title: Lipoplex mediated silencing of membrane regulators (CD46, CD55 and CD59) enhances complement-dependent anti-tumor activity of trastuzumab and pertuzumab.
abstract: The therapeutic potential of anticancer antibodies is limited by the resistance of tumor cells to complement-mediated attack, primarily through the over-expression of membrane complement regulatory proteins (mCRPs: CD46, CD55 and CD59). Trastuzumab, an anti- HER2 monoclonal antibody, approved for the treatment of HER2-positive breast and gastric cancers, exerts only minor complement-mediated cytotoxicity (CDC). Pertuzumab is a novel anti-HER2 monoclonal antibody, which blocks HER2 dimerization with other ligand-activated HER family members. Here, we explored the complement-mediated anti-tumor effects of trastuzumab and pertuzumab on HER2-positive tumor cells of various histological origins. Delivery of chemically stabilized anti-mCRP siRNAs using cationic lipoplexes, AtuPLEXes, to HER2-over-expressing BT474, SK-BR-3 (breast), SKOV3 (ovarian) and Calu-3 (lung) cancer cells reduced mCRPs expression by 85-95%. Knockdown of individual complement regulators variably led to increased CDC only upon combined treatment with trastuzumab and pertuzumab. The combined down-regulation of all the three regulators augmented CDC by 48% in BT474, 46% in SK-BR-3 cells, 78% in SKOV3 cells and by 30% in Calu-3 cells and also increased complement-induced apoptosis and caspase activity on mCRP neutralized tumor cells. In addition, antibody-induced C3 opsonization of tumor cells was significantly enhanced after mCRP silencing and further augmented tumor cell killing by macrophages. Our findings suggest that siRNA-induced inhibition of complement regulator expression clearly enhances complement- and macrophage-mediated anti-tumor activity of trastuzumab and pertuzumab on HER2-positive tumor cells. Thus - if selectively targeted to the tumor - siRNA-induced inhibition of complement regulation may serve as an innovative strategy to potentiate the efficacy of antibody-based immunotherapy.
authors.affiliation: Institute for Immunology, University of Heidelberg, Im Neuenheimer Feld 305, 69120 Heidelberg, Germany.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Mamidi
authors.forename: Marc
authors.initials: M
authors.lastname: Cinci
authors.forename: Max
authors.initials: M
authors.lastname: Hasmann
authors.forename: Volker
authors.initials: V
authors.lastname: Fehring
authors.forename: Michael
authors.initials: M
authors.lastname: Kirschfink
mesh_terms: D061067:Antibodies, Monoclonal, Humanized / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D018958:CD55 Antigens / Q000235:genetics*; D018957:CD59 Antigens / Q000235:genetics*; D020169:Caspases / Q000276:immunology; D045744:Cell Line, Tumor; D003167:Complement Activation / Q000187:drug effects; D006801:Humans; D008264:Macrophages / Q000187:drug effects / Q000276:immunology; D051916:Membrane Cofactor Protein / Q000235:genetics*; D009369:Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000276:immunology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000008:administration & dosage* / Q000235:genetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis / Q000037:antagonists & inhibitors; D000068878:Trastuzumab
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D018958:CD55 Antigens; D018957:CD59 Antigens; D020169:Caspases; D051916:Membrane Cofactor Protein; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C485206:pertuzumab