Abstract P6-21-06: Target N-Ras for degradation by flunarizine to treat basal-like breast cancer

Abstract

Background:Basal-like breast cancer (BLBC) is an aggressive form of breast cancer that are usually triple negative for ER, PR, and HER2. There is no effective targeted therapy for BLBC due to the lack of a druggable driver. Ras GTPases are powerful drivers for tumorigenesis. We have shown that wild type N-Ras, but not K- or H-Ras, is overexpressed in BLBC and driving itsgrowth and transforming activities. However, there is currently no treatment that directly target Ras. This study thus screened existing pharmacologically active and approved compounds for the new ability to induce N-Ras degradation in BLBC. Methods:Compounds in the LOPAC library were screened by an automated microscopy system for the ability to reduce GFP-N-Ras signals in the cells. Isolated compounds were then examined to identify those that can degrade endogenous N-Ras in BLBC cells without impacting levels of other Ras proteins. Final candidate compounds were further examined to determine by which proteolytic pathway N-Ras is induced to be degraded. The potentials of the identified compound to treat BLBC were assessed by examining cell growth and soft agar colony formation in vitroand tumor growth in vivo. Results:We identified flunarizine (FLN), previously approved for treating migraine and epilepsy. The FLN-induced N-Ras degradation was not affected by a 26S-proteasome inhibitor. Rather, it was blocked by autophagy inhibitors. Furthermore, N-Ras can be seen co-localized with active autophagosomes upon FLN treatment, suggesting that FLN alters the autophagy pathway to degrade N-Ras. Importantly, FLN treatment recapitulated the effect of N-RASsilencingin vitroby selectively inhibiting the growth of BLBC cells, but not that of breast cancer cells of other subtypes. In addition, in vivoFLN inhibited tumor growth of a BLBC xenograft model. Conclusion:This proof-of-principle study presents evidence that the autophagy pathway can be coerced by small molecule inhibitors, such as FLN, to degrade Ras as a strategy to treat cancer. FLN has low toxicity and should be further investigated to enrich the toolbox of cancer therapeutics against BLBC. Citation Format: Zheng Z-Y, Li J, Li F, Zhu Y, Cui K, Wong ST, Chang EC, Liao Y-h. Target N-Ras for degradation by flunarizine to treat basal-like breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-21-06.