Structure-Activity Relationship Studies of a Natural Product Inhibitor of Choroidal Angiogenesis

Abstract

Purpose: Preventing pathological angiogenesis in the eye is key to treating retinopathy of prematurity (ROP), diabetic retinopathy and age-related macular degeneration (AMD). At present there is no small molecule drug on the market that specifically targets this process. There is thus a need for developing novel small molecules targeting angiogenesis. Cremastranone is a homoisoflavanone, previously isolated from the bulb of a medicinal orchid, Cremastra appendiculata. This compound has anti-angiogenic activity both in vitro and in vivo. In mouse models of ROP and AMD, homoisoflavanone inhibits pathogenic retinal and choroidal neovascularization respectively. However the mechanism of action and structure-activity relationship (SAR) of this compound are not yet understood. We set out to describe the SAR of cremastranone and show the anti-angiogenic activity of the synthetic compound in vitro.

Methods: We synthesized cremastranone for the first time. The anti-proliferative effects of cremastranone along with more than 50 natural product and synthetic analogs were tested with the Alamar blue cell proliferation assay, using human umbilical vein endothelial cells (HUVECs) and human retinal microvascular endothelial cells (HRMVECs). Retinoblastoma Y-79 and uveal melanoma 92-1 cells were used as control cell lines to detect non-specific ocular cytotoxic compounds. The anti-proliferative activity of the compounds was confirmed by the EdU incorporation assay.

Results: Synthetic cremastranone had growth inhibitory properties comparable to values reported for the natural-source compound. The HRMVEC growth inhibitory (GI₅₀) values of other active analogs ranged from 150 nM to 95 µM. While some compounds showed specific activity against HUVECs and HRMVECs and no toxicity towards Y79 and 92-1, others had nearly equal cytotoxic effects on all the cell lines tested. The fused ring-system of the chromanone moiety is essential for activity, as is the benzyl group. Small modifications on the aromatic rings of the compound are tolerated and can increase the specificity to endothelial cells, providing an opportunity to develop specific angiogenesis inhibitors.

Conclusions: This study offers the first evidence that synthetic cremastranone has antiangiogenic activity, and might be developed as a specific antiangiogenic drug to treat ROP, AMD and diabetic retinopathy.

Keywords: 412 age-related macular degeneration • 453 choroid: neovascularization • 654 proliferation