Randomized phase II study of BR96-doxorubicin conjugate in patients with metastatic breast cancer

Glycans as targets for therapeutic antitumor antibodies

Glycans represent a vast class of molecules that modify either proteins or lipids. They exert and regulate important and complex functions in both normal and cancer cell metabolism. As such, the most immunogenic glycans have been targeted in passive and active immunotherapy in human cancer for the past 25 years but it is only recently that techniques have become available to uncover novel glycan targets. The main focus of this review article is to highlight why and how monoclonal antibodies (mAbs) recognizing glycans, and in particular the glycans expressed on glycolipids, are being used in various strategies to target and kill cancer cells. The article reports on the historical use of mAbs and on very recent progress made in antitumor therapy using the anti-GD2 mAb and the antiganglioside mAbs, anti-N-glycolylneuraminic acid mAb and anti-Lewis mAb. Anti-GD2 is showing great promise in Phase III clinical trials in adjuvant treatment of neuroblastoma. Racotumomab, an anti-idiotypic mAb mimicking N-glycolylneuraminic acid-containing gangliosides, is currently being tested in a randomized, controlled Phase II/III clinical trial. This article also presents various strategies used by different groups to develop mAbs against these naturally poorly immunogenic glycans.

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.

Drug conjugates such as Antibody Drug Conjugates (ADCs), immunotoxins and immunoliposomes challenge daily clinical practice

Drug conjugates have been studied extensively in preclinical in vitro and in vivo models but to date only a few compounds have progressed to the clinical setting. This situation is now changing with the publication of studies demonstrating a significant impact on clinical practice and highlighting the potential of this new class of targeted therapies. This review summarizes the pharmacological and molecular background of the main drug conjugation systems, namely antibody drug conjugates (ADCs), immunotoxins and immunoliposomes. All these compounds combine the specific targeting moiety of an antibody or similar construct with the efficacy of a toxic drug. The aim of this strategy is to target tumor cells specifically while sparing normal tissue, thus resulting in high efficacy and low toxicity. Recently, several strategies have been investigated in phase I clinical trials and some have entered phase III clinical development. This review provides a detailed overview of various strategies and critically discusses the most relevant achievements. Examples of the most advanced compounds include T-DM1 and brentuximab vedotin. However, additional promising strategies such as immunotoxins and immunoliposmes are already in clinical development. In summary, targeted drug delivery by drug conjugates is a new emerging class of anti-cancer therapy that may play a major role in the future.

Designing immunoconjugates for cancer therapy

INTRODUCTION

Antibody-drug conjugates (ADCs), as well as antibody conjugates of protein toxins (immunotoxins) and cytokines (immunocytokines), are showing clinical efficacy, with manageable toxicities, in cancer treatment.

AREAS COVERED

The utility of an ADC is governed by the antibody and the target, as well as by the drug-linker component of the conjugate. The conjugation site, conjugating group, drug/antibody ratios and site-specific conjugation for product homogeneity are all aspects to consider in optimizing the ADC and enhancing its therapeutic window. Immunotoxin and immunocytokine construction by recombinant methods can be modulated to improve efficacy and reduce toxicity. The Dock-and-Lock (DNL) platform technology provides a flexible approach to assemble mono- or bispecific constructs carrying multiple toxin or cytokine molecules for targeted therapy.

EXPERT OPINION

Conjugation chemistry and recombinant technologies have had a significant impact on the therapeutic prospects of immunoconjugates, particularly in hematopoietic diseases. Continued concerted efforts from different scientific disciplines are needed, together with newer treatment paradigms, for greater progress in the more challenging therapy of solid tumors.

Profiling antibody drug conjugate positional isomers: a system-of-equations approach

Antibody drug conjugates enable the targeted delivery of potent chemotherapeutic agents directly to cancerous cells. They are made by the chemical conjugation of cytotoxins to monoclonal antibodies, which can be achieved by first reducing interchain disulfide bonds followed by conjugation of the resulting free thiols with drugs. This process yields a controlled, but heterogeneous, population of conjugated products that contains species with various numbers of drugs linked to different former interchain disulfide cysteine residues on the antibodies. We have developed a mathematical approach using inputs from capillary electrophoresis and hydrophobic interaction chromatography to determine the positional isomer distribution within a population of antibody drug conjugates. The results are confirmed by analyzing isolated samples of specific drug-to-antibody ratio species. The procedure is amenable to rapid determination of positional isomer distributions and features low material requirements. A survey of several antibody drug conjugates based on the same IgG framework and small molecule drug combination has shown a very similar distribution of isomers among all of the molecules using this technique, suggesting a robust conjugation process.

Antibody delivery of drugs and radionuclides: factors influencing clinical pharmacology

The therapeutic rationale of antibody conjugates is the selective delivery of a cytotoxin to tumor cells via binding and internalization of the monoclonal antibodies to a specific cell-surface antigen, thereby enhancing the therapeutic index of the cytotoxin. The key structural and functional components of an antibody conjugate are the antibody, the linker and the cytotoxin (chemical or radionuclide) with each component being critical for the successful development of the conjugate. Considerable efforts have been made in understanding the pharmacokinetics, pharmacodynamics, tissue distribution, metabolism and pharmacologic effects of these complex macromolecular entities. The purpose of this article is to discuss the properties and various structural components of antibody conjugates that influence their clinical pharmacology.

Ultrasmall sub-10 nm near-infrared fluorescent mesoporous silica nanoparticles

Ultrasmall sub-10 nm nanoprobes and carriers are of significant interest due to their favorable biodistribution characteristics in in vivo experiments. Here we describe the one-pot synthesis of PEGylated mesoporous silica nanoparticles with a single pore, tunable sizes around 9 nm and narrow size distributions that can be labeled with near-infrared dye Cy5.5. Particles are characterized by a combination of transmission electron microscopy, dynamic light scattering, fluorescence correlation spectroscopy, optical spectroscopy, nuclear magnetic resonance spectroscopy, and nitrogen sorption/desorption measurements. The possibility to distinguish an "inside" and "outside" may render these particles an interesting subject for further studies in sensing, drug delivery, and theranostics applications.

