# Niclosamide: CRL4AMBRA1 mediated degradation of cyclin D1 following mitochondrial membrane depolarization

## TL;DR

Niclosamide, a drug used for worm infections, can degrade a cancer-related protein called cyclin D1 through a specific cellular pathway.

## Contribution

Niclosamide is identified as a molecular glue degrader targeting cyclin D1 via CRL4AMBRA1, with a novel correlation to mitochondrial membrane depolarization.

## Key findings

- Niclosamide induces rapid cyclin D1 degradation via the ubiquitin-proteasome pathway.
- CRL4AMBRA1 is a key E3 ligase involved in niclosamide-mediated cyclin D1 degradation.
- Mitochondrial membrane potential disruption correlates with cyclin D1 downregulation across multiple compounds.

## Abstract

Targeted protein degradation has emerged as a promising approach in drug discovery, utilizing small molecules like molecular glue degraders to harness the ubiquitin-proteasome pathway for selective degradation of disease-driving proteins. Based on results from proteomics screens we investigated the potential of niclosamide, an FDA-approved anthelmintic drug with a 50 year history in treating tapeworm infections, as a molecular glue degrader targeting the proto-oncogene cyclin D1. Proteomics screens in HCT116 colon carcinoma and KELLY neuroblastoma cells, found that niclosamide induces rapid cyclin D1 degradation through a mechanism involving the ubiquitin-proteasome pathway. A genetic CRISPR screen identified the E3 ligase CRL4AMBRA1 as a key player in this process. Structure–activity relationship studies highlighted critical features of niclosamide necessary for cyclin D1 degradation, demonstrating a correlation between mitochondrial membrane potential (MMP) disruption and cyclin D1 downregulation. Notably, various mitochondrial uncouplers and other compounds with similar drug sensitivity profiles share this correlation suggesting that MMP disruption can trigger cyclin D1 degradation, and that the cellular signal driving the degradation differs from previously described mechanism involving CRL4AMBRA1. Our findings underscore the complexities of proteostatic mechanisms and the multitude of mechanisms that contribute to degrader drug action.

Niclosamide, an FDA-approved anthelmintic drug, known to uncouple the mitochondria induces cyclin D1 degradation via CRL4AMBRA1. We find a striking correlation between the two processes and that it is observed amongst various compounds.