Drug delivery strategies for cathepsin inhibitors in joint diseases

Cathepsins play important roles in the development of joint and bone diseases such as osteoporosis, rheumatoid arthritis (RA) and osteoarthritis (OA). Cathepsin inhibitors are presently in development and clinical testing for use as novel disease-modifying drugs for the improved treatment of osteoporosis. They may also be applicable for the treatment of joint diseases. However, some barriers still hamper their clinical applications in these indications. Based on pathophysiological features of RA and OA, the authors discuss six potential drug delivery strategies for the effective delivery of cathepsin inhibitors or other antiarthritic drugs to the arthritic joint tissue. Successful application of these strategies may significantly contribute to a more effective and safe treatment of RA and OA.     

The clinical potential of matrix metalloproteinase inhibitors in the rheumatic disorders

Rheumatoid arthritis (RA) and osteoarthritis are chronic diseases that result in cartilage degradation and loss of joint function. Currently available drugs are predominantly directed towards the control of pain and/or the inflammation associated with joint synovitis but they do little to reduce joint destruction. In the future, it will be important to have drugs that prevent the structural damage caused by bone and cartilage breakdown. In this review, we will outline the structure and function of cartilage and the key features of matrix metalloproteinases (MMPs), enzymes involved in joint destruction. We will present evidence for the role of MMPs in RA and osteoarthritis, and describe the potential of synthetic inhibitors to control MMP activity and so prevent joint destruction. MMPs are able to cleave all components of the cartilage matrix. Regulation of MMPs is aberrant in osteoarthritis and RA, and MMPs have been implicated in the collagen breakdown that contributes to joint destruction in these diseases. Synthetic MMP inhibitors have been developed. In animal models of osteoarthritis and/or RA, these agents have shown chondroprotective effects. However, results from clinical trials in RA have been equivocal, with some studies being terminated because of lack of efficacy or safety concerns. Nevertheless, this approach remains promising. Increased understanding of the structure, regulation and function of individual MMPs may lead to more effective strategies, and approaches aimed at multiple steps of the pathogenesis of arthritis may be needed to break the chronic cycle of joint destruction.     

Intra-articular drug delivery systems for osteoarthritis therapy: shifting from sustained release to enhancing penetration into cartilage

Osteoarthritis (OA) is a progressive chronic inflammation that leads to cartilage degeneration. OA Patients are commonly given pharmacological treatment, but the available treatments are not sufficiently effective. The development of sustained-release drug delivery systems (DDSs) for OA may be an attractive strategy to prevent rapid drug clearance and improve the half-life of a drug at the joint cavity. Such delivery systems will improve the therapeutic effects of anti-inflammatory effects in the joint cavity. Whereas, for disease-modifying OA drugs (DMOADs) which target chondrocytes or act on mesenchymal stem cells (MSCs), the cartilage-permeable DDSs are required to maximize their efficacy. This review provides an overview of joint structure in healthy and pathological conditions, introduces the advances of the sustained-release DDSs and the permeable DDSs, and discusses the rational design of the permeable DDSs for OA treatment. We hope that the ideas generated in this review will promote the development of effective OA drugs in the future.     

Tumour necrosis factor-α blockade: a new era for effective management of rheumatoid arthritis

Tumour necrosis factor (TNF)-α inhibitors have emerged as a new treatment option for rheumatoid arthritis (RA). The scientific rationale for targeting TNF-α in RA derives from extensive work in the laboratory, showing the importance of this pro-inflammatory cytokine as a mediator of joint inflammation. Proof of principle has now been firmly established in clinical trials where TNF-α inhibitors have been shown to decrease the signs and symptoms of joint inflammation and slow radiological progression of joint damage. Presently, the two TNF-α inhibitors available for use in RA are etanercept and infliximab. Etanercept is a soluble TNF receptor: Fc fusion protein that competes with the endogenous TNF receptors for TNF-α binding. Infliximab is a chimeric anti-TNF-α monoclonal antibody, which also binds with high affinity to soluble TNF-α. Etanercept and infliximab will be rapidly incorporated into current treatment paradigms, which call for early and intensive treatment of RA using disease-modifying antirheumatic drugs (DMARDs), such as methotrexate, sulfasalazine and hydroxychloroquine. A major drawback to the widespread use of these biologics is their high costs. Some patients with limited financial means may be denied access to these effective anti-inflammatory agents. Moreover, long-term experience with TNF-α inhibitor therapy has been limited and concerns linger about the possibility that etanercept and infliximab may cause unforeseen side effects or increase the risk for opportunistic infection. Despite these caveats, TNF-α inhibitors represent a major advance for the treatment of RA and will likely spawn new indications for anti-TNF-α therapy and the development of novel therapeutic compounds with similar biological activity.     

