Morphometric examination for development of reproductive organs in male cynomolgus monkeys

Biology and postnatal development of organ systems of cynomolgus monkeys (Macaca fascicularis)

BACKGROUND

The cynomolgus macaque has become the most used non-human primate species in nonclinical safety assessment during the past decades.

METHODS

This review summarizes the biological data and organ system development milestones of the cynomolgus macaque available in the literature.

RESULTS

The cynomolgus macaque is born precocious relative to humans in some organ systems (e.g., nervous, skeletal, respiratory, and gastrointestinal). Organ systems develop, refine, and expand at different rates after birth. In general, the respiratory, gastrointestinal, renal, and hematopoietic systems mature at approximately 3 years of age. The female reproductive, cardiovascular and hepatobiliary systems mature at approximately 4 years of age. The central nervous, skeletal, immune, male reproductive, and endocrine systems complete their development at approximately 5 to 9 years of age.

CONCLUSIONS

The cynomolgus macaque has no meaningful developmental differences in critical organ systems between 2 and 3 years of age for use in nonclinical safety assessment.

Spontaneous Findings in the Reproductive System of Sexually Mature Male Cynomolgus Macaques

Sexually mature nonhuman primates are often used in nonclinical safety testing when evaluating biopharmaceuticals; however, there is limited information in historical control databases or in the published literature on the spontaneous findings in the male reproductive system. This review evaluated digital slides from the male reproductive tract (testes, epididymides, prostate, and seminal vesicles) in sexually mature cynomolgus macaques ( Macaca fascicularis; n = 255) from vehicle control groups in nonclinical toxicology studies and compared the observations with body weight, organ weight, and geographical origin. The most common microscopic findings were hypospermatogenesis and tubular dilatation in the testes; inflammatory cell infiltrate, cellular debris, and decreased sperm in the epididymides; inflammatory cell infiltrate and acinar dilatation in the prostate; and corpora amylacea and atrophy in the seminal vesicles. There were a few correlative observations in animals when grouped by weight or geographical origin: animals with lower terminal body weights (<5 kg) often displayed features of late puberty despite having sperm in the epididymis, while animals originating from Mauritius had a lower incidence of inflammatory cell infiltrates than those from Southeast Asia/China. This review provides incidence, descriptions, and photomicrographs of the common spontaneous microscopic findings in the reproductive system of mature male cynomolgus macaques.

Scientific and Regulatory Policy Committee Best Practices: Documentation of Sexual Maturity by Microscopic Evaluation in Nonclinical Safety Studies

The sexual maturity status of animals in nonclinical safety studies can have a significant impact on the microscopic assessment of the reproductive system, the interpretation of potential test article-related findings, and ultimately the assessment of potential risk to humans. However, the assessment and documentation of sexual maturity for animals in nonclinical safety studies is not conducted in a consistent manner across the pharmaceutical and chemical industries. The Scientific and Regulatory Policy Committee of the Society of Toxicologic Pathology convened an international working group of pathologists and nonclinical safety scientists with expertise in the reproductive system, pathology nomenclature, and Standard for Exchange of Nonclinical Data requirements. This article describes the best practices for documentation of the light microscopic assessment of sexual maturity in males and females for both rodent and nonrodent nonclinical safety studies. In addition, a review of the microscopic features of the immature, peripubertal, and mature male and female reproductive system and general considerations for study types and reporting are provided to aid the study pathologist tasked with documentation of sexual maturity.

Characterization and population dynamics of germ cells in adult macaque testicular cultures

BACKGROUND

From a biological and clinical perspective, it is imperative to establish primate spermatogonial cultures. Due to limited availability of human testicular tissues, the macaque (Macaca fascicularis) was employed as non-human primate model. The aim of this study was to characterize the expression of somatic as well as germ cell markers in testicular tissues and to establish macaque testicular primary cell cultures.

MATERIALS AND METHODS

Characterization of macaque testicular cell population was performed by immunohistochemical analyses for somatic cell markers (SOX9, VIM, SMA) as well as for germ cell markers (UTF1, MAGEA4, VASA). Testicular cells from adult macaque testes (n = 4) were isolated and cultured for 21 days using three stem cell culture media (SSC, PS and SM). An extended marker gene panel (SOX9, VIM, ACTA2; UTF1, FGFR3, MAGEA4, BOLL, DDX4) was then employed to assess the changes in gene expression levels and throughout the in vitro culture period. Dynamics of the spermatogonial population was further investigated by quantitative analysis of immunofluorescence-labeled MAGEA4-positive cells (n = 3).

RESULTS

RNA expression analyses of cell cultures revealed that parallel to decreasing SOX9-expressing Sertoli cells, maintenance of VIM and ACTA2-expressing somatic cells was observed. Expression levels of germ cell marker genes UTF1, FGFR3 and MAGEA4 were maintained until day 14 in SSC and SM media. Findings from MAGEA4 immunofluorescence staining corroborate mRNA expression profiling and substantiate the overall maintenance of MAGEA4-positive pre- and early meiotic germ cells until day 14.

