Yoko Fujita-Yamaguchi

Down-regulation of Insulin Receptor by Antibodies against the Type I Insulin-Like Growth Factor Receptor: Implications for Anti–Insulin-Like Growth Factor Therapy in Breast Cancer

Insulin-like growth factor-I (IGF-I), IGF-II, and insulin have all been implicated in regulating several aspects of the malignant phenotype via the type I IGF receptor (IGF1R) and insulin receptor (IR). We have previously shown that a chimeric single-chain antibody against IGF1R (scFv-Fc) and a murine antibody EM164 down-regulate IGF1R, making breast cancer cells unresponsive to IGF-I. To determine if IR signaling is affected, we examined regulation of IR in MCF-7 cells after exposure to these antibodies. Surprisingly, both scFv-Fc and EM164 resulted in decreased levels of IR in vitro and in vivo despite their lack of reactivity against IR. Twenty-four-hour pretreatment with EM164 also inhibited insulin-mediated phosphorylation of IR and insulin-stimulated proliferation of MCF-7 cells. Neither scFv-Fc nor EM164 caused down-regulation of IR in cells that express very low levels of IGF1R or no IGF1R. Expression of IGF1R was required for IR down-regulation, which was specific as neither antibody caused down-regulation of beta1 integrin or epidermal growth factor receptor. Reagents that disrupt lipid rafts inhibited IR down-regulation by the antibodies, suggesting that IR in close physical proximity to IGF1R in lipid rafts was being endocytosed. Our data show that down-regulation of IR by monoclonal antibodies against IGF1R requires the coexpression of IGF1R and may be due to endocytosis of hybrid IR/IGF1R or holo-IR. Thus, antibodies against IGF1R provide inhibition of both IGF and insulin signaling in cancer cells.

Isolation and characterization of antibodies against three consecutive Tn-antigen clusters from a phage library displaying human single-chain variable fragments

The Tn-antigen, GalNAcalpha-Ser/Thr, is a tumour-associated carbohydrate antigen that may provide a sensitive and specific marker for pre-clinical detection of carcinoma and a target for cancer therapies. We recently reported that MLS128 monoclonal antibody treatment significantly inhibited colon and breast cancer cell growth. On the basis of our observations, the present study aimed to produce human anti-Tn-antigen antibodies with specificity similar to that of MLS128 monoclonal antibody, which recognizes a structure of three consecutive Tn-antigens (Tn3). Six phage clones displaying human single-chain variable fragments (scFvs) were isolated from a newly constructed phage library by panning and screening with a synthetic Tn3-peptide. Deduced amino-acid sequences of six anti-Tn3 scFvs exhibited a high degree of homology. Of those, anti-Tn3 4E10 and 4G2 scFv proteins were successfully purified from phage-infected Escherichia coli to near homogeneity. Surface plasmon resonance analyses revealed a K(D) of purified scFv proteins for Tn3 on an order of 10(-7) M, which is high for carbohydrate-specific monovalent antibodies. Further analyses suggested that both scFv proteins also bind to Tn2 and cultured colon and breast cancer cells. These results demonstrated the potential for use of these scFvs in developing antibody therapeutics targeting colon and breast cancer.

The role of insulin-like growth factor-II in cancer growth and progression evidenced by the use of ribozymes and prostate cancer progression models

Towards understanding the IGF system during cancer growth and progression, progressive prostate cancer models, such as SV40 large T antigen immortalized human prostate epithelial cells (P69, M2182, M2205, and M12) and LNCaP sublines (C4, C4-2, and C4-2B4), were used. IGF-II mRNA levels progressively increase as prostate cancer cells become more tumorigenic and metastatic, suggesting that IGF-II contributes in part to prostate cancer progression. The role of IGF-II in cancer cell growth was evaluated in LNCaP, PC3, and M12 prostate cancer cell lines and MCF-7 breast cancer cell line by ribozyme/antisense strategies which were previously shown to suppress endogenous IGF-II expression and cell growth in PC-3 cells [Xu et al., Endocrinol 140 (1999) 2134]. Retroviral mediated transient expression of IGF-II-specific ribozyme (RZ) caused extensive cell death. In stably cloned cell lines, both RZ and mutant ribozyme (MRZ) inhibited cancer cell growth, suggesting that antisense effects of MRZ may be sufficient for cell growth inhibition. These results confirm an important role of IGF-II in cancer cell growth and progression, and support further development of gene therapy targeting IGF-II.

