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

Dose-related efficacy and toxicity of gemtuzumab ozogamicin in pediatric acute myeloid leukemia

Gemtuzumab ozogamicin, an anti-tumour antibiotic linked to an anti-CD33 antibody (Mylotarg®), has been well studied in AML in adults but to a lesser extent in children. No review has yet been published on the dose-related toxicity and efficacy of gemtuzumab ozogamicin in pediatric AML patients. Here we looked at 14 studies then scatterplots and linear regressions were used to estimate the relationship between the dose of gemtuzumab and its toxicity and efficacy. A non-significant increase in bilirubin level and in incidence of veno-occlusive disease was seen with higher doses of gemtuzumab ozogamicin when used as single-agent. In terms of efficacy, even a low dose of 3 mg/m(2) of gemtuzumab ozogamicin can have antileukemic effect, but available data do not allow conclusions on its dose-dependency. Data indicate that higher doses of gemtuzumab ozogamicin account for more adverse events. The data do not show that a high dose is required for anti-leukemic efficacy of gemtuzumab ozogamicin. This study also indicates that there seems to be a role for gemtuzumab ozogamicin in the treatment of pediatric AML and further studies are required to assess its optimal dose, schedule and balance between efficacy and side-effects.

Antibody-mediated delivery of therapeutics for cancer therapy

INTRODUCTION

Antibody-conjugated therapies (ACTs) combine the specificity of monoclonal antibodies to target cancer cells directly with highly potent payloads, often resulting in superior efficacy and/or reduced toxicity. This represents a new approach to the treatment of cancer. There have been highly promising clinical trial results using this approach with improvements in linker and payload technology. The breadth of current trials examining ACTs in haematological malignancies and solid tumours indicate the potential for clinical impact.

AREAS COVERED

This review will provide an overview of ACTs currently in clinical development as well as the principles of antibody delivery and types of payloads used, including cytotoxic drugs, radiolabelled isotopes, nanoparticle-based siRNA particles and immunotoxins.

EXPERT OPINION

The focus of much of the clinical activity in ACTs has, understandably, been on their use as a monotherapy or in combination with standard of care drugs. This will continue, as will the search for better targets, linkers and payloads. Increasingly, as these drugs enter routine clinical care, important questions will arise regarding how to optimise ACT treatment approaches, including investigation of resistance mechanisms, biomarker and patient selection strategies, understanding of the unique toxicities of these drugs, and combinatorial approaches with standard therapies as well as emerging therapeutic agents like immunotherapy.

AGS16F Is a Novel Antibody Drug Conjugate Directed against ENPP3 for the Treatment of Renal Cell Carcinoma

PURPOSE

New cancer-specific antigens are required for the design of novel antibody-drug conjugates (ADC) that deliver tumor-specific and highly potent cytotoxic therapy.

EXPERIMENTAL DESIGN

Suppression subtractive hybridization identified ectonucleotide pyrophosphatase/phosphodiesterase 3 (ENPP3 or CD203c) as a potential human cancer-specific antigen. Antibodies targeting the extracellular domain of human ENPP3 were produced and selected for specific binding to ENPP3. Expression of ENPP3 in normal and cancer tissue specimens was evaluated by immunohistochemistry (IHC). ADCs comprising anti-ENPP3 Ab conjugated with maleimidocaproyl monomethyl auristatin F via a noncleavable linker (mcMMAF) were selected for therapeutic potential using binding and internalization assays, cytotoxicity assays, and tumor growth inhibition in mouse xenograft models. Pharmacodynamic markers were evaluated by IHC in tissues and ELISA in blood.

RESULTS

ENPP3 was highly expressed in clear cell renal cell carcinoma: 92.3% of samples were positive and 83.9% showed high expression. By contrast, expression was negligible in normal tissues examined, with the exception of the kidney. High expression was less frequent in papillary renal cell carcinoma and hepatocellular carcinoma samples. AGS16F, an anti-ENPP3 antibody-mcMMAF conjugate, inhibited tumor growth in three different renal cell carcinoma (RCC) xenograft models. AGS16F localized to tumors, formed the active metabolite Cys-mcMMAF, induced cell-cycle arrest and apoptosis, and increased blood levels of caspase-cleaved cytokeratin-18, a marker of epithelial cell death.

CONCLUSIONS

AGS16F is a promising new therapeutic option for patients with RCC and is currently being evaluated in a phase I clinical trial.

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.

The clinical potential of inotuzumab ozogamicin in relapsed and refractory acute lymphocytic leukemia

Antibody-drug conjugates (ADCs) are likely to make a significant contribution in the treatment of acute lymphoblastic leukemia (ALL) by combining the cytotoxicity of chemotherapy with the specificity of monoclonal antibodies. CD22, an endocytic receptor expressed by the majority of B cells, is an excellent target for ADCs. Inotuzumab ozogamicin (INO) is an ADC that consists of a cytotoxic moiety (derivative of calicheamicin) attached to a humanized monoclonal anti-CD22 antibody. As a single agent, INO, was shown to be effective with an objective response rate of 50% in the treatment of relapsed and refractory CD22 positive ALL patients. Clinical trials investigating the combination of INO with the conventional chemotherapies are ongoing. This review summarizes the clinical potential of INO in treatment of relapsed and refractory ALL, based on currently available data in the literature.

