A cancer-specific monoclonal antibody recognizes the aberrantly glycosylated podoplanin. Sci Rep. 2014;4:5924. [PMID: 25080943 PMCID: PMC4118152 DOI: 10.1038/srep05924]

Neoadjuvant chemoradiation changes podoplanin expression in esophageal cancer patients

BACKGROUND

Locally advanced adenocarcinoma of the esophagus (EAC) and squamous cell carcinoma (ESCC) result in a worse prognosis. Neoadjuvant treatment improves survival, however, only for responders. The transmembrane glycoprotein podoplanin is overexpressed in squamous cell carcinomas, miRNA-363 is associated to its regulation in head and neck cancer.

AIM

To predict therapy response and prognosis markers, and targets for novel therapies would individualize treatments leading to more favourable outcomes.

METHODS

Expression of podoplanin protein has been visualized by immunohistochemistry in surgical specimens of 195 esophageal cancer patients who underwent transthoracic esophagectomy: 90 ESCC and 105 EAC with clinical T2-3, Nx, M0. One hundred and six patients received neoadjuvant chemoradiation. RNA was extracted from paraffin-embedded tissue, and miRNA-363 quantified by real-time TaqMan-real-time-PCR. D2-40 mab staining of > 5% was scored as high podoplanin expression (HPE). We related podoplanin and miRNA-363 expression to histopathologic response after neoadjuvant treatment and clinicopathological characteristics, such as histological tumor type, survival rate or clinical tumor category.

RESULTS

We confirmed expression of membrane-bound podoplanin in 90 ESCC patients. 26% showed HPE of > 5%. In addition, absence in EAC patients (only 2% with HPE) was shown. Lower podoplanin expression has been detected in resection-specimen of 58 ESCC patients after neoadjuvant (RTx/CTx) treatment, only 11% with HPE, compared to 50% HPE of 32 non-pretreated primary surgery patients, P = 0.0001. This difference of podoplanin expression was confirmed comparing pre-treatment biopsies with matching post-treatment surgical specimens, P < 0.001. Podoplanin has been identified as a prognostic marker in 32 patients that underwent primary surgery without neoadjuvant treatment. Low (0-5%) podoplanin expression was associated with better prognosis compared to patients with HPE, P = 0.013. Podoplanin expression has been associated with post-transcriptional regulation by miRNA-363. At a cut-off value of miR-363 < 7, lower miR-363 expression correlated with HPE in surgical tissue specimens of primary surgery patients, P = 0.013. Therefore, ESCC patients with miRNA-363 expression < 7 had a worse prognosis than patients expressing miRNA-363 ≥ 7, P = 0.049.

CONCLUSION

Analysis of the molecular process that leads to decrease in podoplanin expression during neoadjuvant treatment and its regulation may provide novel markers and targets to improve targeted therapy of ESCC.

An Anti-Human Epidermal Growth Factor Receptor 2 Monoclonal Antibody H2Mab-19 Exerts Antitumor Activity in Mouse Colon Cancer Xenografts

Trastuzumab is a humanized antibody against human epidermal growth factor receptor 2 (HER2) that offers significant survival benefits to patients with HER2-overexpressing breast or gastric cancer. HER2 is also known to be overexpressed in colon cancers. In this study, a novel anti-HER2 monoclonal antibody (mAb), H₂Mab-19 (IgG_2b, κ) was characterized for its anticancer activity in colon cancers. H₂Mab-19 showed both antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity activities against Caco-2, a colon cancer cell line. Furthermore, H₂Mab-19 significantly reduced tumor development in a Caco-2 xenograft model. These results suggest that treatment with H₂Mab-19 may be a useful therapy for patients with HER2-expressing colon cancers.

Establishment of C20Mab-11, a novel anti-CD20 monoclonal antibody, for the detection of B cells

CD20 is one of several B-lymphocyte antigens that has been shown to be an effective target for the detection and treatment of B-cell lymphomas. Sensitive and specific monoclonal antibodies (mAbs) are required for every application used for the diagnosis of B-cell lymphoma. Although many anti-CD20 mAbs have been established, the types of applications, those anti-CD20 can be used in, are limited. In this study, we aimed to establish novel anti-CD20 mAbs to be used for broad applications, such as flow cytometry, western blot, and immunohistochemical analyses, using the Cell-Based Immunization and Screening (CBIS) method. One of the established mAbs, C₂₀Mab-11 (IgM, kappa), detected overexpression of CD20 in CHO-K1 or LN229 cell lines, indicating that C₂₀Mab-11 is specific for CD20. In western blot analyses, C₂₀Mab-11 detected not only overexpression of CD20 in CHO-K1 or LN229 cell lines, but also CD20 of BALL-1 and Raji cells with both sensitivity and specificity. Furthermore, C₂₀Mab-11 strongly stained B cells of the lymph follicle and B cell lymphomas in immunohistochemical analyses. These results indicate that C₂₀Mab-11 develped by CBIS method, is useful for the detection of CD20 in lymphoma tissues by flow cytometry, western blot, and immunohistochemical analyses and potentially could be beneficial for the treatment of B cell lymphomas.

