Anti‑HER3 monoclonal antibody exerts antitumor activity in a mouse model of colorectal adenocarcinoma

Development of a Sensitive Anti-Mouse CD39 Monoclonal Antibody (C39Mab-1) for Flow Cytometry and Western Blot Analyses

CD39 is involved in adenosine metabolism by converting extracellular ATP to adenosine. As extracellular adenosine plays a critical role in the immune suppression of the tumor microenvironment, the inhibition of CD39 activity by monoclonal antibodies (mAbs) is one of the important strategies for tumor therapy. This study developed specific and sensitive mAbs for mouse CD39 (mCD39) using the Cell-Based Immunization and Screening method. The established anti-mCD39 mAb, C39Mab-1 (rat IgG2a, kappa), reacted with mCD39-overexpressed Chinese hamster ovary-K1 (CHO/mCD39) by flow cytometry. The kinetic analysis using flow cytometry indicated that the dissociation constant of C39Mab-1 for CHO/mCD39 was 7.3 × 10-9 M. Furthermore, C39Mab-1 detected the lysate of CHO/mCD39 by western blot analysis. These results indicated that C39Mab-1 is useful for the detection of mCD39 in many functional studies.

A Rat Anti-Mouse CD39 Monoclonal Antibody for Flow Cytometry

By converting extracellular adenosine triphosphate to adenosine, CD39 is involved in adenosine metabolism. The extracellular adenosine plays a critical role in the immune suppression of the tumor microenvironment. Therefore, the inhibition of CD39 activity by monoclonal antibodies (mAbs) is thought to be one of the important strategies for tumor therapy. In this study, we developed novel mAbs for mouse CD39 (mCD39) using the Cell-Based Immunization and Screening (CBIS) method. One of the established anti-mCD39 mAbs, C39Mab-2 (rat IgG2a, lambda), reacted with mCD39-overexpressed Chinese hamster ovary-K1 (CHO/mCD39) and an endogenously mCD39-expressed cell line (SN36) by flow cytometry. The kinetic analysis using flow cytometry indicated that the dissociation constant (KD) values of C39Mab-2 for CHO/mCD39 and SN36 were 5.5 × 10-9 M and 4.9 × 10-9 M, respectively. These results indicated that C39Mab-2 is useful for the detection of mCD39 in flow cytometry.

HER-3 surface expression increases in advanced colorectal cancer representing a potential therapeutic target

HER-3 (also known as ErbB-3) is a human epidermal growth factor receptor tyrosine kinases family member, and its expression in CRC (colorectal cancer) tissues was previously associated with poor prognosis. In this study, HER-3 expression was analyzed by immunohistochemistry in two cohorts of early and advanced metastatic CRC patients. The first cohort included 180 patients diagnosed with CRC in absence of lymph nodes or distant metastases (Stage I and Stage II), while the second was obtained from 53 advanced metastatic CRC patients who developed synchronous (SM) and metachronous (MM) liver metastases. In the first early-stage CRC cohort, 86 out of 180 (47.8%) tumors showed membranous expression of HER-3, with a mean percentage of positive tumor cells of 25.7%; conversely, in advanced metastatic CRC primary tumors, HER-3 was detected in all specimens, with a mean percentage of positive tumor cells of 76.1%. Kaplan-Meier curves showed that in the advanced metastatic CRC group, patients with HER-3high tumors had a significantly lower Cancer-Specific Survival (CSS) rate compared to patients with HER-3low tumors (p = 0.021). Importantly, this worse CSS rate was observed only in the MM subgroup of patients with HER-3high tumors (p = 0.002). Multivariate analysis confirmed that high HER-3 expression represents a significant and strong risk factor for death in patients developing MM liver metastases (Hazard Ratio = 64.9; 95% Confidence Interval, 4.7-886.6; p = 0.002). In addition, using a specific anti-HER-3 antibody-drug conjugate, named EV20/MMAF, we showed that HER-3 + CRC cells can be efficiently targeted in vitro and in vivo. Overall, this study confirms that surface HER-3 is highly expressed in CRC and reveals that HER-3 expression increases in metastatic CRC patients compared to early stage. Importantly, the results suggest that HER-3 has a prognostic and therapeutic value in patients developing MM liver metastases.

