Human mannose-binding lectin 2 is directly regulated by peroxisome proliferator-activated receptors via a peroxisome proliferator responsive element

Human mannose-binding lectin (MBL) is encoded by the MBL2 gene and is a key player in innate immunity. However, the mechanism of the transcriptional regulation of MBL2 is largely unknown. The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that play an important role in a number of biological responses, including lipid homeostasis, immune function and adipogenesis. In this study, we showed that PPARα and PPARγ up-regulate the expression of human MBL2. Using a luciferase assay, electrophoretic mobility-shift assay and chromatin immunoprecipitation assay, we demonstrated that PPARs regulate the expression of human MBL2 via the peroxisome proliferator responsive element (PPRE). On the other hand, MBL2 mRNA expression was not affected by the PPARα ligand both in vivo in rat liver and in vitro in rat H4IIE hepatoma cells. Thus, there is a species difference in regulation of MBL2 gene expression by PPARs between humans and rodents. We also show that the species differences in response to PPAR could be due in part to sequence-specific differences in the PPRE in the promoter region of MBL2. These results indicate that human, but not rat, MBL2 expression is regulated by PPARs via a PPRE.

Evaluation of the asparagine synthetase level in leukemia cells by monoclonal antibodies

L-Asparaginase (ASNase) is important for the treatment of childhood acute lymphoblastic leukemia. ASNase sensitivity has been shown to correlate with the asparagine synthetase (ASNS) protein content in acute lymphoblastic leukemia cell lines. However, there have been few studies to determine ASNS protein levels in human leukemias, since no appropriate monoclonal antibody is available for such quantitative analysis. In this study, we report the generation of anti-ASNS monoclonal antibodies, which are applicable to flow cytometry and enzyme-linked immunosorbent assay. These monoclonal antibodies should provide a valuable tool for the quantification of ASNS protein level and estimation of ASNase-resistance in leukemia cells.

Novel role of copper transport protein antioxidant-1 in neointimal formation after vascular injury

OBJECTIVE

Vascular smooth muscle cell (VSMC) migration is critically important for neointimal formation after vascular injury and atherosclerosis lesion formation. Copper (Cu) chelator inhibits neointimal formation, and we previously demonstrated that Cu transport protein antioxidant-1 (Atox1) is involved in Cu-induced cell growth. However, role of Atox1 in VSMC migration and neointimal formation after vascular injury is unknown.

APPROACH AND RESULTS

Here, we show that Atox1 expression is upregulated in injured vessel, and it is colocalized with the Cu transporter ATP7A, one of the downstream targets of Atox1, mainly in neointimal VSMCs at day 14 after wire injury. Atox1(-/-) mice show inhibition of neointimal formation and extracellular matrix expansion, which is associated with a decreased VSMCs accumulation within neointima and lysyl oxidase activity. Mechanistically, in cultured VSMC, Atox1 depletion with siRNA inhibits platelet-derived growth factor-induced Cu-dependent VSMC migration by preventing translocation of ATP7A and small G protein Rac1 to the leading edge, as well as Cu- and Rac1-dependent lamellipodia formation. Furthermore, Atox1(-/-) mice show decreased perivascular macrophage infiltration in wire-injured vessels, as well as thioglycollate-induced peritoneal macrophage recruitment.

CONCLUSIONS

Atox1 is involved in neointimal formation after vascular injury through promoting VSMC migration and inflammatory cell recruitment in injured vessels. Thus, Atox1 is a potential therapeutic target for VSMC migration and inflammation-related vascular diseases.

Mutations for decreasing the immunogenicity and maintaining the function of core streptavidin

The defining property of core streptavidin (cSA) is not only its high binding affinity for biotin but also its pronounced thermal and chemical stability. Although potential applications of these properties including therapeutic methods have prompted much biological research, the high immunogenicity of this bacterial protein is a key obstacle to its clinical use. To this end, we have successfully constructed hypoimmunogenic cSA muteins in a previous report. However, the effects of these mutations on the physicochemical properties of muteins were still unclear. These mutations retained the similar electrostatic charges to those of wild-type (WT) cSA, and functional moieties with similar hydrogen bond pattern. Herein, we performed isothermal titration calorimetry, differential scanning calorimetry, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis to gain insight into the physicochemical properties and functions of these modified versions of cSA. The results indicated that the hypoimmunogenic muteins retained the biotin-binding function and the tetramer structure of WT cSA. In addition, we discuss the potential mechanisms underlying the success of these mutations in achieving both immune evasion and retention of function; these mechanisms might be incorporated into a new strategy for constructing hypoimmunogenic proteins.

