Quantitative structure-activity relationships for gammadelta T cell activation by bisphosphonates

Mechanisms underlying γδ T-cell subset perturbations in SIV-infected Asian rhesus macaques

T cells that express the γδ T-cell receptor, which recognize microbial or stress-induced antigens, represent a minority of blood T cells but constitute a major proportion of intraepithelial lymphocytes in the gastrointestinal mucosa. As microbial products have been shown to translocate from the gastrointestinal tract into circulation in chronically HIV/Simian immunodeficiency virus (SIV)-infected individuals, we conducted a study of Vδ1 and Vδ2 T-cell frequency, phenotype, and function in blood, spleen, lymph nodes, gastrointestinal mucosa, and bronchoalveolar lavage of uninfected and chronically SIVsmE543-infected rhesus macaques (RMs). We found: (1) SIV-associated inversion of Vδ1/Vδ2 T cells occurs in blood and in several tissues; (2) γδ T cells are not infected by SIV in vivo; (3) the Vδ1/Vδ2 inversion involves expansion of Vδ1 T cells; (4) expanded Vδ1 T cells are phenotypically and functionally different from Vδ1 T cells from uninfected RMs; and (5) the stimulus underlying expansion of Vδ1 T cells appears to be microbial translocation. These data highlight the importance of microbial translocation-induced immune activation in chronically infected individuals and provide new insights into an immune dysregulation phenomenon that is a hallmark of HIV/SIV infection. These findings may lead to novel therapeutic interventions that improve the immune responses against microbial antigens, and thus, decrease microbial translocation-induced immune activation.

Variation in the Cox-2 Gene May Modify the Effect of Alendronate on Vertebral Fracture Prevention

Bisphosphonates such as alendronate, which are potent specific inhibitors of osteoclast-mediated bone resorption, are widely used for treatment of postmenopausal osteoporosis as well as other diseases related to bone remodeling. We evaluated whether the reportedly functional PTGS2 (prostaglandin-endoperoxide synthase 2/cyclooxygenase [COX] 2) genotypes influence the efficacy of alendronate on vertebral fracture prevention. Sixty postmenopausal osteoporotic women participated in this interventional study. The extent of vertebral fracture was evaluated in all participants before and after intervention using X-ray imaging. Alendronate (10mg/day), calcium (1gr/day) and vitamin D (400mg/day) were given to participants for 2 years. Laboratory measurements included circulating crosslaps, osteocalcin, PTH, osteoporotegrin, RANKL, vitamin D, TNF-α, IL-6, IL-1 levels. Hip and spine BMD (bone mass density) were measured using DEXA. Genotyping for cox-2 gene SNP (−765G/C) was performed using PCR- RFLP method. Genotype frequency of homozygous major allele (GG), heterozygous (GC) and homozygous minor allele (CC) were 61.7%, 33.3% and 5% respectively. Evaluation of vertebral fracture before alendronate therapy in participants demonstrated no significant difference between carriers of G and C alleles, although the difference appeared near to significant after alendronate therapy at the end of 2 years. Serum PTH level and L2-L4 BMD were significantly different between subjects with different alleles. Moreover, IL-1 had prominently higher concentration in C allele carries. Furthermore, there was a significant difference in terms of the extent of vertebral fracture between two allelic groups after two years of treatment. Since bone remodeling process has been proved to be affected by inflammatory factors; it appears that variation in COX-2 genotypes may influence alendronate efficacy in fracture prevention among postmenopausal osteoporotic women.

Inhibition of the Fe(4)S(4)-cluster-containing protein IspH (LytB): electron paramagnetic resonance, metallacycles, and mechanisms

We report the inhibition of the Aquifex aeolicus IspH enzyme (LytB, (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate reductase, EC 1.17.1.2) by a series of diphosphates and bisphosphonates. The most active species was an alkynyl diphosphate having IC(50) = 0.45 microM (K(i) approximately 60 nM), which generated a very large change in the 9 GHz EPR spectrum of the reduced protein. On the basis of previous work on organometallic complexes, together with computational docking and quantum chemical calculations, we propose a model for alkyne inhibition involving pi (or pi/sigma) "metallacycle" complex formation with the unique fourth Fe in the Fe(4)S(4) cluster. Aromatic species had less activity, and for these we propose an inhibition model based on an electrostatic interaction with the active site E126. Overall, the results are of broad general interest since they not only represent the first potent IspH inhibitors but also suggest a conceptually new approach to inhibiting other Fe(4)S(4)-cluster-containing proteins that are of interest as drug and herbicide targets.

