Incidence of urological malignancies such as kidney, bladder, prostate and testicular cancers are gradually increasing worldwide (1). In recent decades, the number of studies on underlying mechanisms of development and progression of urological cancers, particularly kidney and prostate cancers, has increased tremendously. Knowledge of targeted therapies based on genetic alterations of kidney and prostate cancers has substantially progressed, paving the way for a paradigm shift of anti-cancer therapy. Despite accumulating evidences, major hurdle to develop a novel anti-cancer therapy is the translation of findings from bench works to bedside application. Apparently, a myriad of results obtained using pre-clinical cancer models could not translate into real-world clinical practice. In this regard, developing novel
Immortalized traditional two-dimensional (2D) cancer cell lines are tools widely used for human cancer research due to their low handling costs and ease of use (4, 5). However, cancer cell lines mostly do not reflect the parental tumor or their microenvironments because only a subset of tumors can grow in 2D on a culture dish. Additionally, cancer cell lines have unexpected genetic changes caused by passages during long-term culture. Therefore, they poorly recapitulate the heterogeneity of tumors from which they originated (6, 7).
As mentioned above, 2D culture systems cannot accurately recapitulate
PDTO culture can be accomplished in a short time (several weeks) with a high efficiency compared to iPSC-induced organoids (2, 14). With advantages of representing microenvironments and heterogeneities of parental tumors, PDTO systems might be employed in preclinical tumor models of human cancers. For example, PDTO systems can be used to study mechanisms of oncogenesis and anti-cancer drug resistance and to determine the origin of cancer cells. Furthermore, considering that cancer stem cells can contribute to resistance to chemotherapy and initiation of the process of cancer, PDTO can help us identify cancer stem cells initiating tumor that leads to resistance to anti-cancer drugs (10, 13). In this context, PDTO platform opens up the opportunity to apply personalized medicine. It can be used as a convenient model for high-throughput drug screening and for studying anti-cancer drug resistance.
Studies on urological cancers including kidney, prostate, and bladder tumors have elucidated the distinct genetic alterations (15). These genetic alterations are responsible for intra-tumor or inter-tumor heterogeneity. Studies on the underlying molecular mechanisms of urologic cancers have been accumulated with advanced sequencing technologies and experimental methodologies. Particularly, 3D organoid models such as PDTO systems highlight advanced cancer research. They can maintain the heterogeneity of parental cancer and simulate the real environment
Prostate cancer is one of the most common adenocarcinomas among men worldwide. Since most prostate cancers are androgen-driven adenocarcinomas, androgen deprivation therapy (ADT) is the treatment of choice for patients with advanced prostate cancer (20). Tumor volume of prostate cancer is dramatically reduced at an early period of ADT in patients with advanced prostate cancer. However, inhibiting the activation of androgen receptor is no longer sufficient to suppress tumor cell growth after several years of therapy due to the development of castration-resistant prostate cancer (CRPC) or neuroendocrine prostate cancer (NEPC) lacking AR-activity (21, 22). Resistance to AR inhibitors and NEPC can occur due to genomic rearrangements and copy number alterations known to contribute to inter-tumor or intra-tumor heterogeneity (23).
