Importance of preclinical studies in the development of drugs for treatment of osteoporosis: A review related to the 1998 WHO guidelines

Osteoporosis, which is defined as a disease characterized by low bone mass and microarchitectural deterioration of bone tissue leading to enhanced bon e fragility and a consequent increase in fracture risk, is a major health i ssue worldwide. Among the various strategies to prevent and cure this devas tating ailment, an important objective is the development of new efficaciou s and safe drugs. This situation prompted the World Health Organization (WH O) to provide a comprehensive statement of guiding principles for the desig n, implementation and interpretation of both preclinical testing and clinic al trials in osteoporosis. These guidelines, which are now available, under line the crucial importance of the preclinical evaluation, particularly for assessing the effect of an intervention on bone strength. This concept is heightened by the lack of a validated technique for noninvasively evaluatin g bone strength in humans and the multiple difficulties and heavy burden in herent in the evaluation of fracture rate in clinical trials. The WHO guide lines emphasize that a comprehensive and adequate preclinical program is ex pected to provide key information on the relationship between bone mass and strength and thus attenuate the burden of clinical studies. The present re port provides a review of experimental evidence in support of the preclinic al program as proposed in the WHO guidelines. This program is based on the recent development and refinement of animal models of osteoporosis that mim ic the human condition according to the conceptual definition of the diseas e. Many preclinical studies carried out in appropriate animal models with a gents that exert either antiresorbing or anabolic effects on bone indicate that they have been highly predictive of the drug action in humans in terms of both bone mass and remodeling, as well as of bone strength whenever fra cture rate has been documented in clinical trials. Based on this evidence t he WHO guidelines propose strategies according to which the results of prec linical evaluation will determine the end-points required in the different phases of the clinical development of the drug. Such a distribution of task assignment between preclinical and clinical programs should optimize the p rogress of research available to patients already suffering from or at risk of osteoporosis.