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

C-type lectin-like receptor 2: roles and drug target

C-type lectin-like receptor-2 (CLEC-2) is a member of the C-type lectin superfamily of cell surface receptors. The first confirmed endogenous and exogenous ligands of CLEC-2 are podoplanin and rhodocytin, respectively. CLEC-2 is expressed on the surface of platelets, which participates in platelet activation and aggregation by binding with its ligands. CLEC-2 and its ligands are involved in pathophysiological processes, such as atherosclerosis, cancer, inflammatory thrombus status, maintenance of vascular wall integrity, and cancer-related thrombosis. In the last 5 years, different anti- podoplanin antibody types have been developed for the treatment of cancers, such as glioblastoma and lung cancer. New tests and new diagnostics targeting CLEC-2 are also discussed. CLEC-2 mediates thrombosis in various pathological states, but CLEC-2-specific deletion does not affect normal hemostasis, which would provide a new therapeutic tool for many thromboembolic diseases. The CLEC-2-podoplanin interaction is a target for cancer treatment. CLEC-2 may be applied in clinical practice and play a therapeutic role.

A Cancer-Specific Monoclonal Antibody against Podocalyxin Exerted Antitumor Activities in Pancreatic Cancer Xenografts

Podocalyxin (PODXL) overexpression is associated with poor clinical outcomes in various tumors. PODXL is involved in tumor malignant progression through the promotion of invasiveness and metastasis. Therefore, PODXL is considered a promising target of monoclonal antibody (mAb)-based therapy. However, PODXL also plays an essential role in normal cells, such as vascular and lymphatic endothelial cells. Therefore, cancer specificity or selectivity is required to reduce adverse effects on normal cells. Here, we developed an anti-PODXL cancer-specific mAb (CasMab), PcMab-6 (IgG1, kappa), by immunizing mice with a soluble PODXL ectodomain derived from a glioblastoma LN229 cell. PcMab-6 reacted with the PODXL-positive LN229 cells but not with PODXL-knockout LN229 cells in flow cytometry. Importantly, PcMab-6 recognized pancreatic ductal adenocarcinoma (PDAC) cell lines (MIA PaCa-2, Capan-2, and PK-45H) but did not react with normal lymphatic endothelial cells (LECs). In contrast, one of the non-CasMabs, PcMab-47, showed high reactivity to both the PDAC cell lines and LECs. Next, we engineered PcMab-6 into a mouse IgG2a-type (PcMab-6-mG2a) and a humanized IgG1-type (humPcMab-6) mAb and further produced the core fucose-deficient types (PcMab-6-mG2a-f and humPcMab-6-f, respectively) to potentiate the antibody-dependent cellular cytotoxicity (ADCC). Both PcMab-6-mG2a-f and humPcMab-6-f exerted ADCC and complement-dependent cellular cytotoxicity in the presence of effector cells and complements, respectively. In the PDAC xenograft model, both PcMab-6-mG2a-f and humPcMab-6-f exhibited potent antitumor effects. These results indicated that humPcMab-6-f could apply to antibody-based therapy against PODXL-expressing pancreatic cancers.

A Humanized and Defucosylated Antibody against Podoplanin (humLpMab-23-f) Exerts Antitumor Activities in Human Lung Cancer and Glioblastoma Xenograft Models

A cancer-specific anti-PDPN mAb, LpMab-23 (mouse IgG1, kappa), was established in our previous study. We herein produced a humanized IgG1 version (humLpMab-23) and defucosylated form (humLpMab-23-f) of an anti-PDPN mAb to increase ADCC activity. humLpMab-23 recognized PDPN-overexpressed Chinese hamster ovary (CHO)-K1 (CHO/PDPN), PDPN-positive PC-10 (human lung squamous cell carcinoma), and LN319 (human glioblastoma) cells via flow cytometry. We then demonstrated that humLpMab-23-f induced ADCC and complement-dependent cytotoxicity against CHO/PDPN, PC-10, and LN319 cells in vitro and exerted high antitumor activity in mouse xenograft models, indicating that humLpMab-23-f could be useful as an antibody therapy against PDPN-positive lung squamous cell carcinomas and glioblastomas.

A Novel Anti-CD44 Variant 9 Monoclonal Antibody C44Mab-1 Was Developed for Immunohistochemical Analyses against Colorectal Cancers

Cluster of differentiation 44 (CD44) is a type I transmembrane glycoprotein and has been shown to be a cell surface marker of cancer stem-like cells in various cancers. In particular, the splicing variants of CD44 (CD44v) are overexpressed in cancers and play critical roles in cancer stemness, invasiveness, and resistance to chemotherapy and radiotherapy. Therefore, the understanding of the function of each CD44v is indispensable for CD44-targeting therapy. CD44v9 contains the variant 9-encoded region, and its expression predicts poor prognosis in patients with various cancers. CD44v9 plays critical roles in the malignant progression of tumors. Therefore, CD44v9 is a promising target for cancer diagnosis and therapy. Here, we developed sensitive and specific monoclonal antibodies (mAbs) against CD44 by immunizing mice with CD44v3-10-overexpressed Chinese hamster ovary-K1 (CHO/CD44v3-10) cells. We first determined their critical epitopes using enzyme-linked immunosorbent assay and characterized their applications as flow cytometry, western blotting, and immunohistochemistry. One of the established clones, C₄₄Mab-1 (IgG₁, kappa), reacted with a peptide of the variant 9-encoded region, indicating that C₄₄Mab-1 recognizes CD44v9. C₄₄Mab-1 could recognize CHO/CD44v3-10 cells or colorectal cancer cell lines (COLO201 and COLO205) in flow cytometric analysis. The apparent dissociation constant (K_D) of C₄₄Mab-1 for CHO/CD44v3-10, COLO201, and COLO205 was 2.5 × 10^-8 M, 3.3 × 10^-8 M, and 6.5 × 10^-8 M, respectively. Furthermore, C₄₄Mab-1 was able to detect the CD44v3-10 in western blotting and the endogenous CD44v9 in immunohistochemistry using colorectal cancer tissues. These results indicated that C₄₄Mab-1 is useful for detecting CD44v9 not only in flow cytometry or western blotting but also in immunohistochemistry against colorectal cancers.