Cytokine requirements for the differentiation and expansion of IL-17A- and IL-22-producing human Vgamma2Vdelta2 T cells

Human gammadelta T cells expressing the Vgamma2Vdelta2 TCR play important roles in immune responses to microbial pathogens by monitoring prenyl pyrophosphate isoprenoid metabolites. Most adult Vgamma2Vdelta2 cells are memory cytotoxic cells that produce IFN-gamma. Recently, murine gammadelta T cells were found to be major sources of IL-17A in antimicrobial and autoimmune responses. To determine if primate gammadelta T cells play similar roles, we characterized IL-17A and IL-22 production by Vgamma2Vdelta2 cells. IL-17A-producing memory Vgamma2Vdelta2 cells exist at low but significant frequencies in adult humans (1:2762 T cells) and at even higher frequencies in adult rhesus macaques. Higher levels of Vgamma2Vdelta2 cells produce IL-22 (1:1864 T cells), although few produce both IL-17A and IL-22. Unlike adult humans, in whom many IL-17A+ Vgamma2Vdelta2 cells also produce IFN-gamma (Tgammadelta1/17), the majority of adult macaques IL-17A+ Vdelta2 cells (Tgammadelta17) do not produce IFN-gamma. To define the cytokine requirements for Tgammadelta17 cells, we stimulated human neonatal Vgamma2Vdelta2 cells with the bacterial Ag, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate, and various cytokines and mAbs in vitro. We find that IL-6, IL-1beta, and TGF-beta are required to generate Tgammadelta17 cells in neonates, whereas Tgammadelta1/17 cells additionally required IL-23. In adults, memory Tgammadelta1/17 and Tgammadelta17 cells required IL-23, IL-1beta, and TGF-beta, but not IL-6. IL-22-producing cells showed similar requirements. Both neonatal and adult IL-17A+ Vgamma2Vdelta2 cells expressed elevated levels of retinoid-related orphan receptor gammat. Our data suggest that, like Th17 alphabeta T cells, Vgamma2Vdelta2 T cells can be polarized into Tgammadelta17 and Tgammadelta1/17 populations with distinct cytokine requirements for their initial polarization and later maintenance.

Vgamma2Vdelta2 T Cell Receptor recognition of prenyl pyrophosphates is dependent on all CDRs

gammadelta T cells differ from alphabeta T cells in the Ags they recognize and their functions in immunity. Although most alphabeta TCRs recognize peptides presented by MHC class I or II, human gammadelta T cells expressing Vgamma2Vdelta2 TCRs recognize nonpeptide prenyl pyrophosphates. To define the molecular basis for this recognition, the effect of mutations in the TCR CDR was assessed. Mutations in all CDR loops altered recognition and cover a large footprint. Unlike murine gammadelta TCR recognition of the MHC class Ib T22 protein, there was no CDR3delta motif required for recognition because only one residue is required. Instead, the length and sequence of CDR3gamma was key. Although a prenyl pyrophosphate-binding site was defined by Lys109 in Jgamma1.2 and Arg51 in CDR2delta, the area outlined by critical mutations is much larger. These results show that prenyl pyrophosphate recognition is primarily by germline-encoded regions of the gammadelta TCR, allowing a high proportion of Vgamma2Vdelta2 TCRs to respond. This underscores its parallels to innate immune receptors. Our results also provide strong evidence for the existence of an Ag-presenting molecule for prenyl pyrophosphates.

Exercise-induced up-regulation of MMP-1 and IL-8 genes in endurance horses

Background

The stress response is a critical factor in the training of equine athletes; it is important for performance and for protection of the animal against physio-pathological disorders.

In this study, the molecular mechanisms involved in the response to acute and strenuous exercise were investigated using peripheral blood mononuclear cells (PBMCs).

Results

Quantitative real-time PCR (qRT-PCR) was used to detect modifications in transcription levels of the genes for matrix metalloproteinase-1 (MMP-1) and interleukin 8 (IL-8), which were derived from previous genome-wide expression analysis. Significant up-regulation of these two genes was found in 10 horses that had completed a race of 90–120 km in a time-course experimental design.

Conclusion

These results suggest that MMP-1 and IL-8 are both involved in the exercise-induced stress response, and this represents a starting point from which to understand the adaptive responses to this phenomenon.

Photoaffinity antigens for human gammadelta T cells

Vgamma2Vdelta2 T cells comprise the major subset of peripheral blood gammadelta T cells in humans and expand during infections by recognizing small nonpeptide prenyl pyrophosphates. These molecules include (E)-4-hydroxy-3-methyl-but-2-enyl-pyrophosphate (HMBPP), a microbial isoprenoid intermediate, and isopentenyl pyrophosphate, an endogenous isoprenoid intermediate. Recognition of these nonpeptide Ags is mediated by the Vgamma2Vdelta2 T cell Ag receptor. Several findings suggest that prenyl pyrophosphates are presented by an Ag-presenting molecule: contact between T cells and APC is required, the Ags do not bind the Vgamma2Vdelta2 TCR directly, and Ag recognition is abrogated by TCR mutations in CDRs distant from the putative Ag recognition site. Identification of the putative Ag-presenting molecule, however, has been hindered by the inability to achieve stable association of nonpeptide prenyl pyrophosphate Ags with the presenting molecule. In this study, we show that photoaffinity analogues of HMBPP, meta/para-benzophenone-(methylene)-prenyl pyrophosphates (m/p-BZ-(C)-C(5)-OPP), can crosslink to the surface of tumor cell lines and be presented as Ags to gammadelta T cells. Mutant tumor cell lines lacking MHC class I, MHC class II, beta(2)-microglobulin, and CD1, as well as tumor cell lines from a variety of tissues and individuals, will all crosslink to and present m-BZ-C(5)-OPP. Finally, pulsing of BZ-(C)-C(5)-OPP is inhibited by isopentenyl pyrophosphate and an inactive analog, suggesting that they bind to the same molecule. Taken together, these results suggest that nonpeptide Ags are presented by a novel-Ag-presenting molecule that is widely distributed and nonpolymorphic, but not classical MHC class I, MHC class II, or CD1.

