Preclinical and translational pharmacology of afucosylated anti-CCR8 antibody for depletion of tumour-infiltrating regulatory T cells.

BACKGROUND AND PURPOSE: RO7502175 is an afucosylated antibody designed to eliminate C-C motif chemokine receptor 8 (CCR8)+ Treg cells in the tumour microenvironment through enhanced antibody-dependent cellular cytotoxicity (ADCC). EXPERIMENTAL APPROACH: We report findings from preclinical studies characterizing pharmacology, pharmacokinetics (PK)/pharmacodynamics (PD) and safety profile of RO7502175 and discuss the translational PK/PD approach used to inform first-in-human (FiH) dosing strategy and clinical development in solid tumour indications. KEY RESULTS: RO7502175 demonstrated selective ADCC against human CCR8+ Treg cells from dissociated tumours in vitro. In cynomolgus monkeys, RO7502175 exhibited a biphasic concentration-time profile consistent with immunoglobulin G1 (IgG1) antibodies, reduced CCR8+ Treg cells in the blood, induced minimal and transient cytokine secretion, and was well tolerated with a no-observed-adverse-effect level (NOAEL) of 100 mg·kg-1 . Moreover, RO7502175 caused minimal cytokine release from peripheral blood mononuclear cells (PBMCs) in vitro. A quantitative model was developed to capture surrogate anti-murine CCR8 antibody PK/PD and tumour dynamics in mice and RO7502175 PK/PD in cynomolgus monkeys. Subsequently, the model was used to project RO7502175 human PK and receptor occupancy (RO) in patients. Because traditional approaches resulted in a low FiH dose for this molecule, even with its superior preclinical safety profile, an integrated approach based on the totality of preclinical data and modelling insights was used for starting dose selection. CONCLUSION AND IMPLICATIONS: This work demonstrates a translational research strategy for collecting and utilizing relevant nonclinical data, developing a mechanistic PK/PD model and using a comprehensive approach to inform clinical study design for RO7502175.

HESI workshop summary: Interpretation of developmental and reproductive toxicity endpoints and the impact on data interpretation of adverse events.

The Health and Environmental Sciences Institute Developmental and Reproductive Toxicology (HESI-DART) group held a hybrid in-person and virtual workshop in Washington, DC, in 2022. The workshop was entitled, "Interpretation of DART in Regulatory Contexts and Frameworks." There were 154 participants (37 in person and 117 virtual) across 9 countries. The purpose of the workshop was to capture key consensus approaches used to assess DART risks associated with chemical product exposure when a nonclinical finding is identified. The decision-making process for determining whether a DART endpoint is considered adverse is critical because the outcome may have downstream implications (e.g., increased animal usage, modifications to reproductive classification and pregnancy labeling, impact on enrollment in clinical trials and value chains). The workshop included a series of webinar modules to train and engage in discussions with federal and international regulators, clinicians, academic investigators, nongovernmental organizations, contract research organization scientists, and private sector scientists on the best practices and principles of interpreting DART and new approach methodologies in the context of regulatory requirements and processes. Despite the differences in regulatory frameworks between the chemical and pharmaceutical sectors, the same foundational principles for data interpretation should be applied. The discussions led to the categorization of principles, which offer guidance for the systematic interpretation of data. Step 1 entails identifying any hazard by closely analyzing the data at the study endpoint level, while Step 2 involves assessing risk using weight of evidence. These guiding principles were derived from the collective outcomes of the workshop deliberations.

Isoform-selective TGF-ß3 inhibition for systemic sclerosis.

