Novel bone-targeted parathyroid hormone-related peptide antagonists inhibit breast cancer bone metastases.

Patients with advanced breast cancer often develop bone metastases. Treatment is limited to palliative care. Parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) antagonists for bone metastases failed clinically due to short half-life and inadequate concentration in bone. We synthesized two novel PTHrP antagonists fused to an inert bacterial collagen binding domain (CBD) that directs drugs to bone. PTH(7-33)-CBD is an N-terminal truncated PTHrP antagonist. [W2]PTH(1-33)-CBD is an PTHrP inverse-agonist. The aim of this study was to assess PTH(7-33)-CBD to reduce breast cancer bone metastases and prevent osteolytic destruction in mice and to assess both drugs for apoptosis of breast cancer cells in vitro and inhibition of PTH receptor (PTHR1). PTH(7-33)-CBD (1000 µg/kg, subcutaneous) or vehicle was administered 24 h prior to MDA-MB-231 breast cancer cell inoculation into the tibia marrow. Weekly tumor burden and bone density were measured. Pharmacokinetic analysis of PTH(7-33)-CBD in rat serum was evaluated. Drug effect on cAMP accumulation in SaOS-2 osteosarcoma cells and apoptosis of MDA-MB-231 cells was assessed. PTH(7-33)-CBD reduced MDA-MB-231 tumor burden and osteolytic destruction in mice 4-5 weeks post-treatment. PTH(7-33)-CBD (1000 µg/kg i.v. and subcutaneous) in rats was rapidly absorbed with peak concentration 5-min and terminal half-life 3-h. Bioavailability by the subcutaneous route was 43% relative to the i.v. route. PTH(7-33)-CBD was detected only on rat periosteal bone surfaces that stained positive for collagen-1. PTH(7-33)-CBD and [W2]PTH(1-33)-CBD (10-8M) blocked basal and PTH agonist-induced cAMP accumulation in SaOS-2 osteosarcoma cells. Both drugs induced PTHR1-dependent apoptosis of MDA-MB-231 cells in vitro. Novel bone-targeted PTHrP antagonists represent a new paradigm for treatment of breast cancer bone metastases.

PTHrP Drives Pancreatic Cancer Growth and Metastasis and Reveals a New Therapeutic Vulnerability.

Pancreatic cancer metastasis is a leading cause of cancer-related deaths, yet very little is understood regarding the underlying biology. As a result, targeted therapies to inhibit metastasis are lacking. Here, we report that the parathyroid hormone-related protein (PTHrP encoded by PTHLH) is frequently amplified as part of the KRAS amplicon in patients with pancreatic cancer. PTHrP upregulation drives the growth of both primary and metastatic tumors in mice and is highly enriched in pancreatic ductal adenocarcinoma metastases. Loss of PTHrP-either genetically or pharmacologically-dramatically reduces tumor burden, eliminates metastasis, and enhances overall survival. These effects are mediated in part through a reduction in epithelial-to-mesenchymal transition, which reduces the ability of tumor cells to initiate metastatic cascade. Spp1, which encodes osteopontin, is revealed to be a downstream effector of PTHrP. Our results establish a new paradigm in pancreatic cancer whereby PTHrP is a driver of disease progression and emerges as a novel therapeutic vulnerability. SIGNIFICANCE: Pancreatic cancer often presents with metastases, yet no strategies exist to pharmacologically inhibit this process. Herein, we establish the oncogenic and prometastatic roles of PTHLH, a novel amplified gene in pancreatic ductal adenocarcinoma. We demonstrate that blocking PTHrP activity reduces primary tumor growth, prevents metastasis, and prolongs survival in mice.This article is highlighted in the In This Issue feature, p. 1601.

Novel advances in the treatment of osteoporosis.

