Pharmacologic targeting of a stem/progenitor population in vivo is associated with enhanced bone regeneration in mice.

Drug targeting of adult stem cells has been proposed as a strategy for regenerative medicine, but very few drugs are known to target stem cell populations in vivo. Mesenchymal stem/progenitor cells (MSCs) are a multipotent population of cells that can differentiate into muscle, bone, fat, and other cell types in context-specific manners. Bortezomib (Bzb) is a clinically available proteasome inhibitor used in the treatment of multiple myeloma. Here, we show that Bzb induces MSCs to preferentially undergo osteoblastic differentiation, in part by modulation of the bone-specifying transcription factor runt-related transcription factor 2 (Runx-2) in mice. Mice implanted with MSCs showed increased ectopic ossicle and bone formation when recipients received low doses of Bzb. Furthermore, this treatment increased bone formation and rescued bone loss in a mouse model of osteoporosis. Thus, we show that a tissue-resident adult stem cell population in vivo can be pharmacologically modified to promote a regenerative function in adult animals.

Clinical, radiographic, and biochemical characterization of multiple myeloma patients with osteonecrosis of the jaw.

PURPOSE: Osteonecrosis of the jaw (ONJ) has been reported in patients with a history of aminobisphosphonate use. This study was conducted in order to define ONJ clinically and radiographically and gain insights into its pathophysiology. EXPERIMENTAL DESIGN: Eleven multiple myeloma (MM) patients with ONJ were included in the study. Patients underwent clinical, biochemical, radiographic, and molecular profiling. Ten MM patients on aminobisphosphonates without ONJ and five healthy volunteers were used as controls for biochemical and molecular studies. RESULTS: MM patients with ONJ were treated with either pamidronate (n = 3), zoledronate (n = 4), or both agents sequentially (n = 4) for a mean of 38.7 months. Radiographic studies showed bone sclerosis and fragmentation on plain films and computerized tomography. Quantitative regional analysis of NaF-PET and FDG-PET scans confirmed an increased standardized uptake value (SUVmax) in areas of ONJ. The target to background ratio of SUVmax was significantly greater for NaF-PET compared with FDG-PET scan. Biochemical bone marker data and transcriptional profiling studies showed that genes and proteins involved in osteoblast and osteoclast signaling cascades were significantly down-regulated in patients with ONJ. CONCLUSIONS: ONJ was associated with a mean duration of 38.7 months of aminobisphosphonate exposure. Radiographic and functional imaging confirmed sites of clinically established ONJ. Gene and protein studies are consistent with altered bone remodeling, evidenced by suppression of both bone resorption and formation.

Neutralizing B-cell activating factor antibody improves survival and inhibits osteoclastogenesis in a severe combined immunodeficient human multiple myeloma model.

PURPOSE: B-cell-activating factor (BAFF) is a tumor necrosis factor superfamily member critical for the maintenance and homeostasis of normal B-cell development. It has been implicated in conferring a survival advantage to B-cell malignancies, including multiple myeloma (MM). EXPERIMENTAL DESIGN: Here, we validate the role of BAFF in the in vivo pathogenesis of MM examining BAFF and its receptors in the context of patient MM cells and show activity of anti-BAFF antibody in a severe combined immunodeficient model of human MM. RESULTS: Gene microarrays and flow cytometry studies showed increased transcripts and the presence of all three receptors for BAFF in CD138+ patient MM cells, as well as an increase in plasma BAFF levels in 51 MM patients. Functional studies show that recombinant BAFF protects MM cells against dexamethasone-induced apoptosis accompanied by an increase in survival proteins belonging to the BCL family. These in vitro studies led to the evaluation of a clinical grade-neutralizing antibody to BAFF in a severe combined immunodeficient human MM model. Anti-BAFF-treated animals showed decreased soluble human interleukin 6 receptor levels, a surrogate marker of viable tumor, suggesting direct anti-MM activity. This translated into a survival advantage of 16 days (P < 0.05), a decrease in tartrate-resistant acid phosphatase-positive osteoclasts, and a reduction in radiologically evident lytic lesions in anti-BAFF-treated animals. CONCLUSIONS: Our data show a role for BAFF as a survival factor in MM. Importantly, the in vivo antitumor activity of neutralizing anti-BAFF antibody provide the preclinical rationale for its evaluation in the treatment of MM.

MLN3897, a novel CCR1 inhibitor, impairs osteoclastogenesis and inhibits the interaction of multiple myeloma cells and osteoclasts.

The interaction between osteoclasts (OCs) and multiple myeloma (MM) cells plays a key role in the pathogenesis of MM-related osteolytic bone disease (OBD). MM cells promote OC formation and, in turn, OCs enhance MM cell proliferation. Chemokines are mediators of MM effects on bone and vice versa; in particular, CCL3 enhances OC formation and promotes MM cell migration and survival. Here, we characterize the effects of MLN3897, a novel specific antagonist of the chemokine receptor CCR1, on both OC formation and OC-MM cell interactions. MLN3897 demonstrates significant impairment of OC formation (by 40%) and function (by 70%), associated with decreased precursor cell multinucleation and down-regulation of c-fos signaling. OCs secrete high levels of CCL3, which triggers MM cell migration; conversely, MLN3897 abrogates its effects by inhibiting Akt signaling. Moreover, MM cell-to-OC adhesion was abrogated by MLN3897, thereby inhibiting MM cell survival and proliferation. Our results therefore show novel biologic sequelae of CCL3 and its inhibition in both osteoclastogenesis and MM cell growth, providing the preclinical rationale for clinical trials of MLN3897 to treat OBD in MM.