Objectives: Plerixafor (AMD3100, Mozobil) with filgrastim (G-CSF, Neupogen) is approved for hematopoietic stem cell (HSC) mobilization in patients with non-Hodgkin Lymphoma and multiple myeloma (MM). Plerixafor pharmacokinetics (PK) and pharmacodynamics (PD) are well described, with linear, dose-dependent PK following subcutaneous (SC) administration, peak concentrations 30-60 mins post-injection and an elimination half-life (t1/2) of 5.3 hr. In pharmacodynamic studies of plerixafor in conjunction with filgrastim in healthy volunteers, peak CD34+ cell counts occur 10-14 hours following administration, however, data is limited in the 14-24 hr timeframe. Plerixafor labeling requires SC dosing approximately 11 hours prior to apheresis, which translates into dosing 10:00 PM the night before apheresis, and 54% of MM patients collect ≥ 6 x 106 CD34+ cells/kg following a single apheresis procedure. The current regimen is inconvenient for patients and requires additional health care resources. Based on PK and PD, we hypothesized that plerixafor given at 3:00 PM (17 hr prior to apheresis) would yield equivalent CD34+ HSC yield to 10:00 PM dosing in MM patients.

Methods: In a Simon's two-stage design, we enrolled MM patients undergoing cytokine-only HSC mobilization. All subjects received filgrastim 7.5 mcg/kg SC BID for 4 days followed by plerixafor (0.24 mg/kg SC daily) for up to 4 days beginning at 3:00 PM the day prior to the first day of a 24-liter apheresis procedure at 8:00 AM. Target CD34+ HSC collection for stem cell transplant (SCT) was ≥ 10 x 106 CD34+ cells/kg. Blood samples for CD34+ fluorescence-activated cell sorting analysis were collected prior to the first plerixafor dose and at 1, 3, and 17 ± 1 hr, then daily prior to apheresis as needed.

Results: Thirty patients (17 female, median age 59 years [range 44–70]) were evaluable; 27 received 1 pre-mobilization regimen (RVD n=20, VTD n=2, VD n=2, V/PLD/D n=1, VT n=1, RD n=1) for a median of 4 (1-6) cycles. Three received 2 regimens [CMF x 6 (breast cancer), then VTD x 5; RD x 4, then RVD x 4; and V/PLD x 1 with maintenance R]. Six patients received prior radiation. Mean (± SD) CD34+ cell counts in peripheral blood pre-plerixafor and 1, 3, and 17 hr post-first dose increased through the dosing interval (Figure). Twenty-two (73%) patients collected target cell numbers in 1 day of apheresis, 7 (23%) in 2 days, and 1 (3%) in 3 days. Twenty-seven (90%) patients collected ≥ 6 x 106 CD34+ cells/kg in 1 day. Institutional data with filgrastim 7.5 mcg/kg SC BID for 4 days alone in MM in 22 subjects showed a day 1 collection of ≥ 10 x 106 CD34+ cells/kg in 18% of patients (Renfroe H, et al. Transfusion Feb 2011). Adverse events were generally mild and consistent with known side effects of the combination [gastrointestinal disorders (diarrhea, nausea) and injection site reactions]. To date, 16 (53%) patients have proceeded to autologous SCT with melphalan conditioning and all patients have engrafted, with median time to an ANC ≥ 500/mm3 of 13 (range 11-15) days and platelets ≥ 20,000/mm3 of 16 (range 11-21) days.

Conclusion: This is the first prospective trial demonstrating the safety and efficacy of plerixafor given 17 hr prior to apheresis. Pharmacodynamic data showed the peripheral blood CD34+ cell population increased throughout the dosing interval, with a 4.6-fold increase over pre-plerixafor counts at 17 hr. Comparison with historical institutional controls and published data suggests this regimen yields at least equivalent, if not superior, collection rates with one apheresis procedure.