected number of events, and variance for each endpoint in each trial, with the overall treatment effect expressed as Peto's odds ratio with 95 % confidence interval. Meta-analysis of 11 RCTs with 13 randomisations involving GO was undertaken. Although GO increased induction deaths (p = 0.02), it led to a reduction in resistant disease (p = 0.0009); hence, there was no improvement in complete remission. Whilst GO improved relapse-free survival (hazard ratio (HR) = 0.90, 95 % confidence interval (CI) = 0.84-0.98, p = 0.01), there was no overall benefit of GO in overall survival (OS) (HR = 0.96, 95 % CI = 0.90-1.02, p = 0.2). GO improved OS in patients with favourable cytogenetics, with no evidence of benefit in patients with intermediate or adverse cytogenetics (test for heterogeneity between subtotals p = 0.01). GO has a potent clinically detectable anti-leukaemic effect. Further trials to investigate its optimum delivery and identification of patient populations who may benefit are needed.

Is targeted therapy feasible in acute myelogenous leukemia?

The prognosis for patients with acute myeloid leukemia (AML) is determined to a large degree by the biology of the leukemic cell. In recent years, the identification and characterization of genetic aberrations has vastly improved our understanding of the pathogenesis of AML. In contrast, however, there has been a lack of clinically meaningful therapeutic advances. The same chemotherapeutic strategies have been applied to AML for several decades now, and while these regimens are effective in inducing remission, most patients relapse within months after initial treatment. Hence, there is an urgent need for novel therapies. We review herein a number of lines of laboratory and clinical trial data supporting the clinical value of targeted treatment approaches that will likely result in improved outcomes for patients with AML.

Fcγ-receptor-mediated trogocytosis impacts mAb-based therapies: historical precedence and recent developments

A specialized form of trogocytosis occurs when Fcγ receptors on acceptor cells take up and internalize donor cell-associated immune complexes composed of specific monoclonal antibodies (mAbs) bound to target antigens on donor cells. This trogocytosis reaction, an example of antigenic modulation, has been described in recent clinical correlative studies and in vitro investigations for several mAbs used in cancer immunotherapy, including rituximab and ofatumumab. We discuss the impact of Fcγ-receptor-mediated trogocytosis on the efficacy of cancer immunotherapy and other mAb-based therapies.

Current status of antibody therapy in ALL

Despite the significant advances in modern chemotherapy, it remains challenging to treat adult patients with acute lymphoblastic leukaemia (ALL). The relapse rate remains high, and the outcome at the time of relapse is dismal. Antibody-based therapies have demonstrated promising results in this patient group. Variable mechanisms have been applied to target surface antigens (CD20 [also termed MS4A1], CD22, CD52 and CD19) that are commonly expressed on malignant leukaemia cells. In this review, we will focus on the clinical application of such therapies in adult ALL, including the naked antibodies: Rituximab, Ofatumumab, Epratuzumab and Alemtuzumab; the immunotoxins: BL22 and Combotox; the immunoconjugates: inotuzumab and SAR 3419; as well as the Bi-specific T cell engaging (BiTE)-specific antibody, Blinatumomab.

Addition of gemtuzumab ozogamicin to induction chemotherapy in adult patients with acute myeloid leukaemia: a meta-analysis of individual patient data from randomised controlled trials

BACKGROUND

Gemtuzumab ozogamicin was the first example of antibody-directed chemotherapy in cancer, and was developed for acute myeloid leukaemia. However, randomised trials in which it was combined with standard induction chemotherapy in adults have produced conflicting results. We did a meta-analysis of individual patient data to assess the efficacy of adding gemtuzumab ozogamicin to induction chemotherapy in adult patients with acute myeloid leukaemia.

METHODS

We searched PubMed for reports of randomised controlled trials published in any language up to May 1, 2013, that included an assessment of gemtuzumab ozogamicin given to adults (aged 15 years and older) in conjunction with the first course of intensive induction chemotherapy for acute myeloid leukaemia (excluding acute promyelocytic leukaemia) compared with chemotherapy alone. Published data were supplemented with additional data obtained by contacting individual trialists. The primary endpoint of interest was overall survival. We used standard meta-analytic techniques, with an assumption-free (or fixed-effect) method. We also did exploratory stratified analyses to investigate whether any baseline features predicted a greater or lesser benefit from gemtuzumab ozogamicin.

