LpMab-12 Established by CasMab Technology Specifically Detects Sialylated O-Glycan on Thr52 of Platelet Aggregation-Stimulating Domain of Human Podoplanin

Development of Monoclonal Antibody 281-mG2a-f Against Golden Hamster Podoplanin

Golden (Syrian) hamster (Mesocricetus auratus) is a small animal model of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. Pathological analyses of the tissues are required to understand the pathogenesis of SARS-CoV-2 and the evaluation of therapeutic modalities, including neutralizing monoclonal antibodies (mAbs). However, mAbs that recognize the golden hamster-derived antigens and distinguish specific cell types, such as the pneumocytes, are limited. Podoplanin (PDPN) is an essential marker of lung type I alveolar epithelial cells, kidney podocytes, and lymphatic endothelial cells. In this study, an anti-Chinese hamster (Cricetulus griseus) PDPN mAb PMab-281 (IgG₃, kappa) was established using the Cell-Based Immunization and Screening (CBIS) method. A defucosylated mouse IgG_2a version of PMab-281 (281-mG_2a-f) was also developed. The 281-mG_2a-f strongly recognized both the Chinese hamster and the golden hamster PDPN using flow cytometry and could detect lung type I alveolar epithelial cells, lymphatic endothelial cells, and Bowman's capsules in the kidney from the golden hamster using immunohistochemistry. These results suggest the usefulness of 281-mG_2a-f for analyzing the golden hamster-derived tissues and cells for SARS-CoV-2 research.

Development of a Monoclonal Antibody PMab-292 Against Ferret Podoplanin

Ferrets (Mustela putorius furo) have been used as small animal models to investigate severe acute respiratory syndrome coronaviruses (SARS-CoV and SARS-CoV-2) infections. Pathological analyses of these tissue samples, including those of the lung, are, therefore, essential to understand the pathogenesis of SARS-CoVs and evaluate the action of therapeutic monoclonal antibodies (mAbs) against this disease. However, mAbs that recognize ferret-derived proteins and distinguish between specific cell types, such as lung epithelial cells, are limited. Podoplanin (PDPN) has been identified as an essential marker in lung type I alveolar epithelial cells, kidney podocytes, and lymphatic endothelial cells. In this study, an anti-ferret PDPN (ferPDPN) mAb PMab-292 (mouse IgG₁, kappa) was established using the Cell-Based Immunization and Screening (CBIS) method. PMab-292 recognized ferPDPN-overexpressed Chinese hamster ovary-K1 (CHO/ferPDPN) cells by flow cytometry and Western blotting. The kinetic analysis using flow cytometry showed that the K_D of PMab-292 for CHO/ferPDPN was 3.4 × 10^-8 M. Furthermore, PMab-292 detected lung type I alveolar epithelial cells, lymphatic endothelial cells, and glomerular/Bowman's capsule in the kidney using immunohistochemistry. Hence, these results propose the usefulness of PMab-292 in analyzing ferret-derived tissues for SARS-CoV-2 research.

Development of Monoclonal Antibody PMab-269 Against California Sea Lion Podoplanin

The development of protein-specific antibodies is essential for understanding a wide variety of biological phenomena. Parasitic and viral infections and cancers are known to occur within California sea lion (Zalophus californianus) populations. However, sensitive and specific monoclonal antibodies (mAbs) for the pathophysiological analysis of California sea lion tissues have not yet been developed. A type I transmembrane glycoprotein, podoplanin (PDPN), is a known diagnostic marker of lymphatic endothelial cells. We have previously developed several anti-PDPN mAbs in various mammalian species, with applications in flow cytometry, Western blotting, and immunohistochemistry. In this study, we established a novel mAb against California sea lion PDPN (seaPDPN), clone PMab-269 (mouse IgG₁, kappa), using a Cell-Based Immunization and Screening method. PMab-269 is specifically detected in seaPDPN-overexpressed Chinese hamster ovary (CHO)-K1 cells using flow cytometry and Western blotting. Moreover, PMab-269 clearly identified pulmonary type I alveolar cells, renal podocytes, and colon lymphatic endothelial cells in California sea lion tissues using immunohistochemistry. These findings demonstrate the usefulness of PMab-269 for the pathophysiological analysis of lung, kidney, and lymphatic tissues of the California sea lion.

