Using antibodies to target cancer therapeutics

Viro-antibody therapy: engineering oncolytic viruses for genetic delivery of diverse antibody-based biotherapeutics

Cancer therapeutics approved for clinical application include oncolytic viruses and antibodies, which evolved by nature, but were improved by molecular engineering. Both facilitate outstanding tumor selectivity and pleiotropic activities, but also face challenges, such as tumor heterogeneity and limited tumor penetration. An innovative strategy to address these challenges combines both agents in a single, multitasking therapeutic, i.e., an oncolytic virus engineered to express therapeutic antibodies. Such viro-antibody therapies genetically deliver antibodies to tumors from amplified virus genomes, thereby complementing viral oncolysis with antibody-defined therapeutic action. Here, we review the strategies of viro-antibody therapy that have been pursued exploiting diverse virus platforms, antibody formats, and antibody-mediated modes of action. We provide a comprehensive overview of reported antibody-encoding oncolytic viruses and highlight the achievements of 13 years of viro-antibody research. It has been shown that functional therapeutic antibodies of different formats can be expressed in and released from cancer cells infected with different oncolytic viruses. Virus-encoded antibodies have implemented direct tumor cell killing, anti-angiogenesis, or activation of adaptive immune responses to kill tumor cells, tumor stroma cells or inhibitory immune cells. Importantly, numerous reports have shown therapeutic activity complementary to viral oncolysis for these modalities. Also, challenges for future research have been revealed. Established engineering technologies for both oncolytic viruses and antibodies will enable researchers to address these challenges, facilitating the development of effective viro-antibody therapeutics.

New insights into the pretargeting approach to image and treat tumours

Tumour pretargeting is a promising strategy for cancer diagnosis and therapy allowing for the rational use of long circulating, highly specific monoclonal antibodies (mAbs) for both non-invasive cancer radioimmunodetection (RID) and radioimmunotherapy (RIT). In contrast to conventional RID/RIT where the radionuclides and oncotropic vector molecules are delivered as presynthesised radioimmunoconjugates, the pretargeting approach is a multistep procedure that temporarily separates targeting of certain tumour-associated antigens from delivery of diagnostic or therapeutic radionuclides. In principle, unlabelled, highly tumour antigen specific mAb conjugates are, in a first step, administered into a patient. After injection, sufficient time is allowed for blood circulation, accumulation at the tumour site and subsequent elimination of excess mAb conjugates from the body. The small fast-clearing radiolabelled effector molecules with a complementary functionality directed to the prelocalised mAb conjugates are then administered in a second step. Due to its fast pharmacokinetics, the small effector molecules reach the malignant tissue quickly and bind the local mAb conjugates. Thereby, corresponding radioimmunoconjugates are formed in vivo and, consequently, radiation doses are deposited mainly locally. This procedure results in a much higher tumour/non-tumour (T/NT) ratio and is favourable for cancer diagnosis and therapy as it substantially minimises the radiation damage to non-tumour cells of healthy tissues. The pretargeting approach utilises specific non-covalent interactions (e.g. strept(avidin)/biotin) or covalent bond formations (e.g. inverse electron demand Diels-Alder reaction) between the tumour bound antibody and radiolabelled small molecules. This tutorial review descriptively presents this complex strategy, addresses the historical as well as recent preclinical and clinical advances and discusses the advantages and disadvantages of different available variations.

Synthesis of hydrophilic HYNIC-[1,2,4,5]tetrazine conjugates and their use in antibody pretargeting with99mTc

Pretargeted imaging is shown to be an attractive strategy to overcome disadvantages associated with traditional radioimmunoconjugates.

In vivo demonstration of an active tumor pretargeting approach with peptide nucleic acid bioconjugates as complementary system

A novel, promising strategy for cancer diagnosis and therapy is the use of a pretargeting approach. For this purpose, the non-natural DNA/RNA analogues Peptide Nucleic Acids (PNAs) are ideal candidates as in vivo recognition units due to their high metabolic stability and lack of unspecific accumulation. In the pretargeting approach, an unlabeled, highly specific antibody-PNA conjugate has sufficient time to target a tumor before administration of a small fast-clearing radiolabeled complementary PNA that hybridizes with the antibody-PNA conjugate at the tumor site. Herein, we report the first successful application of this multistep process using a PNA-modified epidermal growth factor receptor (EGFR) specific antibody (cetuximab) and a complementary 99mTc-labeled PNA. In vivo studies on tumor bearing mice demonstrated a rapid and efficient in vivo hybridization of the radiolabeled PNA with the antibody-PNA conjugate. Decisively, a high specific tumor accumulation was observed with a tumor-to-muscle ratio of >8, resulting in a clear visualization of the tumor by single photon emission computed tomography (SPECT).