To recapitulate mini organ-like structures and to model organ development or disease for treatment, a suitable medium including growth factors or chemicals can be used to efficiently and successfully culture prostate cancer organoids. Organoid formation also requires the growth factors. Human tissues-derived organoids can be cultured with different factors including FGF10, FGF2, PGE2, nicotinamide, and SB202190 for the efficient organoid formation (26). The general organoid culture method uses a universal organoid medium based on DMEM/F12 medium containing epidermal growth factor (EGF), Noggin, and Wnt agonist R-spondin-1 (27). Additionally, culturing human prostate cancer organoids requires lymphoma kinase (ALK) 3/4/5 inhibitor A83-01, dihydrotestosterone (DHT), fibroblast growth factor-10 (FGF10), fibroblast growth factor-2 (FGF2), prostaglandin E2 (PGE2), nicotinamide, and p38 inhibitor SB202190, nacetylcysteine, B27 supplement, and Rho kinase inhibitor Y-27632 (26, 28). However, culturing murine-derived prostate cancer organoids does not need FGF10, FGF2, PGE2, nicotinamide, or SB202190. Basically, prostate cancer organoids can be stably formed within two weeks (26). Each growth factor has its own functions when culturing prostate cancer organoids. R-Spondin-1 and Noggin can promote the formation and expansion of organoids by activating Wnt signaling and bone morphogenetic protein (BMP) signaling pathways, respectively (28, 29). Addition of EGF can make prostate cancer organoids lose sensitivity to androgen resistance, meaning that elimination of EGF is needed for pharmacological studies on sensitivities of prostate cancer organoids to anti-androgen receptor drugs (30). FGF2, PGE2, nicotinamide, B27 supplement, and transforming growth factor beta (TGF-b) inhibitor A83-01 can promote the proliferation of prostate cancer organoid cells for a long-term culture (31). SB202190 can improve the stemness characteristic ability of prostate organoids (28). DHT can increase the growth rate of organoid cells with activation of androgen receptor and FGF10 signaling pathway (28). Rho kinase inhibitor Y-27632 can promote the proliferation of epithelial cells and inhibit the apoptosis of single stem cells (32). Y-27632 is added to stem cells when organoids are digested into single cells. N-acetylcysteine is an antioxidant scavenger of ROS (reactive oxygen species). It can help cells proliferate (33). These components are basically required for a long-term culture of prostate cancer organoids.
Identifying prostate cancer cells’ origin gives an important clue to discover the pathogenesis of prostate cancer initiation. The differentiating process of cells from human prostate cancer tissues can be simulated in prostate cancer organoids. It can help us identify cells of origin that triggers tumorigenesis. Normal/or cancer stem cells are differentiated into CK5+ basal cells and CK8 luminal cells in PDTOs (34). CK5+ basal cells and CK8+ luminal cells reside the outer layer and the inside of prostate organoids, respectively (28). Therefore, the origin of prostate cancer can be identified according to molecular subtypes during the formation of organoids. The luminal type prostate cancer featured by atypical gland lumens originates from luminal cells, whereas basal cells are able to transform in prostate cancer, leading to tumorigenesis (35). On the other hand, a study reported that both luminal and basal cells can be cells of origin to initiate prostate cancer by overexpressing Myc proto-oncogene and activated Akt, respectively (36). Supporting this result, luminal cells overexpressing Myc proto-oncogene and activated Akt show well-differentiated tumor, whereas basal cells-derived organoids are more aggressive, meaning that both cells are capable of initiating cancer, although their features are different (37). Additionally, castration-resistant cells expressing NKX3-1 reside in the luminal layer of ADT-treated prostate cancer. These luminal cancer stem cells (CD38-low luminal cells) can initiate prostate cancer and generate both luminal and basal cells in the organoids (38). Thus, treatment responses to anti-cancer drugs might greatly vary among different human prostate cancer organoid lines. As an example, Pappas
Kidney cancers have several histologic subtypes, including clear cell, papillary, chromophobe, and collecting duct subtypes. Renal cell carcinoma (RCC) accounts for approximately 90% of all kidney cancers (40). As previously mentioned, there are differences between cell culture or PDX modeling and cancer patients’ tissues depending on heterogeneous trait, tumor microenvironment, and genetic landscape (41, 42). Many scientists have contributed to the establishment of kidney cancer organoid culture. Interestingly, normal kidney cells show greater proliferation than tumor cells in 2D cells and organoid formation than other tissues (43, 44). As disadvantages of
