岡﨑 章悟

Redox regulation is a key mechanism supporting tumor survival and an attractive therapeutic target. In this study, we screened 1161 FDA-approved compounds to identify agents that induce reactive oxygen species (ROS) accumulation in head and neck squamous cell carcinoma (HNSCC) cells. Pimozide, a dopamine D2 receptor antagonist, emerged as the most potent ROS inducer. It selectively suppresses the growth of HNSCC cells with high oxidative stress resistance while exhibiting only modest effects on less resistant cells and normal keratinocytes. Notably, pimozide exhibited anti-tumor effects as a monotherapy and in combination with paclitaxel at clinically relevant doses. Mechanistic analysis revealed that pimozide rapidly induced ROS accumulation via a mechanism distinct from its known action on dopamine D2 receptors and STAT3/5. To identify markers of ROS-induced responses, we examined ROS-responsive genes and found that early growth response 1 (EGR1) was selectively induced in sensitive cells and correlated with pimozide responsiveness. Functional analysis revealed that EGR1 knockdown suppressed pimozide-induced cytotoxicity, suggesting its role as a functional pharmacodynamic marker of pimozide sensitivity. In a patient-derived xenograft model of HNSCC, pimozide significantly reduced the tumor burden alone and in combination with paclitaxel. While tumor volume reduction in the combination group was not statistically greater than that in the monotherapy group, fluorescence immunohistochemistry revealed a marked decrease in undifferentiated tumor cells, indicating enhanced therapeutic effects of combination treatment. Taken together, these findings indicate that pimozide is a promising candidate for repurposing as a novel therapeutic agent against HNSCC.

Porphyromonas gingivalis (Pg) is a periodontal pathogen that has been implicated in the development and progression of head and neck squamous cell carcinoma (HNSCC). However, studying its interaction with HNSCC in vitro is challenging because of the obligatory anaerobic nature of Pg. To overcome this limitation, we developed a coculture system that enables the viability of both HNSCC cells and Pg using spheroid culture combined with Hippo pathway inhibition via treatment with a LATS1/2 inhibitor. In spheroid cultures, many HNSCC cell lines failed to grow in a normal medium. However, stable growth of these cells was achieved through Hippo pathway inhibition, which maintained the cells in an undifferentiated state. Furthermore, the addition of Pg to HNSCC spheroids maintained Pg viability in three out of four HNSCC cell lines, even after 3 days. Hippo pathway inhibition further enhanced Pg survival within the spheroids, likely by suppressing the differentiation-induced expression of antimicrobial genes S100A8 and S100A9. Coculturing HNSCC cells with Pg did not promote spheroid growth but induced p38 activation, leading to increased expression of the proinflammatory cytokines IL-1α and IL-8. Database analysis using The Cancer Microbiome Atlas corroborated these findings, showing upregulation of p38 phosphorylation, IL-1α, and IL-8 in Porphyromonas-positive HNSCC samples. These findings suggest that the established coculture system is a representative model of the clinical properties of Pg-positive HNSCC and can serve as a valuable tool for investigating the long-term interactions between HNSCC and viable Pg.

BACKGROUND: Benzaldehyde (BA) is an aromatic aldehyde found in fruits that has been studied as a potential anticancer agent on the basis of its ability to inhibit transformation in mouse embryo cells and to suppress metastasis in mice. METHODS: We investigated the cytotoxic effects of BA on cancer cells, and probed its effects on intracellular signaling pathways. The anticancer effects of BA in vivo were studied by using a mouse orthotopic transplantation model of pancreatic cancer. RESULTS: BA inhibited the growth of osimertinib- or radiation-resistant cancer cells as well as the interaction between 14-3-3ζ and its client proteins. The interaction of 14-3-3ζ with the Ser28-phosphorylated form of histone H3 (H3S28ph) was implicated in treatment resistance and the transcriptional regulation of genes related to epithelial-mesenchymal transition and stemness, including E2F2, SRSF1, and ID1. Treatment of mice with a BA derivative inhibited pancreatic tumor growth and lung metastasis, as well as suppressed a state of epithelial-mesenchymal plasticity (EMP) of tumor cells. CONCLUSION: The interaction between 14-3-3ζ and H3S28ph plays a key role in EMP and treatment resistance in cancer. The ability of BA to inhibit this and other interactions of 14-3-3ζ offers the potential to overcome treatment resistance and to suppress metastasis.

Most mitochondrial proteins encoded in the nuclear genome are synthesized in the cytoplasm. These proteins subsequently undergo maturation through the cleavage of a signal sequence at the N-terminus by one or two mitochondrial signal peptidases, which is essential for their function within mitochondria. The present study demonstrates that adipocyte-specific knockout of one mitochondrial signal peptidase, mitochondrial intermediate peptidase (MIPEP), resulted in disordered mitochondrial proteostasis of MIPEP substrate proteins and their defective maturation. MIPEP deficiency in white and brown adipocytes suppressed the expression of adipocyte differentiation, lipid metabolism, and mitochondrial biogenesis genes. These alterations led to lipoatrophy in white adipose tissue and the whitening of brown adipose tissue. Additionally, it induced an atypical mitochondrial unfolded protein response and local inflammation in white and brown adipose tissue. Furthermore, it induced fatty liver and splenomegaly and caused systemic impairments in glucose metabolism and inflammation. These findings indicate that maturation defects of certain mitochondrial proteins and subsequent proteostasis disorders in white and brown adipocytes cause chronic and systemic inflammatory and metabolic dysfunctions.

