Scientific and Regulatory Policy Committee Points to Consider Review: Inclusion of Reproductive and Pathology End Points for Assessment of Reproductive and Developmental Toxicity in Pharmaceutical Drug Development.

Standard components of nonclinical toxicity testing for novel pharmaceuticals include clinical and anatomic pathology, as well as separate evaluation of effects on reproduction and development to inform clinical development and labeling. General study designs in regulatory guidances do not specifically mandate use of pathology or reproductive end points across all study types; thus, inclusion and use of these end points are variable. The Scientific and Regulatory Policy Committee of the Society of Toxicologic Pathology (STP) formed a Working Group to assess the current guidelines and practices on the use of reproductive, anatomic pathology, and clinical pathology end points in general, reproductive, and developmental toxicology studies. The Working Group constructed a survey sent to pathologists and reproductive toxicologists, and responses from participating organizations were collected through the STP for evaluation by the Working Group. The regulatory context, relevant survey results, and collective experience of the Working Group are discussed and provide the basis of each assessment by study type. Overall, the current practice of including specific end points on a case-by-case basis is considered appropriate. Points to consider are summarized for inclusion of reproductive end points in general toxicity studies and for the informed use of pathology end points in reproductive and developmental toxicity studies.

Using Histopathologic Evidence to Differentiate Reproductive Senescence from Xenobiotic Effects in Middle-aged Female Sprague-Dawley Rats.

The female reproductive cycle is orchestrated by cyclical and coordinated hormonal changes under the direction of the hypothalamic-pituitary-gonadal (HPG) axis. Any disruption of the HPG axis may lead to functional and structural alterations in the female reproductive system. Test article-related disturbances in the estrous cycle can be recognized in nonclinical toxicity studies by staging the cycle based on microscopic evaluation of female reproductive organs. In chronic rat toxicity studies, an additional complication is the development of reproductive senescence, which is associated with natural alterations in the reproductive cycle leading to changes in the female reproductive system that can potentially be confused with test article effects. The current article describes the features of persistent estrus, one stage of reproductive senescence, in middle-aged Sprague-Dawley rats and discusses elements to help differentiate senescence from induced effects.

Histologic and cytologic detection of endocrine and reproductive tract effects of exemestane in female rats treated for up to twenty-eight days.

The objective of this study was to determine the shortest period of time necessary to detect histologic evidence of estrous cycle disruption in Sprague-Dawley rats treated for up to 28 days with the aromatase inhibitor exemestane at 1,000 mg/kg. Rats were evaluated on day 5, 8, 15, or 29. Vaginal mucification, uterine and cervical epithelial atrophy, uterine luminal epithelial vacuolation, decreased uterine granulocytes, and hypertrophy/hyperplasia of mammary ducts and alveoli were noted by day 5 and persisted throughout the study. From day 8 to day 29, absence of recent basophilic corpora lutea, increased atresia of antral follicles, interstitial cell hyperplasia, and increased luteinized follicles were present in the ovaries of treated rats. Vaginal smears detected persistent diestrus, confirming estrous cycle disruption between days 5 and 8. Ovary and uterine weights were largely unaffected. Serum hormone levels were not useful due to the study design employed. Other effects of exemestane included decreased adrenal weights and decreased cell size in both the adrenal zona fasciculata and the pituitary pars distalis. While early histologic changes were evident on day 5, only after 8 days of treatment were findings considered sufficient to clearly identify exemestane-induced estrous cycle disruption using microscopy alone.

Utility of Orchidometric Parameters for Assessing Sexual Maturation in Male Cynomolgus Macaques (Macaca fascicularis).

Testicular volume is one of several parameters that have been used in preclinical toxicology to facilitate the identification of sexually mature male cynomolgus macaques when semen evaluation is unavailable. Furthermore, testicular volume provides additional information to pathologists to aid in the interpretation of microscopic findings. Orchidometry has been proposed as a useful tool for assessing testicular volume. To assess its utility for this purpose, we used orchidometry to measure testicular volume in untreated control male cynomolgus macaques during preclinical toxicology studies. Additional parameters including age, body weight, testicular weight, serum testosterone, and testicular histology were also evaluated. Serum inhibin B and the diameter of histologic testicular sections were assessed to determine whether they might provide any additional corroborative evidence for differentiating stages of sexual maturity in males. Orchidometry was easy to use in sedated or awake macaques and, in combination with testicular histology, enabled the establishment of cut-off values by which sexually mature male cynomolgus macaques can be identified with a high degree of confidence. The relative utility of the parameters examined for discriminating sexually mature and immature males was testicular volume ≥ serum testosterone > body weight > age; for differentiation of sexually mature and peripubertal males the order was testicular volume ≥ body weight > serum testosterone > age. Testicular weight and the diameter of histologic testicular sections provided corroborative information for discriminating stages of sexual maturity. Serum inhibin B was of little value in helping to differentiate the different stages of sexual maturation evaluated in this study.