Abstract 2392: Development of a new assay system for predicting the degree of antibody-dependent cellular cytotoxicity and the clinical outcome in patients receiving trastuzumab.

Abstract

Abstract Trastuzumab is widely used in the treatment of HER2-positive breast cancer. Despite its promising usefulness in the clinical setting, large differences in the clinical outcomes among patients remain a key issue among patients treated with trastuzumab. The purpose of this study was to investigate the inter-individual differences in the occurrence of trastuzumab-mediated antibody-dependent cell-mediated cytotoxicity (ADCC), one of the significant mechanisms underlying the antitumor activity of trastuzumab, and develop a new system to predict the clinical effectiveness of trastuzumab. We used the peripheral blood mononuclear cells (PBMCs) of three healthy volunteers (HVs) to examine the degree of ADCC by the calcein assay. The ADCC activities of the cells from the three HVs differed from each other. Then, it was confirmed by other independent experiments that the inter-individual differences among the three subjects were consistent and reproducible, regardless of the assay method and type of target cells used. The consistency and reproducibility of the inter-individual differences were also confirmed by using PBMCs of an additional 8 HVs in three independent experiments. To identify molecular markers that might be correlated with ADCC activity, we adopted an ex vivo gene expression analysis (Mitsuhashi, Clin Chem 53:148-149, 2007) in which changes in the mRNA expression can be measured quantitatively. Using this technology, we examined the changes in the expression of 14 candidate genes of leukocytes in 8 HVs triggered by ex vivo exposure to heat-aggregated IgG for 4 hr. We found that the increase (expressed as fold increase (FI)) in the expressions of TNFSF15, IL6 and CXCL3 were significantly correlated with the ADCC activity (R2= 0.58, R2 = 0.72, R2 = 0.76, respectively). Next, we conducted a prospective evaluation in 18 patients who were receiving trastuzumab-based neoadjuvant chemotherapy, to determine whether the FIs in the expressions of these 14 genes were associated with a pathological complete response (pCR). Patients who achieved a pCR showed higher FIs in the expressions of CXCL1, CXCL3, TNFS2 and TNFSF15 than those who did not show a pCR (p = 0.004, p = 0.015, p = 0.0495, and p = 0.014, respectively). This is the first report of demonstration of the consistent stability of inter-individual differences in trastuzumab-mediated ADCC activity in vitro, and of a promising new assay system for predicting the degree of ADCC and pCR in patients receiving trastuzumab-based neoadjuvant chemotherapy. Citation Format: Kodera Yasuo, Mayu Yunokawa, Kazuhiro Obara, Jun Hashimoto, Kenji Tamura, Yasuhiro Fujiwara, Masato Mitsuhashi, Fumiaki Koizumi. Development of a new assay system for predicting the degree of antibody-dependent cellular cytotoxicity and the clinical outcome in patients receiving trastuzumab. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2392. doi:10.1158/1538-7445.AM2013-2392