Effective therapies have yet to be established for pancreatic ductal adenocarcinomas (PDAC) even though it is the most aggressive cancer. In the present study, PDAC was analyzed using novel rat mAbs against membrane proteins in conjunction with flow cytometry and immunohistochemistry. Human epidermal growth receptor (HER)1-4, mesenchymal to epithelial transition factor (MET), sphingosine-1-phospahate receptor 1 (S1PR1), l-type amino acid transporter 1 (LAT1), system x- c transporter (xCT), alanine-serine-cysteine transporter (ASCT2), cationic amino acid transporter 1 (CAT1) and variant CD44 (CD44v) were expressed at high frequencies in both in vitro and in vivo PDAC. Internalization of membrane proteins by mAbs and growth inhibition by toxin-linked mAbs were demonstrated in many PDAC cell lines, and mAbs against S1PR1, ASCT2, HER3 and CD44v inhibited the growth of xenografted MIA PaCa-2 PDAC cells. Furthermore, CD44v-high PDAC showed high mRNA expression of HER1-3, MET and CD44v, and was correlated with poor prognosis. Taken together, our results suggest that CD44v, S1PR1, HER3, MET and the above-mentioned cancer-associated amino acid transporters might be promising targets for the diagnosis and treatment of PDAC.

During the perinatal period, the immune system sets the threshold to select either response or tolerance to environmental Ags, which leads to the potential to provide a lifetime of protection and health. B-1a B cells have been demonstrated to develop during this perinatal time window, showing a unique and restricted BCR repertoire, and these cells play a major role in natural Ab secretion and immune regulation. In the current study, we developed a highly efficient temporally controllable RAG2-based lymphoid lineage cell labeling and tracking system and applied this system to understand the biological properties and contribution of B-1a cells generated at distinct developmental periods to the adult B-1a compartments. This approach revealed that B-1a cells with a history of RAG2 expression during the embryonic and neonatal periods dominate the adult B-1a compartment, including those in the bone marrow (BM), peritoneal cavity, and spleen. Moreover, the BCR repertoire of B-1a cells with a history of RAG2 expression during the embryonic period was restricted, becoming gradually more diverse during the neonatal period, and then heterogeneous at the adult stage. Furthermore, more than half of plasmablasts/plasma cells in the adult BM had embryonic and neonatal RAG2 expression histories. Moreover, BCR analysis revealed a high relatedness between BM plasmablasts/plasma cells and B-1a cells derived from embryonic and neonatal periods, suggesting that these cell types have a common origin. Taken together, these findings define, under native hematopoietic conditions, the importance in adulthood of B-1a cells generated during the perinatal period.

G protein-coupled receptors (GPCRs) regulate many cellular processes in response to various stimuli, including light, hormones, neurotransmitters, and odorants, some of which play critical roles in innate and adaptive immune responses. However, the physiological functions of many GPCRs and the involvement of them in autoimmune diseases of the central nervous system remain unclear. Here, we demonstrate that GPR141, an orphan GPCR belonging to the class A receptor family, suppresses immune responses. High GPR141 mRNA levels were expressed in myeloid-lineage cells, including neutrophils (CD11b + Gr1+), monocytes (CD11b + Gr1-Ly6C+ and CD11b + Gr1-Ly6C-), macrophages (F4/80+), and dendritic cells (DCs) (CD11c+). Gpr141-/- mice, that we independently generated, displayed almost no abnormalities in myeloid cell differentiation and compartmentalization in the spleen and bone marrow under steady-state conditions. However, Gpr141 deficiency exacerbated disease conditions of experimental autoimmune encephalomyelitis (EAE), an autoimmune disease model for multiple sclerosis, with increased inflammation in the spinal cord. Gpr141-/- mice showed increased CD11b + Gr1+ neutrophils, CD11b + Gr1- monocytes, CD11c+ DC, and CD4+ T cell infiltration into the EAE-induced spinal cord compared to littermate control mice. Lymphocytes enriched from Gpr141-/- mice immunized with myelin oligodendrocyte glycoprotein (MOG)35-55 produced high amounts of interferon-γ, interleukin (IL)-17A, and IL-6 compared to those from WT mice. Moreover, CD11c+ DCs purified from Gpr141-/- mice increased cytokine production of MOG35-55 specific T cells. These findings suggest that GPR141 functions as a negative regulator of immune responses by controlling the functions of monocytes and DCs and that targeting GPR141 may be a possible therapeutic intervention for modulating chronic inflammatory diseases.

