Identification of novel therapeutic targets in mastocytosis: Inhibition of survival of neoplastic mast cells by targeting IAPs and TRAIL receptors

Mastocytosis is a rare disease characterized by neoplastic accumulation of mast cells in various organs, particularly in skin and bone marrow. Sporadic mastocytosis is usually caused by somatic point mutations of the receptor tyrosine kinase KIT that occur in exon 17, codon 816, and activates KIT by affecting the intracellular enzymatic site of the molecule. Homeostasis of so altered mast cells is influenced on different levels. These cells show an elevated rate of proliferation and changes in cellular apoptosis. In this thesis the expression of the inhibitor of apoptosis protein (IAP) Survivin in neoplastic mast cells and its importance as a diagnostic marker or therapeutic target has been evaluated. For this purpose the Survivin content of normal and neoplastic mast cells was analyzed. Furthermore Survivin expression in mast cells of bone marrow samples from patients with mastocytosis and healthy donors was compared. The expression of Survivin protein in the neoplastic human mast cell line HMC-1 was downregulated by siRNA and apoptosis was subsequently induced with tyrosine kinase inhibitors or the death receptor ligand TRAIL. It is known from other hematopoietic neoplasia that Smac mimetics, inhibitors of the IAPs XIAP, cIAP1 and cIAP2, are potent therapeutics able to amplify the effect of classical cytotoxic therapies. Here the Smac mimetic LCL161 was used in combination with the tyrosine kinase inhibitor PKC412 and TRAIL to inhibit growth of the neoplastic mast cell line HMC-1. The expression of the IAP Survivin is enhanced in neoplastic altered mast cells and can be detected in significantly higher amounts in mast cell infiltrates of the bone marrow from patients with mastocytosis compared to healthy donors underlining its value as a diagnostic marker. Downregulation of Survivin protein as well as the use of the Smac mimetic LCL161 inhibited the growth of the neoplastic mast cell line HMC-1 synergistically with tyrosine kinase inhibitors and the death receptor ligand TRAIL. These results emphasize the relevance of cellular regulation of apoptosis as a future target for the therapy of mastocytosis

Frequency of PRRS live vaccine virus (European and North American genotype) in vaccinated and non-vaccinated pigs submitted for respiratory tract diagnostics in North-Western Germany

The frequency of PRRSV corresponding to live vaccines and wild-type was determined in 902 pigs from North-Western Germany submitted for post-mortem examination. Overall, 18.5% of the samples were positive for the EU wild-type virus. EU genotype vaccine virus was detected in 1.3% and the NA genotype vaccine virus in 8.9% of all samples. The detection of the EU vaccine was significantly higher in pigs vaccinated with the corresponding vaccine (OR=9.4). Pigs vaccinated with NA genotype had significantly higher detection chances for the corresponding vaccine virus when compared to non-vaccinated animals (OR=3.34) animals, however, NA vaccine was also frequently detected in non-vaccinated pigs. Concluding, the dynamics of NA genotype vaccine and EU wild-type virus corresponds with studies on PRRSV spread in endemically infected herds. The potential of spontaneous spread of the NA genotype vaccine should be considered in the planning of eradication programs