What Is Important Factor of Bone Disease in Multiple Myeloma?.

New International Prognostic Index (IPI) staging system of multiple myeloma (MM) is a combination of the level of serum β₂-microglobulin and serum albumin. Particularly, good survival (median survival >5 years) is associated with absence of chromosome 13q deletion. Recently, correlations between molecular subtypes and prognosis have been identified as a good prognosis with t(11;14) and a poor prognosis with t(4;14) and t(14;16) besides chromosome 13 abnormalities. We have reported that some MM cases with cyclin D1 overexpression detected by competitive RT-PCR were not caused by t(11;14)(q13;q32) or extra copies of 11q13 (In J Oncol, in press). A recent report revealed that subtypes of MM cases with the translocation of cyclin D showed a close correlation with bone disease and high level of DKK1. We also have been studing about the correlation between bone disease and bone morphogenetic protein (BMP) 2, or connective tissue growth factor (CTGF) that is supposed to inhibit the VEGF binding to its receptor or modulate cell signaling by BMP. First, we analyzed IPI staging in 91 MM cases, and then analyzed the relation between IPI staging and existence of cyclin D1 overexpression, or t(11;14)(q13;q32) and extra copies of 11q13. Competitive RT-PCR was performed in 77 cases, and cyclin D1 overexpression was detected in 40/77 (52%). Deletion of chromosome 13q was detected in 32/87 (37%), and t(11;14)(q13;q32) or extra copies of 11q13 was detected in 11/50 (22%) and 7/50 (14%), respectively. There were no significant differences of those factors among IPI staging. And we analyzed the scale of bone lesion by bone x-ray in 81 cases. We could not detect the relation between bone disease and cyclin D1 overexpression or translocation of 11q13. Furthermore, we analyzed the expression of BMP2 and CTGF by quantitative real time-PCR in purified myeloma cells or in bone marrow mononuclear cells (BMMNC) reduced myeloma cells less than 5%. We have gotten results that MM cases have a tendency to show higher CTGF expression in BMMNC compared with that of normal BM, but there was no significant difference of BMP2 expression in BMMNC between them. And there was no correlation between cyclin D1 overexpression and BMP2 or CTGF expression. So far a cause of bone lesions in MM is supposed to be the activity of osteoclast, however, our preliminary examination by TRAP staining revealed that osteoclast differentiation from BMMNC in MM cases by adding M-CSF (25 ng/ml) and RANKL (50 ng/ml) decreased compared with that in normal BM, and osteoblast diffentiation also decreased in MM by cytochemical staining for alkaline phosphatase (AP). We guess that both osteoclast and osteobalst differentiation are suppressed in MM and CTGF is a candidate for the suppressor of osteoblast differentiation. We will be able to show the result of AP activity of osteoblast and the effect of recombinant CTGF on osteoblast in meeting.