In Vitro Oncology Models as an Alternative to Animal Models
In vitro models are reshaping oncology research, providing vital insights into tumor behavior and drug efficacy.
While completely replacing animal testing in cancer research cannot be implemented at present, as animal testing remains essential to drug safety testing, alternative research using in vitro methods is being deployed to learn about human disease and predict the safety of new drugs.1
Guiding principles for more ethical use of animals in testing are the Three Rs (3Rs)2:
- Replacement (preferred use of non-animal methods whenever possible to achieve the same scientific aim)
- Reduction (enabling the obtention of results with fewer animals)
- Refinement (alleviating or minimizing potential pain, suffering or distress, and enhancing animal welfare).
These principles are accepted worldwide as critical elements of the ethical and responsible care and usage of animals for scientific purposes.3
Alternative in vitro models in oncology
Several in vitro models are designed to mimic essential features of tumors, including their differentiation properties, architecture, cellular variability and extracellular environment.4 These model systems allow researchers to study the complexity of tumors and their susceptibility to potential drug treatments.
Cell lines
Cancer cell lines are established human cancer cell models that, while exhibiting specific genetic, epigenetic and gene expression markers, maintain most of the genetic alterations of the original in vivo tumor.5
These cancer cell lines are commonly used models for studying cancer biology, validating therapeutic targets and evaluating drug efficacy. Their usefulness is primarily linked to their ability to provide an indefinite source of biological material for experimental purposes, such as preclinical model systems (Figure 1).6
Furthermore, the easy access to online data that was accumulated from the studies involving cell lines created an important research resource that facilitates the selection of the most appropriate in vitro model systems to test.7
Figure 1: Example of a HCT116 cell line used to model colorectal cancer (CRC) in 3D culture to test RNA/LNP-based therapeutics in vitro. Credit: Tebubio.
Tumoroids
Tumoroids are mini tumor organoids reconstituted from a patient's primary tumor. Put simply, cells from a tumor fragment are dissociated and then grown into self-organized multicellular structures that reflect the mutational status, gene expression levels and phenotypes observed in patient tumors.8
Tumoroids offer a more biologically relevant system that maintains donor-specific characteristics in long-term culture. They are also complex models, which usually require specific and complex culture methods.
By capturing the biological complexity and patients’ specificity, while also offering scalability and cost-effectiveness, tumoroids offer a valuable tool for complex applications that require fast and high-quality results to research questions.9
Microfluidics
While three-dimensional (3D) cell culture models can accurately mimic the cell behavior, morphology and physiology of 3D tumors, they cannot reproduce certain mechanical cues, such as hydrostatic pressure and fluid shear stress.10 These conditions are better modeled in in vivo models. However, barriers to adoption include high cost, low throughput drug optimization, long-term engraftment and ethical controversy.
Moreover, due to the genetic differences between species that result in species-specific responses during drug trials, few human cancers can be tested in patient-derived animal models using patient-derived xenografts (PDX).11 Therefore, models recapitulating the complexity of cancer and the interaction between organs are crucial to understand the impact of cancer therapies to develop drugs.
An organ-on-a-chip system aims to obtain functional tissue-organ constructs, to capture the features of 3D architecture and physiological tumor microenvironment in human organs on a chip in vitro. This technology is based on microfluidics to simulate the microenvironment of native tissue and organs, including different types of living cells, biological fluids and mechanical stimulation.12
AI-Enabled Imaging Solutions for Complex 3D Organoid Screening
This application note demonstrates how next-generation confocal imaging technology combined with AI-powered analysis tools enables researchers to capture high-quality images from 3D organoids.View App Note / Case Study
To form an in vitro vascularized 3D cancer model on a chip, the tissue (including the PDX tumors) is placed into the chips connected to blood vessel models. The vasculatures are then used to administer the drug to ensure that the new anticancer therapeutics display efficient, realistic pharmacokinetics. With further investigation incorporating live-cell microscopy, researchers can study the real-time dynamic cellular response within a perfusion-based system, such as cancer cell migration, invasion, intravasation and extravasation (Figure 2).
Figure 2: Example use of microfluidic chambers to allow the observation of cell migration, change of nuclear shape and cytoskeleton organization during invasion by HCT116 cells, from the tissue compartment to the HUVEC-containing endothelial compartment. Credit: Tebubio.
Advancing cancer research through in vitro innovation
Cancer is a major cause of death worldwide, accounting for an estimated 9.6 million deaths in 2020 and representing nearly 1 in 6 deaths.13 The cancer burden continues to grow globally, exerting tremendous strain on individuals, families, communities and global healthcare systems. Therefore, studying cancer formation, metastasis and treatment is crucial to reduce this shared burden.
In an effort to reduce, replace and refine the use of animals in cancer studies, scientists need systems with the potential to bridge traditional in vitro cell culture with in vivo experiments to accelerate cancer research. 3D oncologic models such as cell lines cultured as spheroids, tumoroids or oncologic microfluidics models, have the potential to recapitulate several aspects of the tumor physiopathological characteristics, while being more affordable to scientists. Choice of experimental model (Table 1) is critical depending on the research topic, sample availability, time and funds constraints.
Table 1: Advantages and disadvantages of in vivo vs in vitro models in cancer research.
| Model | Advantages | Disadvantages |
| Animal |
|
|
| Cell lines |
|
|
| Tumoroids |
|
|
| Microfluidics |
|
|
While still refinable, the use of in vitro models as preclinical screens for toxicity or efficacy of new therapeutics has the potential to greatly accelerate the research for anticancer treatments.
