# Characterization of A Novel Proteasome Inhibitor

> **NIH NIH R01** · JOHNS HOPKINS UNIVERSITY · 2024 · $519,833

## Abstract

The human proteasome plays an essential role in both protein homeostasis and in
the regulation of multiple cellular processes from signal transduction to
transcription. It has also become a proven target for developing drugs for treating
multiple diseases including multiple myeloma and lymphoma. Several inhibitors of
the proteasome, including bortezomib, carfilzomib and ixazomib, have been used
in the clinic, responsible for prolonging lives of multiple myeloma patients.
However, the existing proteasome-targeted drugs suffer from severe toxicity and
rapid emergence of drug resistance, which also limits their potential in treating
other types of diseases. We have developed a rapamycin-inspired macrocycle
library known as rapafucins by fusing the FKBP-binding domain (FKBD) of
rapamycin with a combinatorial peptide library. A screen of the rapafucin library in
multiple myeloma cell line NCI-H929 led to the identification of a potent inhibitor,
Rapaprotin that induces apoptosis in NCI-H929 cells. Rapaprotin exhibited
selective toxicity to cancer cells over normal cells. It also has a unique mechanism
of action, requiring activation by an intracellular protease through cleavage of the
macrocycle into a linear form, Rapaprotin-L, which inhibits all three types of
protease activities of the proteasome. Moreover, Rapaprotin is synergistic with
bortezomib and is capable of resensitizing bortezomib-resistant cancer cells to the
drug. In this application, we will investigate the mechanism of activation of
Rapaprotin by the cellular protease, validating Rapaprotin-L as the active species
for its cellular activity. We will obtain a high-resolution cryo-EM structure of the
complex between proteasome and Rapaprotin-L. We will optimize the potency and
pharmacokinetic property of Rapaprotin through design and synthesis of new
analogs. The optimized analogs of Rapaprotin will be assessed for their efficacy in
animal models of multiple myeloma and other diseases. The newly developed
Rapaprotin analogs will serve as useful chemical probes to facilitate the study of
the function and pharmacology of the proteasome and promising leads for
developing a new class of anticancer and immunosuppressive drugs with lower
adverse effects.

## Key facts

- **NIH application ID:** 10808053
- **Project number:** 5R01GM145793-03
- **Recipient organization:** JOHNS HOPKINS UNIVERSITY
- **Principal Investigator:** Jun O. Liu
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $519,833
- **Award type:** 5
- **Project period:** 2022-04-01 → 2026-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10808053

## Citation

> US National Institutes of Health, RePORTER application 10808053, Characterization of A Novel Proteasome Inhibitor (5R01GM145793-03). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10808053. Licensed CC0.

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