Production and Characterization of Monoclonal Antibodies for Immunoassay of the Lung Cancer Marker proGRP

Covalent Organic Framework Nanosheets for Fluorescence Quantification of Peptide

Rapid and sensitive quantification of peptides plays an important role in clinical diagnosis. Fluorescence assay is one of the most promising peptide detection tools, but it relies on intrinsic fluorescence or additional derivatization, resulting in poor versatility. Covalent organic frameworks (COFs) have shown a good application prospect in the field of fluorescence detection, but their application scope is limited to heavy metal ions and some small polar organic molecules. Herein, we report the application of COFs nanosheet for fluorescence detection of peptides. Fluorescent sp² acrylonitrile-linked COFs nanosheets (TTAN-CON) were prepared by water-assisted ultrasonic exfoliation which performed with excellent fluorescence properties with Stokes shifts of 146 nm and fluorescence quantum yield of up to 24.45%. Compared to the bulk fluorescent COFs, exfoliated CONs films performed with better stability of fluorescence signal in solution. We found the fluorescence of TTAN-CON can be effectively quenched by hydrophobic peptides at a very rapid rate (less than 5 min per sample). TTAN-CON presented good sensitivity and selectivity for hydrophobic peptides detection via the static and dynamic joint quenching mechanism. TTAN-CON was further used to detect NLLGLIEAK and ProGRP_31-98, two target peptide fragments of lung cancer biomarker ProGRP. The fluorescence intensities of TTAN-CON were negative linearly correlated with the amounts of hydrophobic NLLGLIEAK over the range of 5-1000 ng/mL with the correlation coefficients over 0.99, and the limit of detection was 1.67 ng/mL, displaying higher sensitivity and convenience than traditional optical methods. What's more, the quantification of ProGRP_31-98 was achieved by the quantification of hydrophobic peptides in its enzyme hydrolysis products. We anticipate COFs nanosheets to be a universal fluorescence detection work-box for peptides biomarkers with clinical significance.

On-line duplex molecularly imprinted solid-phase extraction for analysis of low-abundant biomarkers in human serum by liquid chromatography-tandem mass spectrometry

In the present work, a pair of molecularly imprinted polymers (MIPs) targeting distinct peptide targets were packed into trap columns and combined for automated duplex analysis of two low abundant small cell lung cancer biomarkers (neuron-specific enolase [NSE] and progastrin-releasing peptide [ProGRP]). Optimization of the on-line molecularly imprinted solid-phase extraction (MISPE) protocol ensured that the MIPs had the necessary affinity and selectivity towards their respective signature peptide targets - NLLGLIEAK (ProGRP) and ELPLYR (NSE) - in serum. Two duplex formats were evaluated: a physical mixture of the two MIPs (1:1 w/w ratio) inside a single trap column, and two separate MIP trap columns connected in series. Both duplex formats enabled the extraction of the peptides from serum. However, the trap columns in series gave superior extraction efficiency (85.8±3.8% and 49.1±6.7% for NLLGLIEAK and ELPLYR, respectively). The optimized protocol showed satisfactory intraday (RSD≤23.4 %) and interday (RSD≤14.6%) precision. Duplex analysis of NSE and ProGRP spiked into digested human serum was linear (R²≥0.98) over the disease range (0.3-30 nM). The estimated limit of detection (LOD) and limit of quantification (LOQ) were 0.11 nM and 0.37 nM, respectively, for NSE, and 0.06 nM and 0.2 nM, respectively, for ProGRP. Both biomarkers were determined at clinically relevant levels. To the best of our knowledge, the present work is the first report of an automated MIP duplex biomarker analysis. It represents a proof of concept for clinically viable duplex analysis of low abundant biomarkers present in human serum or other biofluids.

Liquid chromatography mass spectrometry based characterization of epitope configurations

Here we evaluate a quick and easy tool for determination of epitope configuration using immunocapture and liquid chromatography mass spectrometry (LC-MS) subsequent to pre-treatment of the target protein to disrupt its three-dimensional structure. The approach can be a valuable screening tool to identify antibodies that can be used in peptide capture by anti-protein antibodies. The experimental set-up was established using seven monoclonal antibodies (mAbs) with known linear or conformational epitope recognition. The mAbs were developed to target either of the two biomarkers, progastrin releasing peptide (ProGRP) or human chorionic gonadotropin (hCG). Best coherence with established epitope configuration was seen when using both denaturation, reduction and alkylation as pre-treatment method of the proteins (≥70% reduction in MS signal intensity compared to control) prior to immunocapture and LC-MS determination. The final method was used to determine the epitope configuration of four anti-thyroglobulin mAbs with unknown epitope configuration; all four mAbs showed configurational epitope recognition. These results were also supported by western blots of native, and reduced and alkylated protein using three of the evaluated mAbs, and by analysis native, and reduced and alkylated protein in a routine immunofluorometric assay employing the four evaluated antibodies.

