Abstract 3258: Preclinical evaluation of enhanced irofulven antitumor activity in an ERCC3 mutant background by in vitro and in vivo tumor models

Background: We recently described a recurrent founder mutation (p.R109X) in the ATP dependent helicase ERCC3 in BRCA1/2 negative, breast cancer-affected individuals of Ashkenazi Jewish ancestry. Modeling of the mutation in ERCC3 deficient or CRISPR/Cas9 edited cell lines showed a consistent pattern of reduced expression of the protein and concomitant hypomorphic functionality when treated with the DNA alkylating agent IlludinS. A derivative of IlludinS- Irofulven- has previously been evaluated as an antitumor agent in multiple clinical trials and has shown high antitumor activity. Higher effective doses of this drug have been shown to give rise to side effects, including retinal toxicity. Based on the observation that ERCC3 mutant cell lines are sensitive to lower doses of IlludinS we aimed to explore the IlludinS-derivative Irofulven as a potential therapeutic agent to treat patients with hypomorphic ERCC3 mutations. Experimental procedures and Results: We tested the efficacy of Irofulven in isogenic WT and ERCC3 mutant mammary epithelial cell lines in vitro and in xenograft models. In vitro cells were treated with various doses of Irofulven and cell viability was assessed at 72h following treatment. For generation of xenograft models hRAS-V12 expressing genetically engineered ERCC3 mutant as well as isogenic ERCC3 wild-type cell lines were injected into flanks of nude mice and treated with different doses of Irofulven. Tumor volumes were measured over the course of treatment and tumors excised after termination of treatment for final weighing and for histological and subsequent molecular-genetic analysis. In vitro studies showed an increased sensitivity of the ERCC3 mutant cells towards the drug Irofulven, with a significant difference in sensitivity observed in the lower dose range. An initial xenograft experiment determining the effective in vivo dose range and schedule demonstrates enhanced sensitivity in the ERCC3 mutant background. Additional xenograft experiments under the determined optimal treatment dose and schedule are in progress as are further experiments including RNA sequencing of tumor tissue and exploration of combinatorial therapies. Conclusions: A functionally significant recurrent ERCC3 mutation has been shown to increase the risk for breast cancer in a genetic isolate. Similar to tumors arising in the background of homologous repair defects, mutations in nucleotide excision repair genes such as ERCC3 could constitute potential therapeutic targets in a subset of hereditary breast cancers. Mutated cell lines showed lower survival after in vitro and in vivo exposure to the DNA alkylating agent Irofulven. The present study provides a potential pre-clinical approach to a subset of breast cancer cases with an inherited mutation of a nucleotide excision repair pathway gene, demonstrating sensitivity to the DNA alkylating agent Irofulven. Citation Format: Sabine Topka, Sara Khalil, Elisa De Stanchina, Joseph Vijai, Kenneth Offit. Preclinical evaluation of enhanced irofulven antitumor activity in an ERCC3 mutant background by in vitro and in vivo tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3258.