Inhibition of Yes-Associated Protein (YAP) with Verteporfin Enhances Radiosensitivity in Chordoma by Inducing G2M Arrest and Inhibiting the DNA Damage Response

Chordomas are locally invasive cancers that are highly resistant to radiotherapy. The Brachyury and Yes-Associated Protein (YAP) regulatory axis has been implicated as the primary driver of tumorigenicity in chordoma. Here, we aimed to enhance chordoma radiosensitivity by repurposing the FDA-approved YAP inhibitor, Verteporfin. We used five patient-derived chordoma cell lines and generated two YAP1 knockdown cell lines to validate the YAP-targeting phenotype in chordoma. Verteporfin treatment reduced the expression of DNA damage repair proteins and genes. YAP inhibition with either verteporfin or YAP knockdown resulted in enhanced DNA double-stranded breaks after radiation via inhibition of the DNA damage repair pathway and accumulation of cells in the G2M phase. Verteporfin inhibited chordoma tumor growth alone and in combination with radiation in a xenograft mouse model treated with verteporfin loaded microparticles, resulting in sensitization of chordoma tumors to radiation. YAP inhibition with verteporfin renders chordoma more sensitive to radiation via inhibition of the DNA damage repair cascade and accumulation of cells in G2M when they are most susceptible to radiation damage.