FINDINGS

We obtained data from five randomised controlled trials (3325 patients); all trials were centrally randomised and open label, with overall survival as the primary endpoint. The addition of gemtuzumab ozogamicin did not increase the proportion of patients achieving complete remission with or without complete peripheral count recovery (odds ratio [OR] 0·91, 95% CI 0·77-1·07; p=0·3). However, the addition of gemtuzumab ozogamicin significantly reduced the risk of relapse (OR 0·81, 0·73-0·90; p=0·0001), and improved overall survival at 5 years (OR 0·90, 0·82-0·98; p=0·01). At 6 years, the absolute survival benefit was especially apparent in patients with favourable cytogenetic characteristics (20·7%; OR 0·47, 0·31-0·73; p=0·0006), but was also seen in those with intermediate characteristics (5·7%; OR 0·84, 0·75-0·95; p=0·005). Patients with adverse cytogenetic characteristics did not benefit (2·2%; OR 0·99, 0·83-1·18; p=0·9). Doses of 3 mg/m(2) were associated with fewer early deaths than doses of 6 mg/m(2), with equal efficacy.

INTERPRETATION

Gemtuzumab ozogamicin can be safely added to conventional induction therapy and provides a significant survival benefit for patients without adverse cytogenetic characteristics. These data suggest that the use of gemtuzumab ozogamicin should be reassessed and its licence status might need to be reviewed.

FUNDING

None.

Evaluation of human pancreatic RNase as effector molecule in a therapeutic antibody platform

Human antibody-ribonuclease (RNase) fusion proteins, referred to as immunoRNases, have been proposed as an alternative to heterologous immunotoxins, without their immunogenicity and unspecific toxicity issues. In this study, we investigated if human pancreatic RNase will be suitable as effector component in a therapeutic antibody development platform. We generated several fusion proteins consisting of tumor-specific human immunoglobulins (IgGs) and human pancreatic RNase. Transient mammalian cell production was efficient and IgG-RNases were purified to homogeneity. Antigen binding was comparable to the parental antibodies and RNase catalytic activity was retained even in the presence of 50-fold molar excess of human cytosolic RNase inhibitor (RI). Serum stability, cell binding and internalization of IgG-RNases were comparable to the parental IgGs. Despite these promising properties, none of the IgG-RNases revealed significant inhibition of tumor cell growth in vitro even when targeting different antigens putatively employing different endocytotic pathways. The introduction of different linkers containing endosomal protease cleavage sites into the IgG-RNase did not enhance cytotoxicity. Similarly, RI evasive human pancreatic RNase variants mediated only small inhibiting effects on tumor cell growth at high concentrations, potentially reflecting inefficient cytosolic translocation. Taken together, human pancreatic RNase and variants did not prove to be generally suitable as effector component for a therapeutic antibody drug development platform.

Cloretazine for the treatment of acute myeloid leukemia

Cloretazine is a new sulfonylhydrazine alkylating agent with antileukemic activity. Phase I studies have shown myelosuppression to be the dose limiting toxicity in both solid tumors and leukemias. A large Phase II study of single agent cloretazine (600 mg/m2) confirmed its activity in patients with relapsed acute myeloid leukemia, and in elderly patients with previously untreated acute myeloid leukemia or myelodysplastic syndrome. It also confirmed the limited nonhematological toxicity, even in elderly patients. Cloretazine can be safely combined with cytarabine, and this combination regimen is currently being tested in a large Phase III study in patients with relapsed acute myeloid leukemia. Cloretazine is a promising new antileukemic agent that may be incorporated into an intensive combination regimen.

Antibody therapy for acute myeloid leukaemia

Novel therapies with increased efficacy and decreased toxicity are desperately needed for the treatment of acute myeloid leukaemia (AML). The anti CD33 immunoconjugate, gemtuzumab ozogamicin (GO), was withdrawn with concerns over induction mortality and lack of efficacy. However a number of recent trials suggest that, particularly in AML with favourable cytogenetics, GO may improve overall survival. This data and the development of alternative novel monoclonal antibodies (mAb) have renewed interest in the area. Leukaemic stem cells (LSC) are identified as the subset of AML blasts that reproduces the leukaemic phenotype upon transplantation into immunosuppressed mice. AML relapse may be caused by chemoresistant LSC and this has refocused interest on identifying and targeting antigens specific for LSC. Several mAb have been developed that target LSC effectively in xenogeneic models but only a few have begun clinical evaluation. Antibody engineering may improve the activity of potential new therapeutics for AML. The encouraging results seen with bispecific T cell-engaging mAb-based molecules against CD19 in the treatment of B-cell acute lymphobalstic leukaemia, highlight the potential efficacy of engineered antibodies in the treatment of acute leukaemia. Potent engineered mAb, possibly targeting novel LSC antigens, offer hope for improving the current poor prognosis for AML.

