CD98 Heavy Chain Research Articles

The role of CD98 heavy chain in cancer development.

The glycoprotein CD98, or CD98 heavy chain (CD98hc), encoded by the SLC3A2 gene, plays a crucial role in cancer development and progression. CD98hc, forming heterodimeric complexes with various light chains, regulates neutral amino acid transport across cell membranes. The intricate interplay between CD98hc, integrins, and amino acid transporters shapes the tumor microenvironment and contributes to tumor growth. Elevated expression of CD98hc in various cancers correlates with poor prognosis, making it a potential prognostic marker. In colorectal cancer, CD98hc emerges as a potential therapeutic target, along with its partner LAT1, and inhibitors like JPH203 exhibit promise in preclinical studies. Targeting CD98hc/LAT1, alone or with conventional therapies, shows promise in inhibiting tumor growth. This review focuses on elucidating the multifaceted roles of CD98hc and its partner LAT1 in cancer, particularly its involvement in amino acid transport, signaling pathways, and its prognostic relevance in cancer.

CD98 heavy chain protein is overexpressed in non-small cell lung cancer and is a potential target for CAR T-cell therapy

Chimeric antigen receptor (CAR) T cells are effective against hematological cancers, but are less effective against solid tumors such as non-small cell lung cancer (NSCLC). One of the reasons is that only a few cell surface targets specific for NSCLC cells have been identified. Here, we report that CD98 heavy chain (hc) protein is overexpressed on the surface of NSCLC cells and is a potential target for CAR T cells against NSCLC. Screening of over 10,000 mAb clones raised against NSCLC cell lines showed that mAb H2A011 bound to NSCLC cells but not normal lung epithelial cells. H2A011 recognized CD98hc. Although CAR T cells derived from H2A011 could not be established presumably due to the high level of H2A011 reactivity in activated T cells, those derived from the anti-CD98hc mAb R8H283, which had been shown to lack reactivity with CD98hc glycoforms expressed on normal hematopoietic cells and some normal tissues, were successfully developed. R8H283 specifically reacted with NSCLC cells in six of 15 patients. R8H283-derived CAR T cells exerted significant anti-tumor effects in a xenograft NSCLC model in vivo. These results suggest that R8H283 CAR T cells may become a new therapeutic tool for NSCLC, although careful testing for off-tumor reactivity should be performed in the future.

Mutant p53 sustains serine-glycine synthesis and essential amino acids intake promoting breast cancer growth

Reprogramming of amino acid metabolism, sustained by oncogenic signaling, is crucial for cancer cell survival under nutrient limitation. Here we discovered that missense mutant p53 oncoproteins stimulate de novo serine/glycine synthesis and essential amino acids intake, promoting breast cancer growth. Mechanistically, mutant p53, unlike the wild-type counterpart, induces the expression of serine-synthesis-pathway enzymes and L-type amino acid transporter 1 (LAT1)/CD98 heavy chain heterodimer. This effect is exacerbated by amino acid shortage, representing a mutant p53-dependent metabolic adaptive response. When cells suffer amino acids scarcity, mutant p53 protein is stabilized and induces metabolic alterations and an amino acid transcriptional program that sustain cancer cell proliferation. In patient-derived tumor organoids, pharmacological targeting of either serine-synthesis-pathway and LAT1-mediated transport synergizes with amino acid shortage in blunting mutant p53-dependent growth. These findings reveal vulnerabilities potentially exploitable for tackling breast tumors bearing missense TP53 mutations.

CD98 heavy chain as a prognostic biomarker and target for cancer treatment.

The SLC3A2 gene encodes for a cell-surface transmembrane protein CD98hc (4F2). CD98hc serves as a chaperone for LAT1 (SLC7A5), LAT2 (SLC7A8), y+LAT1 (SLC7A7), y+LAT2 (SLC7A6), xCT (SLC7A11) and Asc1 (SLC7A10) providing their recruitment to the plasma membrane. Together with the light subunits, it constitutes heterodimeric transmembrane amino acid transporters. CD98hc interacts with other surface molecules, such as extracellular matrix metalloproteinase inducer CD147 (EMMPRIN) and adhesion receptors integrins, and regulates glucose uptake. In this way, CD98hc connects the signaling pathways sustaining cell proliferation and migration, biosynthesis and antioxidant defense, energy production, and stem cell properties. This multifaceted role makes CD98hc one of the critical regulators of tumor growth, therapy resistance, and metastases. Indeed, the high expression levels of CD98hc were confirmed in various tumor tissues, including head and neck squamous cell carcinoma, glioblastoma, colon adenocarcinoma, pancreatic ductal adenocarcinoma, and others. A high expression of CD98hc has been linked to clinical prognosis and response to chemo- and radiotherapy in several types of cancer. In this mini-review, we discuss the physiological functions of CD98hc, its role in regulating tumor stemness, metastases, and therapy resistance, and the clinical significance of CD98hc as a tumor marker and therapeutic target.

