Construction and characterization of the chimeric monoclonal antibody E48 for therapy of head and neck cancer

CD44v6-Targeted Imaging of Head and Neck Squamous Cell Carcinoma: Antibody-Based Approaches

Head and neck squamous cell carcinoma (HNSCC) is a common and severe cancer with low survival rate in advanced stages. Noninvasive imaging of prognostic and therapeutic biomarkers could provide valuable information for planning and monitoring of the different therapy options. Thus, there is a major interest in development of new tracers towards cancer-specific molecular targets to improve diagnostic imaging and treatment. CD44v6, an oncogenic variant of the cell surface molecule CD44, is a promising molecular target since it exhibits a unique expression pattern in HNSCC and is associated with drug- and radio-resistance. In this review we summarize results from preclinical and clinical investigations of radiolabeled anti-CD44v6 antibody-based tracers: full-length antibodies, Fab, F(ab′)₂ fragments, and scFvs with particular focus on the engineering of various antibody formats and choice of radiolabel for the use as molecular imaging agents in HNSCC. We conclude that the current evidence points to CD44v6 imaging being a promising approach for providing more specific and sensitive diagnostic tools, leading to customized treatment decisions and functional diagnosis. Improved imaging tools hold promise to enable more effective treatment for head and neck cancer patients.

Choice of labeling and cell line influences interactions between the Fab fragment AbD15179 and its target antigen CD44v6

Medical imaging by use of immunotargeting generally relies on a labeled molecule binding to a specific target on the cell surface. It is important to utilize both cell-based and time-resolved binding assays in order to understand the properties of such molecular interactions in a relevant setting. In this report we describe the detailed characterization of the interaction properties for AbD15179, a promising CD44v6-targeting antibody fragment for radio-immunotargeting. Influence of labeling and cell-line model on the protein interaction kinetics was assessed using three different labeling approaches ((111)In, (125)I and FITC) on three different squamous carcinoma cell lines. Interactions were measured using time-resolved assays on living cells, and further analyzed with Interaction Map®. Results demonstrated a general biphasic appearance of a high- and a low-affinity binding event in all cases. The relative contribution from these two interactions differed between conjugates. For (125)I-Fab, the population of low-affinity binders could be significantly increased by extending the chloramine T exposure during labeling, whereas the (111)In-labeling predominantly resulted in a high-affinity interaction. Interactions were also shown to be cell line dependent, with e.g. SCC-25 cells generally mediating a faster dissociation of conjugates compared to the other cell lines. In conclusion, we report both cell line dependent and labeling associated variations in interaction kinetics for AbD15179 binding to CD44v6. This has implications for cell-based kinetic assays and applications based on labeled conjugates in general, as well as in a clinical setting, where each individual tumor may create different kinetic profiles for the same conjugate.

Selection and in vitro characterization of human CD44v6-binding antibody fragments

The cluster of differentiation (CD) 44v6 antigen has been suggested to be involved in tumor formation, invasion, and metastasis formation, and has been observed in a majority of primary and metastatic squamous cell carcinomas of the head and neck. Probes specifically binding to this region may be utilized as tools for the challenging tasks of early detection and targeted treatments of small residual disease. In this project, an epitope-guided phage display selection of human fragment antigen-binding (Fab) fragments with affinity to the v6 sequence was performed. A selected set of Fab fragments was shown to specifically recognize increasingly complex forms of the target sequence, both in the form of a short synthetic or recombinant peptide and in the context of a purified extracellular domain of CD44. The binding was independent of known v6-sequence variation and posttranslational modifications that are common in the CD44 protein family. Furthermore, real-time interaction measurements on antibody fragments labeled with ¹²⁵I showed specific and high-affinity binding to the antigen present on cultured head and neck squamous cell carcinoma cells. There was no cross-reactivity toward cells that lack the target protein. As hypothesized, characterization of the interaction between Fab fragments and the targets using the mathematical tool Interaction Map revealed more heterogeneous interactions on cells than with pure proteins analyzed by surface plasmon resonance. One main candidate Fab fragment with optimal affinity for all forms of the target sequence was identified. The flexible recombinant source of the Fab fragments might aid the development of tailored molecules adapted for therapeutic or diagnostic applications in the future.

Targeted radionuclide therapy in head and neck cancer

There is great potential for targeted radionuclide therapy (TRT) in the treatment of head and neck cancer. In recent years, developments in fields such as antigen screening, protein engineering, and cancer biology have facilitated the rational design of targeted pharmaceuticals, with monoclonal antibodies forming the most rapidly expanding category. TRT may be a promising way to improve targeted treatment, especially in head and neck cancer, because of the intrinsic radiosensitivity of this tumor type. TRT may also provide a good foundation on which to build rational biologic combination therapies. In the next few years the use of TRT may offer new opportunities for further improvement of the therapeutic ratio that potentially may obviate or reduce the need for conventional cytotoxics.