Construction and expression of anti-Tn-antigen-specific single-chain antibody genes from hybridoma producing MLS128 monoclonal antibody

Anti-Tn-antigen monoclonal antibody MLS128 has affinity for three consecutive Tn-antigens (Tn3) more than Tn2. The major aim of this study was to isolate genes encoding MLS128 variable domains to produce a large quantity of recombinant MLS128 antibodies, in turn, allowing the conduct of studies on precise interactions between Tn3- or Tn2-epitopes and MLS128. This study describes cloning of the variable region genes of MLS128, construction of the variable region genes in single-chain variable fragments (scFv) and two scFvs conjugated with human IgG(1) hinge and Fc regions (scFv-Fc) types, and their respective expression in bacterial and mammalian cell. MLS128 scFv protein with the expected specificity and affinity was successfully prepared from inclusion bodies accumulating in Escherichia coli. Construction, expression and purification of two types of MLS128-scFv-Fc proteins with differing linker lengths in Chinese hamster ovary cells demonstrated that the purified scFv-Fc proteins had binding activity specific to the glycoprotein-expressing Tn-antigen clusters. These results revealed that VL and VH genes cloned from the hybridoma represent those of MLS128 and that recombinant antibodies produced from these genes should provide sufficient amounts of binding domains for use in 3D structural studies such as NMR and X-ray analysis.

Production of anti-carbohydrate antibodies by phage-display technologies: Potential impairment of cell growth as a result of endogenous expression

Anti-mannotriose (Man3) antibodies were previously isolated from a Keio phage library displaying human single chain variable fragments (scFvs) using a neoglycolipid, Man3- dipalmitoylphosphatidylethanolamine. Of three genes constructed, the 5A3 clone was expressed in mouse myeloma NS0 cells as a conjugate with human IgG1 Fc (scFv-Fc) and characterized (Sakai, K., Shimizu, Y., Chiba, T., Matsumoto-Takasaki, A., Kusada, Y., Zhang, W., Nakata, M., Kojima, N., Toma, K., Takayanagi, A., Shimizu, N., and Fujita-Yamaguchi, Y. (2007) Biochemistry 46, 253–262; Zhang, W., Matsumoto-Takasaki, A., Kusada, Y., Sakaue, H., Sakai, K., Nakata, M., and Fujita-Yamaguchi, Y. (2007) Biochemistry 46, 263–270). Similarly, anti-Lex phages were screened from the same library with lacto-N-fucopentaose III (LNFPIII; Lex)-dipalmitoylphosphatidylethanolamine. Of five phage clones isolated, two scFv genes were constructed to express scFv-Fc proteins in NS0 cells. As was experienced with anti-Man3 scFv-Fc clones, only one anti-LNFPIII clone, 1F12, was successfully produced and purified as an scFv-Fc protein. Although anti-LNFPIII 1F12 and anti-Man3 5A3 scFv-Fc proteins were secreted into media, a decline in scFv-Fc production was observed with both stable clones during early passages. Transient expression of anti-LNFPIII and anti-Man3 scFv-Fc genes in COS-7 cells and subsequent analyses of scFv-Fc protein expression revealed accumulation of translated proteins in the endoplasmic reticulum for scFv-Fc proteins derived from clones that did not survive as stable clones. This report describes the following: (i) isolation of anti-LNFPIII scFv genes; (ii) purification of anti-LNFPIII scFv-Fc proteins from stably and transiently expressed cells; and (iii) extracellular or intracellular localization of two anti-LNFPIII and three anti-Man3 scFv-Fc proteins. The results suggest that expression of anti-Man3 and other anti-carbohydrate antibodies in mammalian cells is disadvantageous for cell growth.

Surface plasmon resonance and NMR analyses of anti Tn-antigen MLS128 monoclonal antibody binding to two or three consecutive Tn-antigen clusters

Tn-antigens are tumour-associated carbohydrate antigens that are involved in metastatic processes and are associated with a poor prognosis. MLS128 monoclonal antibody recognizes the structures of two or three consecutive Tn-antigens (Tn2 or Tn3). Since MLS128 treatment inhibits colon and breast cancer cell growth [Morita, N., Yajima, Y., Asanuma, H., Nakada, H., and Fujita-Yamaguchi, Y. (2009) Inhibition of cancer cell growth by anti-Tn monoclonal antibody MLS128. Biosci. Trends 3, 32-37.], understanding the interaction between MLS128 and Tn-clusters may allow us to the development of novel cancer therapeutics. Although MLS128 was previously reported to have specificity for Tn3 rather than Tn2, similar levels of Tn2/Tn3 binding were unexpectedly observed at 37°C. Thus, thermodynamic analyses were performed via surface plasmon resonance (SPR) using synthetic Tn2- and Tn3-peptides at 10, 15, 20, 25 and 30°C. SPR results revealed that MLS128s association constants for both antigens were highly temperature dependent. Below 25°C MLS128s association constant for Tn3-peptide was clearly higher than that for Tn2-peptide. At 30°C, however, the association constant for Tn2-peptide was higher than that for Tn3-peptide. This reversal of affinity is due to the sharp increase in K(d) for Tn3. These results were confirmed by NMR, which directly measured MLS128-Tn binding in solution. This study suggested that thermodynamic control plays a critical role in the interaction between MLS128/Tn2 and MLS128/Tn3.

