Peter I. Croucher

Bisphosphonates induce apoptosis in human myeloma cell lines: a novel anti-tumour activity.

Bisphosphonates are in widespread use to prevent bone resorption in a number of metabolic and tumour‐induced bone diseases including multiple myeloma. Recent reports suggest that bisphosphonate treatment may be associated with an increase in patient survival, raising the possibility that these compounds may have a direct effect on the tumour cells. We have investigated whether the bisphosphonates clodronate, pamidronate and YM175 can directly affect the human myeloma cell lines U266‐B1, JJN‐3 and HS‐Sultan in vitro. The effect of bisphosphonate treatment on cell number and cell cycle progression was examined using flow cytometry. The ability of bisphosphonates to induce apoptosis in human myeloma cell lines was determined on the basis of changes in nuclear morphology and of DNA fragmentation. Pamidronate and the more potent bisphosphonate, YM175, significantly decreased cell number (P < 0.001) in JJN‐3 and HS‐Sultan cells. YM175 also caused cells to arrest in the S‐phase of the cell cycle in the JJN‐3 cell line. Both pamidronate and YM175 also caused an increase in the proportion of cells with altered nuclear morphology (P < 0.05) and fragmented DNA, characteristic of apoptosis, in both JJN‐3 and HS‐Sultan cells. In contrast, clodronate had little effect on cell number and did not cause apoptosis at the concentrations examined. These data raise the possibility that some bisphosphonates could have direct anti‐tumour effects on human myeloma cells in vivo.

The bisphosphonate, zoledronic acid, induces apoptosis of breast cancer cells: evidence for synergy with paclitaxel.

Bisphosphonates are well established in the management of breast-cancer-induced bone disease. Recent studies have suggested that these compounds are effective in preventing the development of bone metastases. However, it is unclear whether this reflects an indirect effect via an inhibition of bone resorption or a direct anti-tumour effect. The breast cancer cell lines, MCF-7 and MDA-MB-231 cells were treated with increasing concentrations of the bisphosphonate, zoledronic acid, for varying time periods, in the presence or absence of paclitaxel. The effects of zoledronic acid were determined by assessing cell number and rate of apoptosis by evaluating changes in nuclear morphology and using a fluorescence nick translation assay. Zoledronic acid caused a dose- and time-dependent decrease in cell number (P< 0.001) and a concomitant increase in tumour cell apoptosis (P< 0.005). Short-term exposure to zoledronic acid was sufficient to cause a significant reduction in cell number and increase in apoptosis (P< 0.05). These effects could be prevented by incubation with geranyl geraniol, suggesting that zoledronic acid-induced apoptosis is mediated by inhibiting the mevalonate pathway. Treatment with zoledronic acid and clinically achievable concentrations of paclitaxel resulted in a 4–5-fold increase in tumour cell apoptosis (P< 0.02). Isobologram analysis revealed synergistic effects on tumour cell number and apoptosis when zoledronic acid and paclitaxel were combined. Short-term treatment with zoledronic acid, which closely resembles the clinical setting, has a clear anti-tumour effect on breast cancer cells. Importantly, the commonly used anti-neoplastic agent, paclitaxel, potentiates the anti-tumour effects of zoledronic acid. These data suggest that, in addition to inhibiting bone resorption, zoledronic acid has a direct anti-tumour activity on breast cancer cells in vitro.

Zoledronic acid treatment of 5T2MM-bearing mice inhibits the development of myeloma bone disease: evidence for decreased osteolysis, tumor burden and angiogenesis, and increased survival.

