Best Practices for Preclinical In Vivo Testing of Cancer Nanomedicines

Abstract

Significant advances have been made in the development of nanoparticles for cancer treatment in recent years. Despite promising results in preclinical animal models, cancer nanomedicines often fail in clinical trials. This failure rate could be reduced by defining stringent criteria for testing and quality control during the design and development stages, and by performing carefully planned preclinical studies in relevant animal models. This article discusses best practices for the evaluation of nanomedicines in murine tumor models. First, a recommended set of experiments to perform is introduced, including discussion of the types of data to collect during these studies. This is followed by an outline of various tumor models and their clinical relevance. Next, different routes of nanoparticle administration are overviewed, followed by a summary of important controls to include in in vivo studies of nanomedicine. Finally, animal welfare considerations are discussed, and an overview of the steps involved in achieving US Food and Drug Administration approval after animal studies are completed is provided. Researchers should use this report as a guideline for effective preclinical evaluation of cancer nanomedicine. As the community adopts best practices for in vivo testing, the rate of clinical translation of cancer nanomedicines is likely to improve.

Keywords: animal welfare; clinical translation; experimental design; murine tumor models; nanoparticles.

Figure 1.. Overview of animal studies used to pre-clinically evaluate cancer nanomedicines.

Maximum tolerated dose (MTD) and safety studies allow for dosing optimization while ADME studies define the absorption, distribution, metabolism, and elimination of therapeutics. Efficacy studies primarily aim to elucidate the impact of treatments on tumor growth and animal survival and are supplemented by studies to confirm the predicted mechanism of action of the therapy. In cases where treatments are designed to attack metastasis, the size and number of metastatic lesions may be measured following treatment to confirm efficacy.

Figure 2.. Available tumor models to evaluate nanomedicines.

(A) Subcutaneous tumors are formed by subcutaneous injection of cancer cells, typically at the flank region. These models offer a simple and cost-effective system for initial evaluation of nanomedicines. (B) Orthotopic tumor models are produced by implanting cancer cells at the relevant tissue site (e.g., breast cancer cells would be implanted in the mammary fat pad). These models are more difficult to produce, but better replicate the physiology of human cancer than subcutaneous tumor models. (C) Metastatic tumor models consist of spontaneous models and experimental models. In spontaneous models, cancer cells are implanted subcutaneously or orthotopically, and then disseminate to distant organs. In experimental models, cancer cells are delivered intravenously, leading to formation of metastatic nodules at sites such as the lung. Spontaneous models can recapitulate the entire cascade of events from primary tumor formation to metastasis but are slower to grow and more challenging to use than simple experimental metastasis models. Researchers must consider the benefits and drawbacks of these models and choose those that will best inform the development of their nanomedicine. Portions of this figure were produced with permission using Servier Medical ART templates, which are licensed under a Creative Commons Attribution 3.0 Unported License from Servier Medical Art; https://smart.servier.com.

Figure 3.. Routes of nanoparticle administration.

When designing animal studies to evaluate cancer nanomedicines, researchers should utilize the most clinically relevant route of administration. Different administration routes and their utility are summarized in this figure. Portions of this figure were produced with permission using Servier Medical ART templates, which are licensed under a Creative Commons Attribution 3.0 Unported License from Servier Medical Art; https://smart.servier.com

Figure 4.. Overview of experimental control groups to include in studies of cancer nanomedicine.

Researchers should include appropriate controls for nanoparticle mode of action and surface functionality in all studies. (A) Scheme depicting appropriate controls to include when evaluating photoresponsive therapeutics. (B) Scheme depicting proper controls to include when evaluating gene regulatory agents. (C) To evaluate targeted nanomedicines, researchers should include both nanoparticle controls and tumor controls in their study design to validate the specificity and efficiency of target-specific binding. Portions of this figure were produced with permission using Servier Medical ART templates, which are licensed under a Creative Commons Attribution 3.0 Unported License from Servier Medical Art; https://smart.servier.com

Figure 5.. Scheme depicting the timeline from nanomedicine discovery to clinical implementation.

Researchers evaluating cancer nanomedicines pre-clinically in vitro and in vivo must be cognizant of the requirements to initiate clinical trials and ultimately gain FDA approval.