Differential effects of tumour necrosis factor-alpha and interleukin-12 on isopentenyl pyrophosphate-stimulated interferon-gamma production by cord blood Vgamma9 T cells

Lower numbers of Vgamma9Vdelta2 T cells in cord blood (CB) than in adult peripheral blood (PB), as well as their impaired ability to produce interferon-gamma (IFN-gamma) in response to stimulation, are associated with functional deficiency in the immune system in newborns. In this study, we stimulated CB Vgamma9 T cells with their T-cell receptor-specific ligand, isopentenyl pyrophosphate (IPP), plus exogenous costimulatory cytokines such as interleukin-2 (IL-2), IL-12 and tumour necrosis factor-alpha (TNF-alpha), which are known to play important roles in the activation of PB gammadelta T cells. Our data show that CB Vgamma9 T cells are able to produce IFN-gamma at levels comparable to PB Vgamma9 T cells by the addition of TNF-alpha in the presence of IPP and IL-2; however, under the same culture conditions, IL-12 does not efficiently activate CB Vgamma9 T cells to produce IFN-gamma. The frequency of TNF-alpha receptor II-positive Vgamma9T cells and the expression levels of TNF-alpha receptor II are similar in CB and PB; in contrast, the frequency of IL-12 receptor betaI (IL-12RbetaI) -positive Vgamma9T cells and expression levels of IL-12RbetaI are significantly lower in CB than PB. TNF-alpha but not IL-12 increases the expression of IL-2Rbeta on CB Vgamma9 T cells. These results provide new insights into the role of TNF-alpha in the activation of CB Vgamma9 T cells.

Quantitative determination of farnesyl and geranylgeranyl diphosphate levels in mammalian tissue

Farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP) are branch point intermediates of isoprenoid biosynthesis. Inhibitors of isoprenoid biosynthesis, such as the statins and bisphosphonates, are widely used therapeutic agents. However, little is known about the degree to which they alter levels of upstream and downstream isoprenoids, including FPP and GGPP. Therefore, we developed a method to isolate and quantify FPP and GGPP from mammalian tissues. Tissues from mice were collected, snap frozen in liquid nitrogen, and stored at -80 degrees C. FPP and GGPP were isolated by a combined homogenization and extraction procedure and were purified with a C18 solid phase extraction column. Farnesyl protein transferase (FTase) or geranylgeranyl protein transferase I (GGTase I) were used to conjugate FPP and GGPP with fluorescent dansylated peptides. FPP and GGPP were quantified by high-performance liquid chromatography (HPLC). The respective concentrations of FPP and GGPP are as follows: 0.355+/-0.030 and 0.827+/-0.082 units of nmol/g wet tissues in brain, 0.320+/-0.019 and 0.293+/-0.035 units of nmol/g wet tissues in kidney, 0.326+/-0.064 and 0.213+/-0.029 units of nmol/g wet tissues in liver, and 0.364+/-0.015 and 0.349+/-0.023 units of nmol/g wet tissues in heart (means+/-SEM). This method allows for determination of FPP and GGPP concentrations in any tissue type and is sensitive enough to detect changes following treatment with inhibitors of isoprenoid biosynthesis.

Exercise-induced redistribution of T lymphocytes is regulated by adrenergic mechanisms

Acute exercise is known for causing considerable changes in leukocyte counts and function. In this paper we report that differentiated changes in T-lymphocyte distribution occur in lymphoid and non-lymphoid organs depending on the type and the intensity of exercise. Using fluorescent cell tracking we observed a release of T-cells from the spleen while lung, bone marrow and Peyer's patches served as target organs. The number of T-cells in the blood rose after intensive running while lymphopenia occurred after swimming exercise. Changes in number of labelled T-cells were neither found in the lymph nodes nor in the thymus regardless of exercise protocol. Following an alpha- or beta-blockade, the exercise-induced release of T-cells from the spleen and the accumulation of T-cells in the lung were inhibited while the enhancement of T-cells in the Peyer's patches was not affected. The administration of epinephrine partially mimicked the effects of exercise and resulted in a release of T-cells from both, the spleen and the liver, as well as in an increase of circulating blood T-cells. In conclusion, exercise induces a substantial re-distribution of T-cells within lymphoid and non-lymphoid organs. The migrating properties of T-cells could be partially explained by adrenergic mechanisms associated with exercise while the involvement of certain homing receptors remains to be shown. Our results suggest that the accumulation of T-cells in both, lung and Peyer's patches, may enhance the immune vigilance in these compartments which serve as the body's major defence barriers.

