Abstract
Nuclear protein of the testis (NUT) midline carcinoma (NMC), is a rare and highly aggressive form of undifferentiated squamous cell carcinoma. NMC is molecularly characterized by chromosomal rearrangement of the NUT gene to another gene, most commonly the bromodomain and extraterminal domain (BET) gene BRD4, forming the BRD4-NUT fusion oncogene. Therefore, inhibiting BRD4-NUT oncogenic function directly by BET inhibitors represents an attractive therapeutic approach but toxicity may limit the use of pan-BET inhibitors treating this cancer. We thus performed a drug screening approach using a library consisting of epigenetic compounds and ‘Donated Chemical Probes’ collated by the Structural Genomics Consortium (SGC) and identified the p300/CBP HAT inhibitor A-485, in addition to the well-known BET inhibitor JQ1, to be the most active candidate for NMC treatment. In contrast to JQ1, A-485 was selectively potent in NMC compared to other cell lines tested. Mechanistically, A-485 inhibited p300-mediated histone acetylation, leading to disruption of BRD4-NUT binding to hyperacetylated megadomains. Consistently, BRD4-NUT megadomain-associated genes MYC, CCAT1 and TP63 were downregulated by A-485. A-485 strongly induced squamous differentiation, cell cycle arrest and apoptosis. Combined inhibition of p300/CBP and BET showed synergistic effects. In summary, we identified the p300/CBP HAT domain as a putative therapeutic target in highly therapy-resistant NMC.
Highlights
These authors contributed : Xin Zhang, Tim Zegar
Because of the critical roles of p300/CBP in creating hyperacetylated chromatin domains associated with BRD4NUT in NMC [3, 4], we explored the consequences of p300/CBP inhibition by A-485
We identified the p300/CBP HAT inhibitor A-485 to be highly potent in NMC but not in tested cell lines derived from other tumor entities
Summary
In agreement with A-485, double knockdown of p300/CBP downregulated MYC, CCAT1 and TP63 mRNA levels supporting target-specific effects of A-485 (Supplementary Fig. 3C) These results indicate that p300/CBP inhibition by A-485 efficiently impairs BRD4-NUT oncogenic functions in NMC. We tested combined treatment in a non-NMC cell line Patu8988S and still observed an albeit smaller synergistic effect (ZIP synergy score 7.531, Supplementary Fig. 6), arguing that combined inhibition of p300/CBP and BET may be synergistic beyond NMC cells. To further explore this synergistic effect, transcriptomic profiling was performed in HCC2429 cells incubated with A-485 and JQ1 alone or combined at concentrations of 1/3
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