EMab-300 Detects Mouse Epidermal Growth Factor Receptor-Expressing Cancer Cell Lines in Flow Cytometry

Epidermal Growth Factor Receptor (EGFR) overexpression or its mutation mediates the sustaining proliferative signaling, which is an important hallmark of cancer. Human EGFR-targeting monoclonal antibody (mAb) therapy such as cetuximab has been approved for clinical use in patients with colorectal cancers and head and neck squamous cell carcinomas. A reliable preclinical mouse model is essential to further develop the mAb therapy against EGFR. Therefore, sensitive mAbs against mouse EGFR (mEGFR) should be established. In this study, we developed a specific and sensitive mAb for mEGFR using the Cell-Based Immunization and Screening (CBIS) method. The established anti-mEGFR mAb, EMab-300 (rat IgG₁, kappa), reacted with mEGFR-overexpressed Chinese hamster ovary-K1 (CHO/mEGFR) and endogenously mEGFR-expressed cell lines, including NMuMG (a mouse mammary gland epithelial cell) and Lewis lung carcinoma cells, using flow cytometry. The kinetic analysis using flow cytometry indicated that the K_D of EMab-300 for CHO/mEGFR and NMuMG was 4.3 × 10^-8 M and 1.9 × 10^-8 M, respectively. These results indicated that EMab-300 applies to the detection of mEGFR using flow cytometry and may be useful to obtain the proof of concept in preclinical studies.

Development of a Novel Anti-Mouse CCR6 Monoclonal Antibody (C6Mab-13) by N-Terminal Peptide Immunization

The CC chemokine receptor 6 (CCR6) is a G protein-coupled receptor family member that is highly expressed in B lymphocytes, certain subsets of effector and memory T cells, and immature dendritic cells. CCR6 has only one chemokine ligand, CCL20. The CCL20-CCR6 axis has been recognized as a therapeutic target for autoimmune diseases and tumor. This study developed specific monoclonal antibodies (mAbs) against mouse CCR6 (mCCR6) using the peptide immunization method. The established anti-mCCR6 mAb, C₆Mab-13 (rat IgG₁, kappa), reacted with mCCR6-overexpressed Chinese hamster ovary-K1 (CHO/mCCR6), and mCCR6-endogenously expressed P388 (mouse lymphoid neoplasma) and J774-1 (mouse macrophage-like) cells in flow cytometry. The dissociation constant (K_D) of C₆Mab-13 for CHO/mCCR6 cells was determined to be 2.8 × 10^-9 M, indicating that C₆Mab-13 binds to mCCR6 with high affinity. In summary, C₆Mab-13 is useful for detecting mCCR6-expressing cells through flow cytometry.

Development of a Sensitive Anti-Human CCR9 Monoclonal Antibody (C9Mab-11) by N-Terminal Peptide Immunization

The C-C chemokine receptor 9 (CCR9) belongs to the G-protein-coupled receptor superfamily, and is highly expressed on the T cells and intestinal cells. CCR9 regulates various immune responses by binding to the C-C chemokine ligand, CCL25, and is involved in inflammatory diseases and tumors. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR9 is necessary for treatment and diagnosis. In this study, we established a specific anti-human CCR9 (hCCR9) mAb; C₉Mab-11 (mouse IgG_2a, kappa), using the synthetic peptide immunization method. C₉Mab-11 reacted with hCCR9-overexpressed Chinese hamster ovary-K1 (CHO/hCCR9) and hCCR9-endogenously expressed MOLT-4 (human T-lymphoblastic leukemia) cells in flow cytometry. The dissociation constant (K_D) of C₉Mab-11 for CHO/hCCR9 and MOLT-4 cells were determined to be 1.2 × 10^-9 M and 4.9 × 10^-10 M, respectively, indicating that C₉Mab-11 possesses a high affinity for both exogenously and endogenously hCCR9-expressing cells. Furthermore, C₉Mab-11 clearly detected hCCR9 protein in CHO/hCCR9 cells using western blot analysis. In summary, C₉Mab-11 can be a useful tool for analyzing hCCR9-related biological responses.