Renewed interest in basic and applied research involving monoclonal antibodies against an oncofetal Tn-antigen

Tn-antigen (GalNAcα-Ser/Thr) is one of the most common aberrations associated with cancer progression and metastasis, and thus is an excellent target for development of cancer diagnostics and therapeutics. MLS128 monoclonal antibody (mAb), derived from a mouse immunized with human colon carcinoma cells, was reported to bind to two or three consecutive Tn-antigens (Tn2 or Tn3) with one-order higher affinity for Tn3 than for Tn2. Our recent studies demonstrated that MLS128 significantly inhibits breast and colon cancer cell growth. Molecular cloning of the variable regions of heavy (VH) and light (VL) chains revealed that the VH sequence of MLS128 shared 97% nucleotide sequence identity with the VH of 83D4 mAb, derived from breast cancer-immunized mice, which has a similar affinity for Tn2/Tn3. MLS128 single-chain antibodies (scFv) and scFv-Fc were constructed to confirm the affinity for synthetic Tn2/Tn3 peptides. Thermodynamic studies on MLS128 binding to Tn2/Tn3 revealed its unique nature of temperature-dependent binding.

Expression and structural characterization of anti-T-antigen single-chain antibodies (scFvs) and analysis of their binding to T-antigen by surface plasmon resonance and NMR spectroscopy

T-antigen (Galβ1-3GalNAcα-1-Ser/Thr), also known as Thomsen-Friedenreich antigen (TF antigen), is an oncofetal antigen commonly found in cancerous tissues. Availability of anti-T-antigen human antibodies could lead to the development of cancer diagnostics and therapeutics. Four groups of single-chain variable fragment (scFv) genes were previously isolated from a phage library (Matsumoto-Takasaki et al. (2009) Isolation and characterization of anti-T-antigen single chain antibodies from a phage library. BioSci Trends 3:87-95.). Here, four anti-T-antigen scFv genes belonging to Group 1-4 were expressed and produced in a Drosophila S2 cell expression system. ELISA and surface plasmon resonance (SPR) analyses confirmed the binding activity of 1E8 scFv protein to various T-antigen presenting conjugates. NMR experiments provided evidence of the folded nature of the 1E8 scFv protein. ScFv-ligand contact was identified by STD NMR, indicating that the galactose unit of T-antigen at the non-reducing end was primarily recognized by 1E8 scFv. This thus provides direct evidence of T-antigen specificity.

Toad skin extract cinobufatini inhibits migration of human breast carcinoma MDA-MB-231 cells into a model stromal tissue

Toad skin extract cinobufatini study has been focused on anticancer activity, especially apoptosis-inducing activity by bufosteroids. The present study examined effect of the toad skin extract on cancer cell migration into model stromal tissues. Human breast carcinoma cell line MDA-MB-231 was incubated in the presence or absence of toad skin extract on a surface of reconstituted type I collagen gel as a model stromal tissue allowing the cells to migrate into the gel. Frozen sections were microscopically observed after azan staining. Data showed a decrease of cell number in a microscopic field and shortening of cell migration into the model stromal tissue in a dose dependent manner. This suggests that toad skin extract may possess migration-preventing activity in addition to cell toxicity such as apoptosis-inducing activity. The multifaceted effects including apoptosis-inducing and cancer cell migration-preventing activities would improve usefulness of toad skin extract cinobufatini as an anticancer medicine.

Characterization of three different single chain antibodies recognizing non-reducing terminal mannose residues expressed in Escherichia coli by an inducible T7 expression system

We previously isolated phage antibodies from a phage library displaying human single chain antibodies (scFvs) by screening with a mannotriose (Man3)-bearing lipid. Of four independent scFv genes originally characterized, 5A3 gene products were purified as fusion proteins such as a scFv-human IgG1 Fc form, but stable clones secreting 1A4 and 1G4 scFv-Fc proteins had never been established. Thus, bacterial expression systems were used to purify 1A4 and 1G4 scFv gene products as soluble forms. Purification of 1A4 and 1G4 scFv proteins from inclusion bodies was also carried out together with purification of 5A3 scFv protein in order to compare their Man3-binding abilities. The present studies demonstrated that 1A4 and 1G4 scFv proteins have a higher affinity for Man3 than 5A3 scFv protein, which may determine whether scFv-Fc proteins expressed in mammalian cells are retained in the ER or secreted. Furthermore, the inhibitory effects of anti-Man3 1G4 scFv and anti-Tn antigen scFv proteins on MCF-7 cell growth were evaluated. Despite the fact that no obvious difference was detected in cell growth, microscopic observations revealed inhibition of foci formation in cells grown in the presence of the anti-carbohydrate scFv proteins. This finding provides a basis for the development of cancer therapeutics.