Abstract
Undifferentiated pleomorphic sarcoma (UPS) and malignant peripheral nerve sheath tumor (MPNST) are aggressive soft tissue sarcomas that do not respond well to current treatment modalities. The limited availability of UPS and MPNST cell lines makes it challenging to identify potential therapeutic targets in a laboratory setting. Understanding the urgent need for improved treatments for these tumors and the limited cellular models led us to generate additional cell lines to study these rare cancers further. Patient-derived tumors were used to establish 5 new UPS models, including one radiation-associated UPS—UPS060.1, UPS271.1, UPS511, UPS0103, and RIS620—and 3 new models of MPNST—MPNST007, MPNST3813E, and MPNST4970. This study examined the utility of the new cell lines as sarcoma models by assessing tumorigenic potential and mutation status for known sarcoma-related genes. All the cell lines formed colonies and migrated in vitro. The in vivo tumorigenic potential of each cell line was determined by either subcutaneous injection of cells or implantation of tumor tissue into immunocompromised mice. UPS060.1, UPS271.1, and UPS511 cells formed tumors in mice upon subcutaneous injection. UPS0103 and RIS620 tumor implants formed tumors in vivo, as did MPNST007 and MPNST3813E tumor implants. Mutation analysis of a panel of genes frequently mutated in sarcomas showed that two of the three MPNST cell lines had NF1 mutations. Two of the three MPNST cell lines had mutations in polycomb repressive complex 2 members. These new cellular models provide the scientific community with powerful tools for detailed studies of sarcomagenesis and investigate novel therapies for UPS and MPNST.
Soft tissue sarcomas are rare malignancies originating from the mesoderm. There exist more than 50 histological subtypes based on their tissues of origin. Undifferentiated pleomorphic sarcoma (UPS) comprises a subset of 5% to 15% of soft tissue sarcomas for which clinicians cannot determine the tissue of origin from analysis of the tumor’s molecular and histologic characteristics 1,2,3. The standard of treatment for UPS is surgical resection. For patients in whom surgery is not feasible, chemotherapy and radiation therapy may be used, but they have low-to-moderate response rates 4, 5. UPS is characterized by a high level of genomic instability, as indicated by its complex karyotype. However, specific recurring genetic alterations are uncommon 6. Malignant peripheral nerve sheath tumors (MPNSTs), which comprise 2% of all soft tissue sarcomas 1, are another rare and genomically unstable sarcoma. Half of MPNSTs occur in patients with the autosomal dominant cancer predisposition syndrome neurofibromatosis type 1 (NF1; OMIM # 162200). Approximately 40% of MPNST cases are sporadic, and the remaining 10% are associated with previous radiation therapy 7–9. Chemotherapy and radiation therapy are ineffective for treating MPNSTs 2, 10, 11; therefore, surgical resection remains the standard treatment 12–15. MPNSTs have a high rate of local recurrence 16, 17. The 5-year survival rate is 35% to 50%, and the 10-year survival rate is 7.5%, stressing the need for improved treatment options 9, 18. Limited treatment options are available for patients with UPS and MPNST, largely because the mechanisms involved in the progression of these heterogeneous sarcomas require further investigation 9, 19, 20,21.
UPS and MPNST both have complex karyotypes, and no specific genomic alterations are unique to the tumor type. UPS has complex cytogenetic rearrangements in 30% to 35% of the genome 22, but to date, no specific alterations have been useful for classifying UPS. Loss of chromosome 13q, which leads to inactivation of the RB pathway, is frequently observed in UPS 23–25, and losses of genes in the TP53/ARF/MDM2 pathway are also common 26, 27. A study of soft tissue sarcoma by The Cancer Genome Atlas Research Network 28 reported several somatic copy number alterations, specifically deep deletions in RB1 in 16%, TP53 in 16%, and CDKN2A in 20% of UPS. The mutation burden was low in soft tissue sarcomas, an average of 1.06 per MB in 206 tumors. The significantly mutated genes in UPS included RB1 and potential driver truncating mutations of NF1 28. MPNST’s complex genomic profile includes copy number aberrations, like microdeletions of NF1 in 5% to 20% of cases 29, 30, as well as CDKN2A inactivation 31, 32, and TP53 mutations. Recently, mutations in the genes of the polycomb repressive complex 2 (PRC2) components SUZ12 and EED and the loss of histone 3 lysine 27 trimethylation (H3K27me3) were proposed as markers for NF1-related and sporadic MPNSTs 20, 33.
Cell line models that can form tumors in mice are valuable tools to advance the understanding of soft tissue sarcomas with no known genetic drivers such as UPS and MPNST. Currently, some UPS and radiation-induced sarcoma (RIS) cell lines are available for study of these tumor types: U2197, NCC-UPS2-C1 34, 35, 2 developed by our laboratory, UPS186 and RIS819 21, and others, some with the ability to form tumors when injected subcutaneously into mice 36, 37. Well-studied NF1-associated MPNST cell lines are also available within the scientific community, including SNF02.2 and SNF94.3, both derived from a metastatic site in the lung, SNF96.2, isolated from a recurrent MPNST; S462, ST88-14, T265, and MPNST642 38, 39,40, 41. All of the NF1-associated MPNST cell lines listed above can form tumors in mice, allowing for the in vivo study of these difficult-to-treat sarcomas 38, 39, 42–44. However, further development of UPS and MPNST cell line models is warranted because cell lines from genomically complex sarcomas are underrepresented in cancer cell line databases such as the Cancer Cell Line Encyclopedia (CCLE) and Catalogue Of Somatic Mutations In Cancer COSMIC 45, 46.
This study aimed to generate and characterize new cellular models of UPS and MPNST that will deepen our understanding of the aberrant cellular processes of these sarcomas known to lack clear genetic or molecular markers. The UPS and MPNST cell lines generated in this study will be available to the scientific community to facilitate the study of these debilitating tumors.
Competing Interest Statement
The authors have declared no competing interest.