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PMC12852540
Choosing the right animal model for sarcoma research
The subsequent phase II trial confirmed that palbociclib achieved clinically meaningful disease stabilisation with a 12-week progression-free rate of approximately 60% in this molecularly selected population and more recent CDK4/CDKN2A-guided phase II work has extended this paradigm to additional sarcoma subtypes .
PMC12852540
Choosing the right animal model for sarcoma research
The primary advantages of CDXs are their reproducibility and ease of use, making them a fundamental tool for preclinical sarcoma research.
PMC12852540
Choosing the right animal model for sarcoma research
Using well-characterised human sarcoma cell lines, such as U-2 OS for osteosarcoma and SW872 for liposarcoma , CDX models provide consistent and predictable tumour growth in immunocompromised mice.
PMC12852540
Choosing the right animal model for sarcoma research
This reproducibility allows researchers to perform standardised experiments, compare therapeutic effects across studies, and reliably evaluate drug efficacy.
PMC12852540
Choosing the right animal model for sarcoma research
Moreover, compared to 2D or 3D cultures of the same cell lines, CDX adds vascular delivery, stromal crosstalk and in vivo pharmacokinetics.
PMC12852540
Choosing the right animal model for sarcoma research
These factors modify the ranking of responses and reveal effects dependent on schedule and exposure that are invisible in vitro.
PMC12852540
Choosing the right animal model for sarcoma research
For example, CDX models have been instrumental in testing chemotherapeutic agents, such as doxorubicin and ifosfamide , which remain the cornerstones of sarcoma treatment.
PMC12852540
Choosing the right animal model for sarcoma research
They have also been used to explore novel targeted therapies , such as CDK4/6 inhibitors, in dedifferentiated liposarcoma, demonstrating their utility in preclinical drug development .
PMC12852540
Choosing the right animal model for sarcoma research
The scalability of CDX systems enables high-throughput drug screening and combination therapy studies, in which multiple agents can be tested simultaneously to identify synergistic effects.
PMC12852540
Choosing the right animal model for sarcoma research
Notably, unlike syngeneic or chemically induced mouse tumours, CDX reproduces the aneuploidy, copy-number changes and fusion landscapes of human sarcomas to some extent because the malignant genome is human.
PMC12852540
Choosing the right animal model for sarcoma research
This improves construct validity for genotype-directed agents.
PMC12852540
Choosing the right animal model for sarcoma research
Imaging technologies, such as bioluminescence and MRI, further enhance CDX models by allowing real-time tracking of tumour growth and treatment response .
PMC12852540
Choosing the right animal model for sarcoma research
For example, VEGF inhibitors have been studied in CDX angiosarcoma models to investigate their impact on tumour angiogenesis .
PMC12852540
Choosing the right animal model for sarcoma research
In addition, the rapid tumour growth and cost-effectiveness of CDX models make them ideal starting points for hypothesis generation and initial therapeutic evaluation before moving on to more complex models such as patient-derived xenografts (PDXs).
PMC12852540
Choosing the right animal model for sarcoma research
The primary limitation of CDX models is their inability to recapitulate the complex microenvironment and immune-tumour interactions of human sarcomas.
PMC12852540
Choosing the right animal model for sarcoma research
Because host mice are immunocompromised, these models cannot be used to study the efficacy of immunotherapies such as checkpoint inhibitors targeting CTLA-4 or PD-1, which are increasingly being investigated in soft tissue sarcomas such as alveolar soft part sarcoma .
PMC12852540
Choosing the right animal model for sarcoma research
CDX can be established either subcutaneously or orthotopically .
PMC12852540
Choosing the right animal model for sarcoma research
The latter improves the fidelity of the microenvironment for bone and soft tissue niches as the subcuteneous implantation does not accurately simulate the native tissue environment of sarcomas such as the periosteal or bone marrow microenvironment critical for osteosarcoma or the retroperitoneal space relevant for liposarcoma .
PMC12852540
Choosing the right animal model for sarcoma research
These discrepancies reduce the ability of these models to study site-specific tumour behaviour or therapeutic responses.
PMC12852540
Choosing the right animal model for sarcoma research
Reliance on established cell lines also presents challenges as these lines often represent highly proliferative or aggressive subclones that lack the genetic heterogeneity of primary sarcomas.
PMC12852540
Choosing the right animal model for sarcoma research
For example, while CDX models are useful for studying general tumour biology, they do not effectively ​​recapitulate key genetic fusions, such as FUS-DDIT3 in myxoid liposarcoma or NAB2-STAT6 in solitary fibrous tumours .
