Most patients with HER2-positive breast or gastric cancer exhibit primary or acquired resistance to trastuzumab emtansine (T-DM1), and such patients may have limited therapeutic options. XMT-1522 is a novel anti-HER2 antibody-drug conjugate. We compared XMT-1522 to T-DM1 in preclinical models. The effects of XMT-1522 and T-DM1 on cell survival and apoptosis were compared in six HER2-positive breast cancer or gastric cancer cell lines, of which three lines were T-DM1-sensitive (N-87, OE-19, JIMT-1) and three T-DM1resistant (RN-87, ROE-19, SNU-216). We compared these agents also in the HER2-negative breast cancer cell line MCF-7, and in mouse RN-87 and JIMT-1 xenograft models. Cell survival was assessed using the AlamarBlue method and apoptosis with the Caspase-Glo 3/7 method. XMT-1522 inhibited the growth of all six HER2-positive cell lines. The proportions of cells that survived XMT-1522 treatment were smaller as compared with T-DM1, particularly in the T-DM1resistant cell lines. XMT-1522 induced more cell apoptosis compared with T-DM1. While RN-87 and JIMT-1 xenograft tumors progressed on T-DM1 treatment, all tumors responded to XMT-1522, and all but one tumor disappeared during the XMT-1522 treatment. XMT-1522 had a strong antitumor effect on RN-87 and JIMT-1 xenografts that progressed on T-DM1. We conclude that XMT-1522 was effective in HER2-positive breast cancer and gastric cancer cell lines resistant to T-DM1, and in xenograft models resistant to T-DM1. The results support the testing of XMT-1522 in clinical trials in patients with HER2-positive cancer.

The majority of HER2-positive breast or gastric cancers treated with T-DM1 eventually show resistance to this agent. We compared the effects of T-DM1 and ARX788, a novel anti-HER2 antibody-drug conjugate, on cell growth and apoptosis in HER2-positive breast cancer and gastric cancer cell lines sensitive to T-DM1, gastric cancer cell lines resistant to T-DM1, HER2-negative breast cancer cell lines, and T-DM1-resistant xenograft models. ARX788 was effective in T-DM1-resistant in vitro and in vivo models of HER2-positive breast cancer and gastric cancer. ARX788 showed a pronounced growth inhibitory effect on all five HER2-positive cell lines tested, of which two gastric cancer cell lines had acquired resistance to T-DM1. ARX788 evoked more apoptotic events compared to T-DM1. While JIMT-1 and RN-87 xenograft tumors progressed on T-DM1 treatment, all such tumors responded to ARX788, and four out of the six JIMT-1 tumors and nine out of the twelve RN-87 tumors disappeared during the ARX788 treatment. Mice treated with ARX788 survived longer than those treated with T-DM1. The data support evaluation of ARX788 in patients with HER2-positive breast cancer or gastric cancer including cancers that progress during T-DM1 therapy.

Merkel cell carcinoma (MCC) is a rare skin cancer with only limited therapeutic options for advanced disease. We previously showed that oncogene ALK is frequently expressed at the RNA level in MCC and further that ALK positivity by immunohistochemistry is frequent and correlates strongly with Merkel cell polyomavirus (MCPyV) positivity. In this study, we investigated whether ALK receptor is active in MCC tumor samples and MCC cell lines, and whether ALK would be a prospective treatment target in MCC. We utilized tissue microarrays constructed from 136 primary MCC tumor samples as well as nine previously established MCC cell lines to determine the presence of ALK and phosphorylated ALK (p-ALK) via immunohistochemistry. Almost half of the analyzed MCC tumors displayed ALK phosphorylation (47.8%). Analysis of MCC tumor samples revealed that the presence of p-ALK correlated to MCPyV positivity, younger age, nonexistence of metastases at diagnosis and ultimately to better MCC-specific survival. In contrast to MCC tumor samples only two out of nine MCC cell lines showed only low ALK phosphorylation by immunohistochemistry. Our study reveals clear disparity in ALK activity between patient derived tumors and cell line samples and therefore, more advanced disease models such as xenografts are necessary to resolve whether ALK is a useful treatment target in MCC.

Merkel cell carcinoma (MCC) is a rare cutaneous neuroendocrine carcinoma that is frequently divided into Merkel cell polyomavirus negative and positive tumors due their distinct genomic and transcriptomic profiles, and disease outcomes. Although some prognostic factors in MCC are known, tumorigenic pathways, which that explain outcome differences in MCC are not fully understood. We investigated transcriptomes of 110 tissue samples of a formalin-fixed, paraffin-embedded MCC series by RNA sequencing to identify genes showing a bimodal expression pattern and predicting outcome in cancer and that potentially could play a role in tumorigenesis. We discovered 19 genes among which IGHM, IGKC, NCAN, OTOF, and USH2A were associated also with overall survival (all p-values < 0.05). From these genes, NCAN (neurocan) expression was detected in all 144 MCC samples by immunohistochemistry. Increased NCAN expression was associated with presence of Merkel cell polyomavirus DNA (p = 0.001) and viral large T antigen expression in tumor tissue (p = 0.004) and with improved MCC-specific survival (p = 0.027) and overall survival (p = 0.034). We conclude that NCAN expression is common in MCC, and further studies are warranted to investigate its role in MCC tumorigenesis.

methods_8.pdf from A Novel Anti-HER2 Antibody–Drug Conjugate XMT-1522 for HER2-Positive Breast and Gastric Cancers Resistant to Trastuzumab Emtansine

<div>Abstract<p>Most patients with HER2-positive breast or gastric cancer exhibit primary or acquired resistance to trastuzumab emtansine (T-DM1), and such patients may have limited therapeutic options. XMT-1522 is a novel anti-HER2 antibody–drug conjugate. We compared XMT-1522 to T-DM1 in preclinical models. The effects of XMT-1522 and T-DM1 on cell survival and apoptosis were compared in six HER2-positive breast cancer or gastric cancer cell lines, of which three lines were T-DM1–sensitive (N-87, OE-19, JIMT-1) and three T-DM1–resistant (RN-87, ROE-19, SNU-216). We compared these agents also in the HER2-negative breast cancer cell line MCF-7, and in mouse RN-87 and JIMT-1 xenograft models. Cell survival was assessed using the AlamarBlue method and apoptosis with the Caspase-Glo 3/7 method. XMT-1522 inhibited the growth of all six HER2-positive cell lines. The proportions of cells that survived XMT-1522 treatment were smaller as compared with T-DM1, particularly in the T-DM1–resistant cell lines. XMT-1522 induced more cell apoptosis compared with T-DM1. While RN-87 and JIMT-1 xenograft tumors progressed on T-DM1 treatment, all tumors responded to XMT-1522, and all but one tumor disappeared during the XMT-1522 treatment. XMT-1522 had a strong antitumor effect on RN-87 and JIMT-1 xenografts that progressed on T-DM1. We conclude that XMT-1522 was effective in HER2-positive breast cancer and gastric cancer cell lines resistant to T-DM1, and in xenograft models resistant to T-DM1. The results support the testing of XMT-1522 in clinical trials in patients with HER2-positive cancer.</p></div>

<p>Supplementary figures and figure legends</p>

methods_8.pdf from A Novel Anti-HER2 Antibody–Drug Conjugate XMT-1522 for HER2-Positive Breast and Gastric Cancers Resistant to Trastuzumab Emtansine