Combination chemoimmunotherapy regimens have shown substantial efficacy in the treatment of lymphoproliferative disorders, particularly in comparison to the efficacy of single-agent therapies. Fludarabine has become an established treatment regimen in CLL, and although overall response rates (ORR) in previously untreated patients range between 60% to 80%, patients who are refractory to fludarabine have poor outcomes. Alemtuzumab, the anti-CD52 monoclonal antibody, is the most effective single-agent therapy in CLL, and is capable of inducing minimal residual disease (MRD)-negative responses even among patients with fludarabine-refractory disease. Our previous clinical experience with the combination of alemtuzumab and fludarabine (FluCam) resulted in 83% ORR in 36 patients with relapsed/refractory CLL, with 30% achieving a complete response (CR;
Elter et al J Clin Oncol 2005;23:7024–7031
). In addition, among 12 patients with fludarabine-refractory disease, 8 achieved responses (4 CRs), and median time-to-progression (TTP) for all patients was 13 months. In order to optimize the dose and schedule of the FluCam combination, we performed pharmacokinetic (PK) analysis of the previously reported 6-cycle regimen. PK data were collected for a 14-patient cohort that participated in the phase 2 FluCam trial. Median patient age was 60 years (range, 49–73), 9 patients had Binet C disease (5 were Binet B), and patients received a mean 2.5 prior therapies. Alemtuzumab 30 mg (after initial dose escalation) and fludarabine 30 mg/m2 were administered on days 1–3 of a 28-day cycle for up to 6 cycles. PK parameters were measured from samples collected before each subsequent cycle, and at days 1, 4, 7, 14, 21, 28, and 42, for a total of 158 patient samples, of which 120 were tested. Plasma concentration of alemtuzumab increased steadily from day 1 to day 4 of therapy to a median Cmax 1.55 mg/mL, but decreased to a median 0.145 mg/mL by 7 days after initiation of treatment. By day 21 of therapy, alemtuzumab plasma concentration decreased to undetectable levels. Because efficacy of alemtuzumab has been shown to correlate with serum levels of this antibody, significant improvement in progression free survival (PFS) may require a elevated plasma levels of alemtuzumab for the duration of the treatment cycle. Therefore, the significant responses seen in this trial can be attributed to documented synergistic activity between alemtuzumab and fludarabine, which has been demonstrated both in vitro and in vivo. Despite low CD4 counts through the duration of therapy, favorable safety results seen in the trial could be attributed to opportunity for hematologic recovery between treatment cycles. Detailed PK analysis is currently being completed and will be presented at the conference.Conclusions: Treatment with the FluCam immunotherapy combination yielded positive results among patients with fludarabine resistant/refractory CLL, a difficult-to-treat population. As shown previously, response rates correlate with higher alemtuzumab plasma concentrations. Therefore, longer PFS durations may require longer, more sustained alemtuzumab plasma levels, which may be achieved with either consolidation or maintenance.
Disclosure: No relevant conflicts of interest to declare.
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