Characterization of a Clival Chordoma Xenograft Model Reveals Tumor Genomic Instability

In vivo efficacy assessment of the CDK4/6 inhibitor palbociclib and the PLK1 inhibitor volasertib in human chordoma xenografts

Background

Management of advanced chordomas remains delicate considering their insensitivity to chemotherapy. Homozygous deletion of the regulatory gene CDKN2A has been described as the most frequent genetic alteration in chordomas and may be considered as a potential theranostic marker. Here, we evaluated the tumor efficacy of the CDK4/6 inhibitor palbociclib, as well as the PLK1 inhibitor volasertib, in three chordoma patient-derived xenograft (PDX) models to validate and identify novel therapeutic approaches.

Methods

From our chordoma xenograft panel, we selected three models, two of them harboring a homozygous deletion of CDKN2A/2B genes, and the last one a PBRM1 pathogenic variant (as control). For each model, we tested the palbociclib and volasertib drugs with pharmacodynamic studies together with RT-PCR and RNAseq analyses.

Results

For palbociclib, we observed a significant tumor response for one of two models harboring the deletion of CDKN2A/2B (p = 0.02), and no significant tumor response in the PBRM1-mutated PDX; for volasertib, we did not observe any response in the three tested models. RT-PCR and RNAseq analyses showed a correlation between cell cycle markers and responses to palbociclib; finally, RNAseq analyses showed a natural enrichment of the oxidative phosphorylation genes (OxPhos) in the palbociclib-resistant PDX (p = 0.02).

Conclusion

CDK4/6 inhibition appears as a promising strategy to manage advanced chordomas harboring a loss of CDKN2A/2B. However, further preclinical studies are strongly requested to confirm it and to understand acquired or de novo resistance to palbociclib, in the peculiar view of a targeting of the oxidative phosphorylation genes.

A chronicle review of new techniques that facilitate the understanding and development of optimal individualized therapeutic strategies for chordoma

Chordoma is a rare malignant bone tumor that mainly occurs in the sacrum and the clivus/skull base. Surgical resection is the treatment of choice for chordoma, but the local recurrence rate is high with unsatisfactory prognosis. Compared with other common tumors, there is not much research and individualized treatment for chordoma, partly due to the rarity of the disease and the lack of appropriate disease models, which delay the discovery of therapeutic strategies. Recent advances in modern techniques have enabled gaining a better understanding of a number of rare diseases, including chordoma. Since the beginning of the 21st century, various chordoma cell lines and animal models have been reported, which have partially revealed the intrinsic mechanisms of tumor initiation and progression with the use of next-generation sequencing (NGS) techniques. In this study, we performed a systematic overview of the chordoma models and related sequencing studies in a chronological manner, from the first patient-derived chordoma cell line (U-CH1) to diverse preclinical models such as the patient-derived organoid-based xenograft (PDX) and patient-derived organoid (PDO) models. The use of modern sequencing techniques has discovered mutations and expression signatures that are considered potential treatment targets, such as the expression of Brachyury and overactivated receptor tyrosine kinases (RTKs). Moreover, computational and bioinformatics techniques have made drug repositioning/repurposing and individualized high-throughput drug screening available. These advantages facilitate the research and development of comprehensive and personalized treatment strategies for indicated patients and will dramatically improve their prognoses in the near feature.

Dramatic In Vivo Efficacy of the EZH2-Inhibitor Tazemetostat in PBRM1-Mutated Human Chordoma Xenograft

Simple Summary

Chordomas are rare bone tumors characterized by a high recurrence rate. Presently, no medical treatment is available for advanced diseases due to the lack of molecular data and preclinical models. The current study showed the establishment and characterization of the largest panel chordoma xenografts, allowing pharmacological studies. In one PBRM1-mutated model, we demonstrated a strong therapeutic efficacy of the EZH2-inhibitor tazemetostat, encouraging further research on EZH2-inhibitors in chordomas.

Abstract

Chordomas are rare neoplasms characterized by a high recurrence rate and a poor long-term prognosis. Considering their chemo-/radio-resistance, alternative treatment strategies are strongly required, but their development is limited by the paucity of relevant preclinical models. Mutations affecting genes of the SWI/SNF complexes are frequently found in chordomas, suggesting a potential therapeutic effect of epigenetic regulators in this pathology. Twelve PDX models were established and characterized on histological and biomolecular features. Patients whose tumors were able to grow into mice had a statistically significant lower progression-free survival than those whose tumors did not grow after in vivo transplantation (p = 0.007). All PDXs maintained the same histopathological features as patients’ tumors. Homozygous deletions of CDKN2A/2B (58.3%) and PBRM1 (25%) variants were the most common genomic alterations found. In the tazemetostat treated PDX model harboring a PBRM1 variant, an overall survival of 100% was observed. Our panel of chordoma PDXs represents a useful preclinical tool for both pharmacologic and biological assessments. The first demonstration of a high antitumor activity of tazemetostat in a PDX model harboring a PBRM1 variant supports further evaluation for EZH2-inhibitors in this subgroup of chordomas.

Personalized chordoma organoids for drug discovery studies

Chordomas are rare tumors of notochordal origin, most commonly arising in the sacrum or skull base. Chordomas are considered insensitive to conventional chemotherapy, and their rarity complicates running timely and adequately powered trials to identify effective treatments. Therefore, there is a need for discovery of novel therapeutic approaches. Patient-derived organoids can accelerate drug discovery and development studies and predict patient responses to therapy. In this proof-of-concept study, we successfully established organoids from seven chordoma tumor samples obtained from five patients presenting with tumors in different sites and stages of disease. The organoids recapitulated features of the original parent tumors and inter- as well as intrapatient heterogeneity. High-throughput screenings performed on the organoids highlighted targeted agents such as PI3K/mTOR, EGFR, and JAK2/STAT3 inhibitors among the most effective molecules. Pathway analysis underscored how the NF-κB and IGF-1R pathways are sensitive to perturbations and potential targets to pursue for combination therapy of chordoma.

Development of a Novel Orthotopic Primary Human Chordoma Xenograft Model: A Relevant Support for Future Research on Chordoma

Chordomas are slow-growing rare malignant neoplasms. The aim of this study was to establish a primary model of chordoma in the lumbosacral orthotopic area, to compare the growth rate to the subcutaneous site, and to show that this new graft site optimizes tumor growth and bony invasion. Eleven chordoma samples were transplanted subcutaneously in the flank and/or in contact with the lumbosacral region and grown into nude mice. Engraftment rate was significantly more successful in the lumbosacral environment compared with the flank at P0. Two xenografts from 2 patients showed bone invasion. One tumor was maintained through multiple rounds of serial transplantation, creating a model for study. Histological and immunostaining analysis confirmed that tumor grafts recapitulated the primary tumor from which they were derived, consisting of a myxoid chordoma expressing brachyury, cytokeratin AE1, EMA, and VEGF. Clear destruction of the bone by the tumor cells could be demonstrated. Molecular studies revealed PIK3CA and PTEN mutations involved in PI3K signaling pathway and most of the frequently reported chromosomal alterations. We present a novel orthotopic primary xenograft model of chordoma implanted for the first time in the lumbosacral area showing bone invasion, PIK3CA, and PTEN mutations that will facilitate preclinical studies.