Thr80 of Sheep Podoplanin Is a Critical Epitope of the Antisheep Podoplanin Monoclonal Antibody: PMab-256

An antisheep podoplanin (sPDPN) monoclonal antibody (mAb), PMab-256, has recently been established. PMab-256 shows positive immunostaining for lymphatic endothelial cells, lung type I alveolar cells, and kidney podocytes. PDPN possesses three platelet-aggregation-stimulating (PLAG) domains, PLAG1, PLAG2, and PLAG3, and a PLAG-like domain (PLD). The binding epitope of many anti-PDPN mAbs is located in PLAG domains or PLD. The purpose of this study is to determine the binding epitope of PMab-256. Analysis of sPDPN deletion mutants revealed that the N-terminus of the PMab-256 epitope exists between amino acids 75 and 80 of sPDPN. Furthermore, analysis of sPDPN point mutations demonstrated that the critical epitope includes Thr80 of sPDPN, indicating that the PMab-256 epitope is in the PLD of sPDPN.

H2Mab-19 Anti-Human Epidermal Growth Factor Receptor 2 Monoclonal Antibody Therapy Exerts Antitumor Activity in Pancreatic Cancer Xenograft Models

Overexpression of human epidermal growth factor receptor 2 (HER2) has been reported in breast cancer, gastric, lung, colorectal, oral, and pancreatic cancers. HER2 expression is associated with poor clinical outcomes. An anti-HER2 humanized antibody, trastuzumab, has improved survival rates in patients with HER2-overexpressing breast and gastric cancers. Previously, we established a novel anti-HER2 monoclonal antibody (mAb), H₂Mab-19 (IgG_2b, kappa). It has also been characterized for breast, oral, and colon cancers. In this study, we investigated the antitumor activities of H₂Mab-19 in pancreatic cancer xenograft models. We selected MIA PaCa-2, a pancreatic cancer cell line which expresses HER2. H₂Mab-19 showed high binding affinity (K_D: 1.2 × 10^-8 M) against MIA PaCa-2 cells. Furthermore, H₂Mab-19 significantly reduced tumor development in a MIA PaCa-2 xenograft model. These results suggest that treatment with H₂Mab-19 may be a useful therapy for patients with HER2-expressing pancreatic cancers.

H2Mab-19, an anti-human epidermal growth factor receptor 2 monoclonal antibody exerts antitumor activity in mouse oral cancer xenografts

Human epidermal growth factor receptor 2 (HER2) is reported to be overexpressed in breast cancers and is associated with poor clinical outcome. Trastuzumab is a humanized anti-HER2 antibody that offers significant survival benefits to patients with HER2-overexpressing breast cancer. In this study, a novel anti-HER2 monoclonal antibody (mAb), H₂Mab-19 (IgG_2b, kappa) was developed. Antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and antitumor activity of H₂Mab-19 were investigated using both breast cancer and oral cancer cell lines. H₂Mab-19 demonstrated cytotoxicity in BT-474 (a human breast cancer cell line) and HSC-2 or SAS (human oral cancer cell lines). H₂Mab-19 also possessed both ADCC and CDC activity against BT-474, HSC-2, and SAS cell lines. In comparison to control mouse IgG, H₂Mab-19 significantly reduced tumor development in BT-474, HSC-2, and SAS xenografts. Collectively, these results suggest that treatment with H₂Mab-19 may be a useful therapy for patients with HER2-expressing breast and 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.

Podoplanin expression is a prognostic biomarker but may be dispensable for the malignancy of glioblastoma

BACKGROUND

Treatment options of glioblastoma, the most aggressive primary brain tumor with frequent relapses and high mortality, are still very limited, urgently calling for novel therapeutic targets. Expression of the glycoprotein podoplanin correlates with poor prognosis in various cancer entities, including glioblastoma. Furthermore, podoplanin has been associated with tumor cell migration and proliferation in vitro; however, experimental data on its function in gliomagenesis in vivo are still missing. Hence, we have functionally investigated the impact of podoplanin on glioblastoma in a preclinical mouse model to evaluate its potential as a therapeutic target.

METHODS

Fluorescence activated cell sorting, genome-wide expression analysis, and clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9 (Cas9)-mediated deletion of podoplanin in patient-derived human glioblastoma cells were combined with organotypic brain slice cultures and intracranial injections into mice.

RESULTS

We defined a malignant gene signature in tumor cells with high podoplanin expression. The increase and/or maintenance of high podoplanin expression in serial transplantations and in podoplaninlow-sorted glioblastoma cells during outgrowth indicated the association of high podoplanin expression and poor outcome. Unexpectedly, similar rates of proliferation, apoptosis, angiogenesis, and invasion were observed in control and podoplanin-deleted tumors. Accordingly, neither tumor growth nor survival was affected upon podoplanin loss.