Bisphosphonates in cancer therapy

Bisphosphonates are the standard of care in the treatment of malignant bone diseases, because of their ability to inhibit osteoclast-mediated bone destruction. We review here preclinical evidence that bisphosphonates also exert direct antitumour effects and antiangiogenic properties. Furthermore, we describe new insights on how bisphosphonates may act synergistically in combination with antineoplastic drugs or gammadelta T cells to exhibit antitumour activity. These findings reveal new exciting possibilities to fully exploit the antitumour potential of bisphosphonates in the clinical practice.

Activity of sulfonium bisphosphonates on tumor cell lines

We investigated three series of sulfonium bisphosphonates for their activity in inhibiting the growth of three human tumor cell lines. The first series consisted of 6 cyclic sulfonium bisphosphonates, the most active species having an (average) IC50 of 89 microM. The second consisted of 10 phenylalkyl and phenylalkoxy bisphosphonates, the most active species having an IC50 of 18 microM. The third series consisted of 17 n-alkyl sulfonium bisphosphonates, the most active species having an IC50 of approximately 240 nM. Three QSAR models showed that the experimental cell growth inhibition results could be well predicted. We also determined the structures of one sulfonium bisphosphonate bound to farnesyl diphosphate synthase, finding that it binds exclusively to the dimethylallyl diphosphate binding site. These results are of interest since they show that sulfonium bisphosphonates can have potent activity against a variety of tumor cell lines, the most active species having IC50 values much lower than conventional nitrogen-containing bisphosphonates.

The farnesyl-diphosphate/geranylgeranyl-diphosphate synthase of Toxoplasma gondii is a bifunctional enzyme and a molecular target of bisphosphonates

Farnesyl-diphosphate synthase (FPPS) catalyzes the synthesis of farnesyl diphosphate, an important precursor of sterols, dolichols, ubiquinones, and prenylated proteins. We report the cloning and characterization of two Toxoplasma gondii farnesyl-diphosphate synthase (TgFPPS) homologs. A single genetic locus produces two transcripts, TgFPPS and TgFPPSi, by alternative splicing. Both isoforms were heterologously expressed in Escherichia coli, but only TgFPPS was active. The protein products predicted from the nucleotide sequences have 646 and 605 amino acids and apparent molecular masses of 69.5 and 64.5 kDa, respectively. Several conserved sequence motifs found in other prenyl-diphosphate synthases are present in both TgFPPSs. TgFPPS was also expressed in the baculovirus system and was biochemically characterized. In contrast to the FPPS of other eukaryotic organisms, TgFPPS is bifunctional, catalyzing the formation of both farnesyl diphosphate and geranylgeranyl diphosphate. TgFPPS localizes to the mitochondria, as determined by the co-localisation of the affinity-purified antibodies against the protein with MitoTracker, and in accord with the presence of an N-terminal mitochondria-targeting signal in the protein. This enzyme is an attractive target for drug development, because the order of inhibition of the enzyme by a number of bisphosphonates is the same as that for inhibition of parasite growth. In summary, we report the first bifunctional farnesyl-diphosphate/geranylgeranyl-diphosphate synthase identified in eukaryotes, which, together with previous results, establishes this enzyme as a valid target for the chemotherapy of toxoplasmosis.

Nonpeptide antigens, presentation mechanisms, and immunological memory of human Vgamma2Vdelta2 T cells: discriminating friend from foe through the recognition of prenyl pyrophosphate antigens

Human Vgamma2Vdelta2 T cells play important roles in mediating immunity against microbial pathogens and have potent anti-tumor activity. Vgamma2Vdelta2 T cells recognize the pyrophosphorylated isoprenoid intermediates (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), an intermediate in the foreign 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway, and isopentenyl pyrophosphate (IPP), an intermediate in the self-mevalonate pathway. Infection with bacteria and protozoa using the MEP pathway leads to the rapid expansion of Vgamma2Vdelta2 T cells to very high numbers through preferential recognition of HMBPP. Activated Vgamma2Vdelta2 T cells produce proinflammatory cytokines and chemokines, kill infected cells, secrete growth factors for epithelial cells, and present antigens to alphabeta T cells. Vgamma2Vdelta2 T cells can also recognize high levels of IPP in certain tumors and in cells treated with pharmacological agents, such as bisphosphonates and alkylamines, that block farnesyl pyrophosphate synthase. Activated Vgamma2Vdelta2 T cells are able to kill most tumor cells because of recognition by T-cell receptor and natural killer receptors. The ubiquitous nature of the antigens converts essentially all Vgamma2Vdelta2 T cells to memory cells at an early age. Thus, primary infections with HMBPP-producing bacteria are perceived by Vgamma2Vdelta2 T cells as a repeat infection. Extensive efforts are underway to harness these cells to treat a variety of cancers and to provide microbial immunity.

