The transient expression of recombinant proteins in plant cell packs facilitates stable isotope labelling for NMR spectroscopy.

Nuclear magnetic resonance (NMR) spectroscopy can be used to determine the structure, dynamics and interactions of proteins. However, protein NMR requires stable isotope labelling for signal detection. The cells used for the production of recombinant proteins must therefore be grown in medium containing isotopically labelled substrates. Stable isotope labelling is well established in Escherichia coli, but bacteria are only suitable for the production of simple proteins without post-translational modifications. More complex proteins require eukaryotic production hosts, but their growth can be impaired by labelled media, thus reducing product yields and increasing costs. To address this limitation, we used media supplemented with isotope-labelled substrates to cultivate the tobacco-derived cell line BY-2, which was then cast into plant cell packs (PCPs) for the transient expression of a labelled version of the model protein GB1. Mass spectrometry confirmed the feasibility of isotope labelling with 15 N and 2 H using this approach. The resulting NMR spectrum featured a signal dispersion comparable to recombinant GB1 produced in E. coli. PCPs therefore offer a rapid and cost-efficient alternative for the production of isotope-labelled proteins for NMR analysis, especially suitable for complex proteins that cannot be produced in microbial systems.

N-Myc expression enhances the oncolytic effects of vesicular stomatitis virus in human neuroblastoma cells.

N-myc oncogene amplification is associated but not present in all cases of high-risk neuroblastoma (NB). Since oncogene expression could often modulate sensitivity to oncolytic viruses, we wanted to examine if N-myc expression status would determine virotherapy efficacy to high-risk NB. We showed that induction of exogenous N-myc in a non-N-myc-amplified cell line background (TET-21N) increased susceptibility to oncolytic vesicular stomatitis virus (mutant VSVΔM51) and alleviated the type I IFN-induced antiviral state. Cells with basal N-myc, on the other hand, were less susceptible to virus-induced oncolysis and established a robust IFN-mediated antiviral state. The same effects were also observed in NB cell lines with and without N-myc amplification. Microarray analysis showed that N-myc overexpression in TET-21N cells downregulated IFN-stimulated genes (ISGs) with known antiviral functions. Furthermore, virus infection caused significant changes in global gene expression in TET-21N cells overexpressing N-myc. Such changes involved ISGs with various functions. Therefore, the present study showed that augmented susceptibility to VSVΔM51 by N-myc at least involves downregulation of ISGs with antiviral functions and alleviation of the IFN-stimulated antiviral state. Our studies suggest the potential utility of N-myc amplification/overexpression as a predictive biomarker of virotherapy response for high-risk NB using IFN-sensitive oncolytic viruses.

The recombinant anti-EGF receptor immunotoxin 425(scFv)-ETA' suppresses growth of a highly metastatic pancreatic carcinoma cell line.

Pancreatic carcinoma still has the highest mortality rate in comparison to any other malignancy. Major reasons are late detection of disease, highly aggressive tumor growth and the early formation of metastases. Thus, novel effective therapies are urgently needed to improve the outcome of the patients. Overexpression of the epidermal growth factor receptor (EGFR) and its ligands has been implicated in the oncogenesis of pancreatic carcinoma and associated with an unfavorable prognosis. Consequently, the EGFR represents a specific target antigen suitable for immunotherapy. We generated a recombinant immunotoxin by fusing the anti-EGFR single chain fragment 425(scFv) to a truncated mutant of Pseudomonas Exotoxin A (ETA'). Using the expression vector pBM1.1, functional 425(scFv)-ETA' was periplasmically expressed under osmotic stress conditions in the presence of compatible solutes. The 72 kDa His10-tagged fusion protein was purified by a combination of metal-ion affinity and molecular size chromatography. Binding activity and specificity of the immunotoxin to the EGFR-positive pancreatic carcinoma cell line L3.6pl was confirmed by flow cytometry and ELISA. Finally, 425(scFv)-ETA' showed significant toxicity toward this cell line reaching 50% inhibition of cell proliferation at a concentration (IC50) of 7.5 ng/ml. This is the first report documenting the specific cytotoxicity of a recombinant immunotoxin towards metastatic pancreatic carcinoma cells, suggesting that EGFR-specific antibody toxins may become valuable therapeutic reagents for the treatment of pancreatic carcinoma.