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.