Crystal structure of an anti-podoplanin antibody bound to a disialylated O-linked glycopeptide

Podoplanin (PDPN) is a highly O-glycosylated glycoprotein that is utilized as a specific lymphatic endothelial marker under pathophysiological conditions. We previously developed an anti-human PDPN (hPDPN) monoclonal antibody (mAb), clone LpMab-3, which recognizes the epitope, including both the peptides and the attached disialy-core-l (NeuAcα2-3Galβl-3 [NeuAcα2-6]GalNAcαl-O-Thr) structure at the Thr76 residue in hPDPN. However, it is unclear if the mAb binds directly to both the peptides and glycans. In this study, we synthesized the binding epitope region of LpMab-3 that includes the peptide (-₆₇LVATSVNSV-T-GIRIEDLP₈₄-) possessing a disialyl-core-1 O-glycan at Thr76, and we determined the crystal structure of the LpMab-3 Fab fragment that was bound to the synthesized glycopeptide at a 2.8 Å resolution. The six amino acid residues and two sialic acid residues are directly associated with four complementarity-determining regions (CDRs; H1, H2, H3, and L3) and four CDRs (H2, H3, L1, and L3), respectively. These results suggest that IgG is advantageous for generating binders against spacious epitopes such as glycoconjugates.

A cancer-specific anti-podocalyxin monoclonal antibody (60-mG2a-f) exerts antitumor effects in mouse xenograft models of pancreatic carcinoma

Overexpression of podocalyxin (PODXL) is associated with progression, metastasis, and poor outcomes in several cancers. PODXL also plays an important role in the development of normal tissues. For antibody-based therapy to target PODXL-expressing cancers using monoclonal antibodies (mAbs), cancer-specificity is necessary to reduce the risk of adverse effects to normal tissues. In this study, we developed an anti-PODXL cancer-specific mAb (CasMab), named as PcMab-60 (IgM, kappa) by immunizing mice with soluble PODXL, which is overexpressed in LN229 glioblastoma cells. The PcMab-60 reacted with the PODXL-overexpressing LN229 (LN229/PODXL) cells and MIA PaCa-2 pancreatic cancer cells in flow cytometry but did not react with normal vascular endothelial cells (VECs), whereas one of non-CasMabs, PcMab-47 showed high reactivity for not only LN229/PODXL and MIA PaCa-2 cells but also VECs, indicating that PcMab-60 is a CasMab. Next, we engineered PcMab-60 into a mouse IgG_2a-type mAb, named as 60-mG_2a, to add antibody-dependent cellular cytotoxicity (ADCC). We further developed a core fucose-deficient type of 60-mG_2a, named as 60-mG_2a-f, to augment its ADCC activity. In vivo analysis revealed that 60-mG_2a-f exerted antitumor activity in MIA PaCa-2 xenograft models at a dose of 100 μg/mouse/week administered three times. These results suggested that 60-mG_2a-f could be useful for antibody-based therapy against PODXL-expressing pancreatic cancers.

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PODXL is associated with poor outcomes in several cancers.

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We developed an anti-PODXL cancer-specific mAb (PcMab-60).

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A core fucose-deficient IgG_2a type of PcMab-60 (60-mG_2a-f) exerted antitumor activity in MIA PaCa-2 xenograft models.

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60-mG_2a-f could be useful for antibody-based therapy against PODXL-expressing pancreatic cancers.

Detection of Lion Podoplanin Using the Antitiger Podoplanin Monoclonal Antibody PMab-231

Monoclonal antibodies (mAbs) that specifically target podoplanin (PDPN), a marker for type I alveolar cells, are needed for immunohistochemical analyses. Anti-PDPN mAbs are available for many species, including human, mouse, rat, rabbit, dog, cat, bovine, pig, Tasmanian devil, alpaca, tiger, whale, goat, horse, bear, and sheep PDPNs. However, no antilion PDPN (lioPDPN) antibody has been developed. In this study, possible cross-reaction between available anti-PDPN mAbs and lioPDPN was examined. Immunohistochemical analysis showed that antitiger PDPN mAb PMab-231 (IgG_2a, kappa) reacted with type I alveolar cells from lion lung, indicating that PMab-231 is useful for the detection of lioPDPN.

