Recognition of peptidyl epitopes by polymorphic epithelial mucin (PEM)-specific monoclonal antibodies

The renascence of continuous-flow peptide synthesis - an abridged account of solid and solution-based approaches

Within a decade of Merrifield's seminal description of solid-phase peptide synthesis, the synergies between solid-phase approaches and flow synthesis were noted by a number of groups. However, despite the various advantages flow brings to peptide synthesis, throughout the 1990s and 2000s, interest in the technique was overshadowed by microwave assisted approaches. However, the current expansion of flow technologies has reinvigorated interest in both solid-phase and solution-phase continuous-flow approaches for assembling peptides. This perspective traces the introduction and evolution of continuous-flow solid-phase synthesis from a practical aspect with a particular focus on solid supports, acylation protocols, and racemisation suppression. Practical aspects of solution-phase continuous-flow peptide synthesis are also considered with an evaluation of microreactor systems, coupling protocols, and fragment-based approaches for assembly of extended peptide units.

P5L mutation in Ank results in an increase in extracellular inorganic pyrophosphate during proliferation and nonmineralizing hypertrophy in stably transduced ATDC5 cells

Ank is a multipass transmembrane protein that regulates the cellular transport of inorganic pyrophosphate. In the progressive ankylosis (ank) mouse, a premature termination mutation at glutamic acid 440 results in a phenotype characterized by inappropriate deposition of basic calcium phosphate crystals in skeletal tissues. Mutations in the amino terminus of ANKH, the human homolog of Ank, result in familial calcium pyrophosphate dihydrate deposition disease. It has been hypothesized that these mutations result in a gain-of-function with respect to the elaboration of extracellular inorganic pyrophosphate. To explore this issue in a mineralization-competent system, we stably transduced ATDC5 cells with wild-type Ank as well as with familial chondrocalcinosis-causing Ank mutations. We evaluated the elaboration of inorganic pyrophosphate, the activity of pyrophosphate-modulating enzymes, and the mineralization in the transduced cells. Expression of transduced protein was confirmed by quantitative real-time PCR and by ELISA. Levels of inorganic pyrophosphate were measured, as were the activities of nucleotide pyrophosphatase phosphodiesterase and alkaline phosphatase. We also evaluated the expression of markers of chondrocyte maturation and the nature of the mineralization phase elaborated by transduced cells. The cell line expressing the proline to leucine mutation at position 5 (P5L) consistently displayed higher levels of extracellular inorganic pyrophosphate and higher phosphodiesterase activity than the other transduced lines. During hypertrophy, however, extracellular inorganic pyrophosphate levels were modulated by alkaline phosphatase activity in this cell system, resulting in the deposition of basic calcium phosphate crystals only in all transduced cell lines. Cells overexpressing wild-type Ank displayed a higher level of expression of type X collagen than cells transduced with mutant Ank. Other markers of hypertrophy and terminal differentiation, such as alkaline phosphatase, osteopontin, and runx2, were not significantly different in cells expressing wild-type or mutant Ank in comparison with cells transduced with an empty vector or with untransduced cells. These results suggest that the P5L Ank mutant is capable of demonstrating a gain-of-function with respect to extracellular inorganic pyrophosphate elaboration, but this effect is modified by high levels of expression of alkaline phosphatase in ATDC5 cells during hypertrophy and terminal differentiation, resulting in the deposition of basic calcium phosphate crystals.

Humanization and epitope mapping of the H23 anti-MUC1 monoclonal antibody reveals a dual epitope specificity

The tumor-associated antigen MUC1 is a cell surface mucin that is expressed on the apical surface of most glandular epithelial cells, including the ducts of the breast, ovary, pancrease, lung and colon. During malignancy, epithelial tissues regularly display elevated levels of MUC1 in a non-polar fashion and in an underglycosylated form, exposing cryptic peptide and carbohydrate epitopes. As such, MUC1 is regarded a potential target for immunotherapeutical intervention. Murine monoclonal H23 antibody specifically recognizes a MUC1 epitope on the surface of human breast cancer cells. We describe the cloning of the variable domains of H23 and their expression in (Escherichia coli) E. coli as maltose-binding protein-scFv (MBP-scFv) fusions. We humanized H23 and evaluated the binding properties of the murine and the humanized recombinant forms, which were similar in affinity and specificity, but lower in apparent affinity in comparison to the original monoclonal IgG. We mapped the epitope of humanized H23 by affinity-selecting a phage-displayed random peptide library on humanized H23 scFv-displaying bacteria. Our results show that humanized H23 binds an epitope corresponding to the MUC1 tandem repeat and an additional epitope not related to MUC1. These epitopes are competitive, bound with similar affinities and are recognized by the original murine H23 monoclonal antibody as well.