INTRODUCTION: Osteoporosis is a significant public health issue affecting over half of women aged over 50. With an aging population, its importance is set to increase further over time. Prevention of fragility fractures avoids significant mortality and morbidity as well as saving significant direct and indirect costs to the economy. In this review, we discuss existing treatments to contextualize the treatment landscape, and demonstrate how our understanding of bone pathophysiology has led to novel therapies-in the form of combinations and altered durations of existing treatments, as well as newer drug therapies. SOURCES OF DATA: PubMed and Embase were searched for randomized controlled trials of new therapies for osteoporosis. These searches were supplemented with material presented in abstract form at international meetings. AREAS OF AGREEMENT: New drugs that appear promising in the treatment of osteoporosis include the cathepsin K inhibitor, monoclonal antibodies against sclerostin and parathyroid hormone-related protein analog. AREAS OF CONTROVERSY: Separate to the development of novel drug therapies is the issue of how best to use agents that are currently available to us; specifically which agent to choose, alone or in combination; duration of therapy; how best to identify patients at highest risk of fracture, and to ensure the highest possible adherence to medication. Many of these issues have been addressed in other excellent review papers, and will not be considered in detail here. GROWING POINTS: As with all new treatments, we await results of long-term use and experience in 'real life' patient populations. AREAS TIMELY FOR DEVELOPING RESEARCH: As alluded to above, data are urgently required regarding the optimal duration of therapy; use of combination therapy; ordering of therapies for best therapeutic effect. As stratified medicine becomes more strongly considered in all areas of therapy, its merits in osteoporosis as in other musculoskeletal conditions, is timely and valuable.

The parathyroid hormone-related protein is secreted during the osteogenic differentiation of human dental follicle cells and inhibits the alkaline phosphatase activity and the expression of DLX3.

The dental follicle is involved in tooth eruption and it expresses a great amount of the parathyroid hormone-related protein (PTHrP). PTHrP as an extracellular protein is required for a multitude of different regulations of enchondral bone development and differentiation of bone precursor cells and of the development of craniofacial tissues. The dental follicle contains also precursor cells (DFCs) of the periodontium. Isolated DFCs differentiate into periodontal ligament cells, alveolar osteoblast and cementoblasts. However, the role of PTHrP during the human periodontal development remains elusive. Our study evaluated the influence of PTHrP on the osteogenic differentiation of DFCs under in vitro conditions for the first time. The PTHrP protein was highly secreted after 4days of the induction of the osteogenic differentiation of DFCs with dexamethasone (2160.5pg/ml±345.7SD. in osteogenic differentiation medium vs. 315.7pg/ml±156.2SD. in standard cell culture medium; Student's t Test: p<0.05 (n=3)). We showed that the supplementation of the osteogenic differentiation medium with PTHrP inhibited the alkaline phosphatase activity and the expression of the transcription factor DLX3, but the depletion of PTHrP did not support the differentiation of DFCs. Previous studies have shown that Indian Hedgehog (IHH) induces PTHrP and that PTHrP, in turn, inhibits IHH via a negative feedback loop. We showed that SUFU (Suppressor Of Fused Homolog) was not regulated during the osteogenic differentiation in DFCs. So, neither the hedgehog signaling pathway induced PTHrP nor PTHrP suppressed the hedgehog signaling pathway during the osteogenic differentiation in DFCs. In conclusion, our results suggest that PTHrP regulates independently of the hedgehog signaling pathway the osteogenic differentiated in DFCs.

Evaluating the role of PTH in promotion of chondrosarcoma cell proliferation and invasion by inhibiting primary cilia expression.

Chondrosarcoma is characterized by secretion of a cartilage-like matrix, with high proliferation ability and metastatic potential. Previous studies have shown that parathyroid hormone-related protein (PTHrP) has a close relationship with various tumor types. The objectives of this study were to research the function played by PTHrP in human chondrosarcoma, especially targeting cell proliferation and invasion, and to search for the potential interaction between PTHrP and primary cilia in tumorigenesis. Surgical resection tissues and the human chondrosarcoma cell line SW1353 were used in the scientific research. Cells were stimulated with an optimum concentration of recombinant PTH (1-84), and siRNA was used to interfere with internal PTHrP. Cell proliferation and invasion assays were applied, including MTS-8 cell proliferation assay, Western blot, RT-PCR, Transwell invasion assay, and immunohistochemistry and immunofluorescence assays. A high level of PTHrP expression was found in human chondrosarcoma tissues, and recombinant PTH exhibited positive promotion in tumor cell proliferation and invasion. In the meantime, PTHrP could inhibit the assembly of primary cilia and regulate downstream gene expression. These findings indicate that PTHrP can regulate tumor cell proliferation and invasion ability, possibly through suppression of primary cilia assembly. Thus, restricting PTHrP over-expression is a feasible potential therapeutic method for chondrosarcoma.

