title: Targeted Combination Therapy: Discovery and Evaluation of Synergistic Anticancer Effects of Anti-HER2-Duocarmycin Antibody-Drug Conjugates Combined with ATR Inhibitors
Creators: name: Rieker, Marcel
Publisher: name: Shaker Verlag GmbH
Year: 2020

description: While the global cancer burden is still high with 10 million people being diagnosed with cancer and 6 million cancer-related deaths yearly, academia and industry are developing more and more sophisticated therapies to combat cancer. One recent development are antibody-drug conjugates (ADCs) which consist of an antibody portion that mediates tumor selectivity and a highly cytotoxic drug designed to efficiently kill cancer cells. The majority of ADCs in clinical trials today carries payloads targeting the cytoskeleton. However, microtubule-targeting agents often lack clinical efficacy and thus, drugs with other mode of actions are in focus of current ADC research. With Mylotarg and Besponsa for example two ADCs carrying DNA damaging agents are already approved and SYD985 an ADC carrying the DNA-alkylating agent duocarmycin is currently showing promising results in a clinical phase III study. Although ADCs have shown promising anticancer effects and often come along with a broadened therapeutic window compared to conventional chemotherapy, there is still room for improvement regarding e.g. saftey aspects. Establishment of combination therapy for ADCs might pose a strategy for increasing efficacy, diminish side-effects and slow down resistance development especially because single agent therapy has seldom been curative. This work aimed at the discovery of a synergistic drug combination that might enhance the efficacy of duocarmycin-based ADCs like the clinically evaluated ADC SYD985. Therefore, 17 DNA-damage response inhibitors (DDRis), potentially involved in the repair of duocarmycin-induced lesions, were selected based on literature and tested in in vitro models. HCC-1954 and MDA-MB-468 cancer cells were treated with a combination of the selected DDRis and duocarmycin and the antiproliferative effects of the combination treatment were compared to the effects of the single agents alone. These experiments clearly demonstrated that inhibitors of the kinase ATR, which plays a central role in the response to replication stress, synergistically enhanced the cytotoxic effects of duocarmycin. This observation was additionally confirmed by treatment of ATR Knock-down cells with duocarmycin. Further drug combination experiments revealed the impact of structural features of different duocarmycins and ATR inhibtors on the synergism level. Besides studying the combinatorial effects of the small molecules alone, it was demonstrated that this combination effect could be translated to a targeted therapy approach like antibody-drug conjugates. Several duocarmycin based ADCs showed strong synergistic effects in combination with different ATR inhibitors in vitro as well as in vivo. rag2 mice bearing a HER2-expressing NCI-N87 tumor were treated with HER2-targeting duocarmycin-ADC and two different ATR inhibitors. The ATR inhibitors monotreatment showed very mild tumor growth inhibition while the treatment with the ADC at concentrations below the maximum effective dose led to a partial tumor response. The combination treatment, however, resulted in very strong anti-tumor effects while being well tolerated. The present study demonstrates the superiority of combining the targeted delivery of duocarmycin to the tumor using an anti-HER2-duocarmycin ADC with systemic application of ATR inhibitors over the treatment with the drugs as single agents. This might support endeavors of evaluating such combinations in a clinical setting.