**6. Treatment of multiple myeloma bone disease**

#### **6.1. Anti-resorptive treatments:**

Until now, bisphosphonates remain the only registered agents for the treatment of osteolytic bone disease in MM. Bisphosphonates are synthetic analogues of pyrophosphate with a high affinity for the hydroxyapatite in the bone. After administration, bisphosphonates are rapidly cleared from the blood and incorporated into the bone matrix or excreted through the kidneys. If imbedded in the bone matrix they remain incorporated for many years, or until the bone is degraded by the osteoclasts [59]. Three generations of bisphosphonates exist, and each is many fold more potent than the previous [60]. The different bisphosphonates can be distinguished by the absence or presences of a nitrogen atom in the R2 position of the bisphosphonate, with the amino-bisphosphonates being the most potent. When the osteoclast degrades bone, the bisphosphonate is taken up through endocytosis and causes apoptosis either through the incorporation into non-functional adenosine triphosphate (non-nitrogen containing bi‐ sphosphonates), or through the inhibition of farnesyl pyrophosphate synthase (nitrogen containing bisphosphonates)[61]. Early studies, using the least potent bisphosphonate, etidronate, showed no clinical benefit on MM bone disease [62], whereas the slightly more potent clodronate could diminish progression of osteolysis, but had no effect on bone pain or pathological fractures [63]. In 1996 and 1998, Berenson *et al.* published two studies, in which patients were randomised to placebo or the amino-bisphosphonate pamidronate. A significant effect was observed with regard to reduced pain, fewer skeletal related events, and improved quality of life [64;65]. Initially, no effect could be observed in overall survival, however using a Cox multivariable regression analysis a slight increase in overall survival was observed for a subgroup of patients. A subsequent phase III trial, comparing the more potent bisphonate zoledronic acid with pamidronate in breast cancer patients with bone metastases and MM patients, demonstrated a superiority of zoledronic acid over pamidronate in reducing skeletal events in the breast cancer group but not in the MM sub-population. No difference was observed in overall survival [66]. Later publications indicated that there could be an effect on overall survival but only with the most potent bisphosphonates [67-70]. In 2010 a large metaanalysis concluded that there was no effect on overall survival in MM provided by bisphosph‐ onates in general [71]. However, later the same year the large MRC IX trial, reported that zoledronic acid was superior to the non-nitrogen containing bisphosphonate clodronate, not only with regard to the control of bone disease, but zoledronic acid also increased overall survival by 5.5 months [49]. Because of the MRC IX data, an updated version of the metaanalysis was published in 2012. Still, no significant effect on overall survival was observed for bisphosphonates in general, but "meta regression analysis indicated that the beneficial effect of bisphosphonates on mortality in patients with MM may be a function of drug potency, with zoledronate being the most potent" [72].

Bisphosphonates are potential nephrotoxic compounds and dosage adjustment according to creatinine clearance are required [73].

**6. Treatment of multiple myeloma bone disease**

collagen breakdown

224 Multiple Myeloma - A Quick Reflection on the Fast Progress

**NTX, CTX, ICTP, DPD PINP, PICP**

*osteoclast cell* 

by the absence or presences of a nitrogen atom in the R2

Until now, bisphosphonates remain the only registered agents for the treatment of osteolytic bone disease in MM. Bisphosphonates are synthetic analogues of pyrophosphate with a high affinity for the hydroxyapatite in the bone. After administration, bisphosphonates are rapidly cleared from the blood and incorporated into the bone matrix or excreted through the kidneys. If imbedded in the bone matrix they remain incorporated for many years, or until the bone is degraded by the osteoclasts [59]. Three generations of bisphosphonates exist, and each is many fold more potent than the previous [60]. The different bisphosphonates can be distinguished

**BONE RESORPTION BONE FORMATION**

**Figure 3.** Biochemical markers of bone remodelling can be divided into markers reflecting bone resorption (left) and marker reflecting bone formation (right). They can also be divided in markers reflecting a change in the collagen ma‐

trix (upper part) or markers reflecting the activity of bone resorbing or bone forming cells (lower part).

