Abstract 25: Identifying new inhibitors of ABCG2 by high-throughput screening

Background: ABCG2, also known as breast cancer resistance protein (BCRP), is a member of the ATP-binding cassette (ABC)-family of membrane transport proteins associated with multidrug resistance (MDR). No ABCG2 inhibitor has shown clinical significance yet. Aim: To identify novel inhibitors of ABCG2 by high-throughput screening. Material & Methods: After higher expression of ABCG2 in HCT-116/BCRP cells was confirmed by flow cytometry (FACSVerse) using 5D3 antibody, high-throughput fluorescent cell-based assay was performed with the original chemical library of Tohoku University containing about 6000 compounds using ABCG2-specific fluorescent substrate, Pheophorbide a (PhA) in HCT-116/BCRP cells overexpressing ABCG2. Ko143, a potent ABCG2 inhibitor, was used as positive control. Fluorescence intensity in the cells was read by a fluorescence plate reader (SpectraMax M2e) in bottom read mode, with 395 nm excitation, 670 nm emission. To validate the results, flow cytometry assay was performed with 10 µM PhA in HCT-116/BCRP cells. The fluorescence intensity was analyzed by flow cytometry (FACSVerse). Results: Fluorescenct cell-based assay with high-throughput screening could detect 23 candidate compounds, which showed higher fluorescence intensity as positive control Ko143 showed. Then, these 23 compounds were validated with flow cytometry assays. The flow cytometry assays revealed that 16 compounds increased fluorescence intensity of PhA in HCT-116/BCRP cells in dose dependent manner, suggesting that these candidate compounds inhibited transport function of ABCG2. Among 16 compounds, 6 compounds showed further inhibitory effect for transport function of ABCG2 as equivalent to that of Ko143. Conclusion: These 6 compounds may provide a basis for further investigation of ABCG2 function. Citation Format: Shoji Kokubo, Shinobu Ohnuma, Hideaki Karasawa, Akihiro Yamamura, Hideyuki Suzuki, Megumi Murakami, Norihiko Sugisawa, Keigo Kanehara, Keisuke Sato, Takanori Ishida, Takashi Kamei, Takeshi Naitoh, Michiaki Unno. Identifying new inhibitors of ABCG2 by high-throughput screening [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 25.