A novel anti-EGFR monoclonal antibody (EMab-17) exerts antitumor activity against oral squamous cell carcinomas via antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity

The epidermal growth factor receptor (EGFR) is a member of the human epidermal growth factor receptor (HER) family of receptor tyrosine kinases; it is a transmembrane receptor involved in cell growth and differentiation. EGFR homodimers or heterodimers in combination with other HER members, such as HER2 and HER3, activate downstream signaling cascades in many types of cancer, including oral squamous cell carcinoma (OSCC). The present study produced novel anti-EGFR monoclonal antibodies (mAbs) possessing antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), and investigated antitumor activity. Mice were immunized with an EGFR-overexpressed glioblastoma cell line, LN229 (LN229/EGFR), after which ELISA was performed using recombinant EGFR. mAbs were subsequently selected according to their efficacy for LN229/EGFR, as determined via flow cytometry. After determining the subclass of mAbs, the EMab-17 (IgG_2a, kappa) clone exhibited ADCC and CDC activities against two OSCC cell lines, HSC-2 and SAS. Furthermore, EMab-17 exerted antitumor activities against mouse xenograft models using HSC-2 and SAS, indicating that EMab-17 may be used in an antibody-based therapy for EGFR-expressing OSCC.

Podoplanin promotes cancer-associated thrombosis and contributes to the unfavorable overall survival in an ectopic xenograft mouse model of oral cancer

Background

Podoplanin (PDPN) is a transmembrane glycoprotein that mediates tumor cell-induced platelets aggregation in different cancer types. Emerging data indicate that PDPN is a marker for poor prognosis of human oral squamous cell carcinoma (OSCC). However, the functional impacts of PDPN on cancer formation and disease progression of OSCC remain to be elucidated.

Methods

The sublines of the OECM-1 oral cancer cells with PDPN knockdown or overexpression were established. The cellular characteristics and the ability to induce platelet aggregation of these cells lines were analyzed. An ectopic xenograft animal model by inoculating cancer cells into the anterior neck region of nude mice was established to investigate the functional impact of PDPN on disease progression and cancer-associated thrombosis of OSCC.

Results

PDPN promoted OSCC cell migration and invasion, but had no effect on cell proliferation in vitro and tumor growth in vivo. Co-incubation of PDPN-positive (PDPN⁺) OSCC cells with platelets induced platelet activation and aggregation. The mice bearing PDPN⁺ tumor had a decrease in overall survival despite that there was no gross appearance of distant metastasis. A speckled immunofluorescence staining pattern of platelet marker mCD41 was defined in the PDPN⁺ tumor sections and the intensity was greater than in the PDPN-low or negative tumor sections. Co-immunofluorescence staining of the tumor sections with mCD41 and the endothelial cell marker mCD31 further demonstrated that platelet aggregates were located in the lumen of blood vessel and were also distributed intratumorally in the mice bearing PDPN⁺ tumors.

Conclusions

These data demonstrated that PDPN expression in the cancer cells is associated with high risk of thrombosis, leading to unfavorable overall survival of the mice. This study provides new insights into the functions of PDPN in cancer-associated thrombosis and in the pathophysiology of OSCC.

The Epitope of PMab-210 Is Located in Platelet Aggregation-Stimulating Domain-3 of Pig Podoplanin

Podoplanin (PDPN)/T1alpha/Aggrus, a small mucin-type transmembrane glycoprotein, has been shown to be expressed on lymphatic endothelial cells and epithelial cells of many organs. PDPN is also upregulated in many cancers, and is involved in cancer metastasis and malignant progression. Human PDPN possesses three platelet aggregation-stimulating (PLAG) domains and the PLAG-like domain, which bind to C-type lectin-like receptor-2 (CLEC-2). Previously, we reported a novel antipig PDPN (pPDPN) monoclonal antibody (PMab-210) using Cell-Based Immunization and Screening (CBIS) method. PMab-210 specifically detected pPDPN-overexpressed Chinese hamster ovary (CHO)-K1 cells by flow cytometry and Western blot analysis. Immunohistochemical analyses demonstrated that PMab-210 stained pulmonary type I alveolar cells strongly and renal corpuscles weakly in pig or microminipig. However, the specific binding epitope of PMab-210 for pPDPN could not be determined by enzyme-linked immunosorbent assay using a series of pPDPN peptides. In this study, deletion mutants or point mutants of pPDPN were produced for analyzing the PMab-210 epitope using flow cytometry. The analysis of deletion mutants showed that N-terminus of PMab-210 epitope exists between 45th amino acid (aa) and 50th aa of pPDPN. In addition, the analysis of point mutants demonstrated that the critical epitope of PMab-210 could include Glu47, Asp48, Tyr49, Thr50, and Val51 of pPDPN, indicating that PMab-210 epitope is located in PLAG3 domain of pPDPN.