CD98hc is a target for brain delivery of biotherapeutics

Brain exposure of systemically administered biotherapeutics is highly restricted by the blood-brain barrier (BBB). Here, we report the engineering and characterization of a BBB transport vehicle targeting the CD98 heavy chain (CD98hc or SLC3A2) of heterodimeric amino acid transporters (TVCD98hc). The pharmacokinetic and biodistribution properties of a CD98hc antibody transport vehicle (ATVCD98hc) are assessed in humanized CD98hc knock-in mice and cynomolgus monkeys. Compared to most existing BBB platforms targeting the transferrin receptor, peripherally administered ATVCD98hc demonstrates differentiated brain delivery with markedly slower and more prolonged kinetic properties. Specific biodistribution profiles within the brain parenchyma can be modulated by introducing Fc mutations on ATVCD98hc that impact FcγR engagement, changing the valency of CD98hc binding, and by altering the extent of target engagement with Fabs. Our study establishes TVCD98hc as a modular brain delivery platform with favorable kinetic, biodistribution, and safety properties distinct from previously reported BBB platforms.

Identification of DNA aptamers that specifically targets EBV+ nasopharyngeal carcinoma via binding with EphA2/CD98hc complex

Nasopharyngeal carcinoma (NPC) is one of the Epstein-Barr virus (EBV)-associated malignancies and has a distinct geographical distribution. The high mortality rates of NPC patients with advanced and recurrent disease highlight the urgent need for biomarkers for early diagnosis and effective treatments. In this study, we developed DNA aptamers that specifically bind to EBV positive NPC cells by the Cell-SELEX procedure. We further identified the EphA2 (ephrin type-A receptor 2)/CD98hc (CD98 heavy chain) complex as the potential target of the aptamer EA-3 by combining aptamer-based separation and mass spectrometry analysis. Our results revealed for the first time that EphA2 colocalized with CD98hc at the plasma membrane and EphA2 coimmunoprecipitated with CD98hc, which may serve as a starting point for exploring the potential functions of the complex of EphA2 and CD98hc in NPCs. Here, we demonstrated that aptamers can be useful for the identification of protein complexes on the surface of cancer cells.

Selective targeting of multiple myeloma cells with a monoclonal antibody recognizing the ubiquitous protein CD98 heavy chain.

Cancer-specific cell surface antigens are ideal therapeutic targets for monoclonal antibody (mAb)-based therapy. Here, we report that multiple myeloma (MM), an incurable hematological malignancy, can be specifically targeted by an mAb that recognizes a ubiquitously present protein, CD98 heavy chain (hc) (also known as SLC3A2). We screened more than 10,000 mAb clones raised against MM cells and identified R8H283, an mAb that bound MM cells but not normal hematopoietic or nonhematopoietic cells. R8H283 specifically recognized CD98hc. R8H283 did not react with monomers of CD98hc; instead, it bound CD98hc in heterodimers with a CD98 light chain (CD98lc), a complex that functions as an amino acid transporter. CD98 heterodimers were abundant on MM cells and took up amino acids for constitutive production of immunoglobulin. Although CD98 heterodimers were also present on normal leukocytes, R8H283 did not react with them. The glycoforms of CD98hc present on normal leukocytes were distinct from those present on MM cells, which may explain the lack of R8H283 reactivity to normal leukocytes. R8H283 exerted anti-MM effects without damaging normal hematopoietic cells. These findings suggested that R8H283 is a candidate for mAb-based therapies for MM. In addition, our findings showed that a cancer-specific conformational epitope in a ubiquitous protein, which cannot be identified by transcriptome or proteome analyses, can be found by extensive screening of primary human tumor samples.

