TTK inhibition radiosensitizes basal-like breast cancer through impaired homologous recombination
Benjamin C. Chandler, … , Arul Chinnaiyan, Corey Speers
Benjamin C. Chandler, … , Arul Chinnaiyan, Corey Speers
Published January 21, 2020
Citation Information: J Clin Invest. 2020;130(2):958-973. https://doi.org/10.1172/JCI130435.
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Research Article Oncology

TTK inhibition radiosensitizes basal-like breast cancer through impaired homologous recombination

Abstract

Increased rates of locoregional recurrence are observed in patients with basal-like breast cancer (BC) despite the use of radiation therapy (RT); therefore, approaches that result in radiosensitization of basal-like BC are critically needed. Using patients’ tumor gene expression data from 4 independent data sets, we correlated gene expression with recurrence to find genes significantly correlated with early recurrence after RT. The highest-ranked gene, TTK, was most highly expressed in basal-like BC across multiple data sets. Inhibition of TTK by both genetic and pharmacologic methods enhanced radiosensitivity in multiple basal-like cell lines. Radiosensitivity was mediated, at least in part, through persistent DNA damage after treatment with TTK inhibition and RT. Inhibition of TTK impaired homologous recombination (HR) and repair efficiency, but not nonhomologous end-joining, and decreased the formation of Rad51 foci. Reintroduction of wild-type TTK rescued both radioresistance and HR repair efficiency after TTK knockdown; however, reintroduction of kinase-dead TTK did not. In vivo, TTK inhibition combined with RT led to a significant decrease in tumor growth in both heterotopic and orthotopic, including patient-derived xenograft, BC models. These data support the rationale for clinical development of TTK inhibition as a radiosensitizing strategy for patients with basal-like BC, and efforts toward this end are currently underway.

Authors

Benjamin C. Chandler, Leah Moubadder, Cassandra L. Ritter, Meilan Liu, Meleah Cameron, Kari Wilder-Romans, Amanda Zhang, Andrea M. Pesch, Anna R. Michmerhuizen, Nicole Hirsh, Marlie Androsiglio, Tanner Ward, Eric Olsen, Yashar S. Niknafs, Sofia Merajver, Dafydd G. Thomas, Powel H. Brown, Theodore S. Lawrence, Shyam Nyati, Lori J. Pierce, Arul Chinnaiyan, Corey Speers

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Figure 4

TTK inhibition reduces HR efficiency.

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TTK inhibition reduces HR efficiency. (A and B) KEGG analysis through GS...
(A and B) KEGG analysis through GSEA correlated the HR pathway with TTK expression in the METABRIC (A) and TCGA (B) data sets. (C and D) siRNA-induced TTK knockdown reduced HR efficiency in an HR-specific report system in MDA-MB-231 (C) and BT-549 (D) cells. (E and F) Inhibition of TTK kinase function, by B909 at 50 nM and 75 nM, reduced HR efficiency in MDA-MB-231 (E) and BT-549 (F) cells. TTKi, TTK inhibition; CHKi, CHK1/2 inhibition; DNAPKi, DNAPK inhibition. TTKi1, TTK inhibition with 50 nM B909; TTKi2, TTK inhibition with 75 nM B909. (G and I) TTK knockdown via a Dox-inducible shRNA reduced Rad51 foci formation after 4 Gy radiation in MDA-MB-231 (G) and BT-549 (I) cell lines. (H and J) Representative images of MDA-MB-231 (H) and BT-549 (J) Rad51 foci and Western blots showing no change in total Rad51 levels after Dox or RT treatment. Original magnification, ×60 (H and I). Data represent the mean of 3 independent experiments, and error bars represent SD. A 1-sided t test corrected for multiple comparisons was used for comparison of HR efficiency assays, and a 2-sided Student’s t test was used for comparisons of Rad51 foci experiments. *P < 0.05, **P < 0.01, and ***P < 0.001. NES, normalized enrichment score.