Multiple myeloma is characterized by the growth of plasma cells in the bone marrow and the development of osteolytic bone disease. Myeloma cells are found closely associated with bone, and targeting this environment may therefore affect both the bone disease and the growth of myeloma cells. We have investigated the effect of the potent bisphosphonate, zoledronic acid, on the development of bone disease, tumor burden, and disease‐free survival in the 5T2MM model of myeloma. 5T2MM murine myeloma cells were injected intravenously into C57BL/KaLwRij mice. After 8 weeks, all animals had a paraprotein. Animals were treated with zoledronic acid (120 μg/kg, subcutaneously, twice weekly) or vehicle, from the time of tumor cell injection or from paraprotein detection for 12 or 4 weeks, respectively. All animals injected with tumor cells developed osteolytic lesions, a decrease in cancellous bone volume, an increase in osteoclast perimeter, and a decrease in bone mineral density. Zoledronic acid prevented the formation of lesions, prevented cancellous bone loss and loss of bone mineral density, and reduced osteoclast perimeter. Zoledronic acid also decreased paraprotein concentration, decreased tumor burden, and reduced angiogenesis. In separate experiments, Kaplan‐Meier analysis demonstrated a significant increase in survival after treatment with zoledronic acid when compared with control (47 vs. 35 days). A single dose of zoledronic acid was also shown to be effective in preventing the development of osteolytic bone disease. These data show that zoledronic acid is able to prevent the development of osteolytic bone disease, decrease tumor burden in bone, and increase survival in a model of established myeloma.

Bisphosphonates: pharmacology, mechanisms of action and clinical uses.

The bisphosphonates represent a novel class of drugs, the use of which have opened up major new approaches to the therapy of bone diseases. It has, however, taken over 30 years since the discovery of their profound effects on calcium metabolism for them to become well established as clinically successful antiresorptive agents. There are several useful recent reviews of the chemistry, pharmacology and clinical applications of bisphosphonates [1–11]. Several bisphosphonates, including etidronate, clodronate, tiludronate, pamidronate, alendronate, risedronate and ibandronate, have been registered for various clinical applications in various countries. Although it is different for each compound, these include use as agents for bone scanning and as drugs for the treatment of Paget’s disease, hypercalcemia of malignancy, bone metastases and osteoporosis. Those most used in cancer are pamidronate given parenterally, or clodronate given orally. In osteoporosis the major drugs are etidronate and alendronate, which are approved therapies in many countries. Bisphosphonates used as inhibitors of bone resorption all contain two phosphonate groups attached to a single carbon atom, to give a ‘P–C–P’ structure. The bisphosphonates are therefore stable analogs of naturally occurring pyrophosphate compounds, which now helps to explain their intracellular as well as their extracellular modes of action. The mechanism of action of bisphosphonates was originally ascribed to their ability to adsorb strongly to hydroxyapatite crystals, and to inhibit their growth and dissolution [12,13]. It has gradually become clear that this explanation is insufficient to account for all their effects, and cellular actions are involved, particularly with the more potent compounds. The Early Development of Bisphosphonates

Bortezomib reduces serum dickkopf-1 and receptor activator of nuclear factor-κB ligand concentrations and normalises indices of bone remodelling in patients with relapsed multiple myeloma

The effect of bortezomib on bone remodelling was evaluated in 34 relapsed myeloma patients. At baseline, patients had increased serum concentrations of dickkopf‐1 (DKK‐1), soluble receptor activator of nuclear factor‐κB ligand (sRANKL), sRANKL/osteoprotegerin ratio, C‐telopeptide of type‐I collagen (CTX) and tartrate‐resistant acid phosphatase isoform‐5b (TRACP‐5b); bone‐alkaline phosphatase and osteocalcin were reduced. Serum DKK‐1 correlated with CTX and severe bone disease. Bortezomib administration significantly reduced serum DKK‐1, sRANKL, CTX, and TRACP‐5b after four cycles, and dramatically increased bone‐alkaline phosphatase and osteocalcin, irrespective of treatment response. This is the first study showing that bortezomib reduces DKK‐1 and RANKL serum levels, leading to the normalisation of bone remodelling in relapsed myeloma.