Parathyroid hormone-related peptide and the hair cycle - is it the agonists or the antagonists that cause hair growth?

While the effects of PTHrP have been studied for almost 20 years, most of these studies have focused on effects on the termination of the anagen phase, giving an incomplete picture of the overall effect of PTHrP on the hair cycle. PTHrP was determined in several experimental models to promote transition of hair follicles from anagen to catagen phase, which by itself would suggest that PTHrP blockade might prolong the anagen phase and promote hair growth. However, clinical trials with topically applied PTHrP antagonists have been disappointing, leading to a reconsideration of this model. Additional studies performed in mouse models where hair follicles are damaged (alopecia areata, chemotherapy-induced alopecia) suggest that PTHrP has effects early in the hair cycle as well, promoting hair follicles' entry into anagen phase and initiates the hair cycle. While the mechanism of this has yet to be elucidated, it may involve activation of the Wnt pathway. Thus, the overall effect of PTHrP is to stimulate and accelerate the hair cycle, and in the more clinically relevant models of hair loss where hair follicles have been damaged or become quiescent, it is the agonists, not the antagonists, which would be expected to promote hair growth.

Parathyroid hormone-related protein: potential therapeutic target for melanoma invasion and metastasis.

The role of PTHrP in the highly metastatic human melanoma disease is not known. This study investigates the mechanisms of action of this secreted factor through homozygous inactivation of the Pthrp gene in A375 human melanoma cells. In vitro, Pthrp-ablated cells (knockout [KO]-A375, -/-) showed decreased motility and anchorage-independent growth, rounder morphology, and a significant reduction in invasion capacity compared with nonablated A375 cells (wild-type [WT]-A375, +/+). PTHrP peptide 1-34 and conditioned medium from WT-A375 cells partially restored the invasive phenotype in KO-A375. Pthrp ablation substantially decreased actin polymerization, matrix metallopeptidase 9 expression and focal adhesion kinase phosphorylation. In vivo, green fluorescent protein-transduced ablated and nonablated A375 cells were injected intracardially or sc into nude mice to study proliferation and multiorgan metastasis. Dissemination of injected Pthrp-ablated cells to lung and liver was reduced by 85% and 50%, respectively, compared with nonablated controls (120 hours after injection). The number of metastatic lesions and the percentage of animals with metastasis were markedly lower in mice injected with Pthrp-ablated A375, and 45% of these animals survived a 7-week period compared with 15% of mice injected with nonablated WT-A375. When mice injected with WT-A375 were treated with our blocking anti-PTHrP monoclonal antibody raised against the first 33 amino acids of human PTHrP, tumor size was decreased by more than 80% over 4 weeks and survival was significantly improved over 8 months. This study provides direct evidence of the major role for PTHrP in melanoma invasion and metastasis and suggests that agents that suppress PTHrP may be beneficial against melanoma progression.

Tumour-derived PTH-related protein triggers adipose tissue browning and cancer cachexia.

