Strong Histone (H4) Acetylation Is Independently Associated with Better Overall Survival in Newly Diagnosed Acute Myeloid Leukemia (AML).

Histone acetylation is a post-translational modification used by proteins to regulate specific chromatin functions. Histone deacetylases (HDACs) play a pivotal role in the pathogenesis of a subset of acute myeloid leukemias (AMLs). HDAC inhibitors are currently being evaluated in clinical trials. We have previously demonstrated an association between increased histone H4 acetylation and increased relapse-free survival (RFS) in patients with newly diagnosed acute lymphocytic leukemia (ALL) (Advani et al., ASH abstract #2798, 2007) and improved overall survival (OS) in ALL patients with first relapse (Advani et al., ASH abstract #1482, 2008). Here, we evaluated the association between histone H4 acetylation with achievement of complete remission (CR) and also with RFS and OS in patients with newly diagnosed AML.

In this retrospective cohort study, we assessed H4 acetylation status in bone marrow biopsies of newly diagnosed AML patients at the Cleveland Clinic between the years 2003-2005. Association with CR, RFS and OS was assessed using univariate and multivariate logistic regression and cox-proportional hazard regression models. Variables used in the models included: age and WBC at diagnosis, gender, cytogenetic (CG) risk group, and history of antecedent hematologic disorder (AHD). CG risk group was ascribed per Cancer and Leukemia Group B criteria. B5-fixed bone marrow core biopsies were reviewed for areas of highest blast concentration. Immunohistochemistry was performed for acetyl-H4 (1:200 dilution; polyclonal; Upstate Biotech, Lake Placid, NY) using automated stainers and heat induced epitope retrieval. In each case, five hundred blasts were counted and only strong nuclear staining was classified as positive. Based on the distribution of cell counts, cases were classified as strongly positive if nuclear staining occurred in > 80% of the blasts.

Eighty-one patients had adequate tissue and clinical data available. We restricted the analysis to sixty patients who received standard induction chemotherapy with cytarabine and an anthracycline. The median age was 58 years (range 20-79) and median WBC was 8.85 × 10⁹/ L (range 0.8-227.9). Seven patients (11.6%) had favorable CG, 41 (68.3%) had intermediate, and 12 (20%) had poor risk CG. Thirty two percent of patients had an AHD. Thirteen patients (21.6%) received an allogeneic bone marrow transplant in first remission. The median follow-up time was 25.5 months (range 2.1-70.6). Forty five patients (75%) achieved CR and the median OS was 12.7 months (range 0.4-70.6). Using the 80% cut-off, 19 patients (31.6%) were positive for H4-acetylation. Histone (H4) acetylation was not associated with achievement of CR (OR=4.1, 95% CI 0.7-24.5, p=0.1) or relapse-free survival (HR 0.62, 95% CI 0.18-2.08, p=0.44). However, in multivariate analysis, histone acetylation was associated with a significantly better OS (HR=0.51, 95% CI 0.29-0.88, p=0.01). Inclusion of allogeneic transplant in the multivariate models did not change these estimates.

Strongly positive histone (H4) acetylation is associated with better OS in multi-variate analysis. The results mimic our previous findings in ALL patients. Further studies will need to include FLT3 and NPM status in patients with normal cytogenetics in the multi-variate model. These results provide a rationale for AML regimens incorporating HDAC inhibitors, and use of this assay as a potentially relevant biomarker during HDAC inhibitor therapy.

No relevant conflicts of interest to declare.