Characterization of 111In and 177Lu-labeled antibodies binding to CD44v6 using a novel automated radioimmunoassay

Targeted cancer therapies rely on bifunctional molecules, typically a protein that specifically recognizes tumor cells and a toxic component which is linked to the protein. Therefore, development of such therapies includes detailed characterizations of protein-cell interactions in order to find a good targeting agent. Knowledge of factors such as antibody-antigen specificity, as well as cellular uptake, retention and affinity of the antibody are necessary in order to be successful. In this paper, we have used a novel instrument, LigandTracer Yellow, to characterize the interactions of (111)In and (177)Lu-labeled monoclonal antibodies (MAbs) with CD44v6. Uptake studies with varying specific radioactivity of the chimeric MAb U36 and with an irrelevant antibody for the CD44v6 receptor verified the reliability of the method, as well as the specificity of the antibody-receptor binding. Uptake, retention, and affinity were very similar for the (111)In and (177)Lu-labeled conjugate, and were in line with earlier studies using manual methods. The fact that no adverse effects from labeling were seen, together with the high retention, could make these conjugates promising candidates for imaging and therapy of certain cancer types in the future. The novel LigandTracer technology reduced the workload and reagent spending while providing data with superior time resolution. The obtained results were in agreement with previously reported findings. In addition the real-time detection and higher time resolution made more detailed studies of the interactions possible.

Anticancer therapeutics: targeting macromolecules and nanocarriers to hyaluronan or CD44, a hyaluronan receptor

The complex system involved in the synthesis, degradation and binding of the high molecular weight glycosaminoglycan hyaluronic acid (hyaluronan or HA) provides a variety of structures that can be exploited for targeted cancer therapy. In many cancers of epithelial origin there is an upregulation of CD44, a receptor that binds HA. In other cancers, HA in the tumor matrix is overexpressed. Both CD44 on cancer cells and HA in the matrix have been targets for anticancer therapy. Even though CD44 is expressed in normal epithelial cells and HA is part of the matrix of normal tissues, selective targeting to cancer is possible. This is because macromolecular carriers predominantly extravasate into the tumor and not normal tissue; thus CD44-HA targeted carriers administered intravenously localize preferentially into tumors. Anti-CD44 antibodies have been used in patients to deliver radioisotopes or mertansine for treatment of CD44 expressing tumors. In early phase clinical trials, patients with breast or head and neck tumors treated with anti-CD44 conjugates experienced stabilized disease. A dose-limiting toxicity was associated with distribution of the antibody-drug conjugate to the skin, a site in the body with a high level of CD44. HA has been used as a drug carrier and a ligand on liposomes or nanoparticles to target drugs to CD44 overexpressing cells. Drugs can be attached to HA via the carboxylate on the glucuronic acid residue, the hydroxyl on the N-acetylglucosamine or the reducing end which are located on a repeating disaccharide. Drugs delivered in HA-modified liposomes exhibited excellent antitumor activity both in vitro and in murine tumor models. The HA matrix is also a potential target for anticancer therapies. By manipulating the interaction of HA with cell surface receptors, either by degrading it with hyaluronidase or by interfering with CD44-HA interactions using soluble CD44 proteins, tumor progression was blocked. Finally, cytotoxic drugs or prodrug converting enzymes can be attached to the HA matrix to generate a cytotoxic fence around the tumor. This review describes how the complex interplay among cancer biology, the CD44-HA interaction, drug carriers and drug targeting has been used to improve anticancer therapies. As these approaches evolve, they hold forth the prospect of significantly improved targeted anticancer treatments.

[177Lu]pertuzumab: experimental therapy of HER-2-expressing xenografts

Pertuzumab (Omnitarg) is a novel antibody against HER-2, domain II. HER-2 is a tyrosine kinase receptor that is overexpressed in several carcinomas, especially breast cancer. Pertuzumab, labeled with the low-energy beta emitter (177)Lu, might be a candidate for targeted radiotherapy of disseminated HER-2-positive micrometastases. The radiolabeled antibody [(177)Lu]pertuzumab showed favorable targeting properties in BALB/c (nu/nu) mice with HER-2-overexpressing xenografts. The absorbed dose in tumors was more than five times higher than the absorbed dose in blood and more than seven times the absorbed dose in any other normal organ. Experimental therapy showed that [(177)Lu]pertuzumab delayed tumor progression compared with controls (no treatment, P < 0.0001; nonlabeled pertuzumab antibody, P < 0.0001; and (177)Lu-labeled irrelevant antibody, P < 0.01). No adverse side effects of the treatment could be detected. Thus, the experimental results support the planning of clinical studies applying [(177)Lu]pertuzumab for therapy.