In vivo biotransformations of antibody–drug conjugates

The selective delivery of potent pharmacologically active compounds to target tissue or cells by antibody–drug conjugates makes this immuno-conjugate a promising modality for the treatment of cancers. A thorough understanding of the structural integrity of the linker, the payload and the conjugation site during biological exposure is critical throughout the process of novel linker-payload design and optimization of PK profile. This understanding is a key aspect of the effort to maximize efficacy while minimizing toxicity in preclinical testing and to ensure the translation to the clinical setting. The complexity of this bioconjugate modality is a source of significant challenge for analytical interrogation and analysis in vivo. Therefore, we report herein a survey of various types of biotransformation events that have been elucidated in recent years.

Antibody-drug conjugates as novel anti-cancer chemotherapeutics

Over the past couple of decades, antibody-drug conjugates (ADCs) have revolutionized the field of cancer chemotherapy. Unlike conventional treatments that damage healthy tissues upon dose escalation, ADCs utilize monoclonal antibodies (mAbs) to specifically bind tumour-associated target antigens and deliver a highly potent cytotoxic agent. The synergistic combination of mAbs conjugated to small-molecule chemotherapeutics, via a stable linker, has given rise to an extremely efficacious class of anti-cancer drugs with an already large and rapidly growing clinical pipeline. The primary objective of this paper is to review current knowledge and latest developments in the field of ADCs. Upon intravenous administration, ADCs bind to their target antigens and are internalized through receptor-mediated endocytosis. This facilitates the subsequent release of the cytotoxin, which eventually leads to apoptotic cell death of the cancer cell. The three components of ADCs (mAb, linker and cytotoxin) affect the efficacy and toxicity of the conjugate. Optimizing each one, while enhancing the functionality of the ADC as a whole, has been one of the major considerations of ADC design and development. In addition to these, the choice of clinically relevant targets and the position and number of linkages have also been the key determinants of ADC efficacy. The only marketed ADCs, brentuximab vedotin and trastuzumab emtansine (T-DM1), have demonstrated their use against both haematological and solid malignancies respectively. The success of future ADCs relies on improving target selection, increasing cytotoxin potency, developing innovative linkers and overcoming drug resistance. As more research is conducted to tackle these issues, ADCs are likely to become part of the future of targeted cancer therapeutics.

Current methods for the synthesis of homogeneous antibody-drug conjugates

Development of efficient and safe cancer therapy is one of the major challenges of the modern medicine. Over the last few years antibody-drug conjugates (ADCs) have become a powerful tool in cancer treatment with two of them, Adcetris® (brentuximab vedotin) and Kadcyla® (ado-trastuzumab emtansine), having recently been approved by the Food and Drug Administration (FDA). Essentially, an ADC is a bioconjugate that comprises a monoclonal antibody that specifically binds tumor surface antigen and a highly potent drug, which is attached to the antibody via either cleavable or stable linker. This approach ensures specificity and efficacy in fighting cancer cells, while healthy tissues remain largely unaffected. Conventional ADCs, that employ cysteine or lysine residues as conjugation sites, are highly heterogeneous. This means that the species contain various populations of the ADCs with different drug-to-antibody ratios (DARs) and different drug load distributions. DAR and drug-load distribution are essential parameters of ADCs as they determine their stability and efficacy. Therefore, various drug-loaded forms of ADCs (usually from zero to eight conjugated molecules per antibody) may have distinct pharmacokinetics (PK) in vivo and may differ in clinical performance. Recently, a significant progress has been made in the field of site-specific conjugation which resulted in a number of strategies for synthesis of the homogeneous ADCs. This review describes newly-developed methods that ensure homogeneity of the ADCs including use of engineered reactive cysteine residues (THIOMAB), unnatural amino acids, aldehyde tags, enzymatic transglutaminase- and glycotransferase-based approaches and novel chemical methods. Furthermore, we briefly discuss the limitation of these methods emphasizing the need for further improvement in the ADC design and development.

An immunosuppressive antibody-drug conjugate

We have developed a novel antibody-drug conjugate (ADC) that can selectively deliver the Lck inhibitor dasatinib to human T lymphocytes. This ADC is based on a humanized antibody that selectively binds with high affinity to CXCR4, an antigen that is selectively expressed on hematopoietic cells. The resulting dasatinib-antibody conjugate suppresses T-cell-receptor (TCR)-mediated T-cell activation and cytokine expression with low nM EC50 and has minimal effects on cell viability. This ADC may lead to a new class of selective immunosuppressive drugs with improved safety and extend the ADC strategy to the targeted delivery of kinase inhibitors for indications beyond oncology.

