Identification of the Receptor Tyrosine Kinase Inibitor Sunitinib, and Related Analogues, as Candidate Molecules for Glaucoma Neuroprotection

Abstract

Purpose: : We employed a high-content screen (HCS) to identify small molecules that can promote retinal ganglion cell (RGC) survival and neurite outgrowth. Our goal is to use the identified molecules as 1) lead compounds for the development of neuroprotective drugs for the treatment of glaucoma and other optic neuropathies, and 2) as molecular probes to deepen our understanding of RGC biology.

Methods: : Primary mouse RGCs were purified by anti-Thy1.2 immunopanning, and used to screen various compound libraries in an image-based assay. Effects of identified compounds were investigated by gene expression profiling and phospho-blot analysis. Structural analogs of drug leads were synthesized to study structure-function relationships. RGC survival promoting activity in vivo was tested using optic nerve injury models.

Results: : Of the molecules identified by HCS, one of the most potent at promoting RGC survival and neurite outgrowth was the broad-spectrum receptor tyrosine kinase inhibitor sunitinib, an FDA approved drug that is used for the treatment of a variety of cancers. Sunitinib strongly promotes RGC survival in vitro, and protects RGC from NMDA excitotoxicity and axon injury-associated degeneration in vivo. Sunitinib simultaneously induces changes in the phospho-protein signaling network that favor the inhibition of cell death pathways and stimulates a pro-survival pathway. Through the synthesis and analysis of structural analogs, we found that the efficacy and safety of sunitinib-mediated RGC survival can be improved by modifying the side chains on its scaffold, and such modifications are associated with changes in the molecule’s ability to modulate cell death and survival promoting pathways. Screening for additional neuroprotective compounds is continuing, as are further studies of the neuroprotective mechanism(s) by which sunitinib acts on RGCs.

Conclusions: : Sunitinib, and some of its analogs, appear to be promising leads for the development of possible neuroprotective drugs for the treatment of glaucoma and other optic nerve diseases. Our study also highlights the advantage of simultaneously targeting multiple kinase signaling pathways in treating RGC degenerative conditions in which multifaceted and complex mechanisms are implicated.

Keywords: ganglion cells • cell survival • retinal culture