Biomedical subjects

Horst Dürkop

Publications and source records attributed to Horst Dürkop.

6 recordsLinked to original sources

PubMed2006

A cleavable molecular adapter reduces side effects and concomitantly enhances efficacy in tumor treatment by targeted toxins in mice.

Two of the main problems associated with administration of receptor-targeted toxins in tumor therapy are severe systemic side effects and low transfer of the toxins into the cytosol after binding to the tumor cell surface. To improve chimeric toxins in this respect we have developed a molecular adapter that links the toxic moiety and ligand. The adapter is designed to improve cytosolic uptake, retain the toxin inside the cytosol and detoxify the drug after cell death. The plant toxin saporin linked either directly or via the adapter to epidermal growth factor (EGF) served to evaluate efficacy to inhibit tumor growth and reduce side effects in vivo. The lethal dose for BALB/c mice was three times less for the adapter-containing toxin (SA2E) than for the adapter-free construct (SE). Furthermore, SE only reduced the average weight of induced tumors by 33% whereas SA2E-treated mice exhibited 71% reduction with an almost complete suppression in 60% of the cases. Additionally, severe side effects like hyperalgesia, alopecia and death were drastically reduced in SA2E-treated animals. Tumors without target receptor were only slightly affected by SA2E and the reduction in side effects less pronounced indicating specific depletion from the blood by target receptor expressing cells.

Alanine Transaminase↗

PubMed2005

cIAP2 is highly expressed in Hodgkin-Reed-Sternberg cells and inhibits apoptosis by interfering with constitutively active caspase-3.

In this study, the expression of activated caspase-3 by the tumor cells of classical Hodgkin lymphoma (cHL), the Hodgkin-Reed-Sternberg (HRS) cells, is confirmed. This raises the question why caspase-3 does not kill HRS cells. There are only a few molecules, which are able to directly inhibit caspase-3. One of them is cIAP2. We show that cIAP2 is expressed in the HRS cells in 20 of 23 cHL cases by in situ hybridization. Suppression experiments with cIAP2 antisense RNA show that down-regulation of cIAP2 significantly reduces apoptosis resistance in cHL cell lines. cIAP2 overexpression appears to be unique for HRS cells since the tumor cells of non-Hodgkin lymphomas are nearly cIAP2-negative. We demonstrate that cIAP2 is inducible by CD30 stimulation in cHL cell lines of T-cell origin and anaplastic large cell lymphoma cell lines, whereas cHL cell lines of B-cell origin constitutively express cIAP2. Inhibition of cIAP2 expression by cIAP2 antisense RNA decreases resistance to apoptosis. The results indicate that cIAP2 contributes to the apoptosis resistance of HRS cells, mainly by inhibiting effector caspases. According to these findings, a therapeutical application of inhibitors of apoptosis proteins antagonists in cHL appears promising.

Apoptosis↗

PubMed2005

Blocking IL-15 prevents the induction of allergen-specific T cells and allergic inflammation in vivo.

IL-15 has been shown to accelerate and boost allergic sensitization in mice. Using a murine model of allergic sensitization to OVA, we present evidence that blocking endogenous IL-15 during the sensitization phase using a soluble IL-15Ralpha (sIL-15Ralpha) suppresses the induction of Ag-specific, Th2-differentiated T cells. This significantly reduces the production of OVA-specific IgE and IgG and prevents the induction of a pulmonary inflammation. Release of proinflammatory TNF-alpha, IL-1beta, IL-6, and IL-12 as well as that of Th2 cytokines IL-4, IL-5, and IL-13 into the bronchi are significantly reduced, resulting in suppressed recruitment of eosinophils and lymphocytes after allergen challenge. It is of clinical relevance that the airway hyper-responsiveness, a major symptom of human asthma bronchiale, is significantly reduced by sIL-15Ralpha treatment. Ex vivo analysis of the draining lymph nodes revealed reduced numbers of CD8, but not CD4, memory cells and the inability of T cells of sIL-15Ralpha-treated mice to proliferate and to produce Th2 cytokines after in vitro OVA restimulation. This phenomenon is not mediated by enhanced numbers of CD4(+)/CD25(+) T cells. These results show that IL-15 is important for the induction of allergen-specific, Th2-differentiated T cells and induction of allergic inflammation in vivo.

Allergens↗

PubMed2003

CS-1, a novel c-kithi+ acute myeloid leukemia cell line with dendritic cell differentiation capacity and absent immunogenicity.