Metastatic progression of tumors is driven by genetic alterations and tumor-stroma interaction. To elucidate the mechanism underlying the oncogene-induced gastric tumor progression, we have developed an organoid-based model of gastric cancer from GAstric Neoplasia (GAN) mice, which express Wnt1 and the enzymes COX2 and microsomal prostaglandin E synthase 1 in the stomach. Both p53 knockout (GAN-p53KO) organoids and KRASG12V -expressing GAN-p53KO (GAN-KP) organoids were generated by genetic manipulation of GAN mouse-derived tumor (GAN wild-type [WT]) organoids. In contrast with GAN-WT and GAN-p53KO organoids, which manifested Wnt addiction, GAN-KP organoids showed a Wnt-independent phenotype and the ability to proliferate without formation of a Wnt-regulated three-dimensional epithelial architecture. After transplantation in syngeneic mouse stomach, GAN-p53KO cells formed only small tumors, whereas GAN-KP cells gave rise to invasive tumors associated with the development of hypoxia as well as to liver metastasis. Spatial transcriptomics analysis suggested that hypoxia signaling contributes to the metastatic progression of GAN-KP tumors. In particular, such analysis identified a cluster of stromal cells located at the tumor invasive front that expressed genes related to hypoxia signaling, angiogenesis, and cell migration. These cells were also positive for phosphorylated extracellular signal-regulated kinase (ERK), suggesting that mitogen-activated protein kinase (MAPK) signaling promotes development of both tumor and microenvironment. The MEK (MAPK kinase) inhibitor trametinib suppressed the development of GAN-KP gastric tumors, formation of a hypoxic microenvironment, tumor angiogenesis, and liver metastasis. Our findings therefore establish a rationale for application of trametinib to suppress metastatic progression of KRAS-mutated gastric cancer.

Copy number alterations detected by comparative genomic hybridization (CGH) can lead to the identification of novel cancer-related genes. We analyzed chromosomal aberrations in a set of 100 human primary colorectal cancers (CRCs) using CGH and found a solute carrier (SLC) 7A1 gene, which encodes cationic amino acid transporter 1 (CAT1) with 14 putative transmembrane domains, in a chromosome region (13q12.3) with a high frequency of gene amplifications. SLC7A1/CAT1 is a transporter responsible for the uptake of cationic amino acids (arginine, lysine, and ornithine) essential for cellular growth. Microarray and PCR analyses have revealed that mRNA transcribed from CAT1 is overexpressed in more than 70% of human CRC samples, and RNA interference-mediated knockdown of CAT1 inhibited the cell growth of CRCs. Rats were immunized with rat hepatoma cells expressing CAT1 tagged with green fluorescent protein (GFP), and rat splenocytes were fused with mouse myeloma cells. Five rat monoclonal antibodies (mAbs) (CA1 ~ CA5) reacting with HEK293 cells expressing CAT1-GFP in a GFP expression-dependent manner were selected from established hybridoma clones. Novel anti-CAT1 mAbs selectively reacted with human CRC tumor tissues compared with adjacent normal tissues according to immuno-histochemical staining and bound strongly to numerous human cancer cell lines by flow cytometry. Anti-CAT1 mAbs exhibited internalization activity, antibody-dependent cellular cytotoxicity, and migration inhibition activity against CRC cell lines. Furthermore, CA2 inhibited the in vivo growth of human HT29 and SW-C4 CRC tumors in nude mice. This study suggested CAT1 to be a promising target for mAb therapy against CRCs.

Death receptor Fas-mediated apoptosis not only eliminates nonspecific and autoreactive B cells but also plays a major role in antitumor immunity. However, the possible mechanisms underlying impairment of Fas-mediated induction of apoptosis during lymphomagenesis remain unknown. In this study, we employed our developed syngeneic lymphoma model to demonstrate that downregulation of Fas is required for both lymphoma development and lymphoma cell survival to evade immune cytotoxicity. CD40 signal activation significantly restored Fas expression and thereby induced apoptosis after Fas ligand treatment in both mouse and human lymphoma cells. Nevertheless, certain human lymphoma cell lines were found to be resistant to Fas-mediated apoptosis, with Livin (melanoma inhibitor of apoptosis protein; ML-IAP) identified as a driver of such resistance. High expression of Livin and low expression of Fas were associated with poor prognosis in patients with aggressive non-Hodgkin's lymphoma. Livin expression was tightly driven by bromodomain and extraterminal (BET) proteins BRD4 and BRD2, suggesting that Livin expression is epigenetically regulated in refractory lymphoma cells to protect them from Fas-mediated apoptosis. Accordingly, the combination of CD40-mediated Fas restoration with targeting of the BET proteins-Livin axis may serve as a promising immunotherapeutic strategy for refractory B-cell lymphoma. SIGNIFICANCE: These findings yield insights into identifying risk factors in refractory lymphoma and provide a promising therapy for tumors resistant to Fas-mediated antitumor immunity. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/20/4439/F1.large.jpg.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Resistance of progressive cancers against chemotherapy is a serious clinical problem. In this context, human epidermal growth factor receptor 3 (HER3) can play important roles in drug resistance to HER1- and HER2- targeted therapies. Since clinical testing of anti-HER3 monoclonal antibodies (mAbs) such as patritumab could not show remarkable effect compared with existing drugs, we generated novel mAbs against anti-HER3. Novel rat mAbs reacted with HEK293 cells expressing HER3, but not with cells expressing HER1, HER2 or HER4. Specificity of mAbs was substantiated by the loss of mAb binding with knockdown by siRNA and knockout of CRISPR/Cas9-based genome-editing. Analyses of CDR sequence and germline segment have revealed that seven mAbs are classified to four groups, and the binding of patritumab was inhibited by one of seven mAbs. Seven mAbs have shown reactivity with various human epithelial cancer cells, strong internalization activity of cell-surface HER3, and inhibition of NRG1 binding, NRG1-dependent HER3 phosphorylation and cell growth. Anti-HER3 mAbs were also reactive with in vivo tumor tissues and cancer tissue-originated spheroid. Ab4 inhibited in vivo tumor growth of human colon cancer cells in nude mice. Present mAbs may be superior to existing anti-HER3 mAbs and support existing anti-cancer therapeutic mAbs.

