An in vitro model that can distinguish between effects on angiogenesis and on established vasculature: actions of TNP-470, marimastat and the tubulin-binding agent Ang-510

In anti-cancer therapy, current investigations explore the possibility of two different strategies to target tumor vasculature; one aims at interfering with angiogenesis, the process involving the outgrowth of new blood vessels from pre-existing vessels, while the other directs at affecting the already established tumor vasculature. However, the majority of in vitro model systems currently available examine the process of angiogenesis, while the current focus in anti-vascular therapies moves towards exploring the benefit of targeting established vasculature as well. This urges the need for in vitro systems that are able to differentiate between the effects of compounds on angiogenesis as well as on established vasculature. To achieve this, we developed an in vitro model in which effects of compounds on different vascular targets can be studied specifically. Using this model, we examined the actions of the fumagillin derivate TNP-470, the MMP-inhibitor marimastat and the recently developed tubulin-binding agent Ang-510. We show that TNP-470 and marimastat solely inhibited angiogenesis, whereas Ang-510 potently inhibited angiogenesis and caused massive disruption of newly established vasculature. We show that the use of this in vitro model allows for specific and efficient screening of the effects of compounds on different vascular targets, which may facilitate the identification of agents with potential clinical benefit. The indicated differences in the mode of action between marimastat, TNP-470 and Ang-510 to target vasculature are illustrative for this approach.

Effects of experimental conditions on the release of 45calcium from prelabeled fetal mouse long bones

Embryonic/neonatal bones in culture are commonly used for the study of osteoclastic resorption in vitro. For this purpose, the release of 45calcium (45Ca) from prelabeled bones is measured as an index of resorption. We studied 45Ca release from two types of long bone explants after different preparation methods: 17-day-old fetal mouse radii/ulnae with and without cartilage ends (intact radii/ulnae and shafts, respectively), and intact 18-day old metacarpals/metatarsals. In addition, we examined the effect of different culture conditions, such as cultures performed under the surface of the medium or at the interphase of medium and air, on 45Ca release and histology. When intact radii/ulnae were cultured under the surface of the medium, there was always a significant amount (10%) of net basal 45Ca release (corrected for physicochemical exchange) that was not due to osteoclastic resorption, as it could not be suppressed by inhibitors of resorption even at high concentrations. Moreover, histologically TRAcP-positive cells were almost absent after culture and the bone marrow/stromal cells in the center of the bone appeared necrotic, possibly due to a lack of oxygen. Under these culture conditions, osteoclasts could survive in shafts as well as in PTH-stimulated intact radii/ulnae, but a constant amount of 10% 45Ca, not due to resorption, was still released in the medium. When these explants were cultured at the interphase of medium and air, basal and stimulated 45Ca release originated from osteoclastic resorption. In contrast, in 18-day-old fetal mouse metacarpals/metatarsals, the experimental conditions applied did not affect 45Ca release, which was always due to resorption of the explants by osteoclasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Parathyroid hormone (PTH) and PTH-like protein (PLP) stimulate interleukin-6 production by osteogenic cells: a possible role of interleukin-6 in osteoclastogenesis

Osteogenic cells mediate PTH-stimulated osteoclastic bone resorption by a yet unidentified mechanism. We show that primairy rat osteoblast-like cells and the clonal osteogenic sarcoma cell line UMR-106 produce interleukin-6 (IL-6) and that bPTH(1-84) and synthetic hPLP(1-34) stimulate this production dose-dependently. With both peptides a close relation between IL-6 and cyclic-AMP production was found, though for PTH concentrations higher than 2.10(-8) M a clear dissociation was observed. Significant IL-6 activity was also detected in media of cultures of 17-day-old fetal mouse radii and metacarpals which was clearly stimulated by PTH. The source of IL-6 in these bone explants seems to be the osteogenic (cartilage) cells. Treatment of bone explants with IL-6 induced osteoclastic resorption which, however, depended on the bone resorption system used. This bone resorbing action of IL-6 is exerted probably through an effect on the formation of osteoclasts (osteoclastogenesis) rather than on the activation of already existing mature osteoclasts. We suggest that IL-6 produced by osteogenic cells may be a mediator in PTH-stimulated osteoclastic bone resorption.