Month: November 2023

The current paradigm in preclinical testing for developing cancer therapeutics is failing. Oncology drug candidates are currently the least likely type of therapeutic to succeed in clinical trials, with only 5.1% of Phase I candidates going on to receive FDA approval. A major reason for this high attrition rate is the preclinical in vitro and in vivo models that cancer researchers rely on. While conventional in vitro cancer models can mimic some parts of human physiology, they often lack critical factors such as cellular heterogeneity and a dynamic, native microenvironment¹. As such, scientists continue to rely on animal models; however, animals often lack human relevance, allowing ineffective and toxic drugs to enter clinical trials. To create more successful drug development programs, scientists need models that provide a more comprehensive and human-relevant view of cancer progression. 

The importance of understanding the tumor microenvironment 

There is growing evidence that the tumor microenvironment (TME) is a crucial modulator of cancer growth, migration, angiogenesis, immunosurveillance evasion, and therapy resistance². The TME is composed of extracellular matrix (ECM) and various non-malignant cell types, including endothelial, mesenchymal (e.g., fibroblasts and adipocytes) and immune cells (e.g., lymphocytes, monocytes, and neutrophils), all of which interact with tumor cells via secretion of molecules such as growth factors, cytokines, extracellular vesicles, and miRNAs (Figure 1). The ECM in particular has a significant effect on the behavior of cells, as it provides structural and biochemical support. During cancer progression, the stiffness of the ECM influences cells’ proliferation, survival, migration, and differentiation. Thus, understanding the TME is key to understanding overall cancer progression and developing effective therapies.  

The Need for Better Models 

Animal models have traditionally been considered the gold standard in disease research and drug development, despite the high failure rate of drugs transitioning to the clinic. To improve the translatability of animal models for cancer research, human tumors are often grafted into animals. The xenograft mouse model, for example, is created when the tissue of interest is implanted under the skin of an immunocompromised mouse^3,4. The orthotopic mouse model differs in that the human tumor is grafted onto the corresponding organ of interest in the mouse. While these models are more difficult to create, they are more physiologically relevant because the tumors are growing in an organ-specific TME⁴. Despite using human tumors, however, xenograft and orthotopic mouse models still have limited human relevance, as the immune components and TME are animal-based and do not recapitulate how a tumor progresses in the human body.  

While researchers can create cancer models entirely from human cell sources, they continue to face challenges in fully recapitulating human biological function in a dish. 2D in vitro models are simple and cost-effective models to incorporate into drug screening assays, but their simplicity results in low physiological relevance. Spheroids offer improved 3D cytoarchitecture, but often have issues in uniformity and reproducibility, lack standardized assessments of growth and drug efficacy, and are not high throughput for drug screening^5,6.  

Organoids are a powerful alternative to 2D culture that preserves many of the structural and functional traits of their in vivo counterparts, such as a hypoxic microenvironment, cell heterogeneity, ECM interactions, and more in vivo-relevant gene expression patterns^7,8. Tumor organoids can either be derived from patient tissue or engineered using induced pluripotent stem cells (iPSCs) and special culture conditions⁹. Those generated from iPSCs and adult stem cells encompass important tissue features such as architecture, differentiated cell types, and tissue function. Taken together, organoids are comparable to certain in vivo models such as traditional genetically engineered mouse models, cell lines, and patient-derived xenografts (PDX)⁸. However, organoids lack an organ-specific environment that includes immune components, blood vessels, and different stromal cells. Finally, growth stimulators and inhibitors used in the growth of organoids can affect drug sensitivity, gene expression, and cell signaling pathways³.  

A New Way Forward: Improving 3D Cancer Modeling with Organ-Chips 

Organ-on-a-Chip technology has been developed to address many of the challenges discussed above. These microfluidic devices emulate in vivo physiology and tissue microenvironments in an organ-specific context by enabling key cellular populations to be added to parallel microfluidic channels that are separated by a porous membrane (Figure 2). Additional features such as biomechanical forces, ECM, and immune cells provide a more human-relevant environment for cells to behave as they would in vivo^10–12.

Recent advances in the design of Organ-Chip consumables have improved the technology’s ability to recreate the tumor microenvironment. The Emulate Chip-A1 Accessible Chip allows researchers to model complex 3D tissues by incorporating gels up to 3 mm thick within the chip’s accessible culture chamber, integrating stroma into the epithelial layer, creating stratified epithelia, and applying organ-specific biomechanical forces (Figure 3). Further complexity and human relevance can be achieved with Chip-A1 by incorporating circulating immune cells such as PBMCs or CAR T cells.  

