Adult patients (pts) diagnosed with acute lymphocytic leukemia (ALL) are known to have a poor clinical outcome as compared to children. Studies report a 2 year event free survival of 30-40% for Philadelphia chromosome negative (Ph-) patients age >30 yrs and 17% for age >50 yrs. In order to improve outcome for adult ALL, agents that are effective, safe and associated with a low morbidity are needed.

Clofarabine, a second generation purine nucleoside analog, has clinical activity as a single agent and in combination with cytosine arabinoside (ara-C) against refractory and relapsed ALL. Clofarabine exerts its cytotoxicity through multiple mechanisms of action, with major effects via inhibition of ribonucleotide reductase (RR) and DNA polymerase-alpha, and incorporation into DNA leading to DNA damage and activation of apoptotic pathways. Histone deacetylases (HDACs) are important regulators of chromatin involved in silencing of tumor suppressor genes. HDAC inhibitors are shown to be apoptogenic in vitro for ALL cell lines and have received FDA approval for the treatment of CTCL and peripheral T cell lymphoma. Pre-treatment with entinostat has been shown to enhance the cytotoxic activity of fludarabine in leukemia cell lines in vitro (Maggio et al, Cancer Research 2004). Given the similarity of clofarabine to fludarabine, and its FDA approval for children with refractory ALL, the combination of entinostat with clofarabine was pursued.


A Phase I window of opportunity study using overlapping schedule of entinostat and clofarabine was used in adult pts with ALL (B precursor) or Acute Bilineage Leukemia (ABL). Pts were enrolled onto one of two arms; arm “A” received repeated cycles of entinostat-clofarabine every 21 days as long as there was evidence of response (CR, CRi, or PR following cycle 1) and pts on arm “B” received one cycle of entinostat-clofarabine prior to standard multi-agent chemotherapy. Entinostat was administered orally on day 1 and day 8 (with dose escalation from flat dosing of 4mg to 6mg to 8mg from cohort 1 to 3). Clofarabine was administered intravenously at a fixed dose for all dose cohorts at 10mg/m2 for 5 days (day 3-7).

Adults >40 yrs with newly diagnosed, Ph- B-lineage ALL or ABL were eligible. Additionally, adults > 21 yrs with relapsed and refractory, Ph- ALL or ABL were eligible. Eligibility criteria included serum creatinine < 2.0 mg/dl, hepatic enzymes < or = 2.5 ULN and bilirubin <2.0 mg/dl. WBC <150,000/mm3 with no evidence for ongoing or impending leukostasis was required.


23 pts from 3 institutions were enrolled on this study (18 at JHH, 3 at UMD, 2 at UColorado). 17 pts were treated on arm A and 6 pts on arm B. 6 pts were treated in each dose level with responses as follows: in dose level one (1 CR, 5 NR) and dose level two (1 CR, 1 CRi, 4NR) and dose level three (3 PR and 3 NR). The dose level 3 cohort was expanded with a total of 5 additional pts to date (1 PR, 1 SD, 3NR). Thus, the overall response rate on dose level 3 was 4PR, 1SD, 6NR. The 4 pts with CR/CRi/PR were all de novo treated elderly pts from Arm A. Notably, one pt on arm A has been in remission for over 1.5 yrs. Toxicities to date included expected but manageable grade (G) 3 and 4 cytopenias. There were G3 elevations of ALT (N=2) and AST (2) and bilirubin (1) and one bacteremia (1) and G4 cellulitis (1). Planned correlative studies are ongoing and include evaluation of acetylation of target proteins using multiparameter flow cytometry and western blot as well as methylation evaluation.


Combination therapy with entinostat-clofarabine is feasible and is well tolerated with minimal toxicity. Promising durable responses were observed in older pts that were not otherwise able to receive multi-agent induction chemotherapy upfront. This is notable given the low dose of clofarabine used in every cohort. Correlative studies evaluating protein hyperacetylation and DNA methylation in serial samples from treated pts are in progress.


Off Label Use: This clinical study is a Phase 1 investigation and it discusses non-FDA approved doses of both clofarabine and entinostat for adults with Acute Lymphocytic Leukemia. The reason for this is that this study examines these agents in combination in a Phase 1 fashion and we started with low doses of each agent. Ordentlich:Syndax: Employment. Trepel:Syndax: Research Funding.

Author notes


Asterisk with author names denotes non-ASH members.