Bisphosphonates: a review of their pharmacokinetic properties

Selective in vitro antioxidant properties of bisphosphonates

The aim of this study was to investigate the in vitro antioxidant profile of different bisphosphonates. Bisphosphonates were tested for their xanthine oxidase and microsomal lipid peroxidation inhibiting capacity. Furthermore, the effect of these different compounds on DPPH, a stable radical, was investigated. Clodronate, risedronate, and pyrophosphate were further tested for their hydroxyl radical scavenging activity. None of the tested compounds showed xanthine oxidase inhibiting activity or DPPH scavenging activity. All the tested bisphosphonates exhibited inhibiting capacities on the microsomal lipid peroxidation. The hydroxyl radical scavenging activity was dependent on the order of adding the different reagents and was highest for risedronate. Bisphosphonates possess an inhibiting activity on the microsomal lipid peroxidation and the Fenton reaction. In these reactions iron plays an important role suggesting that the selective in vitro antioxidant properties of the bisphosphonates are due to their iron chelating characteristics.

Bone as an effect compartment : models for uptake and release of drugs

"Bone-seeking agents" are drugs characterised by high affinity for bone, and are disposed in bone for prolonged periods of time while maintaining remarkably low systemic concentrations. As a consequence, the bone becomes a reservoir for bone-seeking agents, and a site of both desirable and adverse effects, depending on the pharmacological activities of the specific agent. For some agents, significant systemic effects may also be produced following their prolonged release from bone, a process that is governed mostly by the rate of bone remodelling. This review covers the pharmacokinetic and pharmacodynamic features of bone-seeking agents with different pharmacological properties, including drugs (bisphosphonates, drug-bisphosphonate conjugates, radiopharmaceuticals and fluoride), bone markers (tetracycline, bone imaging agents) and toxins (lead, chromium, aluminium). In addition, drugs that do not possess bone-seeking properties but are used for therapy of bone diseases (such as antibacterials for treatment of osteomyelitis) are discussed, along with targeting of these drugs to the bone by conjugation to bone-seeking agents, local delivery systems, and other approaches. The pharmacokinetic and pharmacodynamic behaviour of bone-seeking agents is extremely complex due to heterogeneity in bone morphology and physiology. This complexity, accompanied by difficulties in human bone research caused by ethical and other limitations, gave rise to modelling approaches to study bone drug disposition. This review describes the pharmacokinetic models that have been proposed to describe the pharmacokinetic behaviour of bone-seeking agents and predict bone concentrations of these agents for different doses and patient populations. Models of different types (compartmental and physiologically based) and of different complexity have been applied, but their relevance to drug effects in the bone tissue is limited since they describe the behaviour of the "average" drug molecule. Understanding of the cellular and molecular processes responsible for the heterogeneity of bone tissue will provide better comprehension of the influence of microenvironment on drug bone disposition and the resulting pharmacological response.

Preparation of 1‐hydroxyethylidene‐1,1‐diphosphonic acid‐intercalated layered double hydroxide and its physicochemical properties

The intercalation of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), which is a drug for osteoporosis, in layered double hydroxide (LDH) was examined with the goal of developing a novel drug delivery system (DDS) of HEDP. To prevent side reactions, the intercalation reaction was carried out at 0 degrees C, and at pH 4-6. The uptake of HEDP was determined as 3.5 mmol x g(-1) of LDH, and the interlayer distance increased from 7.8 to 13 A. The HEDP-release profiles into K(2)CO(3) aqueous solution and into various buffer solutions were also examined.

Alendronate has a residual effect on bone mass in postmenopausal Danish women up to 7 years after treatment withdrawal

Alendronate has been shown to reduce bone turnover and increase bone mass. However, little is known about the duration of the effect on bone after treatment withdrawal. The aim of this study was to investigate the long-term effects on bone mineral density (BMD) and bone turnover of various alendronate regimens after treatment withdrawal. In this study, we followed 203 postmenopausal women who previously participated in two alendronate randomized placebo-controlled trials. Daily oral treatment with various doses of alendronate (2.5-20 mg) were given for 2, 4, or 6 yr followed by no treatment for 7, 5, or 3 yr, respectively. Bone mineral density of the lumbar spine, hip, and forearm was measured by dual-energy x-ray absorptiometry. Biochemical markers of bone turnover were induced serum C-terminal telopeptides of type I collagen (CTX) and osteocalcin. Women who received alendronate (2.5-10 mg per day) for 2 yr had a 3.8% higher BMD compared to those receiving placebo when assessed 7 yr after withdrawal. The residual effect was proportionally larger in women who had received treatment for 4 (5.9%, P=0.02) or 6 yr (8.6%, P=0.002), respectively. However, the largest residual effect was found in women treated with alendronate 20 mg per day for 2 yr (9.7%, P=0.01 vs. placebo). The rate of bone loss after alendronate withdrawal was comparable to the bone loss observed in the placebo group. Bone markers tended to reverse back to normal levels, but were still affected even several years after withdrawal of treatment. This study has demonstrated that the efficacy of alendronate in preventing bone loss was proportional to the duration of treatment. The rate of bone loss after withdrawal of alendronate corresponded to the normal postmenopausal rate of bone loss. A residual effect on BMD was found up to 7 yr after treatment withdrawal.

Effects of various absorption enhancers on transport of clodronate through Caco-2 cells

The major disadvantage concerning clinical use of bishosphonate drugs, like clodronate, is their poor and variable absorption after oral administration. The objective of this study was to assess the effects of four different absorption enhancers-palmitoyl carnitine chloride (PCC), N-trimethyl chitosan chloride (TMC), sodium caprate (C10), and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-on the transport of clodronate using Caco-2 cell culture model. The transport experiments were performed in a normal (1.3mM) and in a minimum-calcium concentration (apically calcium-free medium and basolaterally 100 microM calcium concentration). In the normal calcium concentration, a strong enhancement in clodronate permeation was observed with the enhancers: EGTA (2.5mM), TMC (1.5% w/v), and PCC (0.2mM) increased the transport of 1mM clodronate 190-, 20-, and 10-fold, respectively, and the transport of 10mM clodronate 130-, 70-, and 35-fold. In the minimum-calcium concentration, the effects of the absorption enhancers on the transport of clodronate were not so potent: TMC, PCC, and EGTA caused 2- to 20-fold enhancement in clodronate permeation whereas C10 (10mM) was without any effect. According to the results, the permeation of clodronate through Caco-2 cells could be significantly promoted by the absorption enhancers, which cause widening of the tight junctions and, thus, increase the permeability of the paracellular route.

Oral weekly ibandronate prevents bone loss in postmenopausal women

OBJECTIVES

To investigate the efficacy, safety, and dose-response of once-weekly oral ibandronate in the prevention of postmenopausal bone loss.