A case of veno-occlusive disease following liver transplantation

The present case report describes the diagnosis and treatment of a patient with veno-occlusive disease (VOD) following liver transplantation. Combining the clinical data and relevant literature, the study aimed to consider the causes of VOD following liver transplantation, and the pathogenesis, clinical diagnosis and auxiliary examination features of VOD. A 42-year-old man who had a long history of taking traditional Chinese medicine (essential components unknown) underwent an orthotropic liver transplantation on January 14, 2011, due to small venous occlusion disease of the liver. The patient was treated with tacrolimus as an antirejection therapy following the surgery, and gradually developed right upper quadrant pain and fatigue. The examination results were consistent with the diagnostic standards for VOD. Following treatment with methylprednisolone, the patient was treated with alprostadil and Danhong injections. Forty days later, the patient’s total bilirubin (TBIL) level was observed to have decreased significantly, the liver function had returned to normal and the ascites had decreased, but had not completely disappeared. The patient then underwent a transjugular intrahepatic portosystemic shunt (TIPS) procedure, following which the ascites were shown to have completely disappeared.

Gemtuzumab ozogamicin can reduce minimal residual disease in patients with childhood acute myeloid leukemia

BACKGROUND

Gemtuzumab ozogamicin (GO) is an active agent for the treatment of CD33-postive acute myeloid leukemia (AML) and may improve the outcome of specific patient subgroups when combined with conventional chemotherapy. However, to the best of the authors' knowledge, the effects of GO on levels of minimal residual disease (MRD) are unknown.

METHODS

Pediatric patients with AML who received GO, either alone or in combination with chemotherapy on the AML02 multicenter trial, were analyzed to determine the effects of GO on MRD and outcome.

RESULTS

Among 17 patients who received GO alone because of persistent leukemia, 14 had a reduction in their MRD level and 13 became MRD negative. Of the 29 who received chemotherapy in combination with GO after responding poorly to chemotherapy, 28 demonstrated reduced MRD and 13 became MRD negative. Treatment with GO effectively reduced MRD before hematopoietic stem cell transplantation and was not found to be associated with increased treatment-related mortality after transplantation.

CONCLUSIONS

GO is effective in reducing MRD levels in pediatric patients with AML and may improve the outcome of those patients at high risk of disease recurrence.

Drug-conjugated antibodies for the treatment of cancer

Despite considerable effort, application of monoclonal antibody technology has had only modest success in improving treatment outcomes in patients with solid tumours. Enhancing the cancer cell-killing activity of antibodies through conjugation to highly potent cytotoxic 'payloads' to create antibody-drug conjuates (ADCs) offers a strategy for developing anti-cancer drugs of great promise. Early ADCs exhibited side-effect profiles similar to those of 'classical' chemotherapeutic agents and their performance in clinical trials in cancer patients was generally poor. However, the recent clinical development of ADCs that have highly potent tubulin-acting agents as their payloads have profoundly changed the outlook for ADC technology. Twenty-five such ADCs are in clinical development and one, brentuximab vedotin, was approved by the FDA in August, 2011, for the treatment of patients with Hodgkin's lymphoma and patients with anaplastic large cell lymphoma, based on a high rate of durable responses in single arm phase II clinical trials. More recently, a second ADC, trastuzumab emtansine, has shown excellent anti-tumour activity with the presentation of results of a 991-patient randomized phase III trial in patients with HER2-positive metastatic breast cancer. Treatment with this ADC (single agent) resulted in a significantly improved progression-free survival of 9.6 months compared with 6.4 months for lapatinib plus capecitabine in the comparator arm and significantly prolonged overall survival. Besides demonstrating excellent efficacy, these ADCs were remarkably well tolerated. Thus these, and other ADCs in development, promise to achieve the long sought goal of ADC technology, that is, of having compounds with high anti-tumour activity at doses where adverse effects are generally mild.

Antibody-based therapy of acute myeloid leukemia with gemtuzumab ozogamicin

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

New therapeutic approaches to acute myeloid leukemia

BACKGROUND

The heterogeneity of acute myeloid leukemia (AML) has been established by many new insights into the pathogenesis and treatment of patients with AML. Understanding the basic cellular and molecular pathogenesis of leukemic cells is vital to the development of new treatment approaches.

OBJECTIVE/METHODS

To review progress until now with agents that are showing promise in the treatment of AML, we summarize the published preclinical and clinical trials that have been completed.

RESULTS

Based on recent progress of investigations, more specifically targeted agents have been developed for the treatment of AML such as tyrosine kinase inhibitors, monoclonal antibodies, epigenetic agents, antiangiogenic agents, and farnesyl transferase inhibitors.

CONCLUSION

In the future, in addition to performing therapeutic trials of these agents, it will be important to identify other highly specific therapeutic agents based on our evolving understanding of the biology of AML.

