Imbalances in histone acetylation can lead to changes in transcriptional dysregulation of genes involved in cell cycle progression and/or apoptosis. We have previously demonstrated that histone H4 acetylation is associated with improved relapse-free survival in newly diagnosed patients with acute lymphocytic leukemia (ALL) (Advani et al., ASH abstract #2798, 2007). However, the prognostic significance of histone acetylation in the relapsed setting is unclear. Therefore, we evaluated histone H4 acetylation in patients with ALL in first relapse, and the prognostic impact of acetylation on response to salvage therapy and overall survival (OS).

Methods: From 1996 to 2007, patients with ALL in first relapse and an available diagnostic bone marrow biopsy performed at the Cleveland Clinic were evaluated. 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. 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 ≥ 40% of the blasts. Cytogenetic (CG) risk was defined by CALGB criteria. Cox proportional hazards analysis was used to identify univariate and multivariate risk factors for response to salvage therapy and OS at the time of relapse.

Results: Thirty-nine patients had adequate tissue and clinical data for analysis. The median age at relapse was 39 yrs (range 20–67) and median time from diagnosis to first relapse was 13.2 months (range 1.4–39.0). Seventy-nine percent of patients had ALL derived from B-cell, 18% T-cell, and 3% mixed lineage. Thirty-one percent of patients had poor risk CG, 46% normal karyotype, 10% miscellaneous abnormalities, and 13% unknown CG. At the time of relapse, 13% of patients had central nervous system involvement in addition to blood/bone marrow disease. Thirty-three pts (85%) had acetylated histone H4. Most patients received re-induction with a high-dose cytarabine-based regimen (48%). However, the remainder received anthracycline/vincristine/prednisone (30%), methotrexate/vincristine/asparaginase/decadron (13%), or clofarabine/cytarabine (9%). Ten pts (26%) achieved a complete remission (CR) after salvage therapy. Nineteen pts (49%) proceeded to allogeneic bone marrow transplant (BMT) with a related or unrelated donor. The median OS for all patients was 6.1 months. The median OS for pts proceeding to BMT was superior to pts not proceeding to BMT (12.8 months versus 4.7 months, p<0.001). There was a trend towards an improved OS after relapse in patients with histone acetylation, HR=0.40, 95% CI 0.16–1.03, p=0.058 on univariate analysis. This trend remained on multivariate analysis when age, time from diagnosis to relapse, CG risk group, and immunophenotype were included in the analysis (HR=0.40, 95% CI 0.13–1.20, p=0.10). No patients with non-acetylated histone H4 were able to proceed to BMT because of refractory disease or death/complications related to salvage therapy.

Conclusions: Acetylation of histone H4 is associated with a trend towards an improved OS in patients with ALL in relapse. This may be related to the fact that no patients with non-acetylated histone H4 were able to proceed to BMT. Although this data will need to be evaluated prospectively in a larger number of patients, this data provides rationale for the incorporation of histone deacetylase inibitors into salvage regimens for patients with relapsed/refractory ALL, particularly in patients not expressing acetylated histone H4.

Disclosures: No relevant conflicts of interest to declare.

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