The major cellular antioxidant glutathione (GSH) protects cancer cells from oxidative damage that can lead to the induction of ferroptosis, an iron-dependent form of cell death triggered by the aberrant accumulation of lipid peroxides. Inhibitors of the cystine-glutamate antiporter subunit xCT, which mediates the uptake of extracellular cystine and thereby promotes GSH synthesis, are thus potential anticancer agents. However, the efficacy of xCT-targeted therapy has been found to be diminished by metabolic reprogramming that affects redox status in cancer cells. Identification of drugs for combination with xCT inhibitors that are able to overcome resistance to xCT-targeted therapy might thus provide the basis for effective cancer treatment. We have now identified the vasodilator oxyfedrine (OXY) as a sensitizer of cancer cells to GSH-depleting agents including the xCT inhibitor sulfasalazine (SSZ). Oxyfedrine contains a structural motif required for covalent inhibition of aldehyde dehydrogenase (ALDH) enzymes, and combined treatment with OXY and SSZ was found to induce accumulation of the cytotoxic aldehyde 4-hydroxynonenal and cell death in SSZ-resistant cancer cells both in vitro and in vivo. Microarray analysis of tumor xenograft tissue showed cyclooxygenase-2 expression as a potential biomarker for the efficacy of such combination therapy. Furthermore, OXY-mediated ALDH inhibition was found to sensitize cancer cells to GSH depletion induced by radiation therapy in vitro. Our findings thus establish a rationale for repurposing of OXY as a sensitizing drug for cancer treatment with agents that induce GSH depletion.

The spleen is comprised of spatially distinct compartments whose functions, such as immune responses and removal of aged red blood cells, are tightly controlled by the non-hematopoietic stromal cells that provide regionally-restricted signals to properly activate hematopoietic cells residing in each area. However, information regarding the ontogeny and relationships of the different stromal cell types remains limited. Here we have used in vivo lineage tracing analysis and in vitro mesenchymal stromal cell assays and found that Tlx1, a transcription factor essential for embryonic spleen organogenesis, marks neonatal stromal cells that are selectively localized in the spleen and retain mesenchymal progenitor potential to differentiate into mature follicular dendritic cells, fibroblastic reticular cells and marginal reticular cells. Furthermore, by establishing a novel three-dimensional cell culture system that enables maintenance of Tlx1-expressing cells in vitro, we discovered that signals from the lymphotoxin β receptor and TNF receptor promote differentiation of these cells to express MAdCAM-1, CCL19 and CXCL13, representative functional molecules expressed by different subsets of mature stromal cells in the spleen. Taken together, these findings indicate that mesenchymal progenitor cells expressing Tlx1 are a subset of lymphoid tissue organizer-like cells selectively found in the neonatal spleen.

Targeting the function of membrane transporters in cancer stemlike cells is a potential new therapeutic approach. Cystine-glutamate antiporter xCT expressed in CD44 variant (CD44v)-expressing cancer cells contributes to the resistance to oxidative stress as well as cancer therapy through promoting glutathione (GSH)-mediated antioxidant defense. Amino acid transport by xCT might, thus, be a promising target for cancer treatment, whereas the determination factors for cancer cell sensitivity to xCT-targeted therapy remain unclear. Here, we demonstrate that high expression of xCT and glutamine transporter ASCT2 is correlated with undifferentiated status and diminished along with cell differentiation in head and neck squamous cell carcinoma (HNSCC). The cytotoxicity of the xCT inhibitor sulfasalazine relies on ASCT2-dependent glutamine uptake and glutamate dehydrogenase (GLUD)-mediated α-ketoglutarate (α-KG) production. Metabolome analysis revealed that sulfasalazine treatment triggers the increase of glutamate-derived tricarboxylic acid cycle intermediate α-KG, in addition to the decrease of cysteine and GSH content. Furthermore, ablation of GLUD markedly reduced the sulfasalazine cytotoxicity in CD44v-expressing stemlike HNSCC cells. Thus, xCT inhibition by sulfasalazine leads to the impairment of GSH synthesis and enhancement of mitochondrial metabolism, leading to reactive oxygen species (ROS) generation and, thereby, triggers oxidative damage. Our findings establish a rationale for the use of glutamine metabolism (glutaminolysis)-related genes, including ASCT2 and GLUD, as biomarkers to predict the efficacy of xCT-targeted therapy for heterogeneous HNSCC tumors.