Bisphosphonates: mode of action and pharmacology

The profound effects of the bisphosphonates on calcium metabolism were discovered over 30 years ago, and they are now well established as the major drugs used for the treatment of bone diseases associated with excessive resorption. Their principal uses are for Paget disease of bone, myeloma, bone metastases, and osteoporosis in adults, but there has been increasing and successful application in pediatric bone diseases, notably osteogenesis imperfecta. Bisphosphonates are structural analogues of inorganic pyrophosphate but are resistant to enzymatic and chemical breakdown. Bisphosphonates inhibit bone resorption by selective adsorption to mineral surfaces and subsequent internalization by bone-resorbing osteoclasts where they interfere with various biochemical processes. The simpler, non-nitrogen-containing bisphosphonates (eg, clodronate and etidronate) can be metabolically incorporated into nonhydrolysable analogues of adenosine triphosphate (ATP) that may inhibit ATP-dependent intracellular enzymes. In contrast, the more potent, nitrogen-containing bisphosphonates (eg, pamidronate, alendronate, risedronate, ibandronate, and zoledronate) inhibit a key enzyme, farnesyl pyrophosphate synthase, in the mevalonate pathway, thereby preventing the biosynthesis of isoprenoid compounds that are essential for the posttranslational modification of small guanosine triphosphate (GTP)-binding proteins (which are also GTPases) such as Rab, Rho, and Rac. The inhibition of protein prenylation and the disruption of the function of these key regulatory proteins explains the loss of osteoclast activity. The recently elucidated crystal structure of farnesyl diphosphate reveals how bisphosphonates bind to and inhibit at the active site via their critical nitrogen atoms. Although bisphosphonates are now established as an important class of drugs for the treatment of many bone diseases, there is new knowledge about how they work and the subtle but potentially important differences that exist between individual bisphosphonates. Understanding these may help to explain differences in potency, onset and duration of action, and clinical effectiveness.

γδ T cells: novel initiators of adaptive immunity

In this review, we discuss the potential role of human gammadelta T cells in the control of adaptive immunity. Our latest findings emerged as a consequence of our working hypothesis, which predicts a close relationship between the migration control in leukocytes and their function in immune processes as diverse as hematopoiesis, initiation of adaptive immunity, and immune surveillance in peripheral tissues. Leukocyte migration control is defined by the combination of migration and adhesion receptors on their surface and the tissue distribution of the corresponding ligands. According to our hypothesis, leukocytes featuring migration receptors for homing to lymph nodes (LNs) will also display activities that preferentially take place within LNs. Following this line of thought, by showing LN-homing properties in a subset of human gammadelta T cells, we speculated that gammadelta T cells influence the initiation of T- and B-cell responses. Here, we summarize our recent data, showing that LN-homing gammadelta T cells have potent antigen-presenting cell characteristics. This unexpected finding is discussed with regards to microbial sensing by human gammadelta T cells and a possible role for these cells in anti-microbial immunity.

Structural studies of Vgamma2Vdelta2 T cell phosphoantigens

Human gammadelta T cells containing the Vgamma2Vdelta2 (Vgamma9Vdelta2) T cell receptor are stimulated by a broad variety of small, phosphorus-containing antigenic molecules called phosphoantigens. The structures of several species present in both Mycobacteria (TUBags1-4) and in Escherichia coli have been reported to contain a formyl-alkyl diphosphate core. Here we report the synthesis of the lead member of the series, 3-formyl-1-butyl diphosphate. This compound has low activity for gammadelta T cell stimulation, unlike its highly active isomer (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate, necessitating a revision of the structure of TUBag1. Likewise, the structure of the species identified as the pentyl analog (TUBag 2) is revised to 6-phosphogluconate. These results indicate that neither TUBag1 nor the m/e 275 species proposed for TUBag2 are 3-formyl-1-alkyl diphosphates, leading to the conclusion that none of the natural phosphoantigens (TUBags1-4) possess the structures reported previously.

Human gamma delta T cells and tumor immunotherapy

Human Vgamma2Vdelta2 T cells recognize nonpeptide antigens derived from pathogenic microbes in a TCR-dependent manner, such as pyrophosphomonoester compounds from mycobacteria and malaria parasite and alkyl amines from Proteus, suggesting that this subset of gamma delta T cells is involved in infectious immunity. The precise recognition mechanism has been delineated using a site-directed mutagenesis strategy based on crystal structure of gamma delta TCR. On the other hand, several lines of evidence indicate that human gamma delta T cells are involved in tumor immunity. Although activated gamma delta T cells exhibit a cytolytic activity against most of tumor cells, only a small fraction of tumor cells, like Burkitt lymphoma cells and multiple myeloid cells, is recognized by human gamma delta T cells in a TCR-dependent manner. This implicates that human gamma delta T cells have two distinct pathways for anti-tumor immunity. One is a natural killer-like pathway and the other is a TCR-dependent pathway. Recently, it was shown that treatment of human tumor cells with nitrogen-containing bisphosphonates, therapeutic drugs for hypercalcemia in malignancy, generated antigenic structure on the surface of tumor cells, which could be recognized by human gamma delta T cells in a TCR-dependent manner. This tumor labeling system may lead to a novel strategy for cancer immunotherapy.