PMC12852540
Choosing the right animal model for sarcoma research
In addition, cell lines can undergo genetic drift during prolonged culture, which further diverges from the characteristics of the original tumour.
PMC12852540
Choosing the right animal model for sarcoma research
Although subcutaneous CDXs rarely metastasise, orthotopic and tail-vein or intracardiac models using luciferase-labelled sarcoma lines often produce lung or systemic metastases.
PMC12852540
Choosing the right animal model for sarcoma research
This makes longitudinal bioluminescent tracking possible.
PMC12852540
Choosing the right animal model for sarcoma research
To broaden the CDX perspective, luciferase-labelled metastatic models span osteosarcoma, host–genetic susceptibility, and fusion-driven soft-tissue sarcoma.
PMC12852540
Choosing the right animal model for sarcoma research
In osteosarcoma, intratibial implantation of luciferase-tagged Saos2 enabled derivation of a lung-metastasis–enriched subline (Saos2-l) with spontaneous pulmonary dissemination quantified by bioluminescence imaging; the study reports increased adhesion, migration and invasion in Saos2-l relative to parental cells In a host-genetics paradigm, tail-vein S180-Fluc yielded lung-restricted colonisation with marked strain effects – A/J mice develop high burden whereas BTBRT + tf/J clear disease – and resistance is diminished by supralethal irradiation and T-cell depletion, highlighting immune control .
PMC12852540
Choosing the right animal model for sarcoma research
Extending luciferase CDX to a translocation-positive entity, clear cell sarcoma (EWSR1–ATF1/CREB) CCS292-Luc produced multi-organ metastases after intravenous injection into NSG mice with weekly bioluminescence tracking, providing a fusion-driven metastasis model suitable for therapeutic testing .
PMC12852540
Choosing the right animal model for sarcoma research
Despite their utility for initial drug testing, the high failure rate of therapies that perform well in CDX models, but fail in clinical trials, underscores their limited predictive power.
PMC12852540
Choosing the right animal model for sarcoma research
These limitations necessitate complementing CDX models with more advanced systems, such as PDXs or genetically engineered mouse models (GEMMs), to achieve greater translational relevance.
PMC12852540
Choosing the right animal model for sarcoma research
An alternative to CDX is the transplantation of fresh tumour tissue from cancer patients into immunocompromised mice, creating PDX models.
PMC12852540
Choosing the right animal model for sarcoma research
Patient-derived xenografts (PDX) are mainly used to preserve patient-specific histology, genomic complexity and intra-tumour heterogeneity, enabling subtype-appropriate testing of targeted agents and combinations, co-clinical trial designs and exploratory biomarker validation in a setting that closely mirrors the treated human tumour .
PMC12852540
Choosing the right animal model for sarcoma research
Moreover, PDX resources are available for subtypes for which there are no reliable, shareable cell lines, such as EHE, DSRCT and MPNST.
PMC12852540
Choosing the right animal model for sarcoma research
This is a sarcoma-specific issue, and PDX is the only method that enables preclinical testing in this area.
PMC12852540
Choosing the right animal model for sarcoma research
Generation of established PDX models requires at least three consecutive transplantations of developed tumours in mice.
PMC12852540
Choosing the right animal model for sarcoma research
Tumor fragments are implanted subcutaneously into the flanks of nude mice under sterile conditions.
PMC12852540
Choosing the right animal model for sarcoma research
First-generation tumours (P1) are harvested when they reached a volume of 1500 mm³ and reimplanted into additional mice to generate second (P2) and third (P3) generations.
PMC12852540
Choosing the right animal model for sarcoma research
Numerous models have been successfully developed, achieving an engraftment success rate ranging from 32% to 69% and effectively replicating the genetic and phenotypic traits of the original tumour .
PMC12852540
Choosing the right animal model for sarcoma research
PDX models have gained prominence in sarcoma research due to their ability to mimic the complexity and heterogeneity of human tumours.
PMC12852540
Choosing the right animal model for sarcoma research
For example, Gebreyohannes and colleagues demonstrated that the tyrosine kinase inhibitor cabozantinib effectively reduced tumour growth in both imatinib-sensitive and resistant PDX models of GISTs .
PMC12852540
Choosing the right animal model for sarcoma research
Similarly, Van Looy’s team showed that combining PI3K inhibitors with imatinib reduced tumour volumes in GIST PDX models .
PMC12852540
Choosing the right animal model for sarcoma research
PDX models are particularly useful in predicting patient responses to therapies and are increasingly applied in personalised medicine .
PMC12852540
Choosing the right animal model for sarcoma research
For instance, in osteosarcoma, PDX models are particularly important due to the genetic complexity and heterogeneity of the disease .
