Drug discovery is a slow and expensive process, taking an average of approximately 10 years to bring a drug to market. The limited predictive ability of animal models and cell cultures in preclinical studies has led to drug failures in clinical trials.
Organ-on-chip (OoC) are microfluidic in vitro culture systems that mimic the physiological properties of human organs, providing insight into the function or pathophysiology of different organs.
In the pharmaceutical industry, this technique has the potential to replace animal testing in preclinical trials and identify drug candidates with a higher success rate, reducing the time for drug availability and improving patient safety.
Image Credit: Kittyfly/Shutterstock.com
Foundations of Organ-on-a-Chip Technology
Principle
OoC technology combines microfluidics and cell culture to replicate the functions of a tissue or organ. The chips are small and flexible, with upper and lower channels seeded with organ-specific cells.
A porous membrane coated with a tissue-specific extracellular matrix acts as an interface for cell-cell communication and aids tissue maturation.
The continuous perfusion of cells facilitates dynamic interactions with neighboring or distant cells and different concentrations of bioactive molecules. The chips replicate the cellular microenvironment and interorgan interactions by controlling the inlets and outlets and monitoring using biosensors.1
OoCs Design
OoCs can be single, double, or multichannel devices. Each OoC has a different function, but the main components remain unchanged. OoC comprises two channels/compartments: one with endothelial cells and the other with the organ's cells to be investigated.
The compartments are separated using a porous membrane to enable cell-cell communication. The culture medium or drugs are introduced via the inlet and removed via the outlet.2
Fabrication Materials
The material for producing OoC microdevices should demonstrate adequate biocompatibility and a nontoxic environment that supports cell migration without developing an inflammatory response.
The choice of material depends on the microfabrication strategy, desired functionality, and developmental stage of the product.
The common materials used are glass, poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), cyclic olefin copolymer (COC), or polycarbonate (PC). PDMS is the predominantly used material due to its elasticity, biocompatibility, gas permeability, and optical transparency.2
Fabrication Methods and Design Considerations
Several fabrication methods are used, such as soft lithography, hot embossing, injection molding, and 3D printing. The flow rate is controlled using pressure or electroosmosis, as it affects shear, concentration gradients, and polarity. Microfiltration can address clogging.
Bubbles can be removed by controlling the pressure, temperature, roughness, or bubble traps. Sensors are either integrated or externally mounted to monitor the cell environment and behavior, mechanical and electrical stimulations, and glucose, lactate, and hydrogen peroxide concentrations.
A natural medium (plasma, blood, or organ fragments) or an artificial medium (blood substitutes) can be used. The nutrients are continuously delivered to the cells under investigation via the porous membrane.
The application of mechanical forces can mimic breathing or peristalsis. OoCs must be sterilized using ethylene dioxide or gamma irradiation to avoid microbial contamination.2
Applications in Drug Development
Several drugs fail to exhibit adverse effects in animal models in the preclinical stage, whereas they demonstrate impairments in the liver, heart, and kidney in patients during clinical trials.
OoCs have proved to be a potential replacement for animal testing as a preclinical model owing to their ability to mimic human function at the organ level. Below are some examples demonstrating the capability of OoCs in clinical mimicry.
A lung alveolus and airway model supporting the growth of human non-small-cell lung adenocarcinoma cells successfully emulated the resistance to third-generation tyrosine kinase inhibitors and the increased expression and phosphorylation of c-Met similar to those observed in patients.
Decreased IL-8 levels following treatment in the breathing lung alveolus chip were in accordance with the clinical trial results.3
A heart chip containing human iPS-cell-derived cardiomyocytes successfully mimicked the differences in the safety profiles of terfenadine and its nontoxic metabolite fexofenadine observed in patients.4
A two-compartment kidney chip comprising primary proximal tubular epithelium expressing high P-glycoprotein efflux transporter activity mimicked the transporter-specific cisplatin toxicity observed in patients, which could not be detected in static 2D cultures or animal models.5
A blood vessel chip mimicked the clinical thrombotic toxicity of the monoclonal antibody drug Hu5c8, which caused serious complications and had to be withdrawn from clinical trials.
This was not observed in preclinical animal testing. A related antibody with lower thrombotic risk was also validated using this model.6
The consistency of OoC data with the corresponding clinical data underscores the high functionality of these chips, which may help optimize the drug regimen for phase I clinical trials.
Advantages Over Traditional Methods
- These chips are cost-effective; different drug concentrations can be tested to determine the drug’s efficiency, remarkably accelerating scientific research. Initial tests can be performed several times during the new drug development process without financial burden.
- No ethical concerns exist compared with animal testing and the dependency on animal models is reduced.
- OoCs can reproduce the cellular microenvironment, such as temperature, oxygen levels, or pH, and processes, such as breathing and peristalsis, better than cells grown on a Petri dish owing to its three-dimensional characteristics. Multiple cell types can be incorporated to demonstrate in vivo complexity.
