Oral Virtual Presentation (Virtual only) ESA-SRB-ANZBMS 2021

Sequential multi-dose zoledronate therapy prevents rebound bone loss following withdrawal of RANKL inhibition (#78)

Albert S Kim 1 2 , Jad Zamerli 1 , Sindhu Tanaya Mohanty 1 , Ya Xiao 1 , Jackie R Center 1 2 , Christian M Girgis 3 4 5 , Peter I Croucher 1 2 , Michelle M McDonald 1 2
  1. Bone Biology Division, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
  2. St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Kensington, NSW, Australia
  3. Department of Diabetes and Endocrinology, Westmead Hospital, Westmead, NSW, Australia
  4. Department of Endocrinology, Diabetes and Metabolism, Royal North Shore Hospital, St Leonards, NSW, Australia
  5. Faculty of Medicine & Health, University of Sydney, NSW 2600, Australia

Denosumab is an effective osteoporosis treatment, preventing bone loss by inhibiting RANKL. However, stopping denosumab leads to rebound bone mineral density(BMD) loss due to accelerated bone resorption by osteoclasts observed as increasing bone resorption markers. Sequential treatment with zoledronate(ZOL) after denosumab does not consistently prevent this bone loss in patients. We hypothesised that sequential multi-dose ZOL would prevent bone loss following withdrawal of RANKL inhibition.

Ten-week-old female C57BL/6 mice were treated with 2-weeks of thrice-weekly saline(vehicle) or OPG:Fc(10mg/kg) to inhibit RANKL. Mice were then treated with single-dose ZOL(0.01mg/kg) at week 5(OPG+SZ), double-dose ZOL(OPG+DZ) at weeks 5+12, or saline(OPG+S). Longitudinal BMD and serum TRAP5b were measured. MicroCT and histology were performed on samples harvested at week17.

Following OPG:Fc, BMD peaked at week10 in all OPG-treated groups(p<0.0001 vs vehicle. By week14, BMD normalised to vehicle levels in OPG+S mice. OPG+SZ maintained higher BMD than OPG+S to study end(p<0.01). Importantly, BMD remained higher in the OPG+DZ group compared to both OPG+S and OPG+SZ groups(p<0.001), from week10 to study end(A).

MicroCT showed higher femoral trabecular volume(BV/TV) in both OPG+SZ and OPG+DZ groups by 20 and 34% respectively compared to OPG+S and vehicle(p<0.001)(B). Serum TRAP5b was significantly reduced compared to vehicle following OPG:Fc in all treated groups(C). TRAP5b rose rapidly in OPG+S mice at week 12 to levels 68% higher than vehicle(p<0.0001). In ZOL-treated mice, TRAP5b rose to reach vehicle levels at week 12 and remained equivalent to vehicle to week17. Histological TRAP analysis showed higher osteoclast numbers in both OPG+SZ and OPG+DZ groups compared to vehicle and OPG+S mice, despite equivalent serum TRAP5b(D).

Our findings show that multiple-dose sequential ZOL is superior in preventing bone loss following withdrawal of RANKL inhibition through suppressing osteoclast function, with no impact on rebound osteoclast formation. A multi-dose sequential zoledronate strategy could be considered following denosumab cessation.

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