Use of bispecific antibodies in the therapy of tumors

Targeting EGFR and HER-2 receptor tyrosine kinases for cancer drug discovery and development

Conventional anticancer therapy using cytotoxic drugs lacks selectivity and is prone to toxicity and drug resistance. Anticancer therapies targeting aberrant growth factor receptor signaling are gaining interest. The erbB receptor family belongs to the type I, the receptor tyrosine kinases class, and comprises EGFR, HER-2, HER-3, and HER-4. It has been targeted for solid tumor therapy, including breast, ovarian, colon, head-and-neck, and non-small-cell lung cancers. This review summarizes structural aspects of this class of growth factor receptors, their oncogenic expression, and various pharmacological interventions including biological products and small molecules that inhibit these enzymes. We have also discussed various mutations that occur in EGFR and their consequences on anticancer therapy.

Inhibitors of epidermal-growth-factor receptors: a review of clinical research with a focus on non-small-cell lung cancer

Despite aggressive surgical and chemotherapeutic interventions, non-small-cell lung cancer (NSCLC) is the leading cause of cancer-related death in men and women with overall cure rates of less than 15%. Recent advances in our understanding of cellular signalling and its critical role in tumorigenesis has led to the development of novel therapies which may offer new hope. In particular, the epidermal growth-factor receptor superfamily is an attractive therapeutic target because it is commonly overexpressed in malignant disease, regulates many vital cellular processes, and seems to be a negative prognostic indicator. Several selective inhibitors of this family of receptors are currently being evaluated in several cancers including NSCLC. In this review we examine current preclinical and clinical evidence on monoclonal antibodies (cetuximab, ABX-EGF, EMD72000, MAb ICR62, h-R3, MDX-447, MDX-H210, trastuzumab, and 2C4), immunoconjugates (Y10, Ua30:2, Mab806), anti-EGF vaccine (YMB2000), and tyrosine kinase inhibitors (gefitinib, erlotinib, CI1033, GW572016, EKB 569, PKI166, PD158780, and TAK 165).

An efficient route to the production of an IgG-like bispecific antibody

Production of IgG-form bispecific antibody (BsAb-IgG) by co-expressing two antibodies in transfected cells is often inefficient owing to the unwanted pairing between the component heavy and light chains. We have developed an efficient method for the production of a novel IgG-like BsAb by using the natural dimerization mechanism between IgG heavy and light chains. Two single-chain Fv (scFv) of different specificity are fused to the constant domain of human kappa chain (C(L)) and the first constant domain of human heavy chain (C(H1)), to form two polypeptides, (scFv)(1)-C(L) and (scFv)(2)-C(H1)-C(H2)-C(H3), respectively. Co-expression of the two polypeptides in mammalian cells results in the formation of a covalently linked IgG-like hetero-tetramer, Bs(scFv)(4)-IgG, with dual specificity. Our approach yields a homogeneous bispecific IgG-like antibody product with each molecule containing four antigen binding sites, two for each of its target antigens. A Bs(scFv)(4)-IgG was prepared using two scFv antibodies each directed against a different epitope of a vascular endothelial growth factor receptor, the kinase insert domain-containing receptor (KDR). The Bs(scFv)(4)-IgG is capable of simultaneously binding to the two epitopes on the receptor. Further, the Bs(scFv)(4)-IgG also retains the antigen-binding efficacy and biological activity of its component antibodies.

Acquired antagonistic activity of a bispecific diabody directed against two different epitopes on vascular endothelial growth factor receptor 2

Bispecific antibody (BsAb) technology has been successfully used as a means to construct novel antibody (Ab) molecules with increased avidity for binding, by combining two Ab or their fragments directed against different epitopes within the same antigen. Using two single chain antibodies (scFv) isolated from a phage display library, we have constructed a bispecific diabody directed against two different epitopes on the extracellular domain (ECD) of human vascular endothelial growth factor receptor 2 (VEGFR2), the kinase-insert domain-containing receptor (KDR). Neither of the parent scFv blocks KDR/VEGF interactions or inhibits VEGF-induced receptor activation. The diabody binds to KDR with an affinity that is 1.5- to 3-fold higher than its parent scFv, mainly due to a much slower dissociation rate (k(off)), which is approximately 17- to 26-fold slower than that of the individual scFv. In addition, the diabody binds simultaneously to, and thus cross-links, the two epitopes on the receptor(s). It is rather unexpected that the diabody effectively blocked KDR/VEGF interactions, and inhibited both VEGF-induced activation of the receptor and mitogenesis of human endothelial cells. Taken together, our results suggest that the diabody is most likely to exert its effect through steric hindrance and/or causing major conformational changes of the receptor. This is the first report on the construction of a bispecific diabody with acquired novel antagonistic activity.