- The small size allows the integration of multiple OoCs on a single chip, saving space, materials, and cost.7,8
Case Studies and Success Stories
Pharmaceutical companies and academia have widely employed OoC devices for various applications, including disease mechanisms and the efficacy and toxicity of drug candidates before they enter clinical trials.
This ensures quality drugs enter the market, reduces the cost, expedites the drug development process, and improves patient safety.
Blood–Brain Barrier (BBB)-on-Chip
BBB prevents the drugs and antibodies from passively diffusing into the brain. Thus, receptor-mediated transcytosis of antibodies was developed wherein a therapeutic antibody will bind to the transferrin receptor located on the apical side of the brain endothelial cells, following which the antibody is transcytosed and released on the basolateral side (brain).9
An in vitro BBB-on-a-chip was developed by MIMETAS and perfused with the target antibody designed to cross the BBB.
A control antibody that fails to bind human cells was also perfused. Compared with the control antibody, the target antibody demonstrated a two-fold increase in passage rate. This technology can be used to improve neurodegenerative disease treatment.10
Liver-on-Chip for Toxicology Assessment
Drug-induced liver injury (DILI) remains a significant patient safety concern, often leading to drug withdrawals from the market. Researchers validated the Emulate human liver chip against guidelines established by IQ MPS, an affiliate of the International Consortium for Innovation and Quality in Pharmaceutical Development.
The liver chip accurately detected 87% of the tested drugs known to cause DILI in patients, although these drugs had passed animal testing evaluations.
The Chip showed 100% specificity and did not falsely identify any drug as toxic, showing potential to be used in toxicology screening workflows.9
Find out More About Drug Discovery, Manufacturing and Development
Challenges and Limitations and Future Directions
Limitations
- Due to the small size of the microfluidic systems, the surface effect dominates the volume effect, causing poor analysis quality with the product of interest getting adsorbed on the inner linings.
- The laminar flow of fluids in the chips prevents the mixing of fluids.
- Some experiments require specialized equipment to obtain reliable outcomes. For example, bulky equipment is required for processing pluripotent-induced stem cells (iPSCs).8
Challenges
- Replicating the intricate architecture of human tissues and organs in a miniaturized in vitro format and determining their appropriate arrangement to ensure the interconnected systems accurately emulate human tissue and organ interactions.
- Scaling up the manufacturing for large-scale drug screening or high-throughput applications in a reproducible manner is difficult.
- Sourcing and reproducibility of patient-specific iPSCs can be logistically difficult.
- Standardized protocols and quality control measures must be developed to maintain repeatability and consistency across OoC platforms. This will aid in regulatory agencies' acceptance of the technology.
- It is not user-friendly and requires a specialist to operate. Introducing automated fluid-handling systems will resolve this problem.11,12
To overcome these challenges, OoCs should be available as cell culture plates. For high-throughput outcomes, injection molding is a good and cost-effective method for fabrication. OoC technology should be compatible with current analytical and imaging instruments for data measurement.
Emerging Trends
Personalized Medicine
The effect of a drug is not the same when multiple patients receive the same treatment, as seen with capecitabine, a chemotherapeutic used for colorectal cancer, whose effects are highly variable, leading to treatment discontinuation. OoCs with a patient’s iPSC can overcome this problem.
The drug can be directly tested on the cells, and those demonstrating less toxicity and more effectiveness can be selected. The treatment is adapted according to the patient’s characteristics, revolutionizing precision medicine.
Once the drug has been tested on the chip, clinical trials can be conducted on these patients, which will be cost-effective, save time, and increase the probability of success of the trials.13
Multiorgan Chips
Multi-organ chips are being increasingly developed to integrate multiple organ units within a single platform. Gut–liver–kidney and bone marrow–liver–kidney multi-organ chip systems were developed to predict the PK parameters of nicotine (aids in smoking cessation) and cisplatin (anticancer drug), respectively.
The maximum nicotine concentration in the arteriovenous reservoir and the time to reach the maximum level were consistent with clinical data.
When cisplatin was administered at a dose of 160 μM for 24 h, no hepatotoxicity was observed in the liver chip; in contrast, nephrotoxicity and myeloid toxicity were observed in the kidney and bone marrow chips, respectively, consistent with the PDs of cisplatin in vivo.14,15
Efforts are now directed towards developing a body-on-a-chip that emulates the physiology of the entire human body using a unified platform for drug PK/PD assessments.
Considering the complexity of the human body, several technical challenges will need to be addressed before it can be included in preclinical testing.
Conclusion
Many drugs clear the preclinical tests in animal models but prove toxic to humans in clinical trials making the drug development process lengthy and costly. OoCs can simulate human physiology and pathology at the organ level.
