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 FICT1027-an analogue of FICT1026, which lacks an NO-donating moiety. We found that HCT1026 and HCT1027 inhibited bone resorption in interleukin (IL)-lstimulated murine osteoblast-bone marrow cocultures, with half-maximal effects (IC50) at 20 +/- 5 muM for HCT1026 and 25 +/- 6 muM for HCT1027 compared with 399 +/- 25 muM for flurbiprofen (P < 0.0001). These differences were unrelated to cyclooxygenase (COX) inhibition since FICT 1026 and FICT 1027 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 TLJNEL assays. We conclude that HCT1026 andFICT1027 inhibit osteoclast fon-nation andactivity by a mechanism that is independent ofNO 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 FICT 1026 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. (C) 2004 Elsevier Inc. All rights reserved.