PMab-235: A monoclonal antibody for immunohistochemical analysis against goat podoplanin

Sensitive and specific monoclonal antibodies (mAbs) against not only human but also mouse, rat, rabbit, dog, cat, bovine, pig, and horse podoplanins (PDPNs) have been established in our previous studies. However, anti-goat PDPN (gPDPN) has not been established yet. PDPN has been utilized as a lymphatic endothelial cell marker especially in pathological diagnoses; therefore, mAbs for immunohistochemical analyses using formalin-fixed paraffin-embedded tissues are needed. Although we recently demonstrated that an anti-bovine PDPN mAb, PMab-44 cross-reacted with gPDPN, PMab-44 did not detect lymphatic endothelial cells in immunohistochemistry. In this study, we immunized mice with gPDPN-overexpressing Chinese hamster ovary (CHO)–K1 (CHO/gPDPN) cells, and screened mAbs against gPDPN using flow cytometry. One of the mAbs, PMab-235 (IgG₁, kappa), specifically detected CHO/gPDPN cells by flow cytometry. Furthermore, PMab-235 strongly detected lung type I alveolar cells, renal podocytes, and lymphatic endothelial cells of colon by immunohistochemistry. These findings suggest that PMab-235 may be useful as a lymphatic endothelial cell marker for goat tissues.

Immunohistochemical Detection of Sheep Podoplanin Using an Antibovine Podoplanin Monoclonal Antibody PMab-44

Podoplanin (PDPN) obtained from various animal species has been characterized using specific anti-PDPN monoclonal antibodies (mAbs), namely, PMab-1, PMab-2, PMab-32, PMab-38, PMab-44, and PMab-52 against mouse, rat, rabbit, dog, bovine, and cat PDPN, respectively. PDPN is expressed in type I alveolar cells in lungs, lymphatic endothelial cells, and kidney podocytes. In this study, we investigated possible cross-reactions between anti-PDPN mAbs and sheep PDPN. Type I alveolar cells from sheep lung were strongly detected by PMab-44 using immunohistochemical analyses. These results indicate that PMab-44 may be useful for the detection of sheep PDPN.

Identification of mesothelioma-specific sialylated epitope recognized with monoclonal antibody SKM9-2 in a mucin-like membrane protein HEG1

The anti-mesothelioma mAb SKM9-2 recognizes the sialylated protein HEG homolog 1 (HEG1). HEG1 is a 400 kDa mucin-like membrane protein found on mesothelioma. SKM9-2 can detect mesothelioma more specifically and sensitively than other antibodies against current mesothelioma markers; therefore, SKM9-2 would be likely useful for the precise detection and diagnosis of malignant mesothelioma. In the present study, we investigated the epitope of SKM9-2. We analyzed the binding of SKM9-2 to truncated HEG1 and candidate epitope-fused glycosylphosphatidylinositol-anchor proteins. The epitope of SKM9-2 was identified as an O-glycosylated region, 893-SKSPSLVSLPT-903, in HEG1. An alanine scanning assay of the epitope showed that SKM9-2 bound to a simple epitope in HEG1, and the SKxPSxVS sequence within the epitope was essential for SKM9-2 recognition. Mass spectrometry analysis and lectin binding analysis of soluble epitope peptides indicated that the SKM9-2 epitope, in which Ser⁸⁹⁷ was not glycosylated, contained two disialylated core 1 O-linked glycan-modified serine residues, Ser⁸⁹³ and Ser⁹⁰⁰. Neuraminidase treatment analysis also confirmed that the epitope in mesothelioma cells contained a similar glycan modification. The specific detection of mesothelioma with SKM9-2 can thus be performed by the recognition of sialylated glycan modification in the specific region of HEG1.