CONCLUSIONS

Our findings demonstrate maintenance of macaque germ cell subpopulations in vitro. This study provides novel perspective and proof that macaques could be used as a research model for establishing in vitro germ cell-somatic cell cultures, to identify ideal culture conditions for long-term maintenance of primate germ cell subpopulation in vitro.

Toxicologic Pathology Forum*: Opinion on Sexual Maturity and Fertility Assessment in Long-tailed Macaques ( Macaca fascicularis) in Nonclinical Safety Studies

If nonhuman primates represent the only relevant species for nonclinical safety evaluation of biotechnology-derived products, male and female fertility effects can be assessed in repeat dose toxicity studies given that sexually mature monkeys are used. This opinion piece provides recommendations for determining sexual maturity and when/how fertility assessments should be conducted in the cynomolgus monkey. Male sexual maturity should be proven by presence of sperm in a semen sample, female sexual maturity by at least two consecutive menstrual bleedings. As per regulatory guidance, default parameters for an indirect assessment of fertility in both sexes are reproductive organ weight and histopathology. Beyond default parameters, daily vaginal swabs are recommended for females, and for males, it is recommended to include blood collections (for potential analysis of reproductive hormones), testis volume sonography, and collection of frozen testis samples at necropsy. Only if there is a cause for concern, blood collection for potential reproductive hormone analysis should be conducted in females and semen analysis in males. In principle, adverse reproductive effects can be detected within 4 weeks of test article administration, depending on study design and reproductive end point chosen. Therefore, there are options for addressing reproductive toxicity aspects with studies of less than 3 months dosing duration. *This is an opinion article submitted to the Toxicologic Pathology Forum. It represents the views of the authors. It does not constitute an official position of the Society of Toxicologic Pathology, British Society of Toxicological Pathology, or European Society of Toxicologic Pathology, and the views expressed might not reflect the best practices recommended by these Societies. This article should not be construed to represent the policies, positions, or opinions of their respective organizations, employers, or regulatory agencies.

A safety study of newly generated anti-podoplanin-neutralizing antibody in cynomolgus monkey (Macaca fascicularis)

Hematogenous metastases are enhanced by platelet aggregation induced by tumor cell-platelet interaction. Podoplanin is a key molecule to enhance the platelet aggregation and interacts with C-type lectin-like receptor 2 (CLEC-2) on platelet via PLAG domains. Our previous reports have shown that blocking podoplanin binding to platelets by neutralizing antibody specific to PLAG4 domain strongly reduces hematogenous metastasis. However, podoplanin is expressed in a variety of normal tissues such as lymphatic vessels and the question remains whether treatment of tumors with anti-podoplanin neutralizing antibodies would be toxic. Monkeys are the most suitable species for that purpose. PLAG3 and PLAG4 domains had high homology among various monkey species and human. PLAG domain deleted mutants were indicated that monkey PLAG4 domain played a more crucial role in podoplanin-induced platelet aggregation than did the PLAG3 domain as in human. Moreover, newly established neutralizing antibodies (1F6, 2F7, and 3F4) targeting the monkey PLAG4 domain blocked interaction between monkey podoplanin and CLEC-2. Especially, the 2F7 neutralizing antibody strongly suppressed platelet aggregation and pulmonary metastasis. Furthermore, inhibiting podoplanin function with 2F7 neutralizing antibody exhibited no acute toxicity in cynomolgus monkeys. Our results suggested that targeting podoplanin with specific neutralizing antibodies may be an effective anticancer treatment.

Testicular Fibrous Hypoplasia in Cynomolgus Monkeys (Macaca fascicularis): An Incidental, Congenital Lesion

Testicular fibrous hypoplasia is an incidental lesion characterized by replacement of the testicular parenchyma by mature collagen. A retrospective survey of hematoxylin and eosin–stained testicular sections from 722 purpose-bred Asian and 90 Mauritian cynomolgus monkeys from 56 safety assessment studies conducted between 1999 and 2011 was performed. The incidence of the lesion increased markedly over time. No cases occurred between 1999 and 2004. Between 2005 and 2009, the incidence ranged between 8.1% and 11.0% of the monkeys examined and then rose to 26.1% in 2010 and 30.9% in 2011. Overall, the lesion was identified in 10.94% of Asian monkeys with the highest incidence in animals originating from China and Vietnam; severity ranged from minimal to severe and it occurred unilaterally (38.5%) and bilaterally (61.5%). In Mauritian monkeys, the lesion was predominantly minimal in severity, bilateral in distribution, and affected 6.6% of the animals examined. The lesion occurred regardless of sexual maturation status but when present in mature monkeys was often associated with cystic tubular atrophy of the seminiferous epithelium. Based on the morphological characteristics of the lesion and the unilateral/bilateral distribution, the lesion is considered to be a congenital or developmental abnormality.