Patient-derived prostate cancer organoids can be used as a platform to perceive precision medicine by performing drug screening using individual patient samples (51) and to study mechanisms underlying drug resistance. Importantly, the ability to identify drugs showing high clinical effectiveness prior to clinical trials could enhance the efficiency of translational research into clinical practice. Gao
Using cancer patient samples, advances in high-throughput sequencing technologies have enabled us to recapitulate molecular diversity, heterogeneity, and genetic landscape of cancer. However, due to the difficulty of accessing patient tissues multiple times for different experiments, organoid models can be important alternatives for genomic or transcriptomic research. Comparison cancer organoids with corresponding human tissues should be performed to faithfully reflect biological characteristics and genetic diversity in patient tissues. Single-cell sequencing is a more powerful method for assessing the quality of cancer organoids in comparison with patient’ tissues than conventional bulk sequencing. For example, Song
With accumulating data of transcriptomic and genomic sequencing using prostate cancer tissues and PDTO, androgen-independent prostate cancer has been found to have three general mechanisms involved in drug resistance (39). The first is by activating mutations that result in restoration of androgen receptor signaling (56). The second is by activating bypass signaling pathways to escape from androgen receptor inhibitor such as activating glucocorticoid receptor to compensate for the loss of androgen receptor signaling (57). The third resistance mechanism involves lineage plasticity, in which cancer cells can acquire resistance by switching a fate of cell type from a drug target-dependent cell type to a drug target-independent one (58). Furthermore, transcriptomic analyses of metastatic CRPC (mCRPC) tissues, mCRPC organoids, and patient-derived xenografts have been performed to be classified into a positive androgen receptor pathway, mesenchymal stem like prostate cancer, and neuroendocrine prostate cancer (59).
In case of RCC organoids, single-cell RNA sequencing provides genetic landscape of patient-derived RCC organoids to reveal intra-tumor heterogeneity (60). Boclk
In summary, 3D organoid culture systems that can capture phenotypic and molecular heterogeneity found in various organs have been developed (63). Organoids have since been applied to model various type of cancers. In this review, we concisely summarized recent advances in the establishment of PDTO models for patients with prostate cancer and kidney cancer. As a model preserving majority of the characteristics of patients’ tumor, prostate and kidney cancer organoids are promising in various applications such as high-throughput drug screening, disease modeling, platform for biobanks, and personalized treatment. PDTO can overcome limitations of 2D cell lines and PDX that cannot recapitulate heterogeneity, microenvironment, interspecific genetic variation, or genetic landscape. Therefore, 3D organoid culture systems open opportunities to overcome limitations regarding heterogeneity and long-term culture of prostate and kidney cancer cells. We believe that PTDO is an essential platform for personalized medicine. It can be used as an alternative pre-clinical model for more accurate recapitulation of
This work was supported by grants from the Basic Science Research Program of the National Research Foundation (NRF) of Korea, which is funded by the Ministry of Science and ICT (NRF-2020R1A2C2007662 and NRF-2020R1C1C1005054), a grant from Seoul R&BD Program (BT210153), and a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (HR20C0025).
The authors have no conflicting interests.
Comparison of advantages and disadvantages of 2D cell lines, patient-derived xenografts (PDXs) and patient-derived tumor organoid (PDTO) models
|2D cell lines|
|• Infinite growth||• Lack of heterogeneity|
|• Easy handling||• Lack of tumor microenvironment and immune system|
|• Highly available and cheap||• Rare source|
|• Easy access to genome editing|
|• Retains tumor heterogeneity||• Expensive and time-consuming|
|• Correlate with treatment responses in patients||• Differences in genetic interspecies|
|• Low contamination of normal cells||• Gaps between mouse and human system|
|• Making a metastasis model||• Low-throughput screening|
|• Contamination of mouse cells in tumor microenvironment|
|• Retains tumor heterogeneity||• Low success rate of culture|
|• Preserve genomic characteristic||• Hard to long-term expansion|
|• High-throughput screening||• No immune systems|
|• Applied to PDX model||• Contamination of normal cells|
|• Linked to treatment response in patients|
|• Recapitulation of