A Defucosylated Anti-EpCAM Monoclonal Antibody (EpMab-37-mG2a-f) Exerts Antitumor Activity in Xenograft Model

The epithelial cell adhesion molecule (EpCAM) is a stem cell and carcinoma antigen, which mediates cellular adhesion and proliferative signaling by the proteolytic cleavage. In contrast to low expression in normal epithelium, EpCAM is frequently overexpressed in various carcinomas, which correlates with poor prognosis. Therefore, EpCAM has been considered as a promising target for tumor diagnosis and therapy. Using the Cell-Based Immunization and Screening (CBIS) method, we previously established an anti-EpCAM monoclonal antibody (EpMab-37; mouse IgG₁, kappa). In this study, we investigated the antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and an antitumor activity by a defucosylated mouse IgG_2a-type of EpMab-37 (EpMab-37-mG_2a-f) against a breast cancer cell line (BT-474) and a pancreatic cancer cell line (Capan-2), both of which express EpCAM. EpMab-37-mG_2a-f recognized BT-474 and Capan-2 cells with a moderate binding-affinity [apparent dissociation constant (K_D): 2.9 × 10^-8 M and 1.8 × 10^-8 M, respectively] by flow cytometry. EpMab-37-mG_2a-f exhibited ADCC and CDC for both cells by murine splenocytes and complements, respectively. Furthermore, administration of EpMab-37-mG_2a-f significantly suppressed the xenograft tumor development compared with the control mouse IgG. These results indicated that EpMab-37-mG_2a-f exerts antitumor activities and could provide valuable therapeutic regimen for breast and pancreatic cancers.

Antitumor Activity of an Anti-EGFR/HER2 Bispecific Antibody in a Mouse Xenograft Model of Canine Osteosarcoma

The overexpression of epidermal growth factor receptors (EGFRs) has been reported in various human tumors, including breast, gastric, lung, colorectal, and pancreatic cancers. Humanized anti-EGFR and anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibodies (mAbs) have been shown to improve patients' survival. Canine tumors resemble human tumors in the initiation and progression. We previously established a defucosylated mouse-dog chimeric anti-EGFR mAb (E134Bf) and a mouse-dog chimeric anti-HER2 mAb (H77Bf), which exerted antitumor activities in canine tumor xenograft models. Here, we produced E134Bf antibody fused to H77Bf single chain Fv at the light chains (E134Bf-H77scFv). The bispecific E134Bf-H77scFv recognized dog EGFR (dEGFR) and dog HER2 (dHER2)-overexpressed Chinese hamster ovary-K1 cells by flow cytometry. E134Bf-H77scFv also reacted with dEGFR/dHER2-positive canine osteosarcoma D-17 cells, and possesses a high binding-affinity (K_D: 1.3 × 10^-9 M). Furthermore, E134Bf-H77scFv exerted antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity against D-17 cells in the presence of canine mononuclear cells and complement, respectively. Moreover, administration of E134Bf-H77scFv suppressed the development of D-17 xenograft tumor in mice early compared with the control dog IgG, E134Bf and H77Bf alone. These results indicate that E134Bf-H77scFv exerts antitumor activities against dEGFR/dHER2-positive canine tumors, and could be a valuable treatment regimen for canine tumors.

HER3 in cancer: from the bench to the bedside

The HER3 protein, that belongs to the ErbB/HER receptor tyrosine kinase (RTK) family, is expressed in several types of tumors. That fact, together with the role of HER3 in promoting cell proliferation, implicate that targeting HER3 may have therapeutic relevance. Furthermore, expression and activation of HER3 has been linked to resistance to drugs that target other HER receptors such as agents that act on EGFR or HER2. In addition, HER3 has been associated to resistance to some chemotherapeutic drugs. Because of those circumstances, efforts to develop and test agents targeting HER3 have been carried out. Two types of agents targeting HER3 have been developed. The most abundant are antibodies or engineered antibody derivatives that specifically recognize the extracellular region of HER3. In addition, the use of aptamers specifically interacting with HER3, vaccines or HER3-targeting siRNAs have also been developed. Here we discuss the state of the art of the preclinical and clinical development of drugs aimed at targeting HER3 with therapeutic purposes.

