I. Ross Garrett

A causal role for endothelin-1 in the pathogenesis of osteoblastic bone metastases

Osteoblastic bone metastases are common in prostate and breast cancer patients, but mechanisms by which tumor cells stimulate new bone formation are unclear. We identified three breast cancer cell lines that cause osteoblastic metastases in a mouse model and secrete endothelin-1. Tumor-produced endothelin-1 stimulates new bone formation in vitro and osteoblastic metastases in vivo via the endothelin A receptor. Treatment with an orally active endothelin A receptor antagonist dramatically decreased bone metastases and tumor burden in mice inoculated with ZR-75-1 cells. Tumor-produced endothelin-1 may have a major role in the establishment of osteoblastic bone metastases, and endothelin A receptor blockade represents effective treatment.

Detection of myeloma in skeleton of mice by whole-body optical fluorescence imaging

Development of new therapies for myeloma has been hindered by the lack of suitable preclinical animal models of the disease in which widespread tumor foci in the skeleton can be detected reliably. Traditional means of detecting skeletal tumor infiltration such as histopathology are cumbersome and labor-intensive and do not allow temporal monitoring of tumor progression or regression in response to therapy. To resolve this problem, we modified the Radl 5TGM1 model of myeloma bone disease such that fluorescent myeloma tumors can be optically imaged in situ. Here, we show that murine myeloma 5TGM1 tumor cells, engineered to express enhanced green fluorescent protein (eGFP; 5TGM1-eGFP cells), can be imaged in a temporal fashion using a fluorescence illuminator and a charge-coupled device camera in skeletons of live C57BL/KaLwRij mice. High-resolution, whole-body images of tumor-bearing mice revealed that myeloma cells homed almost exclusively to the skeleton, with multiple focal tumor foci in the axial skeleton, consistent with myeloma tumor distribution in humans. Finally, the tested antitumor treatment effect of Velcade (bortezomib), a proteasome inhibitor used clinically in myeloma, was readily detected by GFP imaging, suggesting the power of the technique in combination with the Radl 5TGM1-eGFP model for rapid preclinical assessment and sensitive monitoring of novel and potential therapeutics. Whole-body GFP imaging is practical, convenient, inexpensive, and rapid, and these advantages should enable a high throughput when evaluating in vivo efficacy of new potential antimyeloma therapeutics and assessing response to treatment. [Mol Cancer Ther 2007;6(6):1701–8]

Evidence that interleukin-1 mediates its effects on bone resorption via the 80 kilodalton interleukin-1 receptor

SummaryInterleukin-1 (IL-1) mediates its effects through two distinct receptors, one of 80 kilodaltons (80 kD) present in athymic lymphocytes and fibroblasts, and one of 60 kD present in cells of the monocyte-macrophage lineage. A novel monocyte cytokine in the IL-1 family which binds to both the 80 and the 60 kD receptors has been purified, cloned, and expressed. As the interleukin-1 receptor antagonist (IL-1ra) has been shown to inhibit bone resorption in organ culture, it is not clear whether these effects are mediated through the 80 or the 60 kD receptor. Recently, neutralizing antibodies (35F5) have been developed to the 80 kD receptor which inhibit IL-1 effects mediated through this receptor. To determine the importance of the 80 kD receptor to IL-1-mediated bone resorption, we used the neutralizing antibodies (35F5) to the 80 kD receptor to determine if they inhibited bone resorption stimulated by IL-1 in bone organ cultures. The 35F5 antibody blocked bone-resorbing activity due to IL-1 completely, and also blocked control or “endogenous” bone-resorbing activity present in murine bone organ cultures incubated in control media. The 35F5 antibody had no effect on bone resorption mediated by tumor necrosis factor (TNF), or parathyroid hormone (PTH). These data suggest that the availability of the 80 kD IL-1 receptor is required for osteoclastic bone resorption mediated by IL-1.

A targeted approach for evaluating preclinical activity of botanical extracts for support of bone health

Using a sequential in vitro/in vivo approach, we tested the ability of botanical extracts to influence biomarkers associated with bone resorption and bone formation. Pomegranate fruit and grape seed extracts were found to exhibit anti-resorptive activity by inhibiting receptor activator of nuclear factor-κB ligand (RANKL) expression in MG-63 cells and to reduce IL-1β-stimulated calvarial 45Ca loss. A combination of pomegranate fruit and grape seed extracts were shown to be effective at inhibiting bone loss in ovariectomised rats as demonstrated by standard histomorphometry, biomechanical and bone mineral density measurements. Quercetin and licorice extract exhibited bone formation activity as measured by bone morphogenetic protein-2 (BMP-2) promoter activation, increased expression of BMP-2 mRNA and protein levels, and promotion of bone growth in cultured mouse calvariae. A combination of quercetin and licorice extract demonstrated a potential for increasing bone mineral density in an intact female rat model as compared with controls. The results from this sequential in vitro/in vivo research model yielded botanical extract formulas that demonstrate significant potential benefits for bone health.

The polyphenol resveratrol promotes skeletal growth in mice through a sirtuin 1‐bone morphogenic protein 2 longevity axis

The polyphenol resveratrol (RSV) exists in high quantities in certain foods (e.g. grapes and nuts). However, the capacity of RSV to confer physiological health benefits and a biological mechanism through which this might occur remains unclear.

Bone and Statins

The recent observation that statins stimulate bone formation adds to the list of pleiotropic actions of statins that cannot be accounted for by their effects to lower serum cholesterol. This has led not only to the possibility that statins have an extra therapeutic indication which represents a major market in the aging population, namely established osteoporosis, but also suggests important regulatory mechanisms for the control of osteoclast and osteoblast function. The influence of the mevalonate pathway on osteoclasts and osteoblasts has been emphasized by recent work on the mechanism of action of the nitrogen-containing bisphosphonates. This has led to a flurry of investigation not only on the clinical potential of the statins as stimulators of bone formation, but also on the role of intermediates in the mevalonate pathway as potential targets for drug discovery for osteoporosis.