**TRACP5b bALP** 

procollagen

*osteoblast cell* 

**OC**

the amino-bisphosphonates being the most potent. When the osteoclast degrades bone, the bisphosphonate is taken up through endocytosis and causes apoptosis either through the incorporation into non-functional adenosine triphosphate (non-nitrogen containing bi‐ sphosphonates), or through the inhibition of farnesyl pyrophosphate synthase (nitrogen containing bisphosphonates)[61]. Early studies, using the least potent bisphosphonate, etidronate, showed no clinical benefit on MM bone disease [62], whereas the slightly more potent clodronate could diminish progression of osteolysis, but had no effect on bone pain or

position of the bisphosphonate, with

**6.1. Anti-resorptive treatments:**

In 2003, it was reported for the first time, that exposure to bisphosphonates could also cause osteonecrotic lesions, especially in the oral cavity. This complication was termed bisphosph‐ onate-associated osteonecrosis of the jaw (BON) [74]. BON is commonly observed after surgical dental procedures, e.g. tooth extractions, but spontaneous cases do occur [75]. The incidence of BON increases with treatment duration [76], as well as with the potency of the bisphosph‐ onate used [77]. The aetiology of BON remains controversial. One possible explanation could be that the profound suppression of osteoclast activity results in the accumulation of micro‐ fractures in the bone. This explanation is in accordance with the fact that BON incidence increases with treatment duration and potency of bisphosphonate type and that BON is also observed after treatment with denosumab, a monoclonal antibody that inhibits osteoclast activity by binding to RANKL. It has also been suggested that BON may occur because of the anti-angiogenic effects of bisphosphonates [78]. Indeed, BON seems to be more commonly observed in patients receiving other anti-angiogentic compounds such as thalidomide [77]. Thirdly, it has been speculated that the frequent findings of actinomycosis in the lesions may be part of the pathogenesis and not only a secondary event, especially since prophylactic antibiotics during dental procedures seem to reduce the incidence of BON [79]. Recently, osteomalacia, which in adults is often a consequence of vitamin D deficiency, has been suggested as a risk factor for BON [80]. Once established BON is difficult to cure, and surgical treatment may worsen the situation [75]. Case-reports suggest several treatment modalities, including low-level laser therapy [81;82], hyperbaric oxygen treatment [83], long-term administration of antibiotics [84], autologous bone marrow transplantation [85], and ozone therapy [86]. Because of the difficulties in treating BON, focus has mainly been on preventing the occurrence in the first place. This has been done partly by implementing preventive dental procedures prior to the initiation of therapy with bisphosphonates, but probably more importantly by reducing the exposure time to bisphosphonates. The oral microflora also seems to play a role in the development of BON and antibiotic prophylaxis before dental procedure may reduce the risk of developing BON [79]. Concerning the preventive procedures, there are data indicating a positive effect [87;88]. Concerning the reduced exposure time there are few supportive data, but recommendations based on expert opinion do exist [89-92]. Corso *et al*. demonstrated that monthly infusions for one year followed by four infusions the following year offered equal bone protection but reduced BON incidence compared to the monthly infusions for two years [93]. Lund *et al.* have provided evidence that one year of monthly infusions offers inferior anti-resorptive protection after discontinuation compared with two years of monthly infusions based on consecutive measurement of markers of bone turnover [57]. A more rational approach to reduce the bisphosphonate load without increasing the risk of osteolysis, could be to monitor the patient´s ongoing bone remodelling using biochemical markers of bone turnover in order to provide individualized treatment. Data now exist which indicate that bone remodelling markers may predict osteolysis before it becomes manifest by X-ray or CT-scan [94].

treatment of bone disease in patients with renal failure who are not suitable for treatment with

Bone Disease in Multiple Myeloma http://dx.doi.org/10.5772/55190 227

Several drugs targeting MM bone disease are under development e.g. the CCR1-inhibitor (MLN3897) that blocks the CCR1 receptor on osteoclasts and thereby prevents stimulation by MIP-1α [102]. Another candidate for the treatment of MM bone disease is the anti-DKK1 human antibody BHQ880. The agent has been shown to increase osteoblast differentiation in vivo and in animal models to significantly increase the number of osteoblasts and trabecular thickness [103]. Whether this bone anabolic effect will be found in humans will be of interest because it raises the possibility for not only preventing bone loss, but also supporting new