A Bispecific Diabody That Mediates Natural Killer Cell Cytotoxicity Against Xenotransplantated Human Hodgkin’s Tumors

CD16/CD30 bispecific monoclonal antibodies can induce remissions of Hodgkin’s disease refractory to chemo- and radiotherapy. However, the development of human antimouse immunoglobulin antibodies and allergic reactions precludes repeated applications of the antibody. Moreover, problems of producing and purifying sufficient amounts of material limit the clinical practicability of this novel treatment approach. To overcome these obstacles, we have constructed a bispecific antibody in a diabody form that only employs the variable domains of the CD16/CD30 hybrid hybridoma. The diabody compared favorably with the parent CD16/CD30 bispecific antibody in its ability to activate and target natural killer cells in vitro. Its administration to mice bearing xenografted Hodgkin’s lymphoma resulted in a marked regression of tumor growth, thus proving for the first time the capability of a diabody for immune recruitment in vivo. The CD16/CD30 diabody is a novel reagent that should considerably facilitate the immunotherapy of patients with refractory Hodgkin’s lymphoma.

Bispecific agents target endogenous murine T cells against human tumor xenografts

A variety of immunological approaches to cancer treatment are currently being explored. These include strategies designed to enhance or redirect the activity of T cells against tumors. Bispecific antibodies comprise a class of agents capable of redirecting T cells by binding to a tumor antigen and the T-cell receptor (TCR). In vivo pre-clinical testing of bispecific antibodies against human tumors has to date been limited to the use of immunodeficient mice that receive the bispecific agent, activated human effector T cells, and human tumor cells. In this report, we show that TCR transgenic/RAG-1 knockout mice (TCR/RAG) serve as a unique model allowing endogenous T cells to be redirected against transplanted human tumors. The findings show that TCR/RAG mice (i) accepted transplants of human tumors, including the folate-receptor-positive tumor line KB; (ii) contained endogenous cytotoxic T lymphocytes that could be activated in vivo with an antigenic peptide recognized by the transgenic TCR; (iii) rejected human tumors after treatment with the activating peptide and bispecific agents that contained folic acid co-valently linked to an anti-TCR antibody. Successful rejection was achieved with folate conjugates of Fab or scFv fragments. Treatment with activating agents and bispecific conjugates resulted in the complete eradication of freshly transplanted tumors as well as significantly prolonging the survival of mice bearing established solid tumors. Our results highlight the importance of including T-cell-activating modalities in combination with bispecific antibodies. Additionally, we introduce a system that allows endogenous T cells to be redirected against human tumor xenografts and in which the T cells may be followed in vivo by use of a clonotypic marker.

Antibody dependent cellular phagocytosis (ADCP) and antibody dependent cellular cytotoxicity (ADCC) of breast cancer cells mediated by bispecific antibody, MDX-210

BACKGROUND

MDX-210 is a bispecific antibody (BsAb) with specificity for both the proto-oncogene product of HER-2/neu (c-erbB-2) and FcgammaRI (CD64). HER-2/neu is overexpressed in malignant tissue of approximately 30% of patients with breast cancer, and FcgammaRI is expressed on human monocytes, macrophages, and IFN-gamma activated granulocytes. We investigated phagocytosis and cytolysis of cultured human breast cancer cells by human monocyte-derived macrophages (MDM) mediated by BsAb MDX-210, its partially humanized derivative (MDX-H210), and its parent MoAb 520C9 (anti-HER-2/neu) under various conditions.

MATERIALS AND METHODS

Purified monocytes were cultured with GM-CSF, M-CSF, or no cytokine for five or six days. Antibody dependent cellular phagocytosis (ADCP) and cytolysis (ADCC) assays were performed with the MDM and HER-2/neu positive target cells (SK-BR-3). ADCP was measured by two-color fluorescence flow cytometry using PKH2 (green fluorescent dye) and phycoerythrin-conjugated (red) monoclonal antibodies (MoAb) against human CD14 and CD11b. ADCC was measured with a non-radioactive LDH detection kit.

RESULTS

Both BsAb MDX-210 (via FcgammaRI) and MoAb 520C9 (mouse IgG1, via FcgammaRII) mediated similar levels of ADCP and ADCC. ADCP mediated by BsAb MDX-H210 was identical to that mediated by BsAb MDX-210. Confocal microscopy demonstrated that dual-labeled cells represented true phagocytosis. Both ADCP and ADCC were higher when MDM were pre-incubated with GM-CSF than when incubated with M-CSF.

