Abstract 4451: Developing a PROTAC-based NR4A1 degrader for melanoma cancer therapy
Authors: Master Rohan , Luo Yuewan , Xiao Yufeng , Zhou Daohong , Wang Lei , Zheng Guangrong , Zhang Weizhou 
Published: June 2023

Introduction: Melanoma originates from melanocytes within the epidermis and is one of the most common cancers, with nearly 100000, new cases yearly. Despite numerous advancements in therapies to treat melanoma, a prevalent population of patients still do not respond to currently approved therapies. Recent studies have highlighted the role of transcription factor nuclear receptor subfamily 4 group A member 1 (NR4A1) in melanoma for cancer survival, invasion, and metastasis. NR4A1 is also involved in glucose metabolism. Our project aims to identify an effective degrader of NR4A1 using a PROTAC strategy and then validate its effectiveness in reducing the growth of melanoma. PROTACs consists of three domains: a warhead that binds to the protein of interest, a ligand to an E3 ligase, and a linker that brings both domains in proximity to one another. The PROTAC can recruit an E3 ligase to ubiquitinate NR4A1 and degrade it via the ubiquitin-proteasome system (UPS).

Results: Our first goal was to identify valid PROTAC candidates that can effectively degrade NR4A1. We identified NR-V04, which demonstrated a dose-dependent degradation of NR4A1 in various melanoma cell lines. We further investigated time-dependent degradation, and NR-V04 was able to achieve in vitro degradation of NR4A1 16 hours after treatment. Additionally, we validated the mechanism of degradation via the UPS through various models. NR-V04 treatment of cells with a VHL knockout, which removes the E3 ligase recruited, experienced no degradation of NR4A1, and treatment of cells treated with MG132, a proteasome inhibitor, also showed no degradation. We observed degradation in vitro of numerous mouse and human cell lines. To investigate the cancer-killing effects of NR-V04, we completed MTS assays on the human melanoma cell lines CHL1 and A375, which showed an EC50 of 0.723 μM and 1.025 μM, respectively. When comparing NR-V04 treated and untreated CHL1 cells, NR-V04 was able to significantly decrease melanoma cell viability. NR4A1 knockout in CHL1 also showed decreased melanoma cell viability, and when comparing NR-V04 treated and untreated in NR4A1 knockout, there was no further decrease in melanoma cell viability. As for in vivo models, NR4A1 knockout in CHL1 and A375 exhibited slower tumor growth compared to the wild type. Furthermore, NR-V04 showed suppression of CHL1 and A375 tumor-bearing NSG mice melanoma growth at low dose concentrations of 1 mg/kg after seven days compared to vehicle and warhead treatment. Western blot analysis of tumor tissue provides support for the ability of NR-V04 to degrade tumor-intrinsic NR4A1.

Conclusion: NR-V04 can selectively degrade NR4A1, in vitro and in vivo, to decrease melanoma cancer cell viability via the UPS. NR-V04 holds promising therapeutic potential as a cancer therapy for patients with melanoma.

Citation Format: Rohan Master, Yuewan Luo, Yufeng Xiao, Daohong Zhou, Lei Wang, Guangrong Zheng, Weizhou Zhang. Developing a PROTAC-based NR4A1 degrader for melanoma cancer therapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4451.