DESIGN

This was a multi-centre, placebo-controlled, double-blind, randomized, 24-month phase II/III dose-finding study.

SETTING

Primary care units in 14 osteoporosis centres.

SUBJECTS

A total of 630 women were stratified into four strata according to time since menopause (TSM, 1-3 vs. >3 years) and baseline bone mineral density (BMD; normal: T-score > or =1 vs. osteopenic: -2.5 < or = T-score < or = 1) of the lumbar spine.

INTERVENTIONS

Within each stratum women were further randomized to receive once-weekly ibandronate (5, 10, or 20 mg week-1) or placebo for 24 months.

MAIN OUTCOME MEASURES

Efficacy parameters were the relative changes from baseline in spine (L1-4) and hip BMD, and biochemical markers of bone turnover (serum and urinary C-telopeptide of collagen type I (CTx), osteocalcin, and alkaline phosphatase) measured by dual energy X-ray absorptiometry and enzyme immunoassays, respectively.

RESULTS

Once-weekly therapy with ibandronate induced dose-dependent increases in spine and hip BMD. At month 24, differences between the relative changes in spine and hip BMD induced by 20 mg ibandronate and placebo was 4.0 and 2.7%, respectively. Similar or more pronounced differences were seen in osteopenic women of TSM 1-3 years (5.3 and 3.5%) and of TSM >3 years (3.5 and 2.9%), respectively. A dose-dependent suppression of all biochemical markers of bone turnover was observed with significant decreases in the 20 mg dose groups of all strata at month 24. The overall safety results indicated that once-weekly oral ibandronate was well-tolerated at all three doses.

CONCLUSION

Once-weekly oral therapy with 20 mg ibandronate provides an effective and safe therapy for the prevention of postmenopausal bone loss.

Bisphosphonates antagonise bone growth factors' effects on human breast cancer cells survival

Bone tissue constitutes a fertile 'soil' for metastatic tumours, notably breast cancer. High concentrations of growth factors in bone matrix favour cancer cell proliferation and survival, and a vicious cycle settles between bone matrix, osteoclasts and cancer cells. Classically, bisphosphonates interrupt this vicious cycle by inhibiting osteoclast-mediated bone resorption. We and others recently reported that bisphosphonates can also induce human breast cancer cell death in vitro, which could contribute to their beneficial clinical effects. We hypothesised that bisphosphonates could inhibit the favourable effects of 'bone-derived' growth factors, and indeed found that bisphosphonates reduced or abolished the stimulatory effects of growth factors (IGFs, FGF-2) on MCF-7 and T47D cell proliferation and inhibited their protective effects on apoptotic cell death in vitro under serum-free conditions. This could happen through an interaction with growth factors' intracellular phosphorylation transduction pathways, such as ERK1/2-MAPK. In conclusion, we report that bisphosphonates antagonised the stimulatory effects of growth factors on human breast cancer cell survival and reduced their protective effects against apoptotic cell death. Bisphosphonates and growth factors thus appear to be concurrent compounds for tumour cell growth and survival in bone tissue. This could represent a new mechanism of action of bisphosphonates in their protective effects against breast cancer-induced osteolysis.

Management of glucocorticoid induced osteoporosis in premenopausal women with autoimmune disease

Numerous inflammatory rheumatic diseases occurring in premenopausal women require the use of high doses of glucocorticoids (GC). It was believed for many years that premenopausal women were, at least to some extent, protected from bone loss associated with GC therapy. However, epidemiological studies performed in premenopausal women with systemic lupus erythematosus, demonstrate that these patients have lower bone mineral density as compared to age-matched controls. This is explained in part by the underlying disease and in part by treatment with GC. The American College of Rheumatology recommends life style adaptation, supplementation with calcium and vitamin D in patients receiving, or initiating therapy with >/=5 mg equivalent prednisone/day. Bisphosphonates are recommended, but they should be used with caution in young women as they cross the placenta and can affect skeletal remodeling in the foetus. Bisphosphonates have a prolonged terminal half-life and data on their safety extends to 10 years. It is therefore critical to inform premenopausal women about the risks of bisphosphonates and to recommend bisphosphonates with shorter terminal half-life.

Hydroxy-alkyl bisphosphonic acid partial esters (HABPA-PE): Structures of two symmetrical and non-symmetrical members of a new class of prodrugs in bone disease treatments

Two new hydroxy alkyl bisphosphonate partial esters (HABPA-PE) have been crystallised. The first compound C6H15NaO7P2C2H5O, crystallises as an ethanol solvate and forms rigid infinite β-sheet-like ribbons. The second, C6H16O7P2, displays self-association in dimers. In these new structures, packing analyses confirm the enhanced hydrophobic character due to partial esterification compared to naked hydroxybisphosphonic acids and the simplification of their H bonding patterns.

New bone formation with teriparatide [human parathyroid hormone-(1-34)] is not retarded by long-term pretreatment with alendronate, estrogen, or raloxifene in ovariectomized rats

With the ready availability of several osteoporosis therapies, teriparatide [human PTH-(1-34)] is likely to be prescribed to postmenopausal women with prior exposure to agents that prevent bone loss, such as bisphosphonates, estrogen, or selective estrogen receptor modulators. Therefore, we evaluated the ability of once daily teriparatide to induce bone formation in ovariectomized (Ovx) rats with extended prior exposure to various antiresorptive agents, such as alendronate (ABP), 17 alpha-ethinyl estradiol (EE), or raloxifene (Ral). Sprague Dawley rats were Ovx and treated with ABP (28 microg/kg, twice weekly), EE (0.1 mg/kg per d), or Ral (1 mg/kg per d) for 10 months before switching to teriparatide 30 microg/kg per d for another 2 months. Analysis of the proximal tibial metaphysis showed that all three antiresorptive agents prevented ovariectomy-induced bone loss after 10 months, but were mechanistically distinct, as shown by histomorphometry. Before teriparatide treatment, ABP strongly suppressed activation frequency and bone formation rate to below levels in other treatment groups, whereas these parameters were not different from sham values for EE or Ral. Trabecular area for ABP, EE, and Ral were greater than that in Ovx controls. However, the trabecular bone effects of ABP were attributed not only to effects on the secondary spongiosa, but also to the preservation of primary spongiosa, which was prevented from remodeling. After 2 months of teriparatide treatment, lumbar vertebra showed relative bone mineral density increases of 18%, 7%, 11%, and 10% for vehicle/teriparatide, ABP/teriparatide, EE/teriparatide, and Ral/teriparatide, respectively, compared with 10 month levels. Histomorphometry showed that trabecular area was increased by 105%, 113%, 36%, and 48% for vehicle/teriparatide, ABP/teriparatide, EE/teriparatide, and Ral/teriparatide, respectively, compared with 10 month levels. Teriparatide enhanced mineralizing surface, mineral apposition rate, and bone formation rate in all groups. Compression testing of vertebra showed that teriparatide improved strength (peak load) and toughness in all groups to a proportionately similar extent compared with 10 month levels. These data showed a surprising ability of the rat skeleton to respond to teriparatide despite extensive pretreatment with ABP, EE, or Ral. Therefore, the mature skeleton of Ovx rats remains highly responsive to the appositional effects of teriparatide regardless of pretreatment status in terms of cancellous bone area or rate of bone turnover.