Recruitment of Oligoclonal Viral-Specific T cells to Kill Human Tumor Cells Using Single-Chain Antibody-Peptide-HLA Fusion Molecules

Tumor progression is often associated with the development of diverse immune escape mechanisms. One of the main tumor escape mechanism is HLA loss, in which human solid tumors exhibit alterations in HLA expression. Moreover, tumors that present immunogenic peptides via class I MHC molecules are not susceptible to CTL-mediated lysis, because of the relatively low potency of the tumor-specific CLTs. Here, we present a novel cancer immunotherapy approach that overcomes these problems by using the high affinity and specificity of antitumor antibodies to recruit potent antiviral memory CTLs to attack tumor cells. We constructed a recombinant molecule by genetic fusion of a cytomegalovirus (CMV)-derived peptide pp65 (NLVPMVATV) to scHLA-A2 molecules that were genetically fused to a single-chain Fv Ab fragment specific for the tumor cell surface antigen mesothelin. This fully covalent fusion molecule was expressed in E. coli as inclusion bodies and refolded in vitro. The fusion molecules could specifically bind mesothelin-expressing cells and mediate their lysis by NLVPMVATV-specific HLA-A2-restricted human CTLs. More importantly, these molecules exhibited very potent antitumor activity in vivo in a nude mouse model bearing preestablished human tumor xenografts that were adoptively transferred along with human memory CTLs. These results represent a novel and powerful approach to immunotherapy for solid tumors, as demonstrated by the ability of the CMV-scHLA-A2-SS1(scFv) fusion molecule to mediate specific and efficient recruitment of CMV-specific CTLs to kill tumor cells.

EGFR-expression in primary urinary bladder cancer and corresponding metastases and the relation to HER2-expression. On the possibility to target these receptors with radionuclides

Background

There is limited effect of tyrosine kinase inhibitors or “naked” antibodies binding EGFR or HER2 for therapy of metastasized urinary bladder cancer and these methods are therefore not routinely used. Targeting radio-nuclides to the extracellular domain of the receptors is potentially a better possibility.

Methods

EGFR- and HER2-expression was analyzed for primary tumors and corresponding metastases from 72 patients using immunohistochemistry and the internationally recommended HercepTest. Intracellular mutations were not analyzed since only the receptors were considered as targets and intracellular abnormalities should have minor effect on radiation dose.

Results

EGFR was positive in 71% of the primary tumors and 69% of corresponding metastases. Local and distant metastases were EGFR-positive in 75% and 66% of the cases, respectively. The expression frequency of HER2 in related lesions was slightly higher (data from previous study). The EGFR-positive tumors expressed EGFR in metastases in 86% of the cases. The co-expression of EGFR and HER2 was 57% for tumors and 53% for metastases. Only 3% and 10% of the lesions were negative for both receptors in tumors and metastases, respectively. Thus, targeting these receptors with radionuclides might be applied for most patients.

Conclusions

At least one of the EGFR- or HER2-receptors was present in most cases and co-expressed in more than half the cases. It is therefore interesting to deliver radionuclides for whole-body receptor-analysis, dosimetry and therapy. This can hopefully compensate for resistance to other therapies and more patients can hopefully be treated with curative instead of palliative intention.

Pretargeted imaging and radioimmunotherapy of cancer using antibodies and bioorthogonal chemistry

Selective delivery of radionuclides to tumors may be accomplished using a two-step approach, in which in the first step the tumor is pretargeted with an unlabeled antibody construct and in the second step the tumor is targeted with a radiolabeled small molecule. This results in a more rapid clearance of the radioactivity from normal tissues due to the fast pharmacokinetics of the small molecule as compared to antibodies. In the last decade, several pretargeting approaches have been tested, which have shown improved tumor-to-background ratios and thus improved imaging and therapy as compared to directly labeled antibodies. In this review, we will discuss the strategies and applications in (pre-)clinical studies of pretargeting concepts based on the use of bispecific antibodies, which are capable of binding to both a target antigen and a radiolabeled peptide. So far, three generations of the bispecific antibody-based pretargeting approach have been studied. The first clinical studies have shown the feasibility and potential for these pretargeting systems to detect and treat tumor lesions. However, to fully integrate the pretargeting approach in clinic, further research should focus on the best regime and pretargeting protocol. Additionally, recent developments in the use of bioorthogonal chemistry for pretargeting of tumors suggest that this chemical pretargeting approach is an attractive alternative strategy for the detection and treatment of tumor lesions.

The immune system and head and neck squamous cell carcinoma: from carcinogenesis to new therapeutic opportunities

Head and neck squamous cell carcinomas (HNSCCs) exhibit complex interactions with the host immune system that may simultaneously explain resistance to various therapeutic modalities and that may also provide opportunities for therapeutic intervention. Discoveries in immunologic research over the last decade have led to an increased understanding of these interactions as well as the development of a multitude of investigational immunotherapies. Here, we describe the interaction between HNSCC and the immune system, including a discussion of immune cells involved with tumor carcinogenesis and the role of immune-modulating factors derived from tumors. We also describe the current immunotherapeutic approaches being investigated for HNSCC, including a discussion of the successes and limitations. With this review, we hope to present HNSCC as a model to guide future research in cancer immunology.