Chip-A1 has already enabled researchers to better understand how the surrounding microenvironment influences cancer progression. In their online article titled ‘Epithelial-Stromal Interactions in Barrett’s Esophagus Modeled in Human Organ Chips,” researchers from the Wyss Institute for Biologically Inspired Engineering at Harvard University used a prototype of Chip-A1 and found that it offered a new approach for studying epithelial-stromal interactions and the broader underlying mechanisms associated with esophageal cancer progression. The team also reported that this model could potentially serve as a tool for personalized drug-response assessments between different patients or genetic subpopulations.   

Conclusion 

Understanding how the tumor microenvironment contributes to cancer progression remains critical for developing more effective therapeutics. Organ-on-a-Chip technology is evolving to meet the in vitro modeling needs for research areas such as cancer, which require enhanced 3D models and more physiologically relevant compound dosing options. Preclinical models that enable researchers to model biology that is more complex, like the TME, will improve clinical translation, and Chip-A1 will give researchers this capability.  

References:

1. Smietana K, Siatkowski M, Møller M. Trends in clinical success rates. Nat Rev Drug Discov. 2016;15(6):379-380. 
2. Roma-Rodrigues C, Mendes R, Baptista P V., Fernandes AR. Targeting Tumor Microenvironment for Cancer Therapy. Int J Mol Sci 2019, Vol 20, Page 840. 2019;20(4):840. 
3. Sajjad H, Imtiaz S, Noor T, Siddiqui YH, Sajjad A, Zia M. Cancer models in preclinical research: A chronicle review of advancement in effective cancer research. Anim Model Exp Med. 2021;4(2):87-103. 
4. Li Z, Zheng W, Wang H, et al. Application of Animal Models in Cancer Research: Recent Progress and Future Prospects. Cancer Manag Res. 2021;13:2455. 
5. Pinto B, Henriques AC, Silva PMA, Bousbaa H. Three-Dimensional Spheroids as In Vitro Preclinical Models for Cancer Research. Pharmaceutics. 2020;12(12):1-38. 
6. Han SJ, Kwon S, Kim KS. Challenges of applying multicellular tumor spheroids in preclinical phase. Cancer Cell Int 2021 211. 2021;21(1):1-19. 
7. Salinas-Vera YM, Valdés J, Pérez-Navarro Y, et al. Three-Dimensional 3D Culture Models in Gynecological and Breast Cancer Research. Front Oncol. 2022;12:826113. 
8. Tuveson D, Clevers H. Cancer modeling meets human organoid technology. Science (80- ). 2019;364(6444):952-955. 
9. Fan H, Demirci U, Chen P. Emerging organoid models: Leaping forward in cancer research. J Hematol Oncol. 2019;12(1):1-10. 
10. Huh D, Matthews BD, Mammoto A, Montoya-Zavala M, Hsin HY, Ingber DE. Reconstituting Organ-Level Lung Functions on a Chip. Science (80- ). 2010;328(5986):1662-1668. 
11. Kasendra M, Luc R, Yin J, et al. Duodenum intestine-chip for preclinical drug assessment in a human relevant model. Elife. 2020;9. 
12. Kerns SJ, Belgur C, Petropolis D, et al. Human immunocompetent Organ-on-Chip platforms allow safety profiling of tumor-targeted T-cell bispecific antibodies. Elife. 2021;10. 

In the last decade, the realm of cancer therapy has taken groundbreaking strides, with Chimeric Antigen Receptor (CAR) T-cell therapy being one of the most promising new types of treatment. Having shown potential in treating blood cancers, CAR T-cell therapies are now setting their sights on a more complex adversary: solid tumors. This article explains what CAR T-cell therapy is, why solid tumors are such a challenging target, and how researchers can use advanced in vitro models to gain a more human-relevant understanding of CAR T efficacy. 

Understanding CAR T-Cell Therapy 

At its core, autologous CAR T-cell therapy is a form of immunotherapy where a patient’s own immune cells are modified so they recognize and kill cancer cells more effectively. This is done by adding a gene for a receptor, called a chimeric antigen receptor (CAR), which is designed to identify a specific tumor antigen. These modified cells are infused back into the patient, where they hunt down and kill the cancer cells. 

To date, researchers have successfully developed six FDA-approved CAR T-cell therapies for blood cancers, including leukemia, lymphoma, and multiple myeloma. This has proved invaluable for those in difficult-to-treat patient populations who exhibit little to no response to conventional therapies. 

However, these hematological malignancies only represent a small portion of all cancer cases and deaths—about 90% of cancers are solid tumors. Unfortunately, efforts to adapt CAR T-cell therapy for solid tumors have, to date, proved challenging. 

The Challenges of CAR T for Solid Tumors 

High-mortality, treatment-resistant solid tumors—including lung, breast, colorectal, and pancreatic cancer—are prime candidates for immunotherapy. However, the relative complexity of the heterogeneous solid tumor environment creates novel immunological obstacles that are not seen in blood cancers. 