Phosphine-Catalyzed α-P-Addition on Activated Alkynes: A New Route to P−C−P Backbones

n-Tributylphosphine was found to efficiently catalyze the alpha-P addition of H-phosphonates, H-phosphinates, and H-phosphine oxide pronucleophiles on alkynes bearing phosphane oxide activating moieties. The reaction leads to 2-aryl-1-vinyl-1,1-diphosphane dioxide derivatives in good yields affording a new route to P-C-P backbones. The products of this reaction are easily converted to biologically important 1,1-bis-phosphonates analogues.

New insights into the role of T cells in the vicious cycle of bone metastases

PURPOSE OF REVIEW

Bone metastases interact with the bone microenvironment. Cancer cells modulate the functions of osteoblasts and osteoclasts to induce new bone formation or bone resorption, leading to secondary stimulation of tumor development. Recent findings suggest the involvement of T cells in this process.

RECENT FINDINGS

Bone metastatic cancer cells produce factors such as parathyroid hormone-related protein, interleukin-7, and interleukin-8 that can recruit or activate T cells. T cells are involved in bone remodeling and can induce osteoclastic resorption. Bone resorption releases transforming growth factor-beta, however, which could suppress T-cell antitumor immune responses. Bisphosphonate antiresorptive drugs are the approved treatment for solid tumor bone metastases. They have recently been found to activate the cytolytic activity of gammadelta T cells. Thus, inhibitors of transforming growth factor-beta or antiresorptive therapies may be effective enhancers of antitumor immune responses in bone.

SUMMARY

T cells at the site of bone metastases may be functionally suppressed by factors in the bone microenvironment. Instead of acting against tumor cells, they may increase bone resorption, making bone a privileged site for tumor growth.

Bisphosphonates: From Bench to Bedside

The discovery and development of the bisphosphonates (BPs) as a major class of drugs for the treatment of bone diseases has been a fascinating journey that is still not over. In clinical medicine, several BPs are established as the treatments of choice for various diseases of excessive bone resorption, including Paget's disease of bone, myeloma and bone metastases, and osteoporosis. Bisphosphonates are chemically stable analogues of inorganic pyrophosphate, and are resistant to breakdown by enzymatic hydrolysis. Bisphosphonates inhibit bone resorption by being selectively taken up and adsorbed to mineral surfaces in bone, where they interfere with the action of the bone-resorbing osteoclasts. Bisphosphonates are internalized by osteoclasts and interfere with specific biochemical processes. Bisphosphonates can be classified into at least two groups with different molecular modes of action. The simpler non-nitrogen-containing bisphosphonates (such as clodronate and etidronate) can be metabolically incorporated into nonhydrolyzable analogues of adenosine triphosphate (ATP) that may inhibit ATP-dependent intracellular enzymes. The more potent, nitrogen-containing bisphosphonates (such as pamidronate, alendronate, risedronate, ibandronate, and zoledronate) are not metabolized in this way but can inhibit enzymes of the mevalonate pathway, thereby preventing the biosynthesis of isoprenoid compounds that are essential for the posttranslational modification of small GTP-binding proteins (which are also GTPases) such as rab, rho, and rac. The inhibition of protein prenylation and the disruption of the function of these key regulatory proteins explain the loss of osteoclast activity and induction of apoptosis. The key target for bisphosphonates is farnesyl pyrophosphate synthase (FPPS) within osteoclasts, and the recently elucidated crystal structure of this enzyme reveals how BPs bind to and inhibit at the active site via their critical N atoms. In conclusion, bisphosphonates are now established as an important class of drugs for the treatment of many bone diseases, and their mode of action is being unraveled. As a result their full therapeutic potential is gradually being realized.

Risedronate for prevention and treatment of osteoporosis in postmenopausal women

Risedronate sodium is an N-containing bisphosphonate that has been approved for the prevention and treatment of osteoporosis in postmenopausal women. An increase in the rate of bone remodelling is a regular feature of oestrogen withdrawal during the menopausal transition, but excessive remodelling leads to bone fragility. Risedronate and similar compounds reduce the rate of bone remodelling by suppressing the action of osteoclasts. The antifracture efficacy of risedronate is impressive. In large clinical trials of postmenopausal women with osteoporosis-related fracture(s) at entry, the risk of incident vertebral and non-vertebral fractures was reduced by approximately 40%. In older women at risk for hip fracture, incident hip fractures were also reduced by approximately 40%. Antifracture efficacy develops within the first 6 months, and treatment has been followed for as long as 5 years without deleterious effects on bone. We await reports of experience with risedronate in 'real-world' cases of greater complexity (i.e., in patients with co-morbidities and medications that would have excluded them from published clinical trials).