Tumour necrosis factor-alpha blockade: a new era for effective management of rheumatoid arthritis

Tumour necrosis factor (TNF)-alpha inhibitors have emerged as a new treatment option for rheumatoid arthritis (RA). The scientific rationale for targeting TNF-alpha in RA derives from extensive work in the laboratory, showing the importance of this pro-inflammatory cytokine as a mediator of joint inflammation. Proof of principle has now been firmly established in clinical trials where TNF-alpha inhibitors have been shown to decrease the signs and symptoms of joint inflammation and slow radiological progression of joint damage. Presently, the two TNF-alpha inhibitors available for use in RA are etanercept and infliximab. Etanercept is a soluble TNF receptor: Fc fusion protein that competes with the endogenous TNF receptors for TNF-alpha binding. Infliximab is a chimeric anti-TNF-alpha monoclonal antibody, which also binds with high affinity to soluble TNF-alpha. Etanercept and infliximab will be rapidly incorporated into current treatment paradigms, which call for early and intensive treatment of RA using disease-modifying antirheumatic drugs (DMARDs), such as methotrexate, sulfasalazine and hydroxychloroquine. A major drawback to the widespread use of these biologics is their high costs. Some patients with limited financial means may be denied access to these effective anti-inflammatory agents. Moreover, long-term experience with TNF-alpha inhibitor therapy has been limited and concerns linger about the possibility that etanercept and infliximab may cause unforeseen side effects or increase the risk for opportunistic infection. Despite these caveats, TNF-alpha inhibitors represent a major advance for the treatment of RA and will likely spawn new indications for anti-TNF-alpha therapy and the development of novel therapeutic compounds with similar biological activity.     

New dosage formulations for targeted delivery of cyclo-oxygenase-2 inhibitors: focus on use in the elderly

NSAIDs are a widely used class of analgesic and anti-inflammatory drugs that act by inhibiting the cyclo-oxygenase (COX) enzyme. However, because of their nonspecificity of action, use of these agents as long-term therapy for chronic pain in diseases such as rheumatoid arthritis (RA) and osteoarthritis (OA) is often discouraged. Among NSAIDs, COX-2 inhibitors are promising candidates for long-term therapy of chronic diseases, particularly in the elderly, because of their reduced incidence of gastrointestinal adverse effects. However, in recent times these agents have also been shown to cause adverse effects such as cardiovascular effects (myocardial infarction, stroke and hypertension) and renal effects (decreased renal blood flow/glomerular filtration rate), which in 2004 led to the withdrawal of rofecoxib and in 2005 the withdrawal of valdecoxib from the US market. Importantly, these adverse effects can be effectively reduced by achieving site specific/targeted delivery through new formulation approaches. These formulations not only restrict the drug supply to specific organs but also reduce the dose required. As a result, use of new delivery systems such as nanoparticles, microparticles, microemulsions and nanogels has gained widespread applicability in the management of chronic disease, especially in the elderly, and particularly when there is a need to decrease dose-dependent adverse effects (as is the case with COX-2 inhibitors). This article reviews various new approaches to the delivery of COX-2 inhibitors and highlights issues related to the development of delivery systems for these agents for RA, OA, cancer (familial adenomatous polyposis, prostate, breast and non-small cell lung cancer), ocular diseases (such as diabetic retinopathy) and inflammatory diseases of the skin, with emphasis on their potential for use in the elderly. Emphasis is also placed on the preparation of these particulate systems, their release profile and behaviour in biological systems.     

Toxicity of cadmium in musculoskeletal diseases

Epidemiological studies have reported that exposure to toxic metals like cadmium (Cd) may promote the development of musculoskeletal diseases, such as osteoporosis, rheumatoid arthritis (RA), and osteoarthritis (OA), among others. The objective of this review is to summarize the molecular mechanisms of inflammation and oxidative stress activated by Cd at the bone level, particularly in osteoporosis, RA, and OA. Cadmium can increase bone resorption, affect the activity of osteoclasts and calcium (Ca) absorption, and impair kidney function, which favors the development of osteoporosis. In the case of RA, Cd interferes with the activity of antioxidant proteins, like superoxide dismutase (SOD) and catalase (CAT). It also promotes an inflammatory state, inducing the process of citrullination, which affects the proteins of immune response. On the other hand, accumulation of Cd in the tissues and blood of smokers has been related to the development of some musculoskeletal diseases. Therefore, knowing the negative impact of Cd toxicity at the articular level can help understand the damage mechanisms it produces, leading to the development of such diseases.     