Development of a reporter gene assay for antibody dependent cellular cytotoxicity activity determination of anti-rabies virus glycoprotein antibodies

Rabies is a viral disease that is nearly 100% fatal once clinical signs and symptoms develop. Post-exposure prophylaxis can efficiently prevent rabies, and antibody (Ab) induction by vaccination or passive immunization of human rabies immunoglobulin (HRIG) or monoclonal antibodies (mAbs) play an integral role in prevention against rabies. In addition to their capacity to neutralize viruses, antibodies exert their antiviral effects by antibody-dependent cellular cytotoxicity (ADCC), which plays an important role in antiviral immunity and clearance of viral infections. For antibodies against rabies virus (RABV), evaluation of ADCC activity was neglected. Here, we developed a robust cell-based reporter gene assay (RGA) for the determination of the ADCC activity of anti-RABV antibodies using CVS-N2c-293 cells, which stably express the glycoprotein (G) of RABV strain CVS-N2c as target cells, and Jurkat cells, which stably express FcγRⅢa and nuclear factor of activated T cells (NFAT) reporter gene as effector cells (Jurkat/NFAT-luc/FcγRⅢa cells). The experimental parameters were carefully optimized, and the established ADCC assay was systematically validated according to the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) Q2 guideline. We also evaluated the ADCC activity of anti-RABV antibodies, including mAbs, HRIG, and vaccine induced antisera, and found that all test antibodies exhibited ADCC activity with varied strengths. The established RGA provides a novel method for evaluating the ADCC of anti-RABV antibodies.

Antitumor activities of a defucosylated anti‑EpCAM monoclonal antibody in colorectal carcinoma xenograft models

Epithelial cell adhesion molecule (EpCAM) is a type I transmembrane glycoprotein, which is highly expressed on tumor cells. As EpCAM plays a crucial role in cell adhesion, survival, proliferation, stemness, and tumorigenesis, it has been considered as a promising target for tumor diagnosis and therapy. Anti‑EpCAM monoclonal antibodies (mAbs) have been developed and have previously demonstrated promising outcomes in several clinical trials. An anti‑EpCAM mAb, EpMab‑37 (mouse IgG₁, kappa) was previously developed by the authors, using the cell‑based immunization and screening method. In the present study, a defucosylated version of anti‑EpCAM mAb (EpMab‑37‑mG2a‑f) was generated to evaluate the antitumor activity against EpCAM‑positive cells. EpMab‑37‑mG_2a‑f recognized EpCAM‑overexpressing CHO‑K1 (CHO/EpCAM) cells with a moderate binding‑affinity [dissociation constant (K_D)=2.2x10^‑8 M] using flow cytometry. EpMab‑37‑mG_2a‑f exhibited potent antibody‑dependent cellular cytotoxicity (ADCC) and complement‑dependent cytotoxicity (CDC) for CHO/EpCAM cells by murine splenocytes and complements, respectively. Furthermore, the administration of EpMab‑37‑mG_2a‑f significantly suppressed CHO/EpCAM xenograft tumor development compared with the control mouse IgG. EpMab‑37‑mG_2a‑f also exhibited a moderate binding‑affinity (K_D=1.5x10^‑8 M) and high ADCC and CDC activities for a colorectal cancer cell line (Caco‑2 cells). The administration of EpMab‑37‑mG_2a‑f to Caco‑2 tumor‑bearing mice significantly suppressed tumor development compared with the control. By contrast, EpMab‑37‑mG_2a‑f never suppressed the xenograft tumor growth of Caco‑2 cells in which EpCAM was knocked out. On the whole, these results indicate that EpMab‑37‑mG_2a‑f may exert antitumor activities against EpCAM‑positive cancers and may thus be a promising therapeutic regimen for colorectal cancer.

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.

The Role of Podoplanin in the Immune System and Inflammation

Podoplanin is a small cell-surface mucin-like glycoprotein that participates in multiple physiological and pathological processes. Podoplanin exerts an important function in the immune response and is upregulated in fibroblasts, macrophages, T helper cells, and epithelial cells during inflammation. Herein, we summarize the latest knowledge on the functional expression of podoplanin in the immune system and review the contribution of podoplanin to several inflammatory diseases. Furthermore, we discuss podoplanin as a novel therapeutic target for various inflammatory diseases.