KLMab-1: An Anti-human KLRG1 Monoclonal Antibody for Immunocytochemistry

Immune checkpoint molecules have received attention as targets of cancer immunotherapy. Killer cell lectin-like receptor subfamily G member 1 (KLRG1) is one of the immune checkpoint molecules expressed in CD4⁺ T, CD8⁺ T, and natural killer (NK) cells. KLRG1 exhibits antiviral and antitumor immunity, and its expression in T and NK cells is upregulated by viral infectious diseases and some tumors. Thus, monoclonal antibodies (mAbs) for KLRG1 would be useful tools for the diagnosis and immunotherapy against viral infectious diseases and cancers. We have developed anti-human KLRG1 (hKLRG1) mAb (clone KLMab-1, mouse IgG₁, kappa) by the Cell-Based Immunization and Screening method. We have also demonstrated that KLMab-1 recognizes both exogenous and endogenous hKLRG1 in flow cytometry. In this study, we first showed that KLMab-1 and its recombinant mAb (recKLMab-1) bound to exogenous hKLRG1 overexpressed in Chinese hamster ovary (CHO)-K1 cells, but not in parental CHO-K1 cells, in immunocytochemistry. We next showed that both mAbs detected endogenous hKLRG1 expressed in human NK cells. These results demonstrate that KLMab-1 and recKLMab-1 are available for immunocytochemistry.

Development of an Anti-human CCR2 Monoclonal Antibody (C2Mab-9) by N-Terminal Peptide Immunization

The CC chemokine receptor type-2 (CCR2) is one of the members of the G protein-coupled receptor superfamily, which are expressed on the cell surface of immune and tumor cells. CCR2 binds to the C-C motif chemokine ligand 2 (CCL2)/monocyte chemoattractant protein-1 (MCP-1), which is produced by various cells, including tumor and immune-related cells. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR2 has been desired for treatment and diagnosis. In this study, we established a specific antihuman CCR2 (hCCR2) mAb, C₂Mab-9 (mouse IgG₁, kappa), using the synthetic peptide immunization method. Flow cytometric and immunocytochemical results showed that C₂Mab-9 reacted with hCCR2-expressing U937 (human histiocytic lymphoma) and natural killer cells. Furthermore, C₂Mab-9 showed the moderate binding affinity for both cells. Conclusively, C₂Mab-9 can be a useful tool for analyzing hCCR2-related biological responses.

Defucosylated mouse‑dog chimeric anti‑HER2 monoclonal antibody exerts antitumor activities in mouse xenograft models of canine tumors

Human epidermal growth factor receptor 2 (HER2) overexpression has been reported in various types of cancer, including breast, gastric, lung, colorectal and pancreatic cancer. A humanized anti-HER2 monoclonal antibody (mAb), trastuzumab, has been shown to improve survival of patients in HER2-positive breast and gastric cancer. An anti-HER2 mAb, H₂Mab-77 (mouse IgG₁, kappa) was previously developed. In the present study, a defucosylated version of mouse-dog chimeric anti-HER2 mAb (H77Bf) was generated. H77Bf possesses a high binding-affinity [a dissociation constant (K_D): 7.5×10⁻¹⁰ M, as determined by flow cytometric analysis] for dog HER2-overexpressed CHO-K1 (CHO/dHER2) cells. H77Bf highly exerted antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) for CHO/dHER2 cells by canine mononuclear cells and complement, respectively. Moreover, administration of H77Bf significantly suppressed the development of CHO/dHER2 ×enograft tumor in mice compared with the control dog IgG. H77Bf also possesses a high binding-affinity (K_D: 7.2×10⁻¹⁰ M) for a canine mammary gland tumor cell line (SNP), and showed high ADCC and CDC activities for SNP cells. Intraperitoneal administration of H77Bf in mouse xenograft models of SNP significantly suppressed the development of SNP xenograft tumors compared with the control dog IgG. These results indicated that H77Bf exerts antitumor activities against dHER2-positive canine cancers, and could be valuable treatment regimen for canine cancers.

