F. Wang1, J. Ma1, J. Zhang1, C. Tian1, S. Shang1, S. Bao1, H. Yang1, M. Wu2, J. Yu3, and D. Chen1; 1Department of Radiation Oncology and Shandong Provincial Key Laboratory of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, 2Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, 3Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China
Purpose/Objective(s): Radiotherapy plays a leading role in the treatment of non-small cell lung cancer (NSCLC), but the emergence of radioresistace are still the main causes of treatment failure. Therefore, it is urgent to identify novel prognostic biomarker of radioresistance and explore new therapy strategies. The Rho GTPase CDC42 has been found to play an important role in the occurrence and development of a variety of malignant tumors, but whether it affects the radioresistance of NSCLC remains unclear. The purpose of this study was to verify whether CDC42 inhibitoin could potentiate the radiotherapy efficacy. Materials/
Methods: Tumor puncture samples and follow-up information of 66 NSCLC patients before radiotherapy were collected to analyze the correlation between radiotherapy response/prognosis and CDC42 expression. The effect of CDC42 on radiosensitivity of NSCLC cells was further explored in vitro through colony formation assay, and verified in vivo by mouse xenograft tumor models. Phospho-H2AX immunofluorescence staining, Western blot and Neutral comet electrophoresis experiments were used to investigate the effect of CDC42 on DNA damage repair in NSCLC cells after radiotherapy. In terms of mechanism, transcriptomic sequencing was performed to screen downstream genes of CDC42. CoIP-MS was conducted to detect the potentially interacting proteins of CDC42. The specific sequence of TFAP2A binding to BRCA1 promoter was determined by luciferase reporter assay and chip-qPCR. Results: The expression level of CDC42 in 66 NSCLC patients was negatively correlated with radiotherapy response rates and progression-free survival (PFS). Under the condition of radiotherapy, overexpression of CDC42 promotes colony formation of NSCLC cells in vitro, and enhanced the growth of subcutaneous tumor of mice in vivo. Furthermore, CDC42 could enhance DNA damage repair by activating transcription factor TFAP2A to up-regulate BRCA1 expression in NSCLC cells. TFAP2A could directly bind to the BRCA1 promoter sequence. In addition, CDC42 inhibitor ML141 combined with radiotherapy showed better anti-tumor effects and improved the survival rate of mice in vivo. Conclusion: Thus, we demonstrate that CDC42 induces radioresistance of NSCLC by activating TFAP2A-BRCA1 axis, and CDC42 is an attractive drug target for enhancing radiotherapy efficacy.