The discovery and development of brentuximab vedotin for use in relapsed Hodgkin lymphoma and systemic anaplastic large cell lymphoma

Progress has been made recently in developing antibody-drug conjugates (ADCs) that can selectively deliver cancer drugs to tumor cells. In principle, the idea is simple: by attaching drugs to tumor-seeking antibodies, target cells will be killed and nontarget cells will be spared. In practice, many parameters needed to be addressed to develop safe and effective ADCs, including the expression profiles of tumor versus normal tissues, the potency of the drug, the linker attaching the drug and placement of the drug on the antibody, and the pharmacokinetic and stability profiles of the resulting ADC. All these issues had been taken into account in developing brentuximab vedotin (Adcetris), an ADC that recently received accelerated approval by the US Food and Drug Administration for the treatment of relapsed Hodgkin lymphoma and systemic anaplastic large cell lymphoma (ALCL). Research is under way to extend the applications of brentuximab vedotin and to advance the field by developing other ADCs with new linker and conjugation strategies.

Immunology in the clinic review series; focus on cancer: glycolipids as targets for tumour immunotherapy

Research into aberrant glycosylation and over-expression of glycolipids on the surface of the majority of cancers, coupled with a knowledge of glycolipids as functional molecules involved in a number of cellular physiological pathways, has provided a novel area of targets for cancer immunotherapy. This has resulted in the development of a number of vaccines and monoclonal antibodies that are showing promising results in recent clinical trials.

A phase 1 trial of E7974 administered on day 1 of a 21-day cycle in patients with advanced solid tumors

BACKGROUND

E7974, a synthetic analog of hemiasterlin, interacts with the tubulin molecule and overcomes resistance to other antitubulin drugs (taxanes and vinca alkaloids).

METHODS

In a phase 1 study, E7974 was given intravenously over a 2- to 5-minute infusion on day 1 of every 21-day cycle. Adult patients with advanced refractory solid tumors who had adequate organ function and Eastern Cooperative Oncology Group performance status 0 to 2 were eligible for this study. A modified Fibonacci schema was used. The maximal tolerated dose (MTD) was the dose where <2 of 6 patients developed a dose-limiting toxicity (DLT).

RESULTS

Twenty-eight patients (19 men and 9 women; median age, 64 years) treated at different cohort dose levels (0.18 mg/m(2) , 0.27 mg/m(2) , 0.36 mg/m(2) , 0.45 mg/m(2) , and 0.56 mg/m(2) ) received a total of 66 courses of E7974. The MTD was established at 0.45 mg/m(2) , where 1 of 6 patients experienced DLT (grade 4 febrile neutropenia). Of the 17 refractory colon cancer patients with a median of 3 prior treatments, stable disease was seen in 7 patients (41%). There were no tumor responses. Median progression-free survival was 1.2 months, and median overall survival was 6.7 months. In pharmacokinetic analysis, E7974 was characterized by a fast and moderately large distribution (37.95-147.93 L), slow clearance (2.23-7.15 L/h), and moderate to slow elimination (time to half-life, 10.4-30.5 hours).

CONCLUSIONS

This study shows that E7974 once every 21-day cycle shows antitumor activity in patients with refractory solid tumors. The recommended phase 2 dose is 0.45 mg/m(2).

Theranostic applications of nanomaterials in cancer: drug delivery, image-guided therapy, and multifunctional platforms

Successful cancer management depends on accurate diagnostics along with specific treatment protocols. Current diagnostic techniques need to be improved to provide earlier detection capabilities, and traditional chemotherapy approaches to cancer treatment are limited by lack of specificity and systemic toxicity. This review highlights advances in nanotechnology that have allowed the development of multifunctional platforms for cancer detection, therapy, and monitoring. Nanomaterials can be used as MRI, optical imaging, and photoacoustic imaging contrast agents. When used as drug carriers, nanoformulations can increase tumor exposure to therapeutic agents and result in improved treatment effects by prolonging circulation times, protecting entrapped drugs from degradation, and enhancing tumor uptake through the enhanced permeability and retention effect as well as receptor-mediated endocytosis. Multiple therapeutic agents such as chemotherapy, antiangiogenic, or gene therapy agents can be simultaneously delivered by nanocarriers to tumor sites to enhance the effectiveness of therapy. Additionally, imaging and therapy agents can be co-delivered to provide seamless integration of diagnostics, therapy, and follow-up, and different therapeutic modalities such as chemotherapy and hyperthermia can be co-administered to take advantage of synergistic effects. Liposomes, metallic nanoparticles, polymeric nanoparticles, dendrimers, carbon nanotubes, and quantum dots are examples of nanoformulations that can be used as multifunctional platforms for cancer theranostics. Nanomedicine approaches in cancer have great potential for clinically translatable advances that can positively impact the overall diagnostic and therapeutic process and result in enhanced quality of life for cancer patients. However, a concerted scientific effort is still necessary to fully explore long-term risks, effects, and precautions for safe human use.

Antibody drug conjugates - Trojan horses in the war on cancer

Antibody drug conjugates (ADCs) consist of an antibody attached to a cytotoxic drug by means of a linker. ADCs provide a way to couple the specificity of a monoclonal antibody (mAb) to the cytotoxicity of a small-molecule drug and, therefore, are promising new therapies for cancer. ADCs are prodrugs that are inactive in circulation but exert their cytotoxicity upon binding to the target cancer cell. Earlier unsuccessful attempts to generate ADCs with therapeutic value have emphasized the important role each component plays in determining the efficacy and safety of the final ADC. Scientific advances in engineering antibodies for maximum efficacy as anticancer agents, identification of highly cytotoxic molecules, and generation of linkers with increased stability in circulation have all contributed to the development of the many ADCs that are currently in clinical trials. This review discusses parameters that guide the selection of the components of an ADC to increase its therapeutic window, provides a brief look at ADCs currently in clinical trials, and discusses future challenges in this field.