Epitope Mapping of the Anti-Human CCR2 Monoclonal Antibody C2Mab-9

CC chemokine receptor type-2 (CCR2) belongs to the G protein-coupled receptors superfamily, localized on cell surface of some immune-related cells, including monocytes and macrophages. CCR2 and its ligand CCL2 are involved in the progression of various diseases such as cancers. Therefore, CCR2-targeted monoclonal antibodies (mAbs) are needed for treatment and diagnosis. Previously, we successfully developed an anti-human CCR2 (hCCR2) mAb, C₂Mab-9 (mouse IgG₁, kappa), which is applicable for flow cytometry and immunocytochemistry. In this study, we investigated the critical epitope of C₂Mab-9. We conducted enzyme-linked immunosorbent assay (ELISA) using several N-terminal peptides of hCCR2, and demonstrated that C₂Mab-9 recognizes 11-29 and 21-39 amino acids of hCCR2. We further performed ELISA using 20 peptides, which include alanine substitution of hCCR2. C₂Mab-9 lost the reaction to the alanine-substituted peptides of F23A, F24A, D25A, Y26A, and D27A. Among them, F23A, F24A, D25A, and Y26A did not block the C₂Mab-9 reaction with U937 cells in flow cytometry. These results indicate that the critical binding epitope of C₂Mab-9 includes Phe23, Phe24, Asp25, and Tyr26.

TgMab-2: An Anti-human T Cell Immunoglobulin and Immunoreceptor Tyrosine-Based Inhibitory Motif Domain Monoclonal Antibody for Immunocytochemistry

T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) is one of the immune checkpoint molecules. TIGIT is expressed in T or natural killer (NK) cells and is upregulated in several cancers. Because TIGIT suppresses the antitumor activity of the T or NK cells by binding to its ligand, such as CD155, CD112, and CD113, TIGIT can be a molecular marker or a therapeutic target for cancer immunotherapy. We previously developed an anti-human TIGIT (hTIGIT) monoclonal antibody (mAb; clone TgMab-2; mouse IgG₁, kappa) by the Cell-Based Immunization and Screening method. TgMab-2 binds to hTIGIT with high binding affinity in flow cytometry. In this study, we investigated the availability of TgMab-2 and its recombinant mAb (recTgMab-2) in immunocytochemistry. We found that TgMab-2 and recTgMab-2 bind to hTIGIT-overexpressed Chinese hamster ovary (CHO)-K1 cells, but not parental CHO-K1 cells, indicating that both mAbs specifically recognize hTIGIT. Furthermore, both mAbs recognized endogenous hTIGIT expressed in human NK cells in immunocytochemistry. These results demonstrate that TgMab-2 and recTgMab-2 are applicable for immunocytochemistry against hTIGIT.

Cx6Mab-1: A Novel Anti-Mouse CXCR6 Monoclonal Antibody Established by N-Terminal Peptide Immunization

The CXC chemokine receptor 6 (CXCR6) is a member of the G protein-coupled receptor family that is highly expressed in helper T type 1 cells, natural killer cells, cytotoxic T lymphocytes, and various type of cells in tumor microenvironment (TME). CXCR6 has been proposed as a therapeutic target against tumors through regulation of the tumor TME. In this study, we developed specific and sensitive monoclonal antibodies (mAbs) for mouse CXCR6 (mCXCR6), which are useful for flow cytometry and Western blotting by N-terminal peptide immunization into rat. The established anti-mCXCR6 mAb, Cx₆Mab-1 (rat IgG₁, kappa), reacted with not only mCXCR6-overexpressed Chinese hamster ovary-K1 (CHO/mCXCR6) but also mCXCR6-endogenously expressed cell lines, such as P388 (mouse lymphoid neoplasm) and J774-1 (mouse macrophage-like) through flow cytometry. Kinetic analyses using flow cytometry indicated that the dissociation constants (K_D) of Cx₆Mab-1 for CHO/mCXCR6, P388, and J774-1 cells were 1.7 × 10^-9 M, 3.4 × 10^-7 M, and 3.8 × 10^-7 M, respectively. Furthermore, Cx₆Mab-1 could detect endogenous mCXCR6 in P388 and J774-1 cells by Western blotting. These results indicated that Cx₆Mab-1 is useful for detecting mCXCR6 by flow cytometry and Western blotting, and provides a possibility for targeting CXCR6-expressing cells in vivo experiments.