Cellular uptake and metabolism of clodronate and its derivatives in Caco-2 cells: a possible correlation with bisphosphonate-induced gastrointestinal side-effects

PURPOSE

To investigate possible reasons for the low frequency of GI side-effects of clodronate, even though clodronate is known to be metabolised into a cytotoxic nucleotide analogue (AppCCl(2)p) by many cell types. The effects of some lipophilic prodrugs of clodronate were also studied.

METHODS

The effects of clodronate and its lipophilic derivatives on the proliferation and viability of Caco-2 cells were examined using an MTT assay. The intracellular uptake of 14C-clodronate and the accumulation of a clodronate metabolite (AppCCl(2)p) in Caco-2 cells were evaluated using ion-pairing HPLC-ESI-MS.

RESULTS

Clodronate had little effect on growth of proliferating, or the viability of confluent, Caco-2 cells. The uptake of clodronate by Caco-2 cells was only about 0.04% of total clodronate. The potentially cytotoxic clodronate metabolite, AppCCl(2)p, was detected in Caco-2 cell extracts after 3 h of exposure. Dianhydride- and triPOM-clodronate were metabolised to AppCCl(2)p more efficiently and also affected the viability of Caco-2 cells more than clodronate.

CONCLUSIONS

Clodronate appears to be metabolised into a cytotoxic ATP-analogue (AppCCl(2)p) by any cell type capable of internalising the drug. However, the cytotoxicity depends on the degree of uptake of clodronate. Due to the very low initial uptake of clodronate by epithelial Caco-2 cells, they do not accumulate sufficient intracellular concentrations of AppCCl(2)p to affect cell function. This explains the low frequency of gastrointestinal side-effects caused by oral clodronate therapy.

Zoledronic acid (Zometa) use in bone disease

Zoledronic acid (Zometa) is the most recent addition to the clinically available bisphosphonates. Clinical benefits in metabolic, as well as cancer-related bone disease have been observed. In addition to its profound antiosteoclast effects, it has demonstrated anticancer effects in preclinical models. Zoledronic acid has been evaluated in randomized, double-blind clinical trials of osteoporosis, Paget's disease of bone, and metastatic, osteolytic and osteoblastic bone disease. Antiosteoclast activity has been demonstrated by reductions in the bone breakdown products N-telopeptide, C-telopeptide and deoxypyridinoline. Bone mineral density, measured by dual energy x-ray absorptometry, is increased with administration of zoledronic acid in postmenopausal osteoporosis. Clinical benefit in cancer includes improvement in bone pain, reductions in skeletal events and delay in time-to-first-skeletal-events. These zoledronic acid treatment benefits have been demonstrated in patients with multiple myeloma, breast, prostate and lung cancer, and other solid tumors.

Mandible and maxilla bone mineral density and threshold analysis studies by pQCT in two edentulous women receiving pamidronate

The mandible and maxilla of two edentulous women, treated during 25 weeks with oral pamidronate, were monitored by peripheral quantitative tomography (pQCT). Whole bone volumetric mineral density failed to show meaningful variations after treatment. However, an analysis of separated cortical and medullar areas disclosed focal bone loss at the right mandible cortex of patient #1 and at the left maxilla cortex of patient #2. These and other bone sub-regions were further studied by clustering the internal sites with a different degree of bone mineral density, resorting to the mineral threshold analysis provided by the system. Where bone loss was detected, it corresponded to increased loss of the most osteopenic sites, while medium and high-density portions tended to remain unchanged within the region. There were no significant variations in all other regions, or alternatively, minor losses at osteopenic sites were compensated by an increase at high-density portions. Hence, the pQCT system allowed monitoring volumetric bone mineral density at particular sites of interest, discriminating variations at portions with a dissimilar degree of bone volume. Further studies should confirm whether pamidronate exerts a protective effect on sub-regions with previous medium and high degrees of bone mineralization, as suggested by our present findings.

Prodrugs of biologically active phosphate esters

Bioactivatable protecting groups represent an enormously powerful tool to increase bioavailability or to generally help deliver drugs to cells. This approach is particularly valuable in the case of biologically active phosphates because of the high intrinsic hydrophilicity and the multitude of biological functions phosphate esters exhibit inside cells. Here, the most prominent masking groups used so far are introduced. The stability and toxicology of the resulting prodrugs is discussed. Finally, this review tries to cover briefly some of the work that describes the usefulness and efficiency of the approach in various application areas.

Clodronate treatment of established bone loss in cardiac recipients: a randomized study

BACKGROUND

Bone loss has been reported as a complication after heart transplantation (HTx), and the increase in bone fractures is an effective problem. Treatment of osteoporosis has obtained mixed results. In this study we evaluate the effect of treatment with an oral bisphosphonate.

METHODS

Sixty-four patients with low mineral density 6 months after HTx were randomized as follows: Group A received oral clodronate (1600 mg/day in two divided doses), and Group B received placebo. Every patient was also treated with 2000 mg/day of oral calcium carbonate. Bone mineral density (BMD) was measured by dual energy x-ray absorptiometry at the lumbar spine, 1/3 and 1/10 of the distal nondominant forearm before and after 12 months of treatment. Laboratory tests were performed at 3, 6, and 12 months of treatment.

RESULTS

All patients demonstrated manifest bone loss 6 months after HTx compared with normal non-HTx controls (P=0.0001). After 1 year of clodronate therapy, BMD at the lumbar spine increased from 0.77+/-1.4 g/cm(2) to 0.86 g/cm(2) (P=0.02). Laboratory tests did not show any significant variation, except for the bone isoenzyme of alkaline phosphatase, which showed a significant decrease after 1 year of treatment. The incidence of new fractures was 9.3% in the placebo group and 0% in the clodronate group. Therapy was well tolerated without impact on graft function.

CONCLUSIONS

One year of clodronate therapy induced a significant increase in BMD at the lumbar spine in our HTx patients. Treatment was well tolerated without onset of new bone fractures.