Beyond peptides and mAbs--current status and future perspectives for biotherapeutics with novel constructs

Biotherapeutics are attractive anti-cancer agents due to their high specificity and limited toxicity compared to conventional small molecules. Antibodies are widely used in cancer therapy, either directly or conjugated to a cytotoxic payload. Peptide therapies, though not as prevalent, have been utilized in hormonal therapy and imaging. The limitations associated with unmodified forms of both types of biotherapeutics have led to the design and development of novel structures, which incorporate key features and structures that have improved the molecules' abilities to bind to tumor targets, avoid degradation, and exhibit favorable pharmacokinetics. In this review, we highlight the current status of monoclonal antibodies and peptides, and provide a perspective on the future of biotherapeutics using novel constructs.

Gemtuzumab ozogamicin in children and adolescents with de novo acute myeloid leukemia improves event-free survival by reducing relapse risk: results from the randomized phase III Children’s Oncology Group trial AAML0531

PURPOSE

To improve survival rates in children with acute myeloid leukemia (AML), we evaluated gemtuzumab-ozogamicin (GO), a humanized immunoconjugate targeted against CD33, as an alternative to further chemotherapy dose escalation. Our primary objective was to determine whether adding GO to standard chemotherapy improved event-free survival (EFS) and overall survival (OS) in children with newly diagnosed AML. Our secondary objectives examined outcomes by risk group and method of intensification.

PATIENTS AND METHODS

Children, adolescents, and young adults ages 0 to 29 years with newly diagnosed AML were enrolled onto Children’s Oncology Group trial AAML0531 and then were randomly assigned to either standard five-course chemotherapy alone or to the same chemotherapy with two doses of GO (3 mg/m2/dose) administered once in induction course 1 and once in intensification course 2 (two of three).

RESULTS

There were 1,022 evaluable patients enrolled. GO significantly improved EFS (3 years: 53.1% v. 46.9%; hazard ratio [HzR], 0.83; 95% CI, 0.70 to 0.99; P.04) but not OS (3 years: 69.4% v. 65.4%; HzR, 0.91; 95% CI, 0.74 to 1.13; P = .39). Although remission was not improved (88% v. 85%; P = .15), posthoc analyses found relapse risk (RR) was significantly reduced among GO recipients overall (3 years: 32.8% v. 41.3%; HzR, 0.73; 95% CI, 0.58 to 0.91; P = .006). Despite an increased postremission toxic mortality (3 years: 6.6% v. 4.1%; HzR, 1.69; 95% CI, 0.93 to 3.08; P = .09), disease-free survival was better among GO recipients (3 years: 60.6% v. 54.7%; HzR, 0.82; 95% CI, 0.67 to 1.02; P = .07).

CONCLUSION

GO added to chemotherapy improved EFS through a reduction in RR for children and adolescents with AML.

Site-specific protein labeling in the pharmaceutical industry: experiences from novartis drug discovery

Chemically modified proteins play an important role in several fields of pharmaceutical R&D, starting from various activities in drug discovery all the way down to biopharmaceuticals with improved properties such as antibody-drug conjugates. In the first part of the present chapter the significance and use of labeled proteins in biophysical methods, biochemical and cellular assays, in vivo imaging, and biopharmaceuticals is reviewed in general. In this context, the most relevant methods for site-specific modification of proteins and their application are also described. In the second part of the chapter, in-house (Novartis) results and experience with different techniques for selective protein labeling are discussed, with a focus on chemical or enzymatic (Avi-tag) biotinylation of proteins and their application in biophysical and biochemical assays. It can be concluded that while modern methods of site-specific protein labeling offer new possibilities for pharmaceutical R&D, classical methods are still the mainstay mainly due to being well established. However, site-specific protein labeling is expected to increase in importance, in particular for antibody-drug conjugates and other chemically modified biopharmaceuticals.

Antibody-targeted drugs and drug resistance--challenges and solutions

Antibody-based therapy of various human malignancies has shown efficacy in the past 30 years and is now one of the most successful and leading strategies for targeted treatment of patients harboring hematological malignancies and solid tumors. Antibody-drug conjugates (ADCs) aim to take advantage of the affinity and specificity of monoclonal antibodies (mAbs) to selectively deliver potent cytotoxic drugs to antigen-expressing tumor cells. Key parameters for ADC include choosing the optimal components of the ADC (the antibody, the linker and the cytotoxic drug) and selecting the suitable cell-surface target antigen. Building on the success of recent FDA approval of brentuximab vedotin (Adcetris) and ado-trastuzumab emtansine (Kadcyla), ADCs are currently a class of drugs with a robust pipeline with clinical applications that are rapidly expanding. The more ADCs are being evaluated in preclinical models and clinical trials, the clearer are becoming the parameters and the challenges required for their therapeutic success. This rapidly growing knowledge and clinical experience are revealing novel modalities and mechanisms of resistance to ADCs, hence offering plausible solutions to such challenges. Here, we review the key parameters for designing a powerful ADC, focusing on how ADCs are addressing the challenge of multiple drug resistance (MDR) and its rational overcoming.