Treatment of MM using conventional chemotherapy usually does not induce healing of osteolytic lesions even if patients respond well to the anti-myeloma treatment and obtain long progression free periods [105-107]. Although markers of bone resorption may decrease [55] serum levels of bone formation markers remain suppressed as a sign of continuously impaired bone formation even in patients who have obtained complete response after treatment with

Proteasome inhibitors have a well-documented anti-myeloma effect and they may also have an impact on MM bone disease through the inhibition of osteoclasts and stimulation of

In vitro studies have demonstrated that proteasome inhibitors inhibit osteoclast differentiation and resorptive activity by reducing the activity of NF-κB [109;110]. In vivo studies of the effect of bortezomib on bone resorption markers show a rapid and significant decrease in CTX and urinary NTX, but it has also been observed that the levels begin to increase again already 2-3 days after the intravenous injection of bortezomib [111]. The levels of the bone resorption markers CTX and TRACP-5b and the RANKL/OPG ratio were also found to decrease after four cycles of treatment with bortezomib in a clinical study including 34 myeloma patients [112]. The ubiquitin-proteolytic pathway is a regulator of bone formation [113] and by blocking this pathway proteasome inhibitors can stimulate osteoblast differentiation. Suggestions of the underlying mechanism have been that proteasome inhibitors may increase the level of bone morphogenetic protein 2 [114] and prevent the proteolytic degradation of RUNX-2 [115]. In an in vitro study, it has been suggested the bortezomib may enhance bone formation through the inhibition of DKK1 expression in osteogenic cells [116]. More studies have provided evidence that proteasome inhibitors stimulate osteoblasts and bone formation in vitro as well as in animals models [114;116-118], and histological investigations have demonstrated increased numbers of osteoblasts in bone marrow sections from MM patient treated with bortezomib [115]. Clinical studies have demonstrated that anti-myeloma treatment with bortezomib induces an increased level of biochemical markers of bone formation both with

bisphosphonates due to the risk of aggravation of renal function.

bone formation. Clinical trials with BHQ880 are ongoing [104].

**6.3. Anti-myeloma treatments**

conventional chemotherapy [56;108].

osteoblasts.

**6.2. Possible future anti-resorptive drug treatments**

Denosumab is a humanized antibody with high affinity for RANKL. By targeting RANKL, denosumab mimics physiological OPG and thus blocks the stimulation of the osteoclasts through the NF-κB receptor. Denosumab could be expected to have a favourable impact on MM bone disease due to its effect on the increased RANKL/OPG ratio observed in MM patients. In 2006 Body *et al.* published a study investigating the effect of a single dose of subcutaneous denosumab compared with a single dose of intravenous pamidronate on the urinary and serum levels of the bone resorption marker NTX. The study population consisted of 54 patients with bone lesions and either MM (n=25) or breast cancer (n=29). The study reported that the compounds were well-tolerated and to a similar extent decreased the investigated bone resorption marker NTX [95]. A phase II study including 96 MM patients, in either relapse or plateau phase, where denosumab was administered every fourth week also demonstrated a decrease in bone resorption markers, even in patients previously treated with bisphosphonates, with an acceptable safety profile [96]. In a phase III trial patients (n=1776) with cancer bone metastases (excluding breast and prostate cancer) or MM (10% of the study population) were randomized to treatment with either zoledronic acid or denosumab. Denosumab was found to be equivalent to zoledronic acid in delaying time to first on-study skeletalrelated event. Noteworthy, in a subgroup analysis of the MM patients (n=180), mortality appeared to be increased in those treated with denosumab with a hazard ratio of 2.26 (95% CI: 1.13-4.50) [97]. Recently, new data from this trial has been published. Results of patient-reported outcomes of pain and health-related quality of life were reported to be equal in the two treatments arms [98]. The frequency of osteonecrosis of the jaw seemed to be equal for treatment with denosumab or zoledronic acid [97;99]. Denosumab is currently not regis‐ tered for the treatment of MM bone disease by US Food and Drug Administration or the European Medicines Agency. [100;101], but it could perhaps in the future be used for the treatment of bone disease in patients with renal failure who are not suitable for treatment with bisphosphonates due to the risk of aggravation of renal function.