Cachexia is a wasting disorder of adipose and skeletal muscle tissues that leads to profound weight loss and frailty. About half of all cancer patients suffer from cachexia, which impairs quality of life, limits cancer therapy and decreases survival. One key characteristic of cachexia is higher resting energy expenditure levels than in healthy individuals, which has been linked to greater thermogenesis by brown fat. How tumours induce brown fat activity is unknown. Here, using a Lewis lung carcinoma model of cancer cachexia, we show that tumour-derived parathyroid-hormone-related protein (PTHrP) has an important role in wasting, through driving the expression of genes involved in thermogenesis in adipose tissues. Neutralization of PTHrP in tumour-bearing mice blocked adipose tissue browning and the loss of muscle mass and strength. Our results demonstrate that PTHrP mediates energy wasting in fat tissues and contributes to the broader aspects of cancer cachexia. Thus, neutralization of PTHrP might hold promise for ameliorating cancer cachexia and improving patient survival.

MiR-126-5p regulates osteolysis formation and stromal cell proliferation in giant cell tumor through inhibition of PTHrP.

Parathyroid hormone-related protein (PTHrP) has been identified to play a crucial role in osteolysis formation and stromal cell (GCTSC) proliferation in giant cell tumor (GCT). MiR-126-5p is an intronic miRNA identified as tumor suppressor in many tumors, but its role in GCT is poorly understood. We found that miR-126-5p was decreased in GCT and could directly regulate PTHrP expression. Furthermore, miR-126-5p could control osteoclast (OC) differentiation, GCTSC proliferation and osteolysis formation in GCT through negative regulation of PTHrP. Thus, these results suggest that miR-126-5p could directly target PTHrP and have a tumor suppressor function in GCT.

DLC1-dependent parathyroid hormone-like hormone inhibition suppresses breast cancer bone metastasis.

Bone metastasis is a frequent complication of breast cancer that is often accelerated by TGF-ß signaling; however, little is known about how the TGF-ß pathway is regulated during bone metastasis. Here we report that deleted in liver cancer 1 (DLC1) is an important regulator of TGF-ß responses and osteolytic metastasis of breast cancer cells. In murine models, breast cancer cells lacking DLC1 expression exhibited enhanced capabilities of bone metastasis. Knockdown of DLC1 in cancer cells promoted bone metastasis, leading to manifested osteolysis and accelerated death in mice, while DLC1 overexpression suppressed bone metastasis. Activation of Rho-ROCK signaling in the absence of DLC1 mediated SMAD3 linker region phosphorylation and TGF-ß-induced expression of parathyroid hormone-like hormone (PTHLH), leading to osteoclast maturation for osteolytic colonization. Furthermore, pharmacological inhibition of Rho-ROCK effectively reduced PTHLH production and breast cancer bone metastasis in vitro and in vivo. Evaluation of clinical breast tumor samples revealed that reduced DLC1 expression was linked to elevated PTHLH expression and organ-specific metastasis to bone. Overall, our findings define a stroma-dependent paradigm of Rho signaling in cancer and implicate Rho-TGF-ß crosstalk in osteolytic bone metastasis.

Betulinic acid, a bioactive pentacyclic triterpenoid, inhibits skeletal-related events induced by breast cancer bone metastases and treatment.

Many breast cancer patients experience bone metastases and suffer skeletal complications. The present study provides evidence on the protective and therapeutic potential of betulinic acid on cancer-associated bone diseases. Betulinic acid is a naturally occurring triterpenoid with the beneficial activity to limit the progression and severity of cancer, diabetes, cardiovascular diseases, atherosclerosis, and obesity. We first investigated its effect on breast cancer cells, osteoblastic cells, and osteoclasts in the vicious cycle of osteolytic bone metastasis. Betulinic acid reduced cell viability and the production of parathyroid hormone-related protein (PTHrP), a major osteolytic factor, in MDA-MB-231 human metastatic breast cancer cells stimulated with or without tumor growth factor-ß. Betulinic acid blocked an increase in the receptor activator of nuclear factor-kappa B ligand (RANKL)/osteoprotegerin ratio by downregulating RANKL protein expression in PTHrP-treated human osteoblastic cells. In addition, betulinic acid inhibited RANKL-induced osteoclastogenesis in murine bone marrow macrophages and decreased the production of resorbed area in plates with a bone biomimetic synthetic surface by suppressing the secretion of matrix metalloproteinase (MMP)-2, MMP-9, and cathepsin K in RANKL-induced osteoclasts. Furthermore, oral administration of betulinic acid inhibited bone loss in mice intra-tibially inoculated with breast cancer cells and in ovariectomized mice causing estrogen deprivation, as supported by the restored bone morphometric parameters and serum bone turnover markers. Taken together, these findings suggest that betulinic acid may have the potential to prevent bone loss in patients with bone metastases and cancer treatment-induced estrogen deficiency.

