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Her-2/neu-triggered intracellular tyrosine kinase activation: in vivo relevance of ligand-independent activation mechanisms and impact upon the efficacy of trastuzumab-based treatment

2003; Springer Nature; Volume: 89; Issue: 6 Linguagem: Inglês

10.1038/sj.bjc.6601160

1532-1827

Gernot Hudelist, Wolfgang J. Köstler, Johannes Attems, K. Czerwenka, Rolf Müller, M. Manavi, G. Steger, E. Kubista, Christoph Zielinski, Christian F. Singer,

Peptidase Inhibition and Analysis

Proteolytic cleavage of the Her-2/neu extracellular domain (ECD) has been shown to initiate receptor phosphorylation representing Her-2/neu activation in vitro. The present investigation was performed to evaluate the clinical relevance of ECD cleavage for Her-2/neu activation and the consequences of active intracellular Her-2/neu signalling reflected by tyrosine kinase phosphorylation in patients treated with the anti-Her-2/neu antibody trastuzumab. Sera from 62 patients receiving trastuzumab-based treatment for Her-2/neu overexpressing metastatic breast cancer were assessed for pretreatment ECD levels using an enzyme-linked immunosorbent assay. In parallel, Her-2/neu activation status of tumour specimens was assessed by immunohistochemistry using a Her-2/neu phosphorylation state specific antibody (PN2A) and correlated with the patients’ ECD levels and clinical course of disease. Serum ECD levels were significantly higher in 15 (24%) patients with tumours exhibiting activated Her-2/neu as compared to those without detectable Her-2/neu phosphorylation (median 148.2 vs 28.5 ng ml−1, P=0.010). Whereas response rate only showed a trend to be higher in patients with Her-2/neu-phosphorylated breast cancer (47 vs 34%, P=0.197), both uni- and multivariate analyses revealed that the median progression-free survival under trastuzumab-based treatment was significantly longer in patients with Her-2/neu-phosphorylated breast cancer–11.7 (95% CI 5.2–18.3) months–when compared to the progression-free survival of 4.5 (95% CI 3.4–5.6) months observed in patients with tumours lacking phosphorylated Her-2/neu (P=0.001). Proteolytic cleavage of the ECD represents a biologically relevant ligand-independent mechanism of Her-2/neu activation in vivo. The influence of Her-2/neu activation status upon the outcome of trastuzumab-based therapies merits further investigation in larger prospective trials.