The pharmacokinetics and pharmacodynamics of zoledronic acid in cancer patients with varying degrees of renal function

An open-label pharmacokinetic and pharmacodynamic study of zoledronic acid (Zometa) was performed in 19 cancer patients with bone metastases and known, varying levels of renal function. Patients were stratified according to creatinine clearance (CLcr) into different groups of normal (CLcr > 80 mL/min), mildly (CLcr = 50-80 mL/min), or moderately/severely impaired (CLcr = 10-50 mL/min) renal function. Three intravenous infusions of 4 mg zoledronic acid were administered at 1-month intervals between doses. Plasma concentrations and amounts excreted in urine were determined in all subjects, and 4 patients were administered 14C-labeled zoledronic acid to assess excretion and distribution of drug in whole blood. In general, the drug was well tolerated by the patients. Mean area under the plasma concentration versus time curve and mean concentration immediately after cessation of drug infusion were lower, and mean amounts excreted in urine over 24 hours from start of infusion were higher in normal subjects than in those with impaired renal function (36% vs. 28% of excreted dose), although the differences were not significant. Furthermore, with repeated doses, there was no evidence of drug accumulation in plasma or changes in drug exposure in any of the groups, nor was there any evidence of changes in renal function status. Serum levels of markers of bone resorption (serum C-telopeptide and N-telopeptide) were noticeably reduced after each dose of zoledronic acid across all three renal groups. It was concluded that in patients with mildly to moderately reduced renal function, dosage adjustment of zoledronic acid is likely not necessary.

Bone-Specific Drug Delivery Systems

Despite several decades of progress, bone-specific delivery is still limited by the unique anatomical features of bone, which mainly consists of inorganic hydroxyapatite. A practical approach to this problem is to produce targeted drugs that have a high affinity for hydroxyapatite. Bisphosphonates are a class of synthetic compounds structurally related to pyrophosphate. Bisphosphonates rapidly localise on the bone surface after being administered either intravenously or orally, since the P-C-P portion of the bisphosphonate structure has high affinity for hydroxyapatite. Therefore, bisphosphonate modification might be a promising method for targeting drugs selectively to the bone. Bisphosphonate-conjugated drugs are hydrophilic and highly water-soluble due to the acidic nature of the bisphosphonate moiety at physiological pH, and therefore they hardly permeate through the biological membrane of soft tissues. These physicochemical changes also reduce the intrinsic susceptibility of the drug to metabolism, promoting urinary or biliary excretion as unchanged drug. All these physicochemical and pharmacokinetic alterations contribute to the exceptional skeletal disposition of bisphosphonate-conjugated drugs. Bisphosphonate conjugation is based on chemical modification of the targeting molecule, and therapeutically optimised bisphosphonate derivatives have to be custom-developed on a case-by-case basis. The bisphosphonate moiety is usually coupled with the targeting drug through a specific linkage. The high affinity of bisphosphonate conjugates for the bone is not simply dependent on the bisphosphonate moiety but on the resultant molecule as a whole, including the linker and the linked drug. Lipophilicity (represented as log P) appears to be an appropriate index for predicting the osteotropic properties of bisphosphonate derivatives. Several strategies using bisphosphonate-conjugated drugs have been investigated at a laboratory level with the aim of obtaining therapeutically optimised treatments for conditions such as osteoporosis, osteoarthritis and bone cancer. In each case, the intention is to achieve prolonged local exposure to high concentrations of the targeting drug, thereby improving therapeutic index by enhancing pharmacological efficacy and minimising systemic adverse effects. Although most examples of bone-specific drug delivery via bone-seeking agents still remain in preclinical studies, several phosphonate-coupled radiopharmaceuticals, such as samarium-153 complexed to tetraphosphonate, are expected to be an effective pain palliation therapies for metastatic bone cancer and are currently being developed in clinical trials. Furthermore, recent reports on bisphosphonate-modified proteins have illustrated the feasibility of bone-specific delivery of biologically active protein drugs, such as cytokines and growth factors.

Development and validation of a highly sensitive RIA for zoledronic acid, a new potent heterocyclic bisphosphonate, in human serum, plasma and urine

Zoledronic acid is a new, highly potent bisphosphonate drug under clinical evaluation. A radioimmunoassay has been developed to determine zoledronic acid concentration in human serum, plasma, and urine. The assay utilizes rabbit polyclonal antisera against a zoledronic acid-BSA conjugate and a [125I]zoledronic acid derivative as tracer in a competitive format adapted to microtiter plates. The assay shows a LLOQ 0.4 ng/ml in serum or plasma (interassay%CV=17%, accuracy 97%), 5 ng/ml in urine (21%, 98%). In 23 patients receiving 4, 8 or 16 mg of zoledronic acid, drug concentrations in plasma were dose proportional and showed a multiphasic profile, followed by a prolonged gradual decline to concentrations near the LLOQ. Zoledronic acid disposition in plasma and the recovery of only 40-50% of the dose in urine are consistent with the rapid and extensive uptake by and slow release from bone in parallel with renal clearance, typically shown by bisphosphonates.

Pharmacokinetics and pharmacodynamics of zoledronic acid in cancer patients with bone metastases

The pharmacokinetics, pharmacodynamics, and safety of zoledronic acid (Zometa), a new-generation bisphosphonate, were evaluated in 36 patients with cancer and bone metastases. Zoledronic acid (by specific radioimmunoassay) and markers of bone turnover were determined in plasma and urine after three consecutive infusions (qx28 days) of 4 mg/5 min (n = 5),4 mg/l5 min (n = 7),8 mg/15 min (n = 12), or 16 mg/15 min (n = 12). Zoledronic plasma disposition was multiphasic, with half-lives of 0.2 and 1.4 hours representing an early, rapid decline of concentrations from the end-of-infusion C(max) to < 1% of C(max) at 24 hours postdose and half-lives of 39 and 4526 hours describing subsequent phases of very low concentrations between days 2 and 28 postdose. AUC0-24 h and C(max) were dose proportional and showed little accumulation (AUC0-24 h ratio between the third and first dose was 1.28). Prolonging the infusion from 5 to 15 minutes lowered C(max) by 34%, with no effect on AUC0-24 h. Urinary excretion of zoledronic acid was independent of infusion duration, dose, or number of doses, showing average Ae0-24 h of 38% +/- 13%, 41% +/- 14%, and 37% +/- 17%, respectively, after 4, 8, and 16 mg. Only trace amounts of drug were detectable in post 24-hour urines. Renal clearance (Ae0-24 h)/(AUC0-24 h) was on average 69 +/- 28,81 +/- 40, and 54 +/- 34 ml/min after 4,8, and 16 mg, respectively, and showed a moderate correlation (r = 0.5; p < 0.001) with creatinine clearance, which was 84 +/- 23, 82 +/- 25, and 80 +/- 40 ml/min for the dose groups at baseline. Adverse events and changes from baseline in vital signs and clinical laboratory variables showed no relationship in terms of type, frequency, or severity with zoledronic acid dose or pharmacokinetic parameters. Zoledronic acid produced significant declines from baseline in serum and/or creatinine-corrected urine C-telopeptide (by 74%), N-telopeptide (69%), pyridinium cross-links [19-33%), and calcium (62%), with an increasing trend (by 12%) in bone alkalinephosphatase. There was no relationship of the magnitude and duration of these changes with zoledronic acid dose, Ae0-24 h, AUC0-24 h or C(max). The antiresorptive effects were evident within 1 day postdose and were maintained over 28 days across all dose levels, supporting monthly dosing with 4 mg zoledronic acid.

