Renal tolerability profile of novel, potent bisphosphonates in two short-term rat models

Bisphosphonates are used clinically to inhibit bone resorption but they may also cause renal damage. For the profiling of new potent bisphosphonates, their adverse renal effects were investigated in 2 rat models. In the first model, bisphosphonate was repeatedly injected (1 mg/kg, subcutaneously) over 2 weeks and the urinary excretion of malate dehydrogenase was monitored to assess nephrotoxic potential. Of the 6 new compounds tested, 3 markedly elevated malate dehydrogenase whereas 3 others caused only minor changes similar to those observed with 6 reference bisphosphonates that are already used clinically. On the basis of a therapeutic index (inhibition of bone resorption versus renal effects) 7-180 fold greater than that of other analogues, the compound CGP 42446 was further profiled. In the second model, CGP 42446 or pamidronate was infused (1.5-50 mg/kg, intravenously) into anaesthetized rats and the serum urea concentration was monitored as an indicator of renal dysfunction. Both compounds elevated serum urea in a time- and dose-dependent manner, but the ED100 value for CGP 42446 was 3.8-fold higher than that of pamidronate. It is concluded that CGP 42446 (zoledronate) has a low nephrotoxic potential and can be further developed as a new potent inhibitor of bone resorption.