Target Therapy in Hematological Malignances: New Monoclonal Antibodies

Apart from radio- and chemotherapy, monoclonal antibodies (MoAbs) represent a new, more selective tool in the treatment of hematological malignancies. MoAbs bind with the specific antigens of the tumors. This interaction is a basis for targeted therapies which exhibit few side effects and significant antitumor activity. This review provides an overview of the functional characteristics of MoAbs, with some examples of their clinical application. The promising results in the treatment of hematological malignancies have led to the more frequent usage of MoAbs in the therapy. Development of MoAbs is a subject of extensive research. They are a promising method of cancer treatment in the future.

Using the Lessons Learned From the Clinic to Improve the Preclinical Development of Antibody Drug Conjugates

The treatment options for cancer patients include surgery, chemotherapeutics, radiation therapy, antibody therapy and various combinations of these therapies. The challenge with each therapy is finding the balance between maximizing the anti-tumor efficacy while minimizing the dose limiting toxicities. Antibodies, unlike small molecule chemotherapeutics, selectively bind to cell surface tumor antigens and can be used to deliver radionucleotides or small molecule chemotherapeutic drugs directly to the tumor. Advances in antibody engineering, linker chemistry and the identification of potent cytotoxic drugs led to the recent approval of two antibody drug conjugates to treat breast cancer and lymphoma patients. We will discuss how the observations from the clinical development of antibody drug conjugates can guide the preclinical development of the next generation of antibody drug conjugates.

Structure-guided functional characterization of enediyne self-sacrifice resistance proteins, CalU16 and CalU19

Calicheamicin γ₁^I (1) is an enediyne antitumor compound produced by Micromonospora echinospora spp. calichensis, and its biosynthetic gene cluster has been previously reported. Despite extensive analysis and biochemical study, several genes in the biosynthetic gene cluster of 1 remain functionally unassigned. Using a structural genomics approach and biochemical characterization, two proteins encoded by genes from the 1 biosynthetic gene cluster assigned as “unknowns”, CalU16 and CalU19, were characterized. Structure analysis revealed that they possess the STeroidogenic Acute Regulatory protein related lipid Transfer (START) domain known mainly to bind and transport lipids and previously identified as the structural signature of the enediyne self-resistance protein CalC. Subsequent study revealed calU16 and calU19 to confer resistance to 1, and reminiscent of the prototype CalC, both CalU16 and CalU19 were cleaved by 1in vitro. Through site-directed mutagenesis and mass spectrometry, we identified the site of cleavage in each protein and characterized their function in conferring resistance against 1. This report emphasizes the importance of structural genomics as a powerful tool for the functional annotation of unknown proteins.

The development of immunoconjugates for targeted cancer therapy

Immunoconjugates are specific, highly effective, minimally toxic anticancer therapies that are beginning to show promise in the clinic. Immunoconjugates consist of three separate components: an antibody that binds to a cancer cell antigen with high specificity, an effector molecule that has a high capacity to kill the cancer cell, and a linker that will ensure the effector does not separate from the antibody during transit and will reliably release the effector to the cancer cell or tumour stroma. The high affinity antibody-antigen interaction allows specific and selective delivery of a range of effectors, including pharmacologic agents, radioisotopes, and toxins, to cancer cells. Some anticancer molecules are not well tolerated when administered systemically owing to unacceptable toxicity to the host. However, this limitation can be overcome through the linking of such cytotoxins to specific antibodies, which mask the toxic effects of the drug until it reaches its target. Conversely, many unconjugated antibodies are highly specific for a cancer target, but have low therapeutic potential and can be repurposed as delivery vehicles for highly potent effectors. In this Review, we summarize the successes and shortcomings of immunoconjugates, and discuss the future potential for the development of these therapies.

Siglec-mediated regulation of immune cell function in disease

All mammalian cells display a diverse array of glycan structures that differ from those that are found on microbial pathogens. Siglecs are a family of sialic acid-binding immunoglobulin-like receptors that participate in the discrimination between self and non-self, and that regulate the function of cells in the innate and adaptive immune systems through the recognition of their glycan ligands. In this Review, we describe the recent advances in our understanding of the roles of Siglecs in the regulation of immune cell function in infectious diseases, inflammation, neurodegeneration, autoimmune diseases and cancer.

Novel drugs for older patients with acute myeloid leukemia

Acute myeloid leukemia (AML) is the second most common form of leukemia and the most frequent cause of leukemia-related deaths in the United States. The incidence of AML increases with advancing age and the prognosis for patients with AML worsens substantially with increasing age. Many older patients are ineligible for intensive treatment and require other therapeutic approaches to optimize clinical outcome. To address this treatment gap, novel agents with varying mechanisms of action targeting different cellular processes are currently in development. Hypomethylating agents (azacitidine, decitabine, SGI-110), histone deacetylase inhibitors (vorinostat, pracinostat, panobinostat), FMS-like tyrosine kinase receptor-3 inhibitors (quizartinib, sorafenib, midostaurin, crenolanib), cytotoxic agents (clofarabine, sapacitabine, vosaroxin), cell cycle inhibitors (barasertib, volasertib, rigosertib) and monoclonal antibodies (gentuzumab ozogamicin, lintuzumab-Ac225) represent some of these promising new treatments. This review provides an overview of novel agents that have either completed or are currently in ongoing phase III trials in patients with previously untreated AML for whom intensive treatment is not an option. Other potential drugs in earlier stages of development will also be addressed in this review.