This is useful for identifying drug candidates with higher success rates in clinical trials than traditional preclinical models, avoiding ethical concerns, expediting the drug development process, and providing safer medicine to patients.
Multiorgan on-chip technology helps determine drug side effects on various organs and drug-drug interactions. Continuing research and developmental efforts are overcoming hurdles such as regulatory approval, standardization, scalability, and reproducibility.
Increased collaboration among pharmaceutical companies, research institutions, and biotechnology firms will accelerate OoC development and provide a better understanding of drug responses.
References
- Wells J. (2023). What are organ-chips? Emulate. Available at: https://emulatebio.com/an-introduction-to-organ-on-a-chip-technology/
- Tajeddin A, Mustafaoglu N. Design and fabrication of organ-on-chips: promises and challenges. Micromachines. 2021 Nov 25;12(12):1443. Accessed on [5 July 2024]. https://www.mdpi.com/2072-666X/12/12/1443
- Hassell BA, Goyal G, Lee E, Sontheimer-Phelps A, Levy O, Chen CS, Ingber DE. Human organ chip models recapitulate orthotopic lung cancer growth, therapeutic responses, and tumor dormancy in vitro. Cell reports. 2017 Oct 10;21(2):508-16. https://pubmed.ncbi.nlm.nih.gov/29020635/
- Kujala VJ, Pasqualini FS, Goss JA, Nawroth JC, Parker KK. Laminar ventricular myocardium on a microelectrode array-based chip. Journal of Materials Chemistry B. 2016;4(20):3534-43. https://pubs.rsc.org/en/content/articlelanding/2016/tb/c6tb00324a
- Jang KJ, Mehr AP, Hamilton GA, McPartlin LA, Chung S, Suh KY, Ingber DE. Human kidney proximal tubule-on-a-chip for drug transport and nephrotoxicity assessment. Integrative Biology. 2013 Sep 19;5(9):1119-29. https://pubmed.ncbi.nlm.nih.gov/23644926/
- Barrile R, van der Meer AD, Park H, Fraser JP, Simic D, Teng F, Conegliano D, Nguyen J, Jain A, Zhou M, Karalis K. Organ‐on‐chip recapitulates thrombosis induced by an anti‐CD154 monoclonal antibody: translational potential of advanced microengineered systems. Clinical pharmacology & therapeutics. 2018 Dec;104(6):1240-8. https://pubmed.ncbi.nlm.nih.gov/29484632/
- Zhu J. Application of organ-on-chip in drug discovery. Journal of Biosciences and Medicines. 2020 Mar 2;8(3):119-34. https://www.scirp.org/journal/paperinformation?paperid=98810
- Mauriac H, Pannetier C, Casquillas GV. (2020). Organs on chip review. Elveflow [Online]. Available at: https://www.elveflow.com/microfluidic-reviews/organs-on-chip-3d-cell-culture/organs-chip-review/ [Accessed on 5 July 2024].
- Case study: Antibody transcytosis across the blood-brain barrier (Bbb). Mimetas. [Online]. Available at: https://www.mimetas.com/en/case-study-antibody-transcytosis-across-the-blood-brain-barrier-bbb-/ [Accessed on 5 July 2024].
- Organ-Chips for Toxicology Assessment. [Online]. Emulate. Toxicology. Available at: https://emulatebio.com/toxicology/ [Accessed on 5 July 2024].
- Revolutionizing biomedical research: the promise of organ-on-a-chip technology. [Online]. Available at: https://www.linkedin.com/pulse/revolutionizing-biomedical-research-promise-rajiv-ramrakhyani [Accessed on 5 July 2024].
- Roy M. Organ-on-chip technology: The next wave in the healthcare market. [Online]. Available at: https://www.hcltech.com/trends-and-insights/organ-chip-technology-next-wave-healthcare-market. [Accessed on 5 July 2024].
- Koyilot MC, Natarajan P, Hunt CR, Sivarajkumar S, Roy R, Joglekar S, Pandita S, Tong CW, Marakkar S, Subramanian L, Yadav SS. Breakthroughs and applications of organ-on-a-chip technology. Cells. 2022 Jun 2;11(11):1828. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9180073/
- Herland A, Maoz BM, Das D, Somayaji MR, Prantil-Baun R, Novak R, Cronce M, Huffstater T, Jeanty SS, Ingram M, Chalkiadaki A. Quantitative prediction of human pharmacokinetic responses to drugs via fluidically coupled vascularized organ chips. Nature biomedical engineering. 2020 Apr;4(4):421-36. https://pubmed.ncbi.nlm.nih.gov/31988459/
- Ingber DE. Human organs-on-chips for disease modelling, drug development and personalized medicine. Nature Reviews Genetics. 2022 Aug;23(8):467-91. https://www.nature.com/articles/s41576-022-00466-9
Further Reading