Complex cytogenetic abnormalities confer dismal prognoses in myeloid malignancies. Even bone marrow transplantation from siblings or matched unrelated donors offer minimal chances for cure, suggesting that these cases are not only refractory to chemotherapy but also resist the graft-vs.-leukemia effect. We herein describe the first permanent, factor-independent c-kit(hi+) cell line CS-1 derived from an unrelated donor stem cell transplanted patient with relapsed acute myeloid leukemia (AML)-M5a of high-risk karyotype [monosomy 7, t(2;11)(q31;p13), t(10;12)(q24;q24)]. Having the same karyotype, CS-1 exhibits an autonomous growth pattern and responds to stem cell factor (SCF). CS-1 did not induce T cell activation in mixed-lymphocyte-tumor-cultures (MLTCs) and, when used as third party stimulators, decreased T cell proliferation in mixed-lymphocyte reactions (MLRs). Cytokines added exogenously or secreted from bystander T cells caused CS-1 to differentiate into dendritic cells (DCs). CS-1-derived DCs, in contrast to DCs originating from non-malignant CD34(+) progenitor cells, had virtually no T cell stimulatory effect, indicating that CS-1 is both immunosuppressive and poorly immunogenic. These properties may partially be due to the detected downregulation of costimulatory molecules and appear to involve a soluble factor. CS-1 cells injected subcutaneously (s.c.) to non-obese diabetes/severe combined immunodeficient (NOD/SCID) mice produced solid tumors, disseminating into bone marrow and spleen. The data show that transforming AML blasts with high-risk karyotype into DCs is insufficient to restore their immunogenicity and that the CS-1 cell line is useful to identify tumor-related immunosuppressive mechanisms in vitro and in vivo.

Animals↗

PubMed2003

Differential expression and function of A20 and TRAF1 in Hodgkin lymphoma and anaplastic large cell lymphoma and their induction by CD30 stimulation.

A20 and TRAF1 are two anti-apoptotic components of the intracellular signalling pathway of the tumour necrosis factor receptor (TNFR) family. Induction of apoptosis seems to be a main function of these receptors. It is astonishing that a member of this family, CD30, is overexpressed by highly proliferating tumours such as Hodgkin lymphoma (HL) and anaplastic large cell lymphoma (ALCL). It is known that CD30 stimulation leads to the apoptosis of ALCL tumour cells but not of Hodgkin-Reed-Sternberg (HRS) cells. We have already established the overexpression of TRAF1 in HRS cells. In this study we demonstrate that A20 is highly expressed in the HRS cells in 20/22 of cases of classical HL, in 4/4 cases of nodular lymphocyte-predominant HL (NLPHL), and in 2/2 cases of the anaplastic variant of diffuse large B cell lymphoma. In contrast, all other non-Hodgkin lymphomas, including ALCL, revealed either no A20 reactivity, or reactivity in less than 1% of all tumour cells. CD30 stimulation induced A20 and TRAF1 expression. This effect was most prominent in HL and ALCL cell lines with low basal expression levels of these molecules. Immunohistological studies of reactive lymphoid blasts in tonsillar tissue demonstrated that co-expression of CD30, A20, and TRAF1 also occurs in vivo. Cell lines with high basal A20 and TRAF1 expression were resistant to CD30-mediated apoptosis. The sensitivity to CD30-induced apoptosis was increased by inhibition of protein synthesis. TRAF1 transfection decreased CD30-induced apoptosis. Our data suggest that A20 and TRAF1 contribute to apoptosis resistance and, therefore, play an important role in the pathogenesis of classical HL.

Apoptosis↗

PubMedDate not supplied

Human CD30: structural implications from epitope mapping and modeling studies.

The human CD30 molecule is expressed transiently at very low levels on intrafollicular and perifollicular T and B cell blasts in lymphoid tissues, but is specifically upregulated on certain tumor cells, e.g. Hodgkin and Reed-Sternberg (H-RS) cells. With its specific expression pattern and easy accessibility on the surface of H-RS cells CD30 is a valuable diagnostic marker and holds considerable promise as a target for in vivo immunotherapy. Knowledge of epitopes on the CD30 molecule is expected to facilitate the design of novel non-immunogenic anti-CD30 reagents. Therefore, we have mapped the epitopes of several monoclonal antibodies (mAb) applying a peptide array of overlapping CD30-derived peptides. For the mAb Ber-H2, two linear epitopes with identical sequence were found, while the mAb Ki-2 and the single chain Fv fragment R4-4 each recognized a single linear antigenic determinant, respectively. On the other hand, the mAb Ki-1 bound to a discontinuous epitope composed of two regions, one located near the N-terminus and the other near the membrane-spanning region of CD30. Using molecular modeling, it was possible to visualize the location of the epitopes on exposed loop regions of the molecule within the N-terminal domain. Finally, the results obtained with the mAb Ki-1 imply that the ends of the N- and C-terminal parts of the extracellular portion of CD30 are in close vicinity of each other, suggesting a flower-like structure for the membrane-bound homotrimeric CD30 molecule.

Alanine↗