The challenges are many, but a few highlights include: 

• Selective Trafficking and Migration: For blood cancers, immunotherapies are administered in the same location where the cancerous cells reside—the circulatory system. But for solid tumors, this is just the start of the journey. After being administered into the blood stream, the immune cells must selectively traffic out of the vasculature at the site of the tumor and then migrate to the tumor tissue. This is a challenging but critical journey, as the CAR T cells must reach the tumor in adequate numbers to effectively kill the cancerous cells, while avoid attacking healthy tissue.  
• Tumor antigen heterogeneity: In hematological tumors, antigen expression is relatively stable and uniform. But in sharp contrast, solid tumors can exhibit significant variability in antigen expression, both within a single tumor and between patients. This means that CAR T-cell therapy targeting a specific antigen might only attack certain parts of the tumor, leaving other parts untouched. It may also present the need for a more personalized or multi-antigen-targeted CAR T approach. 
• Tumor Microenvironment (TME): The area surrounding solid tumors is a unique cellular and chemical landscape, where inhibitory immune cells, immune checkpoints, and cytokines create an environment that is naturally hostile to immune cells, including CAR T-cell therapy. This means that once CAR T cells reach the tumor, they can quickly become suppressed or inactivated by immunosuppressive factors in the TME, hindering their ability to effectively destroy cancer cells. 

The Need for Human-Relevant Research Models 

While enthusiasm for solid tumor CAR T-cell therapy is strong, FDA-approved therapies have so far remained out of reach largely due to the challenges described above. A major limiting factor in overcoming these challenges has been a lack of preclinical research models that can adequately recreate the complex journey that CAR T cells must undertake in the human body to be effective. The models that researchers rely on for developing immunotherapy fall into two main categories: in vitro models and animal models. 

2D cell models often include tumor cell lines or patient-derived organoids (PDO) cultured in a static dish, where the CAR T cells are be administered directly to the tumor cells to evaluate killing efficacy. However, these models only allow researchers to evaluate the end of the CAR T cell journey and completely ignore the aspect of CAR T cell tracking and migration. 

Animal models remain the cornerstone of preclinical immunotherapy testing and have provided important contributions to hematological cancer CAR T-cell therapies that are on the market today. One example is patient-derived xenografts (PDX) models, in which human patient-derived tumors are implanted in immunodeficient mice. However, while animal models enable a more complete understanding of immunotherapy effect—allowing the CAR T cells to be intravenously administered and traffic to the tumor as they would in humans—they suffer from large species differences in responses and relatively poor insights into mechanism of action, limiting their successful translation to human clinical response. 

To truly understand the dynamics of cancer immunotherapy for solid tumors and develop effective treatments, researchers need more advanced models that can capture the complex intricacies of human biology and immune response. 

A Path Forward for Solid Tumor Immunotherapy Development 

For CAR T-cell therapy’s potential to be fully realized in solid tumors, it is vital that its therapeutic candidates’ behavior, efficacy, and challenges be studied in a context that is as close to human as possible. 

Fortunately, Organ-on-a-Chip technology can offer a path forward. Organ-Chips are microengineered devices that emulate the architecture, functionality, and physiological responses of vascularized human organs. They provide a dynamic platform that closely replicates human tissue-tissue interfaces, fluid flow, and mechanical forces, creating an environment where CAR T cells can be studied in a setting that more accurately mirrors the human body.  

Recently, this technology has been used to study the efficacy of CAR T-cell therapy in a model of non-small cell lung carcinoma (NSCLC). By co-culturing an NSCLC cell line and lung-specific vascular cells, researchers were able to model the journey that CAR T cells undergo in vivo. After administering the immunotherapy in the chip vasculature—just like its intravenous administration in the body—researchers saw how the CAR T cells attached to the vasculature, migrated to the tumor cell-containing channel, and subsequently exhibited antigen-dependent killing of cancer cells. Through imaging and effluent analysis, they could even quantify the amount of migration and killing as well as the levels of exhaustion markers for CAR T cells. A common treatment approach of administering a co-therapeutic alongside CAR T cells was even modeled on-chip, where it demonstrated improved CAR T-cell migration to the site of the solid tumor cell line. As this technology becomes more widespread, it may enable immunotherapy companies to accelerate the successful development of the first solid tumor CAR T-cell therapy. 

Conclusion 

Solid tumors continue to present numerous challenges for CAR T-cell therapy researchers, including efficient CAR T cell trafficking, migration, and infiltration, as well as overcoming the hostile tumor microenvironment. 

As researchers look to surmount these obstacles, advanced cell culture technologies like Organ-Chips may provide a more human-relevant and predictive assessment of CAR T cell efficacy, improving translation from pre-clinical testing to clinical success. With a number of CAR T-cell therapies in development around the world, the horizon seems promising, providing hope that researchers may be able to widen the reach of CAR T cells beyond blood cancer and into the more formidable realm of solid tumors.