Epigenetic and metabolic reprogramming as a target for prostate tumor radiosensitization

Purpose or Objective
Radiotherapy remains one of the main modalities to treat solid cancers and is one of the mainstays of curative prostate cancer treatment. Nevertheless, the risk of recurrence after radiotherapy still remains substantial in locally advanced disease. Tumor relapse after radiotherapy is attributed to the population of cancer stem cells (CSCs) which survived the treatment. Therefore, analysis of the CSC populations might be an important predictive tool of radiotherapy outcome and individualized treatment selection. However, compelling evidence suggests a high plasticity of CSCs imposed by tumor treatment. This study is aiming to investigate the interconnection of the glutamine metabolism and cancer cell plasticity in the development of tumor radioresistance for the development of new biomarkers to predict radiation treatment outcome.
Material and Methods
The employed methodological approaches include gene expression analysis, comparative genomic hybridization array, proteomic analysis, metabolic profiling, in vitro radiobiological clonogenic survival assays, assessment of the histone methylation marks and CSC marker expression, analysis of DNA damage repair and oxidative stress response. This study is based on the different models including tumor cell lines and their radioresistant derivatives, prostate cancer xenografts, ex vivo treated tissues and analysis of the publicly available TCGA prostate cancer datasets.
Results
Our study revealed that irradiation causes long-term upregulation in the expression of stem cell markers and induces tumor cell reprogramming. Furthermore, radioresistant and tumorigenic cell populations undergo a phenotypic switch during the course of radiotherapy. This phenotypic plasticity is associated with genetic, epigenetic and metabolic changes induced by irradiation. Expression of CSC markers and proteins involved in glutamine metabolism can be used to predict clinical outcome of prostate cancer patients.
Conclusion
Our studies suggest that radioresistant properties of prostate cancer cells are dynamic in nature and that combination of irradiation with therapeutic agents which prevent tumor cell reprogramming and metabolic switch may restore the cytotoxic effects of irradiation in radioresistant CSC populations.
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