The use of bisphosphonates in multiple myeloma: recommendations of an expert panel on behalf of the European Myeloma Network

BACKGROUND Bisphosphonates (BPs) prevent, reduce, and delay multiple myeloma (MM)-related skeletal complications. Intravenous pamidronate and zoledronic acid, and oral clodronate are used for the management of MM bone disease. The purpose of this paper is to review the current evidence for the use of BPs in MM and provide European Union-specific recommendations to support the clinical practice of treating myeloma bone disease. DESIGN AND METHODS An interdisciplinary, expert panel of specialists on MM and myeloma-related bone disease convened for a face-to-face meeting to review and assess the evidence and develop the recommendations. The panel reviewed and graded the evidence available from randomized clinical trials, clinical practice guidelines, and the body of published literature. Where published data were weak or unavailable, the panel used their own clinical experience to put forward recommendations based solely on their expert opinions. RESULTS The panel recommends the use of BPs in MM patients suffering from lytic bone disease or severe osteoporosis. Intravenous administration may be preferable; however, oral administration can be considered for patients unable to make hospital visits. Dosing should follow approved indications with adjustments if necessary. In general, BPs are well tolerated, but preventive steps should be taken to avoid renal impairment and osteonecrosis of the jaw (ONJ). The panel agrees that BPs should be given for 2 years, but this may be extended if there is evidence of active myeloma bone disease. Initial therapy of ONJ should include discontinuation of BPs until healing occurs. BPs should be restarted if there is disease progression. CONCLUSIONS BPs are an essential component of MM therapy for minimizing skeletal morbidity. Recent retrospective data indicate that a modified dosing regimen and preventive measures can greatly reduce the incidence of ONJ.

Inhibiting Dickkopf-1 (Dkk1) removes suppression of bone formation and prevents the development of osteolytic bone disease in multiple myeloma.

Multiple myeloma (MM) is associated with the development of osteolytic bone disease, mediated by increased osteoclastic bone resorption and impaired osteoblastic bone formation. Dickkopf‐1 (Dkk1), a soluble inhibitor of wingless/int (Wnt) signaling and osteoblastogenesis, is elevated in patients with MM and correlates with osteolytic bone disease. In this study, we investigated the effect of inhibiting Dkk1 on the development of osteolytic lesions in the 5T2MM murine model of myeloma. We showed that Dkk1 is expressed by murine 5T2MM myeloma cells. Injection of 5T2MM cells into C57BL/KaLwRij mice resulted in the development of osteolytic bone lesions (p < 0.05), mediated by increased osteoclast numbers (p < 0.001) and a decrease in osteoblast numbers (p < 0.001) and mineralizing surface (p < 0.05). Mice bearing 5T2MM cells were treated with an anti‐Dkk1 antibody (BHQ880, 10 mg/kg, IV, twice weekly for 4 wk) from time of paraprotein detection. Anti‐Dkk1 treatment prevented 5T2MM‐induced suppression of osteoblast numbers (p < 0.001) and surface (p < 0.001). Treatment increased mineralizing surface by 28% and bone formation rate by 25%; however, there was no change in mineral apposition rate. Inhibiting Dkk1 had no effect on osteoclast numbers. μCT analysis showed that anti‐Dkk1 treatment significantly protected against 5T2MM‐induced trabecular bone loss (p < 0.05) and reduced the development of osteolytic bone lesions (p < 0.05). Treatment had no significant effect on tumor burden. These data suggest that inhibiting Dkk1 prevents the suppression of bone formation and in doing so is effective in preventing the development of osteolytic bone disease in myeloma, offering an effective therapeutic approach to treating this clinically important aspect of myeloma.

Serum concentrations of Dickkopf-1 protein are increased in patients with multiple myeloma and reduced after autologous stem cell transplantation.

