Cancer Letters

Cancer Letters

Volume 306, Issue 2, 28 July 2011, Pages 171-179
Cancer Letters

Trastuzumab-DM1 is highly effective in preclinical models of HER2-positive gastric cancer

https://doi.org/10.1016/j.canlet.2011.03.002Get rights and content

Abstract

Background

A novel antibody–drug conjugate (trastuzumab-DM1, T-DM1) is currently in clinical trials for patients with trastuzumab resistant HER2-positive breast cancer. Since no clinical data is available from gastric cancer, we studied T-DM1 on HER2-positive human gastric cancer cells and xenograft tumors.

Methods

Effects of T-DM1 were studied in four HER2-positive gastric cancer cell lines (N-87, OE-19, SNU-216 and MKN-7) in vitro. Xenograft tumors from N-87 and OE-19 were studied to determine the effect of T-DM1 in vivo.

Results

T-DM1 was found more effective than trastuzumab in N-87 and OE-19, and moderately effective in MKN-7 cells. On SNU-216 cells both trastuzumab and T-DM1 showed limited efficacy. In xenograft tumor experiments, complete pathological response was observed in all OE-19 xenografted mice and in half of the N-87 xenografted mice. The results were equally good irrespective of the tumor burden at therapy initiation, or preceding trastuzumab treatment. T-DM1 treatment showed direct effects (apoptotic cell death and aberrant mitosis) as well as it mediated antibody-dependent cellular cytotoxcity (ADCC).

Conclusions

T-DM1 showed a promising anti-tumor effect in HER2-positive gastric cancer cell lines in vitro and in vivo, even in tumors which had developed resistance to trastuzumab. T-DM1 therapy may warrant clinical trials for HER2-positive gastric cancer patients.

Introduction

Gastric cancer is one of the most frequent human malignancies and the second leading cause of cancer-related death in the world [1]. Because the early disease is often asymptomatic, many gastric cancer patients are diagnosed when their cancer is already beyond curative surgery [2], [3]. Treatment options for these patients include radiotherapy and chemotherapy, but cancer progression is common and the 5-year survival rate is less than 30% [2], [3]. Therefore, a high unmet medical need exists to develop new highly potent therapies.

One possible target is HER2 (ErbB2) oncoprotein, a member of the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases. Its overexpression occurs in ∼20% of gastric cancers and is associated with poor clinical outcome [4], [5]. Trastuzumab, a recombinant humanized monoclonal antibody against the extracellular domain of HER2, has shown significant antitumor effect in both in vitro and in vivo models of HER2-positive gastric cancer [4], [5], [6], [7], [8]. Very recently, a randomized phase III clinical trial (ToGA trial) showed that trastuzumab is highly effective in untreated advanced HER2-positive gastric cancer patients and significantly improved overall survival when given in combination with standard chemotherapy [9]. These data show that trastuzumab is a valuable drug for the treatment of the HER2-positive subset of gastric cancers. Unfortunately, a sizable fraction of HER2-positive patients in the ToGA trial did progress on treatment [9], [10]. This denotes that developing trastuzumab resistance might be a problem also in gastric cancer, similar to the situation in breast cancer [11]. For this reason, several research strategies have focused on alternative HER2 directed treatments.

A new strategy of anti-HER2 targeted therapy has been achieved using the antibody–drug conjugate technology. The monoclonal antibody trastuzumab has been conjugated with cytotoxic molecule DM1 (derivative of maytansine 1). The resulting conjugate, named trastuzumab-DM1 (T-DM1) is designed to deliver the highly potent DM1 into the HER2 overexpressing cells via receptor-mediated endocytosis [12]. Active lysine-mcc-DM1 is released by lysosomal degradation [13]. Free intracellular DM1 is a potent inhibitor of microtubule assembly thereby causing cell death [14], [15]. T-DM1 is effective both in vitro and in vivo models of trastuzumab-insensitive breast cancer [12], furthermore, it showed remarkable activity in phase I and II studies in which it was given to patients with trastuzumab-insensitive HER2-positive breast cancer [16], [17], [18].

Because trastuzumab is effective in HER2-positive gastric cancer, and T-DM1 shows promising efficacy in trastuzumab insensitive breast cancer, we wanted to test the efficacy and mechanisms of T-DM1 on gastric cancer cell models. In this paper we report that T-DM1 displayed strong anti-tumor effect in OE-19 and N-87 gastric cancer in vitro and in xenograft tumors in vivo. Furthermore, T-DM1 was highly effective even on large tumors which progressed on prior trastuzumab. This is the first study which shows the efficacy of T-DM1 on gastric cancer cells in vivo.

Section snippets

Cells

OE-19 human gastric cancer cell line was obtained from the European Collection of Cell Culture (CAMR Centre for Applied Microbiology and Research, Wiltshire, United Kingdom). MKN-7 and N-87 human gastric cancer cell lines were obtained from American Type Culture Collection (ATCC, Manassas, VA). SNU-216 human gastric cancer cell line was obtained from the Korean Cell Line Bank (Seoul, Korea). Human breast cancer cell lines MCF-7 and SKBR-3 (ATCC) were used as a control. The cell lines were

HER2 oncogene amplification and protein expression levels of human gastric cancer cell lines

Using FISH analysis we confirmed that the HER2 oncogene is amplified in all gastric cancer cell lines studied. By flow cytometric analysis we showed that HER2 protein is highly overexpressed in N-87 and OE-19, comparable to that of breast cancer cell line SKBR-3. HER2 protein in MKN-7 and SNU-216 cells was also overexpressed, being about one third of that in N-87 and OE-19 (Table 1). Conjugation of trastuzumab with DM1 did not influence of binding to the OE19 gastric cancer cells (Fig. 1A).

Trastuzumab- and T-DM1-mediated ADCC against HER2-positive gastric cancer cells

Discussion

Trastuzumab-DM1 (T-DM1) is a new antibody–drug conjugate which has been developed to improve the therapy of HER2-positive breast cancer. So far T-DM1 has not been extensively studied in preclinical models of gastric cancer. In this study, we showed the efficacy of T-DM1 on gastric cancer xenograft tumors.

We applied different treatment strategies when testing T-DM1 in tumor xenografts. A complete pathological response was observed in all of the OE-19 xenografts and in half of the N-87 xenografts

Conflict of interest

The authors disclose no financial conflicts of interest that could influence the present work.

Role of the funding source

This study was financially supported by the Tampere University Hospital Research Foundation, Academy of Finland, Sigrid Juselius Foundation and Finnish Cancer Foundation. The sponsors had no influence on the study design, in the collection, analysis and interpretation of data; in the writing of the manuscript; and in the decision to submit the manuscript for publication.

Acknowledgements

The skillful technical assistance of Ms. Kristiina Ryömä, Mrs. Sari Toivola and Ms. Barbara Német is greatly appreciated. We thank Genentech Inc. for providing T-DM1.

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