In vitro evaluation of the astatinated chimeric monoclonal antibody U36, a potential candidate for treatment of head and neck squamous cell carcinoma

PURPOSE

The purpose of this study was to analyse the properties of the astatinated chimeric MAb (cMAb) U36 as a conjugate to selectively target and eradicate head and neck squamous cell carcinoma (HNSCC).

METHODS

cMAb U36 was labelled with 211At via the linker N-succinimidyl 4-(trimethylstannyl)benzoate (SPMB). The quality of the conjugate was extensively evaluated for binding and internalisation capacity, and compared with 125I-SPMB-cMAb U36. The cellular toxicity of the astatinated conjugate was assessed in two types of in vitro growth assay and compared with 131I-labelled cMAb U36 (directly labelled).

RESULTS

Comparisons between 211At-cMAb U36 and 125I-cMAb U36 demonstrated an optimal functional capacity of the labelled products. Immunoreactivity and affinity assays showed high immunoreactive fractions (>93%), and an affinity in good agreement between the astatinated and iodinated antibodies. For both conjugates, specific binding to HNSCC cells could be demonstrated, as well as some internalisation. Retention of the astatinated conjugate was just slightly lower than for the iodinated conjugate and still reasonable for therapeutic use (31+/-2% vs 42.6+/-1.0% at 22 h), demonstrating no adverse effects from astatination of the antibody. Studies on cellular toxicity demonstrated a dose-dependent and antigen-specific cellular toxicity for 211At-cMAb U36, with about 10% cell survival at 50 decays per cell. The 131I-labelled conjugate was not as efficient, with a surviving cell fraction of about 50% at 55 decays per cell.

CONCLUSION

These results indicate that 211At-cMAb U36 might be a promising future candidate for eradicating HNSCC micrometastases in vivo.

Plattenepithelkarzinome des Kopf-Hals-Bereichs

Biologic therapies able to induce or up-regulate anti-tumor immune responses could represent a complementary approach to improve the conventional treatment of squamous cell carcinomas of the head and neck (SCCHN). Patients with SCCHN are frequently immunocompromised due to the elimination and dysfunction of critical immune effector cells. Therefore, it might be necessary to restore these immune functions to allow for the generation of effective anti-tumor host responses. Simultaneously, to prevent tumor escape from immunological recognition and destruction, it might also be necessary to alter antigenic and immunogenic attributes of the malignant cells. The present overview summarizes general aspects, historical data, and recent advances in the field of immunotherapy of SCCHN, including non-specific immune stimulation, transfer of immunocompetent cells, gene therapy, use of monoclonal antibodies, and anti-cancer vaccines.

Targeting the immune system: novel therapeutic approaches in squamous cell carcinoma of the head and neck

Despite advances in surgery, radiotherapy, and chemotherapy, the overall survival rates for patients with squamous cell carcinoma of the head and neck (SCCHN) have not changed over the last decades. Clearly, novel therapeutic strategies are needed for this cancer, which is highly immunosuppressive. Therefore, biologic therapies able to induce and/or up-regulate antitumor immune responses could represent a complementary approach to conventional treatments. Because patients with SCCHN are frequently immunocompromised due to the elimination or dysfunction of critical effector cells of the immune system, it might be necessary to restore these immune functions to allow for the generation of more effective antitumor host responses. Simultaneously, to prevent tumor escape, it might be necessary to alter attributes of the malignant cells. The present review summarizes recent advances in the field of immunotherapy of SCCHN, including techniques of nonspecific immune stimulation, the use of monoclonal antibodies, advances in adoptive immunotherapy and genetic engineering, as well as anticancer vaccines. These biologic therapies, alone or in combination with conventional treatment, are likely to develop into useful future treatment options for patients with SCCHN.