Development of a Novel Anti-EpCAM Monoclonal Antibody for Various Applications

The epithelial cell adhesion molecule (EpCAM) is a cell surface glycoprotein, which is widely expressed on normal and cancer cells. EpCAM is involved in cell adhesion, proliferation, survival, stemness, and tumorigenesis. Therefore, EpCAM is thought to be a promising target for cancer diagnosis and therapy. In this study, we established anti-EpCAM monoclonal antibodies (mAbs) using the Cell-Based Immunization and Screening (CBIS) method. We characterized them using flow cytometry, Western blotting, and immunohistochemistry. One of the established recombinant anti-EpCAM mAbs, recEpMab-37 (mouse IgG₁, kappa), reacted with EpCAM-overexpressed Chinese hamster ovary-K1 cells (CHO/EpCAM) or a colorectal carcinoma cell line (Caco-2). In contrast, recEpMab-37 did not react with EpCAM-knocked out Caco-2 cells. The K_D of recEpMab-37 for CHO/EpCAM and Caco-2 was 2.0 × 10⁻⁸ M and 3.2 × 10⁻⁸ M, respectively. We observed that EpCAM amino acids between 144 to 164 are involved in recEpMab-37 binding. In Western blot analysis, recEpMab-37 detected the EpCAM of CHO/EpCAM and Caco-2 cells. Furthermore, recEpMab-37 could stain formalin-fixed paraffin-embedded colorectal carcinoma tissues by immunohistochemistry. Taken together, recEpMab-37, established by the CBIS method, is useful for detecting EpCAM in various applications.

Development of a Novel Anti-CD44 Monoclonal Antibody for Multiple Applications against Esophageal Squamous Cell Carcinomas

CD44 is a cell surface glycoprotein, which is expressed on normal cells, and overexpressed on cancer cells. CD44 is involved in cell adhesion, migration, proliferation, survival, stemness, and chemo-resistance. Therefore, CD44 is thought to be a promising target for cancer diagnosis and therapy. In this study, we established anti-CD44 monoclonal antibodies (mAbs) by immunizing mice with a CD44 variant (CD44v3-10) ectodomain and screening using enzyme-linked immunosorbent assay. We then characterized them using flow cytometry, Western blotting, and immunohistochemistry. One of the established clones (C₄₄Mab-46; IgG₁, kappa) reacted with CD44 standard isoform (CD44s)-overexpressed Chinese hamster ovary-K1 cells (CHO/CD44s) or esophageal squamous cell carcinoma (ESCC) cell lines (KYSE70 and KYSE770). The apparent K_D of C₄₄Mab-46 for CHO/CD44s, KYSE70, and KYSE770 was 1.1 × 10^-8 M, 4.9 × 10^-8 M, and 4.1 × 10^-8 M, respectively. C₄₄Mab-46 detected CD44s of CHO/CD44s and KYSE70, and CD44 variants of KYSE770 in Western blot analysis. Furthermore, C₄₄Mab-46 strongly stained the formalin-fixed paraffin-embedded ESCC tissues in immunohistochemistry. Collectively, C₄₄Mab-46 is very useful for detecting CD44 in various applications.

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.

Establishment of a monoclonal antibody against glycosylated CD271 specific for cancer cells in immunohistochemistry

Various proteins are highly expressed in cancer (e.g., epidermal growth factor receptor); however, the majority are also expressed in normal cells, although they may differ in expression intensity. Recently, we reported that CD271 (nerve growth factor receptor), a glycosylated protein, increases malignant behavior of cancer, particularly stemlike phenotypes in squamous cell carcinoma (SCC). CD271 is expressed in SCC and in normal epithelial basal cells. Glycosylation alterations generally occur in cancer cells; therefore, we attempted to establish a cancer‐specific anti‐glycosylated CD271 antibody. We purified recombinant glycosylated CD271 protein, immunized mice with the protein, and screened hybridomas using an ELISA assay with cancer cell lines. We established a clone G4B1 against CD271 which is glycosylated with O‐glycan and sialic acid. The G4B1 antibody reacted with the CD271 protein expressed in esophageal cancer, but not in normal esophageal basal cells. This specificity was confirmed in hypopharyngeal and cervical cancers. G4B1 antibody recognized the fetal esophageal epithelium and Barrett's esophagus, which possess stem cell–like characteristics. In conclusion, G4B1 antibody could be useful for precise identification of dysplasia and cancer cells in SCC.

TrMab-6 Exerts Antitumor Activity in Mouse Xenograft Models of Breast Cancers

Trophoblast cell surface antigen 2 (TROP2) has been reported to be overexpressed in many cancers, and is involved in cancer cell proliferation, invasion, and metastasis. We previously developed a highly sensitive anti-TROP2 monoclonal antibody (mAb) (clone TrMab-6; mouse IgG_2b, kappa) using a Cell-Based Immunization and Screening method. TrMab-6 is useful for investigations using flow cytometry, Western blotting, and immunohistochemistry and possesses antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against TROP2-expressing triple-negative breast cancer (TNBC) cell lines, such as MDA-MB-231 and MDA-MB-468. This study investigated whether TrMab-6 possesses in vivo antitumor activities via ADCC/CDC activities using mouse xenograft models of TNBC cell lines. In vivo experiments on MDA-MB-231 and MDA-MB-468 xenografts revealed that TrMab-6 significantly reduced tumor growth compared with normal mouse IgG treatment. The findings of this study suggest that TrMab-6 is a promising treatment option for TROP2-expressing TNBC.

Roles of Podoplanin in Malignant Progression of Tumor

Podoplanin (PDPN) is a cell-surface mucin-like glycoprotein that plays a critical role in tumor development and normal development of the lung, kidney, and lymphatic vascular systems. PDPN is overexpressed in several tumors and is involved in their malignancy. PDPN induces platelet aggregation through binding to platelet receptor C-type lectin-like receptor 2. Furthermore, PDPN modulates signal transductions that regulate cell proliferation, differentiation, migration, invasion, epithelial-to-mesenchymal transition, and stemness, all of which are crucial for the malignant progression of tumor. In the tumor microenvironment (TME), PDPN expression is upregulated in the tumor stroma, including cancer-associated fibroblasts (CAFs) and immune cells. CAFs play significant roles in the extracellular matrix remodeling and the development of immunosuppressive TME. Additionally, PDPN functions as a co-inhibitory molecule on T cells, indicating its involvement with immune evasion. In this review, we describe the mechanistic basis and diverse roles of PDPN in the malignant progression of tumors and discuss the possibility of the clinical application of PDPN-targeted cancer therapy, including cancer-specific monoclonal antibodies, and chimeric antigen receptor T technologies.