BACKGROUND: Transforming growth factor ß (TGF-ß) is implicated as a key mediator of pathological fibrosis, but its pleiotropic activity in a range of homeostatic functions presents challenges to its safe and effective therapeutic targeting. There are three isoforms of TGF-ß, TGF-ß1, TGF-ß2, and TGF-ß3, which bind to a common receptor complex composed of TGF-ßR1 and TGF-ßR2 to induce similar intracellular signals in vitro. We have recently shown that the cellular expression patterns and activation thresholds of TGF-ß2 and TGF-ß3 are distinct from those of TGF-ß1 and that selective short-term TGF-ß2 and TGF-ß3 inhibition can attenuate fibrosis in vivo without promoting excessive inflammation. Isoform-selective inhibition of TGF-ß may therefore provide a therapeutic opportunity for patients with chronic fibrotic disorders. METHODS: Transcriptomic profiling of skin biopsies from patients with systemic sclerosis (SSc) from multiple clinical trials was performed to evaluate the role of TGF-ß3 in this disease. Antibody humanization, biochemical characterization, crystallization, and pre-clinical experiments were performed to further characterize an anti-TGF-ß3 antibody. FINDINGS: In the skin of patients with SSc, TGF-ß3 expression is uniquely correlated with biomarkers of TGF-ß signaling and disease severity. Crystallographic studies establish a structural basis for selective TGF-ß3 inhibition with a potent and selective monoclonal antibody that attenuates fibrosis effectively in vivo at clinically translatable exposures. Toxicology studies suggest that, as opposed to pan-TGF-ß inhibitors, this anti-TGF-ß3 antibody has a favorable safety profile for chronic administration. CONCLUSION: We establish a rationale for targeting TGF-ß3 in SSc with a favorable therapeutic index. FUNDING: This study was funded by Genentech, Inc.

Repeat-dose and embryo-fetal developmental toxicity of zinpentraxin alfa.

Zinpentraxin alfa is a recombinant human pentraxin-2 (PTX-2) developed for the treatment of various fibrotic diseases with the hypothesis that supplementing endogenous PTX-2 levels through intravenous administration should increase its regulatory capacity in circulation and at the site of disease, thereby promoting healing and reducing fibrosis. Zinpentraxin alfa has been studied in various clinical trials, particularly in patients with idiopathic pulmonary fibrosis, where it has demonstrated efficacy in slowing decline in lung function in a phase 2 study. In the present investigation, we summarize findings from 14-day repeat-dose toxicity studies in rats and cynomolgus monkeys supporting early clinical development of zinpentraxin alfa. In addition, we also describe the findings from the embryo-fetal developmental (EFD) studies conducted in rats and rabbits, since the intended fibrosis patient population may include patients of childbearing potential. Zinpentraxin alfa was well tolerated by rats and monkeys in general toxicity studies with no treatment-related adverse effects, as well as by pregnant rats over the same dose range in a definitive EFD study. In contrast, substantial toxicity was observed in a rabbit dose-range-finder EFD study. Zinpentraxin alfa was poorly tolerated by pregnant rabbits and effects on the dams correlated with post-implantation fetal losses. The disparate effects of zinpentraxin alfa on embryo-fetal development between the two species suggests a potential unknown biological function of PTX-2 in pregnancy in the rabbit, which may be relevant to humans. Our findings warrant the consideration for highly effective contraceptive measures to avoid pregnancy in patients enrolled in clinical studies with zinpentraxin alfa.

Utilizing PK and PD Biomarkers to Guide the First-in-Human Starting Dose Selection of MTBT1466A: A Novel Humanized Monoclonal Anti-TGFß3 Antibody for the Treatment of Fibrotic Diseases.

MTBT1466A is a high-affinity TGFß3-specific humanized IgG1 monoclonal antibody with reduced Fc effector function, currently under investigation in clinical trials as a potential anti-fibrotic therapy. Here, we characterized the pharmacokinetics (PK) and pharmacodynamics (PD) of MTBT1466A in mice and monkeys and predicted the PK/PD of MTBT1466A in humans to guide the selection of the first-in-human (FIH) starting dose. MTBT1466A demonstrated a typical IgG1-like biphasic PK profile in monkeys, and the predicted human clearance of 2.69 mL/day/kg and t1/2 of 20.4 days are consistent with those expected for a human IgG1 antibody. In a mouse model of bleomycin-induced lung fibrosis, changes in expression of TGFß3-related genes, serpine1, fibronectin-1, and collagen 1A1 were used as PD biomarkers to determine the minimum pharmacologically active dose of 1 mg/kg. Unlike in the fibrosis mouse model, evidence of target engagement in healthy monkeys was only observed at higher doses. Using a PKPD-guided approach, the recommended FIH dose of 50 mg, IV, provided exposures that were shown to be safe and well tolerated in healthy volunteers. MTBT1466A PK in healthy volunteers was predicted reasonably well using a PK model with allometric scaling of PK parameters from monkey data. Taken together, this work provides insights into the PK/PD behavior of MTBT1466A in preclinical species, and supports the translatability of the preclinical data into the clinic.

