Abstract B206: Pharmacokinetic and pharmacodynamic analysis of patients treated with the histone deacetylase inhibitor entinostat in combination with erlotinib

Background: Histone deacetylase (HDAC) inhibition results in hyperacetylation of protein substrates leading to re‐expression of silenced genes as well as down‐regulation of certain actively transcribed genes. Entinostat (ENT) is a novel oral benzamide HDACi characterized by its selectivity for class 1 HDACs as well as a unique pharmacokinetic (PK) and pharmacodynamic (PD) profile. Preclinical data demonstrated ENT synergizes with epidermal growth factor receptor inhibitors (EGFRi) to inhibit growth of non‐small cell lung cancer (NSCLC) cells through a) targeting of EGFR gene and protein expression; b) down‐regulation of EGFR mediated signaling transduction pathway and c) alteration of the tumor phenotype to resensitize cancer cells to EGFRi. This led to the initiation of a clinical study ENCORE‐403 (clinical trials.gov ID NCT00750698) investigating whether ENT could affect acquired resistance to the EGFRi, erotinib (ERB). We report here the initial findings on PK and PD analysis from a study of 8 patients treated with the ENT/ERB combination. Materials and Methods: Previously ERB‐treated relapsed NSCLC patients were continued on ERB. ENT at 10 mg was added to ongoing ERB regimen on days 1 and 15 of a 28‐day cycle. Blood samples for PK analysis and correlative studies were obtained on C1D1 (pre‐entinostat dose), C1D2 (4–36hrs post entinostat dose), C1D8, C1D15 (pre‐entinostat dose) and C2D15 (for PK only). Gene expression in 8 patients was measured by RT‐PCR and effects on protein lysine acetylation (7 patients) and peripheral blood monocytes were measured by multi‐parameter flow cytometry. Results: Initiation of ENT/ERB combination led to induction of protein lysine acetylation of at least 2 fold in 6 of 7 patients for whom samples were available. The lack of acetylation induction in the 7th patient was consistent with PK analysis which indicated no detectable levels of entinostat in this patient. Lysine acetylation was measured in CD14+ monocytes, CD56+ NK cells and CD3+ T cells. The acetylation pattern and magnitude of induction was consistent in all three cell types. In addition, 4 of the 6 patients maintained elevated acetylation levels at 7 days and 3 of the 6 at 14 days after the first dose of entinostat. Initial analysis of gene expression was focused on the previously identified HDACi target p21. Similar to lysine acetylation, p21 expression was increased by 30–80% of the pre‐treatment level in 4 of the 6 patients with increased acetylation; and in 3 patients, elevated p21 expression was detectable on C1D15. Analysis of the combination treatment effects on circulating endothelial cell progenitors (CEPs), apoptotic circulating endothelial cells (CECs), regulatory T cells (Tregs), and myeloid derived suppressor cells (MDSC) was carried out to determine potential anti‐angiogenic (CEP, CEC) and immunomodulatory (Treg, MDSC) activity and will be reported. Conclusions: Results from acetylation and gene expression analysis demonstrate that 10mg ENT induces a prolonged effect (up to 2 weeks) on up‐regulation of a key gene in the cell cycle and importantly that the ENT/ERB combination does not alter the prolonged PD effects of entinostat. Investigations are ongoing into the mechanism of ENT/ERB combination and potential for clinical benefit to NSCLC patients. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B206.