Establishment of Novel Anti-Mouse CCR3 Monoclonal Antibodies (C3Mab-6 and C3Mab-7) by N-terminal Peptide Immunization

The CC chemokine receptor 3 (CCR3) is a member of the G protein-coupled receptor family that is highly expressed in eosinophils and basophils. CCR3 has been proposed as a therapeutic target for human immunodeficiency virus and allergy diagnosis. Therefore, in this study, we developed specific and sensitive monoclonal antibodies (mAbs) for mouse CCR3 (mCCR3), which are useful for flow cytometry by peptide immunization. The established anti-mCCR3 mAbs, C₃Mab-6 (rat IgG₁, kappa) and C₃Mab-7 (rat IgG₁, kappa), reacted with mCCR3-overexpressed Chinese hamster ovary-K1 (CHO/mCCR3), in addition to mCCR3-endogenously expressed cell lines, such as P388 (mouse lymphoid neoplasma) and J774-1 (mouse macrophage-like) through flow cytometry. Kinetic analyses using flow cytometry indicated that the dissociation constants (K_Ds) of C₃Mab-6 for CHO/mCCR3, P388, and J774-1 cells were 8.7 × 10^-9 M, 1.4 × 10^-7 M, and 1.7 × 10^-7 M, respectively, whereas the K_Ds of C₃Mab-7 for these cell lines were 3.7 × 10^-9 M, 5.1 × 10^-7 M, and 3.1 × 10^-7 M, respectively. Results also indicated that C₃Mab-6 and C₃Mab-7 are useful for detecting cells expressing CCR3 through flow cytometry, thereby making them potentially beneficial for treating CCR3-expressing cells.

C3Mab-3: A Monoclonal Antibody for Mouse CC Chemokine Receptor 3 for Flow Cytometry

CC chemokine receptor 3 (CCR3) belongs to the G protein-coupled receptor family and is highly expressed in eosinophils and basophils. CCR3 is essential for recruiting eosinophils into the lung. Moreover, CCR3 was found in the serum of colorectal cancer patients higher than in the control group. Therefore, CCR3 will be a useful target for asthma and colorectal cancer diagnosis. This study developed a specific and sensitive monoclonal antibody (mAb) for mouse CCR3 (mCCR3), which is useful for flow cytometry using the Cell-Based Immunization and Screening method. The established anti-mCCR3 mAb, C₃Mab-3 (rat IgG_2a, kappa), reacted with mCCR3-overexpressed Chinese hamster ovary-K1 (CHO/mCCR3) cells through flow cytometry. C₃Mab-3 also reacted with P388 (mouse lymphoid neoplasma) and J774-1 (mouse macrophage-like) cells, which express mCCR3 endogenously. Kinetic analyses using flow cytometry indicated that K_Ds of C₃Mab-3 for CHO/mCCR3, P388, and J774-1 cells were 4.3 × 10^-8 M, 2.6 × 10^-7 M, and 2.4 × 10^-7 M, respectively. C₃Mab-3 could be a valuable tool for elucidating mCCR3-related biological response using flow cytometry.

Development of a Novel Anti-Mouse CCR4 Monoclonal Antibody (C4Mab-1) by N-Terminal Peptide Immunization