Plasma soluble podoplanin is a novel marker for the diagnosis of tumor occurrence and metastasis

Podoplanin (PDPN) is expressed on many tumors and is involved in tumor metastasis. The objective of the present study was to develop an ELISA for determining soluble PDPN (sPDPN) levels as a potential novel tumor marker in plasma of patients with cancers for detection of tumor occurrence and metastasis. Mouse monoclonal antibodies (mAb) against human PDPN were developed and characterized. Two anti-PDPN mAb, SZ-163 and SZ-168, were used in a sandwich ELISA to detect plasma sPDPN in patients with cancers and in normal individuals. The levels of sPDPN were detected in patients with adenocarcinoma (87 cases, 31.09 ± 5.48 ng/ml), squamous cell carcinoma (86 cases, 6.91 ± 0.59 ng/ml), lung cancer (45 cases, 26.10 ± 7.62 ng/ml), gastric cancer (38 cases, 23.71 ± 6.90 ng/ml) and rectal cancer (27 cases, 32.98 ± 9.88 ng/ml), which were significantly higher than those in normal individuals (99 cases, 1.31 ± 0.13 ng/ml) (P < .0001). Moreover, the sPDPN levels in patients with metastatic cancers were higher (192 cases, 30.35 ± 3.63 ng/ml) than those in non-metastatic cancer patients (92 cases, 6.28 ± 0.77 ng/ml) (P < .0001). The post-treatment sPDPN levels of cancer patients (n = 156) (4.47 ± 0.35 ng/ml) were significantly lower compared with those seen pre-treatment (n = 128) (43.74 ± 4.97 ng/ml) (P < .0001). These results showed that an ELISA method was successfully established for quantitation of plasma sPDPN and plasma sPDPN levels correlate significantly with tumor occurrence and metastasis.

Immunohistochemical Analysis of Inflammatory Rheumatoid Synovial Tissues Using Anti-Human Podoplanin Monoclonal Antibody Panel

Podoplanin (PDPN) is a transmembrane sialoglycoprotein, which is expressed in several normal tissues and malignant tumors. Although PDPN expression in rheumatoid arthritis (RA) has been reported, the role of PDPN in RA and other arthritic conditions has not been fully elucidated. In this study, we examined PDPN expression in inflammatory synovial tissues using an anti-human PDPN (hPDPN) monoclonal antibody (mAb) panel to select the most useful one for evaluation of synovitis. Synovial tissue samples were obtained from 11 RA patients and 9 osteoarthritis (OA) patients undergoing joint surgery. PDPN-positive cells were immunostained by a panel of PDPN mAbs (NZ-1, LpMab-3, LpMab-7, LpMab-10, LpMab-12, LpMab-13, and LpMab-17), followed by cell grading of inflammation and cell counting of PDPN-positivity by a quantitative analyzer. Immunohistochemistry showed that PDPN was markedly expressed in both macrophage-like type A and fibroblast-like type B lining cells of the hyperplastic synovial lining cell layer, and macrophages and fibroblasts in the stroma of RA. Among anti-PDPN mAbs, LpMab-12 showed the highest score. In inflammatory OA synovium, PDPN expression was also detectable. Although LpMab-12 also showed the highest score in OA, the difference was not statistically significant. The inflammatory synovitis score of RA was significantly higher than that of OA. PDPN was expressed in inflammatory lining cells and sublining stroma of RA and OA synovium. In the seven anti-hPDPN antibodies examined, LpMab-12 was the most stainable antibody for PDPN in RA synovitis. Thus, LpMab-12 for PDPN has a possible and promising specific biomarker for evaluating synovitis in RA and inflammatory OA.

Establishment of EMab-134, a Sensitive and Specific Anti-Epidermal Growth Factor Receptor Monoclonal Antibody for Detecting Squamous Cell Carcinoma Cells of the Oral Cavity

