Phase I study of the histone deacetylase inhibitor entinostat in combination with 13-cis retinoic acid in patients with solid tumours

Abstract

Background: Preclinical studies suggest that histone deacetylase (HDAC) inhibitors may restore tumour sensitivity to retinoids. The objective of this study was to determine the safety, tolerability, and the pharmacokinetic (PK)/pharmacodynamic (PD) profiles of the HDAC inhibitor entinostat in combination with 13-cis retinoic acid (CRA) in patients with solid tumours.

Methods: Patients with advanced solid tumours were treated with entinostat orally once weekly and with CRA orally twice daily × 3 weeks every 4 weeks. The starting dose for entinostat was 4 mg m(-2) with a fixed dose of CRA at 1 mg kg(-1) per day. Entinostat dose was escalated by 1 mg m(-2) increments. Pharmacokinetic concentrations of entinostat and CRA were determined by LC/MS/MS. Western blot analysis of peripheral blood mononuclear cells and tumour samples were performed to evaluate target inhibition.

Results: A total of 19 patients were enroled. The maximum tolerated dose (MTD) was exceeded at the entinostat 5 mg m(-2) dose level (G3 hyponatremia, neutropenia, and anaemia). Fatigue (G1 or G2) was a common side effect. Entinostat exhibited substantial variability in clearance (147%) and exposure. CRA trough concentrations were consistent with prior reports. No objective responses were observed, however, prolonged stable disease occurred in patients with prostate, pancreatic, and kidney cancer. Data further showed increased tumour histone acetylation and decreased phosphorylated ERK protein expression.

Conclusion: The combination of entinostat with CRA was reasonably well tolerated. The recommended phase II doses are entinostat 4 mg m(-2) once weekly and CRA 1 mg kg(-1) per day. Although no tumour responses were seen, further evaluation of this combination is warranted.

Figure 1

(A) Proposed model of epigenetic modulation at RARβ gene loci. RARβ gene expression is silenced due to histone deacetylation, partial promoter methylation at the CpG islands and associated recruitment of the TAC, making the transcriptional site inaccessible and resistant to retinoid ligands. However, in the presence of HDAC inhibitors (HDACI), RARβ is re-expressed, and tumour cell sensitivity to retinoids is restored. (B) Treatment schema. Depicted is the schedule of administration of weekly oral entinostat at the starting dose of 4 mg m⁻² and daily oral CRA 1 mg kg⁻¹ for 21 days with 1-week rest. During Cycle 1, FNA was planned for accessible tumours at pre-treatment and day 22.

Figure 2

Patient disposition. The graph illustrates the histological tumour types, duration of treatment, and reason for discontinuation in the patients’ cohorts.

Figure 3

PD analyses. (A) Representative western blot analyses for histone H3 acetylation in PBMCs (first two patients enroled in the study). (B) Western blot analysis of a liver FNA in a patient with prostate cancer liver metastases.

Figure 4

Tumour marker modulation by entinostat and CRA. Representative graphs of PSA and CA 19-9 modulation following treatment with entinostat and CRA in four patients enroled in the study. Concomitant measurement of PSA and serum alkaline phosphatase (SALK) is reported for patient 11. The black bars indicate the time of treatment.