Plerixafor as a chemosensitizing agent in pediatric acute lymphoblastic leukemia: efficacy and potential mechanisms of resistance to CXCR4 inhibition

Abstract

In spite of advances in the treatment of pediatric acute lymphoblastic leukemia (ALL), a significant number of children with ALL are not cured of their disease. We and others have shown that signaling from the bone marrow microenvironment confers therapeutic resistance, and that the interaction between CXCR4 and stromal cell-derived factor-1 (SDF-1 or CXCL12) is a key mediator of this effect. We demonstrate that ALL cells that upregulate surface CXCR4 in response to chemotherapy treatment are protected from chemotherapy-induced apoptosis when co-cultured with bone marrow stroma. Treatment with the CXCR4 inhibitor plerixafor diminishes stromal protection and confers chemosensitivity. Using xenograft models of high-risk pediatric ALL, plerixafor plus chemotherapy induces significantly decreased leukemic burden, compared to chemotherapy alone. Further, treatment with plerixafor and chemotherapy influences surface expression of CXCR4, VLA-4, and CXCR7 in surviving ALL blasts. Finally, prolonged exposure of ALL blasts to plerixafor leads to a persistent increase in surface CXCR4 expression, along with modulation of surface expression of additional adhesion molecules, and enhanced SDF-1α-induced chemotaxis, findings that may have implications for therapeutic resistance. Our results suggest that while CXCR4 inhibition may prove useful in ALL, further study is needed to understand the full effects of targeting the leukemic microenvironment.

A phase 1 study of the CXCR4 antagonist plerixafor in combination with high‐dose cytarabine and etoposide in children with relapsed or refractory acute leukemias or myelodysplastic syndrome: A Pediatric Oncology Experimental Therapeutics Investigators’ Consortium study (POE 10‐03)

“…Peripheral blood mononuclear cells were isolated via Ficoll density centrifugation as previously described . Cells were then prepared for flow cytometry analysis as previously described . Briefly, cells were stained with antibodies against human CD45, CD34, CD19, CD33, CXCR4 (12G5, eBioscience, San Diego, CA), and isotype controls and were read on a FACSCalibur (all from BD Biosciences, San Diego, CA, except as noted).…”

Evaluation of assay interference and interpretation of CXCR4 receptor occupancy results in a preclinical study with MEDI3185, a fully human antibody to CXCR4

“…Plerixafor induced up regulation of CXCR4 in Nalm‐6, a human B cell precursor leukemia, and more pronounced upregulation in HB‐119, a murine hybridoma B‐cell 19. Additionally, the CXCR4 ligand SDF‐1 down regulated CXCR4 on blood leukocytes in vitro through enhanced internalization 24 and, as such, displacement of SDF‐1 with MEDI3185 could result in upregulation of CXCR4.…”

“…As discussed above, a competitive antibody needs to be more rigorously qualified to ensure full competition for effects that can arise due to different affinities of the competing and therapeutic antibodies. For free CXCR4 RO assessments, clone 12G5 18 may compete with MEDI3185 and could offer an ADA‐resistant alternative for monitoring free CXCR4 as it has been reported that both antibodies compete with the ligand SDF‐119 and bind to an epitope on the second extracellular loop 20.…”

Targeting the TAM Receptors in Leukemia

“…Indeed, primary human bone marrow stromal cells protected CLL cells from induction of apoptosis with the AXL inhibitor BGB324 [60]. Therapeutic strategies to overcome this resistance include combined treatment with ligand traps to sequester Gas6 or with bone marrow mobilizing agents such as the CXCR4 antagonist, plerixafor, which has been shown to enhance sensitivity to both cytotoxic chemotherapy and targeted agents in ALL models [132,135]. …”