Nanotechnology and drug delivery: an update in oncology

The field of nanotechnology has exploded in recent years with diverse arrays of applications. Cancer therapeutics have recently seen benefit from nanotechnology with the approval of some early nanoscale drug delivery systems. A diversity of novel delivery systems are currently under investigation and an array of newly developed, customized particles have reached clinical application. Drug delivery systems have traditionally relied on passive targeting via increased vascular permeability of malignant tissue, known as the enhanced permeability and retention effect (EPR). More recently, there has been an increased use of active targeting by incorporating cell specific ligands such as monoclonal antibodies, lectins, and growth factor receptors. This customizable approach has raised the possibility of drug delivery systems capable of multiple, simultaneous functions, including applications in diagnostics, imaging, and therapy which is paving the way to improved early detection methods, more effective therapy, and better survivorship for cancer patients.

Challenges in developing bioanalytical assays for characterization of antibody–drug conjugates

With more than 34 targets being investigated and nearly 20 clinical trials at various phases of development, antibody–drug conjugates (ADCs) hold a lot of promise for improving oncological malignancy therapy. This therapeutic strategy designed to specifically or preferentially deliver a cytotoxic agent to tumor cells through conjugation to a monoclonal antibody is not new. Although this approach is relatively simple conceptually, the history of ADCs clearly attests to the high degree of complexity in their development. Each component of an ADC is important to achieve efficacy with minimal toxicity, and the ability to monitor this multicomponent therapeutic entity is deemed to be critical for their successful optimization. In this article we review the different bioanalytical strategies that have been implemented to characterize various ADCs and discuss the challenges and issues associated with these approaches.

Investigational antibody-drug conjugates for hematological malignancies

IMPORTANCE OF THE FIELD

Antibody-drug conjugates (ADCs) consist of potent cytotoxic drugs linked to antibodies via chemical linkers. ADCs facilitate the specific targeting of drugs to neoplastic cells. This technology is showing efficacy with manageable toxicity for the treatment of hematological malignancies.

AREAS COVERED IN THIS REVIEW

ADCs for the treatment of hematological malignancies are in pre-clinical and early clinical trials. This review describes these ADCs in detail and explores the challenges of optimizing the use of this technology.

WHAT THE READER WILL GAIN

The reader should understand that, although ADCs are conceptually simple, the application of this idea to practice has not been straightforward, and the challenges of developing ADCs include identifying targets with appropriate expression profiles and biology, developing successful linker chemistries, and the selection of a potent cytotoxic drug.

TAKE HOME MESSAGE

Hematological malignancies are particularly suited to the development of ADC therapeutics as their surface proteins are well characterized, and the consequences of expression of the target in the normal tissue like the bone marrow results in manageable toxicities since, in many cases, the normal tissue can regenerate. While this technology is complex, the ADCs for hematological malignancies currently in clinical use show great promise.

[Immunoconjugates, drug-armed antibodies to fight against cancer]

Monoclonal antibodies constitute a growing class of therapeutic agents. They are classically used in combination with chemotherapeutic drugs for cancer treatment. The concept of coupling a cytotoxic agent to an antibody can be viewed as a means to confer a selectivity for tumoral cells to highly cytotoxic drugs which cannot be used in human, or a higher power to antibodies which have a low anti-tumoral activity on their own. Gemtuzumab ozogamicin is the only drug-armed antibody available on the market, for the treatment of acute myeloid leukaemia. Other immunoconjugates are currently under clinical development. The most used cytotoxic agents derive from calicheamicin, maytansin and auristatin, compounds which are 100 to 1 000 fold more toxic than the classical chemotherapeutic drugs. Today, we know that the efficacy of an immunoconjugate depends not only on the coupled cytotoxic agent, but also on the selected target, the coupling method and the linker.

Localized doxorubicin chemotherapy with a biopolymeric nanocarrier improves survival and reduces toxicity in xenografts of human breast cancer

Patients with metastatic breast cancer have a five-year survival rate of 27% compared to 98% for localized cancer, and the presence of even a few cancer cells in lymph nodes, known as isolated tumor cells or nanometastases, significantly increases the risk of relapse in the absence of aggressive treatment. Therefore, diagnosis and treatment of lymphatic metastases in early breast cancer plays an important role in patient survival. Here, we demonstrate the first description of a delivery system for localized doxorubicin chemotherapy to the breast tissue. The hyaluronan-doxorubicin nanoconjugate exhibits a sustained release characteristic in vitro and in vivo in the breast tissues of rodents bearing human breast cancer xenografts. In addition, the conjugate reduces dose-limiting cardiac toxicity with minimal toxicity observed in normal tissues. Finally, the conjugate dramatically inhibits breast cancer progression in vivo, leading to an increased survival rate. Thus, localized chemotherapy to the breast lymphatics with a nanocarrier may represent an improved strategy for treatment of early stage breast cancers.

Co-expression of CD173 (H2) and CD174 (Lewis Y) with CD44 suggests that fucosylated histo-blood group antigens are markers of breast cancer-initiating cells

Histo-blood group antigens CD173 (H2) and CD174 (Lewis Y) are known to be developmentally regulated carbohydrate antigens which are expressed to a varying degree on many human carcinomas. We hypothesized that they might represent markers of cancer-initiating cells (or cancer stem cells, CSC). In order to test this hypothesis, we examined the co-expression of CD173 and CD174 with stem cell markers CD44 and CD133 by flow cytometry analysis, immunocytochemistry, and immunohistochemistry on cell lines and tissue sections from breast cancer. In three breast cancer cell lines, the percentage of CD173(+)/CD44(+) cells ranged from 17% to >60% and of CD174(+)/CD44(+) from 21% to 57%. In breast cancer tissue sections from 15 patients, up to 50% of tumor cells simultaneously expressed CD173, CD174, and CD44 antigens. Co-expression of CD173 and CD174 with CD133 was also observed, but to a lesser percentage. Co-immunoprecipitation and sandwich ELISA experiments on breast cancer cell lines suggested that CD173 and CD174 are carried on the CD44 molecule. The results show that in these tissues CD173 (H2) and CD174 (LeY) are associated with CD44 expression, suggesting that these carbohydrate antigens are markers of cancer-initiating cells or of early progenitors of breast carcinomas.