Future therapies for rheumatoid arthritis: remedies from the horns of a dilemma?

Drugs used to treat arthritis can be broadly classified into either anti-inflammatory or immunosuppressive/immunomodulatory agents. Non-steroidal anti-inflammatory drugs (NSAIDs) are used for both osteoarthritis (OA) and rheumatoid arthritis (RA), while drugs with an immunological mechanism of action are only applicable to RA. The total market value for anti-arthritic drugs is estimated to be 8.4 bn dollars, with the OA segment worth 6.9 bn dollars. In contrast, the major RA markets are valued at approximately 1.5 bn dollars. Drugs currently in late phase development reflect the accepted approaches towards treating the symptoms of arthritis, or suppressing immunological mechanisms considered to be the driving force for the underlying disease process in RA. The size of both the RA and OA markets, however, creates an incentive to develop new therapeutics which do not conform to these two approaches, but target new molecular mechanisms. Compounds currently in preclinical development demonstrate that it may be possible to combine anti-inflammatory and slow-acting antirheumatic activity into a single therapeutic. This new generation of anti-arthritic compounds has the potential to redefine the way in which common forms of arthritis, mixed connective tissue diseases and musculoskeletal diseases are treated in the future.     

New molecular targets for the treatment of osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disorder characterized by destruction of the articular cartilage, subchondral bone alterations and synovitis. Current treatments are focused on symptomatic relief but they lack efficacy to control the progression of this disease which is a leading cause of disability. Therefore, the development of effective disease-modifying drugs is urgently needed. Different initiatives are in progress to define the molecular mechanisms involved in the initiation and progression of OA. These studies support the therapeutic potential of pathways relevant in joint metabolism such as Wnt/β-catenin, discoidin domain receptor 2 or proteinase-activated receptor 2. The dysregulation in cartilage catabolism and subchondral bone remodeling could be improved by selective inhibitors of matrix metalloproteinases, aggrecanases and other proteases. Another approach would favor the activity of anabolic processes by using growth factors or regulatory molecules. Recent studies have also revealed the role of oxidative stress and synovitis in the progression of this disease, supporting the development of a number of inhibitory strategies. Novel targets in OA are represented by genes involved in OA pathophysiology discovered using gene network, epigenetic and microRNA approaches. Further insights into the molecular mechanisms involved in OA initiation and progression may lead to the development of new therapies able to control joint destruction and repair.     

Novel bone-targeted Src tyrosine kinase inhibitor drug discovery

Bone-targeted Src tyrosine kinase (STK) inhibitors have recently been developed for the treatment of osteoporosis and cancer-related bone diseases. The concept of bone targeting derives from bisphosphonates, and from the evolution of such molecules in terms of therapeutic efficacy for the treatment of bone disorders. Interestingly, some of the earliest bisphosphonates were recognized for their ability to inhibit calcium carbonate precipitation (scaling) by virtue of their affinity to chelate calcium. This chelating property was subsequently exploited in the development of bisphosphonate analogs as inhibitors of the bone-resorbing cells known as osteoclasts, giving rise to breakthrough medicines, such as Fosamax (for the treatment of osteoporosis) and Zometa (for the treatment of osteoporosis and bone metastases). Relative to these milestone achievements, there is a tremendous opportunity to explore beyond the limited chemical space (functional group diversity) of such bisphosphonates to design novel bone-targeting moieties, which may be used to develop other classes of promising small-molecule drugs affecting different biological pathways. Here, we review studies focused on bone-targeted inhibitors of STK, a key enzyme in osteoclast-dependent bone resorption. Two strategies are described relative to bone-targeted STK inhibitor drug discovery: (i) the development of novel Src homology (SH)-2 inhibitors incorporating non-hydrolyzable phosphotyrosine mimics and exhibiting molecular recognition and bone-targeting properties, leading to the in vivo-effective lead compound AP-22408; and (ii) the development of novel ATP-based Src kinase inhibitors incorporating bone-targeting moieties, leading to the in vivo-effective lead compound AP-23236. In summary, AP-22408 and AP-23236, which differ mechanistically by virtue of blocking Src-dependent non-catalytic or catalytic activities in osteoclasts, exemplify ARIAD Pharmaceuticals' structure-based design of novel bone-targeted lead compounds, successfully achieving in vivo proof-of-concept and providing the framework for the next-generation molecules that have further advanced, in terms of preclinical studies, for the treatment of osteoporosis and related bone diseases, including osteolytic bone metastases.     