Expression profile of CD98 heavy chain and L-type amino acid transporter 1 and its prognostic significance in colorectal cancer

L-type amino acid transporter (LAT1) is a neutral amino acid transporter, forming a heterodimer complex with the CD98 heavy chain (CD98hc). In this study, we studied the expression profiles of LAT1 and CD98hc in colorectal cancer (CRC) and its precursor lesions. Transcription levels of CD98hc and LAT1 were significantly increased in CRC compared to the matched normal mucosa. CD98hc and LAT1 expression showed no significant correlations with cancer stem cell markers and intestinal stem cell markers, whereas both had positive correlations with Wnt target genes, AXIN2, and EPHB2, suggesting an association with aberrant Wnt signaling activation. Immunohistochemical analysis revealed that CD98hc and LAT1 are not expressed in normal colonic mucosa and various benign lesions including hyperplastic polyps and sessile and traditional serrated adenomas. CD98hc and LAT1 expressions began to appear in tubular adenomas and further increased in carcinomas. Of interest, CD98hc expression decreased during lymph node metastasis. Survival analysis demonstrated that CD98hc and LAT1 have no significant prognostic effect in CRCs. In conclusion, CD98hc and LAT1 are not normally expressed in colonic mucosa and most benign lesions. Their expression began to appear in tubular adenomas and further increased during the adenoma-to-carcinoma transition. CD98hc expression decreased while metastasizing to regional lymph nodes. However, CD98hc and LAT1 expressions had no prognostic value in patients with CRC.

Mast cell surfaceome characterization reveals CD98 heavy chain is critical for optimal cell function

Mast cells are involved in many distinct pathologic conditions, suggesting that they recognize and respond to various stimuli and thus require a rich repertoire of cell surface proteins. However, mast cell surface proteomes have not been comprehensively characterized. We aimed to further characterize the mast cell surface proteome to obtain a better understanding of how mast cells function in health and disease. We enriched for glycosylated surface proteins expressed in mouse bone marrow-derived cultured mast cells (BMCMCs) and identified them using mass spectrometry analysis. The presence of novel surface proteins in mast cells was validated by real-time quantitative PCR and flow cytometry analysis in BMCMCs and peritoneal mast cells (PMCs). We developed a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) gene editing approach to disrupt genes of interest in BMCMCs. The glycoprotein enrichment approach resulted in the identification of 1270 proteins in BMCMCs, 378 of which were localized to the plasma membrane. The most common protein classes among plasma membrane proteins were small GTPases, receptors, and transporters. One such cell surface protein was CD98 heavy chain (CD98hc), encoded by the Slc3a2 gene. Slc3a2 gene disruption resulted in a significant reduction in CD98hc expression, adhesion, and proliferation. Glycoprotein enrichment coupled with mass spectrometry can be used to identify novel surface molecules in mast cells. Moreover, CD98hc plays an important role in mast cell function.

Plasmodium vivax binds host CD98hc (SLC3A2) to enter immature red blood cells.

More than one-third of the world's population is exposed to Plasmodium vivax malaria, mainly in Asia1. P. vivax preferentially invades reticulocytes (immature red blood cells)2-4. Previous work has identified 11 parasite proteins involved in reticulocyte invasion, including erythrocyte binding protein 2 (ref. 5) and the reticulocyte-binding proteins (PvRBPs)6-10. PvRBP2b binds to the transferrin receptor CD71 (ref. 11), which is selectively expressed on immature reticulocytes12. Here, we identified CD98 heavy chain (CD98), a heteromeric amino acid transporter from the SLC3 family (also known as SLCA2), as a reticulocyte-specific receptor for the PvRBP2a parasite ligand using mass spectrometry, flow cytometry, biochemical and parasite invasion assays. We characterized the expression level of CD98 at the surface of immature reticulocytes (CD71+) and identified an interaction between CD98 and PvRBP2a expressed at the merozoite surface. Our results identify CD98 as an additional host membrane protein, besides CD71, that is directly associated with P. vivax reticulocyte tropism. These findings highlight the potential of using PvRBP2a as a vaccine target against P. vivax malaria.

Oncogenic transformation of NIH/3T3 cells by the overexpression of L-type amino acid transporter 1, a promising anti-cancer target.