Enthalpy versus Entropy-Driven Binding of Bisphosphonates to Farnesyl Diphosphate Synthase

We report the results of an ITC (isothermal titration calorimetry) investigation of the binding of six bisphosphonates to the enzyme farnesyl diphosphate synthase (FPPS; EC 2.5.1.10) from Trypanosoma brucei. The bisphosphonates investigated were zoledronate, risedronate, ibandronate, pamidronate, 2-phenyl-1-hydroxyethane-1,1-bisphosphonate, and 1-(2,2-bisphosphonoethyl)-3-iodo pyridinium. At pH = 7.4, both risedronate and the phenylethane bisphosphonate bind in an enthalpy-driven manner (DeltaH approximately -9 to 10 kcal mol-1), but the other four bisphosphonates bind in an entropy-driven manner (DeltaS varying from 31.2 to 55.1 cal K-1 mol-1). However, at pH = 8.5, zoledronate binding switches from entropy to enthalpy-driven. The DeltaG results are highly correlated with FPPS inhibition results obtained using a radiochemical assay (R2 = 0.85, N = 11, P < 0.001). The DeltaH and DeltaS results are interpreted in terms of a model in which bisphosphonates with charged side chains have positive DeltaH values, due to the enthalpic cost of desolvation (due to strong ion-dipole interactions) and, likewise, a positive DeltaS, due to an increase in water entropy (both ligand and protein associated) on ligand binding to FPPS: the hydrophobic effect. For the neutral side chains (risedronate at pH 7.4, 8.5 and zoledronate at pH 8.5, as well as the phenylethane bisphosphonate), binding is overwhelmingly enthalpy-driven, with the enhanced activity of the basic side chain containing species being attributable to their becoming protonated in the active site. Given the large size of the bisphosphonate market and the potential importance of the development of these compounds for cancer immunotherapy and anti-parasitic chemotherapy, these results are of broad general interest in the context of the development of new, potent, and selective FPPS inhibitors.

Ophthalmological Events in Patients Receiving Risedronate

BACKGROUND

In the UK, the nitrogen bisphosphonate risedronate is licensed for the prevention and treatment of osteoporosis and corticosteroid-induced osteoporosis in postmenopausal women. It is also licensed for the treatment of Paget's disease. During a prescription-event monitoring (PEM) study on risedronate we noted a number of ophthalmological events. Recently, case reports of ophthalmological adverse drug reactions in patients taking bisphosphonates were published in the medical literature. The aim of this study was to further evaluate the association of ophthalmological events reported in relation to risedronate treatment during a PEM study on the drug.

METHODS

An observational cohort study (PEM study) was conducted in England between September 2000 and June 2002. General practitioners (GPs) were asked for follow-up information on selected events. Events followed up were classified as either 'probably', 'possibly' or 'unlikely' to be related to risedronate, using a modified WHO classification. If insufficient information was obtained on the follow-up questionnaire, the cases were categorised as 'unassessable'.

RESULTS

Of the total PEM study cohort of 13 643 patients, 11 156 (82%) were females and 2398 (18%) were males. We received 359 reports of ophthalmological events in 313 patients during the entire study period. Of these we followed up 178 events in 178 patients. Nineteen events in 19 patients were assessed as possibly or probably related to risedronate. The age range for these patients was 50-92 years and the time to onset ranged from 7 days to 5 months. Dry eye (six reports), sore eye (five reports) and conjunctivitis (three reports) were the most frequently reported ophthalmological events assessed as probably or possibly related to risedronate therapy. GPs also reported several other inflammatory conditions of the eye, amongst them two events each of iritis and episcleritis as well as one of keratitis. However, the information received on follow up of these events was insufficient to make causality assessments.

CONCLUSION

Patients receiving risedronate can present with a variety of signs and symptoms affecting the eye with different degrees of severity. Patients may present after the first month of treatment. Doctors should have an increased awareness of possible ophthalmological adverse drug reactions in patients receiving this drug, which may affect the eyesight in a population at increased risk of fracture if they fall.

Effect of a convenient single 90-mg pamidronate dose on biochemical markers of bone metabolism in patients with acute spinal cord injury

BACKGROUND/OBJECTIVE

To describe the biochemical and adverse effects of a convenient single 90 mg pamidronate dose in patients with acute spinal cord injury (SCI) and compare these effects with those observed in a previous similar study using a 30 mg/d x 3-day pamidronate dosing regimen.

STUDY DESIGN

Retrospective cohort study.

SETTING

University-based rehabilitation center in New York City.

METHODS

A total of 32 patients with SCI were evaluated for biochemical response and adverse events associated with pamidronate therapy. All patients were screened at or near admission for acute rehabilitation, received calcium (1,000 mg daily) and calcitriol (0.25 micrg daily) therapy daily, and on day 4, received a single dose of pamidronate, 90 mg by intravenous infusion, over 4 hours. Serum calcium and phosphate levels were closely monitored, and 2 weeks after pamidronate, biochemical bone markers were re-evaluated.

RESULTS

Responses of biochemical markers of bone resorption (N-telopeptide and 24-hour urinary calcium excretion) to pamidronate 90 mg were consistent with an antiresorptive effect, although less than that observed with a 30 mg/d x 3-day pamidronate dosing regimen. The frequency of hypocalcemia was greater, and hypophosphatemia was less than the 30 mg/d x 3-day pamidronate dosing regimen. Fever was more frequent (78%) with the 90-mg single dose of pamidronate compared with the 30 mg/d x 3-day pamidronate dosing regimen (20%).