CD44v6: a target for antibody-based cancer therapy

The human CD44 gene encodes type 1 transmembrane glycoproteins involved in cell-cell and cell-matrix interactions. The structural heterogeneity of the gene products is caused primarily by alternative splicing of at least 10 out of 20 exons. Certain CD44 variant isoforms, in particular those containing CD44 variant domain 6 (CD44v6), have been implicated in tumourigenesis, tumour cell invasion and metastasis. Here we will give an overview of immunohistochemically determined CD44v6 expression in human malignancies (primary epithelial and nonepithelial tumours as well as metastases) and normal tissues, and review several examples of the clinical use of CD44v6-specific antibodies. In nonmalignant tissues, CD44v6 expression is essentially restricted to a subset of epithelia. Intense and homogeneous expression of CD44v6 was reported for the majority of squamous cell carcinomas and a proportion of adenocarcinomas of differing origin, but was rarely seen in nonepithelial tumours. This expression pattern has made CD44v6 an attractive target for antibody-guided therapy of various types of epithelium-derived cancers.

Selection of monoclonal antibody E48 IgG or U36 IgG for adjuvant radioimmunotherapy in head and neck cancer patients

Preliminary data from recent clinical radioimmunoscintigraphy studies indicate that 99mTc-labelled murine monoclonal antibodies (MAbs) E48 and U36 have a similar ability to target squamous cell carcinoma of the head and neck (HNSCC) selectively. In the present study we describe additional aspects of murine and chimeric MAb (mMAb and cMAb) E48 and U36, which might influence the selection of one MAb for adjuvant radioimmunotherapy. To make direct comparison possible, ten patients received 11.2 +/- 0.3 and 11.1 +/- 0.2 mg (n = 5) or 51.1 +/- 0.1 and 51.0 +/- 0.4 mg (n = 5) of both mE48 IgG and mU36 IgG labelled with 131I and 125I simultaneously and underwent surgery 7-8 days after injection. The mean uptake of iodine-labelled mE48 IgG and mU36 was highest in tumour tissue, 8.9 +/- 8.9 and 8.2 +/- 4.4 %ID kg(-1) respectively. Tumour to non-tumour ratios for oral mucosa, skin, muscle, blood and bone marrow aspirate were 2.5, 5.5, 25.2, 4.7 and 4.0 respectively in the case of mE48 IgG and 2.3, 4.1, 21.0, 5.8 and 5.8 respectively in the case of mU36 IgG. The distribution of mMAbs E48 and U36 throughout tumours that had been collected in previous studies was heterogeneous when administered at a dose of 1 or 12 mg, and homogeneous when administered at a dose of 52 mg. Administration of mE48 IgG (1-52 mg) resulted in a human anti-mouse antibody response in 12 out of 28 patients, while for mU36 IgG (1-52 mg), this figure was three out of 18 patients. cMAb E48 was shown to be highly effective in mediating antibody-dependent cellular cytotoxicity in vitro, while cMAb U36 and mMAbs E48 and U36 were not effective at all. Rationales are provided that give priority to the start of adjuvant radioimmunotherapy trials with 186Re-labelled cMAb U36 IgG in head and neck cancer patients who are at high risk for the development of locoregional recurrences and distant metastases.

Detection of MET oncogene/hepatocyte growth factor receptor in lymph node metastases from head and neck squamous cell carcinomas

The c-MET oncogene encodes the receptor for hepatocyte growth factor/scatter factor (HGF/SF), which is known to stimulate the invasive growth of epithelial cells cultured in vitro. The Met/HGF receptor is a heterodimeric transmembrane tyrosine kinase, which is a prototype for a new family of growth factor receptors. The c-MET oncogene is expressed in several types of epithelial tissue including keratinocytes and is over-expressed in a number of human carcinomas. Studies on various carcinoma cell lines have shown that over-expression and structural alteration of the receptor result in its activation and confer tumorigenesis. We have studied Met/HGF receptor expression in tissue specimens from 34 patients with head and neck squamous cell carcinomas (HNSCC) and in 17 regional lymph node metastases. Western blot analysis was employed, using monoclonal antibodies directed against either the intracellular or extracellular domain of the receptor. Each sample was compared to its normal counterpart. The receptor did not show any major structural alterations in HNSCC tissues, but its expression was increased from 2- to 50-fold in about 70% of tumors. Immunohistochemistry then showed that the same antibodies stained only a few cells in the basal layer of normal squamous epithelium but intensely marked tumor cells. In the lymph node metastases of Met-positive tumors, receptor expression was maintained and sometimes increased with respect to primary tumors. Immunohistochemical analysis of the metastatic lymph nodes showed that cells were negative in the normal lymphatic tissue and strongly stained in tumor cells. Over-expression of the Met/HGF receptor was found at all tumor stages but was more significant in those associated with enlarged or multiple (N2-N3) lymph node metastases. These data show that expression of the Met/HGF receptor may be involved in the progression of HNSCC towards a metastatic phenotype and may be a useful marker of head and neck tumor cell spread to regional lymph nodes.