DEVELOPMENT OF AN IN-VIVO MODEL OF HUMAN MULTIPLE-MYELOMA BONE-DISEASE

Osteolytic bone destruction and its complications, bone pain, patholog ic fractures, and hypercalcemia, are a major source of morbidity and m ortality in patients with multiple myeloma. The bone destruction in mu ltiple myeloma is due to increased osteoclast (OCL) activity and decre ased bone formation in areas of bone adjacent to myeloma cells. The me chanisms underlying osteolysis in multiple myeloma in vivo are unclear . We used a human plasma cell leukemia cell line, ARH-77, that has dis seminated growth in mice with severe combined immunodeficiency (SCID) and expresses IgG kappa, as a model for human multiple myeloma. SCID m ice were irradiated with 400 rads and mice were injected either with 1 0(6) ARH-77 cells intravenously (ARH-77 mice) or vehicle 24 hours afte r irradiation. Development of bone disease was assessed by blood ioniz ed calcium levels, x-rays, and histology. All ARH-77, but none of cont rol mice that survived irradiation, developed hind limb paralysis 28 t o 35 days after injection and developed hypercalcemia (1.35 to 1.46 mm ol/ L) a mean of 5 days after becoming paraplegic. Lytic bone lesions were detected using x-rays in all the hypercalcemic mice examined. No lytic lesions or hypercalcemia developed in the controls. Controls or ARH-77 mice, after developing hypercalcemia, were then killed and bone marrow plasma from the long bones was obtained, concentrated, and ass ayed for bone-resorbing activity. Bone marrow plasma from ARH-77 mice induced significant bone resorption in the fetal rat long bone resorpt ion assay when compared with controls (percentage of total Ca-45 relea sed = 35% +/- 4% v 11% +/- 1%). Histologic examination of tissues from the ARH-77 mice showed infiltration of myeloma cells in the liver and spleen and marked infiltration in vertebrae and long bones, with loss of bony trabeculae and increased OCL numbers. Interestingly, cultures of ARH-77 mouse bone marrow for early OCL precursors (colony-forming unit-granulocyte-macrophage [CFU-GM]) showed a threefold increase in C FU-GM from ARH-77 marrow versus controls (185 +/- 32 v 40 +/- 3 per 2 x 10(5) cells plated). Bone-resorbing human and murine cytokines such as interleukin-6 (IL-6), IL-1 alpha or beta, TGF alpha, lymphotoxin, a nd TNF alpha were not significantly increased in ARH-77 mouse sera or marrow plasma, compared with control mice, although ARH-77 cells produ ce IL-6 and lymphotoxin in vitro. Conditioned media from ARH-77 cells induced significant bone resorption in the fetal rat long bone resorpt ion assay when compared with untreated media (percentage of total Ca-4 5 released = 22% +/- 2% v 11% +/- 1%). This effect was not blocked by anti-IL-6 or antilymphotoxin (percentage of total Ca-45 released = 19% +/- 1% and 22% +/- 1%, respectively). Thus, we have developed a model of human multiple myeloma bone disease that should be very useful to dissect the pathogenesis of the bone destruction in multiple myeloma. (C) 1996 by The American Society of Hematology.