Host-protective effect of circulating pentraxin 3 (PTX3) and complex formation with neutrophil extracellular traps

Pentraxin 3 (PTX3) is a soluble pattern recognition receptor which is classified as a long-pentraxin in the pentraxin family. It is known to play an important role in innate immunity, inflammatory regulation, and female fertility. PTX3 is synthesized by specific cells, primarily in response to inflammatory signals. Among these various cells, neutrophils have a unique PTX3 production system. Neutrophils store PTX3 in neutrophil-specific granules and then the stored PTX3 is released and localizes in neutrophil extracellular traps (NETs). Although certain NET components have been identified, such as histones and anti-microbial proteins, the detailed mechanisms by which NETs localize, as well as capture and kill microbes, have not been fully elucidated. PTX3 is a candidate diagnostic marker of infection and vascular damage. In severe infectious diseases such as sepsis, the circulating PTX3 concentration increases greatly (up to 100 ng/mL, i.e., up to 100-fold of the normal level). Even though it is clearly implied that PTX3 plays a protective role in sepsis and certain other disorders, the detailed mechanisms by which it does so remain unclear. A proteomic study of PTX3 ligands in septic patients revealed that PTX3 forms a complex with certain NET component proteins. This suggests a role for PTX3 in which it facilitates the efficiency of anti-microbial protein pathogen clearance by interacting with both pathogens and anti-microbial proteins. We discuss the possible relationships between PTX3 and NET component proteins in the host protection afforded by the innate immune response. The PTX3 complex has the potential to be a highly useful diagnostic marker of sepsis and other inflammatory diseases.

Phosphatidylinositol 3-phosphatase myotubularin-related protein 6 (MTMR6) is regulated by small GTPase Rab1B in the early secretory and autophagic pathways

A large family of myotubularin phosphatases dephosphorylates phosphatidylinositol 3-phosphate and phosphatidylinositol 3,5-bisphosphate, which are known to play important roles in vesicular trafficking and autophagy. The family is composed of 16 members, and understanding their regulatory mechanisms is important to understand their functions and related genetic diseases. We prepared anti-myotubularin-related protein 6 (MTMR6) monoclonal antibody and used it to study the regulatory mechanism of MTMR6. Endogenous MTMR6 was present in the cytoplasm and was condensed in the perinuclear region in a microtubule-dependent manner. MTMR6 preferentially interacted with GDP-bound Rab1B via the GRAM domain and partly overlapped with Rab1B in the pericentrosomal and peri-Golgi regions in normal rat kidney cells. Overexpression of GDP-bound Rab1B and the reduction of Rab1B disrupted the localization of MTMR6, suggesting that Rab1B regulates the localization of MTMR6. The reduction of MTMR6 accelerated the transport of vesicular stomatitis virus glycoprotein in which Rab1B is involved. Furthermore, reduction of MTMR6 or Rab1B inhibited the formation of the tubular omegasome that is induced by overexpression of DFCP1 in autophagy. Our results indicate that the cellular localization of MTMR6 is regulated by Rab1B in the early secretory and autophagic pathways. We propose a new regulatory mechanism of myotubularin phosphatase by the small GTPase Rab1B.

Inhibition of DNA damage-induced apoptosis through Cdc7-mediated stabilization of Tob

BACKGROUND

Preventing unnecessary cell death is essential for DNA-damaged cells to carry out the DNA repair process.

RESULTS

Cdc7 inhibits the Cul4-DDB1(Cdt2)-dependent Tob degradation.

CONCLUSION

Cdc7 enables mild DNA-damaged cells to keep their viability by competing with the Tob degradation system.

SIGNIFICANCE

Cells deal with moderate DNA damage not only by cessation of the cell cycle but also through direct mediated pro-survival signaling. Cells respond to DNA damage by activating alternate signaling pathways that induce proliferation arrest or apoptosis. The correct balance between these two pathways is important for maintaining genomic integrity and preventing unnecessary cell death. The mechanism by which DNA-damaged cells escape from apoptosis during DNA repair is poorly understood. We show that the DNA replication-initiating kinase Cdc7 actively prevents unnecessary death in DNA-damaged cells. In response to mild DNA damage, Tob levels increase through both a transcriptional mechanism and protein stabilization, resulting in inhibition of pro-apoptotic signaling. Cells lacking Cdc7 expression undergo apoptosis after mild DNA damage, where Cul4-DDB1(Cdt2) induces Tob ubiquitination and subsequent degradation. Cdc7 phosphorylates and interacts with Tob to inhibit the Cul4-DDB1(Cdt2)-dependent Tob degradation. Thus, Cdc7 defines an essential pro-survival signaling pathway by contributing to stabilization of Tob, thereby the viability of DNA-damaged cells being maintained.

