Abstract P2-26-10: Statins exhibit an anti-tumor effect by attenuating PD-L1 in breast cancer cells and macrophages and reducing breast tumor progression in xenograft mouse model

Abstract Background: Statins were suggested for repurposed drugs, having multifaceted effects which include anti-tumor activities by modulating the immune response. Here, we aimed to demonstrate the effect of statins on programmed death-ligand 1 (PD-L1) expression in triple-negative breast cancer (TNBC) cells. Methods: Thirteen human TNBC cell lines, mouse macrophage cell line (RAW 264.7), cholesterol and 27-hydroxycholesterol, and clinically approved lovastatin and simvastatin were used. Flow cytometry, Annexin V/propidium iodide assay, western blot, qRT-PCR, transwell migration assay, and immunohistochemistry were employed. A co-culture of macrophages with various breast cancer cells was performed. An orthotopic breast tumor mouse model and metastasis model by injection of GFP-tagged MDA-MB-231 cells into mammary gland fat pad and the tail vein injection were produced. In tumor model mice, lovastatin(10mg/kg) was daily injected intraperitoneally. In vivo fluorescent imaging was used to identify primary tumor development and lung metastasis. Results: Among thirteen TNBC cell lines, MDA-MB-231, HCC38, and HCC70 highly expressed endogenous/constitutive PD-L1. Statins reduced PD-L1 expression and exerted anti-proliferative and apoptotic effects in MDA-MB-231, HCC38, HCC70, and Raw264.7 in a dose- and time-dependent manner (p< 0.05). Meanwhile, statins increased the expression of PD-L1 in Hs578T and MDA-MB-468. STAT3 phosphorylation was inhibited in MDA-MB-231 and HCC70, but not in Hs578T, while AKT phosphorylation was reduced in MDA-MB-231, HCC70, Hs578T, and MDA-MB-468 when statins were treated. The migration of MDA-MB-231 and Raw264.7 in statin-treated conditioned media was decreased (p< 0.05). Cholesterol and 27-hydroxy cholesterol did not restore PD-L1 expression in statin-treated MDA-MB-231. Statins suppressed the expression of M2 markers (PD-L1, CD206, YM-1, Fizz1, arginase-1) in RAW26437 stimulated by a conditioned medium of MDA-MB-231. Lovastatin suppressed the primary tumor growth and metastasis in xenograft tumor mice. Conclusions: Our findings show that statins have an anti-tumor effect, which kills breast cancer cells and triggers macrophage reprogramming by reducing PD-L1 expression, impairing the AKT, ERK, and STAT3 signal pathways, and decreasing M2 markers. Further study is needed to investigate an in-depth molecular mechanism study by which statins regulate PD-L1 expression in TNBC and to confirm the safe and effective use of statins as adjuvant therapy in TNBC. Citation Format: Sangeun Lee, Hoe Suk Kim, So-Hyun Yoon, Seungyeon Ryu, Moonjou Baek, A Young Park, Han-Byoel Lee, Wonshik Han. Statins exhibit an anti-tumor effect by attenuating PD-L1 in breast cancer cells and macrophages and reducing breast tumor progression in xenograft mouse model [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P2-26-10.