Synthesis and preliminary biological evaluation of high-drug-load paclitaxel-antibody conjugates for tumor-targeted chemotherapy

The goal of this study was to design paclitaxel (PTX)-monoclonal antibody (mAb) prodrug conjugates (PTXMAbs) with the ability to deliver therapeutically significant doses of the drug to the tumor while avoiding the previously observed solubility limitations of conjugates with PTX:mAb molar ratios of >3. New PTX conjugates were synthesized using the discrete poly(ethylene glycol) (dPEG) as linkers. These compounds, PTX-L-Lys[(dPEG12)(3)-dPEG4]-dPEG6-NHS (9a and 9b, for L = GL or SX, respectively), were then conjugated to the antiepidermal growth factor receptor mAb, C225 at increasing PTX:C225 ratios, producing completely soluble conjugates. Unlike the earlier PTXMAbs, buffered solutions of these conjugates remained homogeneous for extended periods of time. Fluorescence-activated cell sorting (FACS) analysis indicated preserved immunogenicity of the conjugates at all four substitution ratios, while cytotoxicity studies in MDA-MB-468 breast cancer cells indicated preservation of drug cytotoxicity. These conjugates may have potential in the development of high-drug-load tumor-targeting taxanes.

Targeted delivery of low molecular drugs using chitosan and its derivatives

Chitosan has prompted the continuous impetus for the development of safe and effective drug delivery systems because of its unique physicochemical and biological characteristics. The primary hydroxyl and amine groups located on the backbone of chitosan allow for chemical modification to control its physical properties. When the hydrophobic moiety is conjugated to a chitosan molecule, the resulting amphiphile may form self-assembled nanoparticles that can encapsulate a quantity of drugs and deliver them to a specific site of action. Chemical attachment of the drug to the chitosan throughout the functional linker may produce useful prodrugs, exhibiting the appropriate biological activity at the target site. Mucoadhesive and absorption enhancement properties of chitosan increase the in vivo residence time of the dosage form in the gastrointestinal tract and improve the bioavailability of various drugs. The main objective of this review is to provide an insight into various target-specific carriers, based on chitosan and its derivatives, towards low molecular weight drug delivery. The first part of the review is concerned with the organ-specific delivery of low molecular drugs using chitosan and its derivatives. The subsequent section considers the recent developments of drug delivery carriers for cancer therapy with special focus on various targeting strategies.

Molecular-targeted therapy for cancer and nanotechnology

In order to stop malignant tumor growth, >90% of a critical biochemical pathway needs to be blocked. Due to extraordinary advances in molecular biology, there is an increased understanding of rationale and relevant molecular targets in cancer. However, due to the heterogeneity of the molecular abnormalities in multiple tumor types, strategies designed to interfere with multiple molecular abnormalities will be necessary to impact survival. Nanoparticles have the potential to provide therapies not possible with other drug modalities. Researchers and clinicians must take advantage of these opportunities in order for nanotechnology to make an impact in the diagnosis and treatment of malignancy. A discussion of relevant targets either on the cell surface or the cytoplasm and strategies to achieve optimal drug targeting are the focus of this chapter.

Protein-based nanomedicine platforms for drug delivery

Protein-based nanomedicine platforms for drug delivery comprise naturally self-assembled protein subunits of the same protein or a combination of proteins making up a complete system. They are ideal for drug-delivery platforms due to their biocompatibility and biodegradability coupled with low toxicity. A variety of proteins have been used and characterized for drug-delivery systems, including the ferritin/apoferritin protein cage, plant-derived viral capsids, the small Heat shock protein (sHsp) cage, albumin, soy and whey protein, collagen, and gelatin. There are many different types and shapes that have been prepared to deliver drug molecules using protein-based platforms, including various protein cages, microspheres, nanoparticles, hydrogels, films, minirods, and minipellets. The protein cage is the most newly developed biomaterial for drug delivery and therapeutic applications. The uniform size, multifunctionality, and biodegradability push it to the frontier of drug delivery. In this Review, the recent strategic development of drug delivery is discussed with emphasis on polymer-based, especially protein-based, nanomedicine platforms for drug delivery. The advantages and disadvantages are also discussed for each type of protein-based drug-delivery system.

The Lewis-Y carbohydrate antigen is expressed by many human tumors and can serve as a target for genetically redirected T cells despite the presence of soluble antigen in serum

In this study we aimed to determine the suitability of the Lewis-Y carbohydrate antigen as a target for immunotherapy using genetically redirected T cells. Using the 3S193 monoclonal antibody and immunohistochemistry, Lewis-Y was found to be expressed on a range of tumors including 42% squamous cell lung carcinoma, 80% lung adenocarcinoma, 25% ovarian carcinoma, and 25% colorectal adenocarcinoma. Expression levels varied from low to intense on between 1% and 90% of tumor cells. Lewis- was also found in soluble form in sera from both normal donors and cancer patients using a newly developed enzyme-linked immunosorbent assay. Serum levels in patients was often less than 1 ng/mL, similar to normal donors, but approximately 30% of patients had soluble Lewis-Y levels exceeding 1 ng/mL and up to 9 ng/mL. Lewis-Y-specific human T cells were generated by genetic modification with a chimeric receptor encoding a single-chain humanized antibody linked to the T-cell signaling molecules, T-cell receptor-zeta, and CD28. T cells responded against the Lewis-Y antigen by cytokine secretion and cytolysis in response to tumor cells. Importantly, the T-cell response was not inhibited by patient serum containing soluble Lewis-Y. This study demonstrates that Lewis-Y is expressed on a large number of tumors and Lewis-Y-specific T cells can retain antitumor function in the presence of patient serum, indicating that this antigen is a suitable target for this form of therapy.

Potent antibody drug conjugates for cancer therapy

Significant progress has been made in the past few years in the area of antibody drug conjugates (ADCs) for the selective delivery of cytotoxic drugs to tumors. Early work in this field incorporated clinically approved drugs and mouse monoclonal antibodies (mAbs), which had modest activities, and were generally immunogenic. The results of these studies prompted investigation that led to the identity of several key parameters that influenced activity and tolerability. These included the antigen target, the use of non-immunogenic mAb carriers, the incorporation of highly potent drugs and novel conditionally stable linker technologies, and the specific methods used to attach drugs to mAbs. As a result of these investigations, new agents with pronounced clinical activities have been developed. These include SGN-35, an ADC directed against the CD30-positive malignancies such as Hodgkin's disease and anaplastic large cell lymphoma, and trastuzumab-DM1 which has shown activity in metastatic breast carcinoma. This review details many of the technological advancements, and provides examples of promising ADCs that are currently in clinical trials.

