Spontaneous occurrence of a distinctive renal tubule tumor phenotype in rat carcinogenicity studies conducted by the national toxicology program

Historical Control Background Incidence of Spontaneous Neoplastic Lesions of Sprague-Dawley Rats in 104-Week Toxicity Studies

Data collected from approximately 1800 male and 1800 female Sprague-Dawley (SD) rats used in 104-week carcinogenicity studies were archived in a historical control database at Labcorp Early Development, Inc, and the neoplastic microscopic observation data from these rats were retrospectively evaluated. Historical control data can provide useful information on the range and incidence of spontaneously occurring background neoplasms in the species and strain of the test animal used in different types of toxicity studies, including studies of differing lengths, delivery of test article, and test animal. Some of the most common malignant findings noted included fibrosarcoma of skin/subcutis and thyroid C-cell carcinoma in males (2.1% each) while mammary gland carcinoma and pituitary carcinoma (25% and 2.6%) were most common in females. Pituitary adenoma of pars distalis was found to be the most prevalent benign neoplasm in both males and females (56.4% and 77.1%). Fibroadenoma of mammary gland (35.6%) and thyroid C-cell adenoma (8.5%) were the second and third most common benign tumors in female SD rats. In males, the thyroid C-cell adenoma (10.9%) and benign pheochromocytoma (8.9%) were the second and third most common tumors.

Immunohistochemical, pharmacovigilance, and omics analyses reveal the involvement of ATP-sensitive K+ channel subunits in cancers: role in drug-disease interactions

Background: ATP-sensitive-K+ channels (KATP) are involved in diseases, but their role in cancer is poorly described. Pituitary macroadenoma has been observed in Cantu' syndrome (C.S.), which is associated with the gain-of-function mutations of the ABCC9 and KCNJ8 genes. We tested the role of the ABCC8/Sur1, ABCC9/Sur2A/B, KCNJ11/Kir6.2, and KCNJ8/Kir6.1 genes experimentally in a minoxidil-induced renal tumor in male rats and in the female canine breast cancer, a spontaneous animal model of disease, and in the pharmacovigilance and omics databases. Methods: We performed biopsies from renal tissues of male rats (N = 5) following a sub-chronic high dosing topical administration of minoxidil (0.777-77.7 mg/kg/day) and from breast tissues of female dogs for diagnosis (N = 23) that were analyzed by immunohistochemistry. Pharmacovigilance and omics data were extracted from EudraVigilance and omics databases, respectively. Results: An elevated immunohistochemical reactivity to Sur2A-mAb was detected in the cytosol of the Ki67+/G3 cells other than in the surface membrane in the minoxidil-induced renal tumor and the breast tumor samples. KCNJ11, KCNJ8, and ABCC9 genes are upregulated in cancers but ABCC8 is downregulated. The Kir6.2-Sur2A/B-channel opener minoxidil showed 23 case reports of breast cancer and one case of ovarian cancer in line with omics data reporting, respectively, and the negative and positive prognostic roles of the ABCC9 gene in these cancers. Sulfonylureas and glinides blocking the pancreatic Kir6.2-Sur1 subunits showed a higher risk for pancreatic cancer in line with the positive prognostic role of the ABCC8 gene but low risks for common cancers. Glibenclamide, repaglinide, and glimepiride show a lower cancer risk within the KATP channel blockers. The Kir6.2-Sur1 opener diazoxide shows no cancer reactions. Conclusion: An elevated expression of the Sur2A subunit was found in proliferating cells in two animal models of cancer. Immunohistochemistry/omics/pharmacovigilance data reveal the role of the Kir6.1/2-Sur2A/B subunits as a drug target in breast/renal cancers and in C.S.

