Cardiovascular toxicity is one of the more common causes of attrition in preclinical and clinical drug development. Preclinical cardiovascular safety assessment involves numerous in vitro and in vivo endpoints which are being continually reviewed and improved to lower the incidence of cardiovascular toxicity that manifests only after the initiation of clinical trials. An example of notable preclinical toxicity is necrosis in the papillary muscle of the left ventricle in dogs that is induced by exaggerated pharmacological effects of vasodilators or positive inotropic/vasodilating off-target drug effects. Two distinct, small-molecule inhibitors that target an intracellular kinase, Compound A and Compound B, were profiled in 2-week dose-range finding and 4-week toxicity studies. Serum cardiac troponin (cTnI) was evaluated after a single dose and after 2-week and 4-week repeat dose studies with each kinase inhibitor. Acute effects on hemodynamic (heart rate, blood pressures, left ventricular contractility) and electrocardiographic (QTcV, PR, QRS intervals) endpoints by each inhibitor were assessed in an anesthetized dog cardiovascular model. Cardiovascular degeneration/necrosis with and without fibrosis was observed in dogs and correlated to increases in serum cTnI in repeat-dose toxicity studies. At the same doses used in toxicologic assessments, both kinase inhibitors produced sustained increases in heart rate, left ventricular contractility, and cardiac output, and decreases in mean arterial pressure. Cardiac pathology findings associated with these 2 kinase inhibitors were accompanied not only by cardiac troponin elevations but also associated with hemodynamic changes, highlighting the importance of the link of the physiologic—toxicologic interplay in cardiovascular safety assessment.

Integrating clinical pathology data with anatomic pathology data is a common practice when reporting findings in the context of nonclinical toxicity studies and aids in understanding and communicating the nonclinical safety profile of test articles in development. Appropriate pathology data integration requires knowledge of analyte and tissue biology, species differences, methods of specimen acquisition and analysis, study procedures, and an understanding of the potential causes and effects of a variety of pathophysiologic processes. Neglecting these factors can lead to inappropriate data integration or a missed opportunity to enhance understanding and communication of observed changes. In such cases, nonclinical safety information relevant to human safety risk assessment may be misrepresented or misunderstood. This "Points to Consider" manuscript presents general concepts regarding pathology data integration in nonclinical studies, considerations for avoiding potential oversights and errors in data integration, and focused discussion on topics relevant to data integration for several key organ systems including liver, kidney, and cardiovascular system.

Glomerular filtration rate is the gold-standard method for assessment of renal function but is rarely performed in routine toxicity studies. Standard serum biomarkers of renal function are insensitive and become elevated only with significant loss of organ function. Symmetric dimethylarginine (SDMA) is a ubiquitous analyte that is freely filtered by the glomerulus and can be detected in serum. It has shown utility for the detection of renal injury in dogs and cats in clinical veterinary practice, but the potential utility of SDMA to detect renal injury in preclinical species or toxicity studies has not been thoroughly investigated. We utilized a well-characterized glomerular toxicant, puromycin aminonucleoside, to induce podocyte injury and subsequent proteinuria in young male Sprague-Dawley rats. At the end of 1 or 2 weeks, blood, urine, and kidney tissue were collected for analysis. One week following a single 50 mg/kg dose, urea nitrogen, creatinine, and albumin mean values were within historical control ranges, while SDMA was increased. Glomerular changes in these animals included periodic acid-Schiff positive globules within podocytes, podocyte hypertrophy by light microscopy, and podocyte degeneration with effacement of foot processes by electron microscopy (EM). Taken together, our data indicate that SDMA may be a useful biomarker for early detection of glomerular toxicities in rats.

The interpretation of clinical pathology results from nonclinical safety studies is a fundamental component in hazard identification of new drug candidates. The ever-increasing complexity of nonclinical safety studies and sophistication of modern analytical methods have made the interpretation of clinical pathology information by a highly trained subject matter expert imperative. Certain interpretive techniques are particularly effective in the identification and characterization of clinical pathology effects. The purpose of this manuscript is to provide an overview of contemporary interpretive practices for clinical pathology results and to provide nonbinding recommendations aimed at improving consistency, quality, and overall value of clinical pathology interpretations generated in support of nonclinical toxicology studies.

New medullary bone formation has been observed in rats administered a variety of antineoplastic compounds. Similar effects reported in rats administered granulocyte colony-stimulating factor (G-CSF) were attributed to exaggerated pharmacology of G-CSF as a cytokine and growth factor, resulting in stromal proliferation in addition to the intended hematopoietic effects. Similar phenomena of marrow stromal change are reported among other species in association with various growth factors. Case study summaries of test item-related histopathologic changes in bone marrow, reflecting trabecular and/or endosteal new bone formation, are presented. In each of these cases, it was concluded that the new medullary bone and stromal proliferation did not reflect a primary target-related toxicity; rather, the mesenchymal changes were attributed to nonspecific, secondary effects of cytokines elaborated in response to primary cytotoxic effects on hematopoietic cells with subsequent impact on circulating blood cells. The common features associated with marrow stromal changes in the case studies, as well as with a variety of pharmacologic compounds across several species described in the literature, are hematologic effects and/or changes in growth factor levels and cytokine expression.