Functional reconstitution of olfactory receptor complex on baculovirus

Despite that recent progress in genomics has elucidated the genomic structure of the olfactory receptors (ORs), most of them are still orphan receptors. The low expression level of ORs in heterologous cells has hampered many attempts to establish cell biological OR assay systems. Recently, we demonstrated that certain G protein-coupled receptors, such as the leukotriene B4 receptor or the dopamine D1 receptor, were efficiently reconstituted on baculovirus budding from infected Sf9 cells. The budded virus (BV) was shown to be mostly free of exogenous proteins other than those related to viral infection, resulting in low-noise assay conditions. Taking advantage of these conditions, we attempted to reconstitute OR complexes on BV. Sf9 cells were coinfected with recombinant baculoviruses harboring the cDNAs encoding adenylyl cyclase, trimeric G-protein, and the receptor: mOR-EG or S6. The coexpression of these proteins was detected by western blot, and the agonist- or antagonist-dependent receptor response was confirmed using ligand-dependent cyclic AMP production. These results demonstrated the successful reconstitution of functional OR complex on BV. Additionally, the expression of OR8B3 on BV, one of human orphan ORs, was also confirmed. This BV expression system is expected to be a highly effective tool for screening unknown ligands for ORs.

The proteomic profile of circulating pentraxin 3 (PTX3) complex in sepsis demonstrates the interaction with azurocidin 1 and other components of neutrophil extracellular traps

Pentraxin 3 (PTX3), a long pentraxin subfamily member in the pentraxin family, plays an important role in innate immunity as a soluble pattern recognition receptor. Plasma PTX3 is elevated in sepsis (∼200 ng/ml) and correlates with mortality. The roles of PTX3 in sepsis, however, are not well understood. To investigate the ligands of PTX3 in sepsis, we performed a targeted proteomic study of circulating PTX3 complexes using magnetic bead-based immunopurification and shotgun proteomics for label-free relative quantitation via spectral counting. From septic patient fluids, we successfully identified 104 candidate proteins, including the known PTX3-interacting proteins involved in complement activation, pathogen opsonization, inflammation regulation, and extracellular matrix deposition. Notably, the proteomic profile additionally showed that PTX3 formed a complex with some of the components of neutrophil extracellular traps. Subsequent biochemical analyses revealed a direct interaction of bactericidal proteins azurocidin 1 (AZU1) and myeloperoxidase with PTX3. AZU1 exhibited high affinity binding (K_D = 22 ± 7.6 nm) to full-length PTX3 in a calcium ion-dependent manner and bound specifically to an oligomer of the PTX3 N-terminal domain. Immunohistochemistry with a specific monoclonal antibody generated against AZU1 revealed a partial co-localization of AZU1 with PTX3 in neutrophil extracellular traps. The association of circulating PTX3 with components of the neutrophil extracellular traps in sepsis suggests a role for PTX3 in host defense and as a potential diagnostic target.

Oxidation of DJ-1 induced by 6-hydroxydopamine decreasing intracellular glutathione

DJ-1, the causative gene of a familial form of Parkinson's disease (PD), has been reported to undergo preferential oxidation of the cysteine residue at position 106 (Cys-106) under oxidative stress; however, details of the molecular mechanisms are not well known. In the present study, mechanisms of DJ-1 oxidation induced by 6-hydroxydopamine (6-OHDA) were investigated by using SH-SY5Y cells. The treatment of these cells with 6-OHDA caused an obvious acidic spot sift of DJ-1 due to its oxidation. However, when catalase, which is an hydrogen peroxide (H(2)O(2))-removing enzyme, was added during the treatment, it failed to prevent the oxidation induced by 6-OHDA, suggesting that electrophilic p-quinone formed from 6-OHDA, but not H(2)O(2), was responsible for the DJ-1 oxidation. Benzoquinone, another electrophilic p-quinone, also induced DJ-1 oxidation. The intracellular glutathione (GSH) levels were significantly decreased by 6-OHDA, irrespective of the presence or absence of catalase. The inhibition of GSH synthesis by buthionine sulfoximine resulted in a decrease in GSH levels and enhancement of DJ-1 oxidation. The pretreatment of cells with N-acetyl-cysteine prevented the loss of intracellular GSH and subsequently DJ-1 oxidation induced by 6-OHDA. Collectively, these results suggest that electrophilic p-quinone formed from 6-OHDA induces DJ-1 oxidation by decreasing intracellular GSH.

