<p>Genomic profile, describing copy number gains and losses, obtained using low coverage whole genome sequencing of subsequent passages of STS PDX models, revealing a stable copy number profile throughout passaging. Copy number profile of (A) the MPNST model UZLX-STS39 and (B) the mesenchymal chondrosarcoma model UZLX-STS41.</p>
<div>Abstract<p>Soft-tissue sarcomas (STS) represent a heterogeneous group of rare, malignant tumors of mesenchymal origin. Reliable <i>in vivo</i> sarcoma research models are scarce. We aimed to establish and characterize histologically and molecularly stable patient-derived xenograft (PDX) models from a broad variety of STS subtypes. A total of 188 fresh tumor samples from consenting patients with localized or advanced STS were transplanted subcutaneously in NMRI-nu/nu–immunodeficient mice. Once tumor growth was observed, the material was passaged to a next generation of mice. A patient-derived tumor sample was considered “successfully engrafted” whenever the sample was transplanted to passage 1. A PDX model was considered “established” when observing stable morphologic and molecular features for at least two passages. With every passage, histologic and molecular analyses were performed. Specific genomic alterations and copy-number profile were assessed by FISH and low coverage whole-genome sequencing. The tumor engraftment rate was 32% (61/188) and 188 patient samples generated a total of 32 PDX models, including seven models of myxofibrosarcoma, five dedifferentiated liposarcoma, five leiomyosarcoma, three undifferentiated pleomorphic sarcoma, two malignant peripheral nerve sheet tumor models, and single models of synovial sarcoma and some other (ultra)rare subtypes. Seventeen additional models are in early stages of engraftment (passage 1–2). Histopathologic and molecular features were compared with the original donor tumor and were stable throughout passaging. The platform is used for studies on sarcoma biology and suited for <i>in vivo</i> preclinical drug testing as illustrated by a number of completed and ongoing laboratory studies.</p></div>
Soft tissue sarcoma (STS) comprises a family of rare, heterogeneous tumors of mesenchymal origin. Single-agent doxorubicin remains the first-line standard-of-care treatment for advanced and inoperable STS, but response rates are only around 15%. In 2016, phase Ib/II clinical trial results reported an overall survival benefit of 11.8 months when combining doxorubicin and the platelet-derived growth factor receptor alpha (PDGFRA)-directed antibody olaratumab compared to doxorubicin alone, without providing a scientific rationale for such unprecedented therapeutic effect. We decided to evaluate the efficacy of olaratumab in a panel of STS patient-derived xenografts (PDX).NMRI nu/nu mice were bilaterally transplanted with tumor tissue of patient-derived xenograft models expressing PDGFRA, including models of leiomyosarcoma (UZLX-STS22), malignant peripheral nerve sheath tumor (UZLX-STS39), myxofibrosarcoma (UZLX-STS59) and undifferentiated pleomorphic sarcoma (UZLX-STS84). Mice were randomly divided into four different treatment groups: (1) control, (2) doxorubicin (3 mg/kg once weekly), (3) anti-PDGFRA [olaratumab (60 mg/kg twice weekly) + mouse anti-PDGFRA antibody 1E10 (20 mg/kg twice weekly)] and (4) the combination of doxorubicin and anti-PDGFRA (same dose/schedule as in the single treatment arms). Tumor volume, histopathology and Western blotting were used to assess treatment efficacy.Anti-PDGFRA treatment as a single agent did not reduce tumor growth and did not result in significant anti-proliferative or pro-apoptotic activity. Combining doxorubicin and anti-PDGFRA did not reduce tumor burden, though a mild inhibition of proliferation was observed in UZLX-STS39 and -STS59. A pro-apoptotic effect was observed in all models except UZLX-STS22. Antitumor effects on histology were not significantly different comparing doxorubicin and the combination treatment. Moreover, anti-PDGFRA treatment, both as a single agent as well as combined with doxorubicin, did not result in inhibition of the downstream MAPK and PI3K/AKT signaling pathways.We were not able to demonstrate significant antitumor effects of anti-PDGFRA treatment in selected STS PDX models, neither alone nor in combination with doxorubicin. This is in line with the very recent results of the phase III clinical trial NCT02451943 ANNOUNCE, which did not confirm the clinical benefit of olaratumab in combination with doxorubicin over single agent doxorubicin.