PMC12852540
Choosing the right animal model for sarcoma research
Tumours from less aggressive sarcoma subtypes, such as low-grade chondrosarcoma, showed lower engraftment rates, as did samples with extensive necrosis or those collected after chemotherapy.
PMC12852540
Choosing the right animal model for sarcoma research
Nanni et al. .
PMC12852540
Choosing the right animal model for sarcoma research
highlighted the close resemblance between the original tumours and their PDX models by examining molecular markers such as SATB2 and P-glycoprotein in osteosarcoma (OS) and CD99 in Ewing sarcoma (EW).
PMC12852540
Choosing the right animal model for sarcoma research
These characteristics were maintained over multiple in vivo passages, demonstrating the stability of the models.
PMC12852540
Choosing the right animal model for sarcoma research
Gene expression profiling confirmed a high correlation between patient tumours and their corresponding PDX models (Pearson’s r = 0.94–0.96), which remained consistent over successive passages.
PMC12852540
Choosing the right animal model for sarcoma research
The study tested a novel therapeutic combination of anti-CD99 diabody (C7) and irinotecan in EW PDX models and demonstrated that this treatment significantly reduced tumour growth and, in some cases, eliminated metastases.
PMC12852540
Choosing the right animal model for sarcoma research
This finding highlights the utility of PDX models for the novel therapeutic strategies evaluation.
PMC12852540
Choosing the right animal model for sarcoma research
Compared to primary cell cultures derived from patient samples, PDX models more closely recapitulated the molecular and genetic characteristics of the original tumours.
PMC12852540
Choosing the right animal model for sarcoma research
In contrast, in vitro models exhibited significant genetic drift, making them less reliable for translational research.
PMC12852540
Choosing the right animal model for sarcoma research
The PDX models of OS showed faster tumour growth in early passages compared to EW models, but their growth rates stabilised in subsequent passages.
PMC12852540
Choosing the right animal model for sarcoma research
The study also showed that untreated OS samples had a higher engraftment success rate compared to post-chemotherapy samples, highlighting the influence of pre-treatment on the efficiency of PDX establishment.
PMC12852540
Choosing the right animal model for sarcoma research
In addition, the ability to generate PDX models often depended on the specific tumour sample rather than patient-related factors, as samples from the same patient occasionally gave inconsistent results.
PMC12852540
Choosing the right animal model for sarcoma research
By including both paediatric and adult bone sarcoma samples, the study created a valuable resource for investigating tumour biology in different age groups.
PMC12852540
Choosing the right animal model for sarcoma research
The authors ensured the reliability of the PDX models for long-term research by performing multiple in vivo passages and using bioinformatic analysis to confirm their molecular stability.
PMC12852540
Choosing the right animal model for sarcoma research
In addition, by avoiding enzymatic dissociation and using direct implantation, the structural and cellular integrity of the tumours was maintained, increasing the fidelity of the models to the original patient tumours.
PMC12852540
Choosing the right animal model for sarcoma research
Translational signal from PDX-guided decisions is quantifiable: in a 92-patient co-clinical series linking 129 PDX-tested regimens to matched therapies, sensitivity was 96% (80/83), specificity 70% (32/46), positive predictive value 85% (80/94), and negative predictive value 91% (32/35); performance was highest when the PDX screen informed the first post-resection treatment (PPV 94%, NPV 94%) .
PMC12852540
Choosing the right animal model for sarcoma research
Mechanism-anchored sarcoma exemplars underscore practical impact but also limits: CDK4/6 inhibition advanced from xenograft-supported preclinical work to phase II trials in CDK4-amplified WD/DD liposarcoma with 12-week PFS 66% and median PFS 18 weeks on 200 mg 14/21, and 12-week PFS 57.2% with median PFS 17.9 weeks on 125 mg 21/28 , while MDM2 antagonism informed by PDXs shows early activity (brigimadlin disease-control rate 75% in DDLPS) and is now in randomised testing ; together these data indicate that PDXs can enrich for clinical benefit and de-prioritise ineffective options, though predictive accuracy may fall with intervening therapies and the absence of an intact immune system necessitates humanised variants for immunotherapy questions .
PMC12852540
Choosing the right animal model for sarcoma research
Selinexor, a selective inhibitor of nuclear export targeting XPO1, has been evaluated in carefully characterised patient-derived xenograft models of dedifferentiated liposarcoma.
