Histone H4 Acetylation Is Associated with Improved Relapse-Free Survival in Newly Diagnosed Patients with Acute Lymphoblastic Leukemia (ALL) Less Than 60 Years of Age without Poor Risk Cytogenetics.

Imbalances in histone acetylation can lead to changes in transcriptional dysregulation of genes involved in cell cycle progression and/ or apoptosis. Histone deacetylase inhibitors represent a novel antitumor therapy. We evaluated the acetylation of histone H4 in patients with newly diagnosed ALL, and evaluated the prognostic impact of acetylation on time to relapse and overall survival (OS).

Methods: Patients with newly diagnosed ALL and an available diagnostic bone marrow biopsy performed at the Cleveland Clinic were evaluated between 1998 and 2005. B5-fixed bone marrow core biopsies were reviewed for areas with the highest concentration of blasts. A tissue microarray was constructed using 1 mm tissue cores. The cores were arrayed in duplicate in the majority of samples. Immunohistochemistry was performed for acetyl-H4 (1:200 dilution; polyclonal; Upstate Biotech, Lake Placid, NY) using automated stainers and heat induced epitope retrieval. Five hundred blasts were counted in each case and only strong nuclear staining was classified as positive. Based on the distribution of cell counts, there was a clear separation of cases at 40% blasts with strong nuclear staining. Therefore, cases were classified as positive (“acetylated”) if strong nuclear staining occurred in ≥ 40% of the blasts. Cox proportional hazards analysis was used to identify univariate and multivariate risk factors for relapse-free survival (RFS), OS, and CR rate.

Results: Thirty-four patients had adequate tissue and clinical data for analysis. The median age was 40 yrs (range 18–74). Twelve patients (35%) had poor risk cytogenetics (CG), 6 (18%) normal karyotype, 9 (26%) miscellaneous abnormalities, and 7 (21%) unknown CG as defined by CALGB criteria. Thirty-one patients (91%) had precursor B-cell ALL, 1 (3%) mixed lineage, and 2 (6%) had precursor T cell ALL. The median white count was 41.7 × 10⁹/ L (range 0.93–278) and LDH 1033 U/L (range 155–4608). Twenty-three (68%) patients had high levels of acetylated histone H4. Patients received a variety of induction and post-remission therapies. On univariate analysis, acetylation of H4 was associated with an improved RFS [HR 0.19, 95% CI (0.05–0.69), p=0.012] and a trend towards improved OS [HR 0.34, 95% CI (0.11–1.05), p=0.06] and increased CR rate [benefit ratio (BR) 4.12, 95% CI (0.88–19.3), p=0.07] in patients less than 60 years of age without poor risk CG. Using WBC and age at diagnosis in multivariate analysis, histone acetylation was associated with a better RFS [HR 0.20, 95% CI (0.05–0.77), p=0.019] and a trend towards an improved CR rate [BR 3.81, 95% CI (0.80–18.1), p=0.09] and OS [HR 0.33, 95% CI (0.10–1.11), p=0.07] in this same group of patients.

Conclusions: Acetylation of histone H4 is associated with a better RFS and a trend towards an improved OS and CR rate in newly diagnosed patients with ALL less than 60 years of age without poor risk CG. These results should be confirmed in an independent data set and may provide rationale for the design of novel regimens incorporating histone deacetylase inhibitors, especially in patients less than 60 years of age.