Organoid Technology: Disease Modelling, Drug Discovery, and Personalized Medicine

Organoid technology has been used to model diseases across different organ systems, drug screening, and regenerative medicine. Organoid technology better mimics human physiology and can provide a better alternative to in vivo animal models. Recent advances in organoid technology, including developing the novel organoid platform, engineering complex organoids, and introducing pathological aspects, have provided significant progress toward producing miniaturized tissue or organs on a dish. Novel technologies like high-resolution 3D imaging, organ on a chip, 3D printing, gene manipulation, nanotechnology advances, and single-cell sequencing have led to a massive thrust in the organoid technology that can provide a unique insight into the behavior of stem cells, cater to preclinical research and theranostics (therapy plus diagnostics).

The last three decades have witnessed revolutionary growth in the fields of biomedical science and pioneering the same in regenerative medicine and disease modeling. Historically, biological research has been performed using 2-dimensional animal cell culture, but now we are switching to more intricate 3-dimensional models for better replicability of experimental results. Organoids are stem cell-derived 3D cell cultures that are the cornerstone of this new development. They retain the significant features of biological organs and have opened up new, previously not-thought-of avenues to steer research in personalized healthcare and disease modeling. The current chapter encapsulates how organoids came into the picture, addresses the current research occurring worldwide, and discusses futuristic aspects and applications. The significance of organoids in disease modeling is discussed in detail, and the following aspects, such as disease modeling in congenital conditions, cancer, infectious diseases, gene editing, and futuristic microfluidics, were elucidated. This chapter also covers the role of organoids in drug discovery. Drug discovery is a very time and money-intensive process, and many attempts have been made over the years to bring about change in the same. It has been noted that the development of many new drugs is being hindered due to the complexity of the human genome. This point has been elaborately discussed in this present chapter, along with the potential of organoids as a solution in highthroughput drug screening and personalized treatment. The chapter concludes with a look at how the COVID-19 pandemic has underpinned the use of organoids in drug research and disease modeling, and finally, it provides a summary of future research directions. 

The intestinal organoid system is a unique ex-vivo representation of the complex and dynamic mammalian intestinal epithelium. Intestinal organoids are threedimensional, crypt-villus structures with a central lumen that can be sourced from adult intestinal stem cells, embryonic stem cells as well as induced pluripotent stem cells. They serve as a bona fide model for not only understanding intestinal biology and development but also for disease modeling, regenerative therapeutics, and drug discovery. Organoids help bridge the gap in existing model systems by incorporating complex, spatial, and biological parameters such as cell-cell interactions, cell-matrix interactions, gut-microbe interactions, and other components of intestinal in-vivo physiology and pathology. In this chapter, we discuss the basic strategies to generate intestinal organoids and how different bioengineering approaches can be used to effectively model both genetic and infectious intestinal diseases to enhance their utility in research and therapeutics.

Organoids are complex three-dimensional microtissues formed by the selforganization of stem cells and aimed to mimic the structural and functional characteristics of human tissues. Bone comprises multiple cells with a mechanically rigid extracellular matrix (ECM). The diversity of a bone in terms of structure and complexity demands an ideal bone model with limited control of physico-chemical parameters. Potential applications of bone organoids can be seen in bone regeneration, and regulation mechanism studies and to address various bone-related disorders and defects. Approaches to creating bone organoids may include using mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), osteoblasts, and osteoclasts in addition to endothelial cells for the vasculature generation. Moreover, in bone organoids, ECM of biological origin materials that display close resemblance with the native bone ECM are preferred or may be generated using scaffold-free methods. The mechanical load should be the primary parameter that should be considered in the model. Since bone is considered hypoxic, organoid-based bone models should include an O2 regulation mechanism to achieve a physiologic hypoxic environment. Advanced cell isolation, tissue culture, and cell differentiation techniques, along with microfluidics and tissue engineering strategies, might lead to the production of physiologically relevant bone organoids. This chapter outlines prerequisites for bone organoid development and the potential applications of bone organoid-based models in various biomedical research domains. Additionally, their limitations and future perspectives are also explored.

The development of state-of-the-art, In vitro three-dimensional organoid culture methodologies, represents a quantum leap in stem cell technology and tissue engineering. In contrast to traditional two-dimensional cell culture and rodent models, organoids generated from patient-derived cells can dramatically increase the precision and relevance of In vitro approaches to model human development and disease. Currently, the most well-established organoid systems are those for the intestine, brain, bone, kidney, and eye. Surprisingly, research using cardiac organoids, or “cardioids, is still in a nascent phase, lagging significantly behind these other, more mature, tissuespecific organoid platforms. Consequently, there is an ongoing need to develop more robust and reproducible protocols capable of yielding self-organizing cardiac organoids that assemble following valid cardiogenic principles, recapitulating the microanatomy and cellular hierarchy observed during In vivo cardiac development. Cardiovascular disease is currently the primary cause of death in developed countries, and its prevalence is growing worldwide. Improved cardiac organoid technologies have the potential to facilitate and enhance the application of the new wave of personalized medicine aimed at addressing cardiovascular disease. This book chapter will discuss the development of cardiac organoid research, its present state, and future challenges in detail. 