Pulmonary arterial hypertension (PAH) pathogenesis shares similarities with carcinogenesis. One CD44 variant (CD44v) isoform, CD44v8-10, binds to and stabilizes the cystine transporter subunit (xCT), producing reduced glutathione and thereby enhancing the antioxidant defense of cancer stem cells. Pharmacological inhibition of xCT by sulfasalazine suppresses tumor growth, survival, and resistance to chemotherapy. We investigated whether the CD44v-xCT axis contributes to PAH pathogenesis. CD44v was predominantly expressed on endothelial-to-mesenchymal transition (EndMT)-like cells in the neointimal layer of PAH affected pulmonary arterioles. In vitro, CD44 standard form and CD44v were induced as a result of EndMT. Among human pulmonary artery endothelial cells that have undergone EndMT, CD44v+ cells showed high levels of xCT expression on their cell surfaces and high concentrations of glutathione for survival. This made CD44v+ cells the most vulnerable target for sulfasalazine. CD44v+xCThi cells showed the highest expression levels of proinflammatory cytokines, antioxidant enzymes, antiapoptotic molecules, and cyclin-dependent kinase inhibitors. In the Sugen5416/hypoxia mouse model, CD44v+ cells were present in the thickened pulmonary vascular wall. The administration of sulfasalazine started either at the same time as "Sugen5416" administration (a prevention model) or after the development of pulmonary hypertension (a reversal model) attenuated the muscularization of the pulmonary vessels, decreased the expression of markers of inflammation, and reduced the right ventricular systolic pressure, while reducing CD44v+ cells. In conclusion, CD44v+xCThi cells appear during EndMT and in pulmonary hypertension tissues. Sulfasalazine is expected to be a novel therapeutic agent for PAH, most likely targeting EndMT-derived CD44v+xCThi cells.

The prognostic role of CD44v9, a variant isoform of CD44 and a new cell surface marker of cancer stem cells, remains unclear in bladder cancer (BC) patients. Furthermore, limited information is available on the functional role of sulfasalazine (SSZ), which could modulate the CD44v9-xCT system in order to enhance cisplatin (CDDP)-induced cytotoxicity and inhibit the metastatic potential of BC. CD44v9 protein expression was examined immunohistochemically in 63 muscle invasive BC (MIBC) patients who underwent radical cystectomy. CD44v9 expression was independently associated with disease recurrence and cancer-specific death in MIBC. Cytotoxic effects, glutathione levels, and reactive oxygen species production by SSZ and CD44v9 and phospho-p38MAPK protein expression by SSZ with or without CDDP were assessed in MBT-2V cells with highly metastatic potential. Sulfasalazine exerted cytotoxic effects against MBT-2V cells by inhibiting glutathione levels and inducing the production of reactive oxygen species. Sulfasalazine in combination with CDDP appeared to exert strong cytotoxic effects against MBT-2V cells by inhibiting CD44v9 expression and upregulating phospho-p38MAPK expression. The inhibitory effects of SSZ with or without CDDP were also investigated using an MBT-2V lung metastatic model. In the murine lung metastatic BC model, SSZ significantly prolonged animal survival. Furthermore, the combination of SSZ with CDDP exerted stronger inhibitory effects on the establishment of lung tumor nodules than SSZ or CDDP alone. CD44v9 expression could be a clinical biomarker for predicting poor outcomes in MIBC patients. Sulfasalazine in combination with CDDP has potential as a novel therapy against metastatic BC.

L-Type amino acid transporter 1 (LAT1) disulfide linked to CD98 heavy chain (hc) is highly expressed in most cancer cells, but weakly expressed in normal cells. In the present study, we developed novel anti-LAT1 mAbs and showed internalization activity, inhibitory effects of amino acid uptake and cell growth and antibody-dependent cellular cytotoxicity, as well as in vivo antitumor effects in athymic mice. Furthermore, we examined the reactivity of mAbs with LAT1 of Macaca fascicularis to evaluate possible side-effects of antihuman LAT1 mAbs in clinical trials. Antihuman LAT1 mAbs reacted with ACHN human and MK.P3 macaca kidney-derived cells, and this reactivity was significantly decreased by siRNAs against LAT1. Macaca LAT1 cDNA was cloned from MK.P3, and only two amino acid differences between human and macaca LAT1 were seen. RH7777 rat hepatoma and HEK293 human embryonic kidney cells expressing macaca LAT1 were established as stable transfectants, and antihuman LAT1 mAbs were equivalently reactive against transfectants expressing human or macaca LAT1. Dual (high and low) avidity modes were detected in transfectants expressing macaca LAT1, MK.P3, ACHN and HCT116 human colon cancer cells, and KA values were increased by anti-CD98hc mAb, suggesting anti-LAT1 mAbs detect an epitope on LAT1-CD98hc complexes on the cell surface. Based on these results, LAT1 may be a promising anticancer target and Macaca fascicularis can be used in preclinical studies with antihuman LAT1 mAbs.