The application of an alanine-substituted mutant of the C-terminal fragment of Clostridium perfringens enterotoxin as a mucosal vaccine in mice

Efficient delivery of antigen to mucosal immune tissues is an essential part of mucosal vaccination. Claudin-4 is expressed on the epithelial cells that cover the mucosal immune tissues. We previously found that claudin-4-targeting is a promising strategy for mucosal vaccination by using a claudin-4 binder, the C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE). Substitution of Asn and Ser at positions 309 and 313, respectively, with alanine increased the affinity of C-CPE for claudin-4. However, application of the C-CPE mutant as a mucosal vaccine has never been tried. Here, we investigated whether the C-CPE mutant could serve as a mucosal vaccine. We used ovalbumin (OVA) as a model antigen and fused the C-CPE mutant to it. The resultant fusion protein was bound to claudin-4. When mice were immunized with the C-CPE mutant-fused OVA, OVA-specific serum IgG and nasal IgA increased relative to levels in mice immunized with a C-CPE-fused antigen. Immunization with the C-CPE mutant-fused OVA activated Th1- and Th2-type responses and led to increased anti-tumor activity against OVA-expressing thymoma cells relative to that of mice immunized with the C-CPE-fused antigen. These findings suggest that the alanine-substituted C-CPE mutant shows promise as a claudin-targeted mucosal vaccine.

Mutated C-terminal fragments of Clostridium perfringens enterotoxin have increased affinity to claudin-4 and reversibly modulate tight junctions in vitro

Passage across epithelial cell sheets is the first step in drug absorption. Tight junctions (TJs) are located between adjacent epithelial cells and seal the intercellular space preventing leakage of solutes. Claudin, a tetra-transmembrane protein family, is a pivotal functional and structural component of the TJ barrier. Modulation of the claudin-based TJ seal is a strategy for mucosal drug absorption. We previously found that a claudin-4 binder, a C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE194), was a modulator of the TJ seal and a potent mucosal absorption enhancer. In the present study, we attempted to improve claudin-4 binders by modification of C-CPE194. Substitution of Asn at position 309 and Ser at position 313 with Ala increased the affinity to claudin-4 by 9.9-fold as compared to C-CPE194. Deletion of 10 amino acids in the N-terminal domain of the double-alanine-substituted mutant increased affinity to claudin-4 by 23.9-fold as compared to C-CPE194. These C-CPE194 mutants reversibly modulated the TJ seal in human intestinal epithelial cell sheets. The N-terminal-truncated mutant was the most potent modulator of the TJ seal. These findings indicate that the C-CPE mutant may be a promising lead for the development of a clinical TJ modulator.

Fenofibrate suppresses growth of the human hepatocellular carcinoma cell via PPARα-independent mechanisms

Fenofibrate, a peroxisome proliferator-activated receptor (PPAR) α agonist, is a hypolipidemic drug. Although several studies have explored the fenofibrate-induced antiproliferative effect in cultured human cells, it is not clear which role PPARα plays in this antiproliferative effect. Therefore, we investigated the antiproliferative mechanism of fenofibrate in Huh7 (human hepatoma cell line). Cell viability was measured by the WST-8 assay and cell proliferation was assessed using the BrdU incorporation assay. The cell cycle was analyzed by flow cytometry. The cyclins, tumor suppressor proteins and regulators of the AKT signaling pathway were analyzed by immunoblotting. Using flow cytometry, we showed that fenofibrate blocks entry into the S phase of the cell cycle. We certified that this G1 arrest is caused by the reduction of cyclin A and E2F1 and the accumulation of the cyclin-dependent kinase inhibitor p27. Interestingly, the antiproliferative effect of fenofibrate was not affected by the PPARα antagonist (GW6471) or by PPARα-specific siRNA. These results suggest that fenofibrate suppresses Huh7 cell growth through a PPARα independent mechanism. Furthermore, we showed that treatment of Huh7 cells with fenofibrate leads to suppression of AKT phosphorylation. We also found for the first time that fenofibrate increased the C-terminal modulator protein (CTMP), which inhibits AKT phosphorylation. Our data suggest that fenofibrate inhibits the proliferation of Huh7 cells by blocking Akt activation, and that CTMP is one of the key players for this antiproliferative property of fenofibrate in Huh7 cells.

