# Harnessing E3 Ligases for Cancer Therapy

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA BERKELEY · 2023 · $437,813

## Abstract

Targeted protein degradation has arisen as a powerful drug discovery paradigm for targeting undruggable
proteins for proteasomal degradation. This technology utilizes bifunctional degraders called proteolysis targeting
chimeras (PROTACs) that consist of a protein-targeting ligand linked to an E3 ligase recruiter to ubiquitinate and
proteasomally degrade proteins of interest. While targeted protein degradation can potentially be used to target
any intracellular protein for degradation, a major challenge of this approach has been the dearth of E3 ligase
recruiters. Using a chemoproteomic platform termed activity-based protein profiling (ABPP), which uses
reactivity-based chemical probes to profile proteome-wide reactive, functional, and ligandable hotspots, we
recently discovered that the anti-cancer natural product nimbolide, a triterpenoid isolated from Azadirachta
indica or neem, covalently reacts with an N-terminal cysteine (C8) of the E3 ubiquitin ligase RNF114 in triple-
negative breast cancer cells. Our preliminary data revealed that covalent modification of RNF114 by nimbolide
leads to impaired ubiquitination of the tumor suppressor p21 through a nimbolide-dependent destabilization of
the RNF114-substrate binding interaction, thus providing a potential mechanism for the anti-cancer effects of
this natural product. This realization that nimbolide targeted a substrate recognition domain within RNF114
suggested that nimbolide could potentially be used as a novel recruiter for RNF114 for PROTAC applications.
Consistent with this premise, we have shown that a PROTAC, XH2, linking nimbolide to a BRD4 inhibitor JQ1
led to proteasome-dependent degradation of BRD4 in breast cancer cells. This degradation was RNF114-
dependent, as shown by BRD4 degradation in RNF114 wild-type cells, but not in RNF114 knockout cells. In this
proposal, we will combine chemoproteomic and targeted protein degradation platforms to investigate
the therapeutic potential of RNF114 modulators in cancer and exploit nimbolide and other covalent
ligands targeting C8 of RNF114 as recruiters for PROTAC applications.

## Key facts

- **NIH application ID:** 10656333
- **Project number:** 5R01CA240981-05
- **Recipient organization:** UNIVERSITY OF CALIFORNIA BERKELEY
- **Principal Investigator:** Thomas John Maimone
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $437,813
- **Award type:** 5
- **Project period:** 2019-07-01 → 2024-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10656333

## Citation

> US National Institutes of Health, RePORTER application 10656333, Harnessing E3 Ligases for Cancer Therapy (5R01CA240981-05). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10656333. Licensed CC0.

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