Autocrine and paracrine factors, including glutamate and epidermal growth factor (EGF), are potent inducers of brain tumor cell invasion, a pathological hallmark of malignant gliomas. System xc(-) consists of xCT and CD98hc subunits and functions as a plasma membrane antiporter for the uptake of extracellular cystine in exchange for intracellular glutamate. We previously showed that the EGF receptor (EGFR) interacts with xCT and thereby promotes the activity of system xc(-) in a kinase-independent manner, resulting in enhanced glutamate release in glioma cells. However, the molecular mechanism underlying EGFR-mediated glioma progression in a glutamate-rich microenvironment has remained unclear. Here we show that the GluN2B subunit of the N-methyl-d-aspartate-sensitive glutamate receptor (NMDAR) is a substrate of EGFR in glioma cells. In response to EGF stimulation, EGFR phosphorylated the COOH-terminal domain of GluN2B and thereby enhanced glutamate-NMDAR signaling and consequent cell migration in EGFR-overexpressing glioma cells. Treatment with the NMDAR inhibitor MK-801 or the system xc(-) inhibitor sulfasalazine suppressed EGF-elicited glioma cell migration. The administration of sulfasalazine and MK-801 also synergistically suppressed the growth of subcutaneous tumors formed by EGFR-overexpressing glioma cells. Furthermore, shRNA-mediated knockdown of xCT and GluN2B cooperatively prolonged the survival of mice injected intracerebrally with such glioma cells. Our findings thus establish a central role for EGFR in the signaling crosstalk between xCT and GluN2B-containing NMDAR in glioma cells.

The cystine-glutamate antiporter subunit xCT suppresses iron-dependent oxidative cell death (ferroptosis) and is therefore a promising target for cancer treatment. Given that cancer cells often show resistance to xCT inhibition resulting in glutathione (GSH) deficiency, however, we here performed a synthetic lethal screen of a drug library to identify agents that sensitize the GSH deficiency-resistant cancer cells to the xCT inhibitor sulfasalazine. This screen identified the oral anesthetic dyclonine which has been recently reported to act as a covalent inhibitor for aldehyde dehydrogenases (ALDHs). Treatment with dyclonine induced intracellular accumulation of the toxic aldehyde 4-hydroxynonenal in a cooperative manner with sulfasalazine. Sulfasalazine-resistant head and neck squamous cell carcinoma (HNSCC) cells were found to highly express ALDH3A1 and knockdown of ALDH3A1 rendered these cells sensitive to sulfasalazine. The combination of dyclonine and sulfasalazine cooperatively suppressed the growth of highly ALDH3A1-expressing HNSCC or gastric tumors that were resistant to sulfasalazine monotherapy. Our findings establish a rationale for application of dyclonine as a sensitizer to xCT-targeted cancer therapy.

CD44 variant (CD44v) contributes to cancer stemness by stabilizing the xCT subunit of system xc(-) and thereby promoting its glutamate-cystine antiporter activity. CD44 has also been implicated in autoimmune insulitis and inflammation in diabetic islets, but whether CD44v regulates insulin secretion has remained unclear. Here we show that CD44v inhibits insulin secretion by attenuating amino acid transport mediated by the L-type amino acid transporter LAT1. CD44v expression level was inversely related to insulin content in islets of normal and diabetic model mice. Knockdown of CD44 increased insulin secretion, the intracellular insulin level, and the transport of neutral amino acids mediated by LAT1 in Min6 cells. Attenuation of the uptake of neutral amino acids with a LAT inhibitor reduced insulin secretion and insulin content in Min6 cells, whereas overexpression of LAT1 increased insulin secretion. Moreover, inhibition of LAT1 prevented the increase in insulin secretion and content induced by CD44 depletion in Min6 cells. Our results thus implicate CD44v in the regulation of insulin secretion and reveal that amino acid transport is rate limiting for such secretion. They further suggest that amino acid transport mediated by LAT1 is a potential therapeutic target for diabetes.