To date, no known drug therapy is available for COVID-19. Further, the complicated vaccination processes like limited infrastructure, insufficient know-how, and regulatory restrictions on vaccines caused this pandemic episode more badly. Due to the lack of ready-to-use vaccination, millions of people have been severely infected by SARS-CoV-2. Additionally, the increasing contagion risk of the SARS-CoV-2 variants makes drug repurposing studies more critical. Conventionally, antiviral drug repurposing has been conducted on two-dimensional (2D) cell culture systems or in vivo-based experimental setups. Recently, In vitro three-dimensional (3D) cell culture techniques have proven more coherent in mimicking host-pathogen interactions and exploring or repurposing drugs than other 2D cell culture methods. 3D culture techniques like organoids, bioprinting, and microfluidics/organ-on-a-chip have just been started to mimic the natural microenvironment respiratory system infected with SARS-CoV-2. These techniques avoid the need for animals in agreement with the 3R principles (Replacement, Reduction, and Refinement) to enhance animal welfare. Herein, SARS-CoV-2-host interaction and 3D cell culture techniques have been proposed for drug screening and repurposing models through representative examples. This study will frame tissue engineering strategies for studying SARS-CoV-2 infection and enlightening host-virus interactions.

Cancer remains the leading cause of mortality in the world, despite several cutting-edge technologies and established therapeutic regimens for cancer treatment. Therefore, the key to developing accurate and effective therapeutics is having a comprehensive knowledge of these complex molecular events. Patient-derived organoids (PDOs) represent a perfect model for studying cancer drug resistance and therapy. These cancer organoid models are cheaper alternatives to xenograft models and traditional two-dimensional (2D) cell culture model systems. All cancer organoid models are developed using iPSC-derived spheroids and tumor cells from different sources, which are then processed on a matrigel scaffold to get cancer organoids. The major advantage of these model systems is that they can recapitulate many functional and genetic characteristics of the same tumor tissues “in vitro”. These cancer organoids can be passaged, frozen, and preserved for further high-throughput screening analysis. PDOs are powerful tools for evaluating mutational profiles and testing cancer drugs for personalized therapy. Cancer organoids can also be used to study tumor microenvironment cell types by co-culturing the required cell types involved in the process of transformation, which allows us to study tumor microenvironment and tissue-tissue interactions in the tumor development and metastasis process. This leads to more accurate predictions of the process of tumor development and evaluation of responses of cancer drug-resistance in a particular patient to develop personalized therapies for cancer. However, several limitations to these cancer organoid models must be addressed and resolved to get a perfect system for cancer drug evaluation. Several scientists are working on it by developing standardized protocols and reagents to generate individual tissue organoids. It is hoped that major developments in technologies, such as organoids-on-chips, 3D bio-printing, and advanced imaging techniques, will improve the handling of these organoids more precisely. Further CRISPR-Cas9-based gene editing technology allows us to bioengineer normal organoids by introducing any combination of cancer gene alterations to derive cancer organoids. In this review, we focused on the development and improvement of various normal and cancer organoids for targeted tissues such as the lung, breast, colon, liver, and kidney and their use as model systems for cancer drug discovery and personalized therapy. We have also highlighted some of the uses of the latest technologies, such as microfluidics chips and 3D bioprinting, for deriving better cancer organoids-based in vitro models for future research on cancer therapeutics.

Lung epithelium involves adult stem or progenitor cells that possess selfrenewal, differentiation, and self-organizing potential and form the concoction of tissue-specific organoids. Researchers have used genetically modified lung organoids to study different aspects of lung tumorigenesis. Another approach is the patientderived lung organoid to create a more representative lung cancer model with the tumor microenvironment, extracellular matrix, and immune component. The In vitro patientderived organoids histologically and functionally mimic the related parent tumors. Lung cancer organoids and organoid-co-cultures can be used to dissect difficult-t- -answer questions, especially regarding human lung cancer. Lung cancer organoids are used not only for understanding tumor biology but also to undertake biomarker studies, and drug screening, evaluate immunotherapeutics, and target tumor microenvironment, and personalized medicine. Lung organoids can also be used to create organoid biobanks for future gene-specific pre-clinical trials and evaluation. This chapter will present an overview of the therapeutic areas in which lung cancer organoids are transforming therapeutic discovery and development, followed by a discussion of future prospects.

Additive manufacturing (AM) is a rapid and efficient process of creating complex geometries or structures using a digital three-dimensional (3D) printing process. AM has many diverse applications in aerospace, automotive, defense, manufacturing industries, education, and research, most notably in the healthcare and bio-medical industries. 3D bioprinting allows us to create tissue-specific architecture with precise geometries limited to conventional fabrication methods. In this chapter, we have discussed the generalized process of 3D printing of objects in various organoid cultures, focusing on the advantages and limitations of AM technology. Further, we have discussed the major challenges and future direction in the context of organoid bioprinting.

Despite several limitations, two-dimensional cell culture has been widely used in drug and drug-related compound selection and screening studies. A more recent approach of using three-dimensional (3D) organoid culture enables researchers with a more robust and accurate model for drug screening. Numerous studies have reported the successful use of stem cells, including induced pluripotent stem cells (iPSCs) and adult stem cells, for organoid generation to predict therapy response in various disease conditions, including cancer. The development of high-throughput drug screening and organoids-on-a-chip technology can advance the use of patient-derived organoids in clinical practice and facilitate therapeutic decision-making. Although organoids are in complaisant with high-throughput screenings, extensive manipulation studies are required by current methods.