FDA and industry collaboration: Identifying opportunities to further reduce reliance on nonhuman primates for nonclinical safety evaluations.

The nonhuman primate (NHP) has always been a limited resource for pharmaceutical research with ongoing efforts to conserve. This is due to their inherent biological properties, the growth in biotherapeutics and other modalities, and their use in small molecule drug development. The SARS-CoV-2 pandemic has significantly impacted the availability of NHPs due to the immediate need for NHPs to develop COVID-19 vaccines and treatments and the China NHP export ban; thus, accelerating the need to further replace, reduce and refine (3Rs) NHP use. The impact of the NHP shortage on drug development led DruSafe, BioSafe, and the United States (U.S.) Food and Drug Administration (FDA) Center for Drug Evaluation and Research (CDER) to discuss this issue at their 2021 annual meeting. This meeting identified areas to further the 3Rs in NHP use within the current nonclinical safety evaluation regulatory framework and highlighted the need to continue advancing alternative methods towards the aspirational goal to replace use of NHPs in the long term. Alignment across global health authorities is necessary for implementation of approaches that fall outside existing guidelines. This article captures the proceedings from this meeting highlighting current best practices and areas for 3Rs in NHP use.

Neutropenia in Cynomolgus Monkeys With Anti-Drug Antibodies Associated With Administration of Afucosylated Humanized Monoclonal Antibodies.

Removal of the core fucose from the Fc region of humanized monoclonal antibodies (afucosylated antibodies) enhances their antibody-dependent cell cytotoxicity activities in killing cancer cells. Based on the authors' experience and literature, administrations of afucosylated antibodies have been associated with neutropenia in cynomolgus monkeys. However, in a recent general toxicology study conducted with an afucosylated antibody in cynomolgus monkeys, transient neutropenia was observed and correlated with the emergence of anti-drug antibodies (ADAs) in the affected animals. To further explore the relationship between neutropenia, afucosylated antibodies, and ADAs in cynomolgus monkeys, we performed an investigational retrospective meta-analysis of data from general toxicology studies conducted with Genentech's therapeutic antibodies administered to cynomolgus monkeys between 2005 and 2021. In this analysis, transient neutropenia strongly correlated with ADA-induced inflammation in cynomolgus monkeys administered afucosylated antibodies. This may reflect the simultaneous occurrence of two distinct processes of neutrophil elimination and utilization, thus overwhelming bone marrow reserve capacity leading to transient neutropenia. The integrated analysis of immunogenicity, and anatomic and clinical pathology results from these studies highlights the correlation of transient neutropenia in cynomolgus monkeys with ADA-related inflammation, potentially exacerbated by enhanced effector function of afucosylated antibodies.

Nonclinical toxicology development of a novel antibody antibiotic conjugate for treating invasive Staphylococcus Aureus infections.