Epidermal growth factor receptor (EGFR), a receptor tyrosine kinase, activates downstream signaling cascades in many tumors. In this study, we established novel anti-EGFR monoclonal antibodies (mAbs) and characterized their efficacy in flow cytometry, Western blot, and immunohistochemical analyses. We immunized mice with a combination of the extracellular domain of EGFR and EGFR-overexpressing LN229 glioblastoma cells (LN229/EGFR) and performed the first screening using enzyme-linked immunosorbent assay. Next, we selected mAbs using flow cytometry. Among 156 established clones, two mAbs, EMab-51 (IgG₁, kappa) and EMab-134 (IgG₁, kappa), reacted with EGFR in Western blot analysis; EMab-134 showed a much higher sensitivity compared with EMab-51. We compared the binding affinities of EMab-51 and EMab-134 using flow cytometry; the calculated K_D values for EMab-51 and EMab-134 against SAS cells/HSC-2 cells were 9.2 × 10⁻⁹ M/9.9 × 10⁻⁹ M and 2.6 × 10⁻⁹ M/8.3 × 10⁻⁹ M, respectively, indicating that EMab-134 has a higher affinity to EGFR-expressing cells. Immunohistochemical analysis of EMab-51 and EMab-134 showed sensitive and specific reactions against oral cancer cells; EMab-134 demonstrated a much higher sensitivity (36/38 cases; 94.7%) to oral squamous cell carcinomas compared with EMab-51 (6/38 cases; 15.8%). This novel anti-EGFR mAb, EMab-134, could be advantageous for detecting EGFR in the pathological analysis of EGFR-expressing cancers.

Development of EMab-51, a Sensitive and Specific Anti-Epidermal Growth Factor Receptor Monoclonal Antibody in Flow Cytometry, Western Blot, and Immunohistochemistry

The epidermal growth factor receptor (EGFR) is a member of the human epidermal growth factor receptor (HER) family of receptor tyrosine kinases and is involved in cell growth and differentiation. EGFR homodimers or heterodimers with other HER members, such as HER2 and HER3, activate downstream signaling cascades in many cancers. In this study, we developed novel anti-EGFR monoclonal antibodies (mAbs) and characterized their efficacy in flow cytometry, Western blot, and immunohistochemical analyses. First, we expressed the full-length or ectodomain of EGFR in LN229 glioblastoma cells and then immunized mice with LN229/EGFR or ectodomain of EGFR, and performed the first screening using enzyme-linked immunosorbent assays. Subsequently, we selected mAbs according to their efficacy in flow cytometry (second screening), Western blot (third screening), and immunohistochemical (fourth screening) analyses. Among 100 mAbs, only one clone EMab-51 (IgG₁, kappa) reacted with EGFR in Western blot analysis. Finally, immunohistochemical analyses with EMab-51 showed sensitive and specific reactions against oral cancer cells, warranting the use of EMab-51 to detect EGFR in pathological analyses of EGFR-expressing cancers.

Immunohistochemical Analysis Using Antipodocalyxin Monoclonal Antibody PcMab-47 Demonstrates Podocalyxin Expression in Oral Squamous Cell Carcinomas

Podocalyxin is a CD34-related type I transmembrane protein that is highly glycosylated with N-glycan, O-glycan, and keratan sulfate. Podocalyxin was originally found in the podocytes of rat kidney and is reportedly expressed in many types of tumors, including brain tumors, colorectal cancers, and breast cancers. Overexpression of podocalyxin is an independent predictor of progression, metastasis, and poor outcome. We recently immunized mice with recombinant human podocalyxin, which was produced using LN229 glioblastoma cells, and produced a novel antipodocalyxin monoclonal antibody (mAb), PcMab-47, which reacts with endogenous podocalyxin-expressing cancer cell lines and normal cell lines independent of glycosylation in Western blot, flow cytometry, and immunohistochemical analyses. In this study, we performed immunohistochemical analysis against oral cancers using PcMab-47. PcMab-47-stained oral squamous cell carcinoma cells in a cytoplasmic pattern and detected 26/38 (68.4%) of oral squamous cell carcinoma cells on tissue microarrays. These results indicate that PcMab-47 is useful in detecting podocalyxin of oral cancers for immunohistochemical analysis.

H2Mab-77 is a Sensitive and Specific Anti-HER2 Monoclonal Antibody Against Breast Cancer

Human epidermal growth factor receptor 2 (HER2) plays a critical role in the progression of breast cancers, and HER2 overexpression is associated with poor clinical outcomes. Trastuzumab is an anti-HER2 humanized antibody that leads to significant survival benefits in patients with HER2-positive metastatic breast cancers. In this study, we developed novel anti-HER2 monoclonal antibodies (mAbs) and characterized their efficacy in flow cytometry, Western blot, and immunohistochemical analyses. Initially, we expressed the full length or ectodomain of HER2 in LN229 glioblastoma cells and then immunized mice with ectodomain of HER2 or LN229/HER2, and performed the first screening by enzyme-linked immunosorbent assays using ectodomain of HER2. Subsequently, we selected mAbs according to their efficacy in flow cytometry (second screening), Western blot (third screening), and immunohistochemical analyses (fourth screening). Among 100 mAb clones, only three mAbs reacted with HER2 in Western blot, and clone H₂Mab-77 (IgG₁, kappa) was selected. Finally, immunohistochemical analyses with H₂Mab-77 showed sensitive and specific reactions against breast cancer cells, warranting the use of H₂Mab-77 to detect HER2 in pathological analyses of breast cancers.