The CC chemokine receptor type-4 (CCR4) belongs to the G-protein-coupled receptor superfamily, expressed on the cell surface of T cells and its malignancy. Two CCR4 ligands (CCL17 and CCL22) bind to CCR4 that mediate physiological and pathological functions of T cell immune responses. Anti-CCR4 monoclonal antibody (mAb) mogamulizumab is approved for adult T cell leukemia/lymphoma and cutaneous T cell lymphomas. In addition, mogamulizumab can deplete regulatory T cells, implying the application to solid tumors as an immunomodulator. Therefore, the development of sensitive mAbs for CCR4 has been desired for basic research, diagnosis, and therapy. In this study, a specific, and sensitive anti-mouse CCR4 (mCCR4) mAb, C₄Mab-1 (rat IgG₁, kappa), was established using N-terminal peptide immunization. C₄Mab-1 reacted with mCCR4-overexpressed Chinese hamster ovary (CHO)-K1 cells, P388 (mouse lymphoid neoplasm), and J774-1 (mouse macrophage-like) cells in flow cytometry. Kinetic analyses using flow cytometry showed that K_Ds of C₄Mab-1 for CHO/mCCR4, P388, and J774-1 cells were 4.2 × 10^-9 M, 5.4 × 10^-7 M, and 1.1 × 10^-6 M, respectively. C₄Mab-1 could be a valuable tool for elucidating mCCR4-related biological responses.

Antitumor Activities in Mouse Xenograft Models of Canine Fibroblastic Tumor by Defucosylated Anti-Epidermal Growth Factor Receptor Monoclonal Antibody

The epidermal growth factor receptor (EGFR) is involved in tumor malignancy through gene amplification and/or protein overexpression. An anti-human EGFR (hEGFR) monoclonal antibody (clone EMab-134), which explicitly detects hEGFR and dog EGFR (dEGFR), was previously developed. The defucosylated mouse IgG_2a version of EMab-134 (134-mG_2a-f) exhibits antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) in dEGFR-overexpressed CHO-K1 (CHO/dEGFR) cells and antitumor activities in mouse xenografts of CHO/dEGFR cells. In this study, it was shown that 134-mG_2a-f reacts with a canine fibroblastic tumor cell line (A-72) using flow cytometry and immunocytochemistry. Furthermore, 134-mG_2a-f exerted ADCC and CDC on A-72 cell line. The administration of 134-mG_2a-f significantly inhibited the A-72 xenograft growth. These results suggest that 134-mG_2a-f exerts antitumor effects on dEGFR-expressing canine fibroblastic tumors.

Development of a Novel Anti-Mouse CCR2 Monoclonal Antibody (C2Mab-6) by N-Terminal Peptide Immunization

The CC chemokine receptor type-2 (CCR2) belongs to the G-protein-coupled receptor superfamily, expressed on the cell surface of immune cells and tumors. CCR2 binds to the CC motif chemokine 2/monocyte chemoattractant protein-1, a CC chemokine, which is produced by various cells, including immune-related cells and tumors. Therefore, the development of sensitive monoclonal antibodies (mAbs) for CCR2 has been desired for treatment and diagnosis. This study established a novel, specific, and sensitive anti-mouse CCR2 (mCCR2) mAb; C₂Mab-6 (rat IgG₁, kappa), using the mCCR2 synthetic peptide immunization method. C₂Mab-6 reacted with mCCR2-overexpressed Chinese hamster ovary-K1 cells and L1210 (murine leukemia) cells, which express endogenous mCCR2 in flow cytometry. Furthermore, C₂Mab-6 showed a high binding affinity for both cells. Hence, C₂Mab-6 can be a useful tool for analyzing mCCR2-related biological responses, using flow cytometry.

Defucosylated Mouse-Dog Chimeric Anti-EGFR Antibody Exerts Antitumor Activities in Mouse Xenograft Models of Canine Tumors

The epidermal growth factor receptor (EGFR) contributes to tumor malignancy via gene amplification and protein overexpression. Previously, we developed an anti-human EGFR (hEGFR) monoclonal antibody, namely EMab-134, which detects hEGFR and dog EGFR (dEGFR) with high sensitivity and specificity. In this study, we produced a defucosylated mouse–dog chimeric anti-EGFR monoclonal antibody, namely E134Bf. In vitro analysis revealed that E134Bf highly exerted antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity against a canine osteosarcoma cell line (D-17) and a canine fibroblastic cell line (A-72), both of which express endogenous dEGFR. Moreover, in vivo administration of E134Bf significantly suppressed the development of D-17 and A-72 compared with the control dog IgG in mouse xenografts. These results indicate that E134Bf exerts antitumor effects against dEGFR-expressing canine cancers and could be valuable as part of an antibody treatment regimen for dogs.