LAUSR

To overcome the resistance of epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) in non-small cell lung cancer, the mechanism clarification and novel molecular target development are urgently required. From this viewpoint, we previously identified by proteomics analysis progesterone receptor membrane component 1 (PGRMC1) as a new candidate target of EGFR-TKI resistance. However, the detailed mechanism of PGRMC1 in acquired resistance to EGFR-TKI is still obscure. In this study, we investigated the role and mechanism of PGRMC1 in EGFR-TKI resistance. First, to understand the significance of PGRMC1 in EGFR-TKI resistance, PC9/ER, which was constructed with increasing concentration erlotinib for 6 months and required resistance to erlotinib with PGRMC1 up-regulated, and its parental cell line PC9 were used. The wst-8 assay was executed after PGRMC1 inhibitor (AG-205) was treated to cells. The results showed that, compared to PC9 treated with AG-205, PC9/ER showed a significant reduction in viability with AG-205 treatment. Since AG-205 was reported to inhibit PGRMC1-heme complex formation and the ferrous from liberated heme could induce the ferroptosis, we detected the intracellular ferrous by ferroOrange when cells were treated with AG-205. Although PC9/ER showed lower ferrous than PC9, both cells showed induction of free ferrous when treated with AG-205. In the meantime, we measured the viability of two cells when treated by erastin and hemin, which are ferroptosis activators. Similar results to AG-205 were showed in PC9/ER with activators, which had lower viability than PC9 with activators. Since the side effect from high dosage treatment usually, not only the single treatment of AG-205, but low dosage co-treatment of AG-205 and erlotinib was also evaluated. Compared with PC9, which showed little variation in combination treatment, co-treatment in PC9/ER showed significant reductions in viability. Besides, immunofluorescence showed the ferrous decreased when erlotinib was treated and then increased when AG-205 was further added. These results showed that PGRMC1 might reduce ferroptosis and lead to erlotinib resistance. Collectively, these findings suggest important roles of ferroptosis reduction by PGRMC1 in erlotinib resistance. Since the single or co-treatment showed a significant efficiency, PGRMC1 might provide a new therapeutic target for lung adenocarcinoma. Citation Format: Ying LIN, Kazuma HIGASHISAKA, Sachiyo HANAMURO, Kohei IZUSAWA, Hiroto KONISHI, Yuya HAGA, Lili YANG, Hirofumi TSUJINO, Kazuya NAGANO, Yasuo TSUTSUMI. Progesterone receptor membrane component 1 is a candidate key molecule involved EGFR-TKI resistance in lung adenocarcinoma [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr B114. doi:10.1158/1535-7163.TARG-19-B114