Dickkopf‐1 (DKK‐1) protein, a soluble inhibitor of Wnt signalling, has been implicated in the pathogenesis of myeloma bone disease through the suppression of osteoblast differentiation. In this study, serum concentrations of DKK‐1 were measured in 50 myeloma patients (32 at diagnosis and 18 before and after autologous stem cell transplantation (ASCT), 18 patients with monoclonal gammopathy of undetermined significance (MGUS), and 22 healthy controls. Serum DKK‐1 levels were increased in MM at diagnosis compared with MGUS (mean ± SD: 67 ± 54 ng/mL vs. 38 ± 13 ng/mL; p = 0.006) and controls (31 ± 11 ng/mL; p = 0.02), while there was no difference between MGUS patients and controls. Although patients with stage 2 and 3 myeloma had higher DKK‐1 values than stage 1 patients (79 ± 63 vs. 40 ± 13; p = 0.005), no significant correlation between serum DKK‐1 and myeloma bone disease was observed. Myeloma patients before ASCT also had increased levels of DKK‐1 (63 ± 77 ng/mL; p = 0.03) compared with controls, supporting the notion that DKK‐1 may be responsible for the suppressed osteoblast activity even in patients with low tumor burden. After ASCT, there was a sustained decrease in DKK‐1 levels over time, while bone formation markers elevated, suggesting that the reduction of DKK‐1 levels after ASCT may correlate with the normalization of osteoblast function. These results could provide the basis for developing agents that block DKK‐1, thus restoring osteoblast function and counteracting the increased osteoclastogenesis observed in myeloma.

Structural mechanisms of trabecular bone loss in man.

The relationship between trabecular thinning and loss of connectedness of the trabecular bone pattern has been studied in iliac crest bone samples from 89 normal subjects in order to determine the structural mechanisms underlying age-related bone loss. Trabecular width and structure were quantitatively assessed using computerized techniques. Highly significant negative correlations were found between the mean trabecular plate thickness and number of free ends/mm2 both in males (r = -0.571) and in females (r = -0.667) (P less than 0.001). Mean trabecular plate thickness also showed significant negative correlations with other structural indices indicating reduced connectedness, whereas positive correlations were found with those indices representing preservation of connectedness. Examination of the relative frequency of trabecular widths less than 100 microns revealed that only 2-5% of the trabecular surface would be susceptible to erosion by a resorption cavity of normal depth. These results indicate that trabecular thinning and erosion are interdependent processes in age-related bone loss. Since only a small percentage of the trabecular surface is susceptible to erosion, and resorption cavities normally occupy only 1-5% of the total trabecular surface, these findings imply that the site of activation of new BMUs may not be randomly distributed but may instead be preferentially located at sites of lower trabecular width.

Inhibiting activin-A signaling stimulates bone formation and prevents cancer-induced bone destruction in vivo.

Cancers that grow in bone, such as myeloma and breast cancer metastases, cause devastating osteolytic bone destruction. These cancers hijack bone remodeling by stimulating osteoclastic bone resorption and suppressing bone formation. Currently, treatment is targeted primarily at blocking bone resorption, but this approach has achieved only limited success. Stimulating osteoblastic bone formation to promote repair is a novel alternative approach. We show that a soluble activin receptor type IIA fusion protein (ActRIIA.muFc) stimulates osteoblastogenesis (p < .01), promotes bone formation (p < .01) and increases bone mass in vivo (p < .001). We show that the development of osteolytic bone lesions in mice bearing murine myeloma cells is caused by both increased resorption (p < .05) and suppression of bone formation (p < .01). ActRIIA.muFc treatment stimulates osteoblastogenesis (p < .01), prevents myeloma‐induced suppression of bone formation (p < .05), blocks the development of osteolytic bone lesions (p < .05), and increases survival (p < .05). We also show, in a murine model of breast cancer bone metastasis, that ActRIIA.muFc again prevents bone destruction (p < .001) and inhibits bone metastases (p < .05). These findings show that stimulating osteoblastic bone formation with ActRIIA.muFc blocks the formation of osteolytic bone lesions and bone metastases in models of myeloma and breast cancer and paves the way for new approaches to treating this debilitating aspect of cancer.