Multifunctional polymeric micelles for delivery of drugs and siRNA

Polymeric micelles, self-assembling nano-constructs of amphiphilic copolymers with a core-shell structure have been used as versatile carriers for delivery of drugs as well as nucleic acids. They have gained immense popularity owing to a host of favorable properties including their capacity to effectively solubilize a variety of poorly soluble pharmaceutical agents, biocompatibility, longevity, high stability in vitro and in vivo and the ability to accumulate in pathological areas with compromised vasculature. Moreover, additional functions can be imparted to these micelles by engineering their surface with various ligands and cell-penetrating moieties to allow for specific targeting and intracellular accumulation, respectively, to load them with contrast agents to confer imaging capabilities, and incorporating stimuli-sensitive groups that allow drug release in response to small changes in the environment. Recently, there has been an increasing trend toward designing polymeric micelles which integrate a number of the above functions into a single carrier to give rise to “smart,” multifunctional polymeric micelles. Such multifunctional micelles can be envisaged as key to improving the efficacy of current treatments which have seen a steady increase not only in hydrophobic small molecules, but also in biologics including therapeutic genes, antibodies and small interfering RNA (siRNA). The purpose of this review is to highlight recent advances in the development of multifunctional polymeric micelles specifically for delivery of drugs and siRNA. In spite of the tremendous potential of siRNA, its translation into clinics has been a significant challenge because of physiological barriers to its effective delivery and the lack of safe, effective and clinically suitable vehicles. To that end, we also discuss the potential and suitability of multifunctional polymeric micelles, including lipid-based micelles, as promising vehicles for both siRNA and drugs.

HER2 expression in primary gastric cancers and paired synchronous lymph node and liver metastases. A possible road to target HER2 with radionuclides

Resistance has been reported to human epidermal growth factor receptor 2 (HER2)-targeted therapy with the tyrosine kinase inhibitor lapatinib and the antibody trastuzumab in metastatic gastric cancer. An alternative or complement might be to target the extracellular domain of HER2 with therapy-effective radionuclides. The fraction of patients with HER2 expression in primary tumors and major metastatic sites, e.g., lymph nodes and liver, was analyzed to evaluate the potential for such therapy. Samples from primary tumors and lymph node and liver metastases were taken from each patient within a few hours, and to our knowledge, such sampling is unique. The number of analyzed cases was therefore limited, since patients that had received preoperative radiotherapy, chemotherapy, or HER2-targeted therapy were excluded. From a large number of considered patients, only 29 could be included for HER2 analysis. Intracellular mutations were not analyzed since they are assumed to have no or minor effect on the extracellular binding of molecules that deliver radionuclides. HER2 was positive in nearly 52 % of the primary tumors, and these expressed HER2 in corresponding lymph node and liver metastases in 93 and 100 % of the cases, respectively. Similar values for primary tumors and also good concordance with metastases have been indicated in the literature. Thus, relevant radionuclides and targeting molecules for nuclear medicine-based noninvasive, whole-body receptor analysis, dose planning, and therapy can be applied for many patients; see "Discussion" Hopefully, more patients can then be treated with curative instead of palliative intention.

Enhancing immunotherapy using chemotherapy and radiation to modify the tumor microenvironment

The tumor microenvironment is a complex assortment of cells that includes a variety of leukocytes. The overall effect of the microenvironment is to support the growth of tumors and suppress immune responses. Immunotherapy is a highly promising form of cancer treatment, but its efficacy can be severely compromised by an immunosuppressive tumor microenvironment. Chemotherapy and radiation treatment can mediate tumor reduction through cytotoxic effects, but it is becoming increasingly clear that these forms of treatment can be used to modify the tumor microenvironment to liberate tumor antigens and decrease immunosuppression. Chemotherapy and radiotherapy can be used to modulate the tumor microenvironment to enhance immunotherapy.

The promise of the anti-idiotype concept

A basic tenet of antibody-based immunity is their specificity to antigenic determinates from foreign pathogen products to abnormal cellular components such as in cancer. However, an antibody has the potential to bind to more than one determinate, be it an antigen or another antibody. These observations led to the idiotype network theory (INT) to explain immune regulation, which has wax and waned in enthusiasm over the years. A truer measure of the impact of the INT is in terms of the ideas that now form the mainstay of immunological research and whose roots are spawned from the promise of the anti-idiotype concept. Among the applications of the INT is understanding the structural implications of the antibody-mediated network that has the potential for innovation in terms of rational design of reagents with biological, chemical, and pharmaceutical applications that underlies concepts of reverse immunology which is highlighted herein.