HIF inhibitor topotecan suppresses light-induced retinal degeneration in mice

Abstract

Purpose : Retinal degenerative diseases cause progressive and irreversible visual impairment while effective therapies are still not available. Hypoxia-inducible factors (HIFs) are transcriptional factors which regulate angiogenesis, erythropoiesis, intracellular metabolism, and programed cell death mainly depending on oxygen availability. We hypothesize that ectopic activation of HIFs may contribute to the progress of the diseases through an abnormal stress response. A topoisomerase inhibitor topotecan has been previously reported to inhibit HIF activation by blockade of HIF-α synthesis. In this study, we investigate suppressive effect of topotecan against HIF activation in vitro and progression of retinal degeneration induced by excessive light exposure in mice.

Methods : A murine fibroblast cell line NIH/3T3 and a murine cone photoreceptor cell line 661W are individually transfected with a HIF-luc reporter gene construct to monitor HIF activation. The HIF-luc construct encodes firefly luciferase gene under the control of hypoxia response element which binds HIFs. These cells are also co-transfected with CMV-renilla luciferase construct as internal control. 150μM of cobalt chloride is administrated to the cells in order to induce normoxic HIF activation. The suppressive effect of topotecan against HIF activation was evaluated 24hours after induction. To evaluate therapeutic effect of topotecan on retinal degeneration, 8-week-old male BALB/c mice were divided into the topotecan-administrated group (1mg/kg/day, n=6) and the vehicle-administrated group (n=6) which were given 100μL of reagents intraperitoneally for 20days. 17 days after the initial administration, all animals were exposed to 3,000lux cool white fluorescent light for one hour to induce retinal photodamage. Retinal function was evaluated using electroretinography 3days after the exposure. P-value less than 0.05 was considered as statistical significance with Student’s t-test.

Results : In vitro Normoxic HIF activation was suppressed by topotecan in NIH/3T3 (25.6%) and 661W (52.6%), respectively. In the murine light-induced retinal degeneration model, amplitude of a- and b-wave were significantly (p=0.042, p=0.024, respectively) higher in the topotecan-administrated group than in the vehicle-administrated group.

Conclusions : A topoisomerase inhibitor topotecan suppresses HIF activation in retinal cells and light-induced retinal degeneration in mice.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.