Targeting Cancer with a Lupus Autoantibody

Abstract

Systemic lupus erythematosus (SLE) is distinct among autoimmune diseases due to its association with circulating autoantibodies reactive against host DNA. The precise role that anti-DNA antibodies play in SLE pathophysiology remains to be elucidated, and potential applications of lupus autoantibodies in cancer therapy have not previously been explored. Here we report the unexpected finding that a cell-penetrating lupus autoantibody, 3E10, has potential as a targeted therapy for DNA-repair deficient malignancies. We find that 3E10 preferentially binds DNA single-strand tails, inhibits key steps in DNA single-strand and double-strand break repair, and sensitizes cultured tumor cells and human tumor xenografts to DNA-damaging therapy, including doxorubicin and radiation. Moreover, we demonstrate that 3E10 alone is synthetically lethal to BRCA2-deficient human cancer cells and selectively sensitizes such cells to low dose doxorubicin. Our results establish an approach to cancer therapy that we expect will be particularly applicable to BRCA2-related malignancies such as breast, ovarian, and prostate cancers. In addition, our findings raise the possibility that lupus autoantibodies may be partly responsible for the intrinsic deficiencies in DNA repair and the unexpectedly low rates of breast, ovarian, and prostate cancers observed in SLE patients. In summary, this study provides the basis for the potential use of a lupus anti-DNA antibody in cancer therapy and identifies lupus autoantibodies as a potentially rich source of therapeutic agents.

Optimizing a Lupus Autoantibody for Targeted Cancer Therapy

“…Only seven antibodies are presently FDA approved for the treatment of solid tumors, (9), and once inside the nucleus 3E10 appears to incompletely inhibit BER and HDR, which is not toxic to normal cells, but is synthetically lethal to cells that have preexisting defects in HDR due to BRCA2 deficiency (1). The targeted effect of 3E10 and its fragments on HDR-deficient cancer cells, therefore, is not necessarily due to selective penetration into cancer cells, but rather to the selective sensitivity of HDR-deficient cancer cells to further inhibition of DNA repair by 3E10.…”

“…1). The degree to which 3E10 inhibits these DNA repair pathways is not sufficient to kill normal cells, but cancer cells with preexisting defects in HDR due to BRCA2 deficiency are somewhat sensitive to 3E10 (1). These findings revealed the potential to apply 3E10 as a targeted therapy for HDR-deficient tumors.…”

“…3E10 penetrates into cell nuclei, binds DNA, and inhibits both base excision repair (BER) and homologydirected repair (HDR) of DNA double-strand breaks (DSB; ref. 1). The degree to which 3E10 inhibits these DNA repair pathways is not sufficient to kill normal cells, but cancer cells with preexisting defects in HDR due to BRCA2 deficiency are somewhat sensitive to 3E10 (1).…”

“…A 3E10 single-chain variable fragment (hereafter referred to as scFv) that lacks an Fc region and has a D31N mutation in the V H region of the first complementarity determining region (CDR1) has previously been generated (2,3). The D31N mutation significantly increases the DNAbinding affinity and efficiency of nuclear penetration by scFv, but despite this scFv still has only a modest effect on BRCA2-deficient cancer cells (1). We set out to build a more potent 3E10 fragment based on the scFv platform.…”

New Horizons in Therapeutic Antibody Discovery: Opportunities and Challenges versus Small-Molecule Therapeutics

“…3E10 has been shown to transport a variety of LMs, including antibodies, into the cell nucleus. 83,84 A potential route for success with functional intracellular antibodies, or "intrabodies," has come with the engineering of smaller antibody fragments. In situ expression of intracellular mAb fragments could provide an attractive alternative to systemic administration, and advances have been made in both selection technologies and in framework designs to enable correct folding.…”