Interferon-gamma upregulates MUC1 expression in haematopoietic and epithelial cancer cell lines, an effect associated with MUC1 mRNA induction

Epithelial mucin-1 (MUC1) is an important target antigen that it is overexpressed in both epithelial and haematological cancers including multiple myeloma (MM) and some lymphomas and leukaemias. MUC1 has adhesive and immunosuppressive properties, which may promote cancer progression. These studies evaluated the effect of IFNs on MUC1 expression, since these agents are widely used in clinical cancer therapy. MUC1 and interferon (IFN) receptor expression were measured by radioligand binding. Changes in MUC1 mRNA levels in response to IFN-gamma were assessed by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). IFN-gamma was found to be a more potent inducer of MUC1 expression than IFN-alpha. 125I-IFN binding studies indicated that both IFN receptors were expressed in most of the cell lines. With IFN-gamma treatment, there was upregulation of MUC1 mRNA. IFN-gamma has a more consistent and more potent effect upon MUC1 induction than IFN-alpha. The ability to upregulate MUC1 across a broad range of cancer types by a clinically available cytokine, IFN-gamma, has important implications for enhancing immunotherapeutic approaches targeting MUC1.

Humanization of an antibody recognizing a breast cancer specific epitope by CDR-grafting

BACKGROUND

Muc1-H23 is a cell surface mucin that is expressed on normal breast luminal epithelial cells and over-expressed in most breast tumors. In addition, Muc-1 expressed by malignant cells is glycosylated differently than Muc-1 expressed by normal cells. This difference in glycosylation exposes a peptide epitope on malignant cells which is not exposed on normal cells. Murine monoclonal antibody H23 recognizes this epitope and stains 91% of breast cancers, but only 1/56 non-malignant breast tissue samples.

OBJECTIVE

To create a human antibody that was equivalent to H23 for potential uses in imaging and/or the therapy of breast cancer.

STUDY DESIGN

We decided to humanize H23 by CDR-grafting using overlap PCR, and to this end, designed and constructed a bacterial expression vector that would allow V-regions, cloned via unique restriction sites, to be expressed as Fab fragments. In this way, we hoped to be able to rapidly evaluate Fab constructs for binding to Muc-1 and to cells and tissue sections that expressed the antigen.

RESULTS

A fully humanized Fab fragment was able to bind Muc-1 peptide, as well as breast cancer cells known to express the epitope and tissue sections, generally showing the same reactivity as the native antibody. In addition, an analysis of sFab expressed with a [His]6 tag preceded by a factor Xa proteolytic cleavage site suggested that E. coli periplasmic signal peptidase was able to cleave the factor Xa site, thereby removing the [His]6 tag.

CONCLUSION

We have generated a human antibody that is capable of recognizing a tumor specific epitope expressed by 91% of breast cancers.

Generation of murine monoclonal antihuman milk fat globule membrane antibodies using immunoprecipitation and BIAcore analyses

A selection of monoclonal antibodies was developed against deoxycholine-solubilized human milk fat globule membranes (HMFG). The antibodies were selected for their ability to immunoprecipitate 125I-labeled HMFG and then further analyzed by surface plasmon resonance on the BIAcore for their reactivity with HMFG and with a fusion protein containing a 4-mer of the muc-1 tandem repeat. Both the HMFG and the fusion protein proved to be robust surfaces for the analysis of crude supernatants. The BIAcore evaluation was useful in identifying true positives. BIAcore analyses of purified antibody preparations were used to determine binding characteristics such as affinity and intensity. The latter proved useful in selecting a panel for evaluation by immunohistochemistry for breast tissue reactivity. Four of 6 antibodies appeared to react more intensely with tumor compared with normal breast tissues. One of those antibodies reacted with the fusion protein 4-mer of the muc-1 tandem repeat.

