Adaptable and scalable preclinical tumor model systems that conserve the tumor architecture, the microenvironment interactions, and the genetic heterogeneity of the original patient tumor are needed to transfer basic science discoveries into translational cancer research applications. Recently, organoids –an in vitro 3D culture technology–have gained notoriety in cancer research. Organoids can be grown from patient-derived tumor tissues and often mimic the in vivo response to chemotherapy in solid tumors. Another useful patient-derived tumor model system is the patient-derived xenograft (PDX) in vivo model, which, at a greater cost and maintenance requirements, is highly predictive of clinical outcomes as it retains the principal histologic and genetic characteristics of the donor tumor. Complementing both models is promising, but further characterization is needed to establish their fidelity to the original tumor.
In collaboration with Drs. Hung-Ming Lam and Jonathan Wright (Department of Urology at the University of Washington), researchers in Dr. Andrew Hsieh’s lab in the Human Biology Division established and characterized a new bladder cancer PDX and PDX-derived organoid tumor model system. Bladder cancer is a common type of cancer in the United States for which well-characterized preclinical models are scarce. Although often detected early, bladder cancer recurrences are common and more challenging to treat as second-line chemotherapy regimens have not been established. Thus, new model systems that represent the original tumor are urgently needed to advance the discovery of novel therapeutics. The new research is now published in the journal Scientific Reports, and it “provides a newly characterized human model to study bladder cancer both in vivo and in vitro,” added Dr. Hsieh, one of the principal investigators in the study.
The researchers established the CoCaB 1 PDX and organoid models using tissue from an aggressive bladder cancer tumor exhibiting cisplatin resistance –the first-line chemotherapy drug regime for bladder cancer. The tissue was serially passaged in mice and functionally and molecularly characterized at different passages (early, intermediate, late) to determine whether the tumor tissue retained the characteristics from the original tumor. The researchers determined that histologically all PDX passages retained the characteristics of the original tumor. Interestingly, tumor growth rate increased with passaging. Using immunohistochemistry, the researchers calculated a proliferation index that positively correlated with passage number. At the early and late passages, the PDX-derived tissue was used to establish the organoid cultures for genetic manipulation and high-throughput screening. The organoids also recapitulated the PDX growth phenotypes. The authors discussed that the in vivo selection for more aggressive phenotypes might mirror tumor evolution, which could be a powerful tool to identify therapies against advanced chemotherapy-resistance disease.
To investigate the molecular mechanisms associated with accelerated growth in both PDX and organoid models, the investigators analyzed the transcriptome at early and late stages in both tumor model systems. The analysis for PDX showed an increase in transcripts from genes involved in growth and cell migration pathways from early to late passages. Similarly, in the organoids, transcripts from genes associated with cell proliferation and self-renewal pathways increased. However, no specific pathway was identified from the subset of transcripts upregulated from early to late passages shared between PDX and PDX-derived organoids. Dr. Hsieh highlighted the new questions that emerged from these findings: “Why do PDX and organoid models proliferate faster with propagation? Is it cell type selection? Or is it a cell-autonomous mechanism? Furthermore, how do these changes in growth dynamics impact preclinical trial findings using early or late passage tissues or cells?”
From the transcriptome differences between PDX and organoid models, the researchers identified pathways that reflected the differences in cellular composition between the two models. For instance, organoids exhibited upregulated lipid synthesis and metabolism genes in early and late passages, which is likely due to the increased stem cell composition in organoids relative to PDXs. Finally, to determine the genetic fidelity of PDX and organoids to patient tumors, the group assessed the mutational profile of both tumor models and identified missense mutations, which were then matched with a catalog of bladder cancer mutations. In both systems, key pathogenic mutations present in the original tumor were maintained throughout passaging, highlighting the relevance of these models for screening targeted therapies. Dr. Hsieh added that “this paper demonstrates that bladder cancer PDX model growth dynamics are mirrored in their derivative organoids.”
Cai, EY, Garcia, J, Liu, Y, Vakar-Lopez, F, Arora, S, Nguyen, HM, Lakely, B, Brown, L, Wong, A, Montgomery, B, Lee, JK, Corey, E, Wright, JL, Hsieh, AC, & Lam, HM. (2021). A bladder cancer patient-derived xenograft displays aggressive growth dynamics in vivo and in organoid culture. Scientific reports, 11(1), 4609. https://doi.org/10.1038/s41598-021-83662-7
Fred Hutch/UW Cancer Consortium members Drs. Hung-Ming Lam, Andrew Hsieh, Jonathan Wright, Eva Corey, John Lee, Bruce Montgomery, and Funda Vakar Lopez participated in this study.
This work was supported by the Howard J. Cohen Bladder Cancer Foundation, the Seattle Translational Tumor Research Bladder Cancer Program, the Nancy & Dick Bernheimer, Matthews Family, Dan Stinchcomb, and Thomas & Patricia Wright Memorial Funds, a grant from the Department of Defense, grants from the National Institute of Health, career awards from the Burroughs Wellcome Fund, and the Robert J. Kleberg Jr. and Helen C. Kleberg Foundation.