The proteasome inhibitor bortezomib affects osteoblast differentiation in vitro and in vivo in multiple myeloma patients

Abstract

The proteasome inhibitor bortezomib may increase osteoblast-related markers in multiple myeloma (MM) patients; however, its potential osteoblastic stimulatory effect is not known. In this study, we show that bortezomib significantly induced a stimulatory effect on osteoblast markers in human mesenchymal cells without affecting the number of osteoblast progenitors in bone marrow cultures or the viability of mature osteoblasts. Consistently we found that bortezomib significantly increased the transcription factor Runx2/Cbfa1 activity in human osteoblast progenitors and osteoblasts without affecting nuclear and cytoplasmatic active ␤-catenin levels. IntroductionMultiple myeloma (MM) is a plasma cell malignancy characterized by the high capacity to induce osteolytic bone lesions. 1 Hystomorphometric studies showed that osteoblast formation and function are profoundly impaired in MM patients and critical in the bone lesion development. [1][2][3] Several mechanisms are involved in MMinduced osteoblast suppression 1,4,7 including the production of Wnt inhibitors as DKK-1 or sFRP-2 5,6 or the impairment of osteoblast formation and differentiation through the block of the critical osteoblast transcription factor Runx2/Cbfa1. 7 In turn, osteoblastic cells also regulate myeloma cell growth 8,9 and the increase of bone formation in mice results in a reduction of tumoral burden. 10 Recent data suggest that ubiquitin-proteasome pathway, which is the major cellular degradative system and therapeutic target in myeloma cells, 11 also regulates osteoblast differentiation. [12][13][14] The ubiquitin-proteasome pathway can modulate the BMP-2 expression, 12 which can induce osteoblast differentiation through the Wnt signaling 13 and regulates the proteolytic degradation of the osteoblast transcription factor Runx2/ Cbfa1. 14 Recently, Garrett et al 12 demonstrated that proteasome inhibitors as PS1 and epoximicin stimulate bone formation in neonatal murine calvarial bones and in vivo in mice. 12 A strong correlation between the capacity of these compounds to inhibit proteasomal activity in osteoblasts and their bone-forming activity was also demonstrated. 12 Preliminary observations obtained in MM patients treated with the proteasome inhibitor bortezomib show an increase of serum bone-specific alkaline phosphatase and other osteoblast related markers suggesting a potential osteoblast stimulatory effect of this drug. [15][16][17][18] Currently it is not known whether the proteasome inhibitor bortezomib may have a direct effect on osteoblast differentiation and formation in vitro in human cultures and in vivo in MM patients. Patients, materials, and methods DrugsBortezomib was purchased from Janssen-Cilag (Milan, Italy). For in vitro studies, the drug was reconstituted in DMSO at a stock concentration of 50 mM, and this stock was diluted in medium just before use, so that the concentration of DMSO never exceeded 0.1%. The proteasome inhibitors MG-132 and MG-262 were purchased from BIOMOL International (Plymouth Meeting, PA; DBA srl, M...

Bone Anabolic Agents for the Treatment of Multiple Myeloma

“…Importantly, it has a strong anabolic activity, which relies on proteasome inhibition and partly on DKK1 downregulation [80]. The proteasome regulates RUNX2 levels via its degradation, thereby proteasome inhibition results in RUNX2 and osterix upregulation [81][82][83]. Independently from the presence of MM cells, in-vivo treatment with bortezomib stimulates MSC towards osteogenic differentiation, at the expense of adipogenesis [82].…”

The pathogenesis of the bone disease of multiple myeloma

“…In support of these observations, Bortezemib has been demonstrated to reduce tumor burden and increase BMD in myeloma-bearing mice using the SCID-rab model of myeloma, an effect associated with an increase in osteoblasts and a reduction in osteoclasts (77). Clinical studies have demonstrated significant increases in markers of bone formation, including alkaline phosphatase and osteocalcin in those patients who responded to bortezomib treatment (78)(79)(80)(81). In addition to changes in markers of bone formation, bortezomib treatment has also been shown to result in a reduction in serum Dkk1 and RANKL (82).…”

The use of biochemical markers of bone remodeling in multiple myeloma: a report of the International Myeloma Working Group

“…95 Giuliani et al found significant increases in the number of osteoblasts per mm 2 of bone tissue in trephine biopsies of patients responding to bortezomib, but not in subjects who did not respond. 96 Terpos et al showed that, in 34 patients bortezomib monotherapy reduced serum Dkk-1 and RANKL levels. This was associated with a concomitant reduction in bone resorption (serum TRACP-5b and CTX) and increase in markers of bone formation (serum bALP and OC), changes that occurred irrespective of response to therapy.…”