Immunogold labeling of oncogenic and tumor related proteins

Immunogold labeling electron microscopy technique has been used to study the ultrastructural localization of oncogenic proteins: Mos, Met, Ski, and the tumor-associated protein, Muc1, as well as their relationship with other tumor-related proteins. By pre- and postembedding immunogold labeling electron microscopy techniques, we showed that the Mos protein pp39mos colocalized with microtubule bundles, suggesting that microtubulin or microtubule-associated protein(s) may be the substrate of Mos. Met protein was labeled at the microvilli of the lumen that are formed in cultured T47D cells, implying its potential involvement in lumen formation. Ski localization experiments revealed a unique globular structure "Ski body" that is present inside the nucleus of interphase chicken embryo fibroblast infected with Ski cDNA FB29 and FB2-29. Ski bodies were also found scattered in the cytoplasm of metaphase FB29 and FB2-29 Ski expressing chicken embryo fibroblasts. In T47D cells, tumor-associated protein Muc1 was associated with both the plasma membrane and the membranes of secretory vesicles in the cytoplasm. In MUC1 infected NIH3T3 cells, however, labeling showed that in addition to the plasma membrane and the membranes of secretory vesicles, some Muc1 gold spheres were seen inside the secretory vesicles, suggesting that the subcellular localization of the protein may vary in different cell types.

Humanization of an anti-mucin antibody for breast and ovarian cancer therapy

Antibody-drug conjugates utilize the targetting potential of antibodies to improve the potential of cytostatic or cytocidal drugs. One such murine monoclonal antibody, CTM01 (mCTM01), which recognizes an epitope on breast epithelial mucin, has potential for the treatment of breast and ovarian cancers. We examine in this paper the comparative properties of mCTM01 against a number of other anti-mucin antibodies. We then describe the humanization and high level re-expression of humanized CTM01 (hCTM01), a process designed to avoid the immune response to administered murine antibodies in human patients and to produce sufficient material for clinical studies. We show that the humanized form has properties superior to mCTM01 in terms of binding affinity to antigen presented on tumour cells.

Identification of a previously unknown human collagen chain, alpha 1(XV), characterized by extensive interruptions in the triple-helical region

A previously unknown collagen cDNA clone, PF19, was isolated from a human placenta library. The 2.1-kilobase insert has a complete open reading frame of 709 amino acids that includes 12 amino acids of the NH2-terminal domain, a principally collagenous region of 577 residues, and 120 residues of the noncollagenous COOH terminus. The collagenous part of the sequence encoded by PF19 is characterized by 13 interruptions ranging in size from 2 to 45 amino acids. Within four interruptions are consensus sequences for attachment of serine-linked glycosaminoglycans and asparagine-linked oligosaccharides suggesting that this collagen may be extensively glycosylated. A synthetic decapeptide representing a sequence at the beginning of the COOH-terminal noncollagenous domain was used to prepare an antibody in rabbits. This antiserum detected a 125-kDa bacterial collagenase-sensitive protein in Western blots of HeLa cell lysate. Consistent with the size of the collagen chain, Northern blot hybridization revealed a major transcript of 5.3 kilobases and two minor ones of 4.7 and 4.4 kilobases that are present in cultured human fibroblasts but absent from umbilical vein endothelial cells. We propose that the previously unidentified polypeptide described in this report be designated the alpha 1 chain of type XV collagen.

Epithelial membrane antigen expression in breast fluids and 'witch's milk'

We have examined breast fluids from non-lactating women and male neonates for the expression of epithelial membrane antigen (EMA), also termed polymorphic epithelial mucin (PEM). All fluids exhibited significant amounts of EMA as demonstrated by immunoblot analyses and enzyme immunoassay. EMA was present in the breast fluids of both pre- and post-menopausal women, and these results suggest that nipple aspirates could provide an easily accessible source of antigen for assessing the value of EMA as a tumor marker both before and after various therapeutic modalities. The presence of EMA in the 'witch's milks' indicates that full maturation of the breast is not a prerequisite for antigen expression in breast tissue.