Bendamustine (Treanda®)-Based Regimens Are Effective In Mobilizing Peripheral Blood Hematopoietic Stem Cells For Autologous Transplantation

High dose chemotherapy followed by autologous stem cell transplantation (ASCT) is a standard of care for patients with advanced or treatment refractory multiple myeloma (MM) and non-Hodgkin lymphoma (NHL). Stem cell proliferation and mobilization can be enhanced though the addition of myelosuppressive chemotherapy prior to GCSF administration. Chemotherapeutic agents without cross resistance to prior therapies may support peripheral blood stem cell (PBSC) collection and improve patient outcomes by exacting a more potent direct anti-tumor effect prior to ASCT. Bendamustine (Treanda®) is a synthetic chemotherapeutic agent that shares structural similarities to both purine analog and alkylating agents without significant cross resistance to other compounds in either drug class. Bendamustine appears to have low stem cell toxicity in vitro, is well tolerated, and has activity in MM and NHL, but the potential for the purine moiety to adversely impact stem cell reserve is unknown. We hypothesized that bendamustine’s activity in patients with disease resistant to first line therapies makes it a logical candidate for chemotherapy based PBSC mobilization and tested its impact on stem cell yield.

Patients were eligible if they had relapsed or refractory MM, B-cell NHL or T-cell NHL and were candidates for ASCT. Other criteria included: age >18 years, ANC >1,500/mm³, platelets >100,000/mm³, adequate renal and hepatic function, <3 prior myelotoxic regimens, <6 cycles of lenalidomide, no failed mobilization attempt, and no prior pelvic/spinal irradiation. Patients received 1 cycle of BED therapy [bendamustine (120 mg/m² IV d 1, 2 - provided along with financial support for this study by Teva Pharmaceuticals), etoposide (200 mg/m² IV d 1- 3), dexamethasone (40 mg PO d 1- 4), delivered as an outpatient, followed by filgrastim (initially 10 mcg/kg/d sc; starting on d 5 through end of collection)]. Apheresis was initiated when peripheral blood CD34 cell counts were >5/µL. The primary endpoint was successful mobilization, defined as collection of >2.0 x 10⁶CD34 cells/kg. AEs were graded using the CTCAE v4.0.

Thirty-seven patients (32 MM, 4B-cell NHL, 1 NK/T-cell NHL) were treated. The median age was 60 years (range 43-70). The median number of prior therapies was 1 (range 1-3) for MM and 2 (range 1-3) for NHL patients. All patients (37/37) were successfully mobilized. The median number of CD34⁺ cells collected was 19.43 x 10⁶/kg (range 4.35 to 55.51 x 10⁶). All MM patients collected >10 x 10⁶ CD34⁺cells/kg. The median time from the start of BED mobilization therapy to the first day of CD34 stem cell collection was 12 days (range 9 to 20 days). The median number of apheresis days was 1 (range 1 to 4). A predictable pattern of leucocyte nadir and recovery was demonstrated (95% of patients started apheresis between days 9-13). Two patients (5%) were given plerixafor and for 2 patients (5%) GCSF was increased to 16 mcg/kg twice daily. Among the 37 patients mobilized and collected, 31 have thus far undergone ASCT and 100% (31/31) achieved an unsupported neutrophil count >500/µL at a median of 15 days (range 7-19) after PBSC infusion and a platelet count >20K/µL at a median of 11 days (range 8-14). Ten SAEs were observed in 8 patients and 1 patient died due to disease progression prior to ASCT. SAEs include: neutropenic fever (1, grade [GR] 3), bone pain (2, GR 3), renal insufficiency (1, GR 1), atrial fibrillation (1, GR 2), hypotension (1, GR 3), stroke (1, GR 2), and one patient accounted for 3 SAEs including GR 3 tumor lysis syndrome and sepsis and GR 5 disease progression. Among twenty-nine evaluable patients to date, responses include: CR= 4 PR=2, SD=19 and PD=4. The ORR to this single cycle of therapy was 21%.

PBSC mobilization with BED is safe and effective. BED is not an acute stem cell toxin. Large numbers of stem cells were rapidly mobilized and resulted in short durations of apheresis. No patient with MM collected <10 x 10⁶ CD34⁺ cells/kg (sufficient for 2 ASCTs). Twenty-one percent of patients demonstrated a measurable response to a single cycle of BED therapy and an additional 65% of patients had stable disease. In patients who were transplanted, the time to neutrophil and platelet engraftment was comparable to other chemotherapy based mobilization regimens. The BED regimen was well tolerated and these findings suggest that the role of BED in PBSC mobilization should be further explored.

No relevant conflicts of interest to declare.