Project description:The possibility to deliver radioisotopes directly to tumor cells by using monoclonal antibodies has become a promising concept for the elimination of small tumor nodules or single disseminated tumor cells. The alpha-particle emitter Bismut-213 which has a high linear energy transfer and a very short path length appears to be able to kill cells by only few nuclear hits. Bismut-213 based alpha-immunotherapy treatment is currently proved in clinical trials for AML, NHL and preclinically for CLL and multiple myeloma. Because little is known about the biological effects of alpha radiation we examined the molecular effects of the alpha emitter Bismut-213 in malignant and normal B-cells. In this study, we used the cell line Karpas 422 (K422) which had been derived from a malignant B-cell Non-Hodgkin’s lymphoma as well as normal primary CD19+ B-cells which had been selected immunomagnetically from peripheral blood. For the delivery and binding of the alpha emitter we used the monoclonal antibody rituximab which targets the CD20 receptor of malignant and normal B-cells. The lymphoma cell line K422 was incubated in vitro with Bismut-213-CD20 with 100 µCi and 200 µCi respectively, for 46 min (1 half life time of the alpha emitter) or 24 h. Immunomagnetically isolated CD19+ cells from healthy donors were incubated in vitro with Bismut-213-CD20 with 100 µCi or 200 µCi, for 46 min. Gene expression profiles of irradiated cells were analysed using cDNA oligonucleotide arrays (Affymetrix Human Genome Focus Arrays) comprising 8,793 genes and compared with those from untreated control cells. Following normalization significantly altered genes were identified by using the variance stabilization normalization (VSN) method and the significance analysis of microarrays (SAM) algorithm. Differentially expressed genes were defined to exhibit a fold change of 1,4 and higher or 0,7 and lower and a q-value of 5% or lower compared to the genes of the untreated control cells. Irradiated K422 cells with 100 µCi showed 42 differential expressed genes after 46 minutes (one half life time) and 451 deregulated genes after exposure of 24 hours. A similar response could be observed at an exposure of 200 µCi (50 differentially expressed genes after 46 min; 485 genes after 24 h). Hence, a severe radiation induced response could not be detected before 24 hours. 200 µCi irradiated CD19+ cells showed 67 differentially expressed genes after 46 minutes compared to the untreated CD19+ cells (for 100 µCi: 42 differentially expressed genes). By performing cluster analyses the irradiated cells exhibited a distinct homogenous molecular phenotype in comparison to not irradiated cells. Alpha irradiated cells showed transcriptional activation of DNA repair genes. Furthermore, both examined cell types showed up-regulated genes which are known to play a role in general and oxidative stress response. Surprisingly, up-regulation of interferon-stimulated genes in K422 cells could be observed. Because of the transcriptional activation of genes regulating the G1-S- cell cycle transition the supposition came up that the irradiated K422 do progress into the S-phase of the cell cycle and arrest in the S- or G2/M-phase. In contrast to the K422 cells the primary CD19+ B-cells revealed transcriptional activation of cell cycle inhibitors which is an already known reaction following ionizing radiation but no apoptosis associated genes could be observed. In spite of the massive cytotoxic damages which are assumed referring to the gene expression data the K422 cells appear to be able to activate several defense mechanisms in a precise manner. Hence, the malignant K422 cells exhibit a larger amount as well as more various responses than the CD19+ cells. This might be due to the tumorigenic transformation of the malignant cells that exhibit probably more effective defense strategies than the CD19+ cells. The balance between the therapeutic effect of alpha radiation on malignant cells and the damaging effect on normal cells is an essential issue and it is of important clinical relevance concerning radioimmunotherapy with alpha radiation. Keywords: time course and dose dependency

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Transcriptional responses by alpha-emitting radioimmunoconjugate Bi-213-CD20-rituximab

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