Advances in the treatment of rheumatoid arthritis: old versus new therapies

Rheumatoid arthritis (RA) is a common cause of disability in the western population, with an annual incidence of 0.05% and a prevalence of 1%. Although a small percentage of patients go into natural remission, the untreated disease progresses to cause disability, morbidity and early mortality. Unravelling of the cytokine network in the pathogenesis of RA has led to the development of drugs that target these cytokines and prevent joint damage. Three biological anticytokine agents, etanercept, infliximab and anakinra, are now available for use in RA. More experience will quantify their safety and benefits. The potency of the older disease-modifying antirheumatic drugs (DMARDs), such as methotrexate and sulfasalazine, is also being realised, especially when used early in the disease process and in combination. Leflunomide is a new DMARD with efficacy similar to methotrexate and sulfasalazine. Symptomatic treatment of RA with nonsteroidal anti-inflammatory drugs has also undergone a revolution with the availability of a new class of COX-2-specific inhibitors. These drugs control inflammation and provide pain relief with less GI toxicity. Management of comorbid conditions associated with RA and its treatment (i.e., osteoporosis, cardiovascular and lung disease) has also become a priority for the rheumatologist. It is hoped that more aggressive use of conventional DMARDs and biological agents will result in less disability and a higher proportion of patients achieving remission.     

Advances in the treatment of rheumatoid arthritis: old versus new therapies

Rheumatoid arthritis (RA) is a common cause of disability in the western population, with an annual incidence of 0.05% and a prevalence of 1%. Although a small percentage of patients go into natural remission, the untreated disease progresses to cause disability, morbidity and early mortality. Unravelling of the cytokine network in the pathogenesis of RA has led to the development of drugs that target these cytokines and prevent joint damage. Three biological anticytokine agents, etanercept, infliximab and anakinra, are now available for use in RA. More experience will quantify their safety and benefits. The potency of the older disease-modifying antirheumatic drugs (DMARDs), such as methotrexate and sulfasalazine, is also being realised, especially when used early in the disease process and in combination. Leflunomide is a new DMARD with efficacy similar to methotrexate and sulfasalazine. Symptomatic treatment of RA with nonsteroidal anti-inflammatory drugs has also undergone a revolution with the availability of a new class of COX-2-specific inhibitors. These drugs control inflammation and provide pain relief with less GI toxicity. Management of comorbid conditions associated with RA and its treatment (i.e., osteoporosis, cardiovascular and lung disease) has also become a priority for the rheumatologist. It is hoped that more aggressive use of conventional DMARDs and biological agents will result in less disability and a higher proportion of patients achieving remission.     

Osteoblasts and osteoclasts in bone remodeling and inflammation

Bone homeostasis is maintained by a balance between bone resorption by osteoclasts and bone formation by osteoblasts. Osteoblasts not only play a central role in bone formation by synthesizing multiple bone matrix proteins, but regulate osteoclast maturation by soluble factors and cognate interaction, resulting in bone resorption. Osteoclast maturation requires stimulation by RANKL expressed on osteoblasts, and the cognate interaction is mediated by firm adhesion via ICAM-1. During the processes, pro-inflammatory cytokines such as IL-1 and TNF-alpha, cause an imbalance in bone metabolism, by favoring bone resorption via the induction of RANKL and ICAM-1 on osteoblasts. These inflammatory signals originate from the immune system, the largest source of cell-derived regulatory signals, and such immunological signals to the bone are transmitted primarily via osteoblasts to induce osteoclast maturation, resulting in secondary osteoporosis. Actually, such phenomena mainly occur at the interface between proliferating synovium and bone tissue in rheumatoid arthritis (RA). Thus, therapeutic strategies for these conditions, an anti-TNF-alpha antibody and an IL-1 receptor antagonist, effective for treating RA disease activity, also reduce secondary osteoporosis and joint destruction. Based on an improved understanding of immune signals, investigation of the suppression of cell functions may lead to improved understanding and better treatment of diseases of bone metabolism and osteoporosis.     