[Bone targeted therapies: new agents]. / Os et thérapies moléculaires ciblées : nouveaux agents.

The development of bisphosphonates and anti-RANK/RANKL agents was associated with a better understanding of physiological and pathological processes of bone remodeling. New agents are now developed in this context targeting factors associated with osteoclastogenesis (TGFß, PTHrP), with signaling pathways activated during bone remodeling (Src, Cathepsin K) or with tumor cells homing into bone (chemokines). This review aims to present the underlying rationale for these developments as well as the clinical results. The emergence of new bone targeting therapies is discussed.

Construction of recombinant adenoviruses carrying the optimal shRNA template against goat PTHrP and successful suppression of PTHrP expression in mammary epithelial cells.

Parathyroid hormone-related protein (PTHrP) is a protein member of the parathyroid hormone family that regulates the dynamic balance between blood and bone calcium during lactation. However, the mechanism of its regulation is not very clear. In order to establish a framework for further functional studies of the PTHrP gene in goat mammary gland epithelial cells during the lactation period, PTHrP cDNA was isolated from Xinong Saanen dairy goats. Its coding sequence is 534 bp in size. We also designed a short hairpin RNA (shRNA) to efficiently inhibit PTHrP expression and constructed recombinant adenoviruses carrying a template encoding this shRNA (AD-PTHrP-322) using the Block-iT shRNA interference system. Finally, the inhibition of PTHrP expression by the recombinant adenoviruses was confirmed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and Western blotting. qRT-PCR results showed that the expression of PTHrP mRNA in mammary epithelial cells was downregulated by 29.2, 68.1, and 82.6% 24, 48, and 72 h after the cells were infected with AD-PTHrP-322, respectively. Western blotting also showed that the expression of PTHrP was reduced in a time-dependent manner. These results suggest that AD-PTHrP-322 significantly inhibits the expression of PTHrP.

Neuroendocrine-derived peptides promote prostate cancer cell survival through activation of IGF-1R signaling.

BACKGROUND: Neuroendocrine (NE) cells promote the progression of prostate cancer to a castration-resistant state through the production of paracrine growth factors. We have demonstrated this principle using in vitro and in vivo proliferative endpoints; however, the contributions of NE-derived pro-survival factors and anti-apoptosis to this phenomenon have not been thoroughly investigated. METHODS: Here, we utilized conditioned-medium (CM) from LNCaP cells, engineered to undergo NE differentiation, and examined its effects on PC3 and LNCaP cell survival. RESULTS: Statistically significant changes in clonogenic survival, Annexin V staining, PARP cleavage and trypan blue positivity of approximately twofold were observed in the presence of NE-derived CM relative to control-CM for both LNCaP and PC3 cells. These changes were partially abrogated by antagonists of the neuropeptides neurotensin, bombesin, and PTHrP. Selective inhibitors of IGF-1R, EGFR or Src caused significant and nearly complete blockade of prostate cancer cell survival due to NE secretions. Similar increases in cell survival were observed for LNCaP or PC3 cells treated with NE-derived medium in the presence of docetaxel. Increased phosphorylation of IGF-1R, following treatment with NE-derived medium, was accompanied by decreased protein tyrosine phosphatase, receptor type F (PTPRF) mRNA, and protein levels. Overexpression of PTPRF decreased cell survival, the amplitude and duration of IGF-1R phosphorylation, and enhanced PARP cleavage in the presence of NE-derived medium. CONCLUSIONS: These data support the hypothesis that NE-derived factors act upon prostate cancer cells to stimulate pro-survival signaling and describe a novel mechanism of cross-talk between NE-derived factors and IGF-1R, mediated in part by PTPRF.

