Mechanistic aspects of the opposing effects of monoclonal antibodies to the ERBB2 receptor on tumor growth.

Abstract

The ERBB2 (also called HER2, neu, and c-erbB-2) gene product, which encodes a growth factor receptor, was implicated in the malignancy of human adenocarcinomas. An antibody directed to the rat oncogenic receptor has been previously shown to have an antitumor effect in model systems. In an attempt to extend this observation to the protooncogenic human receptor and also to understand the underlying mechanism, we generated a panel of monoclonal antibodies specific to the extracellular portion of the ERBB2 protein. The effects of the antibodies on tumor growth were compared with their cellular and biochemical actions in vitro. Surprisingly, opposing in vivo effects were observed: although some antibodies almost completely inhibited the growth in athymic mice of transfected murine fibroblasts that overexpress Erbb-2, other antibodies either accelerated tumor growth or resulted in intermediate responses. When tested on cultured human breast carcinoma cells or ERBB2 transfectants, the tumor-stimulatory antibody was found to induce significant elevation of tyrosine phosphorylation of the ERBB2 protein. In contrast, only partial correlation was observed between the capacity to restrict tumor growth and the effects of the antibodies on receptor degradation and cellular proliferation in vitro. This suggests that the antitumor antibodies affect both receptor function and host-tumor interactions. Our results may help establish experimental criteria for the selection of specific antibodies for use either alone or in cogiunction with other molecules as pharmacological antitumor agents.Evidence has been accumulated in recent years for the involvement of growth factors and their receptors in the process of malignant transformation. The ERBB2 protein is a receptor tyrosine kinase (1), homologous to the epidermal growth factor (EGF) receptor (2, 3). The rat homologue ofthe gene undergoes oncogenic activation through a single point mutation (4). The ERBB2 protein was found to be overexpressed in several types of human adenocarcinomas, especially in tumors of the breast and the ovary (5-7), and the overexpression was correlated with short time to relapse and poor survival of breast cancer patients (5).The potential use of monoclonal antibodies (mAbs) in diagnosis and treatment of cancer has been studied extensively (8 (20), and the hybridomas were selected with hypoxanthine/aminopterin/thymidine medium. Supernatants of the growing cells were screened by using an indirect binding assay. CHO cells transfected with the ERBB2 gene (HCC cell line) were plated on a flexible 94-well plate, previously coated with polylysine (1 mg/ml). The cells were fixed with 3% (wt/vol) paraformaldehyde, and supernatants of hybridomas were incubated for 1 hr at 22°C with the fixed cells. The bound Abbreviation: mAb, monoclonal antibody. 8691The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Targeting the function of the HER2 oncogene in human cancer therapeutics

“…In addition, anti-HER2 mAbs downregulate mutationally activated HER2 much more effectively than wild-type HER2, reproducing the effects seen with anti-Neu mAbs in the NeuT model (van Leeuween et al, 1990). Adding complexity to the picture is that even growth inhibition in vitro does not correlate with tumor growth inhibition in vivo such that some mAbs are growth stimulatory in cell-culture models yet inhibit tumor growth in mice (Stancovski et al, 1991;Harwerth et al, 1993). The mechanistic principles underlying the diversity of findings from anti-HER2mAbs remain unclear to this day.…”

Monoclonal antibodies directed to the erbB-2 receptor inhibit in vivo tumour cell growth

“…Monoclonal antibodies can induce an analogous effect on the rat neu receptor (Drebin et al, 1985; Yarden, 1990) and on the human erbB-2 receptor (Hudziak et al, 1989;Stancovski et al, 1991;Harwerth et al, 1992). It is likely that down-modulation results from the ability of divalent antibodies to cross-link cell surface receptors, which leads in turn to their internalisation.…”

ERBB2 juxtamembrane domain (trastuzumab binding site) gene mutation is a rare event in invasive breast cancers overexpressing the ERBB2 gene

“…5 The identification of the amplification of ERBB2 gene and the overexpression of its protein product has resulted in targeted monoclonal antibody-based therapy. 6,7 Preclinical studies indicate synergistic anti-tumor activity when trastuzumab is combined with a number of anti-cancer drugs. Additive cytotoxic interactions between trastuzumab and other agents, including paclitaxel, also have been shown.…”