A Phase I Dose-Escalation Trial of Oral Clofarabine for Relapsed/Refractory Non-Hodgkin Lymphoma

Clofarabine is a second-generation purine analogue currently FDA-approved for intravenous use for relapsed/refractory pediatric ALL. Purine analogues demonstrate significant clinical activity in non-Hodgkin lymphomas (NHL), though clofarabine offers potential pharmacologic advantages over existing agents. Clofarabine is a more efficient substrate for deoxycytidine kinase, more completely inhibits ribonucleotide reductase and DNA polymerase α, and demonstrates improved activity in cells that are non-dividing or have a low proliferation rate. This phase I trial is the first evaluation of an oral formulation of clofarabine in relapsed or refractory non-Hodgkin lymphoma.

The primary objective was to determine the maximum tolerated dose (MTD) and define dose-limiting toxicities (DLT). Efficacy was a secondary objective. Patients (pts) were eligible if they had relapsed or refractory B-cell or T-cell NHL without prior stem cell transplant. All pts were required to have adequate organ function and performance status ≤2 as well as absence of both CNS involvement and HIV infection. No routine infectious prophylaxis was given. Patients were treated at 4 dose levels (1mg, 2mg, 4mg and ultimately 3mg) with oral clofarabine administered once daily on days 1–21 of a 28 day cycle for up to 6 cycles. Three to 6 pts were treated at each dose level in a traditional 3+3 design. Response assessment occurred after cycles 2 and 6. DLT was assessed during cycle 1 and was defined as Grade 4 neutropenia or thrombocytopenia occurring for ≥5 days, any grade 3–4 non-hematologic toxicity, and grade 2 non-hematologic toxicity that did not recover prior to the subsequent cycle of therapy.

Twenty-one pts were enrolled on the dose-escalation phase of the study. The median age was 63 years (range 51–85). The median number of prior regimens was 2 (range 1–7). Histologies included follicular lymphomas (FL; 5 pts), small lymphocytic lymphomas (SLL; 5 pts), diffuse large B-cell lymphomas (DLBCL; 4 pts), marginal zone lymphomas (MZL; 4 pts), mantle cell lymphomas (MCL. 2 pts) and lymphoplasmacytic lymphoma (LPL; 1 pt). Median number of cycles administered was 5.5. No DLTs were observed at the 1mg or 2mg dose levels. Three pts were accrued at 4mg with 1 patient experiencing DLT of persistent grade 3 thrombocytopenia and grade 4 neutropenia. No additional DLTs occurred in the cohort, but the majority of pts required late dose reductions due to grade 3–4 hematologic toxicity. The dose was therefore de-escalated to 3mg and 6 additional pts were accrued. No DLTs were observed at the 3mg dose level with a median of 6 cycles administered (range 5–6); 3mg was declared the recommended phase 2 dose. Grade 3–4 hematologic toxicity included neutropenia (7 pts), thrombocytopenia (4 pts), and anemia (2 pts). Grade 1–2 non-hematologic toxicities were uncommon, and included fatigue, diarrhea, cough, and dizziness. There were no grade 3–4 non-hematologic toxicities. Seventeen pts completed one cycle of therapy and were evaluable for response. Radiographic disease reduction was observed in 11 of 17 pts (65%). The overall response rate (ORR) was 35% (6 of 17), all partial responses (PR). Responders included FL (2 pts), MZL (2 pts), SLL and LPL (1 pt ea.). ORR among low grade histologies (FL, MZL, SLL) was 43% in this phase 1 trial. Seven pts had stable disease, including 5 pts with reduction in tumor size that did not reach threshold for PR. Of the 4 pts with progressive disease, 2 had DLBCL, 1 had MCL and 1 had FL with biopsy following relapse identifying ALK-negative anaplastic large T-cell lymphoma. Of the 4 pts not evaluable for response, 1 pt died of progressive DLBCL during cycle 1 on dose level 1 and was replaced, 1 pt was the DLT pt on the 4mg dose level and was removed due to prolonged cytopenias, and 2 pts withdrew consent (1pt at 4mg, 1pt at 3mg), and were replaced. The 3mg dose level has been expanded in a 10-patient dose-expansion cohort limited to low-grade NHL and MCL.

Oral clofarabine demonstrates encouraging tolerability and efficacy in relapsed B-cell NHL, particularly in low-grade histologies, warranting further investigation.

Abramson:Genzyme: Consultancy. Off Label Use: Clofarabine is not FDA approved for NHL.