Monoclonal antibody-based therapies in cancer: advances and challenges

Conventional anticancer therapeutics often suffer from lack of specificity, resulting in toxicities to normal healthy tissues and poor therapeutic index. Antibody-mediated delivery of anticancer drugs or toxins to tumor cells through tumor selective or overexpressed antigens is progressively being recognized as an effective strategy for increasing the therapeutic index of anticancer drugs. In this review we focus on three therapeutic modalities in the field of antibody-mediated targeting, including antibody-drug conjugates (ADCs), immunotoxins (ITs) and immunoliposomes (ILs). Design considerations for development of each of the above therapeutic modalities are discussed. Furthermore, an overview of ADCs, ITs or ILs approved for use in clinical oncology and those currently in clinical development is provided. Challenges encountered by the field of antibody-based targeting are discussed and concepts around development of the next generation of antibody therapeutics are presented.

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.

Proposed mechanism of off-target toxicity for antibody-drug conjugates driven by mannose receptor uptake

Antibody-drug conjugates (ADCs) are developed with the goal of increasing compound therapeutic index by specific and targeted delivery of a toxic payload to the site of action while considerably reducing damage to normal tissues. Yet, off-target hepatic toxicities have been reported for several ADC. Locations of these off-target toxicities coincide with the reported locations of cell surface mannose receptor (MR). The relative proportion of agalactosylated glycans on the Fc domain (G0F vs. G1F and G2F components) in monoclonal antibody (mAb)-based biotherapeutics is closer to some disease state IgG rather than to a normal serum-derived immunoglobulin. The lack of the terminal galactose on a G0F glycan creates an opportunity for the mAb to interact with soluble and cell surface MRs. MR is a known multi-domain lectin that specifically binds and internalizes glycoproteins and immune complexes with relatively high G0F content and has been found on the surface of various cell types, including immune cells of myeloid lineage, endothelial cells, and hepatic and splenic sinusoids. In this review paper it is proposed that the mechanism of the off-target toxicities for ADC biotherapeutics is at least in part driven by the carbohydrates, specifically agalactosylated glycans, such as G0F, their interactions with MR and resulting glycan-derived cellular uptake of ADCs. Several case studies are reviewed presenting corroborating information.

Risks and untoward toxicities of antibody-based immunoconjugates

Antibody-based immunoconjugates are specifically targeted monoclonal antibodies that deliver a cytotoxic payload to their target. The cytotoxic agents can be highly potent drugs, radionuclides or toxins. Such molecules, referred to as antibody-drug conjugates, radioimmunoconjugates and immunotoxins, respectively, represent a promising approach for enhancing the efficacy of unconjugated (naked) antibodies for improved therapeutic results. Though tremendous progress has been achieved over the last few decades, the safety of these molecules still remains a matter of concern and a careful design is required for achieving a relatively safe toxicity profile along with therapeutic effectiveness. This review focuses on the toxicities arising from the use of these potent agents.

Targeted drug delivery for cancer therapy: the other side of antibodies

Therapeutic monoclonal antibody (TMA) based therapies for cancer have advanced significantly over the past two decades both in their molecular sophistication and clinical efficacy. Initial development efforts focused mainly on humanizing the antibody protein to overcome problems of immunogenicity and on expanding of the target antigen repertoire. In parallel to naked TMAs, antibody-drug conjugates (ADCs) have been developed for targeted delivery of potent anti-cancer drugs with the aim of bypassing the morbidity common to conventional chemotherapy. This paper first presents a review of TMAs and ADCs approved for clinical use by the FDA and those in development, focusing on hematological malignancies. Despite advances in these areas, both TMAs and ADCs still carry limitations and we highlight the more important ones including cancer cell specificity, conjugation chemistry, tumor penetration, product heterogeneity and manufacturing issues. In view of the recognized importance of targeted drug delivery strategies for cancer therapy, we discuss the advantages of alternative drug carriers and where these should be applied, focusing on peptide-drug conjugates (PDCs), particularly those discovered through combinatorial peptide libraries. By defining the advantages and disadvantages of naked TMAs, ADCs and PDCs it should be possible to develop a more rational approach to the application of targeted drug delivery strategies in different situations and ultimately, to a broader basket of more effective therapies for cancer patients.

Antibody-drug conjugates in cancer therapy

An antibody-drug conjugate (ADC) provides the possibility of selectively ablating cancer cells by combining the specificity of a monoclonal antibody (mAb) for a target antigen with the delivery of a highly potent cytotoxic agent. ADC target antigens are typically highly expressed on the surface of cancer cells compared to normal cells. The tumor target, the cytotoxic agent, and the manner in which the agent is attached to the antibody are key determinants of clinical activity and tolerability. Recently, several clinical trials have demonstrated that ADCs achieve higher clinical response rates than unconjugated mAbs targeting the same cell surface antigen. Brentuximab vedotin represents one such ADC that has recently been approved for the treatment of relapsed Hodgkin and systemic anaplastic large cell lymphomas--both characterized by high expression of the target antigen, CD30, on the surface of malignant cells. This review summarizes key characteristics of current, clinically active ADCs and highlights recent clinical data illustrating the benefit of antibody-targeted delivery of cytotoxic agents to cancer cells.