Regulatory Experience Assessing the Carcinogenic Potential of a Monoclonal Antibody Inhibiting PCSK9, Bococizumab, Including a 2-Year Carcinogenicity Study in Rats

Bococizumab is an anti-PCSK9 monoclonal antibody that was intended for the treatment of hypercholesterolemia. After reviewing the 6-month rat toxicity study data, in which there was a low spontaneous tumor incidence, unrelated to bococizumab administration, the U.S. FDA granted a carcinogenicity waiver request based on a weight-of-evidence assessment of low carcinogenic risk. Subsequently, after reviewing 6-month rat toxicity study data from another anti-PCSK9 antibody, RN317, with a similar low tumor incidence (unrelated to RN317), the U.S. FDA rescinded the bococizumab carcinogenicity study waiver and requested a full 2-year rat carcinogenicity study be conducted. The resulting 2-year carcinogenicity study demonstrated no bococizumab-related increase in tumors, confirming the weight-of-evidence evaluation and alleviating concerns regarding the carcinogenic potential. Here we report the scientific and regulatory background that led to the request for a rat carcinogenicity study, the feedback on the design of the carcinogenicity study, and the results from this study which affirmed the original weight-of-evidence assessment of low carcinogenic risk.

Confounders for kidney carcinogenesis in rodent cancer bioassays

In the long-term safety testing of chemicals for carcinogenicity the toxicologist needs to be aware of a number of scenarios where renal tubule tumors, or their precursors, arise that are not due to a carcinogenic action of the test article. Situations producing false positive results in the kidney include exacerbation of chronic progressive nephropathy (CPN) in rats, confusion of atypical tubule hyperplasia (the obligate precursor of renal tubule tumor) with foci of benign CPN-related renal tubule cell proliferation, inclusion of spontaneous tumor entities, such as the amphophilic-vacuolar tumor, in the test article tumor count, the possibility of a link between spontaneous forms of tubule dilatation and renal tubule tumor formation in mice, and the supposed predictivity of chemically-induced karyomegaly for renal carcinogenicity in both rats and mice. Examples of these misleading situations are described and discussed.

Histopathology re-examination of the NTP toxicity/carcinogenicity studies of tert-butyl alcohol to identify renal tumor and toxicity modes of action

Tert-butyl alcohol (TBA) targets the rat kidney following repeated exposures, including renal tubule tumors. The mode of action (MOA) of these tumors, concluded by a pathology working group, involves both alpha2u-globulin nephropathy (α2u-gN) and exacerbated chronic progressive nephropathy (CPN), but has been disputed and an undefined MOA proposed. This study further reviews the histology slides of male and female rat kidneys from the NTP drinking water 13-week toxicity and 2-year carcinogenicity studies, including the 15-month interim sacrifice group. The papillary epithelial lining alteration formerly referred to as "transitional cell hyperplasia" develops as part of advanced CPN and does not represent a separate toxicity. No changes were observed in the kidney pelvis urothelium. The only alterations in subchronic male rats involved α2u-gN and CPN, without test article-related alterations in females. Focused examination of areas of parenchyma unaffected by CPN in TBA-treated male and female rats of the chronic studies revealed no renal tubule abnormalities other than from the effects of α2u-gN and CPN. Unrelated to toxicity were spontaneous amphophilic or vacuolar tubule proliferative lesions. All observed TBA-associated non-neoplastic and neoplastic histopathological changes in the kidney can be explained by α2u-gN or enhanced CPN, neither of which are relevant to humans.

Mechanisms of Rodent Renal Carcinogenesis Revisited

The important renal tumors that can be induced by exposure of rats to chemical carcinogens are renal tubule tumors (RTTs) derived from tubule epithelium; renal pelvic carcinoma derived from the urothelial lining of the pelvis; renal mesenchymal tumors (RMTs) derived from the interstitial connective tissue; and nephroblastoma derived from the metanephric primordia. However, almost all of our knowledge concerning mechanisms of renal carcinogenesis in the rodent pertains to the adenomas and carcinomas originating from renal tubule epithelium. Currently, nine mechanistic pathways can be identified in either the rat or mouse following chemical exposure. These include direct DNA reactivity, indirect DNA reactivity through free radical formation, multiphase bioactivation involving glutathione conjugation, mitotic disruption, sustained cell proliferation from direct cytotoxicity, sustained cell proliferation by disruption of a physiologic process (alpha 2u-globulin nephropathy), exaggerated pharmacologic response, species-dominant metabolic pathway, and chemical exacerbation of chronic progressive nephropathy. Spontaneous occurrence of RTTs in the rat will be included since one example is a confounder for interpreting kidney tumor results in chemical carcinogenicity studies in rats.

