Overview of Tumor Organoids

Malignant tumors have become a major challenge in the field of global public health. How to continuously deepen the understanding of the occurrence and development of malignant tumors and continuously optimize the clinical diagnosis and treatment model of tumors is an important issue that needs to be urgently addressed in oncology research. Both basic and clinical scientific research in oncology requires the selection of appropriate research models. However, the common tumor research models currently have many shortcomings. For example, tumor cell line models are difficult to reproduce the pathophysiological characteristics and internal heterogeneity of parental tumors in vitro, and animal models have problems such as low flux, long cycle, high cost, and species differences. In recent years, organoid models have shown great application potential in tumor research. Compared with tumor cell lines and animal models, tumor organoid models are derived from patients and can better retain the characteristics of parental tumors under in vitro culture conditions. They also have a relatively short culture cycle, high flux, and controllable costs. They are potential ideal models for conducting basic and clinical scientific research on tumors. This article comprehensively introduces the development history of tumor organoids, aiming to summarize and analyze the current status, existing problems, and future development directions of research, and provide a reference for the research of tumor organoids.

Development of Tumor Organoid Research

Organoids are special 3D tissues that reproduce the structure of tissues and organs in vivo through in vitro three-dimensional (3D) culture and self-assembly of adult stem cells or pluripotent stem cells in original tissue samples. The history of organoid research can be traced back to the early 20th century. In 1907, American scientists Wilson and others first discovered that sponge cells mechanically separated in vitro could spontaneously assemble and form new sponge organisms with certain physiological functions. In the following decades, this dissociation-recombination phenomenon was reproduced in some special biological tissues such as amphibian pronephros, chicken embryonic cells, and human keratinocytes. However, the research during this period did not clarify what kind of cells could undergo this spontaneous recombination. It was not until 1981 that researchers first revealed that stem cells have the ability to spontaneously recombine to form organ structures in vitro. In 1987, the in vitro 3D culture medium was significantly optimized. Researchers extracted the extracellular matrix of mouse Engelbreth-Holm-Swarm (EHS) sarcoma to make matrix glue, which later became an important component of in vitro 3D culture medium. In 2009, a major breakthrough was made in organoid research. Sato and others used mouse intestinal stem cells expressing LGR5 to culture microtissues with crypt-villus structures for the first time, and maintained genome stability for more than 3 months, marking the official launch of organoids. In 2011, the team further successfully constructed a colorectal cancer organoid model using tumor tissue from colorectal cancer patients, expanding the organoid model to the field of oncology research for the first time. Currently, research on patient-derived organoid (PDO) models is in full swing. Research results based on organoid models continue to emerge in the field of oncology. New technologies such as microfluidics, cell co-culture and vascularization are combined with organoid research, giving rise to new tools such as organ-on-a-Chip (OoC), and the status of organoid models in oncology research has become increasingly prominent.

New Applications of Tumor Organoids

Disease modeling and mechanism research Organoid models have unique advantages in oncology research, which can make up for the shortcomings of existing models and provide new tools for basic tumor research. First, tumor organoids are derived from human tumor tissues, with short culture cycles, high throughput, gene editing, and the ability to reproduce the internal subclonal characteristics of the original tumor. Therefore, they can be used as independent verification models outside of cell lines and mouse models to consolidate the conclusions of basic research. When studying the promotion of gastric cancer invasion and metastasis by the NALCN gene, Rahrmann et al. not only used traditional gastric cancer cell lines and mouse transplant models, but also conducted NALCN knockdown experiments in gastric cancer organoids, demonstrating the function of this gene from multiple dimensions. Mao et al. used in vitro models to study the sensitivity and specific mechanisms of colorectal cancer to drugs such as JAK inhibitors and mitogen-activated protein kinase kinase (MEK) inhibitors, and then further expanded colorectal cancer organoids in vitro and transplanted them into immunodeficient animals to establish organoid-derived mouse transplant models to verify the conclusions obtained from the in vitro model. Compared with the transplanted tumor model constructed by directly transplanting patient tumor tissue into the mouse subcutaneously, this type of mouse model has a higher success rate and faster tumor growth, which can greatly shorten the experimental time. Secondly, organoids can be used to model special tumors that lack basic research models. Many tumors such as pancreatic intraductal papillary mucinous tumors, gastric-esophageal junction tumors, neuroendocrine tumors, and urothelial carcinomas cannot conduct in-depth mechanism exploration due to the lack of satisfactory research models. However, with the establishment of tumor organoid models, researchers have made great progress in their understanding of these diseases.

Research and Development of Innovative Cancer Drugs

The research and development of innovative cancer drugs requires a series of processes such as drug target and drug candidate selection, preclinical safety and effectiveness evaluation, and clinical trials. Traditional preclinical research models are mainly cell and animal models, which suffer from problems such as slow speed, high cost and low efficiency. In recent years, organoid models have gradually emerged in the field of drug research and development, showing good application prospects. First of all, in terms of evaluating the effectiveness of therapeutic drugs, tumor organoids can better simulate the structure and drug sensitivity of tumors in the body, provide a closer to real environment for drug testing, significantly shorten the drug trial cycle, reduce costs, and improve conversion efficiency. Studies have reported that a colorectal cancer organoid sample library was used to perform high-throughput functional screening of more than 500 bispecific antibodies targeting WNT and RTK signaling pathways, and MCLA-158 (a bispecific LGR5 and EGFR Antibodies) can specifically degrade EGFR on the surface of Lgr5+ cancer stem cells to kill tumors, while having little toxicity to normal colon organoids. The following year, MCLA-158 obtained new drug clinical trial approval from the US Food and Drug Administration based solely on organoid experimental data, and was approved to conduct clinical trials in patients with advanced colorectal cancer, gastric cancer, head and neck squamous cell carcinoma and other solid tumors (NCT03526835). In 2023, a study announced the efficacy of MCLA-158 in advanced head and neck squamous cell carcinoma. Among 43 patients evaluated for treatment, the objective response rate reached 37.2% and the disease control rate was 72.1%. Based on these clinical data, The FDA granted it fast track qualification in the same year. This decision is expected to accelerate the subsequent phase II~III clinical trial process and drug marketing approval. The traditional drug development process often takes decades, with preclinical research taking an average of five and a half years and requiring a large number of cell and animal experiments. However, MCLA-158 only took one year from screening to entering clinical trials using organoids. Model-based preclinical research has significantly shortened the development time of new drugs and reduced research and development costs. In addition, organoids can be used for pharmacokinetic studies.

Individualized Treatment

Currently, genetic testing and immunohistochemical staining of special proteins are mainly used to guide the precision treatment of tumors. However, these methods have great limitations. Some patients cannot detect clear drug targets. Even if drug targets are detected in some patients, the complexity of tumor biological characteristics may cause clinical drug ineffectiveness. Under the current model, only about 10% of patients can truly benefit from precision treatment. Drug sensitivity testing based on tumor organoid models is a result-oriented test that is not affected by gene mutations and changes in gene expression profiles. It can provide direct evidence of drug sensitivity and has great potential in guiding the personalized treatment of tumors.