Addition of gemtuzumab ozogamicin to induction chemotherapy improves survival in older patients with acute myeloid leukemia

PURPOSE

There has been little survival improvement in older patients with acute myeloid leukemia (AML) in the last two decades. Improving induction treatment may improve the rate and quality of remission and consequently survival. In our previous trial, in younger patients, we showed improved survival for the majority of patients when adding gemtuzumab ozogamicin (GO) to induction chemotherapy.

PATIENTS AND METHODS

Untreated patients with AML or high-risk myelodysplastic syndrome (median age, 67 years; range, 51 to 84 years) were randomly assigned to receive induction chemotherapy with either daunorubicin/ara-C or daunorubicin/clofarabine, with (n = 559) or without (n = 556) GO 3 mg/m(2) on day 1 of course one of therapy. The primary end point was overall survival (OS).

RESULTS

The overall response rate was 69% (complete remission [CR], 60%; CR with incomplete recovery [CRi], 9%), with no difference between GO (70%) and no GO (68%) arms. There was no difference in 30- or 60-day mortality and no major increase in toxicity with GO. With median follow-up of 30 months (range, 5.5 to 54.6 months), 3-year cumulative incidence of relapse was significantly lower with GO (68% v 76%; hazard ratio [HR], 0.78; 95% CI, 0.66 to 0.93; P = .007), and 3-year survival was significantly better (25% v 20%; HR, 0.87; 95% CI, 0.76 to 1.00; P = .05). The benefit was apparent across subgroups. There was no interaction with other treatment interventions. A meta-analysis of 2,228 patients in two United Kingdom National Cancer Research Institute trials showed significant improvements in relapse (HR, 0.82; 95% CI, 0.72 to 0.93; P = .002) and OS (HR, 0.88; 95% CI, 0.79 to 0.98; P = .02).

CONCLUSION

Adding GO (3 mg/m(2)) to induction chemotherapy reduces relapse risk and improves survival with little increase in toxicity.

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).

Using antibodies to target cancer therapeutics

INTRODUCTION

Over a half a century ago, radiolabeled antibodies were shown to localize selectively in tissues based on the expression of unique antigens. Antibodies have since become the de facto targeting agent, even inspiring the development of non-antibody compounds for targeting purposes.

AREAS COVERED

In this article, we review various aspects of how antibodies are transforming the way cancer is being detected and treated, with the growing demand for unconjugated and many new antibody conjugates. While unconjugated antibodies continue to garner most of the attention, interest in new antibody drug conjugates and immunotoxins has expanded over the past few years. However, there continues to be active research with new radioimmunoconjugates for imaging and therapy, particularly with α-emitters, as well as antibody-targeted cytokines and other biological response modifiers.

EXPERT OPINION

The increasing number of new agents being developed and tested clinically suggests that antibody-targeted compounds will have an expanding role in the future.

Design, synthesis and inhibition activity of a novel cyclic enediyne amino acid conjugates against MPtpA

In course of studies towards the discovery of selective inhibitors of MPtpA, a novel cyclic endiyne malonamic acid has been designed and synthesized. The synthesis involves a crucial intramolecular Knoevenagel reaction. The compound displayed a reversible non-competitive inhibition against MPtpA with inhibition constant K(i) of 22.5 μM. The enediyne acts as a recognition framework in inducing the inhibition and not as a reactive functional moiety. This was confirmed by comparing the inhibiting activity with that of the corresponding saturated cyclic non-enediyne analogue.

Identification of patients with acute myeloblastic leukemia who benefit from the addition of gemtuzumab ozogamicin: results of the MRC AML15 trial

PURPOSE

Antibody-directed chemotherapy for acute myeloid leukemia (AML) may permit more treatment to be administered without escalating toxicity. Gemtuzumab ozogamicin (GO) is an immunoconjugate between CD33 and calicheamicin that is internalized when binding to the epitope. We previously established that it is feasible to combine GO with conventional chemotherapy. We now report a large randomized trial testing the addition of GO to induction and/or consolidation chemotherapy in untreated younger patients.