Renal Tumors in 26-Week Tg.Rash2 Mice Carcinogenicity Studies

We report renal tubular adenomas and a carcinoma in 26-week Tg.rasH2 mouse carcinogenicity studies, which have not been reported to date either at our facility or in other published data. However, during the year 2014, renal tubular tumors were present in 4 studies conducted at our facility. Because of their morphological similarity to the amphophilic-vacuolar (AV) phenotypic variant of renal tubule tumors noted in Sprague-Dawley and Fischer 344 rats, which are thought to be familial, as well as the genetic homogeneity of Tg.rasH2 mice, we tracked the parents of these mice with tumors in each study. The origin of these tumors could not be traced back to any of the parents or even an animal barrier, and these tumors were not attributed to the vehicle or test article. Although the exact mechanism of tumorigenesis was not known, based on the available information, the development of renal tumors in these mice was considered random and spontaneous.

Regulatory Forum Opinion Piece*

Renal tubule lesions often prove troublesome for toxicologic pathologists because of the diverse nature and interrelated cell types within the kidney and the presence of spontaneous lesions with overlapping morphologies similar to those induced by renal toxicants. Although there are a number of guidance documents available citing straightforward diagnostic criteria of tubule lesions for the pathologist to refer to, most are presented without further advice on the when to or to the why and the why not of diagnosing one lesion over another. Documents presenting diagnostic perspectives and recommendations derived from an author’s experience are limited since guidance documents are generally based on descriptive observations. In this Regulatory Forum opinion piece, the authors attempt to dispel confusing renal tubule lesion terminology in laboratory animal species by suggesting histological advice on the recognition and interpretation of these complex entities.

Successful integration of nonclinical and clinical findings in interpreting the clinical relevance of rodent neoplasia with a new chemical entity

Canagliflozin, a sodium glucose co-transporter 2 (SGLT2) inhibitor, has been developed for the treatment of adults with type 2 diabetes mellitus (T2DM). During the phase 3 program, treatment-related pheochromocytomas, renal tubular tumors, and testicular Leydig cell tumors were reported in the 2-year rat toxicology study. Treatment-related tumors were not seen in the 2-year mouse study. A cross-functional, mechanism-based approach was undertaken to determine whether the mechanisms responsible for tumorigenesis in the rat were of relevance to humans. Based on findings from nonclinical and clinical studies, the treatment-related tumors observed in rats were not deemed to be of clinical relevance. Here, we describe the scientific and regulatory journey from learning of the 2-year rat study findings to the approval of canagliflozin for the treatment of T2DM.

Carcinogenicity in rats of the SGLT2 inhibitor canagliflozin

The carcinogenicity potential of canagliflozin, an inhibitor of SGLT2, was evaluated in a 2-year rat study (10, 30, and 100 mg/kg). Rats showed an increase in pheochromocytomas, renal tubular tumors, and testicular Leydig cell tumors. Systemic exposure multiples at the highest dose relative to the maximum clinical dose were 12- to 21-fold. Pheochromocytomas and renal tubular tumors were noted in both sexes at 100 mg/kg. Leydig cell tumors were observed in males in all dose groups and were associated with increased luteinizing hormone levels. Hyperplasia was increased in the adrenal medulla at 100 mg/kg, but only a limited increase in simple tubular hyperplasia was observed in the kidney of males at 100 mg/kg. Hyperostosis occurred and was accompanied by substantial effects on calcium metabolism, including increased urinary calcium excretion and decreased levels of calcium regulating hormones (1,25-dihydroxyvitamin D and parathyroid hormone). A separate study with radiolabeled calcium confirmed that increased urinary calcium excretion was mediated via increased calcium absorption from the gastrointestinal tract. It was hypothesized that, at high doses, canagliflozin might have inhibited glucose absorption in the intestine via SGLT1 inhibition that resulted in glucose malabsorption, which increased calcium absorption by stimulating colonic glucose fermentation and reducing intestinal pH. Pheochromocytomas and adrenal medullary hyperplasia were attributed to altered calcium homeostasis, which have a known relationship in the rat. In conclusion, Leydig cell tumors were associated with increased luteinizing hormone levels and pheochromocytomas were most likely related to glucose malabsorption and altered calcium homeostasis. Renal tubular tumors may also have been linked to glucose malabsorption.