Use of antibodies and immunoconjugates for the therapy of more accessible cancers

There are currently 6 unconjugated antibodies and 3 immunoconjugates approved for use in the United States in a variety of cancers, with a considerable number of new agents in clinical testing and preclinical development. Unconjugated antibodies alone can be effective, but more often, antibodies need to be combined with chemotherapy, which enhances the efficacy of the standard treatment. Immunoconjugates tend to be more effective than their unconjugated counterparts, but their increased toxicity often restricts when and how they are used. In order to improve efficacy, a number of immunoconjugates are being examined in settings where the disease is more easily accessible, such as leukemias, or within compartments that allow easier and more direct access to the tumor, such as in the peritoneal cavity or brain, or both locally and systemically, in adjuvant situations, where the disease burden has been reduced by some other means, and with the main goal of these treatments being to kill residual disease.

Recombinant antibodies for cancer therapy

BACKGROUND

Recombinant antibodies have evolved into successful therapeutics with 10 approved for cancer and more in the pipeline. Four of the top ten cancer therapy drugs are recombinant antibodies.

OBJECTIVES

To survey the current state-of-the-art highlighting the reasons for this success and looking ahead to the next generation of antibody therapy.

METHODS

An analysis was carried out to identify preclinical and clinical examples and the underlying concepts and mechanisms that have shown how to design better therapies.

RESULTS/CONCLUSIONS

Greater understanding of the molecular basis of cancer has led to improved antibodies and a greater selection of targets. Fine tuning of successful antibodies through modification of glycosylation, affinity, size and other parameters are paying dividends. Fc-engineering is likely to be predominant in the near future but conjugates, fragments and fusion proteins will continue to be developed and find their place in the arsenal of antibody therapeutics.

Therapeutic nanoparticles for drug delivery in cancer

Cancer nanotherapeutics are rapidly progressing and are being implemented to solve several limitations of conventional drug delivery systems such as nonspecific biodistribution and targeting, lack of water solubility, poor oral bioavailability, and low therapeutic indices. To improve the biodistribution of cancer drugs, nanoparticles have been designed for optimal size and surface characteristics to increase their circulation time in the bloodstream. They are also able to carry their loaded active drugs to cancer cells by selectively using the unique pathophysiology of tumors, such as their enhanced permeability and retention effect and the tumor microenvironment. In addition to this passive targeting mechanism, active targeting strategies using ligands or antibodies directed against selected tumor targets amplify the specificity of these therapeutic nanoparticles. Drug resistance, another obstacle that impedes the efficacy of both molecularly targeted and conventional chemotherapeutic agents, might also be overcome, or at least reduced, using nanoparticles. Nanoparticles have the ability to accumulate in cells without being recognized by P-glycoprotein, one of the main mediators of multidrug resistance, resulting in the increased intracellular concentration of drugs. Multifunctional and multiplex nanoparticles are now being actively investigated and are on the horizon as the next generation of nanoparticles, facilitating personalized and tailored cancer treatment.

Phase I trial with the CD44v6-targeting immunoconjugate bivatuzumab mertansine in head and neck squamous cell carcinoma

CD44v6 is a tumor associated antigen abundantly expressed in head and neck squamous cell carcinomas (HNSCC) and in normal squamous epithelium. The immunoconjugate bivatuzumab mertansine (BIWI 1) consists of a highly potent antimicrotubule agent coupled to a monoclonal antibody against CD44v6. The maximum tolerated dose (MTD), safety and efficacy of BIWI 1 administered IV in patients with HNSCC has not been determined. In a clinical phase I trial, adult patients with recurrent or metastatic HNSCC were treated intravenously with BIWI 1. Starting with 25mg/m(2), the dose was escalated in steps of 25mg/m(2) until dose limiting toxicity was observed. Six women and 25 men were included. The MTD was 300 mg/m(2). Twelve patients were treated with at least the MTD. The principal toxic effects were maculopapular rashes, focal blister formation and skin exfoliation. Three patients had partial responses at doses of 200, 275 and 325 mg/m(2). The concept that bivatuzumab can direct mertansine activity to CD44v6 expressing tumors was confirmed. Although CD44v6 was abundantly expressed in all tumors, the response to BIWI 1 was variable. Binding to CD44v6 on skin keratinocytes mediated serious skin toxicity with a fatal outcome in a parallel trial, which led to the termination of the development program of bivatuzumab mertansine and the present study.

Targeted cancer therapy: conferring specificity to cytotoxic drugs

The therapeutic activity of most anticancer drugs in clinical use is limited by their general toxicity to proliferating cells, including some normal cells. Although, chemists continue to develop novel cytotoxic agents with unique mechanisms of action, many of these compounds still lack tumor selectivity and have not been therapeutically useful. Monoclonal antibodies that bind to specific markers on the surface of tumor cells offer an alternative therapy that is tumor specific and thus less toxic. Although highly selective, very few monoclonal antibodies are therapeutically useful since they only display modest cell killing activity. The linkage of monoclonal antibodies to highly cytotoxic drugs can be viewed as a means of (a) conferring higher tumor selectivity to cytotoxic drugs that are too toxic to be used on their own or (b) conferring cell killing power to monoclonal antibodies that are tumor-specific but not sufficiently cytotoxic. This Account provides a brief history of the development of antibody-drug conjugates and shows how the lessons learned from the first generation of conjugates has guided the development of more effective antitumor agents. The three components of antibody-drug conjugates, that is, the monoclonal anitbody, the cytotoxic drug, and the linker connecting the drug to the antibody, have been methodically studied and optimized. The antimitotic drug maytansine was chosen for use in the targeted delivery approach because of its high in vitro potency. Analogues of maytansine bearing a disulfide substituent that allowed linkage to monoclonal antibodies via disulfide bonds were prepared. These analogues retain the high potency of the parent drug. The stability of the disulfide link in antibody-maytansinoid conjugates was varied by introduction of methyl substituents on the carbon atoms geminal to the disulfide link. The optimized disulfide linker was stable in circulation in vivo. The circulation half-life of the cytotoxic drug was increased from just a few hours for the unconjugated drug to several days for the conjugate. Upon binding of the conjugate to the tumor cell, internalization and lysosomal processing released the potent cytotoxic agent inside the cell. These conjugates displayed high target-specific cytotoxicity in vitro. The antitumor activity of these targeted agents was superior to that of the antibodies alone or the standard anticancer drugs in human tumor xenograft models. Several conjugates from this new class of tumor-targeted anticancer agents are currrently undergoing clinical evaluation. The progress made in the targeted delivery approach and initial clinical results opens the door to the future development of highly potent drugs that were too toxic on their own to be therapeutically useful.

