Safety of Clofarabine with Multiagent Chemotherapy in Childhood High Risk Relapse of Acute Lymphoblastic Leukemia (Vandevol study of the French SFCE Acute Leukemia Committee).

Current outcome of very early relapse of ALL in children remains poor. Clofarabine, a novel nucleoside analog has proven effective as a single agent in childhood ALL second relapse, providing a CR+CRp ratio of 20 to 28 % (Jeha 2006, Kearns 2006). Clofarabine in combination with cyclophosphamide and Etoposide provided a 44% overal response rate rate in children with advanced ALL (Hijiya 2011) and further multi-drug combinations need to be investigated. The VANDA regimen that has proven effective in high risk ALL and in ALL relapse (Domenech 2008) was used as a template, Cytarabine being replaced by Clofarabine in this combination.

A phase I study combining escalating doses of Clofarabine with fixed doses of Mitoxantrone, Etoposide, Asparaginase and Dexamethasone was undertaken in children presenting very early (18 months or less after initial diagnosis) medullary or combined ALL relapse or children with second relapse or post transplant relapse. A 3+3 rolling design was used for escalating clofarabine doses with 25% increments from 20 to 40mg/m²/d.

Sixteen patients were enrolled, eleven in first marrow relapse, four in second relapse. One patient with an initially refractory disease was secondary excluded as he didn't fulfill the inclusion criteria. Four patients had previously been allografted. Three patients were enrolled at dose level 1 (clofarabine 20 mg/m2), and 3 patients at dose level 2 (clofarabine 26 mg/m2) without any significant dose-limiting toxicity (DLT). Six patients were enrolled at dose level 3 (clofarabine 32 mg/m2), one patient experienced a liver DLT (gamma GT elevation) exceeding 7 days. At the last planned dose level (clofarabine 40 mg/m2), two patients had a grade 3 transaminase elevation exceeding 7 days and 2 patients had a severe fungal infection. Median duration of neutropenia was 20 days (15–31). Other expected toxicities included 3 documented bacterial infections, 3 mucosal toxicities needing parenteral support, one lung aspergillosis, one transient insulin dependant hyperglycemia. There was no toxic death. Out of 15 evaluable patients, 11 (73%) achieved a complete cytological remission (CR). 4 relapses occurred at 1, 1, 2 and 3 months. 6 patients proceeded to allo-SCT with 2 second allografts. One allografted patient died from EBV-PTLD, the others are alive at 2, 13, 13, 15, and 29 months post-transplant.

Clofarabine in combination with four major antileukemic drugs appeared feasible and effective in inducing complete remission in those high risk patients. Clofarabine MTD was 32 mg/m²/d for five days and this dose step is currently being expanded to a total of 10 patients, before a phase II study will be proposed for early and very early ALL relapses. Study registered at ClinicalTrials.gov (http://clinicaltrials.gov/ct2/show/NCT01279096).

Off Label Use: off label use of clofarabine.