NVP-BEZ235, a dual pan class I PI3 kinase and mTOR inhibitor, promotes osteogenic differentiation in human mesenchymal stromal cells

Abstract

Osteoblasts are bone-forming cells derived from mesenchymal stromal cells (MSCs) that reside within the bone marrow. In response to a variety of factors, MSCs proliferate and differentiate into mature, functional osteoblasts. Several studies have shown previously that suppression of the PI3K and mTOR signaling pathways in these cells strongly promotes osteogenic differentiation, which suggests that inhibitors of these pathways may be useful as anabolic bone agents. In this study we examined the effect of BEZ235, a newly developed dual PI3K and mTOR inhibitor currently in phase I-II clinical trials for advanced solid tumors, on osteogenic differentiation and function using primary MSC cultures. Under osteoinductive conditions, BEZ235 strongly promotes osteogenic differentiation, as evidenced by an increase in mineralized matrix production, an upregulation of genes involved in osteogenesis, including bone morphogenetic proteins (BMP2, -4, and -6) and transforming growth factor b1 (TGF-b1) superfamily members (TGFB1, TGFB2, and INHBE), and increased activation of SMAD signaling molecules. In addition, BEZ235 enhances de novo bone formation in calvarial organotypic cultures. Using pharmacologic inhibitors to delineate mechanism, our studies reveal that suppression of mTOR and, to a much lesser extent PI3K p110a, mediates the osteogenic effects of BEZ235. As confirmation, shRNA-mediated knockdown of mTOR enhances osteogenic differentiation and function in SAOS-2 osteoblast-like cells. Taken together, our findings suggest that BEZ235 may be useful in treating PI3K/mTOR-dependent tumors associated with bone loss, such as the hematologic malignancy multiple myeloma. ß

Suppression of PDGF-induced PI3 kinase activity by imatinib promotes adipogenesis and adiponectin secretion

“…However, we failed to detect activation of these pathways in response to PDGF in bone marrow-derived MSCs (data not shown), which may be due to cell-type differences or the PDGF isoform used. In hMSCs, PDGF strongly activates the PI3 kinase pathway and previous studies have suggested that the anti-differentiative effects of PDGF could be inhibited using PI3 kinase inhibitors such as Wortmannin and LY94002 (Kratchmarova et al 2005, Fitter et al 2008, Martin et al 2010. Consistent with this view, we have demonstrated that imatinib is a potent inhibitor of PDGF-induced Akt phosphorylation, a major substrate of the PI3 kinase pathway.…”

“…Suppression of PI3 kinase using pharmacological inhibitors has been shown to promote MSC differentiation (Kratchmarova et al 2005, Fitter et al 2008, Martin et al 2010, suggesting that this pathway is important for transducing the inhibitory effects of PDGF on MSC differentiation. Consistent with this hypothesis, imatinib is a potent inhibitor of PDGF-induced PI3 kinase activation, as evidenced by a dose-dependent decrease in the phosphorylation of Akt (Fig.…”

mTOR inhibition rescues osteopenia in mice with systemic sclerosis

“…Normally, FBN1 is abundant in the connective tissue of the aorta, ligature of the human eye lens, bones, and lungs. Lee et al, 2010b;Martin et al, 2010) osteogenesis, depending on cell type or differentiation stages. Recently, it has been reported that bone matrix secretes IGF-1 (insulin-like growth factor-1) to recruit normal BMMSCs for bone remodeling by activating mTOR signaling (Xian et al, 2012), indicating that mTOR may contribute to the activation of different sets of biological regulatory controls under certain conditions.…”

Defining the role of TORC1/2 in multiple myeloma

“…[5][6][7][8][9][10][11][12][13] MM is frequently associated with dysregulation and/or mutations of signaling genes such as RAS, PTEN, FGF, c-Myc, and CDKN pathways. [6][7][8][9][10][11][12][13] These pathways often signal via TORC1/2 to regulate protein translation and cytoskeletal dynamics that are collectively required for cell division, growth, motility, and survival. [6][7][8][9][10][11][12][13] Recent reports have shown that Deptor is an mTORinteracting protein that is highly overexpressed in MM with cyclin D1/D3 (t:11;14 and t:6;14) or c-MAF/MAFB translocations (t: 14; 16), which are present in 30% of MM patients.…”

“…Although no mutations are present in PI3K/AKT genes, this pathway is activated in the majority of patients with MM through either external signaling from insulin growth factor 1 (IGF-1), receptor tyrosine kinases (RTKs), or other dysregulations, including genetic mutations in other pathways or epigenetics that lead to activation of this pathway. [5][6][7][8][9][10][11][12][13] MM is frequently associated with dysregulation and/or mutations of signaling genes such as RAS, PTEN, FGF, c-Myc, and CDKN pathways. [6][7][8][9][10][11][12][13] These pathways often signal via TORC1/2 to regulate protein translation and cytoskeletal dynamics that are collectively required for cell division, growth, motility, and survival.…”