Combining BET protein inhibitors with radiation in HPV oropharyngeal cancer

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PROJECT SUMMARY/ABSTRACT: During the past decade, oropharyngeal cancer surpassed cervical cancer, becoming the most common cancer caused by human papillomavirus (HPV). Nearly 20,000 oropharyngeal cancer cases are diagnosed among men and women in the United States annually. Despite favorable long-term survival, current non-targeted cisplatin/radiation treatment protocols lead to significant treatment toxicities. De-escalating radiation doses with alternative targeted therapies would be critical for limiting treatment-related toxicities and improving patient quality of life. To address this, we propose to reduce the transcriptional output of viral genes and DNA damage response (DDR) by reducing its dependence on a transcriptional co-regulator bromodomain protein, BRD4, expressed in the oropharyngeal tissue. We propose that DDR deficiencies can be induced by second-generation bromodomain-specific chemical inhibitors in HPV oropharyngeal tumors. This chemically induced DDR deficient state delays the kinetics of DNA repair, thereby causing genomic instability. With tumors in this fragile state, administering optimal radiation doses will result in genomic catastrophe leading to eradicating tumors. We established that a first-generation inhibitor that targets both bromodomains BD1 and BD2 of BRD4 preferentially reduced viral and DDR gene expression of a subset of HPV tumors, which harbored disrupted viral genomes over non-disrupted viral genomes. However, pan-BD domain inhibition could give rise to pleiotropic effects. We used second-generation domain-specific inhibitors introduced in 2020 on HPV tumor cell lines to refine the pan- BD inhibition approach. We observed preferential domain-specific transcriptional regulation. While BD2 domain inhibition downregulated DDR response in disrupted viral tumors, BD1 upregulated anti-viral gene expression in non-disrupted viral tumors. These results guide us to postulate that patients selected upfront for disrupted viral genomes can be matched for BD domain-specific inhibitor and de-escalated radiation treatments. We will use in vitro and in vivo approaches to address a) efficacy of BD domain-specific inhibitors towards creating a DDR- deficient state by measuring viral gene expression and quantifying DDR response kinetics, and test its on-target efficacy in BRD4 knockdown and BD1 and BD2 domain-specific deleted tumor cells, b) Optimize the dose of radiation sufficiently to preserve the efficacy of BD domain-specific inhibition in patient-derived xenograft mice models with secondary endpoint analyses of survival, tumor volume growth, apoptosis, complete blood count panel for toxicity and immunohistochemistry for proliferation and DNA repair proteins.