CONCLUSION

We report that tumor progression occurs independently of podoplanin. Thus, in contrast to previous suggestions, blocking of podoplanin does not represent a promising therapeutic approach. However, as podoplanin is associated with tumor aggressiveness and progression, we propose the cell surface protein as a biomarker for poor prognosis.

Targeted Phototherapy for Malignant Pleural Mesothelioma: Near-Infrared Photoimmunotherapy Targeting Podoplanin

Malignant pleural mesothelioma (MPM) has extremely limited treatment despite a poor prognosis. Moreover, molecular targeted therapy for MPM has not yet been implemented; thus, a new targeted therapy is highly desirable. Near-infrared photoimmunotherapy (NIR-PIT) is a recently developed cancer therapy that combines the specificity of antibodies for targeting tumors with toxicity induced by the photoabsorber after exposure to NIR-light. In this study, we developed a new phototherapy targeting podoplanin (PDPN) for MPM with the use of both NIR-PIT and an anti-PDPN antibody, NZ-1. An antibody–photosensitizer conjugate consisting of NZ-1 and phthalocyanine dye was synthesized. In vitro NIR-PIT-induced cytotoxicity was measured with both dead cell staining and luciferase activity on various MPM cell lines. In vivo NIR-PIT was examined in both the flank tumor and orthotopic mouse model with in vivo real-time imaging. In vitro NIR-PIT-induced cytotoxicity was NIR-light dose dependent. In vivo NIR-PIT led to significant reduction in both tumor volume and luciferase activity in a flank model (p < 0.05, NIR-PIT group versus NZ-1-IR700 group). The PDPN-targeted NIR-PIT resulted in a significant antitumor effect in an MPM orthotopic mouse model (p < 0.05, NIR-PIT group versus NZ-1-IR700 group). This study suggests that PDPN-targeted NIR-PIT could be a new promising treatment for MPM.

Epitope Mapping of PMab-241, a Lymphatic Endothelial Cell-Specific Anti-Bear Podoplanin Monoclonal Antibody

Anti-bear podoplanin (bPDPN) monoclonal antibodies (mAbs), including PMab-247 and PMab-241, have been previously established. Although PMab-247 has shown positive immunostaining for lymphatic endothelial cells (LECs), type I alveolar cells of the lung, and podocytes of the kidney, PMab-241 stains LECs but does not react with lung type I alveolar cells. PDPN possesses three platelet aggregation-stimulating (PLAG) domains (PLAG1, PLAG2, and PLAG3) and the PLAG-like domain (PLD). The binding epitope of PMab-247 was previously determined to include bPDPN residues Asp76, Arg78, Glu80, and Arg82. Among these, Glu80 and Arg82 are included in PLD of bPDPN. The purpose of this study is to determine the binding epitope of PMab-241 and to clarify the difference between these two anti-bPDPN mAbs. Analysis of bPDPN deletion mutants revealed that the N-terminus of the PMab-241 epitope exists between amino acids (aa) 75 and 80 of bPDPN. In addition, analysis of bPDPN point mutants demonstrated that the critical epitope of PMab-241 includes Thr75, Asp76, and Arg78 of bPDPN. The binding epitopes of PMab-241 and PMab-247 seem to overlap, but this slight difference may be sufficient to provide the specificity of PMab-241 to discriminate LECs from type I alveolar cells of the lung.

Platelets and cancer-associated thrombosis: focusing on the platelet activation receptor CLEC-2 and podoplanin

Patients with cancer have an increased risk of thromboembolism, which is the second leading cause of death in these patients. Several mechanisms of the prothrombotic state in these patients have been proposed. Among them are a platelet activation receptor, C-type lectin-like receptor 2 (CLEC-2), and its endogenous ligand podoplanin, which are the focus of this review. CLEC-2 is almost specifically expressed in platelets/megakaryocytes in humans. A membrane protein, podoplanin is expressed in certain types of cancer cells, including squamous cell carcinoma, brain tumor, and osteosarcoma, in addition to several normal tissues, including kidney podocytes and lymphatic endothelial cells but not vascular endothelial cells. In the bloodstream, podoplanin induces platelet activation by binding to CLEC-2 and facilitates hematogenous cancer metastasis and cancer-associated thrombosis. In an experimental lung metastasis model, the pharmacological depletion of CLEC-2 from platelets in mice resulted in a marked reduction of lung metastasis of podoplanin-expressing B16F10 cells. Control mice with B16F10 orthotopically inoculated in the back skin showed massive thrombus formation in the lungs, but the cancer-associated thrombus formation in CLEC-2-depleted mice was significantly inhibited, suggesting that CLEC-2-podoplanin interaction stimulates cancer-associated thrombosis. Thromboinflammation induced ectopic podoplanin expression in vascular endothelial cells or macrophages, which may also contribute to cancer-associated thrombosis. CLEC-2 depletion in cancer-bearing mice resulted in not only reduced cancer-associated thrombosis but also reduced levels of plasma inflammatory cytokines, anemia, and sarcopenia, suggesting that cancer-associated thrombosis may cause thromboinflammation and cancer cachexia. Blocking CLEC-2-podoplanin interaction may be a novel therapeutic strategy in patients with podoplanin-expressing cancer.

