Lipoplex mediated silencing of membrane regulators (CD46, CD55 and CD59) enhances complement-dependent anti-tumor activity of trastuzumab and pertuzumab

Mol Oncol. 2013 Jun;7(3):580-94. doi: 10.1016/j.molonc.2013.02.011. Epub 2013 Feb 20.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal, Humanized / pharmacology*
  • Antineoplastic Agents / pharmacology*
  • CD55 Antigens / genetics*
  • CD59 Antigens / genetics*
  • Caspases / immunology
  • Cell Line, Tumor
  • Complement Activation / drug effects
  • Humans
  • Macrophages / drug effects
  • Macrophages / immunology
  • Membrane Cofactor Protein / genetics*
  • Neoplasms / drug therapy*
  • Neoplasms / genetics
  • Neoplasms / immunology
  • RNA Interference
  • RNA, Small Interfering / administration & dosage*
  • RNA, Small Interfering / genetics
  • Receptor, ErbB-2 / analysis
  • Receptor, ErbB-2 / antagonists & inhibitors
  • Trastuzumab


  • Antibodies, Monoclonal, Humanized
  • Antineoplastic Agents
  • CD55 Antigens
  • CD59 Antigens
  • Membrane Cofactor Protein
  • RNA, Small Interfering
  • Receptor, ErbB-2
  • Caspases
  • pertuzumab
  • Trastuzumab