Invasive Staphylococcus aureus (S. aureus) infections are a leading cause of death and not effectively treated with prolonged standard of care antibiotics. A novel THIOMAB™ antibody antibiotic conjugate (TAC) was developed that uses a bacterial-wall specific antibody to deliver the antibiotic (dmDNA31, a rifamycin analogue) to bacteria to minimize toxicities typically seen with prolonged use of traditional antibiotics. The TAC nonclinical toxicology package included repeat dose rat and cynomolgus monkey toxicology studies for 8 weekly intravenous (IV) doses, a 7-day daily repeat dose IV toxicology study of dmDNA31 and an assessment of genotoxicity, cardiovascular toxicity, neurotoxicity and sperm parameters. TAC and dmDNA31 were well tolerated in rats and monkeys, and there was no evidence of genotoxicity, cardiovascular toxicity or neurotoxicity. Non-adverse findings were observed and included blue discoloration in skin, blood, etc. due to the blue color of dmDNA31, increased globulin due to the high doses of antibodies, and abnormal sperm morphology of small heads in male rats with no histopathology correlate in testis. This is an example of antibody-mediated delivery of an antibiotic that has the potential to offer a more effective way of eradicating infection while providing a better safety profile compared to traditional antibiotics.

Surfactant protein D is a biomarker of influenza-related pediatric lung injury.

BACKGROUND: Biomarkers that can risk-stratify children with influenza virus lower respiratory infection may identify patients for targeted intervention. Early elevation of alveolar-related proteins in the bloodstream in these patients could indicate more severe lung damage portending worse outcomes. METHODS: We used a mouse model of human influenza infection and evaluated relationships between lung pathophysiology and surfactant protein D (SP-D), SP-A, and Club cell protein 16 (CC16). We then measured SP-A, SP-D, and CC16 levels in plasma samples from 94 children with influenza-associated acute respiratory failure (PICFLU cohort), excluding children with underlying conditions explaining disease severity. We tested for associations between levels of circulating proteins and disease severity including the diagnosis of acute respiratory distress syndrome (ARDS), mechanical ventilator, intensive care unit and hospital days, and hospital mortality. RESULTS: Circulating SP-D showed a greater increase than SP-A and CC16 in mice with increased alveolar-vascular permeability following influenza infection. In the PICFLU cohort, SP-D was associated with moderate-severe ARDS diagnosis (p = 0.01) and with mechanical ventilator (r = 0.45, p = 0.002), ICU (r = 0.44, p = 0.002), and hospital days (r = 0.37, p = 0.001) in influenza-infected children without bacterial coinfection. Levels of SP-D were lower in children with secondary bacterial pneumonia (p = 0.01) and not associated with outcomes. CC16 and SP-A levels did not differ with bacterial coinfection and were not consistently associated with severe outcomes. CONCLUSIONS: SP-D has potential as an early circulating biomarker reflecting a degree of lung damage caused directly by influenza virus infection in children. Secondary bacterial pneumonia alters SP-D biomarker performance.

Postnatal Hepatobiliary and Gastrointestinal Systems Development and Impact on ADME.

Toxicity can result from variable target organ sensitivity and exposure based on postnatal development. Changes in the gastrointestinal tract (GIT) in neonates are driven by initial enteral feedings. These are important for nutrient uptake as well as drug disposition and include motility, expansion of enzyme and transporter function, permeability, intestinal microbiome, and species-specific maturation. Some aspects of GIT function do not mature until driven by increased dietary complexity. As with the GIT, postnatal hepatic maturation in the rat includes a variety of anatomic and functional changes that include refinements in the activities or expression of drug transporters and drug-metabolizing enzymes. These changes may impact rodent pharmacokinetics, nonclinical toxicity profiles, and estimation of safe pediatric doses. Pilot or dose range finding studies can help characterize and mitigate toxicity related to drug disposition, especially in juvenile rodents. Interpretation of developmental toxicity requires knowledge of developing systems in humans and nonclinical models.

Current Trends of Practices in Nonclinical Toxicology: An Industry Survey.