Antibody-Drug Conjugates Using Mouse-Canine Chimeric Anti-Dog Podoplanin Antibody Exerts Antitumor Activity in a Mouse Xenograft Model

Antibody-drug conjugates (ADCs), which consist of a monoclonal antibody (mAb), a linker, and a payload, can deliver a drug to cancer tissues. We previously produced an anti-dog podoplanin (dPDPN) mAb, PMab-38, which reacts with dPDPN-expressing canine melanomas and squamous cell carcinomas (SCCs), but not with dPDPN-expressing canine type I alveolar cells or lymphatic endothelial cells, indicating that PMab-38 possesses cancer specificity. In this study, we developed an ADC, P38B-DM1, using the mouse-canine chimeric anti-dPDPN antibody, P38B as the antibody, a peptide linker, and emtansine as the payload using the chemical conjugation by affinity peptide (CCAP) method. We investigated its cytotoxicity against dPDPN-overexpressed Chinese hamster ovary (CHO/dPDPN) cells in vitro and its antitumor activity using a mouse xenograft model of CHO/dPDPN cells. P38B-DM1 showed cytotoxicity to CHO/dPDPN cells in a dose-dependent manner in vitro. Furthermore, P38B-DM1 exhibited higher antitumor activity than P38B in the mouse xenograft model. These results suggest that P38B-DM1, developed using the CCAP method, is useful for antibody therapy against dPDPN-expressing canine SCCs and melanomas.

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.

[Development of cancer-specific monoclonal antibodies against glycoproteins]

Many strategies have been tried to produce monoclonal antibodies (mAbs); however, there have been several problems about focusing on molecular targets and screening methods. For instance, the high tumor/normal ratio of antigen expression using DNA microarray has been thought to be important when we determine the molecular targets for antibody-drug. Although many antigens are expressed highly in tumors, those antigens have been removed from the candidates of antibody-drug targets because they were also expressed in normal tissues. We recently established a novel technology to produce a cancer-specific monoclonal antibody (CasMab). The post-translational difference such as glycans can be utilized to produce the CasMab, although the protein possesses the same amino acid sequence in both cancer and normal cells. We have already produced CasMabs against several glycoproteins such as podoplanin, which is expressed in both cancer and normal cells. Those CasMabs possess antibody-dependent cellular cytotoxicity (ADCC) or complement-dependent cytotoxicity (CDC) in vitro and anti-tumor effect in xenograft models in vivo. In conclusion, the CasMab technology is the platform to develop cancer-specific mAbs, which could attack only cancer cells without side effects.

Platelets and cancer-associated thrombosis: focusing on the platelet activation receptor CLEC-2 and podoplanin

Patients with cancer have an increased risk of thromboembolism, which is the second leading cause of death in these patients. Several mechanisms of the prothrombotic state in these patients have been proposed. Among them are a platelet activation receptor, C-type lectin-like receptor 2 (CLEC-2), and its endogenous ligand podoplanin, which are the focus of this review. CLEC-2 is almost specifically expressed in platelets/megakaryocytes in humans. A membrane protein, podoplanin is expressed in certain types of cancer cells, including squamous cell carcinoma, brain tumor, and osteosarcoma, in addition to several normal tissues, including kidney podocytes and lymphatic endothelial cells but not vascular endothelial cells. In the bloodstream, podoplanin induces platelet activation by binding to CLEC-2 and facilitates hematogenous cancer metastasis and cancer-associated thrombosis. In an experimental lung metastasis model, the pharmacological depletion of CLEC-2 from platelets in mice resulted in a marked reduction of lung metastasis of podoplanin-expressing B16F10 cells. Control mice with B16F10 orthotopically inoculated in the back skin showed massive thrombus formation in the lungs, but the cancer-associated thrombus formation in CLEC-2-depleted mice was significantly inhibited, suggesting that CLEC-2-podoplanin interaction stimulates cancer-associated thrombosis. Thromboinflammation induced ectopic podoplanin expression in vascular endothelial cells or macrophages, which may also contribute to cancer-associated thrombosis. CLEC-2 depletion in cancer-bearing mice resulted in not only reduced cancer-associated thrombosis but also reduced levels of plasma inflammatory cytokines, anemia, and sarcopenia, suggesting that cancer-associated thrombosis may cause thromboinflammation and cancer cachexia. Blocking CLEC-2-podoplanin interaction may be a novel therapeutic strategy in patients with podoplanin-expressing cancer.

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.

