Osteogenic Inhibition in Multiple Myeloma

Multiple myeloma (MM) is a plasma cell malignancy where plasma cells are increased in the bone marrow (BM) and usually do not enter peripheral blood, but produce harmful factors creating problems in these patients (e.g. malignant plasma cells over activate osteoclasts and inhibit osteoblasts with factors like RANKL and DKK). These factors are a main cause of bone lesion in MM patients. Recently SOST gene which responsible to encodes the sclerostin protein was identify. This protein specifically inhibits Wnt signaling in osteoblasts (inhibition of osteoblast differentiation and proliferation) and decrease bone formation and can also cause bone lesion in MM patients. In this experimental study, human myeloma cell lines (U266 b1) were purchased from Pasteur Institute of Iran. Samples consisted of BM aspirates from the iliac crest of MM patients. BM with more than 70% plasma cell were selected for our study (6 patients) and one healthy donor. RNA extraction was done with Qiagen kit. was undertaken on mRNA of samples and cell lines. Also we purchased unrestricted somatic stem cells from Bonyakhte Company to evaluate the effect of soluble factors from myeloma cell lines on osteogenic differentiation medium. Our results showed that SOST is expressed significantly in primary myeloma cells derived from MM patients and myeloma cell lines. In other words, patients with more bone problems, express SOST in their plasma cells at a higher level. In addition, myeloma cells inhibit osteoblast differentiation in progenitor cells from umbilical cord blood stem cell (UCSC) in osteogenic inducing medium. There are many osteoblast maturation inhibitory factors such as DKK, Sfrp and Sclerostin that inhibit maturation of osteoblast in bone. Among osteoblast inhibitory agents (DKK, Sfrp, Sclerostin) sclerostin has the highest specificity and therefore will have less side effect versus non-specific inhibitory agents. Our results also show that based on SOST expression in MM, there is a potential to inhibit sclerostin with antibody or alternative methods and prevent bone lesion in MM patients with the least side effect.