A cross-sectional retrospective assessment of anti-arthritic drugs in patients with arthritis in Korea

BACKGROUND: Selective cyclo-oxygenase-2 (COX-2) inhibitors were recently introduced for the treatment of arthritis because of their lower rates of gastrointestinal adverse events compared with traditional non-steroidal anti-inflammatory drugs (NSAIDs). OBJECTIVE: To examine the medication usage patterns for both osteoarthritis (OA) and rheumatoid arthritis (RA) in Korea. METHODS: The medical charts of a convenience sample of 402 patients with OA or RA were reviewed by the Arthritis Study Group in 14 hospitals and ten clinics in Korea. RESULTS: Traditional oral NSAIDs were the most commonly prescribed drugs for OA (68.3%) and RA (65.1%) patients. Two-thirds (66.7%) of the RA patients taking COX-2 inhibitors were prescribed other arthritis medications concurrently and 85.1% of RA patients taking NSAIDs were prescribed other arthritis medications concurrently. Patients on NSAIDs were almost twice as likely to have a gastroprotective agent (GPA) concurrently compared to COX-2 inhibitor users (OA patients 38.1% vs 21.2%; RA patients 57.9% vs 30.6%). Overall, patients taking COX-2 inhibitors were less likely to take GPAs concurrently compared to patients not taking COX-2 inhibitors (unadjusted OR 0.36; adjusted OR 0.39). CONCLUSIONS: Traditional oral NSAIDs were commonly prescribed to arthritis patients in Korea. In this study, patients taking COX-2 inhibitors were prescribed less adjunctive arthritis treatments and less gastroprotective agents than traditional oral NSAID users.     

Pathophysiological roles for IL-18 in inflammatory arthritis

IL-18 is a unique cytokine with prominently wide spectrum biological actions. Among these, its IFN-gamma/TNF-alpha-inducing activity primarily contributes to the development of various inflammatory diseases including inflammatory arthritis. IL-18 levels correlate with the disease activity of rheumatoid arthritis (RA) and osteoarthritis (OA). IL-18 is spontaneously released from RA synovial cells and OA chondrocytes and seems to participate in the development of the inflammatory and destructive alterations of joints via induction of TNF-alpha, a potent effector molecule. TNF-alpha, in turn, increases IL-18 expression in RA synovial cells. Recent clinical trials have revealed the efficacy of TNF-alpha in RA with a reduction in circulatory IL-18 levels. These may implicate the positive circuit between IL-18 and TNF-alpha for development of RA. As IL-18-deficient mice evade collagen-induced arthritis in a mouse RA model, therapeutics targeting IL-18 may be beneficial against RA/OA. Here, the authors review the possible roles of IL-18 in inflammatory arthritis.     

Targeted treatment for osteoarthritis: drugs and delivery system

The management of osteoarthritis (OA) is a clinical challenge due to the particular avascular, dense, and occluded tissue structure. Despite numerous clinical reports and animal studies, the pathogenesis and progression of OA are still not fully understood. On the basis of traditional drugs, a large number of new drugs have been continuously developed. Intra-articular (IA) administration for OA hastens the development of targeted drug delivery systems (DDS). OA drugs modification and the synthesis of bioadaptive carriers contribute to a qualitative leap in the efficacy of IA treatment. Nanoparticles (NPs) are demonstrated credible improvement of drug penetration and retention in OA. Targeted nanomaterial delivery systems show the prominent biocompatibility and drug loading-release ability. This article reviews different drugs and nanomaterial delivery systems for IA treatment of OA, in an attempt to resolve the inconsonance between in vitro and in vivo release, and explore more interactions between drugs and nanocarriers, so as to open up new horizons for the treatment of OA.     

Biological response modifiers in the management of rheumatoid arthritis.

The management of rheumatoid arthritis (RA) with biological response modifiers (BRMs) is reviewed. RA, an autoimmune disorder affecting 1-2% of the world's population, is characterized by inflammation of synovial tissues, joint swelling, stiffness, and pain that may progress to joint erosion. There is strong evidence that inflammatory mediators, such as tissue necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1), play a critical role in the pathogenesis of this disorder. IL-1-receptor antagonist (IL-1Ra) is produced in healthy subjects and helps to protect against the adverse effects associated with IL-1 overexpression. Administration of IL-1Ra or similar agents may reduce the effects of IL-1 and ameliorate inflammatory conditions. Traditional treatment of RA has been based on symptomatic management with non-steroidal antiinflammatory drugs, disease-modifying antirheumatic drugs, and corticosteroids, each of which has substantial drawbacks in terms of effectiveness or adverse effects. Newer therapeutic strategies for blocking the biological effects of inflammatory cytokines include antibodies directed against TNF (e.g., infliximab), soluble receptors (e.g., etanercept) and receptor antagonists to IL-1 (anakinra) [corrected]. Clinical trials indicate that these BRMs may be more effective than traditional agents because they are able to alter joint remodeling in addition to attenuating symptoms. Anti-TNF therapies may be associated with increased risk for infections, sepsis, tuberculosis reactivation, demyelination disorders, and blood dyscrasias; anakinra appears to be safer. Combination therapy with BRMs may be more appropriate for RA than monotherapy. The role of BRMs in the treatment of RA will evolve as investigators learn more about the drugs and the disorder.     