CONCLUSIONS

BsAb MDX-210 is as active in vitro as the parent MoAb 520C9 in inducing both phagocytosis and cytolysis of MDM. MDX-210 and its partially humanized derivative, MDX-H210, mediated similar levels of ADCP. GM-CSF appears to superior to M-CSF in inducing MDM-mediated ADCC and ADCP. These studies support the ongoing clinical investigations of BsAb MDX-210 and its partially humanized derivative.

High level secretion of a humanized bispecific diabody from Escherichia coli

Clinical development of bispecific antibodies (BsAb) has been effectively stymied by the lack of efficient production methods. We therefore attempted to produce a humanized BsAb fragment using an expression system that has proved very successful for secretion of monospecific Ab fragments from E. coli. An anti-p185HER2/anti-CD3 BsF(ab')2 was first recast into the diabody format and then periplasmically secreted from E. coli grown to high cell density in a fermentor. The diabody was recovered in very high yield (up to 935 mg/l) after protein A purification and predominantly (> or = 80%) as a dimer as judged by size exclusion chromatography. Diabody dimers were found to be mainly functional heterodimers (approximately 75%) by titration with p185HER2 extracellular domain. The diabody binds p185HER2 extracellular domain and human T lymphocytes with affinities close to those of the parent BsF(ab')2. Furthermore, the diabody is capable of simultaneous binding to tumor cells overexpressing p185HER2 and CD3 on T cells as shown by cellular rosetting. The diabody is equally potent as the parent BsF(ab')2 in retargeting IL-2 activated T-enriched peripheral blood lymphocytes to lyse tumor cells overexpressing p185HER2.

Bispecific monoclonal antibodies for intravenous treatment of carcinoma patients: immunobiologic aspects

Immunobiologic parameters measured during a phase I trial of intravenously (i.v.) administered bispecific monoclonal antibodies (BsmAb) in renal cell carcinoma (RCC) patients are described. The BsmAb used, BIS-1, is reactive with a pancarcinoma-associated 38 kDa transmembrane glycoprotein, EGP-2, as well with the CD3 complex. Patients received during a 2 h i.v. infusion F(ab')2 fragments of BIS-1 at doses of 1, 3, or 5 micrograms/kg body weight during concomitantly applied subcutaneous (s.c.) IL-2 treatment. Acute but transient BIS-1 F(ab')2-related toxicity was observed at the 3 and 5 micrograms/kg dose level, and the maximum tolerated dose (MTD) was set at 5 micrograms/kg. A dose-dependent binding of BIS-1 F(ab')2 to circulating T lymphocytes was found. The in vivo occupancy of CD3 molecules on T lymphocytes was highest at teh end of the infusion period and then rapidly decreased, as shown by flow cytometry. A much slower decrease of BIS-1 F(ab')2 binding was observed in vitro, suggesting migration of BIS-1 F(ab')2-loaded T lymphocytes from the circulation. A strong but transitory leukopenia was observed, in which LFA-1 alpha bright, CD3/CD8 double positive T cells left the circulation preferentially. This phenomenon was most likely induced by elevated TNF-alpha and IFN-gamma plasma levels, which were at a maximum shortly after the end of the infusion. Isolated peripheral blood mononuclear cells obtained from patients directly after treatment with BIS-1 F(ab')2 at the 3 and 5 micrograms/kg dose level showed increased EGP-2-directed antitumor activity.

Bispecific antibodies as targeting agents for boron neutron capture therapy of brain tumors

Boron neutron capture therapy (BNCT) is based on the nuclear reaction that occurs when boron-10, a stable isotope, is irradiated with low energy (< or = 0.025 eV) or thermal neutrons to yield alpha particles and recoiling lithium-7 nuclei. A major requirement for the success of BNCT is the selective delivery of a sufficient number of boron atoms (approximately 10(9)) to individual cancer cells to sustain a lethal 10B (n, alpha) 7Li capture reaction. A panel of BsAb reactive with polyhedral borane anions (PBA) and a tumor-associated chondroitin sulfate proteoglycan has been produced. All of these BsAb showed strong reactivity with a panel of human glioblastoma and melanoma cell lines, as demonstrated by indirect membrane immunofluorescence. Two of them (H6 and B8) also reacted with cells that had been exposed to PBA (Na2B10H10 and Na2B12H11SH) and a boronated starburst dendrimer, which contained approximately 250-400 B atoms per molecule. The affinity constant (Ka) of BsAb-B8 was 2.57 x 10(8) M-1 on M21 human melanoma cell and 3.49 x 10(8) M-1 on A172 glioblastoma cells, which were almost identical to those of the parental monoclonal antibody (mAb) 9.2.27 on the same cell lines (2.62 x 10(8) M-1). Since our BsAb recognize both human glioblastoma and melanoma-associated antigens, as well as PBA, they potentially could be used to target 10B to these tumors for BNCT.