Increasing evidence shows that microRNAs (miRNA), a family of small non-coding RNAs, play a pivotal role in regulating mRNA translation. Recently, some miRNAs have been shown to be involved in regulating cancer stem cell (CSC) properties. Because CSCs are highly resistant to conventional chemotherapy and radiation therapy, and heavy ion radiotherapy is effective in treating those of chemo-radioresistant cancers, in this study we attempt to explore new molecular mechanisms of CSC targeted therapies by carbon ion beam alone or in combination with a miRNA200c mimic.
Human pancreatic CSCs (CD44+/ESA+) sorted from hum pancreatic cancer cells PK45 and PANC1 were treated with carbon ion beam, X-ray irradiation alone or in combination with a miRNA200c mimic, followed by cell viability assay, colony and spheroid formation ability assay, caspase 3/7 activity assay, and real-time PCR analysis of apoptosis and autophagy-related gene expression were also performed.
The colony, spheroid formation assays confirmed that a subpopulation of CD44+/ESA+ have exactly CSC properties compared with CD44-/ESA- cells in pancreatic cancer cells. Carbon ion beam combined with a miRNA200c mimic significantly decreased CSC viability. The colony, spheroid formation ability of CD44+/ESA+ cells was significantly inhibited by carbon ion beam combined with miRNA200c compared with X-ray irradiation, carbon ion beam alone. Apoptosis analysis showed that caspase activity of 3/7 was significantly enhanced by carbon ion beam in combination with a miRNA200c mimic. Real-time PCR analysis showed that some of apoptosis-related and autophagy-related genes were significantly induced by carbon ion beam alone or in combination with a miRNA200c mimic in pancreatic cancer cells.
Taken together, because the carbon ion beams have a well-defined range with well-localized energy called “spread out Bragg peak (SOBP)”, and release enormous energy at the end of their range, carbon ion beams therefore can kill radioresistant CSCs more than photon beams, and combination with a miRNA200c mimic further enhances those actions, based on the present data.
National Institutes for Quantum and Radiological Science and Technology
All authors have declared no conflicts of interest.