Establishment of a Monoclonal Antibody PMab-231 for Tiger Podoplanin

Podoplanin (PDPN), also known as T1alpha, has been used as a lung type I alveolar cell marker in the pathophysiological condition. Although we have established several monoclonal antibodies (mAbs) against mammalian PDPNs, mAbs against tiger PDPN (tigPDPN), which are useful for immunohistochemical analysis, remain to be developed. In this study, we immunized mice with tigPDPN-overexpressing Chinese hamster ovary (CHO)-K1 cells (CHO/tigPDPN) and screened hybridomas producing mAbs against tigPDPN using flow cytometry. One of the mAbs, PMab-231 (IgG_2a, kappa), specifically detected CHO/tigPDPN cells using flow cytometry as well as recognized tigPDPN protein using western blotting. In addition, PMab-231 was found to cross-react with cat PDPN (cPDPN). The dissociation constants (K_D) of PMab-231 for CHO/tigPDPN and CHO/cPDPN cells were determined to be 1.2 × 10^-8 and 1.9 × 10^-8, respectively, indicating moderate affinity for CHO/tigPDPN and CHO/cPDPN cells. PMab-231 stained type I alveolar cells of the feline lungs and podocytes of the feline kidneys using immunohistochemistry. Our findings suggest the potential usefulness of PMab-231 for the functional analyses of tigPDPN and cPDPN.

The relationship between pancreatic cancer and hypercoagulability: a comprehensive review on epidemiological and biological issues

It has long been recognised that pancreatic cancer induces a hypercoagulable state that may lead to clinically apparent thrombosis. Although the relationship between pancreatic cancer and hypercoagulability is well described, the underlying pathological mechanism(s) and the interplay between these pathways remain a matter of intensive study. This review summarises existing data on epidemiology and pathogenesis of thrombotic complications in pancreatic cancer with a particular emphasis on novel pathophysiological pathways. Pancreatic cancer is characterised by high tumoural expression of tissue factor, activation of leukocytes with the release of neutrophil extracellular traps, the dissemination of tumour-derived microvesicles that promote hypercoagulability and increased platelet activation. Furthermore, other coagulation pathways probably contribute to these processes, such as those that involve heparanase, podoplanin and hypofibrinolysis. In the era in which heparin and its derivatives—the currently recommended therapy for cancer-associated thrombosis—might be superseded by direct oral anticoagulants, novel data from mouse models of cancer-associated thrombosis suggest the possibility of future personalised therapeutic approaches. In this dynamic era for cancer-associated thrombosis, the discovery of novel prothrombotic and proinflammatory mechanisms will potentially uncover pharmacological targets to prevent and treat thrombosis without adversely affecting haemostasis.

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.

Anti-Human Epidermal Growth Factor Receptor 2 Monoclonal Antibody H2Mab-41 Exerts Antitumor Activity in a Mouse Xenograft Model of Colon Cancer

The expression of human epidermal growth factor receptor 2 (HER2) has been reported to be overexpressed in several cancers, such as breast, lung, gastric, pancreatic, and colorectal cancers, and be associated with poor clinical outcomes. Trastuzumab, a humanized anti-HER2 antibody, provides significant survival benefits for patients with HER2-overexpressing breast cancers and gastric cancers. In this study, we developed a novel anti-HER2 monoclonal antibody (mAb), H₂Mab-41 (IgG_2b, kappa), and the antitumor activity of H₂Mab-41 was investigated using mouse xenograft models. Caco-2 cells (human colon cancer cell line), which expresses HER2, were subcutaneously implanted into the flanks of nude mice. H₂Mab-41 and control mouse IgG were injected three times into the peritoneal cavity of mice. H₂Mab-41 significantly reduced tumor development of Caco-2 xenograft in comparison with the control mouse IgG on days 5, 8, 11, 15, and 19. Taken together, these results suggest that H₂Mab-41 is useful for antibody therapy against HER2-expressing colon cancers.

PMab-213: A Monoclonal Antibody for Immunohistochemical Analysis Against Pig Podoplanin

Podoplanin (PDPN) is known to be expressed in normal tissues, including lymphatic endothelial cells, renal podocytes, and type I lung alveolar cells. Monoclonal antibodies (mAbs) against human, mouse, rat, rabbit, dog, cat, and bovine PDPN have already been established; however, mAbs against pig PDPN (pPDPN) are lacking. In the present study, mice were immunized with pPDPN-overexpressing Chinese hamster ovary (CHO)-K1 cells (CHO/pPDPN), and hybridomas producing mAbs against pPDPN were identified by flow cytometric screening. One of the mAbs, PMab-213 (IgG_2b, kappa), could specifically detect CHO/pPDPN cells through flow cytometry and detect pPDPN through western blot analysis. K_D of PMab-213 for CHO/pPDPN was determined to be 2.1 × 10^-9 M, indicating a high affinity for CHO/pPDPN. Furthermore, PMab-213 strongly stained lymphatic endothelial cells, renal podocytes, and type I lung alveolar cells through immunohistochemistry. PMab-213 is expected to be useful in investigating the function of pPDPN.

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.