Acute lymphoblastic leukemia (ALL) with mixed lineage leukemia (MLL) gene rearrangements (MLL+ALL) has a dismal prognosis and is characterized by high surface CD44 expression. Known that CD44 has the specific binding sites for a natural ligand hyaluronan (HA), we investigated biological effects of HA with different molecular sizes on MLL+ALL cell lines, and found that the addition of ultra-low-molecular-weight (ULMW)-HA strongly suppressed their thymidine uptakes. The MLL+ALL cell line lacking surface CD44 expression established by genome editing showed no suppression of thymidine uptake. Surface CD44-high B-precursor ALL cell lines other than MLL+, but not T-ALL cell lines, were also suppressed in their thymidine uptakes. The inhibition of thymidine uptakes was because of induction of cell death, but dead cells lacked features of apoptosis on cytospin smears and flow cytometric analysis. The cell death was neither blocked by pan-caspase inhibitor nor autophagy inhibitor, but was completely blocked by necrosis inhibitor necrostatin-1. Necrotic cell death was further supported by a marked release of a high-mobility protein group B1 and morphological changes on transmission electron microscopy. Elevation of intracellular reactive oxygen species production suggested a role for inducing this necrotic cell death. ULMW-HA-triggered cell death was similarly demonstrated in surface CD44-high primary B-precursor leukemia cells. Assuming that ULMW-HA is abundantly secreted at the site of infection and inflammation, this study sheds light on understanding the mechanism of a transient inflammation-associated remission of leukemia. Further, the CD44-targeting may become an effective approach in future for the treatment of refractory B-precursor ALL by its capability of predominantly eradicating CD44-high leukemia-initiating cells.

Expression of CD44, especially the variant isoforms (CD44v) of this major cancer stem cell marker, contributes to reactive oxygen species (ROS) defense through stabilizing xCT (a cystine-glutamate transporter) and promoting glutathione synthesis. This enhances cancer development and increases chemotherapy resistance. We investigate the role of CD44v in the regulation of the ROS defense system in cholangiocarcinoma (CCA). Immunohistochemical staining of CD44v and p38(MAPK) (a major ROS target) expression in Opisthorchis viverrini-induced hamster CCA tissues (at 60, 90, 120, and 180 days) reveals a decreased phospho-p38(MAPK) signal, whereas the CD44v signal was increased during bile duct transformation. Patients with CCA showed CD44v overexpression and negative-phospho-p38(MAPK) patients a significantly shorter survival rate than the low CD44v signal and positive-phospho-p38(MAPK) patients (P = 0.030). Knockdown of CD44 showed that xCT and glutathione levels were decreased, leading to a high level of ROS. We examined xCT-targeted CD44v cancer stem cell therapy using sulfasalazine. Glutathione decreased and ROS increased after the treatment, leading to inhibition of cell proliferation and induction of cell death. Thus, the accumulation of CD44v leads to the suppression of p38(MAPK) in transforming bile duct cells. The redox status regulation of CCA cells depends on the expression of CD44v to contribute the xCT function and is a link to the poor prognosis of patients. Thus, an xCT inhibitor could inhibit cell growth and activate cell death. This suggests that an xCT-targeting drug may improve CCA therapy by sensitization to the available drug (e.g. gemcitabine) by blocking the mechanism of the cell's ROS defensive system.

Extracellular free amino acids contribute to the interaction between a tumor and its microenvironment through effects on cellular metabolism and malignant behavior. System xc(-) is composed of xCT and CD98hc subunits and functions as a plasma membrane antiporter for the uptake of extracellular cystine in exchange for intracellular glutamate. Here, we show that the EGFR interacts with xCT and thereby promotes its cell surface expression and function in human glioma cells. EGFR-expressing glioma cells manifested both enhanced antioxidant capacity as a result of increased cystine uptake, as well as increased glutamate, which promotes matrix invasion. Imaging mass spectrometry also revealed that brain tumors formed in mice by human glioma cells stably overexpressing EGFR contained higher levels of reduced glutathione compared with those formed by parental cells. Targeted inhibition of xCT suppressed the EGFR-dependent enhancement of antioxidant capacity in glioma cells, as well as tumor growth and invasiveness. Our findings establish a new functional role for EGFR in promoting the malignant potential of glioma cells through interaction with xCT at the cell surface. Cancer Res; 76(10); 2954-63. ©2016 AACR.

The use of monoclonal antibodies (mAbs) for cancer therapy is one of the most important strategies for current cancer treatment. The epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases, which regulates cancer cell proliferation, survival, and migration, is a major molecular target for antibody-based therapy. ErbB4/HER4, which contains a ligand-binding extracellular region, is activated by several ligands, including neuregulins (NRGs), heparin-binding EGF-like growth factor, betacellulin and epiregulin. Although there are clinically approved antibodies for ErbB1 and ErbB2, there are no available therapeutic mAbs for ErbB4, and it is not known whether ErbB4 is a useful target for antibody-based cancer therapy. In this study, we developed an anti-ErbB4 mAb (clone P6-1) that suppresses NRG-dependent activation of ErbB4 and examined its effect on breast cancer cell proliferation in the extracellular matrix.