New antiangiogenic strategies for the treatment of proliferative synovitis

Angiogenesis inhibition, which has been extensively studied for the treatment of various malignancies, is beginning to emerge as a new potential therapy for proliferative synovitis, particularly rheumatoid arthritis (RA). The rheumatoid pannus, the site of inflammation and joint destruction in the rheumatoid synovium, relies on the development of new vasculature to sustain its growth. A host of mediators have been shown to induce angiogenesis at the site of the inflamed synovium; these include vascular endothelial growth factor, fibroblast growth factor, integrin alpha(V)beta3, angiopoietin, prosta-glandin E1 and prostaglandin E2, and matrix metalloproteinases. In addition, hypoxia at the site of synovial inflammation contributes to angiogenesis stimulation. Several naturally-occurring inhibitors exist, such angiostatin and endostatin. There are a number of drugs undergoing study in the treatment of proliferative synovitis, which capitalise on the correlation between angiogenesis inhibition and the reduction of signs and symptoms of RA. Paclitaxel and an anti-integrin alpha(V)beta3 antibody, LM-609, are currently in clinical trials. Other drugs that may inhibit angiogenesis in RA include TNP-470 (formerly called AGM-1470), PPI-2458, PTK-787, bevacizumab and thalidomide. Many of these drugs have shown promise for the treatment of oncologic disorders, and are now being evaluated for the treatment of proliferative synovitis.     

Biochemical markers of bone turnover in the clinical development of drugs for osteoporosis and metastatic bone disease: potential uses and pitfalls

Biochemical markers of bone turnover are used increasingly during the clinical development of drugs for the treatment of metabolic bone diseases such as Paget's disease, osteoporosis and cancer that has metastasised to the bone. However, assessing the optimal value of these markers is often complicated, and such an assessment is an obvious prerequisite for rational use of the markers and, consequently, potential improvement of clinical drug development.Biochemical markers of bone turnover are substances in the blood or urine that are produced or released during bone remodelling. They provide semiquantitative information on bone remodelling, and are often the most adequate tool to describe the pharmacodynamics of the drug. Their use has increased considerably because of dose-effect relationships that have been seen with certain drugs, but also because they have proven relationships with clinical outcomes in several metabolic bone diseases. However, there is a lack of information on the kinetics of these markers, and the immunoassays that are frequently used in their monitoring often measure a mixture of fragments rather than a single molecular entity. For drug development it should also be realised that different markers, but also different assays for the same marker, may provide different results, considerably limiting the ability to compare results.In postmenopausal osteoporosis, relationships have been shown between several biochemical markers of bone turnover, and either fracture risk and/or the antifracture efficacy of drugs. Such relationships can be used for the development of drugs with similar mechanisms of action, but also for the development of these drugs for closely related indications, such as corticosteroid-induced osteoporosis. In both of these instances, data on effects on biochemical markers of bone turnover are usually employed in combination with information about effects on bone mineral density. However, the relationships of these parameters with clinical outcomes may be remarkably different for drugs with alternative mechanisms of action, challenging the use of the markers for the development of new drugs for the treatment of patients with osteoporosis.At present, the pharmacological treatment of cancer that has metastasised to the bone is limited to several bisphosphonates. Recent studies have shown relationships between the normalisation of levels of biochemical markers of bone turnover and clinical outcomes, and prospective studies investigating the application of such relationships are ongoing. The markers may play an important role in the optimisation of registered bisphosphonate treatments. However, their role in the development of new drugs is still limited to dose selection, and potential relationships with clinical outcomes remain to be investigated in instances of new mechanisms of action.Biochemical markers of bone turnover are a valuable asset for drug development, but their rational use is determined by a number of variables. Correctly manipulating these may improve clinical development of drugs for the treatment of patients with metabolic bone diseases such as osteoporosis and cancer metastatic to the bone.