Abstract 4344: Low mitochondrial copy number induces resistance to chemotherapy in esophageal cancer

Introduction: Esophageal squamous cell carcinoma (ESCC) is the one of the deadliest gastrointestinal cancers. The important problem in treating ESCC is resistance to chemotherapy. A few previous reports showed that mitochondrial DNA (mtDNA) copy number was decreased in esophageal squamous cell carcinoma (ESCC). However, it is unclear whether alteration of mtDNA copy number affects the effect of chemotherapy for ESCC. In the present study, we investigated the relationship between mtDNA copy number and the effect of chemotherapy in ESCC. Methods: To analyze the mtDNA copy number of surgically resected primary tumors from ESCC patients, qPCR for Cytochrome Oxidase I was performed. Human ESCC cells (TE8 and TE11) with decreased mtDNA copy number were established by knockdown of mitochondrial transcription factor A (TFAM). Those cells were treated with 5FU, cisplatin and docetaxel. The response of chemotherapy was accessed by cell viability assay (WST assay) and apoptosis assay (flow cytometry). To investigate the mechanism of resistance of chemotherapy, expression of EMT-related genes such as CDH1, CDH2, vimentin and zeb1 was measured by qPCR. Wound healing assay and invasion assay were performed to access the cell migration and invasion. Results: Patients were categorized into higher and lower subgroups according to the median value of the mtDNA copy number. Lower mtDNA copy number group was significantly correlated with tumor depth and pathologic response of chemotherapy. ESCC patients with lower mtDNA copy number had significantly poorer 5-year recurrence-free and overall survival than higher group. By shRNA knockdown of TFAM gene expression, mtDNA copy number decreased to 40% in TE8 and 60% in TE11 compared with non-target control cells. Viability of mtDNA-depleted TE8 and TE11 treated with chemotherapy was higher than that of control cells. Apoptosis assay showed the percentages of apoptosis induced by chemotherapy in mtDNA-depleted TE8 and TE11 were lower than those of control cells. Invasion assay and wound healing migration assay showed that mtDNA-depleted TE8 and TE11 were significantly more invaded and migrated than the control-sh cells. Conclusions: These results suggest that low mitochondrial copy number induces resistance to chemotherapy in esophageal cancer. Citation Format: Moyuru Yamada, Koji Tanaka, Yasunori Masuike, Tomoki Makino, Tsuyoshi takahashi, Yukinori Kurokawa, Makoto Yamasaki, Kiyokazu Nakajima, Masaki Mori, Yuichiro Doki, Kabuki Odagiri. Low mitochondrial copy number induces resistance to chemotherapy in esophageal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4344.