Neoglycosylation and neoglycorandomization: Enabling tools for the discovery of novel glycosylated bioactive probes and early stage leads

This review focuses upon the development, scope, and utility of the highly versatile chemoselective alkoxyamine-based 'neoglycosylation' reaction first described by Peri and Dumy. The fundamentals of neoglycosylation and the subsequent development of a 'neoglycorandomization' platform to afford differentially-glycosylated libraries of plant-based natural products, microbial-based natural products, and small molecule-based drugs for drug discovery applications are discussed.

Antibody therapy for pediatric leukemia

Despite increasing cure rates for pediatric leukemia, relapsed disease still carries a poor prognosis with significant morbidity and mortality. Novel targeted therapies are currently being investigated in an attempt to reduce adverse events and improve survival outcomes. Antibody therapies represent a form of targeted therapy that offers a new treatment paradigm. Monoclonal antibodies are active in pediatric acute lymphoblastic leukemia (ALL) and are currently in Phase III trials. Antibody-drug conjugates (ADCs) are the next generation of antibodies where a highly potent cytotoxic agent is bound to an antibody by a linker, resulting in selective targeting of leukemia cells. ADCs are currently being tested in clinical trials for pediatric acute myeloid leukemia and ALL. Bispecific T cell engager (BiTE) antibodies are a construct whereby each antibody contains two binding sites, with one designed to engage the patient's own immune system and the other to target malignant cells. BiTE antibodies show great promise as a novel and effective therapy for childhood leukemia. This review will outline recent developments in targeted agents for pediatric leukemia including monoclonal antibodies, ADCs, and BiTE antibodies.

New horizons for old drugs and drug leads

There is mounting urgency to find new drugs for the treatment of serious infectious diseases and cancer that are rapidly developing resistance to previously effective drugs. One approach to addressing this need is through drug repurposing, which refers to the discovery of new useful activities for "old" clinically used drugs through screening them against relevant disease targets. A large number of potential drug that, for various reasons, have failed to advance to clinical and commercial use can be added to the candidates available for such purposes. The application of new techniques and methodology developed through the impressive progress made in multidisciplinary, natural product-related research in recent years should aid substantially in expediting the discovery and development process. This review briefly outlines some of these developments as applied to a number of selected natural product examples, which may also include advances in chemical synthesis of derivatives with extended biological activities.

Targeting CD22 in B-cell malignancies: current status and clinical outlook

CD22 is a B-cell-specific transmembrane glycoprotein found on the surface of most B cells; it modulates B-cell function, survival and apoptosis. CD22 has emerged as an ideal target for monoclonal antibody (mAb)-based therapy of B-cell malignancies including most lymphomas and many leukemias. Epratuzumab, an anti-CD22 mAb, has been developed in various forms, including as an unlabeled (naked) mAb, as a radioimmunotherapeutic, as an antibody drug conjugate (ADC), and as a vehicle for CD22-targeted nanoparticles. While clinical trials with unlabeled epratuzumab have demonstrated modest results, its combination with rituximab in phase II studies has been more encouraging. Based on the potential for CD22 to become internalized, CD22-targeted constructs carrying radioisotopes or toxins have generated promising results. Radioimmunotherapy, utilizing ⁹⁰Y-labeled epratuzumab, was shown to be highly effective in patients with follicular lymphoma, generating a complete response (CR) rate of 92 % and progression-free survival of more than 2 years. ADC therapy is a promising therapeutic approach to B-cell malignancies which includes the direct conjugation of mAbs with cytotoxic agents. Phase II studies of inotuzumab ozogamicin, an ADC which combines anti-CD22 mAb with calicheamicin, an enediyne antibiotic which mediates apoptosis, in patients with acute lymphoblastic leukemia have produced an overall response rate (ORR) of greater than 50 % in treatment-refractory patients. Phase I trials of moxetumomab pasudotox, an ADC which combines anti-CD22 with PE38, a fragment of Pseudomonas exotoxin A, have been completed in hairy cell leukemia with a ORR of 86 %. Finally, a review of CD22-targeted nanoparticles, that include a doxorubicin-containing lipid complex that uses synthetic high-affinity CD22 ligand mimetics as well as anti-CD22 mAb-coated pegylated liposomas doxorubin (PLD), has demonstrated promising results in pre-clinical models of human lymphoma. Moreover, novel anti-CD22 mAb that block CD22 ligand binding as well as second generation ADC that utilize biodegradable linkers and more potent toxins hold great hope for the future of CD22-targeted therapeutics that may translate into better outcomes for patients with CD22-positive malignancies.