L-type amino acid transporter 1 (LAT1)/SLC7A5 is the first identified CD98 light chain disulfide linked to the CD98 heavy chain (CD98hc/SLC3A2). LAT1 transports large neutral amino acids, including leucine, which activates mTOR, and is highly expressed in human cancers. We investigated the oncogenicity of human LAT1 introduced to NIH/3T3 cells by retrovirus infection. NIH/3T3 cell lines stably expressing human native (164C) or mutant (164S) LAT1 (naLAT1/3T3 or muLAT1/3T3, respectively) were established. We confirmed that endogenous mouse CD98hc forms a disulfide bond with exogenous human LAT1 in naLAT1/3T3, but not in muLAT1/3T3. Endogenous mouse CD98hc mRNA increased in both naNIH/3T3 and muLAT1/3T3, and a similar amount of exogenous human LAT1 protein was detected in both cell lines. Furthermore, naLAT1/3T3 and muLAT1/3T3 cell lines were evaluated for cell growth-related phenotypes (phosphorylation of ERK, cell-cycle progression) and cell malignancy-related phenotypes (anchorage-independent cell growth, tumor formation in nude mice). naLAT1/3T3 had stronger growth- and malignancy- related phenotypes than NIH/3T3 and muLAT1/3T3, suggesting the oncogenicity of native LAT1 through its interaction with CD98hc. Anti-LAT1 monoclonal antibodies significantly inhibited in vitro cell proliferation and in vivo tumor growth of naLAT1/3T3 cells in nude mice, demonstrating LAT1 to be a promising anti-cancer target.

Characterization of the mast cell surface proteome leads to the identification of CD98hc as a critical surface molecule for optimal mast cell function

Abstract Mast cells are known for their involvement in many distinct pathological conditions, suggesting that mast cells recognize and respond to various stimuli and thus require a rich cell surface protein repertoire. Mast cell surface proteomes have not been comprehensively characterized. In this study, we aimed to further characterize the mast cell surface proteome to obtain a better understanding of how mast cells function in health and disease. We enriched for glycosylated surface proteins expressed in murine bone marrow-derived mast cells (BMCMCs) and identified them using mass spectrometry analysis. This approach resulted in the identification of 1270 proteins in BMCMCs, 403 of which were localized to the plasma membrane. The most common protein classes among plasma membrane proteins are represented by small GTPases, receptors and transporters. Novel surface proteins in mast cells was validated by qPCR and flow cytometry analysis in BMCMCs and peritoneal mast cells (PMCs). Among the novel surface proteins, we found that CD98 heavy chain (CD98hc) encoded by the Slc3a2 gene, was highly expressed in mast cells. Slc3a2 gene disruption by CRISPR/Cas9 gene editing resulted in a significant reduction in CD98hc expression, mast cell degranulation, adhesion and proliferation. Our study indicates that we can use glycoprotein enrichment coupled with mass spectrometry to identify novel surface molecules in mast cells. Moreover, we found that CD98hc plays an important role in mast cell function.

The Harmonious Interplay of Amino Acid and Monocarboxylate Transporters Induces the Robustness of Cancer Cells.

There is a growing body of evidence that metabolic reprogramming contributes to the acquisition and maintenance of robustness associated with malignancy. The fine regulation of expression levels of amino acid and monocarboxylate transporters enables cancer cells to exhibit the metabolic reprogramming that is responsible for therapeutic resistance. Amino acid transporters characterized by xCT (SLC7A11), ASCT2 (SLC1A5), and LAT1 (SLC7A5) function in the uptake and export of amino acids such as cystine and glutamine, thereby regulating glutathione synthesis, autophagy, and glutaminolysis. CD44 variant, a cancer stem-like cell marker, stabilizes the xCT antiporter at the cellular membrane, and tumor cells positive for xCT and/or ASCT2 are susceptible to sulfasalazine, a system Xc(-) inhibitor. Inhibiting the interaction between LAT1 and CD98 heavy chain prevents activation of the mammalian target of rapamycin (mTOR) complex 1 by glutamine and leucine. mTOR signaling regulated by LAT1 is a sensor of dynamic alterations in the nutrient tumor microenvironment. LAT1 is overexpressed in various malignancies and positively correlated with poor clinical outcome. Metabolic reprogramming of glutamine occurs often in cancer cells and manifests as ASCT2-mediated glutamine addiction. Monocarboxylate transporters (MCTs) mediate metabolic symbiosis, by which lactate in cancer cells under hypoxia is exported through MCT4 and imported by MCT1 in less hypoxic regions, where it is used as an oxidative metabolite. Differential expression patterns of transporters cause functional intratumoral heterogeneity leading to the therapeutic resistance. Therefore, metabolic reprogramming based on these transporters may be a promising therapeutic target. This review highlights the pathological function and therapeutic targets of transporters including xCT, ASCT2, LAT1, and MCT.

