Abstract 393: Deoxymab: A targeted biologic that is synthetically lethal to TNBC brain metastases

Abstract

Abstract Brain metastases in triple-negative breast cancer (TNBC) harbor defects in homology-directed DNA repair that may be exploited to develop new therapeutic strategies. However, these tumors are protected by the blood-brain barrier (BBB), and mechanisms of DNA repair are sequestered in the nucleus. Methods to cross the BBB and target intranuclear processes are needed. 3E10 is a nuclear-penetrating lupus anti-DNA autoantibody that inhibits the DNA damage response to selectively kill cancer cells with defects in DNA repair. 3E10 localizes to DNA in tumor environments, and penetrates cells via the ENT2 equilibrative nucleoside transporter. ENT2 is expressed in the BBB, and 3E10 has previously delivered cargo proteins to the brain. We believe 3E10 can be turned against TNBC brain metastases, and used MDA-MB-231-BR brain-seeking human TNBC cells and tumors as a model system to test this hypothesis. We re-engineered 3E10 into an optimized fragment, called Deoxymab-1 (DX1), to maximize effect on cancer cells and minimize toxicity. DX1 expressed in CHO cells was purified over a HiTrap Capto S column by FPLC, and purity and quality was confirmed by SDS-PAGE and SEC-HPLC. Immunostaining and colony formation assays demonstrated that DX1 penetrated the nuclei of ~100% of MDA-MB-231-BR cells in culture and was synthetically lethal to the cells, with doses of 5 and 10 μM reducing surviving fractions to 0.47±0.15 (P<0.03) and 0.29±0.07 (P<0.01), respectively. TNBC brain metastases were established in nude mice by intracardiac injection of 1.75x105 MDA-MB-231-BR cells transfected with luciferase. One week later the presence of brain metastases was confirmed by IVIS. Mice were treated with tail vein injection of vehicle control (n=7) or DX1 (20 mg/kg) (n=7) 3x/week for 3 weeks. Tumor burden was monitored by weekly IVIS. DX1 significantly suppressed growth of the brain metastases (Table 1). These results establish proof of the novel concept of use of a modified lupus autoantibody against TNBC brain metastases. Table 1:Brain Radiance Efficiencies (x105)TreatmentWeek 0Week 1Week 2Week 3Control1.2±0.22.5±0.45.1±0.720±5DX11.3±0.21.4±0.32.0±0.23.8±0.8Pns<0.01<0.01<0.02 Citation Format: Shenqi Zhang, Christopher May, Anupama Shirali, Valentina Dubljevic, James A. Campbell, Jiangbing Zhou, James E. Hansen. Deoxymab: A targeted biologic that is synthetically lethal to TNBC brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 393.