Image courtesy of AM Biotech
Animal models, long the basis of academic research and preclinical drug discovery, continue to play an important role in advancing our understanding of basic pharmacology and bringing critical therapies to those in need. However, animal models have some natural drawbacks (e.g., not being humans) that hamper their ability to fully predict the interaction of new chemical entities with human physiology. Nonetheless, animal models remain the lynchpin of preclinical research the world over. Given the long-standing paucity of suitable human-based models to replace them, this should come as no surprise. Indeed, while both primary and immortalized human cells have long been available for in vitro research using standard tissue culture techniques, the primarily 2D nature of such in vitro studies is not sufficient to replicate human tissue’s complex structure and function.
These fundamental limitations of animal and in vitro studies are beginning to change with the advent of 3D human cell culture, namely organ-on-a-chip technologies. As these technologies become more widely available and better understood, academic researchers and pharmaceutical development scientists around the globe see the advantages that organ-on-a-chip systems can have in their programs. Namely, such organ-on-a-chip systems recapitulate functional human organ-like structures that react to pharmacological intervention with in vivo-like physiological responses.
The tricky transition from mouse models to human trials
It is well known that mice are typically the animal model of choice for preclinical research. Even if there is a high percentage of gene homology and both species are mammals, the long history of differing pharmacological responses between mice and humans tells a different story. No matter how many experiments were performed in mice or how successful they were, the failure percentage when transitioning from mouse to human trials is incredibly high.
One quite telling example is the story of Vadimezan1, also known as DMXAA or ASA404. This drug candidate was found to be a ligand for STING protein, for “Stimulator of Interferon Genes,” in mice. When injected intratumorally in mice with cancer, this drug was highly efficient in reducing tumor size. As the drug progressed through clinical testing, Phase 3 trial results did not demonstrate the efficacy observed in mice. Why?
In mice, Vadimezan injection increased the production of TNF, IL-6, type I interferons and other pro-inflammatory cytokines that stimulate T cells to attack tumor cells. In humans, the Vadimezan treated group did not show any difference when compared to the placebo group. The reason was that Vadimezan was not activating human STING. In this case, the 83% protein homology shared between mouse and human protein didn’t guarantee the same Vadimezan affinity in both species.
Ultimately, this example is illustrative of a critical limitation of animal models and underpins the need for the broader adoption of models capable of reproducing a human tissue environment to assay drug candidates. This is where 3D cell culture techniques, particularly organ-on-a-chip technologies, become compelling for this purpose.
Mimicking human microphysiology with 3D cell cultures
Technically speaking, the main advantage of 3D cell culture, and why it is so crucial for the future of drug discovery, is its ability to accurately and functionally recreate the microenvironment of human organs in an in vitro format. Jim McGorry, CEO of AIM Biotech, a Boston- and Singapore-based organ-on-a-chip technology company captures this sentiment: “We believe that human 3D cell cultures will become imperative for the transition from animal models to human assays. We created our idenTx 3D cell culture system to simplify the process. As a result, not only researchers but also biopharma and biotech companies can exploit this product. It is an easy-to-use, reproducible and scalable technology that facilitates and predicts human data before stepping to human trails.”
Briefly, 3D cell cultures are grown in a hydrogel matrix, are typically composed of more than one (human) cell type, and allow separate, controlled media exposure to the different cell surfaces or cell types.
A particularly notable feature of these systems, and one that is difficult to overstate, is the potential of the added cells to accurately self-assemble into functional biological structures, as in blood vessel networks2. Importantly, scientists may use human pluripotent stem cells (hiPSCs) and induce differentiation into the cell lineage they want to study, resulting in the possibility of recreating virtually any type of human tissue. These features make 3D cell culture systems natural models for the study of cancer immunotherapies.
Studying cancer therapies with human 3D cell cultures
The fight against cancer has been hard-fought and is not nearly over. After decades of research and thousands of clinical trials, an ultimate cure has not been found. Nevertheless, a promising treatment has arisen during the last ten years: an immunotherapy known as adoptive T cell therapy.
This immunotherapy involves taking patient or healthy donor immune cells and genetically modifying them ex vivo to express specific proteins of therapeutic value. These engineered cells are then injected into the cancer patient to attack and kill the tumor cells.
As with many promising new technologies, obstacles are faced and overcome. For adoptive T cell therapy, it has been observed that cell exhaustion can nullify the tumor-killing effect of the therapy. Scientists used organ-on-a-chip technology from AIM Biotech to study engineered cell behavior in an in vitro human tumor model to solve this issue. They created 3D tumors in the chip to compare the efficacy of different treatment protocols. The group found that engineered T cells with suppressed checkpoint protein expression improved tumor killing3, creating a pathway for effective therapy.
In another example, which perhaps demonstrates that technical points make critical differences, another group of scientists showed the beneficial properties of using 3D cell culture versus the much more widely used 2D cell culture employed for in vitro pharmacology. Again, researchers4 used 3D cell culture technology from AIM Biotech, and they showed that in 2D cell culture, T cells respond identically in the presence of either low or high oxygen concentration; while in 3D cell culture conditions, T cell migration is reduced when oxygen concentration is low. Considering the low oxygen concentration of the human tumor microenvironment, this detail may be most appreciated at the early stages of the drug discovery pathway, where ‘getting a signal’ is so important.
Moving with the pace of development for new therapeutics
While these are only some examples, they are representative of the advantages of 3D cell culture as a way to better predict therapeutic responses in human tissues in vitro, particularly in the backdrop of the current limitations of animal and 2D in vitro models. As both basic research institutes and drug discovery organizations move toward developing increasingly sophisticated therapeutic modalities to overcome both the rarest and most prevalent of human diseases, it is likely that 3D cell culture models will be part of the fight.
Francina Agosti, Ph.D., is a freelance science communicator. After working for ten years in academia in the neuroscience field, she started her own agency communicating science. She works with biopharma and biotech companies writing press releases and website articles, and designing deck presentations. Francina is a scientific editor for a non-profit association of cancer in pets, and she also writes health and science news for online magazines.
References
1. D. F. A. A, J.-E. R, S. K, S.-R. S, and Z. N, “An overview on Vadimezan (DMXAA): The vascular disrupting agent,” Chem. Biol. Drug Des., vol. 91, no. 5, pp. 996–1006, May 2018, doi: 10.1111/CBDD.13166.
2. M. Chen et al., “On-chip human microvasculature assay for visualization and quantification of tumor cell extravasation dynamics,” Nature Protocols, vol. 12, Mar. 2017, doi: 10.1038/nprot.2017.018
3. I. Otano et al., “Molecular Recalibration of PD-1+ Antigen-Specific T Cells from Blood and Liver,” Mol. Ther., vol. 26, no. 11, pp. 2553–2566, Nov. 2018, doi: 10.1016/J.YMTHE.2018.08.013.
4. A. Pavesi et al., “A 3D microfluidic model for preclinical evaluation of TCR-engineered T cells against solid tumors,” JCI Insight, vol. 2, no. 12, Jun. 2017, doi: 10.1172/JCI.INSIGHT.89762.