CD98 regulates the phosphorylation of HER2 and a bispecific anti-HER2/CD98 antibody inhibits the growth signal of human breast cancer cells.

Human epidermal growth factor receptor (HER) family proteins are currently major targets of therapeutic monoclonal antibodies against various epithelial cancers. However, the resistance of cancer cells to HER family-targeted therapies, which may be caused by cancer heterogeneity and persistent HER phosphorylation, often reduces overall therapeutic effects. We herein showed that a newly discovered molecular complex between CD98 and HER2 affected HER function and cancer cell growth. The immunoprecipitation of the HER2 or HER3 protein from lysates of SKBR3 breast cancer (BrCa) cells revealed the HER2-CD98 or HER3-CD98 complex. The knockdown of CD98 by small interfering RNAs inhibited the phosphorylation of HER2 in SKBR3 cells. A bispecific antibody (BsAb) that recognized the HER2 and CD98 proteins was constructed from a humanized anti-HER2 (SER4) IgG and an anti-CD98 (HBJ127) single chain variable fragment, and this BsAb significantly inhibited the cell growth of SKBR3 cells. Prior to the inhibition of AKT phosphorylation, BsAb inhibited the phosphorylation of HER2, however, significant inhibition of HER2 phosphorylation was not observed in anti-HER2 pertuzumab, trastuzumab, SER4 or anti-CD98 HBJ127 in SKBR3 cells. The dual targeting of HER2 and CD98 has potential as a new therapeutic strategy for BrCa.

Antitumor effects of novel mAbs against cationic amino acid transporter 1 (CAT1) on human CRC with amplified CAT1 gene.

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.

Altered binding avidities and improved growth inhibitory effects of novel anti-HER3 mAb against human cancers in the presence of HER1-or HER2-targeted drugs.

HER1-and HER2-targeted drugs are effective in cancer therapy, especially against lung, breast and colon malignancies; however, resistance of cancer cells to HER1-and HER2-targeted therapies is becoming a serious problem. The avidity/affinity constant (KA) and growth inhibitory effect of anti-HER3 rat monoclonal antibodies (mAb, Ab1∼Ab6) in the presence of therapeutic mAb or low-molecular-weight inhibitors against HER family proteins were analyzed by flow cytometry-based Scatchard plots (Splot) and cell proliferation assay. The KA of Ab3 and Ab6, but not Ab1 or Ab4, split into dual (high and low) modes of KA, and Ab6 exhibited greater anti-proliferative effects against LS-174T colon cancer cells in the presence of Pertuzumab (anti-HER2 mAb). A high KA by Ab6 and Ab6-mediated increased growth inhibition were observed against NCI-H1838 lung or BT474 breast cancer cells, respectively, in the presence of Panitumumab (anti-HER1 mAb) or Perutuzumab. A high KA by Ab6 and Ab6-mediated increased anti-proliferative effects against NCI-H1838 or BT474 were also respectively observed in the presence of Erlotinib (HER1 inhibitor) or Lapatinib (HER1/HER2 inhibitor). In HER1-knockout (KO) NCI-H1838, the reactivity and KA of Ab4 increased compared with in parent NCI-H1838. In HER1-KO or HER3-KO SW1116 colon cancer cells, dual modes of KA with Pertuzumab were noted, and the combination Ab6 and Pertuzumab promoted growth inhibition of HER1-KO, but not of parent SW1116.

Dual-targeting therapy against HER3/MET in human colorectal cancers.

