Metastasis is a final stage of tumor progression. Breast and prostate cancer cells preferentially metastasize to bone, wherein they cause incurable osteolytic and osteoblastic lesions. The bone matrix is rich in factors, such as transforming growth factor-B and insulin-like growth factors, which are released into the tumor microenvironment by osteolysis. These factors stimulate the growth of tumor cells and alter their phenotype, thus promoting a vicious cycle of metastasis and bone pathology. Physical factors within the bone microenvironment, including low oxygen levels, acidic pH, and high extracellular calcium concentrations, may also enhance tumor growth. These elements of the microenvironment are potential targets for chemotherapeutic intervention to halt tumor growth and suppress bone metastasis. [Mol Cancer Ther 2007;6(10):2609 -17]

Melanoma has a propensity to metastasize to bone, where it is exposed to high concentrations of transforming growth factor-B (TGF-B). Because TGF-B promotes bone metastases from other solid tumors, such as breast cancer, we tested the role of TGF-B in melanoma metastases to bone. 1205Lu melanoma cells, stably transfected to overexpress the natural TGF-B/Smad signaling inhibitor Smad7, were studied in an experimental model of bone metastasis whereby tumor cells are inoculated into the left cardiac ventricle of nude mice. All mice bearing parental and mock-transfected 1205Lu cells developed osteolytic bone metastases 5 weeks post-tumor inoculation. Mice bearing 1205Lu-Smad7 tumors had significantly less osteolysis on radiographs and longer survival compared with parental and mock-transfected 1205Lu mice. To determine if the reduced bone metastases observed in mice bearing 1205Lu-Smad7 clones was due to reduced expression of TGF-B target genes known to enhance metastases to bone from breast cancer cells, we analyzed gene expression of osteolytic factors, parathyroid hormone-related protein (PTHrP) and interleukin-11 (IL-11), the chemotactic receptor CXCR4, and osteopontin in 1205Lu cells. Quantitative reverse transcription-PCR analysis indicated that PTHrP, IL-11, CXCR4, and osteopontin mRNA steady-state levels were robustly increased in response to TGF-B and that Smad7 and the TBRI small-molecule inhibitor, SB431542, prevented such induction. In addition, 1205Lu-Smad7 bone metastases expressed significantly lower levels of IL-11, connective tissue growth factor, and PTHrP. These data suggest that TGF-B promotes osteolytic bone metastases due to melanoma by stimulating the expression of prometastatic factors via the Smad pathway. Blockade of TGF-B signaling may be an effective treatment for melanoma metastasis to bone. [Cancer Res 2007;67(5):2317-24]

BackgroundMost patients with advanced breast cancer develop bone metastases, which cause pain, hypercalcemia, fractures, nerve compression and paralysis. Chemotherapy causes further bone loss, and bone-specific treatments are only palliative. Multiple tumor-secreted factors act on the bone microenvironment to drive a feed-forward cycle of tumor growth. Effective treatment requires inhibiting upstream regulators of groups of prometastatic factors. Two central regulators are hypoxia and transforming growth factor (TGF)- β. We asked whether hypoxia (via HIF-1α) and TGF-β signaling promote bone metastases independently or synergistically, and we tested molecular versus pharmacological inhibition strategies in an animal model.Methodology/Principal FindingsWe analyzed interactions between HIF-1α and TGF-β pathways in MDA-MB-231 breast cancer cells. Only vascular endothelial growth factor (VEGF) and the CXC chemokine receptor 4 (CXCR4), of 16 genes tested, were additively increased by both TGF-β and hypoxia, with effects on the proximal promoters. We inhibited HIF-1α and TGF-β pathways in tumor cells by shRNA and dominant negative receptor approaches. Inhibition of either pathway decreased bone metastasis, with no further effect of double blockade. We tested pharmacologic inhibitors of the pathways, which target both the tumor and the bone microenvironment. Unlike molecular blockade, combined drug treatment decreased bone metastases more than either alone, with effects on bone to decrease osteoclastic bone resorption and increase osteoblast activity, in addition to actions on tumor cells.Conclusions/SignificanceHypoxia and TGF-β signaling in parallel drive tumor bone metastases and regulate a common set of tumor genes. In contrast, small molecule inhibitors, by acting on both tumor cells and the bone microenvironment, additively decrease tumor burden, while improving skeletal quality. Our studies suggest that inhibitors of HIF-1α and TGF-β may improve treatment of bone metastases and increase survival.

Melanoma represents approximately 4% of human skin cancers, yet accounts for approximately 80% of deaths from cutaneous neoplasms (1). Although progress has been made in understanding the genetics of the molecular events underlying melanoma oncogenesis (2-4), the clinical challenge remains enormous. A genetic hallmark of melanoma is the presence of activating mutations in the oncogenes BRAF and NRAS, which are present in 70% and 15% of melanomas, respectively, and lead to constitutive activation of mitogen-activated protein kinase pathway signaling (3,5). However, molecules that inhibit mitogen-activated protein kinase pathway-associated kinases, like BRAF and MEK, have shown only limited efficacy in the treatment of metastatic melanoma (6). Thus, a deeper understanding of the cross talk between signaling networks and the complexity of melanoma progression should lead to more effective therapy.Hedgehog (HH) signaling is controlled at the cell surface by two transmembrane proteins, the tumor suppressor Patched-1 (PTCH1), which acts as a HH receptor, and the oncoprotein Smoothened (SMO). In the absence of HH, PTCH1 maintains SMO in an inactive state. In the presence of any of the three HH ligands (Sonic, Indian, or Desert HH), inhibition of SMO by PTCH1 is alleviated and a signal is transduced that leads to the nuclear translocation and activation of GLI family transcription factors (7,8). GLIs are often overexpressed in cancers and contribute to the progression of a variety of neoplasms via regulation of cell cycle progression and apoptosis (9,10). One recent study (11) Article

