Comparison of microbial and transient expression (tobacco plants and plant-cell packs) for the production and purification of the anticancer mistletoe lectin viscumin.

Cancer is the leading cause of death in industrialized countries. Cancer therapy often involves monoclonal antibodies or small-molecule drugs, but carbohydrate-binding lectins such as mistletoe (Viscum album) viscumin offer a potential alternative treatment strategy. Viscumin is toxic in mammalian cells, ruling them out as an efficient production system, and it forms inclusion bodies in Escherichia coli such that purification requires complex and lengthy refolding steps. We therefore investigated the transient expression of viscumin in intact Nicotiana benthamiana plants and Nicotiana tabacum Bright Yellow 2 plant-cell packs (PCPs), comparing a full-length viscumin gene construct to separate constructs for the A and B chains. As determined by capillary electrophoresis the maximum yield of purified heterodimeric viscumin in N. benthamiana was ~7 mg/kg fresh biomass with the full-length construct. The yield was about 50% higher in PCPs but reduced 10-fold when coexpressing A and B chains as individual polypeptides. Using a single-step lactosyl-Sepharose affinity resin, we purified viscumin to ~54%. The absence of refolding steps resulted in estimated cost savings of more than 80% when transient expression in tobacco was compared with E. coli. Furthermore, the plant-derived product was ~3-fold more toxic than the bacterially produced counterpart. We conclude that plants offer a suitable alternative for the production of complex biopharmaceutical proteins that are toxic to mammalian cells and that form inclusion bodies in bacteria.

Novel EGFR-specific immunotoxins based on panitumumab and cetuximab show in vitro and ex vivo activity against different tumor entities.

PURPOSE: The epidermal growth factor receptor (EGFR) is overexpressed in many solid tumors. EGFR-specific monoclonal antibodies (mAbs), such as cetuximab and panitumumab, have been approved for the treatment of colorectal and head and neck cancer. To increase tissue penetration, we constructed single-chain fragment variable (scFv) antibodies derived from these mAbs and evaluated their potential for targeted cancer therapy. The resulting scFv-based EGFR-specific immunotoxins (ITs) combine target specificity of the full-size mAb with the cell-killing activity of a toxic effector domain, a truncated version of Pseudomonas exotoxin A (ETA'). METHODS: The ITs and corresponding imaging probes were tested in vitro against four solid tumor entities (rhabdomyosarcoma, breast, prostate and pancreatic cancer). Specific binding and internalization of the ITs scFv2112-ETA' (from cetuximab) and scFv1711-ETA' (from panitumumab) were demonstrated by flow cytometry and for the scFv-SNAP-tag imaging probes by live cell imaging. Cytotoxic potential of the ITs was analyzed in cell viability and apoptosis assays. Binding of the ITs was proofed ex vivo on rhabdomyosarcoma, prostate and breast cancer formalin-fixed paraffin-embedded biopsies. RESULTS: Both novel ITs showed significant pro-apoptotic and anti-proliferative effects toward the target cells, achieving IC50 values of 4 pM (high EGFR expression) to 460 pM (moderate EGFR expression). Additionally, rapid internalization and specific in vitro and ex vivo binding on patient tissue were confirmed. CONCLUSIONS: These data demonstrate the potent therapeutic activity of two novel EGFR-specific ETA'-based ITs. Both molecules are promising candidates for further development toward clinical use in the treatment of various solid tumors to supplement the existing therapeutic regimes.

Targeted ex vivo reduction of CD64-positive monocytes in chronic myelomonocytic leukemia and acute myelomonocytic leukemia using human granzyme B-based cytolytic fusion proteins.

CMML (chronic myelomonocytic leukemia) belongs to the group of myeloid neoplasms known as myelodysplastic and myeloproliferative diseases. In some patients with a history of CMML, the disease transforms to acute myelomonocytic leukemia (AMML). There are no specific treatment options for patients suffering from CMML except for supportive care and DNA methyltransferase inhibitors in patients with advanced disease. New treatment strategies are urgently required, so we have investigated the use of immunotherapeutic directed cytolytic fusion proteins (CFPs), which are chimeric proteins comprising a selective domain and a toxic component (preferably of human origin to avoid immunogenicity). The human serine protease granzyme B is a prominent candidate for tumor immunotherapy because it is expressed in cytotoxic T lymphocytes and natural killer cells. Here, we report the use of CD64 as a novel target for specific CMML and AMML therapy, and correlate CD64 expression with typical surface markers representing these diseases. We demonstrate that CD64-specific human CFPs kill CMML and AMML cells ex vivo, and that the mutant granzyme B protein R201K is more cytotoxic than the wild-type enzyme in the presence of the granzyme B inhibitor PI9. Besides, the human CFP based on the granzyme B mutant was also able to kill AMML or CMML probes resistant to Pseudomonas exotoxin A.

In vivo imaging of immunotoxin treatment using Katushka-transfected A-431 cells in a murine xenograft tumour model.