BACKGROUND: Colorectal cancer (CRC) is the most common malignancy in the world, and novel molecular targeted therapies for CRC have been vigorously pursued. We searched for novel combination therapies based on the expression patterns of membrane proteins in CRC cell lines. RESULTS: A positive correlation was observed between the expression of human pidermal growth factor receptor (HER) 3 and mesenchymal-to-epithelial transition factor (MET) on the cell surface of CRC cell lines. The brief stimulation of HER3/MET-high SW1116 CRC cells with both neuregulin-1 (NRG1) and hepatocyte growth factor enhanced ERK phosphorylation and cell proliferation more than each stimulation alone. In addition, a prolonged NRG1 stimulation resulted in the tyrosine phosphorylation of MET. In this context, the Forkhead Box protein M1 (FOXM1)-regulated tyrosine phosphorylation of MET by NRG1 was demonstrated, suggesting the existence of a signaling pathway mediated by FOXM1 upon the NRG1 stimulation. Since the co-expression of HER3 and MET was also demonstrated in in vivo CRC tissues by immunohistochemistry, we investigated whether the co-inhibition of HER3 and MET could be an effective therapy for CRC. We established HER3-and/or MET-KO SW1116 cell lines, and HER3/MET-double KO resulted in the inhibition of in vitro cell proliferation and in vivo tumor growth in nude mice by SW1116 cells. Furthermore, the combination of patritumab, an anti-HER3 fully human mAb, and PHA665752, a MET inhibitor, markedly inhibited in vitro cell proliferation, 3D-colony formation, and in vivo tumor growth in nude mice by SW1116 cells CONCLUSION: The dual targeting of HER3/MET has potential as CRC therapy.

Novel functional anti-HER3 monoclonal antibodies with potent anti-cancer effects on various human epithelial cancers.

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.

Separation of phosphoprotein isotypes having the same number of phosphate groups using phosphate-affinity SDS-PAGE.

Herein, we demonstrate the separation of phosphoprotein isotypes having the same number of phosphate groups using phosphate-affinity SDS-PAGE. The phosphate-affinity site is a polyacrylamide-bound Phos-tag that enables the mobility shift detection of phosphoproteins from their nonphosphorylated counterparts. As the first practical example of the separation, we characterized the monophosphorylated Tau isotypes by each of three tyrosine kinases, c-Abl, MET, and Fyn. Each monophosphoisotype phosphorylated at the Tyr-394, Tyr-197, or Tyr-18 was detected as three distinct migration bands. As a further application, we extended this technique to the mobility shift analysis of His and Asp phosphoisotypes in the Sinorhizobium meliloti FixL/FixJ two-component system. FixL is autophosphorylated at the His-285 with ATP, and the phosphate group is transferred to the Asp-54 of FixJ and subsequently removed by the FixL phosphatase activity. Using this method, we first performed simultaneous detection of the phosphorylated and nonphosphorylated isotypes of FixL and FixJ generated in their phosphotransfer reaction in vitro. As a result, a monophosphoisotype of FixL containing the phosphorylated His residue was confirmed. As for FixJ, on the other hand, two monophosphoisotypes were detected as two distinct migration bands. One is a well-known isotype phosphorylated at the Asp-54. The other is a novel isotype phosphorylated at the His-84.

Crystal structure of human mono-phosphorylated ERK1 at Tyr204.

Extracellular signal-regulated kinase (ERK) is a member of the MAP kinase family, and can regulate several cellular responses. The isoforms ERK1 and ERK2 have markedly similar amino acid sequences, but exhibit distinctive physiological functions. As well as ERK2, ERK1 was auto- and mono-phosphorylated at Tyr204 in the activation loop during Escherichia coli production, resulting in basal level activity, approximately 500-fold less compared with fully-active ERK1 dual-phosphorylated at Thr202 and Tyr204. Crystal structure demonstrated that the mono-phosphorylated ERK1 kinase possessed a novel conformation distinguishable from the un-phosphorylated (inactive) and the dual-phosphorylated (full-active) forms. The characteristic structural features in both the C-helix and the activation loop likely contribute to the basal activity of the mono-phosphorylated ERK1. The structural dissection of ERK1 compared to ERK2 suggests that the structural differences in the D-motif binding site and in the backside binding site are putative targets for development of selective ERK1/ERK2 inhibitors.

Promotion of malignant phenotype after disruption of the three-dimensional structure of cultured spheroids from colorectal cancer.