The Role of Podoplanin in Skin Diseases

Podoplanin is a sialomucin-like type I transmembrane receptor glycoprotein that is expressed specifically in lymphatic vessels, sebaceous glands, and hair follicles in normal skin. However, under pathological conditions podoplanin expression is upregulated in various cells, such as keratinocytes, fibroblasts, tumor cells, and inflammatory cells, and plays pivotal roles in different diseases. In psoriasis, podoplanin expression is induced in basal keratinocytes via the JAK-STAT pathway and contributes toward epidermal hyperproliferation. Podoplanin expression on keratinocytes can also promote IL-17 secretion from lymphocytes, promoting chronic inflammation. During wound healing, the podoplanin/CLEC-2 interaction between keratinocytes and platelets regulates re-epithelialization at the wound edge. In skin cancers, podoplanin expresses on tumor cells and promotes their migration and epithelial-mesenchymal transition, thereby accelerating invasion and metastasis. Podoplanin is also expressed in normal peritumoral cells, such as cancer-associated fibroblasts in melanoma and keratinocytes in extramammary Paget's disease, which promote tumor progression and predict aggressive behavior and poor prognosis. This review provides an overview of our current understanding of the mechanisms via which podoplanin mediates these pathological skin conditions.

Epitope Mapping of an Anti-CD20 Monoclonal Antibody (C20Mab-60) Using the HisMAP Method

CD20 is one of the B-lymphocyte antigens and an effective target for the detection and treatment of B cell lymphomas; specific and sensitive monoclonal antibodies (mAbs) are required thus for their diagnosis. Recently, we developed a novel anti-CD20 mAb (clone C₂₀Mab-60), which is not only useful for flow cytometry but also for Western blot and immunohistochemical analyses. However, the epitope of C₂₀Mab-60 has not been determined. To clarify the binding region of mAbs against their target molecules, it is essential to understand the pharmacological function of each mAb. In this study, we aimed to identify the epitope of C₂₀Mab-60 for CD20 using the novel histidine tag (His-tag) insertion for epitope mapping (HisMAP) method. We first established an anti-His-tag mAb, HisMab-1 (mouse IgG_2b, kappa), by immunizing mice with recombinant proteins containing an N-terminal His-tag. Although HisMab-1 detected the 4x, 5x, and 6xHis tag-inserted CD20 proteins using flow cytometry, 5xHis tag was selected. While HisMab-1 recognized all the 5xHis tag-inserted CD20 from the 142nd to the 183rd amino acid (aa), C₂₀Mab-60 did not react with the 5xHis tag-inserted CD20 from the 171st to the 174th aa. These results indicate that the main epitope of C₂₀Mab-60 for CD20 is a peptide from 171st to 174th aa of CD20. HisMAP method could be advantageous in the determination of the critical epitope of functional mAbs against many target molecules.

Epitope Mapping of an Anti-Human Epidermal Growth Factor Receptor Monoclonal Antibody (EMab-51) Using the RIEDL Insertion for Epitope Mapping Method

The classic method for identifying the epitope that monoclonal antibodies (mAbs) bind uses deletion mutants and point mutants of the target protein. However, determining the epitope of mAbs-reactive membrane proteins is often challenging. We recently developed the RIEDL insertion for epitope mapping (REMAP) method to identify mAb-binding epitopes. Herein, we first checked the reactivity of an anti-epidermal growth factor receptor (EGFR) mAb (EMab-51) to several EGFR deletion mutants such as EGFR/dN152, EGFR/dN313, EGFR/dN370, EGFR/dN375, EGFR/dN380, and EGFR/dN482. We found the N-terminus of the EMab-51-binding epitope between residues 375 and 380 of EGFR. We next produced EGFR/dN313 mutants with the RIEDL peptide tag inserted at each possible position of ₃₇₅-AFRGDSFTHTPPLDP-₃₈₉. EMab-51 lost its reactivity with the mutants having a RIEDL tag inserted at each position of ₃₇₇-RGDSFTHTPP-₃₈₆, whereas LpMab-7 (an anti-RIEDL mAb) detected every mutant. Thus, using the REMAP method, we identified the EMab-51-binding epitope of EGFR as ₃₇₇-RGDSFTHTPP-₃₈₆.

Development of a Novel Epitope Mapping System: RIEDL Insertion for Epitope Mapping Method

To clarify the binding region of monoclonal antibodies (mAbs) to target molecules, it is very essential to understand the pharmacological function of each mAb. Although deletion mutants and point mutants are usefully utilized for epitope mapping, we often experience the difficulty of determining the mAb epitope against membrane proteins. We aimed to develop a novel method to determine the binding region of mAbs using epitope tag system. We first checked the reactivity of an anti-CD44 mAb (C₄₄Mab-5) to several deletion mutants of CD44. We then employed the RIEDL tag system ("RIEDL" peptide and LpMab-7 mAb). We inserted the "RIEDL" peptide into the CD44 protein from the 21st to 41st amino acid (AA). The transfectants produced were stained by LpMab-7 and C₄₄Mab-5 in flow cytometry. C₄₄Mab-5 did not react with 30th-361st AA of the deletion mutant of CD44. Furthermore, the reaction of C₄₄Mab-5 to RIEDL tag-inserted CD44 from 25th to 36th AA was lost, although LpMab-7 detected most of the RIEDL tag-inserted CD44 from 21st to 41st AA. The epitope of C₄₄Mab-5 for CD44 was determined to be the peptide from 25th to 36th AA of CD44 using RIEDL insertion for epitope mapping (REMAP) method. The REMAP method might be useful for determining the critical epitope of functional mAbs against many target molecules.