#### **6.2. Possible future anti-resorptive drug treatments**

Several drugs targeting MM bone disease are under development e.g. the CCR1-inhibitor (MLN3897) that blocks the CCR1 receptor on osteoclasts and thereby prevents stimulation by MIP-1α [102]. Another candidate for the treatment of MM bone disease is the anti-DKK1 human antibody BHQ880. The agent has been shown to increase osteoblast differentiation in vivo and in animal models to significantly increase the number of osteoblasts and trabecular thickness [103]. Whether this bone anabolic effect will be found in humans will be of interest because it raises the possibility for not only preventing bone loss, but also supporting new bone formation. Clinical trials with BHQ880 are ongoing [104].

#### **6.3. Anti-myeloma treatments**

administration of antibiotics [84], autologous bone marrow transplantation [85], and ozone therapy [86]. Because of the difficulties in treating BON, focus has mainly been on preventing the occurrence in the first place. This has been done partly by implementing preventive dental procedures prior to the initiation of therapy with bisphosphonates, but probably more importantly by reducing the exposure time to bisphosphonates. The oral microflora also seems to play a role in the development of BON and antibiotic prophylaxis before dental procedure may reduce the risk of developing BON [79]. Concerning the preventive procedures, there are data indicating a positive effect [87;88]. Concerning the reduced exposure time there are few supportive data, but recommendations based on expert opinion do exist [89-92]. Corso *et al*. demonstrated that monthly infusions for one year followed by four infusions the following year offered equal bone protection but reduced BON incidence compared to the monthly infusions for two years [93]. Lund *et al.* have provided evidence that one year of monthly infusions offers inferior anti-resorptive protection after discontinuation compared with two years of monthly infusions based on consecutive measurement of markers of bone turnover [57]. A more rational approach to reduce the bisphosphonate load without increasing the risk of osteolysis, could be to monitor the patient´s ongoing bone remodelling using biochemical markers of bone turnover in order to provide individualized treatment. Data now exist which indicate that bone remodelling markers may predict osteolysis before it becomes manifest by

Denosumab is a humanized antibody with high affinity for RANKL. By targeting RANKL, denosumab mimics physiological OPG and thus blocks the stimulation of the osteoclasts through the NF-κB receptor. Denosumab could be expected to have a favourable impact on MM bone disease due to its effect on the increased RANKL/OPG ratio observed in MM patients. In 2006 Body *et al.* published a study investigating the effect of a single dose of subcutaneous denosumab compared with a single dose of intravenous pamidronate on the urinary and serum levels of the bone resorption marker NTX. The study population consisted of 54 patients with bone lesions and either MM (n=25) or breast cancer (n=29). The study reported that the compounds were well-tolerated and to a similar extent decreased the investigated bone resorption marker NTX [95]. A phase II study including 96 MM patients, in either relapse or plateau phase, where denosumab was administered every fourth week also demonstrated a decrease in bone resorption markers, even in patients previously treated with bisphosphonates, with an acceptable safety profile [96]. In a phase III trial patients (n=1776) with cancer bone metastases (excluding breast and prostate cancer) or MM (10% of the study population) were randomized to treatment with either zoledronic acid or denosumab. Denosumab was found to be equivalent to zoledronic acid in delaying time to first on-study skeletalrelated event. Noteworthy, in a subgroup analysis of the MM patients (n=180), mortality appeared to be increased in those treated with denosumab with a hazard ratio of 2.26 (95% CI: 1.13-4.50) [97]. Recently, new data from this trial has been published. Results of patient-reported outcomes of pain and health-related quality of life were reported to be equal in the two treatments arms [98]. The frequency of osteonecrosis of the jaw seemed to be equal for treatment with denosumab or zoledronic acid [97;99]. Denosumab is currently not regis‐ tered for the treatment of MM bone disease by US Food and Drug Administration or the European Medicines Agency. [100;101], but it could perhaps in the future be used for the

X-ray or CT-scan [94].

