Low‐Dose Irinotecan Improves Advanced Lupus Nephritis in Mice Potentially by Changing DNA Relaxation and Anti–Double‐Stranded DNA Binding

Abstract

Objective. Despite clear advances in the treatment of systemic lupus erythematosus (SLE), many patients still present with refractory lupus nephritis, requiring new treatment strategies for this disease. This study was undertaken to determine whether reduced doses of the topoisomerase I (topo I) inhibitor irinotecan, which is known as a chemotherapeutic agent, suppress SLE in (NZB ؋ NZW)F1 (NZB/NZW) mice, and to evaluate the potential mechanism by which irinotecan influences the course of SLE.Methods. NZB/NZW mice were treated with lowdose irinotecan beginning at either 24 weeks of age or established glomerulonephritis, defined as proteinuria of grade >3؉. Binding of anti-double-stranded DNA (anti-dsDNA) antibodies was measured by enzymelinked immunosorbent assay (ELISA), and DNA relaxation was visualized by gel electrophoresis.Results. Significantly reduced irinotecan doses improved lupus nephritis and prolonged survival in NZB/NZW mice. The lowest dose successfully used for the treatment of established murine lupus nephritis was >50 times lower than the dose usually used for chemotherapy in humans. As a mechanism, low-dose irinotecan reduced B cell activity. However, the levels of B cell activity in irinotecan-treated mice were similar to those in BALB/c mice of the same age, suggesting that irinotecan did not induce clear immunosuppression. In addition, incubation of dsDNA with topo I increased binding of murine and human anti-dsDNA antibodies, showing for the first time that relaxed DNA is more susceptible to anti-dsDNA antibody binding. This effect was reversed by addition of the topo I inhibitor camptothecin.Conclusion. Our findings indicate that topo I inhibition may be a novel and targeted therapy for SLE.

The Topoisomerase I Inhibitor Irinotecan and the Tyrosyl‐DNA Phosphodiesterase 1 Inhibitor Furamidine Synergistically Suppress Murine Lupus Nephritis

“…Previous data from our group demonstrated that low‐dose irinotecan alone yielded moderate immunosuppression, which we interpreted as the correction of enhanced immune activation under autoimmune conditions . We therefore examined whether the effects of combined treatment with irinotecan and furamidine were accompanied by more pronounced immunosuppression.…”

“…In summary, although low‐dose irinotecan was previously suggested to be an entirely new and feasible treatment option for SLE , the combination of low‐dose irinotecan and the TDP‐1 inhibitor furamidine seemed to be superior to irinotecan alone. However, a number of questions need to be answered in upcoming experiments.…”

“…In previous experiments, we demonstrated that inhibition of topo I diminished DNA relaxation and subsequent binding of anti‐dsDNA antibodies derived from plasma of lupus‐prone mice or from human SLE serum . Using the monoclonal anti‐dsDNA antibody HYB331‐01, we first determined whether increased anti‐dsDNA binding following topo I–mediated DNA relaxation could be reversed by inhibition of topo I. To this end, supercoiled plasmid DNA pBR322 was incubated with recombinant topo I and increasing amounts of camptothecin, a water‐insoluble analog of irinotecan that is widely used for in vitro experiments.…”

Topoisomerase 1B poisons: Over a half‐century of drug leads, clinical candidates, and serendipitous discoveries

“…Irinotecan treatment could also prevent the development of the disease itself while prolonging survival of the affected animals. Reduced does of 4 (3‐12.5 mg/kg, including those fifty times lower than those used for cancer treatment) were also effective in this mouse model . Compound 4 was also tested in the MRL/ lpr mouse model (which rapidly develops severe lupus‐like symptoms including skin lesions), and high doses could reduce spleen inflammation, whereas high and low‐doses could prevent proteinuria, improve skin condition, and prolong lifespan …”

“…Reports suggest otherwise in this case: irinotecan had no effects in models of autoimmune diabetes, systemic sclerosis, or multiple sclerosis, low‐dose 4 did not cause a reduction in T‐ or B‐lymphocytes (either in number or activity), and high‐dose 4 did not suppress T‐cell activity or antibody production. One hypothesis for the observed effect is that Top1‐mediated relaxation enhances the binding of antidouble‐stranded DNA antibodies (a hallmark of lupus), and Top1 inhibition can prevent this process . This could be a promising novel avenue for lupus treatment, especially given the high sequence homology between murine and human Top1.…”