Immunocapture sample clean-up in determination of low abundant protein biomarkers – a feasibility study of peptide capture by anti-protein antibodies

Immunocapture in mass spectrometry based targeted protein analysis using a bottom-up workflow is nowadays mainly performed by target protein extraction using anti-protein antibodies followed by tryptic digestion. Already available monoclonal antibodies (mAbs) which were developed against intact target proteins (anti-protein antibodies) can capture proteotypic epitope containing peptides after tryptic digestion of the sample. In the present paper considerations when developing a method for targeted protein quantitation through capture of epitope containing peptides are discussed and a method applying peptide capture by anti-protein antibodies is compared with conventional immunocapture MS. The model protein used for this purpose was progastrin releasing peptide (ProGRP), a validated low abundant biomarker for Small Cell Lung Cancer with reference values in serum in the pg mL⁻¹ range. A set of mAbs which bind linear epitopes of ProGRP are available, and after a theoretical consideration, three mAbs (E146, E149 and M18) were evaluated for extraction of proteotypic epitope peptides from a complex sample. M18 was the best performing mAb for peptide capture by anti-protein antibodies, matching the LOD (54 pg mL⁻¹) and LOQ (181 pg mL⁻¹) of the existing conventional immunocapture LC-MS/MS method for determination of ProGRP. Peptide and protein capture using the same mAb were also compared with respect to sample clean-up, and the peptide capture workflow yielded cleaner extracts and therewith less complex chromatograms. Analysis of five patient samples demonstrated that peptide capture by anti-protein antibodies can be used for the determination of various levels of endogenously present ProGRP.

Targeted protein biomarker determination by immunocapture LC-MS/MS: comparison of peptide and protein capture using anti-protein antibodies.

Automated Protein Biomarker Analysis: on-line extraction of clinical samples by Molecularly Imprinted Polymers

Robust biomarker quantification is essential for the accurate diagnosis of diseases and is of great value in cancer management. In this paper, an innovative diagnostic platform is presented which provides automated molecularly imprinted solid-phase extraction (MISPE) followed by liquid chromatography-mass spectrometry (LC-MS) for biomarker determination using ProGastrin Releasing Peptide (ProGRP), a highly sensitive biomarker for Small Cell Lung Cancer, as a model. Molecularly imprinted polymer microspheres were synthesized by precipitation polymerization and analytical optimization of the most promising material led to the development of an automated quantification method for ProGRP. The method enabled analysis of patient serum samples with elevated ProGRP levels. Particularly low sample volumes were permitted using the automated extraction within a method which was time-efficient, thereby demonstrating the potential of such a strategy in a clinical setting.

Identification of binding sites for C-terminal pro-gastrin-releasing peptide (GRP)-derived peptides in renal cell carcinoma: a potential target for future therapy

OBJECTIVE

To determine the expression and biology of the neuroendocrine growth factor gastrin-releasing peptide (GRP) and other proGRP-derived peptides in renal cancer.

MATERIALS AND METHODS

Receptor binding studies, enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay, were used to quantitate the presence of proGRP-derived peptide receptors and their ligands in renal cancer cell lines and human renal cancers. Biological activity of proGRP peptides was confirmed with proliferation, migration, and extracellular-signal-regulated kinases 1 and 2 (ERK1/2) activation assays in vitro. In vivo, ACHN renal cancer xenografts were treated with proGRP-derived peptides to assess tumour size and necrosis. hypoxia-inducible factor 1α (HIF1α) and vascular endothelial growth factor (VEGF) expression were investigated with Western blotting and ELISA respectively, to determine the possible contribution of the proGRP peptides to tumour viability.

RESULTS

In ACHN cells that expressed both proGRP- and GRP-receptors, the expression of proGRP binding sites was 80-fold greater than the GRP-receptor (GRPR). C-terminal proGRP-derived peptides stimulated the activation of ERK1/2, but with a different time course to GRP, consistent with the suggestion that these peptides may have unique cellular functions. Both GRP and proGRP47-68 stimulated proliferation and migration of ACHN cells in vitro, but only GRP reduced the extent of tumour necrosis in ACHN xenografts. GRP, but not proGRP47-68, was able to induce HIF1α and VEGF expression in ACHN cells. This may account in part for the reduction in necrosis after GRP treatment. C-terminal proGRP-derived peptides were present in all three renal cancer cell lines and a panel of human renal cancers, but mature amidated GRP was absent.