Initial experience with CMC-544 (inotuzumab ozogamicin) in pediatric patients with relapsed B-cell acute lymphoblastic leukemia

Survival is poor in pediatric patients with relapsed or refractory acute B-cell lymphoblastic leukemia (ALL) and therapeutic options are limited. CMC-544 (inotuzumab ozogamicin) has shown significant activity in adult patients with relapsed and refractory ALL. We evaluated CMC-544 in pediatric patients with multiply relapsed ALL. Five children 4-15 years old with relapsed, CD 22 positive B-cell ALL were enrolled on a phase II non-randomized trial of CMC-544. CMC-544 was initially administered at 1.3 mg/m(2) every 3 weeks. The dose then increased to 1.8 mg/m(2) every 3 weeks. Subsequently, a weekly schedule of CMC-544 given as 0.8 mg/m(2) on day 1 followed by 0.5 mg/m(2) on days 8 and 15 was administered. All five patients had refractory relapsed B-cell ALL. Lymphoblasts for all patients highly expressed CD22. Four patients had two or more relapses before starting the study drug. One patient achieved a complete remission in the bone marrow and normal peripheral counts, and two patients achieved bone marrow morphologic remission with absolute neutrophils >1,000/µl but platelets <100,000/µl. Two patients had no response to the drug. Toxicities consisted of fever, sepsis, and liver enzyme elevation. Single agent CMC-544 given at the single dose of 1.8 mg/m(2) every 3 weeks or given as a split, weekly dose was generally well tolerated considering the inherent risks in this population of patients and showed promising activity in pediatric patients with relapsed and refractory ALL.

Sequential treatment with cytarabine and decitabine has an increased anti-leukemia effect compared to cytarabine alone in xenograft models of childhood acute myeloid leukemia

The current interest in epigenetic priming is underpinned by the belief that remodelling of the epigenetic landscape will sensitise tumours to subsequent therapy. In this pre-clinical study, paediatric AML cells expanded in culture and primary AML xenografts were treated with decitabine, a DNA demethylating agent, and cytarabine, a frontline cytotoxic agent used in the treatment of AML, either alone or in combination. Sequential treatment with decitabine and cytarabine was found to be more effective in reducing tumour burden than treatment with cytarabine alone suggesting that the sequential delivery of these agents may a have real clinical advantage in the treatment of paediatric AML. However we found no evidence to suggest that this outcome was dependent on priming with a hypomethylating agent, as the benefits observed were independent of the order in which these drugs were administered.

Conjugates of Small Molecule Drugs with Antibodies and Other Proteins

Conjugates of small molecule drugs with antibodies (ADCs) and with other proteins (protein-drug conjugates, PDC) are used as a new class of targeted therapeutics combining the specificity of monoclonal antibodies (mAbs) and other proteins with potent cytotoxic activity of small molecule drugs for the treatment of cancer and other diseases. A(P)DCs have three major components, antibody (targeting protein), linker and payload, the cytotoxic drug. Recently, advances in identifying targets, selecting highly specific mAbs of preferred isotypes, optimizing linker technology and improving chemical methods for conjugation have led to the approval of two ADCs by Food and Drug Administration (FDA) and more than 30 ADCs in advanced clinical development. However, the complex and heterogeneous nature of A(P)DCs often cause poor solubility, instability, aggregation and eventually unwanted toxicity. This article reviews the main components of A(P)DCs, and discusses the choices for drugs, linkers and conjugation methods currently used. Future work will need to focus on developments and strategies for overcoming such major problems associated with the A(P)DCs.

A dose-escalation study of SAR3419, an anti-CD19 antibody maytansinoid conjugate, administered by intravenous infusion once weekly in patients with relapsed/refractory B-cell non-Hodgkin lymphoma

PURPOSE

To determine recommended dose, dose-limiting toxicity, safety profile, pharmacokinetics, preliminary antitumor activity, and exploratory pharmacodynamics of SAR3419, an antibody-drug conjugate targeting CD19, administered alone by intravenous infusion weekly (qw), in a dose-escalation phase I study in patients with refractory/relapsed (R/R) non-Hodgkin lymphoma (NHL).

EXPERIMENTAL DESIGN

Patients with R/R CD19(+) B-NHL were treated with escalating doses of SAR3419 repeated qw for eight to 12 doses. On the basis of clinical evidence of late or cumulative toxicities, the study protocol was amended to test an "optimized" administration schedule consisting of four qw doses followed by four biweekly (q2w) doses (qw/q2w) at the recommended dose with the intent of reducing drug accumulation.

RESULTS

Forty-four patients were treated on seven dose levels ranging from 5 to 70 mg/m(2). SAR3419 recommended dose was determined as 55 mg/m(2) qw. Twenty-five patients received the qw/q2w schedule at 55 mg/m(2), which showed an improved safety profile compared with the qw schedule. Antilymphoma activity was observed with both schedules in around 30% of patients with either indolent or aggressive diseases. SAR3419 displayed a long terminal half-life (approximately 7 days) and a low clearance (approximately 0.6 L/d), with no dose effect. The qw/q2w schedule allowed limiting accumulation with a decrease in SAR3419 plasma trough and average concentrations by around 1.4-fold compared with the qw schedule.

CONCLUSION

While administered weekly, SAR3419 is well tolerated and active. The qw/q2w schedule that shows an improved safety profile and preserves antilymphoma activity is selected for clinical phase II studies.