CD74: a new candidate target for the immunotherapy of B-cell neoplasms

CD74 is an integral membrane protein that functions as a MHC class II chaperone. Moreover, it has recently been shown to have a role as an accessory-signaling molecule and has been implicated in malignant B-cell proliferation and survival. These biological functions combined with expression of CD74 on malignant B cells and limited expression on normal tissues implicate CD74 as a potential therapeutic target. The anti-CD74 monoclonal antibody LL1 has been humanized (hLL1 milatuzumab or IMMU-115) and can provide the basis for novel therapeutic approaches to B-cell malignancies, particularly because this antibody shows rapid internalization into CD74+ malignant cells. This article reviews the preclinical evaluations of LL1, its humanized form, and isotope, drug, and toxin conjugates. These studies show that unconjugated hLL1 and conjugates of hLL1 constructs with radioisotopes, doxorubicin, and frog RNase have high antitumor activity in non-Hodgkin's lymphoma and multiple myeloma in vitro and in tumor xenograft models. Single-dose studies of hLL1 in monkeys showed no adverse effects but did decrease circulating B and T lymphocytes and natural killer cells. When evaluated in combination with rituximab, either equivalent or improved efficacy, compared with either antibody alone, was observed. CD74 is a new candidate target for the immunotherapy of neoplasms expressing this antigen, which can be exploited using either a naked antibody or conjugated to isotopes, drugs, or toxins.

Nanocarriers as an emerging platform for cancer therapy

Nanotechnology has the potential to revolutionize cancer diagnosis and therapy. Advances in protein engineering and materials science have contributed to novel nanoscale targeting approaches that may bring new hope to cancer patients. Several therapeutic nanocarriers have been approved for clinical use. However, to date, there are only a few clinically approved nanocarriers that incorporate molecules to selectively bind and target cancer cells. This review examines some of the approved formulations and discusses the challenges in translating basic research to the clinic. We detail the arsenal of nanocarriers and molecules available for selective tumour targeting, and emphasize the challenges in cancer treatment.

Targeting Lewis Y (Ley) in Small Cell Lung Cancer with a Humanized Monoclonal Antibody, hu3S193: A Pilot Trial Testing Two Dose Levels

INTRODUCTION

Lewis Y (Le(y)) is a blood group antigen with robust expression on the surface of epithelial tumors, including small cell lung cancer (SCLC), making it a potential target for antibody-based immunotherapy. 3S193, an immunoglobulin G3 monoclonal antibody, has demonstrated superior specificity, affinity, and cytotoxicity over other anti-Le(y) antibodies. A phase I trial of humanized 3S193 (hu3S193) with dosing up to 40 mg/m2 demonstrated tumor targeting without serious toxicities or the development of human anti-human antibodies.

METHODS

We tested the targeting and pharmacokinetics of hu3S193 in patients with SCLC. Eligibility required progressive SCLC treated with up to three previous chemotherapy regimens, measurable disease not previously irradiated, and tumor samples positive for 3S193 by immunohistochemistry. Patients received four weekly injections of hu3S193, five patients at 10 mg/m2 and five patients at 20 mg/m2. The first and fourth injections were radiolabeled with indium-111 for gamma camera imaging.

RESULTS

Of 40 patients screened, 25 of 34 (74%) assessable SCLC tumor samples were 3S193 positive by immunohistochemistry. Ten patients were treated with hu3S193; nine completed all four injections. All fluorodeoxyglucose (FDG)-avid lesions >2 cm were visualized on antibody single-photon emission computed tomography. Some lesions overlying vascular structures could not be visualized. No difference was noted in imaging or pharmacokinetics between the first and fourth injections. Toxicities included grade 2 urticaria (n = 1), grade 1 vomiting (n = 2), and grade 2 hypertension (n = 1) transiently after infusion at the higher dose.

CONCLUSIONS

Given the strong tumor targeting, particularly at the higher dose, the favorable toxicity profile, and the potential for immunomodulatory effects, hu3S193 warrants further investigation in SCLC.

A phase I biodistribution and pharmacokinetic trial of humanized monoclonal antibody Hu3s193 in patients with advanced epithelial cancers that express the Lewis-Y antigen

PURPOSE

We report a first-in-man trial of a humanized antibody (hu3S193) against the Le(y) antigen.

EXPERIMENTAL DESIGN

Patients with advanced Le(y)-positive cancers received four infusions of hu3S193 at weekly intervals, with four dose levels (5, 10, 20, and 40 mg/m(2)). The first infusion of hu3S193 was trace labeled with Indium-111, and biodistribution, pharmacokinetics, tumor uptake, and immune response were evaluated in all patients.

RESULTS

A total of 15 patients (7 male/8 female; age range, 42-76 years; 6 breast, 8 colorectal cancer, and 1 non-small-cell lung cancer) were entered into the study. Transient grade 1 to 2 nausea and vomiting was observed following infusion of hu3S193 at the 40 mg/m(2) dose level only. There was one episode of dose-limiting toxicity with self-limiting Common Toxicity Criteria grade 3 elevated alkaline phosphatase observed in one patient with extensive liver metastases. The biodistribution of (111)In-hu3S193 showed no evidence of any consistent normal tissue uptake, and (111)In-hu3S193 uptake was observed in cutaneous, lymph node, and hepatic metastases. Hu3S193 displayed a long serum half-life (T(1/2)beta = 189.63 +/- 62.17 h). Clinical responses consisted of 4 patients with stable disease and 11 patients with progressive disease, although one patient experienced a 89% decrease in a lymph node mass, and one patient experienced inflammatory symptoms in cutaneous metastases, suggestive of a biological effect of hu3S193. No immune responses (human anti-human antibody) to hu3S193 were observed.