PATIENTS AND METHODS

In this open-label trial, 1,113 patients, predominantly younger than age 60 years, were randomly assigned to receive a single dose of GO (3 mg/m(2)) on day 1 of induction course 1 with one of the following three induction schedules: daunorubicin and cytarabine; cytarabine, daunorubicin, and etoposide; or fludarabine, cytarabine, granulocyte colony-stimulating factor, and idarubicin. In remission, 948 patients were randomly assigned to GO in course 3 in combination with amsacrine, cytarabine, and etoposide or high-dose cytarabine. The primary end points were response rate and survival.

RESULTS

The addition of GO was well tolerated with no significant increase in toxicity. There was no overall difference in response or survival in either induction of consolidation. However, a predefined analysis by cytogenetics showed highly significant interaction with induction GO (P = .001), with significant survival benefit for patients with favorable cytogenetics, no benefit for patients with poor-risk disease, and a trend for benefit in intermediate-risk patients. An internally validated prognostic index identified approximately 70% of patients with a predicted benefit of 10% in 5-year survival.

CONCLUSION

A substantial proportion of younger patients with AML have improved survival with the addition of GO to induction chemotherapy with little additional toxicity.

Advances in the management of acute myeloid leukemia in older adult patients

PURPOSE/OBJECTIVES

To update oncology nurses on new developments in the care of older adult patients with acute myeloid leukemia (AML).

DATA SOURCES

Clinical trial data, published guidelines, review articles, and conference proceedings.

DATA SYNTHESIS

Therapies for older adult patients with AML include cytarabine-based intensive-induction chemotherapy, investigational therapy, and supportive care. Nonmyeloablative allogeneic hematopoietic stem cell transplantation may provide the best opportunity for cure following remission if a human leukocyte antigen-matched hematopoietic stem cell donor is available. Careful assessment of patient- and disease-related factors is critical in determining the appropriate treatment modality for individuals. Assessment tools and algorithms may identify patients likely to be intolerant of intensive therapies. Supportive care may improve treatment tolerance and quality of life.

CONCLUSIONS

Survival outcomes have not improved significantly for older adult patients with AML. Novel therapies, coupled with better understanding of prognostic factors, may allow more highly individualized care. Performance status or comorbidity score may provide insights regarding outcome, particularly when combined with age, cytogenetic risk, or molecular markers. Efforts to improve transplantation safety may increase use in the older adult patient population.

IMPLICATIONS FOR NURSING

Nurses provide disease and treatment information, manage adverse effects, and offer emotional support. Knowledge of the key management issues for older adult patients with AML is critical in fulfilling this role.

Complete remissions observed in acute myeloid leukemia following prolonged exposure to lintuzumab: a phase 1 trial

A multi-institutional, phase 1 dose-escalation trial of lintuzumab (humanized anti-CD33 antibody; SGN-33, HuM195) was performed in patients with CD33-positive myeloid malignancies. In this study, higher doses than previously tested and prolonged duration of treatment for responding patients were evaluated. Over the dose range of 1.5-8 mg/kg/week, lintuzumab was well tolerated, and a maximum tolerated dose was not defined. The most common adverse event was transient chills with the initial lintuzumab infusion (39%). Responses were observed in 7 of 17 patients with acute myeloid leukemia: morphologic complete remission (n = 4), partial remission (n = 2), and morphologic leukemia-free state (n = 1). Of 14 patients with myelodysplastic syndrome or myeloproliferative diseases, 1 patient had major hematologic improvement and 9 patients had stable disease. In contrast to aggressive conventional chemotherapy, lintuzumab was administered in an ambulatory clinic setting with acceptable toxicity.

Insights into defibrotide: an updated review

Defibrotide is a polydisperse oligonucleotide with antiatherosclerotic, anti-inflammatory, anti-ischaemic, pro-fibrinolytic and antithrombotic actions without significant systemic anticoagulant effects. It has been used in the treatment of various cardiovascular disorders, and especially in endothelial complications of allogeneic stem-cell transplantation. We reviewed the published work for the mechanism of action and clinical use of defibrotide to consolidate data and to describe new applications of this drug. We reviewed the most relevant papers on defibrotide published from November 1982 to January 2008. (selected through PubMed), and used recent meeting abstracts as sources for this review. Reports have suggested that defibrotide has clinical efficacy for treatment and prophylaxis of hepatic sinusoidal obstruction syndrome occurring after stem-cell transplantation. Animal models have clearly shown the potential antineoplastic effect of this drug. Further clinical investigations are needed to clarify this new application.

