Olaparib and Radiotherapy in Head and Neck Cancer

Plain-language summary

Accelerated, normofractionated radiotherapy is the treatment of choice in stage II-III laryngeal and oropharyngeal squamous cell carcinoma (SCC). However, twenty to thirty percent of patients with stage II-III laryngeal and HPV negative oropharyngeal SCC develop disease progression, mainly due to lack of locoregional control. Radiosensitizers such as cisplatin and cetuximab are added to radiotherapy in more advanced stage of head and neck (H\&N) cancer. These radiosensitizers improve loco-regional control and overall survival. Unfortunately, as these radiosensitizers, notably cisplatin, also dose intensify the radiation dose in normal tissues, they also significantly increase toxicity. Adding a more tumor-specific radiosensitizing agent could improve loco-regional control and overall survival without significantly increasing toxicity. Radiotherapy kills tumor cells by inducing DNA damage. The efficacy of radiotherapy is limited by the ability of tumor cells to repair this DNA damage. Poly(ADP-ribose)polymerase (PARP) is an essential enzyme in base excision repair and single strand break DNA repair, DNA lesions arising from radiation treatment. PARP inhibition and consequently the inhibition of PARP-facilitated DNA repair enhances the anti-tumor activity of radiotherapy, as shown in preclinical studies including head and neck xenograft studies. This radiosensitization is thought to be proliferation dependent and is more pronounced in homologous recombination (HR) deficient cells, providing an opportunity for tumor specific targeting. Genetic analyses suggest that HR deficiency is commonly found in H\&N SCC: ATM loss has been reported in 60% of human H\&N SCC biopsies and FANC-F defects were reported in 15-21% of human H\&N SCC biopsies and cell lines. The efficacy of radiotherapy is also limited by tumor hypoxia, as tumor hypoxia results in radioresistance. Some PARP inhibiting compounds increase tumor perfusion in xenograft models, thereby reducing hypoxia and specifically sensitizing tumor cells to radiotherapy. Hypoxia is commonly found in H\&N SCC and a high pre-treatment hypoxic fraction in H\&N SCC tumors is associated with worse outcome. The high prevalence of both hypoxia and HR deficiencies in H\&N SCC support the concept of tumor-specific radiosensitization by PARP inhibition in head and neck cancer patients. Olaparib is a potent PARP inhibitor developed as an anti-cancer drug for HR defected tumors and as a dose intensifier for chemo- and radiotherapy. In humans, olaparib has a low toxicity profile as a single agent, with increasing bone marrow toxicity when combined with chemotherapy. The combination of olaparib and radiotherapy for H\&N SCC is expected to improve locoregional control and thereby overall survival. However, this combination treatment has never been tested in humans before. The purpose of this study is to determine the safety and tolerability of radiotherapy for stage II-III laryngeal and stage II-III HPV-negative oropharyngeal SCC with concurrent olaparib.

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