CONCLUSIONS

Single-dose pamidronate 90 mg is effective at reducing biochemical markers of bone hyperresorption in patients with acute SCI but is associated with a greater incidence of fever compared with a 30 mg/d x 3-day dosing regimen.

Solid-State Molecular Organization and Solution Behavior of Methane-1,1-Diphosphonic Acid Derivatives of Heterocyclic Amines: The Role of the Topochemical Ring Modification and the Intramolecular Hydrogen Bonds in Monosubstituted Piperid-1-ylmethane-1,1-diphosphonic Acids

The crystal structures of 3-methylpiperid-1-ylmethane-1,1-diphosphonic (2), 4-methylpiperid-1-ylmethane-1,1-diphosphonic (3), 2-ethylpiperid-1-ylmethane-1,1-diphosphonic (4), and 2-methylpiperid-1-ylmethane-1,1-diphosphonic (5) acids have been determined and are discussed with respect to their molecular organization and crystal-packing preferences. The chair conformation, predominant also in solution, favors equatorial positioning of the bulky substituents of the heterocyclic N and C atoms. The molecular geometry also provides access to intramolecular hydrogen-bond formation between the axial protons located on the nitrogen atoms, as well as the carbon atoms closest to it, and phosphonic/phosphonate oxygen atoms. The molecules preferably arrange in monolayers, observed in all crystals with an exception of 3. The layers are held in place in the third direction through van der Waals interactions. The analysis of two-dimensional hydrogen-bonded networks is concentrated on revealing how the substituent's topology of the molecule affects the solid-state organization in well-defined structures and is aimed at unraveling the consequences and the possible conformational changes by stepwise network disruption upon crystal dissolution in water. The solution NMR studies are focused on revealing the role that the topochemistry of the substituent plays for the stereodynamics in 2-5. It is demonstrated that in contrast to piperid-1-ylmethane-1,1-diphosphonic acid (1), in which the ring inversion/rotation around the C-N bond concerted with the N-H...O hydrogen-bond breaking/formation process leads to a mixture of two interconverting conformers, the concerted N-H...O breaking/rotation/N-H...O formation process in 2 and 3 allows for a predominance of one conformer in solution. However, placement of a substituent at 2-position in the ring hampers the rotation around the C-N bond; this makes 4 and 5 significantly less flexible relative to compounds 1-3. In addition, both compounds 4 and 5 are proved to exist as a mixture of two conformers, the equilibrium of which in acidic solution is shifted towards the conformer found in solid state. In alkaline solutions of 4 and 5, the equilibrium is shifted towards the conformer that is forced by the flipping of the heterocyclic ring. These results correlate well with recently documented differences in the biological potency of this group of compounds.

The bisphosphonate acute phase response: rapid and copious production of proinflammatory cytokines by peripheral blood gd T cells in response to aminobisphosphonates is inhibited by statins

The bisphosphonates are a novel class of drug that have been registered for various clinical applications worldwide. Bisphosphonates, and in particular the aminobisphosphonates (nBPs), are known to have a number of side-effects including a rise in body temperature and accompanying flu-like symptoms that resemble a typical acute phase response. The mechanism for this response has been partially elucidated and appears to be associated with the release of tumour necrosis factor (TNF)alpha and interleukin (IL)6, although the effector cells that release these cytokines and the mechanism of action remain enigmatic. Here, we show that the nBP-induced acute phase response differs from the typical acute phase response in that CD14+ cells such as monocytes and macrophages are not the primary cytokine producing cells. We show that by inhibiting the mevalonate pathway, nBPs induce rapid and copious production of TNFalpha and IL6 by peripheral blood gammadelta T cells. Prior treatment with statins, which inhibit 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, blocks nBP-induced production of these proinflammatory cytokines by gammadelta T cells and may offer a means of avoiding the associated acute phase response. In addition, our findings provide a further mechanism for the anti-inflammatory effects attributed to inhibitors of HMG CoA reductase.

Synthesis of chiral phosphoantigens and their activity in gamma delta T cell stimulation

Gammadelta T cells expressing Vgamma2Vdelta2 T cell receptors are activated by a broad range of phosphorus-containing small molecules, termed phosphoantigens, and are of interest in the context of the chemotherapy of B cell malignancies. Here, we report the synthesis of four pairs of chiral phosphoantigens: the bromohydrins of isopentenyl diphosphate (Phosphostim), the epoxides of isopentenyl diphosphate (EIPP); and the corresponding bromohydrin and epoxide analogs of but-3-enyl diphosphate. The ability of each compound to stimulate human Vgamma2Vdelta2 T cells was determined by TNF-alpha release and cell proliferation. In these assays, the (R)-bromohydrin diphosphates were, on average, about twice as active as the (S)-bromohydrin diphosphates. In contrast, the (S)-form of EIPP was about twice as active as (R)-EIPP. The activities of the epoxy but-3-enyl diphosphates were both very low. These results suggest that chiral phosphoantigens, as opposed to racemic mixtures, may have utility in immunotherapy.