A Treatment Study With RhOPG-Fc For Multiple Myeloma Bone Disease

Multiple myeloma (MM) is characterized by the accumulation of malignant plasma cells in the bone marrow leading to impaired hematopoiesis and bone disease, which includes mainly lytic lesions, pathological fractures, hypercalcemia and osteoporosis. Myeloma bone disease is the result of an increased activity of osteoclasts, which is not accompanied by a comparable increase of osteoblast function, thus leading to enhanced bone resorption. The interaction of plasma cells with bone marrow microenvironment is crucial for the activation of osteoclasts.RANKL/RANK/OPG system has recently been shown to play a key role in the normal development of osteoclasts. RANKL has been shown to be expressed by stromal cells and osteoblasts in the local bone marrow microenvironement, where it can bind to its receptor RANK on the surface of osteoclast precursors. The interaction between RANKL and RANK plays a critical role in promoting osteoclast differentiation and bone resorption and may also be responsible for activating mature osteoclasts to increase bone resorption A soluble decoy receptor, called osteoprotegerin (OPG), has also been identified, which binds to RANKL, inhibiting its interaction with RANK and blocking osteoclast formation.Myeloma cells have the ability to up-regulate the expression of RANKL and down-regulate the expression of OPG at both mRNA and protein level in pre-osteoblastic or stromal cell co-cultures. Therefore, RANKL expression has been found to be increased in bone marrow biopsies from patients with MM, while RANKL is over-produced by stromal cells, osteoblasts and activated T-cells in areas infiltrated by MM. An interesting and controversial question has arisen recently about the direct expression or production of RANKL by human myeloma cells. Some researchers have found that myeloma cells did not express RANKL and did not produce sRANKL. Furthermore, microarray technology studies showed that RANKL gene expression has not been detected in myeloma cells of MM patients. However, other groups have detected RANKL expression in myeloma cells.In this ex vivo experiment, we try to study the mechanism of myeloma bone disease by co-cultured myeloma cells SP2/0-AG14 and preosteoclasts RAW264.7. The results showed that myeloma cells SP2/0-AG14 can recruit preosteoclasts RAW264.7 and directly induce their differentiation into mature osteoclasts. Then we accessed rhOPG-Fc on this new co-cultured system. We find that rhOPG-FC had great inhibition effect on mature osteoclasts and their precursor cells' differentiation. These results proved indirectly that myeloma cells do express RANKL.In the animal experiment using the multiple myeloma model of rat, we measured the bone turnovers maker in urine and serum (such as ALP and BGP), BMD, biomechanics tests of femur and vertebral body and pathological test and parameters of bone morphometry. The results showed that rhOPG-FC worked effectively in treating the bone loss in myeloma rats. The drug effect correlate with both using time and dose. The rational drug using time is 2 weeks and the rational drug dose is 6mg/kg/d.In sum, myeloma cells can recruit preosteoclasts and directly induce their differentiation into mature osteoclasts by express RANKL, which can be inhibited by rhOPG-FC. The rhOPG-FC can improve the lytic bone disease of myeloma and the effect depends on the using time and dose. The rational drug using time is 2 weeks and the rational drug dose is 6mg/kg/d.