ChLpMab-23: Cancer-Specific Human-Mouse Chimeric Anti-Podoplanin Antibody Exhibits Antitumor Activity via Antibody-Dependent Cellular Cytotoxicity

Podoplanin is expressed in many cancers, including oral cancers and brain tumors. The interaction between podoplanin and its receptor C-type lectin-like receptor 2 (CLEC-2) has been reported to be involved in cancer metastasis and tumor malignancy. We previously established many monoclonal antibodies (mAbs) against human podoplanin using the cancer-specific mAb (CasMab) technology. LpMab-23 (IgG₁, kappa), one of the mouse anti-podoplanin mAbs, was shown to be a CasMab. However, we have not shown the usefulness of LpMab-23 for antibody therapy against podoplanin-expressing cancers. In this study, we first determined the minimum epitope of LpMab-23 and revealed that Gly54-Leu64 peptide, especially Gly54, Thr55, Ser56, Glu57, Asp58, Arg59, Tyr60, and Leu64 of podoplanin, is a critical epitope of LpMab-23. We further produced human-mouse chimeric LpMab-23 (chLpMab-23) and investigated whether chLpMab-23 exerts antibody-dependent cellular cytotoxicity (ADCC) and antitumor activity. In flow cytometry, chLpMab-23 showed high sensitivity against a podoplanin-expressing glioblastoma cell line, LN319, and an oral cancer cell line, HSC-2. chLpMab-23 also showed ADCC activity against podoplanin-expressing CHO cells (CHO/podoplanin). In xenograft models with HSC-2 and CHO/podoplanin, chLpMab-23 exerts antitumor activity using human natural killer cells, indicating that chLpMab-23 could be useful for antibody therapy against podoplanin-expressing cancers.

Antiglycopeptide Mouse Monoclonal Antibody LpMab-21 Exerts Antitumor Activity Against Human Podoplanin Through Antibody-Dependent Cellular Cytotoxicity and Complement-Dependent Cytotoxicity

The interaction between podoplanin (PDPN) and C-type lectin-like receptor 2 (CLEC-2) is involved in tumor malignancy. We have established many monoclonal antibodies (mAbs) against human podoplanin using the cancer-specific mAb (CasMab) technology. LpMab-21, one of the mouse antipodoplanin mAbs, is of the IgG_2a subclass, and its minimum epitope was determined to be Thr76-Arg79 of the human podoplanin. Importantly, sialic acid is linked to Thr76; therefore, LpMab-21 is an antiglycopeptide mAb (GpMab). In this study, we investigated whether LpMab-21 shows antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against human podoplanin-expressing cancer cell lines in vitro and also studied its antitumor activities using a xenograft model. LpMab-21 showed high ADCC and CDC activities against not only podoplanin-expressing Chinese hamster ovary cells but also LN319 glioblastoma cells and PC-10 lung cancer cells, both of which endogenously express podoplanin. Furthermore, LpMab-21 decreased tumor growth in vivo, indicating that LpMab-21 could be useful for antibody therapy against human podoplanin-expressing cancers.

PcMab-47: Novel Antihuman Podocalyxin Monoclonal Antibody for Immunohistochemistry

Podocalyxin (PODXL) is a CD34-related sialomucin and a well-known marker of embryonic stem cells. PODXL is expressed in many types of tumors including colorectal cancers, breast cancers, and brain tumors. Overexpression of PODXL is an independent predictor of progression, metastasis, and poor outcome. PODXL is also expressed in many normal cells such as renal podocytes and endothelial cells (ECs). However, high-sensitive and high-specific anti-PODXL monoclonal antibodies (mAbs) have not been established. Herein, we immunized mice with recombinant human PODXL, which was produced using LN229 glioblastoma cells. The anti-PODXL mAb, PcMab-47, reacted with endogenous PODXL-expressing cancer cell lines and normal cells independently of glycosylation in flow cytometry. Immunohistochemical analysis showed that PcMab-47 detected PODXL-expressing normal cells such as podocytes of kidney or ECs. Furthermore, PcMab-47 stained PODXL-expressing cancer cells of colon or breast cancers. These results suggest that PcMab-47 could be useful for investigating the expression and function of PODXL in cancers and normal tissues.

