Abstract 1390: Combination of carbon ion beam and gemcitabine causes unrepairable DNA damage and death of radioresistant pancreatic cancer stem-like cells in vitro and in vivo

Abstract

Abstract Purpose To elucidate whether carbon ion beam alone or in combination with gemcitabine has advantages over X-ray irradiation in targeting putative human pancreatic cancer stem cells (CSCs). Materials and Methods Human pancreatic CSCs sorted from PANC1 and PK45 cells were treated with carbon ion beam, X-ray alone or in combination with gemcitabine, and then colony, spheroid and tumor formation assays, RT Profiler PCR Array assay, immunofluorescence γH2AX foci assay as well as in vivo tumor control analysis were performed. Results The colony, spheroid formation as well as tumorigenicity assays confirmed that CD44+/ESA+ cells exactly have CSC properties compared to CD44-/ESA- cells. CSCs were more highly enriched after X-ray or gemcitabine compared to carbon ion beam alone, but extremely enhanced either X-ray or carbon ion beam in combination with gemcitabine. The number of colony and spheroid formed from CSCs after carbon ion beam was significantly reduced compared to that of X-ray, and it was extremely suppressed when combined with gemcitabine. The relative biological effectiveness (RBE) values for the carbon ion beam relative to X-ray at the D10 levels for CSCs were 2.13-2.78. RT Profiler PCR Array analysis showed that expressions of apoptosis-related genes (Bax, Cytochrome c), autophagy-related genes (LC3, p62), and senescence-related gene p21 were remarkably induced after carbon ion beam combined with gemcitabine compared to carbon ion beam alone or X-ray combined with gemcitabine. Immunofluorescence assay showed that not only the number but also the size of γH2AX foci in CSCs were lager 24 h after carbon ion beam combined with gemcitabine compared to carbon ion beam alone or X-ray combined with gemcitabine. Xenograft tumor control analysis showed that the tumors were not completely controlled even treated with 60 Gy of X-ray, but it was destroyed with 25 Gy of carbon ion beam combined with 50 mg/kg gemcitabine. Conclusions Carbon ion beam combined with gemcitabine has superior potential to kill pancreatic CSCs via unrepairable clustered DSB, and multiple cell death pathways at relatively lower doses compared to carbon ion alone or X-ray combined ith gemcitabine. Citation Format: Sei Sai, Toshifumi Wakai, Guillaumes Vares, Shigeru Yamada, Takehiko Kamijo, Eun Ho Kim, Tadashi Kamada, Toshiyuki Shirai. Combination of carbon ion beam and gemcitabine causes unrepairable DNA damage and death of radioresistant pancreatic cancer stem-like cells in vitro and in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1390. doi:10.1158/1538-7445.AM2015-1390