T cells stimulate catabolic gene expression by the stromal cells from giant cell tumor of bone.

The factors that promote the localized bone resorption by giant cell tumor of bone (GCT) are not fully understood. We investigated whether T cells could contribute to bone resorption by stimulating expression of genes for parathyroid hormone-related protein (PTHrP), matrix metalloproteinase (MMP)-13, and the receptor activator of nuclear-factor κB ligand (RANKL). Two cell lines, Jurkat clone E6-1 and D1.1, were co-cultured with isolated GCT stromal cells. Real-time PCR analyses demonstrated a significant increase of all three genes following 48h incubation, and PTHrP and MMP-13 gene expression was also increased at 24h. Further, we examined the expression of CD40 ligand (CD40L), a protein expressed by activated T cells, and its receptor, CD40, in GCT. Immunohistochemistry results revealed expression of the CD40 receptor in both the stromal cells and giant cells of the tumor. RNA collected from whole GCT tissues showed expression of CD40LG, which was absent in cultured stromal cells, and suggests that CD40L is expressed within GCT. Stimulation of GCT stromal cells with CD40L significantly increased expression of the PTHrP and MMP-13 genes. Moreover, we show that inhibition of PTHrP with neutralizing antibodies significantly decreased MMP13 expression by the stromal cells compared to IgG-matched controls, whereas stimulation with PTHrP (1-34) increased MMP-13 gene expression. These results suggest that T cells may potentiate the catabolic effect of GCT.

Changes in serum parathyroid hormone-related protein in breastfed preterm infants.

BACKGROUND: Parathyroid hormone-related protein (PTHrP) has the ability to activate parathyroid hormone receptors and cause hypercalcemia. In a previous study we have demonstrated high concentrations of PTHrP in both term and preterm human milk (HM). PTHrP intestinal absorption and its influence upon calcium homeostasis of the preterm infant have not been studied yet. This study assessed the correlation between PTHrP concentrations in preterm HM and PTHrP in maternal and neonatal serum. STUDY DESIGN: We collected samples of expressed HM obtained from 16 mothers of preterm infants (25-34 weeks of gestation) and drew blood samples from both mothers and infants on postpartum days 2 and 10. PTHrP concentrations were measured by two-site immunoradiometric assay. Blood calcium (Ca), phosphorus (P), and alkaline phosphatase (ALP) concentrations were also measured. RESULTS: Neither maternal nor neonatal PTHrP serum concentrations varied significantly after 10 days of breastfeeding. There was a correlation between PTHrP concentrations in maternal serum and HM concentrations (R² = 0.24, p = 0.04), but not between HM and neonatal serum concentrations or between PTHrP concentrations in HM and preterm serum concentrations of Ca, P, and ALP. CONCLUSIONS: Despite high concentrations of PTHrP in preterm HM, serum concentrations of PTHrP of breastfed preterm infants did not increase over time. There was no correlation between PTHrP concentrations in HM and neonatal serum Ca concentration.

6-Thioguanine inhibition of parathyroid hormone-related protein expression is mediated by GLI2.

BACKGROUND: Breast cancer cells frequently metastasize to bone, where they up-regulate their expression of the transcription factor GLI2 and the downstream osteolytic factor parathyroid hormone-related protein (PTHrP). The guanosine nucleotide 6-thioguanine (6-TG) inhibits PTHrP expression and blocks osteolytic bone destruction in mice inoculated with bone metastatic cells; however, the mechanism by which 6-TG inhibits PTHrP remains unclear. We hypothesized that 6-TG inhibition of PTHrP is mediated through GLI2 signaling. MATERIALS AND METHODS: Human MDA-MB-231 breast cancer cells and RWGT2 squamous-cell lung carcinoma cells were treated with 100 µM 6-TG and examined for GLI2 mRNA expression and stability by Q-PCR, promoter activity by luciferase assay, and protein expression by Western blot. RESULTS: 6-TG significantly blocked GLI2 mRNA and protein expression, but did not affect stability. Additionally, 6-TG directly inhibited GLI2 promoter activity, and when cells were transfected with constitutively expressed GLI2, the inhibitory effect of 6-TG on PTHrP expression was abolished. CONCLUSION: Taken together, these data indicate that 6-TG regulates PTHrP in part through GLI2 transcription, and therefore the clinical use of 6-TG or other guanosine nucleotides may be a viable therapeutic option in tumor types expressing elevated levels of GLI proteins.