CONCLUSION

C-terminal proGRP peptides are more abundant in renal cancers and their cell lines than the more extensively studied amidated peptide, GRP. These results suggest that C-terminal proGRP-derived peptides may be a better target for novel renal cancer treatments.

Determining ProGRP and isoforms in lung and thyroid cancer patient samples: comparing an MS method with a routine clinical immunoassay

This paper compares two methods to determine the tumor marker progastrin-releasing peptide (ProGRP): as routine assay, the automated time-resolved immunofluorometric assay (TR-IFMA), which allows total ProGRP determination; and the immunocapture liquid chromatography selected reaction monitoring mass spectrometry (LC-SRM-MS) method, which additionally allows isoform differentiation. The investigation included 60 serum samples from patients suffering from various cancer diseases which may cause elevated ProGRP levels (small cell lung carcinoma; SCLC, non-small cell lung carcinoma; NCLC; and medullary thyroid cancer; MTC, as well as some with unspecific diagnosis). The two methods showed good correlation (R (2) = 0.887). However, the MS method determines the total ProGRP concentration systematically approximately 30 % lower than the TR-IFMA, implying that the absolute values generated by the methods are not interchangeable. The MS method gives additional information about isoform levels in the samples, providing novel insight into isoform expression on the protein level.

Digging deeper into the field of the small cell lung cancer tumor marker ProGRP: a method for differentiation of its isoforms

In this paper, we have used a newly developed immunocapture and LC-MS method to demonstrate for the first time the presence of protein isoforms 1 and 3 of the small cell lung cancer (SCLC) marker progastrin-releasing peptide (ProGRP) in sera. In addition, the method allows for indirect determination of the relative presence of the other known isoform of ProGRP, also known as ProGRP isoform 2. This new method is able to determine total ProGRP as a marker in sera at clinically relevant levels and to differentiate between isoforms at the low-pM level through combining selective sample preparation by immunoextraction, tryptic digestion, and separation followed by detection with LC-SRM-MS of the signature peptides, NLLGLIEAK (total ProGRP), LSAPGSQR (ProGRP isoform 1), and DLVDSLLQVLNVK (ProGRP isoform 3), with accuracies ≤ 25% for lower limit of quantification (LLOQ) and precisions ≤ 33%. By analyzing serum samples from four patients diagnosed with SCLC using the here described new and fully validated method, the ability is shown to both determine total ProGRP concentration and to differentiate between ProGRP isoforms 1 and 3 in one single run. Quantification of various ProGRP isoforms in one single run may be helpful for further understanding of the underlying biochemical processes in SCLC and differentiation of small cell lung cancer.

Characteristics and clinical validity of two immunoassays for ProGRP

Progastrin-releasing peptide (proGRP) is a promising serum tumor marker for small cell lung cancer (SCLC). We have tested assay specificity and performed a correlation study between a recently developed time-resolved immunofluorometric assay (TR-IFMA) for proGRP and the established Advanced Life Science Institute (ALSI) ELISA method. Between-method correlation and comparison of clinical performance were studied in 481 individuals, among them, 178 lung cancers, 84 benign diseases of the lung, and 219 healthy controls. Follow-up time >6 years was observed for 89 patients with SCLC. The two assays had quite different epitope specificities where the TR-IFMA recognized a considerable smaller proGRP fragment than the ALSI ELISA. However, the correlation between the two methods for elevated proGRP values (>85 ng/l) was good (ρ = 0.948). Both assays displayed good discrimination between benign lung diseases and SCLC. The cut-off values for positive classification of SCLC versus non-small cell lung cancers and benign lung diseases at >95% specificity were 85 ng/l for the TR-IFMA and 42 ng/l for the ALSI ELISA. Both proGRP assays showed good clinical validity. However, due to differences in the recommended cut-off values, switching methods is not recommended. There was a significant difference in survival of patients with TR-IFMA proGRP values over the cut-off (85 ng/l) compared with patients with values under the cut-off, p = 0.0002. In contrast, the ALSI ELISA assay failed to provide statistically significant prognostic information, p = 0.066.