Individual and small clusters of cancer cells may detach from the edges of a main tumor and invade vessels, which can act as the origin of metastasis; however, the mechanism for this phenomenon is not well understood. Using cancer tissue-originated spheroids, we studied whether disturbing the 3D architecture of cancer spheroids can provoke the reformation process and progression of malignancy. We developed a mechanical disruption method to achieve homogenous disruption of the spheroids while maintaining cell-cell contact. After the disruption, 9 spheroid lines from 9 patient samples reformed within a few hours, and 3 of the 9 lines exhibited accelerated spheroid growth. Marker expression, spheroid forming capacity, and tumorigenesis indicated that stemness increased after spheroid disruption. In addition, the spheroid forming capacity increased in 6 of 11 spheroid lines. The disruption signature determined by gene expression profiling supported the incidence of remodeling and predicted the prognosis of patients with colorectal cancer. Furthermore, WNT and HER3 signaling were increased in the reformed spheroids, and suppression of these signaling pathways attenuated the increased proliferation and stemness after the disruption. Overall, the disruption and subsequent reformation of cancer spheroids promoted malignancy-related phenotypes through the activation of the WNT and ERBB pathways.

Immuno-PET Imaging of HER3 in a Model in which HER3 Signaling Plays a Critical Role.

HER3 is overexpressed in various carcinomas including colorectal cancer (CRC), which is associated with poor prognosis, and is involved in the development of therapy resistance. Thus, an in vivo imaging technique is needed to evaluate the expression of HER3, an important therapeutic and diagnostic target. Here, we report successful HER3 PET imaging using a newly generated anti-human HER3 monoclonal antibody, Mab#58, and a mouse model of a HER3-overexpressing xenograft tumor. Furthermore, we assessed the role of HER3 signaling in CRC cancer tissue-originated spheroid (CTOS) and applied HER3 imaging to detect endogenous HER3 in CTOS-derived xenografts. Cell binding assays of 89Zr-labeled Mab#58 using the HER3-overexpressing cell line HER3/RH7777 demonstrated that [89Zr]Mab#58 specifically bound to HER3/RH7777 cells (Kd = 2.7 nM). In vivo biodistribution study in mice bearing HER3/RH7777 and its parent cell xenografts showed that tumor accumulation of [89Zr]Mab#58 in HER3/RH7777 xenografts was significantly higher than that in the control from day 1 to day 4, tending to increase from day 1 to day 4 and reaching 12.2 ± 4.5%ID/g. Radioactivity in other tissues, including the control xenograft, decreased or remained unchanged from day 1 to day 6. Positron emission tomography (PET) in the same model enabled clear visualization of HER3/RH7777 xenografts but not of RH7777 xenografts. CTOS growth assay and signaling assay revealed that CRC CTOS were dependent on HER3 signaling for their growth. In PET studies of mice bearing a CRC CTOS xenograft, the tumor was clearly visualized with [89Zr]Mab#58 but not with the 89Zr-labeled control antibody. Thus, tumor expression of HER3 was successfully visualized by PET with 89Zr-labeled anti-HER3 antibody in CTOS xenograft-bearing mice, a model that retains the properties of the patient tumor. Non-invasive targeting of HER3 by antibodies is feasible, and it is expected to be useful for cancer diagnosis and treatment.

Structure of human Fyn kinase domain complexed with staurosporine.

The tyrosine kinase Fyn is a member of the Src kinase family. Besides the role of Fyn in T cell signal transduction in concert with Lck, its excess activity in the brain is involved with conditions such as Alzheimer's and Parkinson's diseases. Therefore, inhibition of Fyn kinase may help counteract these nervous system disorders. Here, we solved the crystal structure of the human Fyn kinase domain complexed with staurosporine, a potent kinase inhibitor, at 2.8 A resolution. Staurosporine binds to the ATP-binding site of Fyn in a similar manner as in the Lck- and Csk-complexes. The small structural differences in the staurosporine-binding and/or -unbinding region among the three kinase domains may help obtaining the selective inhibitors against the respective kinases.