Bisphosphonate therapy in multiple myeloma: past, present, future

Bone disease characterised by osteolytic lesions, pathological fractures and hypercalcaemia is an important clinical feature in multiple myeloma. Pain, decreased performance status, and the need for palliative radiotherapy and surgical interventions are common sequelae. Bisphosphonates act primarily on osteoclasts to inhibit excessive bone resorption, and have therefore been investigated in myeloma patients to ameliorate the clinical consequences of the bone disease. Bisphosphonates are currently the therapy of choice in myeloma patients with hypercalcaemia. In long-term management, both oral clodronate and intravenous pamidronate are effective in reducing skeletal-related events. Zoledronic acid seems to be as effective as pamidronate. Whether bisphosphonates have antimyeloma activity is currently unknown. Cost-benefit analyses have shown reasonable efficacy with acceptable costs. Bisphosphonate therapy is now accepted as an important part of care in myeloma patients, although much still has to be learned in order to optimise this therapy in multiple myeloma.

The absolute bioavailability of clodronate from two different oral doses

Clodronate (disodium clodronate tetrahydrate) is a bisphosphonate used in the treatment of hypercalcemia and osteolysis due to malignancy. Like all bisphosphonates, clodronate has low and variable oral bioavailability. The purpose of this study was to examine the absolute bioavailability of clodronate from two different oral doses. Thirty-one healthy young volunteers participated in this open, randomized, three-period, single-dose, cross-over study. The absolute bioavailability was calculated from the area under the serum clodronate-time curve in 48 h (AUC(0-48 h)) after administration of 800 or 1600 mg (Bonefos 400 mg capsules) of oral clodronate, or 30 mg (Bonefos 60 mg/mL infusion concentrate) of intravenous clodronate. The maximum concentration of clodronate in serum (C(max)), the time to maximum concentration (t(max)), the elimination half-life (t(1/2)), and the cumulative amount of clodronate excreted into urine in 48 h (Ae(0-48 h)) were also determined. The geometric mean of the absolute bioavailability of 800 mg of clodronate was 1.9% and that of 1600 mg 2.1%. The difference in the absolute bioavailability of these two doses was statistically nonsignificant. All treatments were well tolerated, and the AE profiles were similar in the different treatment groups. There were no serious adverse events during the study.

Bisphosphonates influence the proliferation and the maturation of normal human osteoblasts

The key pharmacological action for the clinical use of bisphosphonates lies in the inhibition of osteoclast-mediated bone resorption. Osteoblasts could be other target cells for bisphosphonates. We studied the effects of bisphosphonates on the proliferation and the differentiation of normal human bone trabecular osteoblastic cells (hOB). We tested 4 different compounds: clodronate, pamidronate and 2 newer compounds: ibandronate, a nitrogen-containing bisphosphonate and zoledronate, which is a heterocyclic imidazole compound. Ibandronate and zoledronate stimulated hOB cell proliferation by up to 30% (p<0.05) after 72 h for concentrations ranging from 10(-8) M to 10(-5) M. Clodronate transiently enhanced hOB cell survival after only 24 h (+60%, p<0.001) whereas pamidronate had no effect. Longer time course studies, in presence of fetal calf serum, revealed that cell growth was finally reduced by all 4 bisphosphonates (40% after 7 days). Type I collagen synthesis was transiently increased by all 4 bisphosphonates after only 48 h incubation (+17% to +67%, p<0.05). Clodronate increased ALP activity by up to 1.7-fold after 4 days of culture (p<0.05) whereas ibandronate or zoledronate exhibited lesser stimulatory effects (+17 to +30%), and pamidronate had no significant effect. In conclusion, we found that different bisphosphonates, currently used or tested in various clinical conditions, transiently stimulated the growth of preosteoblastic cells and thereafter increased their differentiation according to sequential events (type I collagen synthesis first, then ALP activity to a lesser extent). Our data suggest that the beneficial effects of bisphosphonate treatment on bone mass and integrity could be partly mediated through a direct action on osteoblasts.

Further insight into mechanism of action of clodronate: inhibition of mitochondrial ADP/ATP translocase by a nonhydrolyzable, adenine-containing metabolite

Bisphosphonates are currently the most important class of antiresorptive drugs used for the treatment of diseases with excess bone resorption. Recent studies have shown that bisphosphonates can be divided into two groups with distinct molecular mechanisms of action depending on the nature of the R(2) side chain. Alendronate, like other nitrogen-containing bisphosphonates, inhibits bone resorption and causes apoptosis of osteoclasts and other cells in vitro by preventing post-translational modification of GTP-binding proteins with isoprenoid lipids. Clodronate, a bisphosphonate that lacks a nitrogen, does not inhibit protein isoprenylation but can be metabolized intracellularly to a beta-gamma-methylene (AppCp-type) analog of ATP, which is cytotoxic to macrophages in vitro. The detailed molecular basis for the cytotoxic effects of adenosine-5'-[beta,gamma-dichloromethylene]triphosphate (AppCCl(2)p) has not been determined yet. We addressed this question by studying the effects of alendronate, clodronate, and the clodronate metabolite AppCCl(2)p on isolated mitochondria, mitochondrial fractions, and mitochondrial membrane potential in isolated human osteoclasts. We found that AppCCl(2)p inhibits mitochondrial oxygen consumption by a mechanism that involves competitive inhibition of the ADP/ATP translocase. Alendronate or the native form of clodronate did not have any immediate effect on mitochondria. However, longer treatment with liposome-encapsulated clodronate caused collapse of the mitochondrial membrane potential, although prominent apoptosis was a late event. Hence, inhibition of the ADP/ATP translocase by the metabolite AppCCl(2)p is a likely route by which clodronate causes osteoclast apoptosis and inhibits bone resorption.