Antibody therapeutics in cancer

In a relatively short period of time, monoclonal antibodies have entered the mainstream of cancer therapy. Their first use was as antagonists of oncogenic receptor tyrosine kinases, but today monoclonal antibodies have emerged as long-sought vehicles for the targeted delivery of potent chemotherapeutic agents and as powerful tools to manipulate anticancer immune responses. With ever more promising results from the clinic, the future will likely see continued growth in the discovery and development of therapeutic antibodies and their derivatives.

A novel anti-CD37 antibody-drug conjugate with multiple anti-tumor mechanisms for the treatment of B-cell malignancies

CD37 has gathered renewed interest as a therapeutic target in non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL); however, CD37-directed antibody-drug conjugates (ADCs) have not been explored. Here, we identified a novel anti-CD37 antibody, K7153A, with potent in vitro activity against B-cell lines through multiple mechanisms including apoptosis induction, antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and complement-dependent cytotoxicity. The antibody was conjugated to the maytansinoid, DM1, a potent antimicrotubule agent, via the thioether linker, N-succinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC), and the resulting ADC, IMGN529, retained the intrinsic antibody activities and showed enhanced cytotoxic activity from targeted payload delivery. In lymphoma cell lines, IMGN529 induced G2/M cell cycle arrest after internalization and lysosomal processing to lysine-N(ε)-SMCC-DM1 as the sole intracellular maytansinoid metabolite. IMGN529 was highly active against subcutaneous B-cell tumor xenografts in severe combined immunodeficient mice with comparable or better activity than rituximab, a combination of cyclophosphamide, vincristine, and prednisone, or bendamustine. In human blood cells, CD37 is expressed in B cells at similar levels as CD20, and IMGN529 resulted in potent and specific depletion of normal and CLL B cells. These results support evaluation of the CD37-targeted ADC, IMGN529, in clinical trials in patients with B-cell malignancies including NHL and CLL.

Microbial natural products: molecular blueprints for antitumor drugs

Microbes from two of the three domains of life, the Prokarya, and Eukarya, continue to serve as rich sources of structurally complex chemical scaffolds that have proven to be essential for the development of anticancer therapeutics. This review describes only a handful of exemplary natural products and their derivatives as well as those that have served as elegant blueprints for the development of novel synthetic structures that are either currently in use or in clinical or preclinical trials together with some of their earlier analogs in some cases whose failure to proceed aided in the derivation of later compounds. In every case, a microbe has been either identified as the producer of secondary metabolites or speculated to be involved in the production via symbiotic associations. Finally, rapidly evolving next-generation sequencing technologies have led to the increasing availability of microbial genomes. Relevant examples of genome mining and genetic manipulation are discussed, demonstrating that we have only barely scratched the surface with regards to harnessing the potential of microbes as sources of new pharmaceutical leads/agents or biological probes.

CD33 in Alzheimer's disease

The amyloid-beta peptide (Aβ) cascade hypothesis posits that Aβ accumulation is the fundamental initiator of Alzheimer's disease (AD), and mounting evidence suggests that impaired Aβ clearance rather than its overproduction is the major pathogenic event for AD. Recent genetic studies have identified cluster of differentiation 33 (CD33) as a strong genetic locus linked to AD. As a type I transmembrane protein, CD33 belongs to the sialic acid-binding immunoglobulin-like lectins, mediating the cell-cell interaction and inhibiting normal functions of immune cells. In the brain, CD33 is mainly expressed on microglial cells. The level of CD33 was found to be increased in the AD brain, which positively correlated with amyloid plaque burden and disease severity. More importantly, CD33 led to the impairment of microglia-mediated clearance of Aβ, which resulted in the formation of amyloid plaques in the brain. In this article, we review the recent epidemiological findings of CD33 that related with AD and discuss the levels and pathogenic roles of CD33 in this disease. Based on the contributing effects of CD33 in AD pathogenesis, targeting CD33 may provide new opportunities for AD therapeutic strategies.

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.

On-chip synthesis and screening of a sialoside library yields a high affinity ligand for Siglec-7

The Siglec family of sialic acid-binding proteins are differentially expressed on white blood cells of the immune system and represent an attractive class of targets for cell-directed therapy. Nanoparticles decorated with high-affinity Siglec ligands show promise for delivering cargo to Siglec-bearing cells, but this approach has been limited by a lack of ligands with suitable affinity and selectivity. Building on previous work employing solution-phase sialoside library synthesis and subsequent microarray screening, we herein report a more streamlined 'on-chip' synthetic approach. By printing a small library of alkyne sialosides and subjecting these to 'on-chip' click reactions, the largest sialoside analogue library to date was generated. Siglec-screening identified a selective Siglec-7 ligand, which when displayed on liposomal nanoparticles, allows for targeting of Siglec-7(+) cells in peripheral human blood. In silico docking to the crystal structure of Siglec-7 provides a rationale for the affinity gains observed for this novel sialic acid analogue.