Development of RAP Tag, a Novel Tagging System for Protein Detection and Purification

Affinity tag systems, possessing high affinity and specificity, are useful for protein detection and purification. The most suitable tag for a particular purpose should be selected from many available affinity tag systems. In this study, we developed a novel affinity tag called the “RAP tag” system, which comprises a mouse antirat podoplanin monoclonal antibody (clone PMab-2) and the RAP tag (DMVNPGLEDRIE). This system is useful not only for protein detection in Western blotting, flow cytometry, and sandwich enzyme-linked immunosorbent assay, but also for protein purification.

Antitumor activity of chLpMab-2, a human-mouse chimeric cancer-specific antihuman podoplanin antibody, via antibody-dependent cellular cytotoxicity

Human podoplanin (hPDPN), a platelet aggregation‐inducing transmembrane glycoprotein, is expressed in different types of tumors, and it binds to C‐type lectin‐like receptor 2 (CLEC‐2). The overexpression of hPDPN is involved in invasion and metastasis. Anti‐hPDPN monoclonal antibodies (mAbs) such as NZ‐1 have shown antitumor and antimetastatic activities by binding to the platelet aggregation‐stimulating (PLAG) domain of hPDPN. Recently, we developed a novel mouse anti‐hPDPN mAb, LpMab‐2, using the cancer‐specific mAb (CasMab) technology. In this study we developed chLpMab‐2, a human–mouse chimeric anti‐hPDPN antibody, derived from LpMab‐2. chLpMab‐2 was produced using fucosyltransferase 8‐knockout (KO) Chinese hamster ovary (CHO)‐S cell lines. By flow cytometry, chLpMab‐2 reacted with hPDPN‐expressing cancer cell lines including glioblastomas, mesotheliomas, and lung cancers. However, it showed low reaction with normal cell lines such as lymphatic endothelial and renal epithelial cells. Moreover, chLpMab‐2 exhibited high antibody‐dependent cellular cytotoxicity (ADCC) against PDPN‐expressing cells, despite its low complement‐dependent cytotoxicity. Furthermore, treatment with chLpMab‐2 abolished tumor growth in xenograft models of CHO/hPDPN, indicating that chLpMab‐2 suppressed tumor development via ADCC. In conclusion, chLpMab‐2 could be useful as a novel antibody‐based therapy against hPDPN‐expressing tumors.

Development and characterization of anti-glycopeptide monoclonal antibodies against human podoplanin, using glycan-deficient cell lines generated by CRISPR/Cas9 and TALEN

Human podoplanin (hPDPN), which binds to C-type lectin-like receptor-2 (CLEC-2), is involved in platelet aggregation and cancer metastasis. The expression of hPDPN in cancer cells or cancer-associated fibroblasts indicates poor prognosis. Human lymphatic endothelial cells, lung-type I alveolar cells, and renal glomerular epithelial cells express hPDPN. Although numerous monoclonal antibodies (mAbs) against hPDPN are available, they recognize peptide epitopes of hPDPN. Here, we generated a novel anti-hPDPN mAb, LpMab-21. To characterize the hPDPN epitope recognized by the LpMab-21, we established glycan-deficient CHO-S and HEK-293T cell lines, using the CRISPR/Cas9 or TALEN. Flow cytometric analysis revealed that the minimum hPDPN epitope, in which sialic acid is linked to Thr76, recognized by LpMab-21 is Thr76-Arg79. LpMab-21 detected hPDPN expression in glioblastoma, oral squamous carcinoma, and seminoma cells as well as in normal lymphatic endothelial cells. However, LpMab-21 did not react with renal glomerular epithelial cells or lung type I alveolar cells, indicating that sialylation of hPDPN Thr76 is cell-type-specific. LpMab-21 combined with other anti-hPDPN antibodies that recognize different epitopes may therefore be useful for determining the physiological function of sialylated hPDPN.