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.

Deregulation of extracellular matrix modeling with molecular prognostic markers revealed by transcriptome sequencing and validations in Oral Tongue squamous cell carcinoma

Oral Tongue Squamous Cell Carcinoma (OTSCC), a distinct sub-group of head and neck cancers, is characteristically aggressive in nature with a higher incidence of recurrence and metastasis. Recent advances in therapeutics have not improved patient survival. The phenomenon of occult node metastasis, even among the purportedly good prognosis group of early-stage and node-negative tongue tumors, leads to a high incidence of locoregional failure in OTSCC which needs to be addressed. In the current study, transcriptome analysis of OTSCC patients identified the key genes and deregulated pathways. A panel of 26 marker genes was shortlisted and validated using real-time PCR in a prospective cohort of 100 patients. The gene expression was correlated with clinicopathological features including occult node metastasis, survival, and therapeutic outcome. The up-regulation of a panel of 6 genes namely, matrix metalloproteinase 9 (MMP9), Laminin subunit Gamma 2 (LAMC2), Desmoglein 2 (DSG2), Plasminogen Activator Urokinase (PLAU), Forkhead Box M1 (FOXM1), and Myosin 1B (MYO1B) was associated with failure of treatment in the early stage (T1, T2). Up-regulation of Tenacin C (TNC) and Podoplanin (PDPN) was significantly correlated with occult node positivity. Immunohistochemical analysis of LAMC2, MMP9, and E-Cadherin (ECAD) confirmed these markers to be indicators of poor prognosis. We propose this panel of valuable prognostic markers can be clinically useful to identify poor prognosis and occult node metastasis in OTSCC patients.

Effects of Maackia amurensis seed lectin (MASL) on oral squamous cell carcinoma (OSCC) gene expression and transcriptional signaling pathways

PURPOSE

Oral cancer causes over 120,000 deaths annually and affects the quality of life for survivors. Over 90% of oral cancers are derived from oral squamous cell carcinoma cells (OSCCs) which are generally resistant to standard cytotoxic chemotherapy agents. OSCC cells often exhibit increased TGFβ and PDPN receptor activity compared to nontransformed oral epithelial cells. Maackia amurensis seed lectin (MASL) can target the PDPN receptor and has been identified as a novel agent that can be used to treat oral cancer. However, mechanisms by which MASL inhibits OSCC progression are not yet clearly defined.

METHODS

Here, we performed cell migration and cytotoxicity assays to assess the effects of MASL on OSCC motility and viability at physiologically relevant concentrations. We then performed comprehensive transcriptome analysis combined with transcription factor reporter assays to investigate the how MASL affects OSCC gene expression at these concentration. Key data were then confirmed by western blotting to evaluate the effects of MASL on gene expression and kinase signaling activity at the protein level.

RESULTS

MASL significantly affected the expression of about 27% of approximately 15,000 genes found to be expressed by HSC-2 cells used to model OSCC cells in this study. These genes affected by MASL include members of the TGFβ-SMAD, JAK-STAT, and Wnt-βCTN signaling pathways. In particular, MASL decreased expression of PDPN, SOX2, and SMAD5 at the RNA and protein levels. MASL also inhibited SMAD and MAPK activity, and exhibited potential for combination therapy with doxorubicin and 5-fluorouracil.

CONCLUSIONS

Taken together, results from this study indicate that MASL decreases activity of JAK-STAT, TGFβ-SMAD, and Wnt-βCTN signaling pathways to inhibit OSCC growth and motility. These data suggest that further studies should be undertaken to determine how MASL may also be used alone and in combination with other agents to treat oral cancer.

Anti‑EpCAM monoclonal antibody exerts antitumor activity against oral squamous cell carcinomas

The epithelial cell adhesion molecule (EpCAM) is a calcium-independent, homophilic, intercellular adhesion factor classified as a transmembrane glycoprotein. In addition to cell adhesion, EpCAM also contributes to cell signaling, differentiation, proliferation, and migration. EpCAM is an essential factor in the carcinogenesis of numerous human cancers. In the present study, we developed and validated an anti-EpCAM monoclonal antibody (mAb), EpMab-16 (IgG_2a, kappa), by immunizing mice with EpCAM-overexpressing CHO-K1 cells. EpMab-16 specifically reacted with endogenous EpCAM in oral squamous cell carcinoma (OSCC) cell lines in flow cytometry and Western blot analyses. It exhibited a plasma membrane-like stain pattern in OSCC tissues upon immunohistochemical analysis. The K_D for EpMab-16 in SAS and HSC-2 OSCC cells were assessed via flow cytometry at 1.1×10⁻⁸ and 1.9×10⁻⁸ M, respectively, suggesting moderate binding affinity of EpMab-16 for EpCAM. We then assessed whether the EpMab-16 induced antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against OSCC cell lines, and antitumor capacity in a murine xenograft model. In vitro experiments revealed strong ADCC and CDC inducement against OSCC cells treated with EpMab-16. In vivo experiments on OSCC xenografts revealed that EpMab-16 treatment significantly reduced tumor growth compared with the control mouse IgG. These data indicated that EpMab-16 could be a promising treatment option for EpCAM-expressing OSCCs.