PURPOSE: Preclinical in vivo analyses of treatment responses are an important prerequisite to evaluate new therapeutics. Molecular in vivo imaging in the far red (FR)/near infra red (NIR) is a promising method, as it enables measurements at different time points in individual animals, thereby reducing the number of animals required, while increasing statistical significance. Here, we show the establishment of a method to monitor response to treatment using fluorescent cells, expressing the epidermal growth factor receptor (EGFR), a target already used in therapy. METHODS: We transfected A-431 tumour cells with the far red-emitting protein Katushka (Kat2), resulting in strong fluorescence allowing for the monitoring of tumour growth when implanted in BALB/c nu/nu mice with a CRi Maestro in vivo imager. We targeted A-431 cells with a previously reported immunotoxin (IT), consisting of the anti-EGFR antibody single-chain variable fragment (scFv) 425, fused to Pseudomonas aeruginosa Exotoxin A' (ETA'). In addition, EGFR expression was verified using the 425(scFv) conjugated to a NIR dye BG-747 through a SNAP-tag linker. RESULTS: The results show the feasibility to evaluate response to treatment in vivo by FR imaging, while at the same location detecting EGFR expression. Treatment with 425(scFv)-ETA' resulted in decelerated tumour growth, while not affecting the overall health of the animals. This is in contrast to treatment with Doxorubicin, which, although decreasing the tumour size, resulted in poor health. CONCLUSIONS: We developed a novel method to non-invasively determine treatment responses by in vivo imaging of multiple parameters which showed the efficacy of 425(scFv)-ETA'.

Immunokinases, a novel class of immunotherapeutics for targeted cancer therapy.

Certain characteristics of tumor cells make it possible to develop rational strategies for targeting tumors without harming normal cells. These include the presence of cell surface molecules that characterize the current state of the tumor (e.g. CD30 on Hodgkin lymphoma cells) and the genetic and epigenetic changes that activate oncogenes and inactivate tumor suppressor genes (e.g. the inactivation of tumor suppressor gene DAPK2 in Hodgkin lymphoma cells, which blocks apoptosis). We have developed a novel tumor-targeting fusion protein by combining a selective ligand (CD30L) with a constitutively active version of DAPK2 (DAPK2'-CD30L), thus increasing tumor specificity and reducing systemic toxicity. We showed that this immunokinase fusion protein induces apoptosis specifically in CD30(+)/DAPK2(-) tumor cells in vitro and significantly prolonged overall survival in a disseminated Hodgkin lymphoma xenograft SCID mouse model. Therapeutic strategies based on the cell-specific restoration of a defective, tumor-suppressing kinase demonstrate the feasibility of targeted therapy using recombinant immunokinases.

Process development in Hansenula polymorpha and Arxula adeninivorans, a re-assessment.

A range of industrial H. polymorpha-based processes exist, most of them for the production of pharmaceuticals. The established industrial processes lean on the use of promoters derived from MOX and FMD, genes of the methanol metabolism pathway. In Hansenula polymorpha these promoters are de-repressed upon depletion of a range of carbon sources like glucose and glycerol instead of being induced by methanol as reported for other methylotrophs. Due to these characteristics screening and fermentation modes have been defined for strains harbouring such expression control elements that lean on a limited supplementation of glycerol or glucose to a culture medium. For fermentation of H. polymorpha a synthetic minimal medium (SYN6) has been developed. No industrial processes have been developed so far based on Arxula adeninivorans and only a limited range of strong promoter elements exists, suitable for heterologous gene expression. SYN6 originally designed for H. polymorpha provided a suitable basis for the initial definition of fermentation conditions for this dimorphic yeast. Characteristics like osmo- and thermotolerance can be addressed for the definition of culture conditions.

Genetic linkage analysis of the X chromosome in autism, with emphasis on the fragile X region.

The higher prevalence of autism in males than in females suggests the possible involvement of the X chromosome. To test the hypothesis that there are mutations increasing susceptibility to autism on the X chromosome, and in particular the distal portion of the long arm that encompasses the FMRI and MECP2 loci, a genetic linkage study was performed. Twenty-two fragile X-negative families multiplex for autism and related disorders were used for the study. Linkage analysis, for markers in the Xq27-q28 region, using model-free likelihood-based analysis, produced a maximum MLOD of 1.7 for the narrowest diagnostic category of the typical autism/severe autism spectrum, and nonparametric analysis produced a maximum non-parametric lod (NPL) score of 2.1 for a broad phenotype diagnostic model. Thus, this study offers modest support for a susceptibility locus for autism within the Xq27-q28 region. Further genetic investigations of this region are warranted.

GAG BioScience GmbH.

Completion of the human genome project led to an explosion in available genomic information. Single nucleotide polymorphisms (SNPs) have emerged as a versatile and powerful tool for genotyping almost all variant species. The unique technological platform developed by GAG BioScience is exclusively based on SNP detection and allows genotyping of up to 60,000 samples per day. An analysis robot, a mass spectrometer and a database form a practically self-controlled analysis and documentation system that achieves high-throughput rates of samples with absolute precision. By using a Laboratory Information and Management System, up to 150 million genotypes can be simultaneously retrieved and stored. In cooperation with a partner, GAG BioScience develops new and powerful tools for further data analysis.