Our proprietary in vitro osteoclast assays have been designed for pharmacodynamic testing of new therapeutic agents against osteoporosis and cancer-induced bone disease before entering animal studies. They involve culturing osteoclast precursor cells that are first allowed to differentiate into mature bone-resorbing osteoclasts, enabling to study direct effects of drug candidates on osteoclast formation. The culture period can then be extended to allow the formed mature osteoclasts to resorb bone, enabling to study direct effects of drug candidates on resorption activity of mature osteoclasts.

Tartrate-resistant acid phosphatase 5b (TRACP 5b) secreted into the culture medium is determined as an index of the number of formed osteoclasts at the end of the osteoclast differentiation period, and C-terminal cross-linked telopeptides of type I collagen (CTX-I) released into the culture medium as an index of resorption activity of mature osteoclasts at the end of the resorption period.

We use commercially available bone marrow derived human osteoclast precursor cells that are cultured on bovine bone slices in the presence of appropriate growth factors such as RANKL and M-CSF. Rapid determination of TRACP 5b and CTX-I as endpoint measurements saves a substantial amount of time and workload and gives more reliable results than using conventional microscopic techniques. Effects on resorption activity of mature osteoclasts can also be studied using rat osteoclasts, if requested.