226 Multiple Myeloma - A Quick Reflection on the Fast Progress

Treatment of MM using conventional chemotherapy usually does not induce healing of osteolytic lesions even if patients respond well to the anti-myeloma treatment and obtain long progression free periods [105-107]. Although markers of bone resorption may decrease [55] serum levels of bone formation markers remain suppressed as a sign of continuously impaired bone formation even in patients who have obtained complete response after treatment with conventional chemotherapy [56;108].

Proteasome inhibitors have a well-documented anti-myeloma effect and they may also have an impact on MM bone disease through the inhibition of osteoclasts and stimulation of osteoblasts.

In vitro studies have demonstrated that proteasome inhibitors inhibit osteoclast differentiation and resorptive activity by reducing the activity of NF-κB [109;110]. In vivo studies of the effect of bortezomib on bone resorption markers show a rapid and significant decrease in CTX and urinary NTX, but it has also been observed that the levels begin to increase again already 2-3 days after the intravenous injection of bortezomib [111]. The levels of the bone resorption markers CTX and TRACP-5b and the RANKL/OPG ratio were also found to decrease after four cycles of treatment with bortezomib in a clinical study including 34 myeloma patients [112]. The ubiquitin-proteolytic pathway is a regulator of bone formation [113] and by blocking this pathway proteasome inhibitors can stimulate osteoblast differentiation. Suggestions of the underlying mechanism have been that proteasome inhibitors may increase the level of bone morphogenetic protein 2 [114] and prevent the proteolytic degradation of RUNX-2 [115]. In an in vitro study, it has been suggested the bortezomib may enhance bone formation through the inhibition of DKK1 expression in osteogenic cells [116]. More studies have provided evidence that proteasome inhibitors stimulate osteoblasts and bone formation in vitro as well as in animals models [114;116-118], and histological investigations have demonstrated increased numbers of osteoblasts in bone marrow sections from MM patient treated with bortezomib [115]. Clinical studies have demonstrated that anti-myeloma treatment with bortezomib induces an increased level of biochemical markers of bone formation both with regard to markers of osteoblast activation and also bone matrix deposition [118;119]. Alkaline phosphatase was found to be significantly increased in patients who responded to bortezomib treatment [119]. In another clinical study bone-specific alkaline phophatase (bALP) and osteocalcin were found to be increased not only in responding patients, but also in patients who did not achieve an anti-myeloma response to treatment with bortezomib [120]. This result supports the assumption that bortezomib may have a bone anabolic effect independent of its anti-myeloma effect. Enhancement of bone matrix deposition after mono-therapy with bortezomib, has also been shown by the demonstration of increased serum levels of PINP (Procollagen Type-I N-terminal propeptide) [118]. Both bALP and osteocalcin were found to be increased after treatment with bortezomib in a clinical study of 34 relapsed myeloma patients in non-responders and responders but the increase was highest in responding patients. However no radiographic signs of healing of the baseline osteolytic lesions were observed six month post-treatment [112]. Radiologic evidence of healing of lytic lesions was observed in six out of 11 patients who responded to combination treatment with bortezomib, melphalan, and prednisone while none of the evaluated patients who had achieved a response to treatment with melphalan and prednisone without bortezomib showed radiological signs of healing [121].

metabolism are affected in different ways, suggesting that different targets for treatment may be identified. The notion that myeloma-induced stimulation of osteoclast may promote growth of myeloma cells and thus create a vicious circle emphasise the importance of improved understanding as well as development of more efficient treatment of myeloma-induced bone disease. Bisphosphonates remain so far the only registered drugs for treatment of multiple myeloma bone disease. Due to risk of renal damage and bisphosphonate-associated osteonec‐ rosis of the jaw after treatment with the potent amino-bisphosphonates, alternatives are wanted and several new drugs are under investigation. Furthermore, the optimal duration of

Bone Disease in Multiple Myeloma http://dx.doi.org/10.5772/55190 229

Treatment with conventional chemotherapy does not induce healing of osteolytic lesion even in patients who have obtained complete response. However, novel drugs used for treatment of multiple myeloma seem to affect bone metabolism besides their anti-myeloma effect and cases with radiological signs of healing following treatment with bortezomib have been