Pharmacokinetic and pharmacodynamic evaluation of intermittent versus continuous alendronate administration in rats

We studied the differences in pharmacokinetics and pharmacodynamics of the same dose of alendronate administered subcutaneously as intermittent bolus injection or continuous infusion in rats. Two rat models of bone disease were applied. Bone cancer was produced by intratibial inoculation of Walker carcinosarcoma cells, and a model of augmented bone resorption was produced by vitamin D(3) treatment of rats that had undergone thyroidparathyroidectomy. Higher amounts of alendronate were found in bones and in internal organs after bolus drug administration as compared with continuous infusion. Drug effects on plasma calcium levels and on urine calcium excretion were similar in both modes of alendronate administration. Results of the study indicate that the pharmacokinetics (disposition) of alendronate is administration-dependent. The total amount found in bone does not directly represent the amount of alendronate that is pharmacologically active at the site of action in the bone and that affects bone remodeling. The findings suggest that there is no pharmacodynamic advantage for continuous infusion of alendronate. It is concluded that the preferred mode of administration should be selected according to secondary clinical criteria (like incidence of adverse effects and convenience of administration).

The cellular uptake and metabolism of clodronate in RAW 264 macrophages

PURPOSE

Non-nitrogen-containing bisphosphonates, such as clodronate (dichloromethylene bisphosphonate), appear to act as prodrugs, their active form being the AppCp-type analogues of ATP. To further elucidate this, we examined the cellular uptake of clodronate and intracellular accumulation of the metabolite of clodronate (AppCCl2p) in RAW 264 macrophages, the influence of clodronate metabolism on the intracellular ATP concentration, and the time course of clodronate metabolism and the effects of clodronate on cytokine secretion from macrophages.

METHODS

The cellular uptake of clodronate was measured using 14C-labeled clodronate. AppCCl2p was determined in cell extracts by using an ion-pairing HPLC-ESI-MS. The cytokine concentrations in the culture supernatants were measured with time-resolved fluoroimmunoassay. Intracellular ATP concentration was measured with a luminometer using a luciferin-luciferase assay.

RESULTS

Of the clodronate internalized by macrophages in vitro, 30-55% is metabolized to AppCCl2p, which accumulates to high intracellular concentrations during the first 12 h of exposure. This accumulation does not affect the ATP levels in the cells. The time course of metabolite appearance in the cells and the inhibition of cytokine secretion were very similar.

CONCLUSIONS

These results strongly support the idea that clodronate acts as a prodrug, the active form being its intracellular AppCCl2p metabolite.

Mode of administration-dependent pharmacokinetics of bisphosphonates and bioavailability determination

We investigated the influence of mode of administration on the pharmacokinetics of a clinically used bisphosphonate, pamidronate, and of suberoylbisphosphonate (SuBP), a novel bisacylphosphonate of the P-CO-(C)(n)-CO-P type, in rats. Serum drug levels and tissue disposition were determined following administration of the drugs by different modes: intravenous bolus (iso-osmotic and hypo-osmotic solutions), continuous intravenous infusion, and peroral administration. Results of the study indicate that the disposition of the bisphosphonates in soft tissue (liver, kidney and spleen) was dependent on route and rate of drug administration, and on the osmoticity of the vehicle. Consequently, main pharmacokinetic parameters (AUC, CL, and V(ss)) were influenced by the mode of drug administration, precluding accurate determination of bioavailability from AUC values. On the other hand, bone and urine bisphosphonate accumulation were considerably less dependent on mode of administration, and, therefore, are recommended for bioavailability calculation.

Comparative safety of bone remodeling agents with a focus on osteoporosis therapies

This article reviews the different treatments currently available for osteoporosis and examines the benefits and adverse events that are associated with each. While emphasizing safety considerations, this review summarizes the following treatments for osteoporosis: calcium supplements, fluoride, hormone replacement therapy, raloxifene, bisphosphonates, salmon calcitonin, and calcitriol. Before prescribing any of these agents, the clinician should review the risk/benefit profile of each drug in the context of the individual patient's history, concomitant diseases, concurrent medications, and general physical condition.

Quantitative studies of bone with the use of 18F-fluoride and 99mTc-methylene diphosphonate

This article discusses methods for quantifying bone turnover based on tracer kinetic studies of the short-lived radiopharmaceuticals 99mTc-MDP and 18F-fluoride. Measurements of skeletal clearance obtained by using these tracers reflect the combined effects of skeletal blood flow and osteoblastic activity. The pharmacokinetics of each tracer is described, together with some of the quantitative tests of skeletal function that have been described in the literature. The physiologic interpretation of quantitative measurements of bone obtained with the use of short half-life radionuclides is discussed, and the advantages and limitations of 99mTc-MDP and 18F-fluoride are compared and contrasted. Currently, 18F-fluoride dynamic positron emission tomography (PET) is the technique of choice for physiologically precise quantitative studies of bone. However, comparable data could probably be obtained by using 99mTc-MDP if methods for single photon emission computed tomography (SPECT) quantitation were improved.

Administration routes and delivery systems of bisphosphonates for the treatment of bone resorption

Geminal bisphosphonates (BPs) are a class of drugs considered to be stable analogs of pyrophosphate (P-O-P), a physiological regulator of calcification and bone resorption. A number of BPs have been approved for clinical use in Paget's disease, hypercalcemia of malignancy, and osteoporosis. The major disadvantage of the clinically utilized BPs is their poor oral absorption from the GI tract, typically less than 1% is absorbed. In addition, the BPs have been associated with adverse gastrointestinal effects in humans. The challenge for novel drug delivery systems is to achieve improved bioavailability and safety. In the first part of this review, we discuss the bioavailability of BPs, the effect of food on the absorption of BPs, the mechanism of BPs' absorption and the adverse gastrointestinal effects. In the second part of the review, various methods that have been used for improving the bioavailability of BPs are described. Dosage form strategies reviewed include the use of particular formulations for increasing oral absorption as well as decreasing adverse gastrointestinal effects, absorption enhancers, BP compounds and the solubility of their calcium complex/salts, and the prodrug approach. Because of the poor GI absorption, attempts have been made to enhance the bioavailability of BPs by several parenteral routes other than i.v. injections. Description of nasal administration, s.c. and i.m. injections, BP implants and targeted osteotropic delivery systems are reviewed.

Transdermal delivery of drugs for the treatment of bone diseases

The current status of transdermal drug delivery for the treatment of bone diseases is described in this review. The structure, physiology and function of skin and their importance in determining delivery into and across skin are discussed. Special emphasis has been devoted to a description of the major pathways of transport across the skin and the quite continuing controversy over the importance of the transfollicular route. An overview of anatomic site-dependent drug absorption is also provided and is particularly relevant to determination of transdermal patch location. Brief descriptions of the criteria for selection of transdermal drug candidate, transdermal patch designs and currently marketed transdermal products are also included. Transdermal estradiol delivery systems are examined in more detail for their clinical and biological effects. Finally, the feasibility of delivering drugs such as bisphosphonates across skin is discussed.

