Page 94 - SRPSKO DRUŠTVO ISTRAŽIVAČA RAKA

Serbian Association for Cancer Research SDIRSACR

tumors, maintaining close molecular, morphological, and immunohistochemical similarity to human cancers [3]. They
faithfully reproduce the microenvironment and cellular heterogeneity found in clinical settings, allowing the tumor
structure and behavior to remain stable across several generations of host animals. Moreover, PDTX models mirror
tumor metabolism and vascularization, accurately reflecting nutrient flow and drug distribution as it occurs in patients.
Importantly, these models retain functional activity: the tumor cells remain viable and biologically active through
serial transplantation, enabling long-term study of tumor dynamics and drug interactions.In addition to preserving
tumor integrity, PDTX models provide valuable advantages in the development of cancer therapies. These models
offer a more dependable platform for in vivo drug testing, increasing the likelihood that preclinical findings align with
clinical outcomes. Critically, PDTX-derived organoids (PDTOs) [4] enhance the predictability of clinical therapeutic
response in a quick, cost-effective way, contributing to enhanced decision-making in personalized medicine. PDTX
models represent a transformative advance in preclinical oncology, offering a more accurate and clinically predictive
framework for the development and evaluation of cancer therapies, enabling a shift from simplified cell-based
assays to biologically complex, patient-mimicking systems [5]. Their application in drug efficacy testing, biomarker
validation, resistance mechanism studies, and co-clinical trial design is crucial in reliable cancer therapy development.
Vascularization and tumor stroma are preserved, making PDTX a vital platform to test modalities that do not directly
target cancer cells but instead kill tumors via tumor microenvironment (TME) alteration. Furthermore, they have
application for in-detail genomic analysis of tumor stages: size-dependent, metastasis vs. primary tumor effects, drug
naïve vs. treated vs. resistant, etc. On the other hand there are limitations to using PDTX models [3]. Antibodies and
immunotherapies cannot be properly tested with this technology, while murine antibodies can be tested in allografts
or Genetically engineered mouse models (GEMMs) or short-term in humanized mice. Lack of a human immune system:
PDTXs are typically implanted into immunodeficient mice to avoid rejection, but this prevents accurate modeling of
immune responses, making them unsuitable for studying immunotherapies. Engraftment bias: not all patient tumors
successfully engraft, where fast-growing, aggressive tumors are more likely to take hold, potentially skewing research
away from slower-growing but clinically relevant cancers. Loss of stromal components: human stromal and immune
cells in the tumor microenvironment are gradually replaced by murine cells, which can alter tumor–host interactions
and drug responses over time. Routine use of PDTX banking in clinical centers is urgent but complex, time-consuming,
and costly, requiring cooperation of surgical, pathological, administrative (patient consent) and research teams/animal
house/biobank.
Results: Our lab develops patient-derived tumor xenograft (PDTX) models that preserve tumor heterogeneity and
microenvironmental complexity, offering a highly predictive platform for studying therapeutic responses. By sourcing
samples from numerous cancer types, we have established a diverse and well-documented PDTX model collection,
including rare malignancies and metastatic lesions. These models support both basic and translational research
by mimicking clinically relevant tumor behavior in vivo.Our biobanked PDTX models are serially xenografted in
immunodeficient mice and are accompanied by complete histological and molecular documentation. Additionally, we
establish PDTX-derived cell line cultures (PDTC) or organoids (PDTO) to compare in vitro and in vivo tumor behavior,
enhancing our understanding of model fidelity and tumor dynamics, and effectively prescreening and extensively
study possible drug effects. As part of our research activity, within a wide range of PDTX models from different tissue
origins and molecular signature, we have developed a vemurafenib-resistant PDTX model from a BRAF V600E-mutant
melanoma patient [6]. This model, characterized both molecularly and morphologically, was subjected to long-term
BRAF inhibitor vemurafenib treatment, resulting in an in vivo therapy-resistant phenotype. Bulk mRNA sequencing
analysis did not align with previously described resistance mechanisms, prompting further investigation of novel,
differentially expressed genes. Notably, in this model we also found the role of the ABCB1 multidrug transporter, a
rarely studied factor in melanoma, which may contribute to drug efflux and therapeutic resistance, given vemurafenib
is its substrate and can be expelled from ABCB1-positive cells. Furthermore, the same model was successfully used to
identify potentially druggable metabolic changes affecting cysteine metabolism during the evolution of resistance to
dabrafenib-trametinib dual treated melanoma [7]. PDTX platform enables the discovery of resistance-driving pathways
and facilitates preclinical testing of next-generation therapies. By focusing on complex and underrepresented tumor
models, we aim to accelerate the development of personalized cancer treatments and support metastasis-targeted
drug discovery by collecting multiple samples and establishing multiple PDTXs from the same patient’s primary and
disseminated tumor sites.
Conclusion: PDTX models serve as a critical bridge between basic research and clinical application by preserving tumor
heterogeneity, microenvironment, and drug response profiles. They offer a more accurate and predictive platform
than traditional models, supporting drug development, resistance mechanism discovery, and personalized therapy
design. Despite certain limitations, their integration into translational research enhances the ability to model real-
world tumor behavior and identify more effective cancer treatments. PDTX models are reshaping the approach to
precision oncology and accelerating the path from bench to bedside.

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