Establishment of a monoclonal antibody PMab-233 for immunohistochemical analysis against Tasmanian devil podoplanin

Monoclonal antibodies (mAbs) against not only human, mouse, and rat but also rabbit, dog, cat, bovine, pig, and horse podoplanins (PDPNs) have been established in our previous studies. PDPN is used as a lymphatic endothelial cell marker in pathological diagnoses. However, mAbs against Tasmanian devil PDPN (tasPDPN), which are useful for immunohistochemical analysis, remain to be developed. Herein, mice were immunized with tasPDPN-overexpressing Chinese hamster ovary (CHO)-K1 (CHO/tasPDPN) cells, and hybridomas producing mAbs against tasPDPN were screened using flow cytometry. One of the mAbs, PMab-233 (IgG₁, kappa), specifically detected CHO/tasPDPN cells by flow cytometry and recognized tasPDPN protein by western blotting. Furthermore, PMab-233 strongly detected CHO/tasPDPN cells by immunohistochemistry. These findings suggest that PMab-233 may be useful as a lymphatic endothelial cell marker of the Tasmanian devil.

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

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Sensitive and specific PMab-233 mAb against Tasmanian devil PDPN was produced.

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PMab-233 strongly reacted with Tasmanian devil PDPN in flow cytometry.

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PMab-233 is useful for IHC using paraffin-embedded cell sections.

PMab-219: A monoclonal antibody for the immunohistochemical analysis of horse podoplanin

Monoclonal antibodies (mAbs) against human, mouse, rat, rabbit, dog, cat, and bovine podoplanin (PDPN), a lymphatic endothelial cell marker, have been established in our previous studies. However, mAbs against horse PDPN (horPDPN), which are useful for immunohistochemical analysis, remain to be developed. In the present study, mice were immunized with horPDPN-overexpressing Chinese hamster ovary (CHO)-K1 cells (CHO/horPDPN), and hybridomas producing mAbs against horPDPN were screened using flow cytometry. One of the mAbs, PMab-219 (IgG_2a, kappa), specifically detected CHO/horPDPN cells via flow cytometry and recognized horPDPN protein using Western blotting. Furthermore, PMab-219 strongly stained CHO/horPDPN via immunohistochemistry. These findings suggest that PMab-219 is useful for investigating the function of horPDPN.

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

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Sensitive and specific PMab-219 mAb against horse PDPN was produced.

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PMab-219 reacted with a horse renal cell line sensitively in flow cytometry.

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PMab-219 is useful for IHC using paraffin-embedded cell sections.

Establishment of P38Bf, a Core-Fucose-Deficient Mouse-Canine Chimeric Antibody Against Dog Podoplanin

Podoplanin (PDPN), a type I transmembrane sialoglycoprotein, is expressed in normal tissues, including lymphatic endothelial cells, pulmonary type I alveolar cells, and renal podocytes. The overexpression of PDPN in cancers is associated with hematogenous metastasis by interactions with the C-type lectin-like receptor 2 (CLEC-2). We have previously reported the development of a mouse monoclonal antibody (mAb) clone, PMab-38 (IgG₁, kappa), against dog PDPN (dPDPN). PMab-38 reacted strongly with canine squamous cell carcinomas and melanomas, but not with lymphatic endothelial cells, indicating its cancer specificity. In this study, we developed and produced several mouse-canine chimeric antibodies originating from PMab-38. A mouse-canine chimeric antibody of subclass A (P38A) and a mouse-canine chimeric antibody of subclass B (P38B) were transiently produced using ExpiCHO-S cells. Core-fucose-deficient P38B (P38Bf) was developed using FUT8 knockout ExpiCHO-S cells. We compared the binding affinities, antibody-dependent cellular cytotoxicity (ADCC), and complement-dependent cytotoxicity (CDC) of P38A, P38B, and P38Bf against Chinese hamster ovary (CHO)/dPDPN cells. Flow cytometry analysis showed that the K_D of P38A, P38B, and P38Bf were 1.9 × 10⁻⁷, 5.2 × 10⁻⁹, and 6.5 × 10⁻⁹, respectively. Both P38B and P38Bf revealed high ADCC activities against CHO/dPDPN cells; P38Bf demonstrated significantly higher ADCC compared with P38B, especially at low concentrations. P38B and P38Bf exhibited higher CDC activities against CHO/dPDPN cells. Conversely, P38A did not exhibit any ADCC or CDC activity. In summary, P38Bf is a good candidate for antibody therapy against dPDPN-expressing canine cancers.

Functional significance of the platelet immune receptors GPVI and CLEC-2

Although platelets are best known for their role in hemostasis, they are also crucial in development, host defense, inflammation, and tissue repair. Many of these roles are regulated by the immune-like receptors glycoprotein VI (GPVI) and C-type lectin receptor 2 (CLEC-2), which signal through an immunoreceptor tyrosine-based activation motif (ITAM). GPVI is activated by collagen in the subendothelial matrix, by fibrin and fibrinogen in the thrombus, and by a remarkable number of other ligands. CLEC-2 is activated by the transmembrane protein podoplanin, which is found outside of the vasculature and is upregulated in development, inflammation, and cancer, but there is also evidence for additional ligands. In this Review, we discuss the physiological and pathological roles of CLEC-2 and GPVI and their potential as targets in thrombosis and thrombo-inflammatory disorders (i.e., disorders in which inflammation plays a critical role in the ensuing thrombosis) relative to current antiplatelet drugs.