Gemtuzumab Ozogamicin for Relapsed and Refractory Acute Myeloid Leukemia and Myeloid Sarcomas

Antibody-targeted chemotherapy is a promising approach in patients with hematological malignancies. In particular, gemtuzumab ozogamicin (GO, formerly CMA-676), an anti-CD33 antibody linked to calicheamicin, has been approved for the treatment of elderly patients with acute myeloid leukemia (AML) in relapse. Nevertheless, no data are until now available concerning the possible efficacy of GO for myeloid sarcomas (MS). We treated with GO 24 AML patients, in 5 cases presenting with myeloid sarcomas of the skin or bones. The overall complete response rate was 21%. The median duration of response was 6 months. Four out of the 5 patients with myeloid sarcoma showed a regression of the masses, in two cases also obtaining a clearance of marrow blasts. The most common adverse events included thrombocytopenia, neutropenia, infections, elevation of bilirubin and hepatic transaminases. Notably, severe bleeding occurred in 5 cases (21%). VOD was documented in 1 case. We conclude that GO is effective as a single agent in AML and myeloid sarcomas. Further data are required to clarify the possible correlation between GO administration and occurrence of bleeding.

pH-sensitive immunoliposomes specific to the CD33 cell surface antigen of leukemic cells

A promising avenue in cancer therapy using liposomal formulations is the combination of site-specific delivery with triggered drug release. The use of trigger mechanisms in liposomes could be relevant for drugs susceptible to lysosomal hydrolytic/enzymatic degradation. Here, we propose a polymeric pH-sensitive liposome system that is designed to release its content inside the endosomes through a polymer structural change following receptor-mediated internalization. Specifically, pH-sensitive immunoliposomes (ILs) were obtained by including a terminally alkylated copolymer of N-isopropylacrylamide (NIPAM) in the liposome bilayer and by coupling the anti-CD33 monoclonal antibody to target leukemic cells. In vitro release of encapsulated fluorescent probes and cytosine arabinoside (ara-C) revealed that pH-sensitivity of the vector was retained in the presence of the antibody upon incubation in plasma. Flow cytometry and confocal microscopy analyses demonstrated that the pH-sensitive ILs were efficiently internalized by various CD33+ leukemic cell lines while limited interaction was found for liposomes decorated with an isotype-matched control antibody. Finally, the pH-sensitive ILs-CD33 formulation exhibited the highest cytotoxicity against HL60 cells, confirming the role of the NIPAM copolymer in promoting the escape of intact ara-C in the endosomes. These results suggest that this pH-sensitive liposomal formulation could be beneficial in the treatment of acute myeloid leukemia.

A novel AML-selective TRAIL fusion protein that is superior to Gemtuzumab Ozogamicin in terms of in vitro selectivity, activity and stability

Gemtuzumab ozogamicin (GO, Mylotarg) is a targeted therapeutic agent in which an anti-CD33 antibody is chemically coupled to a highly cytotoxic calicheamicin derivative through a hydrolysable linker. GO has improved the treatment outcome for a subgroup of acute myeloid leukemia (AML) patients, but its use is associated with severe myelosuppression and hepatotoxicity. Here, we report on a novel anti-leukemia agent, designated scFvCD33:sTRAIL, in which an anti-CD33 single chain fragment of variable regions (scFv) antibody fragment is genetically linked to soluble tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL). Normal CD33-positive monocytes were fully resistant to prolonged treatment with scFvCD33:sTRAIL, whereas treatment with GO resulted in substantial cytotoxicity. The activity of scFvCD33:sTRAIL towards AML cells was up to 30-fold higher than GO. The CD33-restricted anti-leukemia activity of scFvCD33:sTRAIL remained stable during prolonged storage at 37 degrees C, whereas GO showed a rapid increase in CD33-independent cytotoxicity. Moreover, scFvCD33:sTRAIL showed potent anti-leukemia activity towards CD33+ CML cells when treatment was combined with the Bcr-Abl tyrosine kinase inhibitor, Gleevec. Importantly, ex vivo treatment of patient-derived CD33+ AML tumor cells with scFvCD33:sTRAIL resulted in potent apoptosis induction that was enhanced by valproic acid, mitoxantrone and 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG). Taken together, scFvCD33:sTRAIL is superior to GO in terms of tumor selectivity, activity and stability, warranting its further development for the treatment of CD33-positive leukemias.

Role of Metabolism in Drug-Induced Idiosyncratic Hepatotoxicity

Rare adverse reactions to drugs that are of unknown etiology, or idiosyncratic reactions, can produce severe medical complications or even death in patients. Current hypotheses suggest that metabolic activation of a drug to a reactive intermediate is a necessary, yet insufficient, step in the generation of an idiosyncratic reaction. We review evidence for this hypothesis with drugs that are associated with hepatotoxicity, one of the most common types of idiosyncratic reactions in humans. We identified 21 drugs that have either been withdrawn from the U.S. market due to hepatotoxicity or have a black box warning for hepatotoxicity. Evidence for the formation of reactive metabolites was found for 5 out of 6 drugs that were withdrawn, and 8 out of 15 drugs that have black box warnings. For the other drugs, either evidence was not available or suitable studies have not been carried out. We also review evidence for reactive intermediate formation from a number of additional drugs that have been associated with idiosyncratic hepatotoxicity but do not have black box warnings. Finally, we consider the potential role that high dosages may play in these adverse reactions.