Negative regulation of parathyroid hormone-related protein expression by steroid hormones.

Elevated parathyroid hormone-related protein (PTHrP) is responsible for humoral hypercalcemia of malignancy (HHM), which is of clinical significance in treatment of terminal patients with malignancies. Steroid hormones were known to cause suppression of PTHrP expression. However, detailed studies linking multiple steroid hormones to PTHrP expression are lacking. Here we studied PTHrP expression in response to steroid hormones in four cell lines with excessive PTHrP production. Our study established that steroid hormones negatively regulate PTHrP expression. Vitamin D receptor, estrogen receptor α, glucocorticoid receptor, and progesterone receptor, were required for repression of PTHrP expression by the cognate ligands. A notable exception was the androgen receptor, which was dispensable for suppression of PTHrP expression in androgen-treated cells. We propose a pathway(s) involving nuclear receptors to suppress PTHrP expression.

[Encounter of cancer cells with bone. Development of bone metastasis-specific targeting therapy].

Bone, as well as liver and lungs, is one of the most preferential metastatic targets for solid cancers including breast, prostate, and lung cancers. Control of the bone metastasis is clinically important ; because they are frequently associated with bone pain and pathological fracture which greatly diminish the quality of life for patients. Interaction between cancer cells and microenvironment of metastatic site play an important role for establishment of cancer metastasis. The understanding of their mechanisms has been improved in recent years, and they will be new therapeutic strategies to cure the bone metastasis. Bisphosphonates has been clinically used for the bone metastasis. In addition, RANKL-RANK targeted drugs and cathepsin K inhibitors are also expected to be fruitful drugs for the bone metastasis. In this review paper, we summarize the molecular mechanism of these drugs, especially with regarding to the breast cancer bone metastasis. Furthermore, we touch upon the ubiquitin ligase CHIP which recently found as a master gene in the progression and metastasis of breast cancer.

Combinatorial library discovery of small molecule inhibitors of lung cancer proliferation and parathyroid hormone-related protein expression.

PTHrP (parathyroid hormone-related protein) is abnormally expressed in a substantial majority of lung cancers, especially non-small cell lung cancers, and plays a key role in tumor progression. Thus, this oncoprotein could be a target for treating patients with lung cancer. This study screened combinatorial libraries of heterocyclic amines for inhibitory effects on PTHrP expression and cell proliferation. Two libraries of over 780,000 bis-cyclic thiourea and guanidine compounds each were tested in BEN lung carcinoma cells. The number of PTHrP inhibitors and the magnitude of the reduction in PTHrP were greater for thioureas. Selected lead thiourea compounds decreased cell PTHrP protein content in dose-dependent fashion, reduced relative abundance of PTHrP mRNA, decreased transcripts derived from the PTHrP P3 promoter and reduced activity of a full length PTHrP promoter luciferase construct. Similar effects on PTHrP mRNA were observed in A549 and H441 lung adenocarcinoma cells and in H727 lung carcinoid cells. However, the compounds only inhibited PTHrP protein levels in BEN cells and H727 cells. The compounds reduced the rate of cell proliferation in BEN cells and H727 cells, but not in lines that showed no inhibition of PTHrP protein. These results suggest that cyclic thiourea compounds inhibit PTHrP expression mediated by the P3 promoter, which is widely used in the majority of PTHrP-expressing cells, and that they may inhibit growth of lung cancer cells through the same mechanism. Further work will be necessary to investigate their mechanism for effects on growth of PTHrP-positive tumors in vivo.