Abstract 4329: Novel HER2 targeting antibody-drug conjugates based on DNA-interacting duocarmycin and an unique linker technology with great potential in breast cancer and NSCLC.

We have generated cleavable linker-duocarmycin payloads that previously have been shown to be highly stable in human plasma and to cause excellent in vitro and in vivo efficacy when conjugated to antibodies directed against multiple targets in different models. In our HER2 program, we have used these linker-duocarmycin payloads to generate HER2-targeting antibody-drug conjugates (ADCS) and prepare these for FIM studies. HER2 is a validated target in breast (BC) and gastric cancer (GC) that is currently used to target trastuzumab towards HER2-positive BC and GC tumors. We have generated a set of cysteine-coupled ADCs using newly developed duocarmycins conjugated to a therapeutic HER2/neu antibody. In vitro studies with the anti-Her2 ADCs showed that compared to the naked Ab, the ADCs tested have gained a more than 100-fold potency and more than two-fold efficacy in cell killing capacity. Studies in HER2 positive and negative cell lines indicated that cytotoxicity was HER2- mediated. HER2 binding and ADCC activity was not affected by conjugation. Single dose and multiple dose xenograft studies in mice using a human HER2-positive breast cancer cell line showed dose-dependent anti-tumor activity of the ADCs in vivo. Patient-derived xenografts (PDx) using primary tumors from HER2-positive breast cancer and NSCLC patients demonstrated the ability of the ADC to induce complete remission of tumors that remained unresponsive to the naked Ab trastuzumab. Also taken into account toxicology studies in rodents and cynomolgous monkeys, we conclude that we have generated a new class of HER2-based ADCs that have great potential to become effective treatment for HER2-positive tumors, including breast cancer and NSCLC. From a series of compounds, a preclinical candidate was selected that is currently being prepared for Phase I clinical trials that will start in 2014. Citation Format: Wim Dokter, Patrick Beusker, Gijs Verheijden, Ruud Ubink, Miranda van der Lee, Diels van den Dobbelsteen, Peter Goedings, Jacques Lemmens, Vincent de Groot, Marco Timmers. Novel HER2 targeting antibody-drug conjugates based on DNA-interacting duocarmycin and an unique linker technology with great potential in breast cancer and NSCLC. [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 4329. doi:10.1158/1538-7445.AM2013-4329