The growth in drug development over the past years reflects significant advancements in basic sciences and a greater understanding of molecular pathways of disease. Benchmarking industry practices has been important to enable a critical reflection on the path to evolve pharmaceutical testing, and the outcome of past industry surveys has had some impact on best practices in testing. A survey was provided to members of SPS, ACT, and STP. The survey consisted of 37 questions and was provided to 2550 participants with a response rate of 24%. Most respondents (∼75%) came from the US and Europe. The survey encompassed multiple topics encountered in nonclinical testing of pharmaceuticals. The most frequent target indications were oncology (69%), inflammation (55%), neurology/psychiatry/pain (46%), cardiovascular (44%), and metabolic diseases (39%). The most frequent drug-induced toxicology issues confronted were hepatic, hematopoietic, and gastrointestinal. Toxicological effects that impacted the no observed adverse effect level (NOAEL) were most frequently based on histopathology findings. The survey comprised topics encountered in the use of biomarkers in nonclinical safety assessment, most commonly those used to assess inflammation, cardiac/vascular, renal, and hepatic toxicity as well as common practices related to the assessment of endocrine effects, carcinogenicity, genotoxicity, juvenile and male-mediated developmental and female reproductive toxicity. The survey explored the impact of regulatory meetings on program design, application of the 3 Rs, and reasons for program delays. Overall, the survey results provide a broad perspective of current practices based on the experience of the scientific community engaged in nonclinical safety assessment.

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.

Atypical presentation and pathogenesis of a macaque lymphocryptoviral-associated B-cell lymphoma in a cynomolgus monkey.

We report the unique pathogenesis and presentation of a rapidly progressive B-cell lymphoma in a 3-year-old female cynomolgus monkey on day 50 of a 13-week toxicity study. Clinical pathology evaluation revealed a marked leukocytosis with bicytopenia. A serum protein electrophoresis was consistent with monoclonal gammopathy. The architecture of the lymph node, spleen, and thymus were variably effaced by neoplastic cells, which also infiltrated other tissues. Immunohistochemistry of the affected tissues confirmed a predominant population of CD20+, CD79a+, CD3-, CD68-, and CD34-neoplastic cells. The full data best support a diagnosis of Stage V lymphoma. Nextgen sequencing and negative prestudy serology results suggested a recent infection by macaque lymphocryptovirus (mLCV) with a unique transcriptional profile comparable with a rarely observed direct LCV infection model. This infection model might be associated with a temporary lack of an LCV antigen-specific cytotoxic T-cell adaptive immune response. Consistent with the established mechanisms of LCV-related lymphoproliferation, MYC and BCL2L11 gene expression were increased and decreased, respectively. While there was no overt immunosuppression, immunophenotyping revealed the index animal had a relatively low NK cell count, which further decreased by >50% on day 24 of the study. In addition to the temporary lack of adaptive immunity, the low NK cell counts were suggestive of an impaired innate immunity to control the virally-transformed cells and the subsequent unchecked lymphoproliferation. To our knowledge, this is the first report of a Stage V lymphoma with a unique pathogenesis in an otherwise immunocompetent cynomolgus monkey.

In Vivo Assessment of Antibody-Dependent Enhancement of Influenza B Infection.

A theoretical safety concern proposed in the influenza literature is that therapeutic antiviral antibodies could have the potential for antibody-dependent enhancement (ADE) of infection and disease. ADE may occur when virus-specific antibodies at subtherapeutic, nonneutralizing concentrations facilitate virus uptake and, in some cases, enhance replication, which can lead to an exacerbation of virus-mediated disease. Alternatively, ADE may occur due to antibody-dependent complement activation exacerbating virus-mediated disease in the absence of increased replication. As a result of this theoretical safety concern, safety assessment of anti-influenza antibodies may include an in vivo evaluation of ADE of infection and/or disease. These studies were conducted to investigate the potential of MHAB5553A, a broadly specific, neutralizing therapeutic anti-influenza B antibody, to elicit ADE of infection and disease in mouse models of influenza B infection. In parallel studies, female DBA/2J mice were infected with either influenza B/Victoria/504/2000 or influenza B/Brisbane/60/2008 representing distinct lineages. Assessment of ADE was based on an integration of results from multiple endpoints, including infectious lung viral titers and genomes, body weight, mortality, lung weight, and histopathology. In these studies, the high dose of 15 mg/kg MHAB5553A resulted in substantial attenuation of influenza pneumonia, with more modest effects at 1.5 mg/kg; whereas MHAB5553A treatment at 0.15 or 0.015 mg/kg was generally comparable to vehicle-treated controls. Our results demonstrate that MHAB5553A across a broad range of doses did not enhance primary influenza B infection or disease in this model, and represent a nonclinical de-risking of the ADE potential with this antibody.