Loss of parietal cells initiates the development of spasmolytic polypeptide-expressing metaplasia (SPEM), a precancerous lesion in stomach. CD44 variant (CD44v) that enhances the ability to defend against reactive oxygen species (ROS) in epithelial cells is expressed de novo in SPEM of K19-Wnt1/C2mE mice, a transgenic model of gastric tumorigenesis, and is required for the efficient development of SPEM and gastric tumor in these animals. The role of ROS and its downstream signaling in CD44-dependent gastric tumorigenesis has remained unknown, however. With the use of the K19-Wnt1/C2mE mouse, we now show that parietal cells in the inflamed stomach are highly sensitive to oxidative stress and manifest activation of p38(MAPK) signaling by ROS. Oral treatment with the antioxidant ascorbic acid or genetic ablation of the Ink4a/Arf locus, a major downstream target of ROS-p38(MAPK) signaling, inhibited parietal cell loss and the subsequent gastric tumorigenesis. Our results indicate that signaling activated by oxidative stress in parietal cells plays a key role in CD44-dependent gastric tumorigenesis. .

CD98 is a heterodimeric glycoprotein of 125-kDa, which consists of a 90-kDa heavy chain (hc) subunit and 35-kDa to 55-kDa light chain (lc) subunits. It is strongly expressed on the surface of proliferating normal cells and almost all tumor cells. To investigate the participation of CD98 in cellular proliferation and malignant transformation, we analyzed cell-cycle progression of NIH3T3 clones transfected with cDNA of human CD98hc. Although NIH3T3 and control transfectant cells grown to the subconfluent state were arrested in the G0/G1 phase by serum starvation, considerable portions of CD98hc-transfected cells resided at S and G2/M phases. Under serum-starved and confluent conditions, significant fractions (20-25%) of NIH3T3 and control transfectant cells contained less than 2n content DNA, indicating occurrence of apoptosis, whereas no apoptotic cells were detected in CD98hc-transfectant cells. Under serum-starved conditions, a marked increase in the levels of cyclin D1 and cyclin E and a decrease in p16 were observed in CD98hc-transfectant cells. The reverse was true for NIH3T3 and control transfectant cells. Our results suggest that resistance to G1 arrest and apoptosis by CD98 overexpression are associated with high G1-cyclins and low p16 levels.

BACKGROUND: CD44 is a major cellular receptor for hyaluronic acids. The stem structure of CD44 encoded by ten normal exons can be enlarged by ten variant exons (v1-v10) by alternative splicing. We have succeeded in preparing MV5 fully human IgM and its class-switched GV5 IgG monoclonal antibody (mAb) recognizing the extracellular domain of a CD44R1 isoform that contains the inserted region coded by variant (v8, v9 and v10) exons and is expressed on the surface of various human epithelial cancer cells. METHODS AND PRINCIPAL FINDINGS: We demonstrated the growth inhibition of human cancer xenografts by a GV5 IgG mAb reshaped from an MV5 IgM. The epitope recognized by MV5 and GV5 was identified to a v8-coding region by the analysis of mAb binding to various recombinant CD44 proteins by enzyme-linked immunosorbent assay. GV5 showed preferential reactivity against various malignant human cells versus normal human cells assessed by flow cytometry and immunohistological analysis. When ME180 human uterine cervix carcinoma cells were subcutaneously inoculated to athymic mice with GV5, significant inhibition of tumor formation was observed. Furthermore, intraperitoneal injections of GV5markedly inhibited the growth of visible established tumors from HSC-3 human larynx carcinoma cells that had been subcutaneously transplanted one week before the first treatment with GV5. From in vitro experiments, antibody-dependent cellular cytotoxicity and internalization of CD44R1 seemed to be possible mechanisms for in vivo anti-tumor activity by GV5. CONCLUSIONS: CD44R1 is an excellent molecular target for mAb therapy of cancer, possibly superior to molecules targeted by existing therapeutic mAb, such as Trastuzumab and Cetuximab recognizing human epidermal growth factor receptor family.

L-type amino-acid transporter 1 (LAT1) is the first identified light chain of CD98 molecule, disulfide-linked to a heavy chain of CD98. Following cDNA cloning of chicken full-length LAT1, we have constructed targeting vectors for the disruption of chicken LAT1 gene from genomic DNA of chicken LAT1 consisting of 5.4kb. We established five homozygous LAT1-disrupted (LAT1(-/-)) cell clones, derived from a heterozygous LAT1(+/-) clone of DT40 chicken B cell line. Reactivity of anti-chicken CD98hc monoclonal antibody (mAb) with LAT1(-/-) DT40 cells was markedly decreased compared with that of wild-type DT40 cells. All LAT1(-/-) cells were deficient in L-type amino-acid transporting activity, although alternative-splice variant but not full-length mRNA of LAT1 was detected in these cells. LAT1(-/-) DT40 clones showed outstandingly slow growth in liquid culture and decreased colony-formation capacity in soft agar compared with wild-type DT40 cells. Cell-cycle analyses indicated that LAT1(-/-) DT40 clones have prolonged cell-cycle phases compared with wild-type or LAT1(+/-) DT40 cells. Knockdown of human LAT1 by small interfering RNAs resulted in marked in vitro cell-growth inhibition of human cancer cells, and in vivo tumor growth of HeLa cells in athymic mice was significantly inhibited by anti-human LAT1 mAb. All these results indicate essential roles of LAT1 in the cell proliferation and occurrence of malignant phenotypes and that LAT1 is a promising candidate as a molecular target of human cancer therapy.