Design of a surrogate Anticalin protein directed against CD98hc for preclinical studies in mice.

The human CD98 heavy chain (CD98hc) offers a promising biomedical target both for tumor therapy and for drug delivery to the brain. We have previously developed a cognate Anticalin protein with picomolar affinity and demonstrated its effectiveness in a xenograft animal model. Due to the lack of cross‐reactivity with the murine ortholog, we now report the development and X‐ray structural analysis of an Anticalin with high affinity toward CD98hc from mouse. This binding protein recognizes the same protruding epitope loop—despite distinct structure—in the membrane receptor ectodomain as the Anticalin selected against human CD98hc. Thus, this surrogate Anticalin should be useful for the preclinical assessment of CD98hc targeting in vivo and support the translational development for medical application in humans.

CD98hc (SLC3A2) sustains amino acid and nucleotide availability for cell cycle progression

CD98 heavy chain (CD98hc) forms heteromeric amino acid (AA) transporters by interacting with different light chains. Cancer cells overexpress CD98hc-transporters in order to meet their increased nutritional and antioxidant demands, since they provide branched-chain AA (BCAA) and aromatic AA (AAA) availability while protecting cells from oxidative stress. Here we show that BCAA and AAA shortage phenocopies the inhibition of mTORC1 signalling, protein synthesis and cell proliferation caused by CD98hc ablation. Furthermore, our data indicate that CD98hc sustains glucose uptake and glycolysis, and, as a consequence, the pentose phosphate pathway (PPP). Thus, loss of CD98hc triggers a dramatic reduction in the nucleotide pool, which leads to replicative stress in these cells, as evidenced by the enhanced DNA Damage Response (DDR), S-phase delay and diminished rate of mitosis, all recovered by nucleoside supplementation. In addition, proper BCAA and AAA availability sustains the expression of the enzyme ribonucleotide reductase. In this regard, BCAA and AAA shortage results in decreased content of deoxynucleotides that triggers replicative stress, also recovered by nucleoside supplementation. On the basis of our findings, we conclude that CD98hc plays a central role in AA and glucose cellular nutrition, redox homeostasis and nucleotide availability, all key for cell proliferation.

Characterization of Single-Protein Dynamics in Polymer-Cushioned Lipid Bilayers Derived from Cell Plasma Membranes.

Native cell-membrane-derived supported lipid bilayers (SLBs) are an emerging platform with broad applications ranging from fundamental research to next-generation biosensors. Central to the success of the platform is the proper accommodation of membrane proteins so that their dynamics and functions are preserved. Polymer cushions have been commonly employed to avoid direct contact between the bilayer membrane and the supporting substrate, and thus, the mobility of the transmembrane proteins is maintained. However, little is known about how the polymer cushion affects the absolute mobility of membrane molecules. Here, we characterized the dynamics of single membrane proteins in polymer-cushioned lipid bilayers derived from cell plasma membranes and investigated the effects of polymer length. Three membrane proteins with distinct structures, i.e., a GPI-anchored protein, single-pass transmembrane protein CD98 heavy chain, and seven-pass transmembrane protein SSTR3, were fused with green fluorescent protein (GFP), and their dynamics were measured by fluorescent single-molecule tracking. An automated data acquisition was implemented to study the effects of PEG polymer length on protein dynamics with large statistics. Our data showed that increasing the PEG polymer length (molecular weight from 1000 to 5000) enhanced the mobile fraction of the membrane proteins. Moreover, the diffusion coefficients of transmembrane proteins were augmented with the polymer length, whereas the diffusion coefficient of the GPI-anchored protein remained almost identical for different polymer lengths. Importantly, the diffusion coefficients of the three membrane proteins became identical (2.5 μm2/s approximately) for the cushioned membrane with the longest polymer length (molecular weight of 5000), indicating that at the microscopic length scale, the SLBs were fully suspended from the substrate by the polymer cushion. Transient confinements were observed for all three proteins, and increasing the polymer length reduced the tendency of transient confinement. The measured dynamics of membrane proteins were found to be nearly unchanged after the depletion of cholesterol, suggesting that the observed immobilization and transient confinement were not due to cholesterol-enriched membrane nanodomains (lipid rafts). Our single-molecule dynamics elucidate the biophysical properties of polymer-cushioned plasma membrane bilayers that are potentially useful for the future developments of membrane-based biosensors and analytical assays.