Physiology of the Neonatal Gastrointestinal System Relevant to the Disposition of Orally Administered Medications.

A thorough knowledge of the newborn (age, birth to 1 month postpartum) infant's gastrointestinal tract (GIT) is critical to the evaluation of the absorption, distribution, metabolism, and excretion (ADME) of orally administered drugs in this population. Developmental changes in the GIT during the newborn period are important for nutrient uptake as well as the disposition of orally administered medications. Some aspects of gastrointestinal function do not mature until driven by increased dietary complexity and nutritional demands later in the postnatal period. The functionalities present at birth, and subsequent maturation, can also impact the ADME parameters of orally administered compounds. This review will examine some specific contributors to the ADME processes in human neonates, as well as what is currently understood about the drivers for their maturation. Key species differences will be highlighted, with a focus on laboratory animals used in juvenile toxicity studies. Because of the gaps and inconsistencies in our knowledge, we will also highlight areas where additional study is warranted to better inform the appropriate use of medicines specifically intended for neonates.

Resolution of unexpected pregnancy-related findings in a rat embryofetal development and toxicokinetic study of monoclonal antibodies specific for hCMV.

BACKGROUND: Developmental and reproductive toxicity testing is not uniformly warranted for biopharmaceuticals that lack relevant targets in test species. However, RG7667, consisting of two monoclonal antibodies specific for human cytomegalovirus (hCMV), was intended for administration to pregnant women to prevent transmission of CMV to the developing fetus. METHODS: Considering the target indication, a Pilot Embryo Fetal Development/Toxicokinetic study was conducted to assess toxicokinetics in the dam and fetuses and general tolerability. RESULTS: RG7667 administered intravenously to presumed pregnant Sprague-Dawley rats was well tolerated with no clinical signs in any dam and comparable litter sizes and viability across groups. However, at cesarean section, hepatic necrosis and pancreatic edema were identified in two dams administered RG7667, with no clear dose relationship. Investigation of total protein, albumin, and transaminase activity in residual serum from TK samples demonstrated striking hypoproteinemia and elevated transaminases limited to these two dams. Overall, these pathology findings in dams were considered of uncertain relationship to RG7667; therefore, a subsequent Pivotal EFD study was conducted, which did not repeat the liver or pancreatic findings. CONCLUSIONS: The results of the Pivotal study confirmed the lack of overt toxicity, teratogenicity, or effects on litter size and viability when human or humanized monoclonal antibodies that lack an endogenous target are administered IV to rats during pregnancy. With these additional data, we concluded that the unexpected pathology findings in the Pilot study were not specific to RG7667, but rather highlight some clinical pathology and macroscopic/microscopic findings that can occur during pregnancy in rats.

Applying a weight of evidence approach to the evaluation of developmental toxicity of biopharmaceuticals.

Toxicity studies in pregnant animals are not always necessary for assessing the human risk of developmental toxicity of biopharmaceuticals. The growing experience and information on target biology and molecule-specific pharmacokinetics present a powerful approach to accurately anticipate effects of target engagement by biopharmaceuticals using a weight of evidence approach. The weight of evidence assessment should include all available data including target biology, pharmacokinetics, class effects, genetically modified animals, human mutations, and a thorough literature review. When assimilated, this weight of evidence evaluation may be sufficient to inform risk for specific clinical indications and patient populations. While under current guidance this approach is only applicable for drugs and biologics for oncology, the authors would like to suggest that this approach may also be appropriate for other disease indications. When there is an unacceptable level of uncertainty and a toxicity study in pregnant animals could impact human risk assessment, then such studies should be considered. Determination of appropriate nonclinical species for developmental toxicity studies to inform human risk should consider species-specific limitations, reproductive physiology, and pharmacology of the biopharmaceutical. This paper will provide considerations and examples of the weight of evidence approach to evaluating the human risk of developmental toxicity of biopharmaceuticals.