37 Background: STS is a family of rare, heterogeneous tumors with > 70 subtypes. There is an urgent need for reliable preclinical models, especially for orphan subtypes of STS, given the limited treatment options. Methods: A panel of PDX models was established by s.c. implantation of fresh tumor specimens in athymic NMRI mice. Growing pieces of tumor were re-transplanted to next generations of mice. At each passage fragments were collected for histological/molecular characterization. A model was considered “established” after observing stable features for at least 2 passages. Ex-mouse tissue samples were stored, characterized by immunohistochemistry/flow cytometry and used for in vitro drug testing. Results: Between 2011-2019, 329 samples from 301 consenting patients were transplanted; 56 models are established, 16 additional models are in early passaging. Clinical information about donor and tumor (including sensitivity to standard and experimental agents) is available. The platform includes models of dedifferentiated lipo- (10 models), myxofibro- (8), leiomyo- (7), synovial (2), intimal (2), CIC-positive round cell (1), mesenchymal chondro- (1), extraskeletal osteo- (1), myxoid lipo- (1), myxoinflammatory fibroblastic (1), rhabdomyo- (2) and high-grade undifferentiated pleomorphic sarcoma (7), as well as GIST (8), MPNST (4) and epithelioid hemangioendothelioma (1). Models are well-characterized, with molecular information on copy number changes (low-coverage whole genome sequencing) and gene expression profile (RNA-Seq) available. We also constructed tissue microarrays from the xenografts which are used for target identification and model selection for preclinical studies. Xenografts are available for in vivo testing of novel agents, and results already served as a rationale for a number of prospective clinical trials. Conclusions: XenoSarc offers opportunities for studying the biology of a variety of sarcoma subtypes including ultra-rare entities and is a valuable tool for early drug screening in preparation of clinical STS trials. The platform is well maintained and continuously expanded, and available to collaborators from academia and industry.
<p>Supplementary Table S1. The outlier mRNA expression profiles of the gene tissue index (GTI) outlier analysis. The list of 2415 outlier genes in GIST is ranked by the gene tissue index.</p>
e22556 Background: Soft tissue sarcoma (STS) comprises a heterogeneous family of rare tumors of mesenchymal origin. Single-agent doxorubicin (DOX) remains the standard-of-care for advanced and inoperable STS, but response rates are < 15% and survival is generally poor. In 2016, Tap et al. reported impressive results of a phase Ib/II trial combining DOX and the platelet-derived growth factor receptor a (PDGFRA)-directed antibody olaratumab (OLA), suggesting an unprecedented survival advantage of the combination over DOX alone, without providing a mechanistic rationale for the observed activity (Lancet 2016;388:488-97). We decided to evaluate the efficacy of OLA in a panel of patient-derived STS xenografts (PDX). Methods: NMRI nu/nu mice were transplanted bilaterally with tumor tissue of models expressing PDGFRA, including PDX of leiomyosarcoma (UZLX-STS22), malignant peripheral nerve sheath tumor (STS39), myxofibrosarcoma (STS59) and undifferentiated pleomorphic sarcoma (STS84). Mice were randomly divided into 4 treatment groups: (1) control, (2) DOX (3 mg/kg once weekly), (3) anti-PDGFRA [OLA (60 mg/kg twice weekly) + mouse anti-PDGFRA antibody 1E10 (20 mg/kg twice weekly)] and (4) the combination of DOX and anti-PDGFRA (same dose/schedule as single treatment arms). Tumor volume, histopathology and Western blotting were used to assess treatment efficacy. Results: Anti-PDGFRA treatment as single agent did not reduce tumor growth and did not result in significant anti-proliferative or pro-apoptotic activity. Combining DOX and anti-PDGFRA did not reduce tumor burden, though a mild inhibition of proliferation was observed in models STS39 and STS59 and a pro-apoptotic effect was seen in all models except STS22. Antitumor effects on histology were not significantly different comparing DOX and the combination treatment. Anti-PDGFRA treatment, both as a single agent as well as with DOX, did not inhibit downstream MAPK and PI3K/AKT signaling pathways. Conclusions: In vivo findings in PDX models selected for PDGFRA expression support negative findings of the phase III trial NCT02451943 with OLA reported at this meeting.