Long pentraxin 3 (PTX3) expression and release by neutrophils in vitro and in ulcerative colitis

Pentraxin 3 (PTX3) is the first identified long pentraxin, and it is rapidly produced and released by several cell types in response to proinflammatory signals. The aim of this study was to investigate the behavior of neutrophils to produce PTX3 protein in response to proinflammatory cytokine IL-8 in vitro, as well as identify the expression pattern of PTX3 in human ulcerative colitis lesions. Pentraxin 3 protein was found to be present following release upon IL-8 stimulation in cultured neutrophils together with lactoferrin(+)-specific granules localized in neutrophil extracellular traps (NETs) formed by extruded DNA. Neutrophils in colonic mucosal tissue of patients with ulcerative colitis were the main cellular source of PTX3 protein, the expression of which is correlated well with the histological grades of inflammation. Immunofluorescence analysis against anti-lactoferrin antibody revealed the formation of NETs released from neutrophils within crypt abscess lesions, which were found to be activated through the expression of IL-8 receptor B (CXCR2). Of interest, neutrophils depleted of PTX3 protein were displayed, supporting the release of PTX3 from neutrophils in crypt abscess. We suspected that PTX3 protein may contribute to cell-mediated immune defense in inflamed colon tissue, and in particular in crypt abscess lesions, of patients with ulcerative colitis.

The predominant expression of hepatocyte nuclear factor 4α (HNF4α) in thyroid transcription factor-1 (TTF-1)-negative pulmonary adenocarcinoma

AIMS

To investigate TTF-1-negative pulmonary adenocarcinoma, focusing upon mucin production and the expression of hepatocyte nuclear factor-4α (HNF4α).

MATERIALS AND METHODS

Two hundred and sixty-two cases of pulmonary adenocarcinoma were examined histologically and immunohistochemically; TTF-1 was expressed in 222 cases (84.7%), and 40 cases (15.3%) were negative. Among TTF-1-negative cases there were 31 mucinous-type tumours, and HNF4α, MUC5AC and MUC2 were expressed in 34 cases (85%), 29 cases (72.5%) and four cases (10%), respectively. In contrast, their expression was rare in TTF-1-positive tumours. A statistically inverse correlation was confirmed between the expression of TTF-1 and that of HNF4α and MUC5AC.

CONCLUSION

Most TTF-1-negative pulmonary adenocarcinomas are mucinous lesions with the predominant expression of HNF4α and MUC5AC.

Proteomic analysis of native hepatocyte nuclear factor-4α (HNF4α) isoforms, phosphorylation status, and interactive cofactors

Hepatocyte nuclear factor-4α (HNF4α, NR2A1) is a nuclear receptor that has a critical role in hepatocyte differentiation and the maintenance of homeostasis in the adult liver. However, a detailed understanding of native HNF4α in the steady-state remains to be elucidated. Here we report the native HNF4α isoform, phosphorylation status, and complexes in the steady-state, as shown by shotgun proteomics in HepG2 hepatocarcinoma cells. Shotgun proteomic analysis revealed the complexity of native HNF4α, including multiple phosphorylation sites and inter-isoform heterodimerization. The associating complexes identified by label-free semiquantitative proteomic analysis include the following: the DNA-dependent protein kinase catalytic subunit, histone acetyltransferase complexes, mRNA splicing complex, other nuclear receptor coactivator complexes, the chromatin remodeling complex, and the nucleosome remodeling and histone deacetylation complex. Among the associating proteins, GRB10 interacting GYF protein 2 (GIGYF2, PERQ2) is a new candidate cofactor in metabolic regulation. Moreover, an unexpected heterodimerization of HNF4α and hepatocyte nuclear factor-4γ was found. A biochemical and genomewide analysis of transcriptional regulation showed that this heterodimerization activates gene transcription. The genes thus transcribed include the cell death-inducing DEF45-like effector b (CIDEB) gene, which is an important regulator of lipid metabolism in the liver. This suggests that the analysis of the distinctive stoichiometric balance of native HNF4α and its cofactor complexes described here are important for an accurate understanding of transcriptional regulation.