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.

The mouse-canine chimeric anti-dog podoplanin antibody P38B exerts antitumor activity in mouse xenograft models

Podoplanin (PDPN) is a type I transmembrane heavily glycosylated sialoglycoprotein that is expressed in normal tissues such as pulmonary type I alveolar cells, renal podocytes, and lymphatic endothelial cells. PDPN overexpression in cancerous tissue is associated with hematogenous metastasis through interactions with the C-type lectin-like receptor 2 (CLEC-2). Previously, we have reported the development of a mouse monoclonal antibody (mAb), PMab-38 (IgG₁, kappa) against dog PDPN (dPDPN). PMab-38 was found to strongly react with canine squamous cell carcinomas (SCCs) and melanomas; however, it showed no reaction with lymphatic endothelial cells. Recently, we have developed and produced the mouse–canine mAb of subclass B, P38B that showed antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity against Chinese hamster ovary (CHO)/dPDPN cells. In the present study, we investigated the antitumor activity using mouse xenograft model. To induce ADCC activity by P38B, canine mononuclear cells were injected surrounding the tumors in a xenograft model. It was demonstrated that P38B exerted antitumor activity against the mouse xenograft model using CHO/dPDPN. These results suggest that P38B is useful for antibody therapy against dPDPN-expressing canine SCCs and melanomas.

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Dog PDPN is expressed in canine squamous cell carcinomas and melanomas.

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A mouse-canine mAb of canine subclass B, P38B against dog PDPN was produced.

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P38B exerted antitumor activities via ADCC and CDC.

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P38B could be useful for antibody therapy against dPDPN-expressing canine tumors.

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.

Epitope Mapping of Anti-Telomerase Reverse Transcriptase Monoclonal Antibodies

Telomerase reverse transcriptase (TERT) is the main catalytic subunit of telomerase-associated protein machinery. Upregulation of TERT at the transcriptional level results in immortal cell phenotype associated with cancer. To date we have developed eight anti-TERT monoclonal antibodies (mAbs) (TMab-4, TMab-5, TMab-6, TMab-7, TMab-9, TMab-10, TMab-11, and TMab-12) by immunizing mice with synthetic peptides (₃₀₂-QHHAGPPSTSRPPRPWDTPC-₃₂₁) of TERT. We further characterized those epitopes using enzyme-linked immunosorbent assay, and here we discuss the critical epitope of an anti-TERT mAb, which is applicable for immunohistochemical analysis.

Disodium Cromolyn and Anti-podoplanin Antibodies Strongly Inhibit Growth of BHK 21/C13-derived Fibrosarcoma in a Chick Embryo Chorioallantoic Membrane Model

AIM

To characterize baby hamster kidney fibroblast (BHK 21/C13) cells and test the effects of antibodies against podoplanin and disodium cromolyn on BHK 21/C13 cell line-derived tumors grown on chick embryo chorioallantoic membrane (CAM).

MATERIAL AND METHODS

BHK 21/C13 cell-derived fibrosarcomas developed in hamsters were implanted on CAM and treated with anti-podoplanin antibodies and disodium cromolyn. BHK 21/C13 cell immunophenotype was assessed.

RESULTS

Fibrosarcoma cells were positive for vimentin, CD117, smooth muscle actin, vascular endothelial growth factor epidermal growth factor receptor, homebox prospero gene 1 and negative for platelet-derived growth factor B, neuron-specific enolase, S100, CD34, Ewing sarcoma and podoplanin. CAM-grown fibrosarcomas were highly sensitive to disodium cromolyn and anti-podoplanin antibodies.

CONCLUSION

Immunophenotyping BHK 21/C13 cells and their response to drugs represent the first step in revealing cell line utility and a reliable tool for experimental cancer research.

Disodium Cromolyn and Anti-podoplanin Antibodies Strongly Inhibit Growth of BHK 21/C13-derived Fibrosarcoma in a Chick Embryo Chorioallantoic Membrane Model

AIM

To characterize baby hamster kidney fibroblast (BHK 21/C13) cells and test the effects of antibodies against podoplanin and disodium cromolyn on BHK 21/C13 cell line-derived tumors grown on chick embryo chorioallantoic membrane (CAM).

MATERIAL AND METHODS

BHK 21/C13 cell-derived fibrosarcomas developed in hamsters were implanted on CAM and treated with anti-podoplanin antibodies and disodium cromolyn. BHK 21/C13 cell immunophenotype was assessed.

RESULTS

Fibrosarcoma cells were positive for vimentin, CD117, smooth muscle actin, vascular endothelial growth factor epidermal growth factor receptor, homebox prospero gene 1 and negative for platelet-derived growth factor B, neuron-specific enolase, S100, CD34, Ewing sarcoma and podoplanin. CAM-grown fibrosarcomas were highly sensitive to disodium cromolyn and anti-podoplanin antibodies.

