Abstract CT014: GSK525762, a selective bromodomain (BRD) and extra terminal protein (BET) inhibitor: results from part 1 of a phase I/II open-label single-agent study in patients with NUT midline carcinoma (NMC) and other cancers

Background: GSK525762 is a potent, selective pan-BET inhibitor that abrogates binding of BET family proteins (BRD2, BRD3, BRD4 and BRD-T) to acetylated histones. In pre-clinical models this results in suppression of BET target genes that drive oncogenic pathways, resulting in growth inhibition of cancer cell lines (median IC50 of 50-1698 nM for solid tumors and 50 nM for NMC). GSK525762 is being evaluated clinically for treatment of pts with hematologic malignancies and solid tumors including NMC, a rare, aggressive cancer with few treatment options. NMC is characterized by BRD3-/BRD4-NUT fusion oncoproteins that represents a rational therapeutic target for BET inhibitors. Methods: Primary objectives of Part 1 were to determine safety, tolerability, and maximum tolerated dose (MTD) for GSK525762 in solid tumors, using a combined N-CRM and 3+3 dose escalation. Secondary objectives include PK and PD analysis and preliminary evaluation of activity. Oral once daily (qd) and twice daily (bid) schedules have been evaluated. PD activity was assessed with [18F]-deoxy-glucose-PET scans and changes in cytokine release from LPS-stimulated PBMC of treated pts. The dose-limiting toxicity (DLT) observation period was 28 days. Response evaluation was by RECIST 1.1 and pts were followed to disease progression, discontinuation due to adverse events, withdrawal of consent or death. Results: As of 28-Jan 2016, a total of 70 (including 17 NMC) pts have been treated at doses of 2-100 mg qd and 20 and 30 mg bid. The most common adverse events (all grades, ?20%) observed were thrombocytopenia (44%), nausea (40%), vomiting (29%), anemia (26%), fatigue (26%), decreased appetite (24%), diarrhoea (23%) and dysgeusia (20%). DLTs occurred in 5 pts at doses of 60 mg (n = 1, 11%), 80 mg (n = 3, 14%) and 100 mg (n = 1, 11%). The most common AEs leading to dose interruption were thrombocytopenia and hyperbilirubinemia (each n = 7, 10%). Limited data shows similar tolerability at bid doses. PK was dose-proportional after single and repeat dosing with large between patient variability. Dose dependent inhibition of LPS stimulated BRD regulated cytokine (IL-6, TNF-α, MCP-1, IL-8) release suggests target engagement. Of 11 NMC pts treated at 60-100 mg qd, evaluation is awaited on 1 pt. Of 10 pts evaluated, 2 (20%; 95% CI (2.5%, 56%)) had confirmed PR (15 and 23 weeks) and 4 (40%; 95% CI (12%, 74%)) had SD. An 80mg once-daily dose will be evaluated in NMC and other solid tumor expansion cohorts. Conclusion: GSK525762 is an active, orally bio-available BET inhibitor showing dose-proportional PK and good tolerability up to 80 mg qd dosing. Preliminary evidence of clinical activity observed in pts with NMC provides a rational targeted therapy for this aggressive tumor and proof of concept for BET inhibitors in the clinic. Study funded by GSK (NCT01587703). Citation Format: Peter J. O’Dwyer, Sarina A. Piha-Paul, Christopher French, Sara Harward, Gerladine Ferron-Brady, Yuehui Wu, Olena Barbash, Anastasia Wyce, Meg Annan, Thierry Horner, Nigel J. Parr, Rab K. Prinjha, Christopher Carpenter, Geoffrey Shapiro, Arindam Dhar, Christine Hann. GSK525762, a selective bromodomain (BRD) and extra terminal protein (BET) inhibitor: results from part 1 of a phase I/II open-label single-agent study in patients with NUT midline carcinoma (NMC) and other cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT014.