PO-031 Sensitising P53 mutant HNSCC to oncolytic reovirus (RT3D) by targeting the unfolded protein response

Abstract

Introduction Oncolytic viruses are able to enter and selectively replicate in cancer cells. These self-propagating agents kill through multiple mechanisms and have the potential to promote anti-tumour immune responses. Reovirus strain type 3 Dearing (RT3D) is an oncolytic virus actively under clinical investigation. RT3D has been shown to induce ER stress and trigger the downstream unfolded protein response (UPR) in a variety of tumour types. Recent evidence has indicated that proteasome inhibition in multiple myeloma, and BRAF inhibition in BRAF mutant melanoma, sensitise to RT3D through perturbation of the normal cellular response to ER stress. We sought to investigate if more direct modulation of UPR signalling could sensitise head and neck squamous cell carcinoma (HNSCC) to RT3D. Material and methods ER stress agents including novel agents targeting UPR signalling were screened for sensitisation to RT3D in a panel of HNSCC cell lines. Alterations to reovirus protein levels and viable virus particle production was assessed. A 3D tumour spheroid model was used as a more accurate method to study stress in vitro. Recombinant protein expression and shRNA techniques were utilised to study how the unfolded protein response impacts reovirus replication. ER stress measured by GRP78 expression was also assessed in HNSCC patient samples. Results and discussions The PERK inhibitor GSK2606414 and the canonical ER stress agent thapsigargin were shown to sensitise HNSCC to RT3D. PERK inhibition resulted in increased viral capsid protein levels and increased viable RT3D production from target cells. PERK inhibition enhanced the ability of RT3D to eradicate HNSCC 3D tumour spheroids. PERK inhibition increased RT3D spread in 3D spheroids while perturbing normal ER chaperone levels and inhibiting RT3D induced LC3A/B. In HNSCC patient samples, GRP78 was found to be elevated in tumour vs stroma with significant variation between patients. This highlights the importance in understanding the link between ER stress levels/UPR signalling and reovirus efficacy. Conclusion We demonstrate that modulators of the ER stress response represent a novel mechanism of sensitisation to RT3D in head and neck.