The flurbiprofen derivatives HCT1026 and HCT1027 inhibit bone resorption by a mechanism independent of COX inhibition and nitric oxide production.

Prostaglandins and nitric oxide both modulate bone resorption and bone formation. We previously reported that a nitrosylated derivative of flurbiprofen, termed HCT1026, exerted inhibitory effects on osteoclastic bone resorption, which could not be reproduced by combining the parent compound with nitric oxide (NO) donors. The aim of this study was to investigate the mechanism by which HCT1026 inhibits bone resorption. We compared the effects of flurbiprofen and HCT1026 on osteoclast and osteoblast activity with those of HCT1027--an analogue of HCT1026, which lacks an NO-donating moiety. We found that HCT1026 and HCT1027 inhibited bone resorption in interleukin (IL)-1-stimulated murine osteoblast-bone marrow cocultures, with half-maximal effects (IC50) at 20 +/- 5 microM for HCT1026 and 25 +/- 6 microM for HCT1027 compared with 399 +/- 25 microM for flurbiprofen (P < 0.0001). These differences were unrelated to cyclooxygenase (COX) inhibition since HCT1026 and HCT1027 were about seven to eight times less potent than flurbiprofen at inhibiting COX-1 activity and half as potent at inhibiting COX-2 activity. Further studies showed that HCT1026 and HCT1027 activated caspase-3 in rabbit osteoclasts and promoted osteoclast apoptosis, as assessed by nuclear morphology and TUNEL assays. We conclude that HCT1026 and HCT1027 inhibit osteoclast formation and activity by a mechanism that is independent of NO production and COX inhibition. This raises the possibility that both compounds interact with a novel molecular target expressed on osteoclasts to promote apoptosis and inhibit bone resorption. This demonstrates that HCT1026 and derivatives could represent a novel class of antiresorptive drugs with therapeutic value in the treatment of bone diseases associated with accelerated bone loss due to osteoclast activation.

Hydrogen sulphide-releasing diclofenac derivatives inhibit breast cancer-induced osteoclastogenesis in vitro and prevent osteolysis ex vivo.

BACKGROUND AND PURPOSE: Hydrogen sulphide (H(2)S) and prostaglandins are both involved in inflammation, cancer and bone turnover, and non-steroidal anti-inflammatory drugs (NSAIDs) and H(2)S donors exhibit anti-inflammatory and anti-tumour properties. H(2)S-releasing diclofenac (S-DCF) derivatives are a novel class of NSAIDs combining the properties of a H(2)S donor with those of a conventional NSAID. EXPERIMENTAL APPROACH: We studied the effects of the S-DCF derivatives ACS15 and ACS32 on osteoclast and osteoblast differentiation and activity in vitro, human and mouse breast cancer cells support for osteoclast formation and signalling in vitro, and osteolysis ex vivo. KEY RESULTS: The S-diclofenac derivatives ACS15 and ACS32 inhibited the increase in osteoclast formation induced by human MDA-MB-231 and MCF-7 and mouse 4T1 breast cancer cells without affecting breast cancer cell viability. Conditioned media from human MDA-MB-231 cells enhanced IκB phosphorylation and osteoclast formation and these effects were significantly inhibited following treatment by ACS15 and ACS32, whereas the parent compound diclofenac had no effects. ACS15 and ACS32 inhibited receptor activator of NFκB ligand-induced osteoclast formation and resorption, and caused caspase-3 activation and apoptosis in mature osteoclasts via a mechanism dependent on IKK/NFκB inhibition. In calvaria organ culture, human MDA-MB-231 cells caused osteolysis, and this effect was completely prevented following treatment with ACS15 and ACS32. CONCLUSIONS AND IMPLICATIONS: S-diclofenac derivatives inhibit osteoclast formation and activity, suppress breast cancer cell support for osteoclastogenesis and prevent osteolysis. This suggests that H(2)S-releasing diclofenac derivatives exhibit anti-resorptive properties, which might be of clinical value in the treatment of osteolytic bone disease.