CONCLUSION

Hu3S193 is well tolerated and selectively targets tumors, and the long half-life and biological function in vivo of this antibody makes it an attractive potential therapy for patients with Le(y)-expressing cancers.

Novel antibodies as anticancer agents

In recent years antibodies, whether generated by traditional hybridoma technology or by recombinant DNA strategies, have evolved from Paul Ehrlich's 'magic bullets' to a modern age 'guided missile'. In the recent years of immunologic research, we are witnessing development in the fields of antigen screening and protein engineering in order to create specific anticancer remedies. The developments in the field of recombinant DNA, protein engineering and cancer biology have let us gain insight into many cancer-related mechanisms. Moreover, novel techniques have facilitated tools allowing unique distinction between malignantly transformed cells, and regular ones. This understanding has paved the way for the rational design of a new age of pharmaceuticals: monoclonal antibodies and their fragments. Antibodies can select antigens on both a specific and a high-affinity account, and further implementation of these qualities is used to target cancer cells by specifically identifying exogenous antigens of cancer cell populations. The structure of the antibody provides plasticity resonating from its functional sites. This review will screen some of the many novel antibodies and antibody-based approaches that are being currently developed for clinical applications as the new generation of anticancer agents.

Folate Receptor–Specific Antitumor Activity of EC131, a Folate-Maytansinoid Conjugate

EC131, a new folate receptor (FR)-targeted drug conjugate, was prepared by covalently attaching the vitamin folic acid (FA) to a potent microtubule-inhibiting agent, maytansinoid DM1, via an intramolecular disulfide bond. When tested on cells in culture, EC131 was found to retain high affinity for FR-positive cells and to provide FR-specific cytotoxicity with an IC(50) in the low nanomolar range. The activity of EC131 was completely blocked in the presence of an excess of free FA, and no activity was detected against FR-negative cells. When evaluated against s.c. FR-positive M109 tumors in BALB/c mice, EC131 showed marked antitumor efficacy. Furthermore, this therapeutic effect occurred in the apparent absence of weight loss or noticeable organ tissue degeneration. In contrast, no significant antitumor activity was observed in EC131-treated animals that were codosed with an excess of FA, thus demonstrating the targeted specificity of the in vivo activity. EC131 also showed marked antitumor activity against FR-positive human KB tumors, but not against FR-negative A549 tumors, in nude mice with no evidence of systemic toxicity during or after the therapy. In contrast, therapy with the free maytansinoid drug (in the form of DM1-S-Me) proved not to be effective against the KB model when administered at its maximum tolerated dose (MTD). Taken together, these results indicate that EC131 is a highly potent agent capable of producing therapeutic benefit in murine tumor models at sub-MTD levels.

Anticancer carrier-linked prodrugs in clinical trials

Coupling of low molecular weight anticancer drugs to antibodies, serum proteins or polymers through a cleavable linker has been an effective method for improving the therapeutic index of cytotoxic established agents. Modern drug-antibody conjugates that have recently entered clinical trials have primarily used highly potent drugs such as calicheamicin or maytansins. Gemtuzumab ozogamicin, a conjugate of calicheamicin and an anti-CD33 humanized antibody, is the first drug-antibody conjugate to receive market approval. Drug conjugates that have undergone clinical assessment include N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer conjugates with doxorubicin, camptothecin, paclitaxel and Pt(II) complexes, poly(ethylene glycol) conjugates with camptothecin and paclitaxel, polyglutamate conjugates with paclitaxel and camptothecin, a methotrexate-albumin conjugate and an albumin-binding doxorubicin prodrug. This review summarizes the Phase I-III studies that have been performed with these macromolecular prodrugs.

Recombinant full-length human IgG1s targeting hormone-refractory prostate cancer

We have used a naive human single-chain fragment variable (scFv) library as a source of random shape repertoire to directly probe the altered surface chemistry of tumor cells. We reported previously the identification of more than 90 internalizing phage monoclonal antibodies targeting prostate cancer cells, including those that are hormone refractory. In this report, we describe the conversion of a panel of those scFvs into full-length human immunoglobulins (IgGs) and show that tumor specificity is retained. We have further shown that antibodies isolated from a naive phage display library can nevertheless be of high affinity towards target tumor cells. In addition, full-length IgGs retain the functionality of parental scFvs including the ability to rapidly enter target cells through receptor-mediated endocytosis and thereby to mediate efficient and specific intracellular payload delivery to tumor cells. We have used recombinant IgGs to immunoprecipitate target antigens and analyzed their molecular composition by mass spectrometry. We have identified one target antigen as activated leukocyte cell adhesion molecule (ALCAM)/MEMD/CD166 and have further studied tissue specificity of this internalizing ALCAM epitope by immunohistochemistry. Our study shows that cell type-specific internalizing human antibody can be readily identified from a naive phage antibody display library, characterized with regards to sequence, affinity, tissue specificity, and antigen identity, and modified genetically and chemically to generate various forms of targeted therapeutics.

DOXO-EMCH (INNO-206): the first albumin-binding prodrug of doxorubicin to enter clinical trials

The (6-maleimidocaproyl)hydrazone derivative of doxorubicin (DOXO-EMCH) is an albumin-binding prodrug of doxorubicin with acid-sensitive properties that demonstrates superior antitumor efficacy in murine tumor models and a favorable toxicity profile in mice, rats and dogs, including significantly reduced cardiotoxicity. After intravenous administration, DOXO-EMCH binds rapidly to the Cys-34 position of circulating albumin and accumulates in solid tumors due to passive targeting. In a clinical Phase I study, the dose of doxorubicin could be increased by a factor of 4.5-340 mg/m(2) when 75 mg/m(2) of free doxorubicin is considered to be the dose that can be administered as a single agent concomitant with the typical spectrum of side effects (i.e., myelotoxicity and mucositis). DOXO-EMCH was able to induce tumor regressions in anthracycline-sensitive tumors (i.e., breast cancer, small cell lung cancer and sarcoma). Phase II studies will be initiated at the beginning of 2007.

