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-β 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]

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.

Melanoma often metastasizes to bone where it is exposed to high concentrations of TGF-β. Constitutive Smad signaling occurs in human melanoma. Because TGF-β promotes metastases to bone by several types of solid tumors including breast cancer, we hypothesized that pharmacologic blockade of the TGF-β 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-β receptor I kinase (TβRI), 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-β induction of Smad3 phosphorylation, Smad3/4-specific transcription, Matrigel invasion and expression of the TGF-β 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 2days 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 4weeks treatment with SD-208 compared with vehicle-treated mice. Our results demonstrate that therapeutic targeting of TGF-β may prevent the development of melanoma bone metastases and decrease the progression of established osteolytic lesions. Cancer Res; 71(1); 175–84. ©2010 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.

Most 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. We 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. Hypoxia 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.