Defibrotide: a review on clinical use and future development

BACKGROUND

Defibrotide is a deoxyribonucleic acid derivative that has been developed for the treatment of different vascular disorders.

OBJECTIVE

The authors reviewed the literature to give due representation to the spectrum of pharmacological properties and clinical application of this drug, evaluating consolidate and innovative application.

METHODS

The authors used PubMed from November 1982 to December 2007 and meeting abstracts (form American Society of Hematology Annual Meeting) with updated data as the sources for this review and selecting the most relevant papers when two or more articles covered the same point of interest.

CONCLUSIONS

Defibrotide has been used effectively in the treatment of endothelial complications of allogeneic stem cell transplantation and recent preclinical evidences suggest an antiangiogenic effect and an anticancer activity. Further in vivo and in vitro investigations are needed.

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.

Impaired CD163-mediated hemoglobin-scavenging and severe toxic symptoms in patients treated with gemtuzumab ozogamicin

We describe a novel syndrome of severe toxic symptoms during intravascular hemolysis due to impaired hemoglobin scavenging in 2 children with acute myeloid leukemia undergoing CD33-directed therapy with the immunotoxin gemtuzumab ozogamicin (GO). A simultaneous high plasma hemoglobin, haptoglobin, and low bilirubin after septicemia-induced intravascular hemolysis indicated abrogated clearance of haptoglobin-hemoglobin complexes. This was further supported by low levels of plasma soluble CD163 and a concordant low number of CD163-expressing monocytes. We show that CD163 positive monocytes and macrophages from liver, spleen, and bone marrow coexpress CD33, thus suggesting that the GO-induced cellular cytotoxicity of CD33 positive cells eradicates a significant part of the CD163 positive monocytes and macrophages. The risk of severe toxic symptoms from plasma hemoglobin should be considered after CD33-targeted chemotherapy when the disease is complicated by a pathologic intravascular hemolysis. Furthermore, the cases provide further circumstantial evidence of a key role of (CD163-expressing) monocytes/macrophages in plasma hemoglobin clearance in vivo.

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-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 patients over the age of 60 years who are unfit for conventional cytotoxic therapy. In this setting, it produces a complete response (CR) rate of 13%, with another 13% achieving CR with inadequate platelet recovery (CRp). The most common adverse effects associated with GO are infusion-related reactions and myelosuppression. GO monotherapy at the dose of 9 mg/m(2) is complicated with hepatic veno-occlusive disease in approximately 5% of cases, particularly prior to or following stem cell transplantation. Attenuated doses of GO or fractionated doses appear to be equally effective and better tolerated. GO has shown remarkable activity in acute promyelocytic leukemia, particularly for the elimination of minimal residual disease. Combinations of GO with chemotherapy as induction or post-remission therapy are promising, and phase III trials are ongoing.

Monoclonal antibodies as therapeutic agents in oncology and antibody gene therapy

Antibodies as therapeutic agents are mostly used in oncology, as illustrated by their applications in lymphoma, breast cancer or colorectal cancer. This review provides a brief historical sketch of the development of monoclonal antibodies for cancer treatment and summarizes the most significant clinical data for the best-established reagents to date. It also discusses strategies to improve the anti-tumor efficacy of antibody therapy, including antibody gene therapy and exploitation of bone marrow derived primary mesenchymal stem cells as the antibody gene transporter.

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.

Monoclonal antibody-based therapeutics for leukemia

Monoclonal antibodies (mAbs) represent a unique class of therapeutics because of their exquisite antigen specificity and effector mechanisms. Clinically, antibody-based therapy has increasingly become an established modality for the treatment of cancer. Among the nine mAbs and immunoconjugates approved by the FDA for therapeutic indications in oncological diseases, five are for use in hematological malignancies. Alemtuzumab is approved for B cell chronic lymphocytic leukemia; rituximab, an anti-CD20 antibody approved for the treatment of B cell non-Hodgkin's lymphoma, is being tested in patients with chronic lymphocytic leukemia; and gemtuzumab ozogamicin is marketed for relapsed acute myelogenous leukemia in patients of > 60 years of age. A number of other mAbs are in different stages of clinical development for antileukemia therapy. This article discusses the general aspects and mechanisms of action of therapeutic mAbs, and highlights the development of antibody-based therapies in leukemia.