CONCLUSION

Immunophenotyping BHK 21/C13 cells and their response to drugs represent the first step in revealing cell line utility and a reliable tool for experimental cancer research.

MicroRNA-21 in cancer-associated fibroblasts supports lung adenocarcinoma progression

Cancer-associated fibroblasts (CAFs) interact closely with cancer cells, supporting their growth and invasion. To investigate the role of microRNA-21 (miR-21) in lung adenocarcinoma, and especially in its CAF component, in situ hybridisation was applied to samples from 89 invasive lung adenocarcinoma cases. MiR-21 expression was observed in both cancer cells and CAFs. When the patients were stratified by expression, miR-21 levels in CAFs (n = 9), but not in cancer cells (n = 21), were inversely correlated with patient survival; patients with miR-21^high CAFs exhibited lower survival than those with miR-21^low CAFs. The underlying mechanism was investigated in vitro. Conditioned medium (CM) from A549 lung cancer cells increased miR-21 expression in MRC-5 and IMR-90 lung fibroblasts through the transforming growth factor-β pathway, and induced CAF-like morphology and migratory capacity. MiR-21 up-regulation in lung fibroblasts induced a novel CAF-secreted protein, calumenin, as well as known CAF markers (periostin, α-smooth muscle actin, and podoplanin). Moreover, CM from the lung fibroblasts increased A549 cell proliferation in a calumenin-dependent manner. Thus, miR-21 expression in lung fibroblasts may trigger fibroblast trans-differentiation into CAFs, supporting cancer progression. Therefore, CAF miR-21 represents a pivotal prognostic marker for this scar-forming cancer of the lungs.

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.

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.

LpMab-23-recognizing cancer-type podoplanin is a novel predictor for a poor prognosis of early stage tongue cancer

Purpose

We report that the reactivity of a novel monoclonal antibody LpMab-23 for human cancer-type podoplanin (PDPN) is a predictor for a poor prognosis of tongue cancer.

Patients and Methods

The association between LpMab-23-recognizing cancer-type PDPN expression and clinical/pathological features were analyzed on 60 patients with stage I and II tongue cancer treated with transoral resection of the primary tumor.

Results

In the mode of invasion, the LpMab-23-dull/negative cases were significantly larger in cases with low-grade malignancies and without late cervical lymph node metastasis, than in cases with high-grade malignancies and the metastasis. In the high-grade malignant cases, LpMab-23-positive cases were significantly larger than LpMab-23-dull/negative cases. The Kaplan–Meier curves of the five-year metastasis-free survival rate (MFS) were significantly lower in the LpMab-23 positive patients than in LpMab-23 dull/negative patients. The LpMab-23-dull/negative cases showed the highest MFS in all of the clinical/pathological features and particularly, the MFS of the LpMab-23 positive cases decreased to less than 60% in the first year. In the Cox proportional hazard regression models a comparison of the numbers of LpMab-23 dull/negative with positive cases showed the highest hazard ratio with statistical significance in all of the clinical/pathological features.

Conclusions

LpMab-23 positive cases may be considered to present a useful predictor of poor prognosis for early stage tongue cancer.

Platelet-activating factor podoplanin: from discovery to drug development

Tumor cell-induced platelet aggregation facilitates hematogenous metastasis by promoting tumor embolization, preventing immunological assaults and shear stress, and the platelet-releasing growth factors support tumor growth and invasion. Podoplanin, also known as Aggrus, is a type I transmembrane mucin-like glycoprotein and is expressed on wide range of tumor cells. Podoplanin has a role in platelet aggregation and metastasis formation through the binding to its platelet receptor, C-type lectin-like receptor 2 (CLEC-2). The podoplanin research was originally started from the cloning of highly metastatic NL-17 subclone from mouse colon 26 cancer cell line and from the establishment of 8F11 monoclonal antibody (mAb) that could neutralize NL-17-induced platelet aggregation and hematogenous metastasis. Later on, podoplanin was identified as the antigen of 8F11 mAb, and its ectopic expression brought to cells the platelet-aggregating abilities and hematogenous metastasis phenotypes. From the 8F11 mAb recognition epitopes, podoplanin is found to contain tandemly repeated, highly conserved motifs, designated platelet aggregation-stimulating (PLAG) domains. Series of analyses using the cells expressing the mutants and the established neutralizing anti-podoplanin mAbs uncovered that both PLAG3 and PLAG4 domains are associated with the CLEC-2 binding. The neutralizing mAbs targeting PLAG3 or PLAG4 could suppress podoplanin-induced platelet aggregation and hematogenous metastasis through inhibiting the podoplanin–CLEC-2 binding. Therefore, these domains are certainly functional in podoplanin-mediated metastasis through its platelet-aggregating activity. This review summarizes the platelet functions in metastasis formation, the role of platelet aggregation-inducing factor podoplanin in pathological and physiological situations, and the possibility to develop podoplanin-targeting drugs in the future.