Clofarabine in Combination with High-Dose Cytarabine and Liposomal Daunorubicin in Pediatric AML: Results of a Phase 1B Combination Study By the ITCC Consortium

Introduction: Relapsed/refractory pediatric AML has a poor prognosis. Chemotherapy using FLAG plus liposomal daunorubicine (FLAG-DNX) followed by stem-cell transplantation (SCT) is currently considered the standard in 1^strelapse in Europe (Kaspers, JCO 2013), and ~results in ~40% survival. FLAG is based on potentiation of high-dose cytarabine (Ara-C) by fludarabine (Flu) by increasing Ara-CTP levels. Clofarabine (CLO) is a novel purine nucleoside analog, designed to have improved efficacy.

Methods: We initiated a phase 1B study using a ‘3x3 design’ to define the optimal dose of CLO, replacing Flu in FLAG-DNX. Dosages consisted of Ara-C 2gr/m²/day (day 1-5), with escalation of DNX from 40 to 60 mg/m²/day (day 1, 3 and 5), and CLO from 20, 30 to 40 mg/m²/day (day 1-5) in 4 dose-levels (DL). At day 6 intrathecal Ara-C was administered. Patients with early 1^st relapse, refractory 1^st relapse and 2^nd relapse of AML were eligible. Responding patients received a consolidation with CLARA-DNX or treated by investigator discretion. DL 5 was open for patients with early 1^st relapse only, and dose-escalated DNX to 80 mg/m². MTD was the primary endpoint. At the MTD the cohort was expanded to 10 patients. Hematologic DLTs were defined as count recovery in responding pts >42 days. Overall response rate (ORR) was defined as: partial remission (PR, 50% reduction BM blasts), no evidence of leukemia (NEL, <5% blasts, no regeneration), complete remission with insufficient recovery (CRi, platelets below 80/μl and neutrophils below 1000/μl) and complete remission (CR). Morphology was centrally reviewed by the AML-BFM SG in Hannover. The study is registered in the Dutch Trial Registry (nr. 1880), and was open in 14 ITCC/I-BFM-sites.

Results: DL 1-4 accrued 29 AML patients (≥2^nd relapse, n=8; refractory 1^st relapse, n=11; early 1^strelapse, n=10). Patients were treated at dose-level (DL) 1, n=4; 2, n=3; 3, n=12 (split in 3A and 3B); 4, n=10. Twelve patients had been transplanted prior to enrollment. In total 38 CLARA-DNX courses were administered. Median age was 8.8 years, 18 patients were male, median WBC at enrollment 8.7x10.9/l. 26 SAEs were reported, consisting of febrile neutropenia (n=14), typhlitis (n=1), lung-infection fungal (n=3), lung-infection bacterial (n=2), candida sepsis (n=1), streptococcal sepsis (n=2), rash (hand-foot skin reaction) (n=1), and tumor lysis/capillary leak syndrome (n=1), cardiovascular failure (n=1) and vomiting (n=1). Other grade 3-4 AEs reported consisted of abdominal pain, nausea and vomiting, diarrhea, anorexia. blood pressure changes, DIC, rash and renal failure. Three pts had bilirubin elevation (>2.5xULN, max 61 µmol/l); 8 transaminitis (> 100 U/l; max. 998U/l), 1 elevated creatinine (83µmol/l) and 1 renal failure, 5 low potassium (<3 mmol/l) and 3 low sodium (<130mmol/l). At DL 3A, DLTs (fungal infection) halted dose-escalation. Detailed analysis showed subclinical fungal infections prior to enrollment. A protocol amendment was issued requiring screening patients with CT-scan and serum-galactomannan. After enrolling DL3B this appeared to be safe (1 DLT of Candida sepsis out of 6 patients). One DLT occurred at dose-level 4 (sepsis). Time to recovery of peripheral blood values in patients with CR/CRi was median 30 days for neutropenia and 26 days for platelets.

Considering outcome, the ORR was 59% in the 26 pts evaluable for response. In the 11 pts with refractory 1st relapse after FLAG the ORR was 38%. In the expansion cohort (10 pts in DL4) there was 1 CR, 7 CRi, 1 PR, and 1 early death. 18 pts were transplanted post clofarabine treatment (1 HLA-id, 13 MUD, 1 MFD, 2 haplo, 1 unkown). The median follow-up time of the 9 survivors was 16 months. The 1-year overall survival was 48±9%, and the 1-year EFS was 33±9%.

Five patients were recruited in DL5. Two DLTs occurred in 2 pts, i.e. a severe pseudomonas cellulitis and a Gram-negative sepsis, and hence this cohort was closed.

Conclusions: The RP2D of CLO in a CLARA/DNX course in relapsed/refractory pediatric AML is 40 mg/m² combined with DNX 60 mg/m² and Ara-C 2 gr/m², excluding patients with evidence of prior subclinical fungal infection. This combination resulted in a high response rate in the expansion cohort. We observed responses in 38% of patients refractory to FLAG. This regimen therefore has greater anti-leukemic potential than FLAG.

Acknowledgment: This study was financially supported by Sanofi, and by the KiKa-foundation grant nr. 26.