Bisphosphonate prodrugs: synthesis and in vitro evaluation of alkyl and acyloxymethyl esters of etidronic acid as bioreversible prodrugs of etidronate

The synthesis and preliminary evaluation of novel alkyl and acyloxymethyl esters of etidronic acid as etidronate prodrugs is reported. Tetramethyl ester of etidronic acid was found be isomerized at pH 7.4 and P-C-P bridge was rearranged to P-C-O-P. This unwanted process was prevented via acylation of the bridging carbon's alcohol group. Acylation showed to be stable if one or more phosphonic OH- groups were substituted. However, when none of the phosphonic OH- groups were substituted, the acylation was chemically hydrolysed and the parent drug was released. This finding was successfully applied in the design of tetrapivaloyloxymethyl ester of acetylated etidronic acid which released etidronic acid via enzymatic (first step) and chemical (second step) hydrolysis in liver homogenate. However, the corresponding tri-substituted pivaloyloxymethyl ester having adequate water-solubility and lipophilicity (logP(app) 0.6 at pH 7.4), is probably the most potential prodrug candidate reported to enhance the oral bioavailability of etidronate.

Timing of food intake has a marked effect on the bioavailability of clodronate

Because of the low and variable bioavailability of bisphosphonates and the huge effect of food on their gastrointestinal absorption, it is of utmost importance to know the optimal timing of drug intake in relation to food intake. We investigated the effect of time on the bioavailability of clodronate when the drug was administered 2, 1, or 0.5 h before breakfast, with breakfast, or 2 h after breakfast (in the middle of a 4-h fast). The study was conducted as a single-center, open, balanced, randomized, crossover pharmacokinetic study in 31 healthy subjects aged 21 to 34 years. The volunteers participated in five different sessions with 800 mg of oral clodronate, and these sessions were separated by washout phases, each for at least 1 week. The primary pharmacokinetic variables were the area under the serum concentration time curve in 24 h (AUC(0-24)) for clodronate and the maximal concentration of clodronate in serum (C(max)). Clodronate was absorbed rather similarly when taken in the morning on an empty stomach 2, 1, or 0.5 h before breakfast, but because the best absorption occurred (as expected) when the drug was taken 2 h before breakfast, this scheme served as the reference treatment. As evaluated by area under the serum concentration time curves, the dose-breakfast interval of 1 h scarcely reduced absorption from the reference treatment level (relative absorption 91%, p = 1.0). Compared with the reference treatment, clodronate was absorbed with 69% efficacy (p = 0.65) when breakfast followed only 0.5 h later. The dose-breakfast intervals of 0.5 and 1 h did not differ significantly from each other (p = 0.85). Absorption was, however, only 34% (p < 0.0001) of the optimum when the drug was taken 2 h after breakfast, and only 10% of optimal when clodronate was taken with breakfast (p < 0.0001). In conclusion, it can be recommended to take Bonefos capsules in the morning on an empty stomach at least 0.5 h before breakfast.

Use of the bisphosphonate drug alendronate for palliative management of osteosarcoma in two dogs

The bisphosphonate drug alendronate was used to suppress bone remodelling and tumour osteolysis as a palliative treatment for two dogs with osteosarcoma, one of the tibia and one of the maxilla. A spiral fracture associated with the tibial tumour healed after it was stabilised with an external skeletal fixator. Both dogs remained comfortable and survived for 12 and 10 months respectively after diagnosis, despite the fact that neither primary tumour was resected.

Levels of C-telopeptide fragments of collagen type I enable the monitoring and early adjustment of clodronate therapy in patients with postmenopausal osteoporosis

We monitored the efficacy of therapy with clodronate, a bisphosphonate drug, in women with postmenopausal osteoporosis, using urinary immunoenzymatic assay of C-telopeptide of collagen type I, an eight amino acid fragment (collagen fragment) of the C-telopeptide of the alpha1-chain of collagen type I (EKAHDGGR). The analysis of the dynamics of collagen fragment concentrations (a marker of bone resorption) during treatment suggests the possibility of early modulation and customization of therapy based on the levels of this marker. This could enable improved control over secondary effects and side effects of clodronate therapy. Pharmacologic inhibition of bone resorption by osteoclasts could be indirectly responsible for the increase in parathyroid hormone found during treatment with clodronate. Increased levels of parathyroid hormone are probably necessary to stimulate residual osteoclast activity and are sufficient for the maintenance of calcium-phosphate homeostasis in a new pharmacologically-induced equilibrium. Outside this context the levels of parathyroid hormone of certain patients would be considered pathologic.

Selective drug delivery system to bone: small peptide (Asp)6 conjugation

Targeting a drug on hydroxyapatite (HA) could be a promising way for selective drug delivery to bone, because HA, an inorganic component in hard tissues (bone and teeth), does not exist in soft tissues. Several bone noncollagenous proteins, which bind to HA, have repeating sequences of acidic amino acids in their structures as possible HA-binding sites. Thus, we think that a small peptide of repetitive acidic amino acid could work as a carrier for selective drug delivery to the bone. To test this hypothesis, we conjugated (Asp)6 to fluorescein isothiocyanate (FITC), evaluated its affinity to HA in vitro, and examined its tissue distribution after injection into rats. Although fluorescein itself did not bind to HA, (Asp)6-FITC bound to HA as well as calceine and tetracycline. Twenty-four hours after intravenous injection of (Asp)6-FITC to rats, animals were killed, and ground sections of hard tissues and cryosections of soft tissues were made. Under a confocal laser scanning microscope, clear labeling lines were observed in bones and teeth, whereas no labeling was detected in soft tissues. In the rats administered with fluorescein alone, the fluorescent labeling was detected in neither hard nor soft tissues. Fluorescent analysis of blood, urine, and bones after (Asp)6-FITC administration revealed that biological half-life of FITC in blood was short (60 minutes) and that within 24 h, 95% of the administered FITC was excreted as urine whereas 2% of the FITC accumulated in bones. After subcutaneous administration of (Asp)6-FITC to mice, fluorescent intensity remaining in the femurs was measured periodically. In these mice the biological half-life of FITC in the femur was 14 days. Present results indicate that (Asp)6 is effective as a carrier for selective drug delivery to bone.

