Purpose
This phase I/II study sought to determine the safety and maximum-tolerated dose (MTD) of a novel schedule of belinostat, a histone deacetylase inhibitor administered prior to and in combination with cisplatin (P), doxorubicin (A) and cyclophosphamide (C) in thymic epithelial tumors (TET). Anti-tumor activity, pharmacokinetics, and biomarkers of response were also assessed.
Patients and methods
Patients with advanced, unresectable TET received increasing doses of belinostat as a continuous intravenous infusion over 48-hours with chemotherapy in 3-week cycles. In phase II, belinostat at the MTD was used.
Results
26 patients were enrolled (thymoma: 12; thymic carcinoma: 14). Dose-limiting toxicities at 2000 mg/m2 belinostat were grade 3 nausea and diarrhea and grade 4 neutropenia and thrombocytopenia, respectively, in two patients. 24 patients were treated at the MTD of 1000 mg/m2 with chemotherapy (P 50 mg/m2 on day 2; A 25 mg/m2 on days 2, 3; C 500 mg/m2 on day 3). Objective response rates in thymoma and thymic carcinoma were 64% [95% confidence interval: 30.8%–89.1%] and 21% (4.7%–50.8%) respectively. Modulation of pharmacodynamic markers of HDAC-inhibition and declines in regulatory T cell (Tregs) and exhausted CD8+ T cell populations were observed. Decline in Tregs was associated with response (p=0.0041) and progression-free survival (p=0.021). Declines in TIM-3+ CD8+T cells were larger in responders than non-responders (p=0.049).
Conclusion
This study identified the MTD of belinostat in combination with PAC and indicates that the combination is active and feasible in TETs. Immunomodulatory effects on regulatory T cells and TIM3+ CD8+ T cells warrant further study.