PMC12852540
Choosing the right animal model for sarcoma research
Three PDXs (LS-GD-1 with rhabdomyoblastic, LS-BZ-1 and LS-BP-1 with myogenic dedifferentiation) were established from the dedifferentiated component of primary, treatment-naïve, retroperitoneal FNCLCC grade 3 tumours harbouring amplification of MDM2, CDK4 and HMGA2; 3-mm³ fragments were implanted subcutaneously into CB17/SCID mice, serially passaged, then engrafted into nude mice for efficacy studies .When tumours reached about 150 mm³, mice (n = 8 per group) received selinexor 10 mg/kg orally twice weekly for eight doses versus doxorubicin 4 mg/kg intravenously every 7 days × 3, with selinexor achieving greater maximum tumour volume inhibition (46–80% vs. 37–60%) and longer growth delay, without excess weight loss or overt toxicity .Pharmacodynamic analyses showed reduced XPO1 and survivin expression, nuclear accumulation of p53 and p21, and increased cleaved caspase-3 and TUNEL positivity, indicating apoptosis driven by nuclear retention of tumour suppressors and depletion of cytoplasmic survivin .More recently, GIST PDX collections recapitulating specific primary and secondary KIT/PDGFRA mutations have been used prospectively to select mutation-specific inhibitor candidates – such as AZD3229 – and to define dose levels yielding sustained KIT blockade and regression in vivo before entry into first-in-human trials .illustrating how contemporary PDX platforms can provide a “ready-to-use” translational filter for next-generation TKIs .
PMC12852540
Choosing the right animal model for sarcoma research
Despite their advantages, PDX models have limitations.
PMC12852540
Choosing the right animal model for sarcoma research
The need for immunodeficient mice to prevent graft rejection means that critical immune-tumour interactions, such as those involving T cells or macrophages, can only be studied in combination with humanised immune systems .
PMC12852540
Choosing the right animal model for sarcoma research
In addition, establishing a PDX model can take several months and the success rate depends on factors such as tumour type, tissue quality and pre-treatment status.
PMC12852540
Choosing the right animal model for sarcoma research
Shimade et al. .
PMC12852540
Choosing the right animal model for sarcoma research
aimed to establish a PDX model for pleomorphic leiomyosarcoma (PLMS), a rare and aggressive subtype of leiomyosarcoma, using tissue obtained from a single patient.
PMC12852540
Choosing the right animal model for sarcoma research
Among the ten tumor samples transplanted into SCID mice, only one successfully proliferated, reflecting the significant challenges in establishing sarcoma PDX models due to variability in tumor biology and host compatibility.
PMC12852540
Choosing the right animal model for sarcoma research
The resulting PDX tumor retained the key histological features of primary PLMS, including spindle cell proliferation and marked nuclear pleomorphism.
PMC12852540
Choosing the right animal model for sarcoma research
Immunohistochemistry further confirmed the expression of smooth muscle markers such as SMA, caldesmon, and M-actin, demonstrating that the PDX model closely recapitulates the differentiation characteristics of PLMS.
PMC12852540
Choosing the right animal model for sarcoma research
Despite the low initial engraftment rate, the established PDX model exhibited stable growth across successive passages (P1 to P3), with its histological and immunohistochemical features remaining consistent.
PMC12852540
Choosing the right animal model for sarcoma research
Tumor growth rates increased with each passage, likely reflecting adaptation to the murine microenvironment.
PMC12852540
Choosing the right animal model for sarcoma research
This PDX model provides a valuable platform for studying the rare pathology of PLMS, offering insights into its aggressive growth behavior and distinct histological features.
PMC12852540
Choosing the right animal model for sarcoma research
While specific drug trials were not conducted in this study, the model was proposed as a potential tool for screening therapies for PLMS, a cancer with limited treatment options and poor prognosis.
PMC12852540
Choosing the right animal model for sarcoma research
The exceptionally low engraftment rate (10%) underscores the inherent difficulties in establishing sarcoma PDX models, particularly for rare and aggressive subtypes such as PLMS.
PMC12852540
Choosing the right animal model for sarcoma research
The authors speculated that high malignancy, rapid cell division, and eventual adaptation to the murine environment were key factors contributing to the ultimate success of the model.
PMC12852540
Choosing the right animal model for sarcoma research
The observation that only one of ten tumour fragments engrafted highlights the importance of spatial heterogeneity in terms of both biology and stromal content.
PMC12852540
Choosing the right animal model for sarcoma research
It also suggests that a single PDX may not capture the full range of subclonal, therapeutically relevant diversity.
PMC12852540
Choosing the right animal model for sarcoma research
In another study focusing on the generation of PDX models for challenging tumour types such as GISTs, a total of 185 tumour samples from 176 patients were used.