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.

Anti‑EGFR monoclonal antibody 134‑mG2a exerts antitumor effects in mouse xenograft models of oral squamous cell carcinoma

The epidermal growth factor receptor (EGFR), a transmembrane receptor and member of the human epidermal growth factor receptor (HER) family of receptor tyrosine kinases, is a critical mediator of cell growth and differentiation. EGFR forms homo- or heterodimers with other HER family members to activate downstream signaling cascades in a number of cancer cells. In a previous study, the authors established an anti-EGFR monoclonal antibody (mAb), EMab-134, by immunizing mice with the ectodomain of human EGFR. EMab-134 binds specifically to endogenous EGFR and can be used to detect receptor on oral cancer cell lines by flow cytometry and western blot analysis; this antibody is also effective for the immunohistochemical evaluation of oral cancer tissues. In the present study, the subclass of EMab-134 was converted from IgG₁ to IgG_2a (134-mG_2a) to facilitate antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). The dissociation constants (K_Ds) of EMab-134 and 134-mG_2a against EGFR-expressing CHO-K1 (CHO/EGFR) cells were deter-mined by flow cytometry to be 3.2×10⁻⁹ M and 2.1×10⁻⁹ M, respectively; these results indicate that 134-mG_2a has a higher binding affinity than EMab-134. The 134-mG_2a antibody was more sensitive than EMab-134 with respect to antigen detection in oral cancer cells in both western blot analysis and immunohistochemistry applications. Analysis in vitro revealed that 134-mG_2a contributed to high levels of ADCC and CDC in experiments targeting CHO/EGFR, HSC-2, and SAS cells. Moreover, the in vivo administration of 134-mG_2a significantly inhibited the development of CHO/EGFR, HSC-2, and SAS mouse xenografts in comparison to the results observed in response to EMab-134. Taken together, the findings of the present study demonstrate that the newly-formulated 134-mG_2a is useful for detecting EGFR by flow cytometry, western blot analysis and immunohistochemistry. Furthermore, the in vivo results suggested that it may also be useful as part of a therapeutic regimen for patients with EGFR-expressing oral cancer.

A defucosylated anti-PD-L1 monoclonal antibody 13-mG2a-f exerts antitumor effects in mouse xenograft models of oral squamous cell carcinoma

Programmed cell death ligand-1 (PD-L1) is a type I transmembrane glycoprotein expressed on antigen-presenting cells and several tumor cells, including melanoma and lung cancer cells. A strong correlation has been reported between PD-L1 expression in tumor cells and negative prognosis in cancer patients. Previously, we established an anti-PD-L1 monoclonal antibody (mAb), L₁Mab-13 (IgG₁, kappa), by immunizing mice with PD-L1-overexpressing CHO-K1 cells. L₁Mab-13 specifically reacts with endogenous PD-L1 in lung cancer cell lines in flow cytometry and Western blot applications, and stains a plasma membrane-like pattern in lung cancer tissues via immunohistochemical analysis. In this study, we investigated whether L₁Mab-13 reacts with oral cancer cell lines and exerts antitumor activities. Because L₁Mab-13 lacks antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), we first converted the subclass of L₁Mab-13 from IgG₁ into IgG_2a (13-mG_2a), and further produced a defucosylated version (13-mG_2a-f) using FUT8-deficient ExpiCHO-S (BINDS-09) cells. Defucosylation of 13-mG_2a-f was confirmed using fucose-binding lectins, such as Aleuria aurantia and Pholiota squarrosa lectins. The dissociation constants (K _D) for 13-mG_2a-f in SAS and HSC-2 oral cancer cells were determined via flow cytometry to be 2.8 × 10^-9 M and 4.8 × 10^-9 M, respectively, indicating that 13-mG_2a-f possesses extremely high binding affinity. In vitro analysis demonstrated that 13-mG_2a-f showed moderate ADCC and CDC activities against SAS and HSC-2 oral cancer cells. In vivo analysis revealed that 13-mG_2a-f significantly reduced tumor development in SAS and HSC-2 xenografts in comparison to control mouse IgG, even after injection seven days post-tumor inoculation. Taken together, these data demonstrate that treatment with 13-mG_2a-f may represent a useful therapy for patients with PD-L1-expressing oral cancers.

A defucosylated anti‑CD44 monoclonal antibody 5‑mG2a‑f exerts antitumor effects in mouse xenograft models of oral squamous cell carcinoma

