Existing guidelines on the preparation (Planning Research and Experimental Procedures on Animals: Recommendations for Excellence (PREPARE)) and reporting (Animal Research: Reporting of In Vivo Experiments (ARRIVE)) of animal experiments do not provide a clear and standardized approach for refinement during in vivo cancer studies, resulting in the publication of generic methodological sections that poorly reflect the attempts made at accurately monitoring different pathologies. Compliance with the 3Rs guidelines has mainly focused on reduction and replacement; however, refinement has been harder to implement. The Oncology Best-practices: Signs, Endpoints and Refinements for in Vivo Experiments (OBSERVE) guidelines are the result of a European initiative supported by EurOPDX and INFRAFRONTIER, and aim to facilitate the refinement of studies using in vivo cancer models by offering robust and practical recommendations on approaches to research scientists and animal care staff. We listed cancer-specific clinical signs as a reference point and from there developed sets of guidelines for a wide variety of rodent models, including genetically engineered models and patient derived xenografts. In this Consensus Statement, we systematically and comprehensively address refinement and monitoring approaches during the design and execution of murine cancer studies. We elaborate on the appropriate preparation of tumor-initiating biologicals and the refinement of tumor-implantation methods. We describe the clinical signs to monitor associated with tumor growth, the appropriate follow-up of animals tailored to varying clinical signs and humane endpoints, and an overview of severity assessment in relation to clinical signs, implantation method and tumor characteristics. The guidelines provide oncology researchers clear and robust guidance for the refinement of in vivo cancer models.

According to the EU Directive 2010/63, all animal procedures must be classified as non-recovery, mild, moderate or severe. Several examples are included in the Directive to help in severity classification. Since the implementation of the Directive, different publications and guidelines have been disseminated on the topic. However, due to the large variety of disease models and animal procedures carried out in many different animal species, guidance on the severity classification of specific procedures or models is often lacking or not specific enough. The latter is especially the case in disease models where the level of pain, suffering, distress and lasting harm depends on the duration of the study (for progressive disease models) or the dosage given (for infectious or chemically induced disease models). This, in turn, may lead to inconsistencies in severity classification between countries, within countries and even within institutions. To overcome this, two Belgian academic institutions with a focus on biomedical research collaborated to develop a severity classification for all the procedures performed. This work started with listing all in-house procedures and assigning them to 16 (sub)categories. First, we determined which parameters, such as clinical signs, dosage or duration, were crucial for severity classification within a specific (sub)category. Next, a severity classification was assigned to the different procedures, which was based on professional judgment by the designated veterinarians, members of the animal welfare body (AWB) and institutional animal ethics committee (AEC), integrating the available literature and guidelines. During the classification process, the use of vague terminology, such as ‘minor impact’, was avoided as much as possible. Instead, well-defined cut-offs between severity levels were used. Furthermore, we sought to define common denominators to group procedures and to be able to classify new procedures more easily. Although the primary aim is to address prospective severity, this can also be used to assess actual severity. In summary, we developed a severity classification for all procedures performed in two academic, biomedical institutions. These include many procedures and disease models in a variety of animal species for which a severity classification was not reported so far, or the terms that assign them to a different severity were too vague.

Surgical resection is a cornerstone of glioblastoma (GBM) treatment in patients; yet, it remains underrepresented in preclinical studies with mouse models. This narrative review analyzes the current resection techniques used in mouse GBM studies and evaluates their feasibility, reproducibility and translational relevance. A total of 27 eligible studies were included in the review and categorized by resection method: non-guided biopsy punch, non-guided freehand resection, fluorescence-guided freehand resection (using fluorescent cell lines or dyes), and magnetic resonance imaging (MRI)-guided approaches. While non-guided techniques (biopsy punch or freehand) are commonly employed due to their simplicity and affordability, they lack the precision and adaptability of more advanced methods. Fluorescence-guided resection improves tumor visualization but requires costly equipment and can introduce immunological biases. So-called MRI-guided strategies remain rare, and MRI is not actually used intraoperatively. Despite technically challenging, GBM surgical resection in mice is feasible and several effective techniques are currently available. The systematic implementation of tumor resection in GBM preclinical studies could allow to more closely mimic the human scenario thereby improving the predictive value of GBM animal experiments.

OBJECTIVES: Little is known of the haemodynamic changes following chronic ventricular volume deprivation, which impact understanding the disease course and treatment results. An animal model was created to study the effects of chronic ventricular volume deprivation and acute reloading. METHODS: In 13 lambs, a polytetrafluoroethylene strip was placed around the inferior and superior caval vein through thoracotomy resulting in progressive ventricular volume deprivation during growth. After 10 months, the polytetrafluoroethylene bands were relieved. Magnetic resonance imaging and haemodynamic measurements including pressure–volume loops were performed before and after debanding and compared to age and weight-matched controls (n = 6). RESULTS: The end-diastolic pressure was elevated compared to healthy animals (median [interquartile range] 8.1 [7.2–9.1] vs 1.0 [1.0–2.7] mmHg, P 0.030). The end-diastolic pressure after debanding increased to 11.1 (10.4–17.2) mmHg, P 0.038. The end-diastolic volume and end-systolic volume of the intervention group were also significantly less than the healthy controls (71.5 [66.7–74.7] vs 81.5 [74.3–86.3] ml, P 0.004 and 34.5 [27.5–37.6] vs 42.7 [35.0–50.5] ml P 0.001). The end-diastolic pressure–volume relationship was significantly shifted upwards and to the left compared to controls, indicative of a decreased compliance of the chronically deprived left ventricle. Histologic assessment revealed no significant differences in fibrosis between the ventricles of the intervention group and healthy animals. CONCLUSIONS: When a healthy ventricle is chronically deprived of an adequate preload, it becomes less compliant with elevated filling pressures. Acute reloading does not lead to ventricular systolic dysfunction, but in the early phase, diastolic pressure may rise. A better understanding of this phenomenon might help to recognition and treatment of impaired ventricular compliance.