The last decade has brought the understanding of multiple myeloma bone disease to a higher level, new anti-myeloma drugs with positive effect on bone disease have been registered and more are undergoing investigation. Still many questions regarding the pathophysiology and

1 Department of Clinical Cell Biology, Vejle/Lillebælt Hospital, University of Southern

3 Department of Internal Medicine, Division of Haematology, Vejle/Lillebælt Hospital,

[1] Kyle RA, Therneau TM, Rajkumar SV, Larson DR, Plevak MF, Melton LJ, III. Inci‐ dence of multiple myeloma in Olmsted County, Minnesota: Trend over 6 decades.

and Torben Plesner3

treatment of multiple myeloma bone disease remain to be answered.

, Jean-Marie Delaisse1

2 Department of Haematology, Odense University Hospital, Odense, Denmark

\*Address all correspondence to: maja.hinge@slb.regionsyddanmark.dk

treatment with bisphosphonates remains unknown.

reported.

**Author details**

Maja Hinge1\*, Thomas Lund2

Denmark, Vejle, Denmark

**References**

University of Southern Denmark, Denmark

Cancer 2004 Dec 1;101(11):2667-74.

Pomalidomide (originally CC-4047), is a derivative of thalidomide that is anti-angiogenic and acts as an immunomodulator. Pomalidomide is now tested in Phase III clinical trials and will hopefully soon become available treatment of patients with relapsed or refractory MM. The drug has been granted orphan status for the treatment of MM by the European Medicines Agency [122]. Pomalidomide has been shown to inhibit osteoclasts differentiation in bone marrow cultures which leads to a strong inhibition of bone resorption [123]. The inhibition of osteoclast formation seems to occur through a reduction of the PU.1 expression. PU.1 is a critical transcription factor in the development of mature osteoclasts. Lenalidomide, another thalidomide derivative, has been shown to inhibit both an early step in osteoclastogenesis through reduction of PU.1 expression and to reduce secretion of RANKL from bone marrow stroma cells derived from patients with MM [124]. In a clinical study including 20 MM patients with bone disease Breitkreuts *et al.* found a significant decrease in the serum levels of the RANKL/OPG ratio after two cycles of treatment with lenalidomide [124]. Likewise, treatment with thalidomide in combination with dexamethasone has a favourable effect on the RANKL/ OPG ratio [125]. Treatment with thalidomide in combination with dexamethasone can also decrease the levels of the bone resorption markers CTX, NTX and TRACP-5b, however the treatment does not increase the bone formation marker bALP or osteocalcin [126]. The failure to increase bone formations markers in serum, correlates with the observation that none of the responding patients in a clinical study of patients treated with a thalidomide/dexamethasone combination, showed any radiological signs of healing of osteolytic lesions [125].

#### **7. Conclusion**

The pathophysiology in multiple myeloma bone disease is complex. There is evidence that not only osteoclast activity but also other cells and structures responsible for normal bone metabolism are affected in different ways, suggesting that different targets for treatment may be identified. The notion that myeloma-induced stimulation of osteoclast may promote growth of myeloma cells and thus create a vicious circle emphasise the importance of improved understanding as well as development of more efficient treatment of myeloma-induced bone disease. Bisphosphonates remain so far the only registered drugs for treatment of multiple myeloma bone disease. Due to risk of renal damage and bisphosphonate-associated osteonec‐ rosis of the jaw after treatment with the potent amino-bisphosphonates, alternatives are wanted and several new drugs are under investigation. Furthermore, the optimal duration of treatment with bisphosphonates remains unknown.

Treatment with conventional chemotherapy does not induce healing of osteolytic lesion even in patients who have obtained complete response. However, novel drugs used for treatment of multiple myeloma seem to affect bone metabolism besides their anti-myeloma effect and cases with radiological signs of healing following treatment with bortezomib have been reported.

The last decade has brought the understanding of multiple myeloma bone disease to a higher level, new anti-myeloma drugs with positive effect on bone disease have been registered and more are undergoing investigation. Still many questions regarding the pathophysiology and treatment of multiple myeloma bone disease remain to be answered.