CD44 is widely expressed on the surface of most tissues and all hematopoietic cells, and regulates many genes associated with cell adhesion, migration, proliferation, differentiation, and survival. CD44 has also been studied as a therapeutic target in several cancers. Previously, an anti-CD44 monoclonal antibody (mAb), C₄₄Mab-5 (IgG₁, kappa) was established by immunizing mice with CD44-overexpressing Chinese hamster ovary (CHO)-K1 cells. C₄₄Mab-5 recognized all CD44 isoforms, and showed high sensitivity for flow cytometry and immunohistochemical analysis in oral cancers. However, as the IgG₁ subclass of C₄₄Mab-5 lacks antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC), the antitumor activity of C₄₄Mab-5 could not be determined. In the present study, we converted the mouse IgG₁ subclass antibody C₄₄Mab-5 into an IgG_2a subclass antibody, 5-mG_2a, and further produced a defucosylated version, 5-mG_2a-f, using FUT8-deficient ExpiCHO-S (BINDS-09) cells. Defucosylation of 5-mG_2a-f was confirmed using fucose-binding lectins, such as AAL and PhoSL. The dissociation constants (K_D) for 5-mG_2a-f against SAS and HSC-2 oral cancer cells were determined through flow cytometry to be 2.8×10⁻¹⁰ M and 2.6×10⁻⁹ M, respectively, indicating that 5-mG_2a-f possesses extremely high binding affinity. Furthermore, immunohistochemical staining using 5-mG_2a-f specifically stained the membranes of oral cancer cells. In vitro analysis demonstrated that 5-mG_2a-f showed moderate ADCC and CDC activities against SAS and HSC-2 oral cancer cells. In vivo analysis revealed that 5-mG_2a-f significantly reduced tumor development in SAS and HSC-2 ×enografts in comparison to control mouse IgG, even after injection seven days post-tumor inoculation. Collectively, these results suggest that treatment with 5-mG_2a-f may represent a useful therapy for patients with CD44-expressing oral 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.

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.

Establishment of a monoclonal antibody PMab-225 against alpaca podoplanin for immunohistochemical analyses

Podoplanin (PDPN) is known as a lymphatic endothelial cell marker. Monoclonal antibodies (mAbs) against human, mouse, rat, rabbit, dog, cat, bovine, pig, and horse PDPN have been established in our previous studies. However, mAbs against alpaca PDPN (aPDPN), required for immunohistochemical analysis, remain to be developed. In the present study, we employed the Cell-Based Immunization and Screening (CBIS) method for producing anti-aPDPN mAbs. We immunized mice with aPDPN-overexpressing Chinese hamster ovary (CHO)-K1 cells (CHO/aPDPN), and hybridomas producing mAbs against aPDPN were screened using flow cytometry. One of the mAbs, PMab-225 (IgG_2b, kappa), specifically detected CHO/aPDPN cells via flow cytometry and recognized the aPDPN protein on Western blotting. Further, PMab-225 strongly stained lung type I alveolar cells, colon lymphatic endothelial cells, and kidney podocytes via immunohistochemistry. These findings demonstrate that PMab-225 antibody is useful to investigate the function of aPDPN via different techniques.

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PDPN is known as a specific lymphatic endothelial cell (LEC) marker.

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Sensitive and specific PMab-225 mAb against alpaca PDPN was produced.

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PMab-225 strongly reacted with alpaca PDPN in flow cytometry.

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PMab-225 is useful for IHC using paraffin-embedded cell sections.

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.

Roles of the CLEC-2-podoplanin interaction in tumor progression

Podoplanin is a type-I transmembrane sialomucin-like glycoprotein expressed on the surface of several kinds of tumor cells. The podoplanin receptor is a platelet activation receptor known as C-type lectin-like receptor 2 (CLEC-2), which has been identified as a receptor for the platelet-activating snake venom protein rhodocytin. CLEC-2 is highly expressed in platelets and megakaryocytes and expressed at lower levels in liver Kupffer cells. Podoplanin is expressed in certain types of tumor cells, including squamous cell carcinomas, seminomas, and brain tumors. Podoplanin is also expressed in a wide range of normal cells, including fibroblastic reticular cells in lymph nodes, kidney podocytes, and lymphatic endothelial cells, but not vascular endothelial cells. Metastasis of podoplanin-positive lung tumors injected from the tail vein is greatly inhibited in CLEC-2-depleted mice or in anti-podoplanin antibody-treated mice. These findings suggest that the CLEC-2-podoplanin interaction facilitates hematogenous tumor metastasis. Platelets may increase the survival of tumor cells by covering tumor cells and physically protecting them from shear stress or immune cells in the bloodstream. Alternatively, platelets may stimulate the epithelial-mesenchymal transition of tumor cells to facilitate their extravasation from blood vessels. Cell proliferation is stimulated in podoplanin-expressing tumor cells by the coculture with platelets, but the effects of the CLEC-2-podoplanin interaction on tumor growth in vivo are not yet resolved. It is possible that the CLEC-2-podoplanin interaction facilitates tumor-related thrombosis, subsequent inflammation, inflammation-induced cachexia, and reduced survival. Considering these findings, anti-podoplanin and anti-CLEC-2 drugs are promising therapies for the prevention of tumor metastasis, progression, and tumor-related symptoms, which may result in longer survival in cancer patients. There are advantages and disadvantages of anti-podoplanin vs. anti-CLEC-2 therapy. Side effects in podoplanin-expressing normal tissues due to treatment with anti-podoplanin and temporal thrombocytopenia due to treatment with anti-CLEC2 are potential problems, although solutions to these problems have been reported.

Podoplanin: An emerging cancer biomarker and therapeutic target

Podoplanin (PDPN) is a transmembrane receptor glycoprotein that is upregulated on transformed cells, cancer associated fibroblasts and inflammatory macrophages that contribute to cancer progression. In particular, PDPN increases tumor cell clonal capacity, epithelial mesenchymal transition, migration, invasion, metastasis and inflammation. Antibodies, CAR-T cells, biologics and synthetic compounds that target PDPN can inhibit cancer progression and septic inflammation in preclinical models. This review describes recent advances in how PDPN may be used as a biomarker and therapeutic target for many types of cancer, including glioma, squamous cell carcinoma, mesothelioma and melanoma.