Pro-GRP-derived peptides are expressed in colorectal cancer cells and tumors and are biologically active in vivo

Amidated gastrin-releasing peptide (GRP) is the prototypical autocrine growth factor. Nonamidated peptides derived from the C terminus of pro-GRP are also biologically active in colorectal cancer (CRC) cell lines in vitro, via a receptor distinct from the GRP receptor. The aims of this study were to measure the amounts of pro-GRP-derived peptides in human CRC cell lines and tumors, characterize the immunoreactive peptide, and investigate its effect on proliferation in vitro and in vivo. Pro-GRP-derived peptides were quantitated by region-specific ELISA in extracts of five human CRC cell lines and 20 tumors. The immunoreactive material was purified by HPLC and its mass and sequence established by mass spectrometry. The concentration of GRPamide was determined by RIA. Proliferation of DLD-1 cells and murine gastrointestinal mucosa was measured by [(3)H]-thymidine incorporation and mitotic index, respectively. In CRC cell extracts, ELISA for pro-GRP-derived peptides detected 3-152 fmol/10(6) cells. The immunoreactive peptide was purified and identified as pro-GRP42-98. Resected stage III tumors contained significantly less pro-GRP immunoreactivity than stage II tumors, and no amidated GRP was detected in cell lines or tumors. Stable transfection of DLD-1 cells with pro-GRP short hairpin RNA, or treatment with a monoclonal anti-pro-GRP antibody, significantly reduced proliferation. Pro-GRP42-98, pro-GRP47-68, and pro-GRP80-97 significantly stimulated mitosis in colonic, but not small intestinal, mucosa of 10-wk-old mice. We conclude that nonamidated peptides derived from the C terminus of pro-GRP are expressed in significant quantities in CRC cell lines and tumors and stimulate the proliferation of CRC cells and of normal colonic mucosa. Such peptides are attractive targets for novel CRC therapies.

Splenic marginal zone lymphoma with VH1-02 gene rearrangement expresses poly- and self-reactive antibodies with similar reactivity

One-third of all splenic marginal zone lymphomas (SMZL) use the IgH VH1-02 gene. These cases are usually not associated with hepatitis C virus infection. Of interest, the rearranged VH1-02 genes display similar complementarity determining regions 3, a finding confirmed by our study. The latter suggests that these SMZL may produce antibodies with similar reactivity. We produced recombinant antibodies from 5 SMZL cases with VH1-02 gene rearrangement to study the binding reactivity of these antibodies. Surprisingly, the recombinant antibodies demonstrated poly- and self-reactivity as demonstrated by their reactivity with nuclear, cytoplasmic, as well as membranous antigens expressed by human cells and by reactivity with human serum. This polyreactivity was specific as demonstrated by ELISA. The antibodies did not react with proteins on the cell surface that are induced by apoptosis as shown for antibodies produced by chronic lymphatic leukemia with VH1-02 gene rearrangement. The results indicate that a common subset of SMZL arises from polyreactive B cells, a subset of marginal zone B cells that are important in the immunologic defense against infection.

Study on biodistribution and radioimmunoimaging of (131)iodine-labeled monoclonal antibody D-D3 against progastrin-releasing peptide31-98 in tumor-bearing mouse

This study was aimed at investigating the biodistribution and radioimmunoimaging of (131)I-D-D3 in nude mice bearing different types of tumor xenografts. Radioiodination of the D-D3 antibody was performed with the chloramine-T method. The radiochemical purity was determined through thin-layer chromotography. (131)I-D-D3 was injected into healthy Kunming mice via a tail vein, and the %ID/g for various organs was obtained. Similarly, the %ID/g and tumor/nontumor tissue ratio of (131)I-D-D3 in nude mice bearing small cell lung cancer (SCLC) xenografts were obtained. Planar images of (131)I-D-D3 in tumor-bearing nude mice were acquired at different times after injection. The (131)I-D-D3 labeling rate was 86.56%  ± 3.8%. The radiochemical purity of (131)I-D-D3 was 99.27%  ± 0.6%. After 12 hours of incubation in 37°C water bath, the radiochemical purity was 97.64%  ±  0.5% and remained at 88.38% ± 0.4% after 48 hours. After being mixed with healthy human serum for 24 hours, the radiochemical purity was more than 64%. The metabolism of (131)I-D-D3 in healthy Kunming mice was consistent with a two-compartment model with first-order absorption; T(1/2α) and T(1/2β) were 0.25 and 37.89 hours, respectively. The %ID/g of (131)I-D-D3 in SCLC xenografts was much higher than those of other tissues at 48 hours after injection, and the tumor/nontumor tissue ratio also gradually increased with time. After 24 hours of injection, planar imaging was obtained, which clearly showed a contrasting tumor on the right armpit of nude mice bearing SCLC with high concentrations of radioactivity. Also, nude mice bearing gastric cancer showed similar results as that of the SCLC with a lower radioactivity level. No observable accumulation was observed in nude mice bearing pancreatic cancer or lung adenocarcinoma. The labeling rate and radiochemical purity of (131)I-D-D3 were high and stable. (131)I-D-D3 selectively accumulated at tumors that highly expressed progastrin-releasing peptide; therefore, it is a promising radioimmunoimaging reagent for SCLC.

