A Phase II Study of Elacytarabine/Idarubicin As Second Course Remission-Induction in Patients with Acute Myeloid Leukemia Who Failed Cytarabine/Anthracycline, and Evaluation of the Impact of the Nucleoside Transporter hENT1 on Response

Elacytarabine is a fatty acid derivative (elaidic acid ester) of cytarabine. The mechanism of action is similar to cytarabine, but unlike cytarabine, cellular uptake and activity of elacytarabine are independent of nucleoside transporters. Resistance to cytarabine has been associated with decreased expression of the human equilibrative nucleoside transporter 1 (hENT1) (Hubeek et al., 2005). An agent such as elacytarabine, active in low hENT1 expressing, cytarabine resistant acute myeloid leukemia (AML), could therefore improve clinical outcome in patients.

To determine the efficacy and safety of elacytarabine given in combination with idarubicin to patients who have failed the first ”standard” induction course with a cytarabine based regimen, as well as to explore the relationship between the hENT1 status in AML cells and response.

Study therapy consisted of one course elacytarabine 1000 mg/m²/d CIV on d1-5 administered in combination with idarubicin 12 mg/m²/d IV d1-3 in adult patients with AML who after a first cytarabine based induction course have not attained blast clearance (bone marrow (BM) >5 % blasts, circulating blasts, or chloroma etc). Assessment of response was at least 12d after induction start. Responding patients could receive the same course or elacytarabine 2000 mg/m²/d CIV on d1-5 d and then consolidation therapy with two courses of either elacytarabine monotherapy or combination with idarubicin as described above or could proceed to allogeneic SCT at any time point. The hENT1 expression level of BM blasts was analyzed by immunocytochemistry at time of initial AML diagnosis (pre-cytarabine course) and/or before elacytarabine treatment.

The planned sample size is 50 evaluable patients, and with a target of 40% CR/CRi rate, the lower limit of the 90% confidence interval for the CR/CRi rate will be greater than 22% with at least 80% probability. The CR/CRi rate will be estimated and its corresponding two-sided 90% confidence interval will be provided.

The significance of the association between the hENT1 expression level and response status will be assessed through a Chi-square test of hENT1 expression level (high, low) versus CR/CRi (yes, no).

In the ongoing study, 26 patients [16 male, 10 female, median age 61 years (range 18–71), ECOG PS 0–2] have been treated with elacytarabine and idarubicin. 23 patients have currently been response evaluated, and 11 attained a CR/CRi and 3 a PR (post one elacytarabine course). The most frequently reported related non-hematologic adverse events (AEs) CTCAE grade ≥ 3 were febrile neutropenia, infections/sepsis and increased liver function tests. 30 patients have been scored for hENT1 expression level at time of diagnosis. Preliminary results indicate that approximately 50 % of the patients hENT1 expression is low (defined as less than 10% of blasts stained). As to response, only approximately 1/3 of patients with low hENT1 blasts respond to cytarabine while for the high hENT1 2/3 respond.

Three deaths occurred within 30 days after start of treatment and were all due to sepsis. All 3 patients had secondary leukemia.

Elacytarabine administered at 1000 mg/m²/d CIV d1-5 in combination with idarubicin 12mg/m²/d IV d1-3 showed promising clinical activity with a CR/CRi rate of approximately 45 %. The adverse event profile, is as expected for cytarabine combination therapy. Preliminary data indicate that the assessment of hENT1 transporter expression in blasts could be used to select patients less likely to benefit from cytarabine and for whom elacytarabine could be an effective therapy.

Gianelli-Borradori:Clavis Pharma: Employment. Flem Jacobsen:Clavis Pharma: Employment. Krug:MedA Pharma: Honoraria; Novartis: Honoraria; Alexion: Honoraria; Boehringer Ingelheim: Research Funding; Sunesis: Honoraria.