Development of a Drug for Dry-AMD

This project aims to develop specific inhibitors to treat AMD patients based on the protein structure and the natural substrate specificity profile of HTRA1. Aim 1 of this study is to determine the atomic-resolution structure of the HTRA1 PC-PDZ domain trimer using cryogenic electron microscopy (Cryo-EM), which will establish the empirical basis for structure-function-guided drug development. Aim 2 of this study is to design and test peptidomimetics (peptide-like compounds) derived from the natural substrate specificity profile of HTRA1 in choroid based on proteomic analysis. The compounds will be tested in eye tissue derived from human stem cells with AMD mutations.

Age-related Macular Degeneration (AMD) is the leading cause of central vision loss in the elderly. Currently, there are no therapeutics to delay or stop the progression of AMD. Genetic studies identified a correlation between AMD-pathogenicity and a genetic mutation resulting in overexpression of HTRA1 protein. HTRA1 regulates other proteins by cleaving them. Although the molecular mechanism for HTRA1-dependent AMD is not fully understood, many studies have shown that overexpression of HTRA1 disrupts the balance among regulatory/signaling proteins in cells through excessive cleavage. This molecular imbalance causes inflammation and abnormal blood vessel growth which leads to AMD. Thus, inhibition of excessive cleavage by HTRA1 is a desired therapeutic strategy.

We have profiled the natural cleavage targets of HTRA1 in eye tissues and designed HTRA1 inhibitors mimicking common chemical features of the identified targets. One compound showed promising efficacy and specificity in the test tube, and it was not toxic in cells or mice eyes. We propose to characterize the efficacy of our ‘lead-like’ compound in cells. Moreover, we will further optimize our compound through a structure-activity relationship strategy. This strategy will be supported by the protein structures that we will determine using a cutting-edge atomic resolution microscopy technique called CryoEM.

There are no HTRA1 specific inhibitors targeting the two functional domains (i.e., protease core domain and PDZ domain) at the same time. Moreover, our inhibitors may exclusively target the AMD specific pathway of HTRA1 in patients, since the compounds’ design-origin is the choroidal substrates of HTRA1.

We expect the success of this study will result in a therapeutic candidate for AMD which will be especially beneficial for the patients that has high-AMD-risk-factor gene mutation in HTRA1. In addition, this study will provide atomic-resolution protein structures of the HTRA1 PC-PDZ domain, which will establish the molecular and mechanistic basis to better understand the HTRA1-dependent pathology in AMD, Alzheimer disease, and arthritis.