Trastuzumab-DM1 causes tumour growth inhibition by mitotic catastrophe in trastuzumab-resistant breast cancer cells in vivo

Mark Barok,Minna Tanner,Katri Köninki,Jorma Isola

doi:10.1186/bcr2868

Abstract

IntroductionTrastuzumab is widely used for the treatment of HER2-positive breast cancer. Despite encouraging clinical results, a significant fraction of patients are, or become, refractory to the drug. To overcome this, trastuzumab-DM1 (T-DM1), a newer, more potent drug has been introduced. We tested the efficacy and mechanisms of action of T-DM1 in nine HER2-positive breast cancer cell lines in vitro and in vivo. The nine cell lines studied included UACC-893, MDA-453 and JIMT-1, which are resistant to both trastuzumab and lapatinib.MethodsAlamarBlue cell-proliferation assay was used to determine the growth response of breast cancer cell lines to trastuzumab and T-DM1 in vitro. Trastuzumab- and T-DM1-mediated antibody-dependent cellular cytotoxicity (ADCC) was analysed by measuring the lactate dehydrogenase released from the cancer cells as a result of ADCC activity of peripheral blood mononuclear cells. Severe Combined Immunodeficient (SCID) mice were inoculated with trastuzumab-resistant JIMT-1 cells to investigate the tumour inhibitory effect of T-DM1 in vivo. The xenograft samples were investigated using histology and immunohistochemistry.ResultsT-DM1 was strongly growth inhibitory on all investigated HER2-positive breast cancer cell lines in vitro. T-DM1 also evoked antibody-dependent cellular cytotoxicity (ADCC) similar to that of trastuzumab. Outgrowth of JIMT-1 xenograft tumours in SCID mice was significantly inhibited by T-DM1. Histologically, the cellular response to T-DM1 consisted of apoptosis and mitotic catastrophe, the latter evidenced by an increased number of cells with aberrant mitotic figures and giant multinucleated cells.ConclusionsOur results suggest mitotic catastrophe as a previously undescribed mechanism of action of T-DM1. T-DM1 was found effective even on breast cancer cell lines with moderate HER2 expression levels and cross-resistance to trastuzumab and lapatinib (MDA-453 and JIMT-1).

Highlights

Trastuzumab is widely used for the treatment of HER2-positive breast cancer
The cellular response to T-DM1 consisted of apoptosis and mitotic catastrophe, the latter evidenced by an increased number of cells with aberrant mitotic figures and giant multinucleated cells
In vitro sensitivity of HER2 positive breast cancer cells to trastuzumab and T-DM1 We studied a panel of nine HER2 overexpressing breast cancer cell lines, which have been previously determined as sensitive to both trastuzumab and lapatinib (ZR-7530, BT-474, EFM-192A, SKBR-3 UACC-812), sensitive to trastuzumab and resistant to lapatinib (MDA-361), or resistant to both trastuzumab and lapatinib (JIMT-1, UACC-893, MDA-453) [39]

Summary

Introduction

Trastuzumab is widely used for the treatment of HER2-positive breast cancer. Despite encouraging clinical results, a significant fraction of patients are, or become, refractory to the drug. The mechanisms underlying the action of trastuzumab are still not fully determined, its clinical benefit is attributed to internalization and down-regulation of cell surface HER2 [5], preventing the activation of AKT by reducing signaling in the PI3K-PTEN pathway [6], cell cycle arrest in G1 [7], HLA-I-restricted antigen presentation of HER2 [8], inhibition of angiogenesis [9] and evoking antibody-dependent cellular cytotoxicity (ADCC) [10,11] In spite of these multiple actions, a significant number of breast cancer patients are primarily resistant to trastuzumab, and a majority of those initially responding become resistant during prolonged treatment [12]. Primary or secondary resistance to trastuzumab is attributed to autocrine production of EGF-related ligands [13], activation of the insulin-like growth factor-I (IGF-I) receptor pathway [14], defects in the PI3K-PTEN-AKT pathway [6,15], masking of the trastuzumab epitope by MUC4 [16] or hyaluronan [17], expression of p95HER2, a constitutively active truncated form of HER2 [18], or impaired ADCC reaction [19]

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Results

Discussion

Conclusion