Anti-podocalyxin antibody exerts antitumor effects via antibody-dependent cellular cytotoxicity in mouse xenograft models of oral squamous cell carcinoma

Podocalyxin (PODXL) overexpression is associated with progression, metastasis, and poor outcomes in cancers. We recently produced the novel anti-PODXL monoclonal antibody (mAb) PcMab-47 (IgG₁, kappa). Herein, we engineered PcMab-47 into 47-mG_2a, a mouse IgG_2a-type mAb, to add antibody-dependent cellular cytotoxicity (ADCC). We further developed 47-mG_2a-f, a core fucose-deficient type of 47-mG_2a to augment its ADCC. Immunohistochemical analysis of oral cancer tissues using PcMab-47 and 47-mG_2a revealed that the latter stained oral squamous cell carcinoma (OSCC) cells in a cytoplasmic pattern at a much lower concentration. PcMab-47 and 47-mG_2a detected PODXL in 163/201 (81.1%) and in 197/201 (98.0%) OSCC samples, respectively. 47-mG_2a-f also detected PODXL in OSCCs at a similar frequency as 47-mG_2a. In vitro analysis revealed that both 47-mG_2a and 47-mG_2a-f exhibited strong complement-dependent cytotoxicity (CDC) against CHO/hPODXL cells. In contrast, 47-mG_2a-f exhibited much stronger ADCC than 47-mG_2a against OSCC cells, indicating that ADCC and CDC of those anti-PODXL mAbs depend on target cells. In vivo analysis revealed that both 47-mG_2a and 47-mG_2a-f exerted antitumor activity in CHO/hPODXL xenograft models at a dose of 100 μg or 500 μg/mouse/week administered twice. 47-mG_2a-f, but not 47-mG_2a, exerted antitumor activity in SAS and HSC-2 xenograft models at a dose of 100 μg/mouse/week administered three times. Although both 47-mG_2a and 47-mG_2a-f exerted antitumor activity in HSC-2 xenograft models at a dose of 500 μg/mouse/week administered twice, 47-mG_2a-f also showed higher antitumor activity than 47-mG_2a. These results suggested that a core fucose-deficient anti-PODXL mAb could be useful for antibody-based therapy against PODXL-expressing OSCCs.

Expression and Dynamics of Podoplanin in Cultured Osteoblasts with Mechanostress and Mineralization Stimulus

This study investigates the significance of the expression and dynamics of podoplanin in mechanostress and mineralization in cultured murine osteoblasts. Podoplanin increased in osteoblasts subjected to straining in non-mineralization medium, suggesting that the mechanostress alone is a podoplanin induction factor. In osteoblasts subjected to vertical elongation straining in the mineralization medium, the mRNA amounts of podoplanin, osteopontin, and osteocalcin were significantly larger than those in cells not subjected to straining, suggesting that mechanostress is the cause of a synergistic effect in the expression of these proteins. In osteoblasts in the mineralization medium, significant increases in osteocalcin mRNA occurred earlier in cells subjected to straining than in the cells not subjected to straining, suggesting that the mechanostress is a critical factor to enhance the expression of osteocalcin. Western blot and ELISA analysis showed increased podoplanin production in osteoblasts with longer durations of straining. There was significantly less mineralization product in osteoblasts with antibodies for podoplanin, osteopontin, and osteocalcin. There was also less osteopontin and osteocalcin produced in osteoblasts with anti-podoplanin. These findings suggest that mechanostress induces the production of podoplanin in osteoblasts and that podoplanin may play a role in mineralization in cooperation with bone-associated proteins.

Podoplanin emerges as a functionally relevant oral cancer biomarker and therapeutic target

Oral cancer has become one of the most aggressive types of cancer, killing 140,000 people worldwide every year. Current treatments for oral cancer include surgery and radiation therapies. These procedures can be very effective; however, they can also drastically decrease the quality of life for survivors. New chemotherapeutic treatments are needed to more effectively combat oral cancer. The transmembrane receptor podoplanin (PDPN) has emerged as a functionally relevant oral cancer biomarker and chemotherapeutic target. PDPN expression promotes tumor cell migration leading to oral cancer invasion and metastasis. Here, we describe the role of PDPN in oral squamous cell carcinoma progression, and how it may be exploited to prevent and treat oral cancer.

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.

Establishment of CMab-43, a Sensitive and Specific Anti-CD133 Monoclonal Antibody, for Immunohistochemistry

CD133, also known as prominin-1, was first described as a cell surface marker on early progenitor and hematopoietic stem cells. It is a five-domain transmembrane protein composed of an N-terminal extracellular tail, two small cytoplasmic loops, two large extracellular loops containing seven potential glycosylation sites, and a short C-terminal intracellular tail. CD133 has been used as a marker to identify cancer stem cells derived from primary solid tumors and as a prognostic marker of gliomas. Herein, we developed novel anti-CD133 monoclonal antibodies (mAbs) and characterized their efficacy in flow cytometry, Western blot, and immunohistochemical analyses. We expressed the full length of CD133 in LN229 glioblastoma cells, immunized mice with LN229/CD133 cells, and performed the first screening using flow cytometry. After limiting dilution, we established 100 anti-CD133 mAbs, reacting with LN229/CD133 cells but not with LN229 cells. Subsequently, we performed the second and third screening with Western blot and immunohistochemical analyses, respectively. Among 100 mAbs, 11 strongly reacted with CD133 in Western blot analysis. One of 11 clones, CMab-43 (IgG_2a, kappa), showed a sensitive and specific reaction against colon cancer cells, warranting the use of CMab-43 in detecting CD133 in pathological analyses of CD133-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.