PMC12852540
Choosing the right animal model for sarcoma research
These samples were collected from patients both before (35.7%) and after (64.3%) tyrosine kinase inhibitor (TKI) treatment.
PMC12852540
Choosing the right animal model for sarcoma research
Tumour fragments were implanted subcutaneously into NSG mice shortly after surgical resection.
PMC12852540
Choosing the right animal model for sarcoma research
Successfully engrafted tumours were excised when they reached 1.5–2 cm in diameter and re-implanted in subsequent generations of mice (F1, F2).
PMC12852540
Choosing the right animal model for sarcoma research
Despite these efforts, only 31 PDX models were successfully established, resulting in a low overall success rate of 16.8%.
PMC12852540
Choosing the right animal model for sarcoma research
Interestingly, the success rate was significantly higher for tumours harvested after TKI treatment (25.2%) compared to untreated tumours (1.5%).
PMC12852540
Choosing the right animal model for sarcoma research
Several factors influenced the likelihood of successful transplantation.
PMC12852540
Choosing the right animal model for sarcoma research
Larger tumours (> 100 mm) had a much higher success rate (37.5%) compared to smaller tumours (6.5% for tumours ≤ 50 mm).
PMC12852540
Choosing the right animal model for sarcoma research
Tumours with high mitotic counts and a Ki-67 index of ≥ 1/3 had a 42.9% success rate, while those with lower Ki-67 indices had a success rate of only 5.4%.
PMC12852540
Choosing the right animal model for sarcoma research
High cellularity was another critical factor, with a success rate of 26.2% compared to only 4.9% for tumours with low cellularity.
PMC12852540
Choosing the right animal model for sarcoma research
The presence of necrosis was also associated with a higher engraftment rate (26.4% compared to 8.3% for tumours without necrosis).
PMC12852540
Choosing the right animal model for sarcoma research
In addition, samples with KIT exon 11 mutations had a higher engraftment rate (22.4%) than those with other mutations or wild-type tumours.
PMC12852540
Choosing the right animal model for sarcoma research
The resulting PDX tumours retained the histological characteristics of the original patient tumours, including cell morphology and mitotic activity.
PMC12852540
Choosing the right animal model for sarcoma research
Molecular stability over multiple passages was confirmed using Ki-67 staining and immunohistochemistry, further validating the reliability of the models for preclinical research.
PMC12852540
Choosing the right animal model for sarcoma research
Similarly, in alveolar rhabdomyosarcoma, PDX models have been used to study the role of the PAX3‒FOXO1 fusion in driving oncogenesis and resistance to chemotherapy .These models are particularly valuable for evaluating precision therapies because they can be used to test targeted agents in tumours with actionable mutations or amplifications, such as FGFR2 in myxofibrosarcoma or PDGFRA in gastrointestinal stromal tumours (GISTs) .
PMC12852540
Choosing the right animal model for sarcoma research
For example, they have been used to study how ALK mutations in inflammatory myofibroblastic tumours confer resistance to ALK inhibitors and to provide a platform for testing next-generation inhibitors.
PMC12852540
Choosing the right animal model for sarcoma research
Another key advantage is their use in personalised medicine; PDX models can serve as avatars for individual patients, allowing researchers to test multiple treatment regimens on a patient’s tumor to identify the most effective therapy.
PMC12852540
Choosing the right animal model for sarcoma research
For example, PDX models derived from dedifferentiated liposarcoma have been used to test novel combinations of CDK4/6 inhibitors with chemotherapy, providing critical insights for optimising therapeutic strategies.
PMC12852540
Choosing the right animal model for sarcoma research
Additional limitations of PDX models are their complexity, cost, and the time required to develop and maintain them.
PMC12852540
Choosing the right animal model for sarcoma research
Establishing a PDX model requires fresh patient tumour samples, often obtained through invasive surgery or biopsy, and the engraftment process can take several months.
PMC12852540
Choosing the right animal model for sarcoma research
Success rates vary by sarcoma subtype, with more aggressive tumours such as undifferentiated pleomorphic sarcoma having higher engraftment rates than indolent subtypes such as low-grade chondrosarcoma.
PMC12852540
Choosing the right animal model for sarcoma research
This variability limits their scalability to high-throughput drug screening and large-scale studies.
PMC12852540
Choosing the right animal model for sarcoma research
In addition, PDX models rely on immunocompromised mice that lack a functional immune system, making them unsuitable for studying immuno-oncology therapies, such as anti-CTLA-4 or PD-1/PD-L1 checkpoint inhibitors, which are gaining traction in sarcomas, such as deddifferentiated liposarcoma .