Selection of appropriate tumour data sets for Benchmark Dose Modelling (BMD) and derivation of a Margin of Exposure (MoE) for substances that are genotoxic and carcinogenic: considerations of biological relevance of tumour type, data quality and uncertainty assessment

This article addresses a number of concepts related to the selection and modelling of carcinogenicity data for the calculation of a Margin of Exposure. It follows up on the recommendations put forward by the International Life Sciences Institute - European branch in 2010 on the application of the Margin of Exposure (MoE) approach to substances in food that are genotoxic and carcinogenic. The aims are to provide practical guidance on the relevance of animal tumour data for human carcinogenic hazard assessment, appropriate selection of tumour data for Benchmark Dose Modelling, and approaches for dealing with the uncertainty associated with the selection of data for modelling and, consequently, the derived Point of Departure (PoD) used to calculate the MoE. Although the concepts outlined in this article are interrelated, the background expertise needed to address each topic varies. For instance, the expertise needed to make a judgement on biological relevance of a specific tumour type is clearly different to that needed to determine the statistical uncertainty around the data used for modelling a benchmark dose. As such, each topic is dealt with separately to allow those with specialised knowledge to target key areas of guidance and provide a more in-depth discussion on each subject for those new to the concept of the Margin of Exposure approach.

Spontaneous renal tumors in two rats from a thirteen week rodent feeding study with grain from molecular stacked trait lepidopteran and coleopteran resistant (DP-ØØ4114-3) maize

A thirteen week feeding study was conducted by feeding young adult male and female Sprague Dawley [Crl:CD®(SD)] rats diets containing grain from genetically modified (GM) DP-ØØ4114-3 maize that was either untreated (4114) or treated in the field with glufosinate ammonium (4114GLU). Control rats were fed diets containing the same concentration of near isogenic, non-GM maize grain (091) or one of three types of commercially available non-GM maize grain. At the end of the in-life phase, renal tubule tumors were reported in two male rats consuming diets containing 4114 maize grain. An expert panel of pathologists was convened as a Pathology Working Group (PWG) to review coded kidney histology sections from control (091) and treated (4114 and 4114GLU) male rats. The objectives were for the panel to characterize the histopathologic findings and to interpret their relationship to consumption of the indicated diet. The PWG concluded unanimously that the kidney tumors were characteristic of amphophilic-vacuolar (AV) tumors and AV atypical tubular hyperplasia which represent a distinctive phenotype that has been reported to occur sporadically in young Sprague Dawley Rats. The PWG determined that the neoplasms and atypical tubular hyperplasias were multicentric and bilateral which typifies tumors of familial origin. Degenerative/regenerative or cytotoxic changes consistent with nephrotoxicity leading to tumor induction were not observed in these rats and thus supports the conclusion that tumors were unrelated to consumption of the test diet. It was the unanimous opinion of the PWG that the proliferative renal tubule cell lesions were spontaneous and not related to consumption of diets containing 4114 maize grain.

Meeting report: Urinary Pathology; sixth Research Triangle Park Rodent Pathology Course

Urinary system toxicity is a significant concern to pathologists in the hazard identification, drug and chemical safety evaluation, and diagnostic service industries worldwide. There are myriad known human and animal urinary system toxicants, and investigatory renal toxicology and pathology is continually evolving. The system-specific Research Triangle Park (RTP) Rodent Pathology Course biennially serves to update scientists on the latest research, laboratory techniques, and debates. The Sixth RTP Rodent Pathology Course, Urinary Pathology, featured experts from the government, pharmaceutical, academic, and diagnostic arenas sharing the state of the science in urinary pathology. Speakers presented on a wide range of topics including background lesions, treatment-related non-neoplastic and neoplastic lesions, transgenic rodent models of human disease, diagnostic imaging, biomarkers, and molecular analyses. These seminars were accompanied by case presentation sessions focused on usual and unusual lesions, grading schemes, and tumors.

