Clinical Evaluation of Combined Epigenetic Therapies on the Induction of Fetal Hemoglobin in Patients with Hematologic Malignancies

Fetal hemoglobin induction with hydroxyurea (HU) is a mainstay of therapy for β-hemoglobinopathies, especially sickle cell disease (SCD). A high level of fetal hemoglobin (HbF) has a direct relationship with acute clinical status in SCD patients including pain crises, acute chest syndrome, and death. However, not all patients benefit from HU, and more effective HbF induction strategies are needed. DNA methyl transferase (DNMT) inhibitors and histone deacetylase (HDAC) inhibitors have been shown in vitro to induce HbF production through epigenetic modification of the β-globin gene cluster. Azacitidine (AZA) is a DNMT already used in some SCD patients resistant to HbF modulation with HU. Entinostat (MS-275) is an orally available histone deacetylase inhibitor with a long half-life and established antitumor activity in preclinical models. Recent studies suggest that drugs, which act with different molecular and epigenetic mechanisms, have synergistic effects on induction of fetal hemoglobin (Fard et al. IJHOSCR 2013).

In this study, we evaluated the effects of a combination of AZA and MS-275 on HbF levels. This was preformed as a correlative study of a phase I clinical trial (J0443 trial) of these drugs in patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). We sequentially measured the level of HbF the peripheral blood in 33 patients receiving different doses of AZA (range: 30mg/m² to 50mg/m² per day for 10 doses) and MS-275 (range: 2 to 8 mg/m² orally on days 3 and 10). Patients completed a minimum of four 28-day cycles of combined therapy. HbF levels were measured in peripheral blood at baseline, at day 15 or 16 and day 29 or 30 of cycle 1, and after cycles 2, 4, and if applicable 6.

Azacitidine dose positively correlated with HbF fold increase (mean of 1.1, 2.3, and 2.1 for doses of 30, 40, and 50 mg respectively, p=0.07) while MS-275 dose had a slightly negative correlation with HbF level (mean of 3.0, 1.8, and 1.3 for doses of 2, 4, and 6mg respectively, p=0.13). There was no correlation between baseline HbF and HbF fold increase after exposure to treatment (p=NS) and no correlation between baseline HbF levels and clinical disease response (p=0.19). Interestingly, we demonstrated a correlation between HbF fold increase and clinical disease response: median fold increase of 3.5 for patients achieving hematologic normalization (complete response, partial response, or trilineage hematological improvement) versus 1.4 in non-responders (p=0.006).

The positive correlation between AZA dose and HbF increase is consistent with prior work showing that this drug induces HbF production. The correlation between clinical response and HbF induction could reflect a greater susceptibility to AZA potentially related to differing methylomes. Alternatively, it may also represent a known increase in HbF in the setting of stress erythropoiesis. The slight inverse correlation between MS-275 and HbF level was surprising, as other HDAC inhibitors are known to induce HbF in vitro. However, these results are in line with the methylation data found in the more recent randomized phase 2 trial of AZA +/- MS-275 (E1905 trial) that showed a potential pharmacodynamic antagonism of the combination (Prebet et al. J Clin Oncol. 2014). Overall, this work supports the use of AZA as a clinical inducer of HbF. It also shows the importance of trialing various combinations of HbF inducers, as not all drugs work synergistically and some may even be antagonistic in combination.