Head and neck squamous cell carcinoma (HNSCC) is a leading cause of cancer-related deaths, with increasingly more cases arising due to high-risk human papillomavirus (HPV) infection. Cisplatin-based chemoradiotherapy is a standard-of-care for locally-advanced head and neck cancer but is frequently ineffective. Research into enhancing radiation responses as a means of improving treatment outcomes represents a high priority. Here, we evaluated a CHK1 inhibitor (CCT244747) as a radiosensitiser and investigated whether a mechanistically rational triple combination of radiation/paclitaxel/CHK1 inhibitor delivered according to an optimised schedule would provide added benefit. CCT244747 abrogated radiation-induced G2 arrest in the p53-deficient HNSCC cell lines, HN4 and HN5, causing cells to enter mitosis with unrepaired DNA damage. The addition of paclitaxel further increased cell kill and significantly reduced tumour growth in an HN5 xenograft model. Importantly, a lower dose of paclitaxel could be used when CCT244747 was included, therefore potentially limiting toxicity. Triple therapy reduced the expression of several markers of radioresistance. Moreover, the more radioresistant HN5 cell line exhibited greater radiation-mediated CHK1 activation and was more sensitive to triple therapy than HN4 cells. We analysed CHK1 expression in a panel of head and neck tumours and observed that primary tumours from HPV+ patients, who went on to recur post-radiotherapy, exhibited significantly stronger expression of total and activated CHK1. CHK1 may serve as a biomarker for identifying tumours likely to recur and, therefore, patients who may benefit from concomitant treatment with a CHK1 inhibitor and paclitaxel during radiotherapy. Clinical translation of this strategy is under development.
- Received December 23, 2015.
- Revision received June 6, 2016.
- Accepted June 10, 2016.
- Copyright ©2016, American Association for Cancer Research.