Therapeutic aptamer targeting sclerostin loop3 for promoting bone formation without increasing cardiovascular risk in osteogenesis imperfecta mice

<b>Rationale:</b> Sclerostin inhibition demonstrated bone anabolic potential in osteogenesis imperfecta (OI) mice, whereas humanized therapeutic sclerostin antibody romosozumab for postmenopausal osteoporosis imposed clinically severe cardiac ischemic events. Therefore, it is desirable to develop the next generation sclerostin inhibitors to promote bone formation without increasing cardiovascular risk for OI. <b>Methods and Results:</b> Our data showed that sclerostin suppressed inflammatory responses, prevented aortic aneurysm (AA) and atherosclerosis progression in <i>hSOST^ki.Col1a2^+/G610C.ApoE^-/-</i> mice. Either loop2&3 deficiency or inhibition attenuated sclerostin's suppressive effects on expression of inflammatory cytokines and chemokines <i>in vitro</i>, whilst loop3 deficiency maintained the protective effect of sclerostin on cardiovascular system both <i>in vitro</i> and <i>in vivo</i>. Moreover, loop3 was critical for sclerostin's antagonistic effect on bone formation in <i>Col1a2^+/G610C</i> mice. Accordingly, a sclerostin loop3-specific aptamer aptscl56 was identified by our lab. It could recognize both recombinant sclerostin and sclerostin in the serum of OI patients via targeting loop3. PEG40k conjugated aptscl56 (Apc001PE) demonstrated to promote bone formation, increase bone mass and improve bone microarchitecture integrity in <i>Col1a2^+/G610C</i> mice via targeting loop3, while did not show influence in inflammatory response, AA and atherosclerosis progression in <i>Col1a2^+/G610C.ApoE^-/-</i> mice with Angiotensin II infusion. Further, Apc001PE had no influence in the protective effect of sclerostin on cardiovascular system in <i>hSOST^ki.Col1a2^+/G610C.ApoE^-/-</i> mice, while it inhibited the antagonistic effect of sclerostin on bone formation in <i>hSOST^ki.Col1a2^+/G610C</i> mice via targeting loop3. Apc001PE was non-toxic to healthy rodents, even at ultrahigh dose. Apc001PE for OI was granted orphan drug designation by US-FDA in 2019 (DRU-2019-6966). <b>Conclusion:</b> Sclerostin loop3-specific aptamer Apc001PE promoted bone formation without increasing cardiovascular risk in OI mice.