# Rational design of CNS-permeable cathepsin L inhibitors for treatment of chronic toxoplasmosis

> **NIH NIH R33** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2020 · $442,937

## Abstract

PROJECT SUMMARY
 The complete absence of treatment options for chronic Toxoplasma gondii (Tg) infection renders ~2
billion people at risk for reactivated toxoplasmosis. Congenitally infected individuals or those with weakened
immune systems are particularly vulnerable to reactivated toxoplasmosis manifested as fatal encephalitis,
myocarditis or loss of vision. As the leading cause of infectious posterior uveitis and second leading cause of
foodborne deaths in the USA, reactivated toxoplasmosis could be substantially reduced in high-risk
individuals by eliminating Tg tissue cysts. We used new genetic tools to identify an essential role for a
cathepsin protease L (CPL) activity during chronic Tg infection, creating an exciting opportunity to exploit a
new target for combatting reactivated toxoplasmosis. To begin addressing this key unmet need, we
identified an initial lead dipeptide nitrile CPL inhibitor based on its potential for CNS penetrance and
conducted primary SAR studies against Tg and human cathepsin L, demonstrating that we could achieve
over 100-fold improvement in selectivity for the Tg enzyme in under 20 analogs. In the R21 phase we will
use structure-based design to further optimize potency and selectivity along with improving stability and
permeability in in vitro models, delivering one or more potent, selective, stable, and cell-permeable leads. In
the R33 phase we will evaluate and further refine PK and CNS penetrance in mice before measuring
maximum tolerated dose and efficacy in an established murine treatment model for chronic Tg infection.
Both phases will feature first-of-their-kind assays for cyst viability developed for the studies. Upon successful
completion, this project will yield one or more Tg CPL inhibitors effective for reducing or eliminating tissue
cysts, thereby advancing a potential new solution for chronic Tg infection.
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## Key facts

- **NIH application ID:** 9831091
- **Project number:** 5R33AI127492-04
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** Vernon Bruce Carruthers
- **Activity code:** R33 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $442,937
- **Award type:** 5
- **Project period:** 2016-12-01 → 2021-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9831091

## Citation

> US National Institutes of Health, RePORTER application 9831091, Rational design of CNS-permeable cathepsin L inhibitors for treatment of chronic toxoplasmosis (5R33AI127492-04). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9831091. Licensed CC0.

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