Merck & Co has reported preliminary data which shows that its investigational osteoporosis drug odanacatib reduced measures of bone turnover (breakdown and rebuilding of bone) in women with breast cancer.

The Phase II study, the findings of which will be presented at the upcoming American Society of Clinical Oncology conference in Chicago, involved 43 women with breast cancer and metastatic bone disease who were randomised to receive either oral odanacatib once-daily or intravenous zoledronic acid, which is sold by Novartis as Zometa. The data revealed that the patients with odanacatib experienced a 77% reduction from baseline over four weeks on a measure of bone breakdown, while a 73% reduction was observed in the Zometa arm.

Odanacatib, which is also known as MK-0822, is an inhibitor of the cathepsin K enzyme, which plays a key role in breaking down the protein in bone. Merck noted that by inhibiting cathepsin K activity, the compound represents “a potential novel therapeutic approach for metastatic bone disease that works differently from other commonly used medicines”.

Antonio Lombardi, senior director at Merck Research Laboratories, noted that this is the first study to evaluate the drug in cancer patients and based on these findings, “larger Phase III studies using the 5mg daily dose of odanacatib are being planned for patients with breast and prostate cancer."

A Phase III trial evaluating odanacatib for the treatment of osteoporosis in postmenopausal women also is underway.