The human epidermal growth factor receptor (HER) family plays an important role in cell survival and proliferation, and is implicated in oncogenesis. Overexpression of HER2 is associated with aggressive disease and poor prognosis. Trastuzumab is a humanized monoclonal antibody targeting HER2 and has proven survival benefit for women with HER2-positive early and metastatic breast cancer. Pertuzumab, another monoclonal antibody, is a HER2 dimerization inhibitor that binds to a different epitope on HER2 than trastuzumab and inhibits HER2 dimer formation with other HER family members such as HER3 and HER1. We investigated the antitumor activity of these agents alone and in combination in HER2-positive breast and non-small cell lung cancer xenografts. Our data show that the combination of trastuzumab and pertuzumab has a strongly enhanced antitumor effect and induces tumor regression in both xenograft models, something that cannot be achieved by either monotherapy. The enhanced efficacy of the combination was also observed after tumor progression during trastuzumab monotherapy. Near-IR fluorescence imaging experiments confirm that pertuzumab binding to tumors is not impaired by trastuzumab pretreatment. Furthermore, we show by in vitro assay that both trastuzumab and pertuzumab potently activate antibody-dependent cellular cytotoxicity. However, our data suggest that the strongly enhanced antitumor activity is mainly due to the differing but complementary mechanisms of action of trastuzumab and pertuzumab, namely inhibition of HER2 dimerization and prevention of p95HER2 formation. [Cancer Res 2009;69(24):9330-6]

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.

Increasing the efficacy of targeted cancer therapies requires the identification of robust biomarkers suitable for patient stratification. This study focused on the identification of molecular mechanisms causing resistance against the anti-ERBB2-directed therapeutic antibodies trastuzumab and pertuzumab presently used to treat patients with ERBB2-amplified breast cancer. Immunohistochemistry and clinical data were evaluated and yielded evidence for the existence of ERBB2-amplified breast cancer with high-level epidermal growth-factor receptor (EGFR) expression as a separate tumor entity. Because the proto-oncogene EGFR tightly interacts with ERBB2 on the protein level, the hypothesis that high-level EGFR expression might contribute to resistance against ERBB2-directed therapies was experimentally validated. SKBR3 and HCC1954 cells were chosen as model systems of EGFR-high/ERBB2-amplified breast cancer and exposed to trastuzumab, pertuzumab and erlotinib, respectively, and in combination. Drug impact was quantified in cell viability assays and on the proteomic level using reverse-phase protein arrays. Phosphoprotein dynamics revealed a significant downregulation of AKT signaling after exposure to trastuzumab, pertuzumab or a coapplication of both antibodies in SKBR3 cells but no concomitant impact on ERK1/2, RB or RPS6 phosphorylation. On the other hand, signaling was fully downregulated in SKBR3 cells after coinhibition of EGFR and ERBB2. Inhibitory effects in HCC1954 cells were driven by erlotinib alone, and a significant upregulation of RPS6 and RB phosphorylation was observed after coincubation with pertuzumab and trastuzumab. In summary, proteomic data suggest that high-level expression of EGFR in ERBB2-amplified breast cancer cells attenuates the effect of anti-ERBB2-directed antibodies. In conclusion, EGFR expression may serve as diagnostic and predictive biomarker to advance personalized treatment concepts of patients with ERBB2-amplified breast cancer.

Background:Trastuzumab and pertuzumab target the Human Epidermal growth factor Receptor 2 (HER2). Combination therapy has been shown to provide enhanced antitumour activity; however, the downstream signalling to explain how these drugs mediate their response is not clearly understood.Methods:Transcriptome profiling was performed after 4 days of trastuzumab, pertuzumab and combination treatment in human ovarian cancer in vivo. Signalling pathways identified were validated and investigated in primary ovarian xenografts at the protein level and across a timeseries.Results:A greater number and variety of genes were differentially expressed by the combination of antibody therapies compared with either treatment alone. Protein levels of cyclin-dependent kinase inhibitors p21 and p27 were increased in response to both agents and further by the combination; pERK signalling was inhibited by all treatments; but only pertuzumab inhibited pAkt signalling. The expression of proliferation, apoptosis, cell division and cell-cycle markers was distinct in a panel of primary ovarian cancer xenografts, suggesting the heterogeneity of response in ovarian cancer and a need to establish predictive biomarkers.Conclusion:This first comprehensive study of the molecular response to trastuzumab, pertuzumab and combined therapy in vivo highlights both common and distinct downstream effects to agents used alone or in combination, suggesting that complementary pathways may be involved.

The quality control testing of chemical degradations in the bio-pharmaceutical industry is currently under controversial debate. Here we have systematically applied in vitro and in vivo stress conditions to investigate the influence of protein degradation on structure-function. Extensive purification and characterization enabled identification and functional assessment of the physiological degradation of chemical modification sites in the variable complementarity-determining regions (CDRs) and conserved region of trastuzumab. We demonstrate that the degradation of the solvent-accessible residues located in the CDR and the conserved fragment crystallizable region (Fc) occurs faster in vivo (within days) compared to the levels observed for bio-process and real-time storage conditions. These results hence question the rationality of extreme monitoring of low level alterations in such chemical modifications as critical patient safety parameters in product quality control testing, given that these modifications merely mirror the natural/physiological aging process of endogenous antibodies.

Purpose: Attempts to selectively initiate tumor cell death through inducible apoptotic pathways are increasingly being exploited as a potential anticancer strategy. Inhibition of NAD + synthesis by a novel agent FK866 has been recently reported to induce apoptosis in human leukemia, hepatocarcinoma cells in vitro, and various types of tumor xenografts in vivo. In the present study, we used 1 H-decoupled phosphorus ( 31 P) magnetic resonance spectroscopy (MRS) to examine the metabolic changes associated with FK866 induced tumor cell death in a mouse mammary carcinoma. Experimental Design: Induction of apoptosis in FK866-treated tumors was confirmed by histology and cytofluorometric analysis. FK866-induced changes in mammary carcinoma tumor metabolism in vivo were investigated using 1 H-decoupled 31 P MRS. To discern further the changes in metabolic profiles of tumors observed in vivo, high-resolution in vitro 1 H-decoupled 31 P MRS studies were carried out with perchloric acid extracts of mammary carcinoma tumors excised after similar treatments. In addition, the effects of FK866 on mammary carcinoma tumor growth and radiation sensitivity were studied. Results:Treatment with FK866 induced a tumor growth delay and enhanced radiation sensitivity in mammary carcinoma tumors that was associated with significant increases in the 31 P MR signal in the phosphomonoester region and a decrease in NAD + levels, pH, and bioenergetic status. The 31 P MRS of perchloric acid extracts of treated tumors identified the large unresolved signal in the phosphomonoester region as the resultant of resonances originating from intermediates of tumor glycolysis and guanylate synthesis in addition to alterations in pyridine nucleotide pools and phospholipid metabolism. Conclusion:The present results suggest that FK866 interferes with multiple biochemical pathways that contribute to the increased cell death (apoptosis) and subsequent radiation sensitivity observed in the mammary carcinoma that could be serially monitored by 31 P MRS.

In many solid tumors, overexpression of human epidermal growth factor receptors (e.g

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