Technology Insight: cytotoxic drug immunoconjugates for cancer therapy

The successful introduction of genetically engineered human and chimeric immunoglobulin proteins has established monoclonal antibodies (mAbs) as a validated approach for treating malignancies. The unique properties of mAb therapies including their high affinity and specificity, and the differential expression of target antigen in tumor cells versus normal cells make them attractive agents for cancer immunotherapy. The field of immunoconjugate development attempts to combine the specificity of mAb therapies with cytotoxic and radionuclide molecules, thereby combining the best characteristics of these two different modalities. Two radiolabeled mAbs, (90)Y-ibritumomab tiuxetan and (131)I-tositumomab, and one drug conjugate, gemtuzumab ozogamicin have been approved for the treatment of malignancies. Other conjugates carrying toxic payloads of calicheamicin, geldanamycin, maytansinoids and taxoids as well as peptide exotoxins are undergoing preclinical and clinical development. Nevertheless, several obstacles have limited robust antitumor activity and broad application of imunoconjugates, including the optimization of three structural components of the immunoconjugate (i.e. mAb and target specificity, chemical linker design, and the cytotoxin), as well as issues common to mAb therapy such as heterogeneous antigen expression, which can limit uniform antibody delivery. This Review examines optimal design, the lessons learned from clinical immunoconjugate development, and the promising agents in early preclinical/clinical development for the treatment of cancer.

Combined flow cytometry and confocal laser scanning microscopy for evaluation of BR96 antibody cancer cell targeting and internalization

BACKGROUND

Monoclonal antibodies (mAb) are important tools in the management of tumor disease, and the discovery of antibodies with both specific cancer cell targeting and capacity to enter the cells by internalization are critical to improve the therapeutic efficacy.

METHOD

Antibody cancer cell targeting and internalization properties of fluoroscein-conjugated mAb made against Lewis Y (BR96) were evaluated quantitatively and qualitatively by means of flow cytometry (FCM) and confocal laser scanning microscopy (CLSM), respectively, on cells from a rat tumor cell line (BN7005-H1D2).

RESULTS

The study demonstrated a specific binding of BR96 to LewisY (LeY) located in the cell membrane and as BR96/LeY immunocomplexes (BR96/LeY) internalized into the cytoplasm. BR96/LeY was internalized into about 15% of the cells, usually distributed throughout the cytoplasm, but also located close to the nuclei. Cytotoxic effects by BR96 were indicated, and CLSM visualized subpopulations containing cells with bound or internalized BR96/LeY that possessed morphologically pyknotic nuclei and disrupted DNA.

CONCLUSION

The spatial-temporal pattern by BR96 cell targeting and internalization processes of BR96/LeY into the cancer cells expressing LeY was demonstrated by FCM and CLSM. Used together, the FCM and CLSM techniques provide a valuable tool for preclinical analyses of antibody targeting and their capacities as carriers of cytotoxic conjugates for the use in cancer therapy.

Doxorubicin-Conjugated Anti-Midkine Monoclonal Antibody as a Potential Anti-Tumor Drug

BACKGROUND

Midkine is a heparin-binding growth factor preferentially expressed in tumor cells. The present study was performed to utilize anti-midkine antibody for tumor therapy.

METHODS

A monoclonal antibody to midkine was raised by immunizing mice deficient in the midkine gene. The binding site of the antibody was studied by using N-terminal half and C-terminal half of midkine, both of which were chemically synthesized. Doxorubicin (DOX)-conjugate of the antibody was produced by chemical conjugation. The effects of the antibody and the conjugate on cell growth were examined using a midkine-secreting tumor cell, i.e. human hepatocellular carcinoma cell (HepG2).

RESULTS

The monoclonal antibody bound to the N-terminal half of midkine. The antibody did not inhibit the growth of HepG2 cells probably because the active domain of midkine is in the C-terminal half. We produced the antibody conjugated with DOX with the hope that the conjugate would be internalized accompanied with midkine. Indeed, the antibody-DOX conjugate significantly inhibited the growth of HepG2 cells compared with DOX-conjugated control IgG.

CONCLUSION

The result raises the possibility of using anti-midkine antibody conjugated with DOX for cancer therapy.

Folate receptor specific anti-tumor activity of folate–mitomycin conjugates

PURPOSE

Folate receptor (FR) targeted drug conjugates were prepared by covalently attaching the vitamin folate, to the potent anticancer drug, mitomycin C (MMC). One such conjugate, called EC72, was synthesized with an intramolecular disulfide bond, and it was found to exhibit efficacious anti-tumor activity against FR-expressing M109 tumors in a manner that yielded no gross or microscopic toxicity, even to FR-positive kidneys.

METHODS

EC72's specificity was demonstrated by two methods: (1) blocking EC72's activity with an excess of co-administered folic acid (FA) in M109 tumor bearing mice and (2) the absence of therapeutic activity in mice bearing FR-negative tumors. The importance of having a cleavable bond in the conjugate was also exemplified, since EC110 (a folate-MMC conjugate constructed with a more resilient amide bond) failed to produce anti-M109 tumor activity. EC72's therapeutic potential was found to decrease with respect to the increasing size of subcutaneous tumor. However, a combination therapy with paclitaxel reproducibly improved the anti-tumor efficacy relative to either agent alone at well tolerated dose levels and with no apparent increase in toxicity. A more advanced folate-MMC conjugate was also synthesized in an effort to improve activity. Thus, EC118, a molecule constructed with both a reducible disulfide bond and an acid-labile hydrazone bond in the linker region, was tested and found to produce a significantly greater number of tumor regressions of more established M109 tumors than that achieved with EC72.

CONCLUSION

Overall, these data indicate that folate-targeted drug therapy alone, or in combination with paclitaxel, may be a novel and effective clinical approach towards treating FR-positive cancers.