Cryo-EM structure of the human L-type amino acid transporter 1 in complex with glycoprotein CD98hc.

The L-type amino acid transporter 1 (LAT1 or SLC7A5) transports large neutral amino acids across the membrane and is crucial for brain drug delivery and tumor growth. LAT1 forms a disulfide-linked heterodimer with CD98 heavy chain (CD98hc, 4F2hc or SLC3A2), but the mechanism of assembly and amino acid transport are poorly understood. Here we report the cryo-EM structure of the human LAT1-CD98hc heterodimer at 3.3-Å resolution. LAT1 features a canonical Leu T-fold and exhibits an unusual loop structure on transmembrane helix 6, creating an extended cavity that might accommodate bulky amino acids and drugs. CD98hc engages with LAT1 through the extracellular, transmembrane and putative cholesterol-mediated interactions. We also show that two anti-CD98 antibodies recognize distinct, multiple epitopes on CD98hc but not its glycans, explaining their robust reactivities. These results reveal the principles of glycoprotein-solute carrier assembly and provide templates for improving preclinical drugs and antibodies targeting LAT1 or CD98hc.

The CD98 Heavy Chain Is a Marker and Regulator of Head and Neck Squamous Cell Carcinoma Radiosensitivity.

The heavy chain of the CD98 protein (CD98hc) is encoded by the SLC3A2 gene. Together with the light subunit LAT1, CD98hc constitutes a heterodimeric transmembrane amino acid transporter. High SLC3A2 mRNA expression levels are associated with poor prognosis in patients with head and neck squamous cell carcinoma (HNSCC) treated with radiochemotherapy. Little is known regarding the CD98hc protein-mediated molecular mechanisms of tumor radioresistance. CD98hc protein expression levels were correlated with corresponding tumor control dose 50 (TCD50) in HNSCC xenograft models. Expression levels of CD98hc and LAT1 in HNSCC cells were modulated by siRNA or CRISPR/Cas9 gene editing. HNSCC cell phenotypes were characterized by transcription profiling, plasma membrane proteomics, metabolic analysis, and signaling pathway activation. Expression levels of CD98hc and LAT1 proteins were examined by IHC analysis of tumor tissues from patients with locally advanced HNSCC treated with primary radiochemotherapy (RCTx). Primary endpoint was locoregional tumor control (LRC). High expression levels of CD98hc resulted in an increase in mTOR pathway activation, amino acid metabolism, and DNA repair as well as downregulation of oxidative stress and autophagy. High expression levels of CD98hc and LAT1 proteins were significantly correlated and associated with an increase in radioresistance in HNSCC in vitro and in vivo models. High expression of both proteins identified a poor prognosis subgroup in patients with locally advanced HNSCC after RCTx. We found that CD98hc-associated signaling mechanisms play a central role in the regulation of HNSCC radioresistance and may be a promising target for tumor radiosensitization.

Structural differences between the ectodomains of murine and human CD98hc.

The CD98 heavy chain (CD98hc) constitutes both a promising cell surface target for the treatment of cancers and a transcytosis receptor potentially useful for the brain delivery of therapeutics. However, pharmacokinetic studies and safety assessment of cognate antibodies or nonimmunoglobulin binding proteins in rodents is hampered by cross-species variability of both amino acid sequence and glycosylation pattern. Here, we report the crystal structure of the murine CD98hc extracellular domain and a comprehensive comparison with its human ortholog, revealing only one conserved surface patch that is neither shielded by glycosylation nor by the cell membrane with an accessible surface area typical for an antibody epitope. Our results imply the necessity of a surrogate approach for CD98hc-specific binding proteins with predictive power for clinical investigations.

Anti-tumor effects of mAb against L-type amino acid transporter 1 (LAT1) bound to human and monkey LAT1 with dual avidity modes.

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.