Die Bedeutung der Modulation der Exosomensekretion durch den ABC-Transporter A3 für die intrinsische Zytostatikaresistenz von aggressiven B-Zell-Lymphomen
The role of modulating the exosome secretion via the ABC transporter A3 for the intrinsic resistance against cytostatic drugs of aggressive B-cell lymphomas
von Thiha Aung
Datum der mündl. Prüfung:2020-06-10
Erschienen:2020-05-28
Betreuer:Prof. Dr. Gerald Wulf
Gutachter:Prof. Dr. Gerald Wulf
Gutachter:Prof. Dr. Martin Oppermann
Dateien
Name:Aung_Thiha_elektronische Dissertation.pdf
Size:1.14Mb
Format:PDF
Zusammenfassung
Englisch
During the therapy of malignant B-cell lymphomas the humoral immunochemotherapy with anthracycline-based chemotherapy and with monoclonal antibodies against the differencing antigen CD20 is the basis of the primary therapy. This medical thesis summarizes results that show that exosomes from lymphoma cells can bind anti-CD20 antibodies, consume complement factors and hence can protect malignant tumor cells against complement attacks. Additional experiments by using the CAM-in-vivo-model showed that the cytostatic activity of chemotherapeutic agents (type anthracyclines) can be increased by modulators of the cytoplasmatic sequestration. By using the substances rapamycin, indomethacin and U18666A that interact with the secretion of exosomes, an inhibition of the exosome-based resistance mechanisms against humoral immunochemotherapy in aggressive lymphomas could be demonstrated in cell line models. Using differential ultracentrifugation, a method was optimized to accumulate exosomes from the supernatant of lymphoma cell cultures. The exosomes of the lymphoma cell lines were characterized by the expression of the exosome marker CD63, flotillin-2 and alix. Furthermore, the antigen CD20 and the complement-regulatory proteins CD46, CD55 and CD59 were detected on the exosomes. It was functionally shown that the complement-regulatory proteins limit the complement attack, consume complement factors and hence, the cytolytic effectivity of the anti-CD20 antibody rituximab was reduced. Based on the importance of the ABC-transporter A3 for the exosome secretion, the role of ABCA3 inhibitors like rapamycin, indomethacin and U18666A were checked on exosome secretion. Inhibitors of ABCA3 reduced the exosomes secretion and enhanced the cytolytic effect of the anti-CD20 antibody rituximab. Moreover, a genetic suppression of the ABCA3 expression using specific shRNA-constructs reduced the biogenesis of exosomes and increased the CDC activity of the antibody rituximab. In addition, it was demonstrated that the inhibition of the exosome secretion using indomethacin also resulted in a reduced secretion of anthracyclines from the cell and thus, the retention of cytostatic drugs in the nucleus was increased.
Keywords: B-cell lymphoma; exosomes; CAM-model; rituximab