Spontaneous renal tumors suspected of being familial in sprague-dawley rats

Spontaneous renal tubule tumors (RTTs), with a distinctive morphological phenotype, were present in three Sprague-Dawley rats, 1 male and 2 females, out a total of 120 animals of each sex from untreated and placebo control groups in a 2-year carcinogenicity study. One female had one carcinoma, adenoma and hyperplasia, and the other female had five adenomas and many hyperplastic lesions; the male case had one carcinoma. From these cases, a biological continuum of hyperplasia, adenoma and carcinoma could be recognized. The tumors were present in the renal cortex and appeared as solid lobulated growths with occasional central necrosis. The lobules were divided by a small amount of fibrovascular tissue. Occasionally the larger tumors contained a cystic area. Tumor cells appeared distinctive and exhibited variable amounts of eosinophilic/amphophilic and vacuolated cytoplasm. Nuclei were round to oval with a prominent nucleolus. Mitotic figures were uncommon, and no distant metastasis was noted. The tumors were seen as multiple and bilateral lesions in two animals and had no apparent relationship to chronic progressive nephropathy (CPN). Foci of tubule hyperplasia were also noted to contain the same type of cellular morphology. The morphological and biological features of these 3 cases resembled the amphophilic-vacuolar (AV) variant of RTT that has been posited to be of familial origin. This is a report of spontaneous familial renal tumors in Sprague-Dawley rats from Japan.

Occurrence of Spontaneous Amphophilic-Vacuolar Renal Tubule Tumors in Sprague-Dawley Rats from Subchronic Toxicity Studies

The low background incidence of tumors in rodents from subchronic toxicity studies makes it difficult to assess their relevance, especially when present only in treated animals. This report investigates the occurrence of renal tubule tumors (RTTs), specifically the amphophilic-vacuolar (AV) phenotypic variant, in young Sprague-Dawley (SD) rats from a survey of laboratories conducting subchronic toxicity studies spanning a period of 10 years (2002–2012). This survey establishes a general profile of tumor occurrence; it does not estimate overall incidence or prevalence. AV tumors are spontaneous, nontreatment-related tumors of familial origin, and morphologically distinct from conventional RTTs induced by exposure to renal carcinogens. They are composed of distinct lobules of large, round to polyhedral cells with vacuolated amphophilic to eosinophilic cytoplasm and prominent nucleoli. Data from five collaborating laboratories, representing 37 qualifying studies, are presented. In total, 58 renal tubule neoplasms were recorded in this data set. The AV tumor variant was reported more commonly than the conventional RTT ( n = 45 and 13, respectively), and it was recorded in both experimental ( n = 32) and control ( n = 13) groups. AV tumors occurred more often in females ( n = 34) than in males ( n = 11); conventional RTTs were recorded more often in males ( n = 9) than in females ( n = 4). AV tumors often occurred in more than one rat within the same study (up to 7) and were documented to occur in rats as young as 7 to 10 weeks of age. Results from this survey indicate that AV tumors are being reported more commonly in recent years; the majority ( n = 33) were reported in studies commencing since 2009. In conclusion, this study reaffirms that AV tumors are spontaneous, nontreatment-related lesions, and suggests that they may be more common than conventional RTTs in young SD rats. The authors propose that AV tumors be recorded separately from conventional RTTs in order to clearly distinguish these two renal tubule neoplasms from one another and allow for appropriate interpretation of a compound’s potential carcinogenic effect in the kidney.

Proliferative and nonproliferative lesions of the rat and mouse urinary system

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the urinary tract of rats and mice. The standardized nomenclature of urinary tract lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for urinary tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.