Abstract 4220: A cell-penetrating nucleolytic lupus autoantibody damages DNA and is toxic to BRCA2-deficient cancer cells

Identification of therapeutic agents that are more toxic to malignant cells than normal cells is a key goal in cancer research. Many tumor cells harbor genetic defects that distinguish them from normal cells, and some of these defects have the potential to be exploited in the development of targeted therapies for cancer. Cancer cells with defects in DNA repair are highly susceptible to DNA-damaging agents, but delivery of therapeutic agents into cell nuclei can be challenging. A subset of lupus autoantibodies is associated with nucleolytic activity, and some of these antibodies are capable of nuclear penetration. We hypothesized that such antibodies might be capable of damaging DNA in cell nuclei and therefore have potential as therapeutic agents targeted towards DNA repair-deficient malignancies, such as tumors that are BRCA2-deficient. To test this hypothesis we screened a panel of cell-penetrating lupus autoantibodies for nucleolytic activity, and we identified 5C6 as an antibody of interest. 5C6 catalyzes degradation of single and double-stranded DNA in vitro and induces phospho-H2AX formation in BRCA2-deficient cells. When tested on a matched pair of BRCA2-proficient and deficient cancer cells, 5C6 selectively suppressed the growth of and was significantly more toxic to the BRCA2-deficient cells. These findings demonstrate the potential utility of 5C6 in targeted therapy for DNA repair-deficient malignancies and strengthen the rationale for studies of additional lupus autoantibodies in order to identify the best candidates for development as therapeutic agents. In addition, the toxicity of 5C6 for BRCA2-deficient cells provides further support for the hypothesis that some lupus autoantibodies contribute to the unusual cancer risk profile associated with systemic lupus erythematosus. Citation Format: Philip W. Noble, Melissa R. Young, Richard H. Weisbart, James E. Hansen. A cell-penetrating nucleolytic lupus autoantibody damages DNA and is toxic to BRCA2-deficient cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4220. doi:10.1158/1538-7445.AM2014-4220