Interplay of DNA repair and stem-like phenotype determines the sensitizing effect of CHK1, RAD51 and PARP1 inhibition in TNBC


Interplay of DNA repair and stem-like phenotype determines the sensitizing effect of CHK1, RAD51 and PARP1 inhibition in TNBC

Meyer, F.; Becker, S.; Niecke, A.; Riepen, B.; Zielinski, A.; Werner, S.; Peitzsch, C.; Hein, L.; Dubrovska, A.; Wikman, H.; Windhorst, S.; Goy, Y.; Parplys, A.; Petersen, C.; Rothkamm, K.; Borgmann, K.

Breast cancer comprises a heterogeneous group of tumors of whom 20% are categorized as triple-negative (TNBC). Important biological characteristics and potential therapeutic targets of TNBC include high proliferation, a basal-like and mesenchymal phenotype and a defect in the DNA repair pathway Homologous Recombination (HR), which feeds the observed elevated chromosomal instability in these tumors. TNBCs show an enrichment of cancer stem cells and therapy resistance. This project aims to develop treatment intensification strategies based on the simultaneous exploitation of the HR-deficiency and the stem-like phenotype, using specific inhibitors for RAD51, CHK1 and PARP1 in combination with irradiation.
Expression of HR-related (RAD51, BRCA1, PTEN, CHK1, MRE11, ATR, ATM) and stem-like factors (ZEB1, E-Cadherin, ß-Catenin, ALDH1) as well as HR functionality (via RAD51 foci, MMC-sensitivity and plasmid reporter assay) were determined in the TNBC line MDA-231 WT, its two sublines preferentially metastasizing to brain (BR) or bone (SA) and in the luminal BC line MCF7. DNA replication (fiber assay) and migration assay were also tested. Radiosensitivity and the radiosensitizing effect of different inhibitors was analyzed by colony assay and correlated to the CIN in the METABRIC database.
Distinct differences in the expression of HR-related proteins were observed, with an elevated expression of CHK1, MRE11 and ATM in BR and SA relative to WT and MCF7. BR and SA showed a typical stem cell-like protein expression profile, together with a higher migration capacity, increased HR-capacity, resistance against MMC and less DNA damage. After irradiation no advantage in survival for the BR and SA cell lines was observed, suggesting that not HR, but superordinate CHK1 signaling promotes radioresistance. This was confirmed by a distinct radiosensitization after CHK1i; the most radioresistant WT cell line was most strongly sensitized, by a factor of 3. The extent of sensitization was also linked to the extent of replication inhibition. The effect of other inhibitors on radiosensitivity is currently being investigated. A second promising target is RAD51, because a METABRIC analysis (952 TNBCs) showed that in TNBC with high CIN RAD51 and CHK1 are significantly stronger expressed than in TNBC with low CIN.
In conclusion the results presented here show that DNA repair and a stem-like phenotype collude to determine resistance to tumor therapy of TNBCs with high CIN.

Keywords: Breast cancer; Homologous Recombination; DNA repair

  • Contribution to proceedings
    The 15th International Wolfsberg Meeting on Molecular Radiation Biology/Oncology, 17.-19.06.2017, Ermatingen, Switzerland
    Program 15th International Wolfsberg Meeting on Molecular Radiation Biology/Oncology

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Publ.-Id: 25110