CCR1 Blockade by An Orally-Available CCR1 Antagonist Reduces Tumor Burden and Osteolysis In Vivo In a Mouse Model of Myeloma Bone Disease

Abstract 3000

Myeloma bone disease has been shown to revolve around a complex interplay of multiple myeloma tumor cells and osteoclasts, each supporting the growth and development of the other. This pathogenic interplay is mediated, in part, by CCL3/MIP-1α, expressed by the myeloma cells, and its cognate receptor CCR1, expressed by precursor and mature osteoclasts. In this study, we show that osteoclast precursor cells respond to CCL3 with increased formation of mature osteoclasts, and this is blocked in the presence of a specific CCR1 antagonist, CCX721, that specifically inhibits mouse leukocyte migration. CCX721, an analogue of CCX354, a CCR1 antagonist currently in Phase 2 studies for RA, has high affinity for mouse CCR1 and thus is suitable for evaluation in rodent studies. We show in the immunocompetent murine 5TGM1 model of myeloma bone disease that blockade of CCR1 with CCX721, either prophylactically or therapeutically using an oral dosing regimen that results in plasma concentrations of antagonist that provide 85–95% CCR1 coverage of blood leukocytes at all times, reduces tumor burden and the level of osteolysis. 5TGM1-GFP myeloma cells express minimal levels of CCR1 but secrete high levels of CCL3 constitutively. Syngeneic C57BL/KaLwRij mice bearing 5TGM1-GFP cells were treated with CCX721 (100 mg/kg dosed orally, twice daily), vehicle (100% sesame oil, 2.5 ml/kg) or a positive control, zoledronic acid (0.12 mg/kg, sc injection, dosed twice weekly). In the first study, treatment was initiated one day before 5TGM1-GFP cells were injected into the mice (d0) and the study continued for 28 days. At the conclusion of this treatment regimen, the serum monoclonal paraprotein (IgG2bκ) levels (surrogate marker of tumor burden) were reduced from 19.9 ± 5.9 mg/ml to 1.7 ± 0.2 mg/ml for the mice treated with CCX721 (p<0.0001, Mann Whitney), and the number of TRAP-stained osteoclasts in the femurs of CCX721-treated tumor-bearing mice was concomitantly reduced. The reduction in overall tumor burden was consistent with reduced tumor-associated green fluorescence on whole body live GFP scans. In addition, the attenuation of serum paraprotein levels was comparable to that achieved with the positive control, zoledronic acid (0.8 ± 0.1 mg/ml). In a second study, treatment with the CCR1 antagonist was only initiated 18 days after tumor cell inoculation, when establishment of tumors in the medullary cavities was confirmed by whole animal GFP scans. Administration of CCX721 in this setting for 10 days thereafter also resulted in a significant reduction in serum IgG2bκ levels in the CCX721-treated group compared to the vehicle group (1.9 ± 0.2 mg/ml versus 6.0 ± 0.6 mg/ml, p=0.001, Mann Whitney), an effect that compared favorably to that of zoledronic acid (1.7 ± 0.1 mg/ml) and which was also confirmed by whole body GFP scans. Together, these results provide a strong rationale for further development of CCX721 and/or other CCR1 antagonists for the treatment of multiple myeloma.