Activation of EphA receptors on CD4+CD45RO+ memory cells stimulates migration

We have demonstrated previously that binding of ephrin-A1 to EphA receptors on human CD4(+) and CD8(+) T cells stimulates migration. Two EphA receptors have been reported in T cells: EphA1 at the protein level and EphA4 at the mRNA level. In this study, we wanted to investigate the expression profile of these receptors in T cell subpopulations and to test if expression differences would affect the potential of cells to migrate upon ephrin-A1 binding. We have generated an anti-EphA4 mAb for expression analysis. Our data show that functional EphA4 is expressed on the cell surface of CD4(+) and CD8(+) T cells. In addition, EphA4 receptor expression is induced after overnight incubation in serum-free medium, in particular, on CD4(+)CD45RO(+) T cells. Migration of CD4(+) T cells in response to ephrin-A1 is observed for memory cells (CD45RO(+)) and much weaker for naïve cells (CD45RA(+)). A signaling complex associated with the EphA4 receptor has also been isolated and includes EphA1, the Src family kinases Fyn and Lck, Slp76, and Vav1. To conclude, T cells express EphA1 and EphA4 receptors. Expression differences of EphA4 are observed in subpopulations of CD4(+) T cells. This is related to the cell migration potential after ephrin-A1 binding.

Automated Time-Resolved Immunofluorometric Assay for Progastrin-Releasing Peptide

Background: Small cell lung cancer accounts for approximately 20% of new cases of lung cancer, and advanced disease is prevalent at the time of diagnosis. Neuron-specific enolase (NSE) has been the primary tumor marker in small cell lung cancer but it has relatively low sensitivity in early-stage disease. Progastrin-releasing peptide (proGRP) is a promising alternative or complementary marker for NSE. We have previously described a time-resolved immunofluorometric assay (TR-IFMA) for proGRP that lacked the necessary sensitivity and robustness for use in the routine clinical laboratory. Herein we describe the development of an improved assay using a novel monoclonal antibody pair.

Methods: Mice were immunized with different conjugated proGRP peptides, including residues 31–98, 1–98, and preproGRP(-23–125). Pair combinations of the resulting monoclonal antibodies (mAb) were tested. The improved TR-IFMA was compared with the only other available proGRP assay, the proGRP ELISA (IBL).

Results: A panel of 12 high-affinity mAbs was produced. The best assay combination was between our original E146 mAb as solid-phase antibody and the new mAb M16 as tracer. The new TR-IFMA had a linear dose-response curve, a wide dynamic range (13–13 500 ng/L), and a limit of detection of 2.8 ng/L. Total CV was <5.6% over the whole measuring range. Bland-Altman difference analysis indicated a significant positive bias between the IFMA and the ELISA.

Conclusions: We describe a sensitive and robust mAb-based TR-IFMA for proGRP. The assay is fully automated and displays high quality performance.

Targeted determination of the early stage SCLC specific biomarker pro-gastrin-releasing peptide (ProGRP) at clinical concentration levels in human serum using LC-MS

Pro-gastrin-releasing peptide (ProGRP) is used as a specific diagnostic marker for small cell lung cancer (SCLC), a rapidly growing neoplasm with high mortality. Our object was to develop an LC-MS method for the detection and quantification of ProGRP in human serum using the specific tryptic digestion product NLLGLIEAK (m/z 485.8 for [M + 2H](2+)). For this purpose the sample pretreatment, clean-up, enrichment, and LC-MS conditions were evaluated. Sample pretreatment was carried out using ACN precipitation to decrease the sample complexity. Although ProGRP (31-98) standards were soluble in 99% ACN, it showed that optimal signal intensities were obtained by adding ACN to the serum in a 1:1 ratio v/v. A simplified tryptic digest protocol was carried out using 100 mM triethanolamine buffer to ensure pH stability during the whole procedure. The simplified protocol also includes omission of reducing and alkylating reagents. Necessary additional sample clean-up was achieved by trapping NLLGLIEAK on a RAM column (ADS-C8) which was back-flushed onto the analytical BioBasic C8 column. Volume of injection, sample enrichment, and column capacity are among the factors optimized to reach a mass LOD of 150 pg on column (OC) ProGRP (31-98). Detection of ProGRP in the serum sample of a patient suffering from SCLC with a clinically relevant concentration shows the potential of the method in diagnosis, prognosis, and monitoring of the disease.