Targeting Ras-MAPK pathway to enhance radiosensitivity in colorectal cancer cell lines

Introduction Radiotherapy (RT) plays a central role in the neoadjuvant treatment of locally advanced rectal cancer. However, their intrinsic radioresistance is a major clinical challenge that limits the therapeutic efficacy. Therefore, the availability of radiosensitizers would improve the treatment of rectal cancers. Aberrant Ras-MAPK signaling is a hallmark of colorectal cancer (CRC). The impact of Ras-MAPK signaling on cellular response to RT in CRC and the therapeutic value of targeting the pathway to increase radiosensitivity is still unclear.

Aims Our study aims to determine if pharmacological inhibition of the Ras-MAPK pathway at different levels can sensitize CRC cells to ionizing radiation (IR) and to explore potential underlying mechanisms.

Methods Short-term cell viability assay and long-term colony formation assay were used to evaluate and confirm the radiosensitizing effects of candidate Ras-MAPK pathway inhibitors in three CRC cell lines. Immunofluorescence-based γH2X foci assay, immunoblotting, and qPCR were used to identify IR-induced kinetic changes of Ras-MAPK pathway signaling and altered DNA damage responses.

Results Our data revealed that clinically-approved MEK inhibitors exhibit a strong radiosensitizing effects in colorectal cancer cell lines. The phenotypical effect of this inhibitor was comparable to that of the known radiosensitizer nutlin-3a, an inhibitor of MDM2/p53 interaction, but was achieved at much lower drug concentrations. Mechanistically, two mode-of-actions were identified in our study that underlie the radiosensitizing effect. First, the radiosensitizing effect was mediated by the efficient suppression of the IR-induced activation of Ras-MAPK signaling in CRC cell lines. Second, and more importantly, the inhibition of Ras-MAPK signaling selectively downregulated key DNA damage response-related proteins and thus interfered with IR-induced DNA damage repair.

Conclusion Our study demonstrated that targeting the Ras-MAPK pathway enhanced radiosensitivity in CRC cell lines via interference with IR-induced DNA damage repair. These results may contribute to improving clinical response in patients receiving radiotherapy for rectal cancer.

 

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Artikel online veröffentlicht:
28. August 2023