Novel therapeutic strategies in adult acute lymphoblastic leukemia--a focus on emerging monoclonal antibodies

The outcomes in adult B-cell acute lymphoblastic leukemia (ALL) remain inferior to those achieved in pediatric populations. Targeted therapy with monoclonal antibodies may improve outcomes in adult B-cell ALL without significant additive toxicity. Rituximab is the best known monoclonal antibody and is routinely used in combination chemo-immunotherapy for treatment of adult B-cell ALL and Burkitts leukemia. A number of other monoclonal antibodies are currently under investigation for treatment of adult B-cell ALL including unconjugated antibodies (eg., ofatumumab, alemtuzumab and epratuzumab), antibodies conjugated to cytotoxic agents (eg., inotuzumab ozogamycin and SAR3419), antibodies conjugated to toxins such Pseudomonas or Diptheria toxins (eg., BL22 and moxetumomab pasudotox), and T-cell engaging bi-specific antibodies that redirect cytotoxic T lymphocytes to lyse target ALL cells (eg., blinatumomab). In this article we review the therapeutic implications, current status and results of monoclonal antibody-based therapy in adult B-cell ALL.

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.

A galactosidase-responsive doxorubicin-folate conjugate for selective targeting of acute myelogenous leukemia blasts

Cytarabine combined with an anthracycline or an anthracenedione represents the usual intensive induction therapy for the treatment of AML. However, this protocol induces severe side effects and treatment-related mortality due to the lack of selectivity of these cytotoxic agents. In this paper, we present the study of the first galactosidase-responsive molecular "Trojan Horse" programmed for the delivery of doxorubicin exclusively inside AML blasts over-expressing the folate receptor (FR). This targeting system allows the selective killing of AML blasts without affecting normal endothelial, cardiac or hematologic cells from healthy donors suggesting that FDC could reduce adverse events usually recorded with anthracyclines.

Alzheimer's disease risk gene CD33 inhibits microglial uptake of amyloid beta

The transmembrane protein CD33 is a sialic acid-binding immunoglobulin-like lectin that regulates innate immunity but has no known functions in the brain. We have previously shown that the CD33 gene is a risk factor for Alzheimer's disease (AD). Here, we observed increased expression of CD33 in microglial cells in AD brain. The minor allele of the CD33 SNP rs3865444, which confers protection against AD, was associated with reductions in both CD33 expression and insoluble amyloid beta 42 (Aβ42) levels in AD brain. Furthermore, the numbers of CD33-immunoreactive microglia were positively correlated with insoluble Aβ42 levels and plaque burden in AD brain. CD33 inhibited uptake and clearance of Aβ42 in microglial cell cultures. Finally, brain levels of insoluble Aβ42 as well as amyloid plaque burden were markedly reduced in APP(Swe)/PS1(ΔE9)/CD33(-/-) mice. Therefore, CD33 inactivation mitigates Aβ pathology and CD33 inhibition could represent a novel therapy for AD.

Monoclonal antibodies in conditioning regimens for hematopoietic cell transplantation

Monoclonal antibodies are increasingly being incorporated in conditioning regimens for autologous or allogeneic hematopoietic cell transplantation (HCT). The benefit of adding rituximab to autologous HCT regimens is purportedly related to in vivo purging of clonal B cells. Randomized trials comparing the addition (or not) of rituximab to high-dose therapy regimens are lacking. No benefit of standard-dose radioimmunotherapy-based regimens for autografting in aggressive lymphomas was seen in a randomized controlled study. The incorporation of rituximab into allogeneic HCT regimens aims to improve responses while reducing nonrelapse mortality resulting from acute graft-versus-host disease. The optimal dose and administration schedule of rituximab in this setting are unknown, and potentially serious complications from increased infections owing to prolonged (and profound) cytopenias or persistent hypogammaglobulinemia are of concern. Radioimmunotherapy-based conditioning for allografting holds promise as a modality to optimize tumor control and synergize adoptive immunotherapy effects, but it remains experimental at this time. The addition of alemtuzumab to allogeneic HCT regimens is associated with prolonged lymphopenia and impaired immune reconstitution, high relapse rates, and serious infections. The optimal dose and schedule of alemtuzumab to avoid prolonged immune paresis remain elusive. It is anticipated that additional monoclonal antibodies will soon become available that can be incorporated into HCT regimens after safety and clinical efficacy are demonstrated.

Antibody–drug conjugates for the treatment of B-cell non-Hodgkin’s lymphoma and leukemia

Antibody–drug conjugates (ADCs) are a broad class of molecules comprising of a potent cytotoxic agent conjugated with a monoclonal antibody using a chemically stable linker. By selecting a monoclonal antibody directed against a tumor-specific or tumor-associated antigen, ADCs allow the targeted delivery of highly potent cytotoxic agents that result in unacceptable toxicity when administered as free agents. ADCs are currently being developed for the treatment of a wide variety of tumors. In this review, the current clinical and preclinical status of ADCs for the treatment of B-cell non-Hodgkin’s lymphoma and B-cell leukemia will be discussed. ADCs have the potential to alter treatment paradigms for these diseases by providing both increased efficacy and improved safety and tolerability over current chemotherapy-based regimens.