Final Results of the Phase I/II Study of Chemosensitization Using the CXCR4 Inhibitor Plerixafor in Combination with Bortezomib in Patients with Relapsed or Relapsed/Refractory Multiple Myeloma

PURPOSE: This study aimed to determine activity and safety of the CXCR4 inhibitor plerixafor in combination with bortezomib and dexamethasone in patients with relapsed or refractory Multiple Myeloma (MM). This was based on our preclinical studies showing that plerixafor (Mozobil, Sanofi Corporation) induces de-adhesion of MM cells and sensitization to bortezomib in preclinical animal models.

PATIENTS AND METHODS: Theprimary endpoint of the phase I study was the maximum tolerated dose (MTD) and for the phase II study, the safety and response rate of the combination. Eligibility criteria included patients with relapsed or relapsed/refractory MM with 1-5 prior lines of therapy including bortezomib (unless patients were refractory to bortezomib). The phase I included 8 cohorts with different doses and two treatment schedules. In cohorts 1-5, patients received plerixafor at the recommended dose sq on days 1-6 of each cycle and bortezomib at the recommended dose twice a week on days 3, 6, 10, and 13 every 21 days. In cohort 5b-6, plerixafor was given at the recommended dose sq on days 1, 3, 6, 10, and 13 and bortezomib was given at the recommended dose twice a week on days 3, 6, 10, and 13 every 21 days. For the phase II portion patients received plerixafor at the MTD established in phase I of trial, 320 mcg/kg sq on days 1, 2, 3, 6, 10, and 13. Bortezomib was given 1.3 mg/m2 IV or sq twice a week on days 3, 6, 10, 13, every 21 days. Dexamethasone was given at 40mg on days of Bortezomib.

RESULTS: A total of 58 patients were enrolled on this study from June 2009 to March 2015, with 25 on the phase I and 33 on the phase II study. In the phase I study, the median age was 60 years (range, 43-85), the median number of prior therapies was 2 (range, 1-4), with all but 3 patients receiving prior bortezomib. The median number of cycles on therapy was 4 (1-12). Dose limiting toxicities including insomnia, restlessness, and psychosis were observed in two patients at dose level 6 (plerixafor 0.40 mg/kg and bortezomib 1.3 mg/m2). Therefore, 3 additional patients were enrolled at dose level 5b (plerixafor 0.32 mg/kg and bortezomib 1.3 mg/m2). There were no grade 4 toxicities. Grade 3 toxicities included lymphopenia (40%), hypophosphatemia (20%), anemia (10%), hyponatremia (10%), hypercalcemia (10%), and bone fracture due to myeloma bone disease (10%). Twenty-three patients were evaluable for response, including 1 (4%) complete response (CR), 1 (4%) very good partial response (VGPR), 1 partial remission (PR) and 2 (9%) MR, and 15 (65%) having stable disease with only 3 (13%) progressive disease (PD). In the phase II study, the median age was 63 (46-83). The median number of prior therapies was 2 (1-5), with 22 (66%) who have received prior bortezomib. The median number of cycles on therapy is 5 (1-24). The response rate included 5 VGPR (16%), 11 PR (35%) with an overall response rate of 51% and another 11 (35%) stable disease. Grade 3/4 toxicities included thrombocytopenia (68%), lymphopenia (6%), hypophosphatemia (2%), anemia (4%), infections (4%), hyponatremia (2%), hypercalcemia (2%) and neurological toxicity (2%). We also examined in vivo mobilization of plasma cells, CD34+ hematopoietic stem cells and other accessory bone marrow cells. Analysis of these samples showed rapid mobilization of plasma cells at 2 hours post-plerixafor with a rapid return to normal levels at 4 and 24 hours post plerixafor. CONCLUSIONS: The combination of plerixafor and bortezomib is generally well tolerated with minimal neuropathy or other toxicities seen to date. The responses observed are strongly encouraging with 51% ORR in this relapsed and refractory population. This study was supported by R01CA133799-01, and by Sanofi and Takeda Corporations.