Vorschau

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Abstract

Although widely used in cancer therapy, chemotherapeutic drugs and anticancer antibodies are still unable to provide a desirable cure for all cancer patients. A major obstacle is the development of resistance mechanisms against chemotherapeutic drugs and immuotherapy. Most tumors are resistant to complement-mediated cytotoxicity (CDC), primarily due to over-expression of the membrane-associated regulatory proteins (mCRP) CD46, CD55 and CD59. This complement resistance has been shown to be modified (mostly augmented) not only by inflammatory cytokines and even sublytic complement and perforin, but also by various chemotherapeutic drugs in-vitro upon longterm treatment. The present work aimed at analyzing the possible short-term impact of selected chemotherapeutic drugs on tumor cell lysis by CDC and/or opsonisation as well as the potential involvement of complement regulatory proteins. A semi-kinetic approach was carried out in this study by choosing two different intervals (24h, 48h), applying different concentrations of the chemotherapeutic drugs doxorubicin, taxol, fludarabin and bortezomib on cancer cell lines of various histological origin (breast: BT474; SKBR-3; Lymphoma: Raji). Expression of mCRP, cancer cells opsonisation with iC3b and binding of the soluble complement regulator factor H to cancer cells were assessed by cytofluorometric analysis, cytotoxicity by 51Cr-release assay and secretion of soluble inhibitors by ELISA. The results indicate a close association between the modified expression of the mCRP and response of cancer cells to CDC. The strongest influence on expression was on CD55 and CD59. I could show for the first time that bortezimib inhibits mCRP expression on breast cancer cell lines leading to increased sensitivity to CDC. Although expression of membrane complement regulators was not enhanced in Raji cells upon treatment with bortezomib, a reduced sensitivity to CDC was still observed. Soluble complement inhibitors, such as C1-inhibitor, fH and fI potentially contributing to resistance of cancer cells to complement, were not detectable. However, I could demonstrate that drug-treated cells often efficiently bound higher levels of fH, in part in a dose dependency manner, another possible protective mechanism against complement attack. To improve the synergistic effect of the combined treatment regimens, I tried to abolish drug-induced complement resistance by blocking membrane regulators using specific neutralising antibodies. Neutralisation of the mCRP partially enhanced sensitivity of doxorubicin-treated BT474 cells to CDC but not of taxol–treated cells. In SKBR-3 cells treated with taxol for 48h, mCRP neutralisation could enhance their sensitivity to CDC, but was only partially able to improve sensitivity of bortezomib-treated and fludarabine-treated Raji cells to complement-mediated lysis. Interestingly, drug-treated cancer cells were often more efficiently opsonised with iC3b than untreated cells. In conclusion, the here presented data demonstrate that even upon short-term exposure cancer cells develop an increased resistance to CDC. However, a more efficient opsonisation with iC3b could enhance their elimination through an augmented complement-mediated cellular cytotoxicity (CDCC) and antibody-dependent cellular cytotoxicity (ADCC).