Neural RNA-binding protein Musashi1 controls midline crossing of precerebellar neurons through posttranscriptional regulation of Robo3/Rig-1 expression

Precisely regulated spatiotemporal gene expression is essential for the establishment of neural circuits. In contrast to the increasing evidence for transcriptional regulation of axon guidance cues and receptors, the role of posttranscriptional regulation in axon guidance, especially in vivo, remains poorly characterized. Here, we demonstrate that the expression of Slit receptor Robo3/Rig-1, which plays crucial roles in axonal midline crossing, is regulated by a neural RNA-binding protein Musashi1 (Msi1). Msi1 binds to Robo3 mRNA through RNA recognition motifs and increases the protein level of Robo3 without affecting its mRNA level. In Msi1-deficient precerebellar neurons, Robo3 protein, but not its mRNA, is dramatically reduced. Moreover, similar to defects in Robo3-deficient mice, axonal midline crossing and neuronal migration of precerebellar neurons are severely impaired in Msi1-deficient mice. Together, these findings indicate that Msi1-mediated posttranscriptional regulation of Robo3 controls midline crossing of precerebellar neurons.

Human ROBO1 is cleaved by metalloproteinases and gamma-secretase and migrates to the nucleus in cancer cells

ROBO1 is a receptor mediating Slit-induced repulsive action on axon guidance and differentially expressed in human cancers. Although ROBO1 ectodomain has been detected, the cleavage site had not been determined. In this study we identified the precise cleavage site of ROBO1. We also report multi-step proteolysis of ROBO1 by metalloproteinases and gamma-secretase, producing two carboxy-terminal fragments, ROBO1-CTF1 at 129-kDa and ROBO1-CTF2 at 118-kDa. We have further demonstrated nuclear accumulation of ROBO1, which is abolished by either a metalloproteinase inhibitor TAPI-1 or a gamma-secretase inhibitor L-685,458. ROBO1 may function beyond the receptor through stepwise cleavages and translocation to the nucleus.

Abstract 2426: Anti-Glypican3 antibody for treatment of human liver cancer

Glypican-3 (GPC3) is a member of the glypican family of heparan sulfate proteoglycans, which are linked to the cell surface through a glycosyl phosphatidyl inositol anchor. GPC3 has been reported to be highly expressed in the majority (70-100%) of HCC, and considered to play a role in the tumorigenesis of HCC. Although the molecular mechanism by which GPC3 functions in tumorigenesis has not been fully elucidated, the high prevalence in HCC has led to considerable interest in GPC3 as a diagnostic marker and therapeutic target.

In this study, we obtained a monoclonal antibody (mAb) against the COOH-terminal part of GPC3, which induced antibody-dependent cellular cytotoxicity (ADCC). The mAb, designated mGC33, exhibited marked tumor growth inhibition of s.c. transplanted Hep G2 and HuH-7 xenografts that expressed GPC3 but did not inhibit growth of the SK-HEP-1 that was negative for GPC3. mGC33 was efficacious even in an orthotopic model; it markedly reduced the blood alpha-fetoprotein levels of mice intrahepatically transplanted with Hep G2 cells. To develop an antibody-based immunotherapy, we generated humanized GC33 (hGC33) by complementarily determining region (CDR) grafting. hGC33 was as efficacious as mGC33 against the Hep G2 xenograft, but hGC33 lacking carbohydrate moieties caused neither ADCC nor tumor growth inhibition. Depletion of CD56+ cells from human peripheral blood mononuclear cells markedly abrogated the ADCC caused by hGC33. The results show that the antitumor activity of hGC33 is mainly attributable to ADCC, and in human, natural killer cell-mediated ADCC is one possible mechanism of the antitumor effects by GC33. We also evaluated the antitumor activity of hGC33 combined with standard chemotherapy agent sorafenib. hGC33 and sorafenib combination was more potent in inhibiting tumor growth than sorafenib alone in the s.c. transplanted Hep G2 xenograft model. Administration of sorafenib alone did not change the GPC3 expression level in xenograft tumor. These suggest that this combination regimen may be clinically useful as an anti-liver cancer therapy.

In careful examination of the safety of hGC33 in nonclinical studies, specific adverse findings on GPC3 expressed tissue or organs were not observed after repeated administration. Therefore hGC33 will provide a novel treatment option for liver cancer patients with GPC3-positive tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2426.