Neutralization of complement regulatory proteins CD55 and CD59 augments therapeutic effect of herceptin against lung carcinoma cells.

Human monoclonal anti-Her2/neu antibody (herceptin, also named trastuzumab) failed in the treatment of lung cancer when in combination with two chemotherapy agents gemcitabine and cisplatin, despite of its clinical benefit in women with Her2 positive breast cancer. The capacity of herceptin to activate human complement and complement-dependent cytotoxicity against tumor cells was investigated in a study of tumor immunotherapy. We found that the expression of membrane complement regulatory proteins (mCRPs), CD55 and CD59 on non-small cell lung cancer (NSCLC) cells was closely correlated with histological types, prognosis and preoperational adjutant chemotherapy of the disease. Herceptin-mediated complement cytotoxicity to two human lung carcinoma cell lines exerted stronger killing effect on tumor cells after the neutralization of mCPRs via their antibodies. Furthermore, treatment of herceptin combined with chemo-agents had advantages over chemotherapy alone, while CD55 and CD59 expression levels both declined remarkably in A549 and H157 cell lines after incubation with IC50 cisplatin for 72 h. Our data indicated that overexpression of mCRPs on tumor cells contributes to herceptin's acquisition of resistance to NSCLC, and its anticancer efficacy was enhanced when mCRPs were neutralized or cisplatin could be used to down-regulate their expression.