Clofarabine Combinations in Acute Myeloid Leukemia (AML) Salvage: A Dose-Finding Phase I Study of Clofarabine Plus Idarubicin and Clofarabine/Idarubicin Plus Cytarabine (ara-C).

Clofarabine is a second-generation nucleoside analog with single agent activity in acute leukemias. To try and improve efficacy, various combination trials are being conducted. In studies of clofarabine plus ara-C we reported overall response rates of 41% (CR 24%) in AML salvage and 60% (CR 52%) in untreated elderly AML with acceptable toxicity profile. To explore additional clofarabine combinations in AML we conducted a phase I study of clofarabine (C) with idarubicin (I) [CI] alone and with ara-C (A) [CIA] in pts with relapsed AML and high-grade MDS. Dose-limiting toxicities (DLT) were defined as ≥ grade 3 drug-related toxicities. Maximum tolerated dose (MTD) was determined by “3+3” method. Thirty-three patients (18 on CI and 15 on CIA) have been treated and are evaluable. Of 18 pts on CI, 6 were primary refractory and 12 in first relapse (median first remission duration [CRD1] 2 mos. [range 0–9]. Eleven pts had abnormal cytogenetics. Fourteen pts received prior ara-C-based regimens, 2 relapsed from allogeneic transplant (SCT). Median age: 57 yrs (range 24–71). Four dose levels have been explored. When C was given at 22.5mg/m² i.v. daily x 5d and I at 12mg/m² i.v. daily x 3d, 2 ≥ gr. 3 toxicities (diarrhea, rash, ↑ bili) occurred necessitating dose de-escalation. Subsequent levels included C at 15mg/m² x 5d/I at 8mg/m² x 3d (6 pts, 1 ≥ gr.3 toxicity [↑ bili]), C at 18 mg/m² x 5d, I at 10mg/m² x 3 d (3 pts, no DLT), and C at 22.5mg/m² x 5d, I at 10mg/m² x 3d (3 pts, no DLT). Three (17%) responses (2 CRp, 1 CR) occurred. Of 15 pts on CIA, 4 were primary refractory and 11 in first relapse. Median CRD1 was 9 mos (0–24). Eight pts had an abnormal karyotype. Seven pts received prior ara-C-based regimens and 2 failed unrelated donor SCT. Median age: 58 yrs (23–78). Three dose levels were evaluated. At C 22.5mg/m² i.v. daily x 5d, I 8mg/m² i.v. daily x 3d, A 1g/m² i.v. daily x 5d, 2 of 3 pts developed ≥ gr.3 toxicities (↑ bili, diarrhea) necessitating dose de-escalation. Subsequent levels included C at 15mg/m² x 5d, I at 6mg/m² x 3d, A at 0.75g/m² x 5d (6 pts, 1 with ≥ gr. 3 rash, ↑ bili), and C at 22.5mg/m² x 5d, I at 6mg/m² x 3d, and A at 0.75g/m² x 5d (6 pts, 1 with ≥ gr. 3 ↑ bili). Nine (60%) responses (8 CR, 1 CRp) occurred. Further dose escalation of clofarabine is planned in both trials. The preliminary results indicate feasibility of the combinations. The higher response rates with CIA need to be evaluated in view of different pt. characteristics between the two trials.