Bromodomain Inhibitors to Prevent Development of Resistance to Targeted Kinase Inhibitors in Schwannomas [RNA-seq]

Neurofibromatosis type 2 (NF2) is an inherited disorder that promotes tumor growth on nerves throughout the nervous system. NF2 affects around 1 in 33,000 individuals worldwide and is caused by loss of function of the merlin tumor suppressor encoded by the NF2 gene. Tumor control early in life is critical for maintaining quality of life. Currently, treatments available for NF2-associated tumors are surgery and radiation therapy. Off-label use of cancer drugs are being tried, as there are no Food and Drug Administration (FDA)-approved drug therapies for NF2. As a member of the SYNODOS for NF2 consortium, we performed unbiased drug combination screening using schwannoma model cell lines. We identified a BRD4 and a PAK inhibitor that acted in concert to selectively slow growth of a human schwannoma line compared to its merlin-expressing parental line. BRD4 is a member of the BET family of bromodomain containing proteins that bind acetylated lysine in transcription regulatory proteins to alter gene expression. BRD proteins contribute to development of resistance to cancer drugs. Follow-up studies confirmed the drugs’ interaction in multiple mouse and human schwannoma lines. We will extend this research by assessing the ability of BRD4 inhibitors in combination with multiple PAK, PI3K, MEK, and FAK inhibitors, some of which are in NF2 clinical trials (selumetinib, crizotinib, brigatinib, trametinib) to reduce the viability of schwannoma lines. We will measure whether the combinations provide long-lasting inhibition of cell proliferation, induce cell death, and block compensatory escape pathways that often arise when cells are treated with a single kinase inhibitor. We will use an established mouse xenograft model to test the effectiveness of the best performing in vitro drug combination. Mechanisms of action studies will complete the preclinical evaluation of the advanced drug combination in a representative cell line. Our proposed study is timely because the results will indicate whether drug resistance could develop for several of the kinase inhibitors in ongoing NF2 clinical trials. Moreover, the results could indicate whether BRD4 inhibitors could serve as an adjuvant therapy to prevent drug resistance. By assessing the RNAome and methylome of single and dual treated human schwannoma cells, we will uncover the genes and RNAs that undergo BRD4-dependent epigenetic regulation to trigger compensatory pathways. With further validation, these candidate genes and RNAs may serve as biomarkers for treatment response and/or resistance development. Thus, these preclinical studies are at the forefront of addressing questions critical to ongoing efforts to develop a pharmacotherapy for NF2 schwannomas.