Placental and Fetal Effects of Onartuzumab, a Met/HGF Signaling Antagonist, When Administered to Pregnant Cynomolgus Monkeys.

Onartuzumab is an engineered single arm, monovalent monoclonal antibody that targets the MET receptor and prevents hepatocyte growth factor (HGF) signaling. Knockout mice have clearly demonstrated that HGF/MET signaling is developmentally critical. A pre- and postnatal development study (enhanced design) was conducted in cynomolgus monkeys to evaluate the potential developmental consequences following onartuzumab administration. Control or onartuzumab, at loading/maintenance doses of 75/50 mg/kg (low) or 100/100 mg/kg (high), was administered intravenously once weekly to 12 confirmed pregnant female cynomolgus monkeys per group from gestation day (GD) 20 through GD 174. Onartuzumab administration resulted in decreased gestation length, decreased birth weight, and increased fetal and perinatal mortality. A GD147 C-section was conducted for a subset of Control and High Dose monkeys, and identified placental infarcts with hemorrhage in the chorionic plate, chorionic villus and/or decidual plate. These findings were limited to placentas from onartuzumab-treated animals. In addition, decreased cellularity of the hepatocytes with dilated hepatic sinusoids was inconsistently observed in the liver of a few fetal or infant monkeys that died in the perinatal period. Surviving offspring had some evidence of developmental delay compared with controls, but no overt teratogenicity. Overall, effects on the perinatal fetuses were consistent with those reported in knockout mice, but not as severe. Onartuzumab concentrations were low or below the level of detection in most offspring, with cord blood concentrations only 1%-2% of maternal levels on GD 147. Malperfusion secondary to onartuzumab-induced placental injury could explain the adverse pregnancy outcomes, fetal growth restriction and relatively low fetal exposures.

Use of Severity Grades to Characterize Histopathologic Changes.

The severity grade is an important component of a histopathologic diagnosis in a nonclinical toxicity study that helps distinguish treatment-related effects from background findings and aids in determining adverse dose levels during hazard characterization. Severity grades should be assigned based only on the extent (i.e., amount and complexity) of the morphologic change in the examined tissue section(s) and be clearly defined in the pathology report for critical lesions impacting study interpretation. However, the level of detail provided and criteria by which severity grades are assigned can vary, which can lead to inappropriate comparisons and confusion when evaluating pathology results. To help address this issue, a Working Group of the Society of Toxicologic Pathology's Scientific and Regulatory Policy Committee was formed to provide a "points to consider" article on the assignment and application of pathology severity grades. Overall, the Working Group supports greater transparency and consistency in the reporting of grading scales and provides recommendations to improve selection of diagnoses requiring more detailed severity criteria. This information should enhance the overall understanding by toxicologic pathologists, toxicologists, and regulatory reviewers of pathology findings and thereby improve effective communication in regulatory submissions.

Regulatory Forum Opinion Piece: Review of FDA Draft Guidance Testicular Toxicity-Evaluation during Drug Development Guidance for Industry.

In July 2015, the U.S. Food and Drug Administration (FDA) posted a new draft guidance entitled "Testicular Toxicity: Evaluation during Drug Development Guidance for Industry," with a 90-day public comment period. As the nonclinical assessment of testicular toxicity often relies on the expert interpretation of pathology affecting the male reproductive tract, this draft guidance is considered directly relevant to the toxicologic pathology community. Therefore, a working group was formed through the Scientific and Regulatory Policy Committee of the Society of Toxicologic Pathologists (STPs) to provide a detailed review of the draft guidance. Specific comments on the guidance were submitted to the FDA by the STP. The draft guidance and all comments received are currently under review with the FDA. This commentary provides a summary of the components of the draft guidance and the comments submitted by the STP with acknowledgment of different perspectives reflected in comments from other respondents.