Zoledronic Acid Reduces Osteonecrosis and Anti-Leukemic Efficacy in Murine Models of Acute Lymphoblastic Leukemia Therapy

Background: Osteonecrosis and osteopenia frequently complicate acute lymphoblastic leukemia (ALL) therapy. Interventions which reduce these bony toxicities without impairing the anti-leukemic efficacy of therapy are lacking. Case reports suggest that bisphosphonates may reduce the pain associated with osteonecrosis; however, it is unclear if they are effective in preventing or reducing the progression of osteonecrosis or modifying bone density loss during therapy. Their impact on the anti-leukemic efficacy of therapy is also unknown. Methods: We tested the efficacy of the bisphosphonate zoledronic acid (ZA) in the murine model of osteonecrosis. Four-week-old Balb/c mice were treated with dexamethasone (2mg/L in drinking water) and PEGylated-asparaginase [1200IU/kg intraperitoneal (IP) weekly] for 6 weeks. To test whether ZA could prevent osteonecrosis, mice received ZA 100ug/kg IP weekly starting with therapy initiation (early zoledronic acid group, receiving 6 total doses). To test whether ZA could prevent the progression of osteonecrosis, ZA administration was delayed until the fourth week of therapy (late zoledronic acid group, receiving 2 total doses) after osteonecrosis processes have already begun. All mice were humanly euthanized at 10 weeks post-natal. At the end of the 6 week therapy, osteonecrosis was assessed histologically at the distal femur, while bone density and quality measurements were obtained from the proximal tibia using the Siemeons Inveon uCT system. To test the impact of zoledronic acid on the anti-leukemic efficacy of therapy, nine-week-old B6 mice were injected with 2000 Arf-/- Bcr/Abl+ syngeneic acute lymphoblastic leukemia cells. Mice received three weeks of therapy identical to the osteonecrosis studies (including zoledronic acid randomization), except dexamethasone was increased to 4mg/L in the drinking water. Mice were sacrificed when moribund and leukemia as cause of death was confirmed by peripheral white blood cell count and spleen weight. Results: Osteonecrosis was reduced in the early zoledronic acid group compared to the control group (12/69 limbs vs. 25/72 limbs, p=0.03). The incidence of osteonecrosis in the late zoledronic acid group (19/56 limbs) was identical to that in the control group (p=1). Both zoledronic acid interventions increased the cortical thickness of the tibia [median 0.12mm in therapy treated controls; 0.18mm in early zoledronic acid group (p=