Melanoma often metastasizes to bone where it is exposed to high concentrations of TGF-b. Constitutive Smad signaling occurs in human melanoma. Because TGF-b promotes metastases to bone by several types of solid tumors including breast cancer, we hypothesized that pharmacologic blockade of the TGF-b signaling pathway may interfere with the capacity of melanoma cells to metastasize to bone. In this study, we tested the effect of a small molecule inhibitor of TGF-b receptor I kinase (TbRI), SD-208, on various parameters affecting the development and progression of melanoma, both in vitro and in a mouse model of human melanoma bone metastasis. In melanoma cell lines, SD-208 blocked TGF-b induction of Smad3 phosphorylation, Smad3/4-specific transcription, Matrigel invasion and expression of the TGF-b target genes PTHrP, IL-11, CTGF, and RUNX2. To assess effects of SD-208 on melanoma development and metastasis, nude mice were inoculated with 1205Lu melanoma cells into the left cardiac ventricle and drug was administered by oral gavage on prevention or treatment protocols. SD-208 (60 mg/kg/d), started 2 days before tumor inoculation prevented the development of osteolytic bone metastases compared with vehicle. In mice with established bone metastases, the size of osteolytic lesions was significantly reduced after 4 weeks treatment with SD-208 compared with vehicle-treated mice. Our results demonstrate that therapeutic targeting of TGF-b may prevent the development of melanoma bone metastases and decrease the progression of established osteolytic lesions. Cancer Res; 71(1); 175-84. Ó2010 AACR.

Bisphosphonates are primarily known for their ability to inhibit osteoclast-mediated bone resorption. They are an indispensable part of therapy for patients with cancers that cause osteolysis. However, there is now a growing body of evidence from preclinical research showing that bisphosphonates also exhibit antitumor activity, both in vitro and in vivo. They can affect molecular mechanisms of tumor cell adhesion, invasion, and proliferation; reinforce the effects of cytotoxic agents in a synergistic manner; and exhibit antiangiogenic and immunomodulatory effects. These preclinical findings reveal exciting ways of optimizing bisphosphonate therapy in oncology to fully exploit their antitumor potential. (Cancer Res 2005; 65(12): 4971-4)

SUMMARY Transforming growth factor-β (TGFβ) regulates the expression of genes supporting breast cancer cell in bone but little is known about prostate cancer bone metastases and TGFβ. Our study reveals that the TGFBR1 inhibitor SD208 effectively reduces prostate cancer bone metastases. TGFβ upregulates in prostate cancer cells a set of genes associated with cancer aggressiveness and bone metastases, and the most upregulated gene was PMEPA1. In patients, PMEPA1 expression decreased in metastatic prostate cancer and low Pmepa1 correlated with decreased metastasis-free survival. Only membrane-anchored isoforms of PMEPA1 interacted with R-SMADs and ubiquitin ligases, blocking TGFβ signaling independently of the proteasome. Interrupting this negative feedback loop by PMEPA1 knockdown increased prometastatic gene expression and bone metastases in a mouse prostate cancer model.

The ability of microorganisms to generate resistance outcompetes with the generation of new and efficient antibiotics; therefore, it is critical to develop novel antibiotic agents and treatments to control bacterial infections. An alternative to this worldwide problem is the use of nanomaterials with antimicrobial properties. Silver nanoparticles (AgNPs) have been extensively studied due to their antimicrobial effect in different organisms. In this work, the synergistic antimicrobial effect of AgNPs and conventional antibiotics was assessed in Gram-positive and Gram-negative bacteria. AgNPs minimal inhibitory concentration was 10–12 μg mL-1 in all bacterial strains tested, regardless of their different susceptibility against antibiotics. Interestingly, a synergistic antimicrobial effect was observed when combining AgNPs and kanamycin according to the fractional inhibitory concentration index, FICI: <0.5), an additive effect by combining AgNPs and chloramphenicol (FICI: 0.5 to 1), whereas no effect was found with AgNPs and β-lactam antibiotics combinations. Flow cytometry and TEM analysis showed that sublethal concentrations of AgNPs (6–7 μg mL-1) altered the bacterial membrane potential and caused ultrastructural damage, increasing the cell membrane permeability. No chemical interactions between AgNPs and antibiotics were detected. We propose an experimental supported mechanism of action by which combinatorial effect of antimicrobials drives synergy depending on their specific target, facilitated by membrane alterations generated by AgNPs. Our results provide a deeper understanding about the synergistic mechanism of AgNPs and antibiotics, aiming to combat antimicrobial infections efficiently, especially those by multi-drug resistant microorganisms, in order to mitigate the current crisis due to antibiotic resistance.