Prevention of early postmenopausal bone loss with cyclical etidronate

Cyclical etidronate has been shown to be effective in the treatment of established postmenopausal osteoporosis but less is known about its effects on early menopausal bone loss. The aim of the study was to establish the effects of cyclic etidronate therapy on spinal and proximal femoral bone mineral loss in early postmenopausal women. One hundred and seven women who were within 6 months to 3 years of the menopause were recruited into a 2-year, randomised, placebo-controlled, double-blind trial. Spinal bone mineral density was within 2 SD of the age-matched mean reference value at baseline. Bone mineral density in the lumbar spine and proximal femur was assessed by dual energy X-ray absorptiometry at baseline and thereafter at 6 monthly intervals for 2 years. Urinary collagen cross-links (deoxypyridinoline and pyridinoline) were measured at the same time points. Seventy-seven women completed the study. At the end of the treatment period, the mean bone mineral density change from baseline in the treated group was +0.14% and -0.06% in the lumbar spine and femoral neck, respectively, compared to -1.49 and -2.22 in the control group. Overall, there was a significant difference between the two groups at both these sites (p=0.01 and 0.001, respectively). No significant differences between the groups were demonstrated at the greater trochanter or Ward's triangle. The conclusion was that cyclical etidronate therapy prevents bone loss in the spine and femoral neck in early postmenopausal women. It provides a safe and effective therapeutic option for the prevention of postmenopausal osteoporosis in women who are unwilling or unable to tolerate hormone replacement therapy.

The time of day that etidronate is ingested does not influence its therapeutic effect in osteoporosis

To investigate whether the therapeutic effect of etidronate is affected by the time of ingestion we have retrospectively studied 110 osteoporotic patients. They had been taking etidronate according to the manufacturer's instructions for a mean duration of 2.6 years either on waking (n=47), on retiring (n=47), or during the day (n= 16). No significant differences were found between the three groups with respect to percentage change in bone mineral density at all sites either for the first year of treatment or for the mean yearly percent change throughout the total course of treatment. These findings suggest that the time of ingestion of etidronate does not influence the therapeutic effect if a two hour fast before and after ingestion is adhered to.

Multiple Myeloma: New Insights and Therapeutic Approaches

This review discusses the evolution of novel diagnostic and treatment strategies for multiple myeloma based upon increased understanding of basic disease pathogenesis. Although myeloma has remained an incurable illness to date, these new developments will derive treatments to improve outcome and achieve eventual cure.

In Section I, Dr. Kyle reviews the results of current therapy for multiple myeloma, including high dose therapy and stem cell transplantation which have proven to achieve improved response rates, event-free, and overall survival. Supportive therapy, such as erythropoietin to treat disease-related anemia, and methods of prophylaxis against infection, which both lessen toxicities of treatment and improve quality of life for patients, are also addressed.

In Section II, Dr. Dalton with Drs. Landowski, Shain, Jove and Hazlehurst discusses mechanisms of drug resistance in myeloma, with emphasis on novel treatment approaches to prevent development of drug resistance and to overcome drug resistance. Laboratory studies delineating mechanisms whereby myeloma cells resist drug-induced apoptosis provide the framework for related treatment protocols for patients with refractory disease.

In Section III, Dr. Berenson reviews the management of complications in bone, which occur in the majority of patients with myeloma and are the major cause of decreased quality of life. New insights into the mediators of bone resorption and new bone formation in the marrow milieu have already derived effective bisphosphonate therapy. These drugs not only reduce bone complications and related pain, thereby improving quality of life, but also may have intrinsic anti-tumor activity by virtue of inducing tumor cell adherence to marrow, reducing interleukin-6 secretion, inducing tumor cell apoptosis, or inhibiting angiogenesis.

In the last section, Dr. Anderson explores the potential for future therapies which offer great promise to improve patient outcomes. First, drugs which alter the marrow microenvironment include thalidomide and its derivative immunomodulatory drugs, which act directly on tumor cells to induce apoptosis or G1 growth arrest, alter tumor cell adhesion to marrow stroma, inhibit angiogenesis, and trigger a cellular anti-tumor response. The proteasome inhibitors both act directly on tumor cells and also inhibit the transcription factor NFκB-dependent upregulation of IL-6 secretion triggered by tumor cell adhesion. Second, delineation of both growth and apoptotic pathways has derived novel treatment strategies. Third, the preclinical basis and early clinical trial results using vaccination and adoptive immunotherapy to harness autoimmune and alloimmune anti-myeloma responses are presented. This review sets the stage for an evolving new biologically based treatment paradigm in myeloma targeting both the tumor and its microenvironment to improve outcome and achieve eventual cure.

Multiple Myeloma: New Insights and Therapeutic Approaches

This review discusses the evolution of novel diagnostic and treatment strategies for multiple myeloma based upon increased understanding of basic disease pathogenesis. Although myeloma has remained an incurable illness to date, these new developments will derive treatments to improve outcome and achieve eventual cure.

In Section I, Dr. Kyle reviews the results of current therapy for multiple myeloma, including high dose therapy and stem cell transplantation which have proven to achieve improved response rates, event-free, and overall survival. Supportive therapy, such as erythropoietin to treat disease-related anemia, and methods of prophylaxis against infection, which both lessen toxicities of treatment and improve quality of life for patients, are also addressed.

In Section II, Dr. Dalton with Drs. Landowski, Shain, Jove and Hazlehurst discusses mechanisms of drug resistance in myeloma, with emphasis on novel treatment approaches to prevent development of drug resistance and to overcome drug resistance. Laboratory studies delineating mechanisms whereby myeloma cells resist drug-induced apoptosis provide the framework for related treatment protocols for patients with refractory disease.

In Section III, Dr. Berenson reviews the management of complications in bone, which occur in the majority of patients with myeloma and are the major cause of decreased quality of life. New insights into the mediators of bone resorption and new bone formation in the marrow milieu have already derived effective bisphosphonate therapy. These drugs not only reduce bone complications and related pain, thereby improving quality of life, but also may have intrinsic anti-tumor activity by virtue of inducing tumor cell adherence to marrow, reducing interleukin-6 secretion, inducing tumor cell apoptosis, or inhibiting angiogenesis.

In the last section, Dr. Anderson explores the potential for future therapies which offer great promise to improve patient outcomes. First, drugs which alter the marrow microenvironment include thalidomide and its derivative immunomodulatory drugs, which act directly on tumor cells to induce apoptosis or G1 growth arrest, alter tumor cell adhesion to marrow stroma, inhibit angiogenesis, and trigger a cellular anti-tumor response. The proteasome inhibitors both act directly on tumor cells and also inhibit the transcription factor NFκB-dependent upregulation of IL-6 secretion triggered by tumor cell adhesion. Second, delineation of both growth and apoptotic pathways has derived novel treatment strategies. Third, the preclinical basis and early clinical trial results using vaccination and adoptive immunotherapy to harness autoimmune and alloimmune anti-myeloma responses are presented. This review sets the stage for an evolving new biologically based treatment paradigm in myeloma targeting both the tumor and its microenvironment to improve outcome and achieve eventual cure.