Soft-tissue sarcomas (STS) represent a heterogeneous group of rare, malignant tumors of mesenchymal origin. Reliable in vivo 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 in vivo preclinical drug testing as illustrated by a number of completed and ongoing laboratory studies.

The majority of patients with gastrointestinal stromal tumors (GIST) eventually become resistant with time due to secondary mutations in the driver receptor tyrosine kinase. Novel treatments that do not target these receptors may therefore be preferable. For the first time, we evaluated a tubulin inhibitor, plocabulin, in patient-derived xenograft (PDX) models of GIST, a disease generally considered to be resistant to cytotoxic agents. Three PDX models of GIST with different KIT genotype were generated by implanting tumor fragments from patients directly into nude mice. We then used these well characterized models with distinct sensitivity to imatinib to evaluate the efficacy of the novel tubulin inhibitor. The efficacy of the drug was assessed by volumetric analysis of the tumors, histopathology, immunohistochemistry and Western blotting. Plocabulin treatment led to extensive necrosis in all three models and significant tumor shrinkage in two models. This histological response can be explained by the drug's vascular-disruptive properties, which resulted in a shutdown of tumor vasculature, reflected by a decreased total vascular area in the tumor tissue. Our results demonstrated the in vivo efficacy of the novel tubulin inhibitor plocabulin in PDX models of GIST and challenge the established view that GIST are resistant to cytotoxic agents in general and to tubulin inhibitors in particular. Our findings provide a convincing rationale for early clinical exploration of plocabulin in GIST and warrant further exploration of this class of drugs in the management of this common sarcoma subtype.

Objective: Soft tissue sarcomas (STS) constitute a heterogeneous group of rare, malignant tumors arising in mesenchymal tissue. Doxorubicin (DOX)-based chemotherapy has been the standard of care for patients with advanced and metastatic STS, despite providing low response rates and poor disease control in this disease. Even for patients who respond to treatment, the outcome of advanced and metastatic STS is poor. In light of this, there is a clear need for more effective and novel therapeutic compounds for STS. In the current study, we explored the activity of plocabulin (PLO; PM060184, PharmaMar), a novel cytotoxic tubulin-dynamics modifier, in patient-derived xenograft (PDX) models of some common and some rare histologic subtypes of STS. Methods: Female NMRI nu/nu mice (n=80) were transplanted bilaterally with human STS xenografts: UZLX-STS134CRS (CIC-rearranged sarcoma), UZLX-STS124DDLPS (dedifferentiated liposarcoma), UZLX-STS22_2FLMS (leiomyosarcoma) and UZLX-STS122FIS (intimal sarcoma). Xenografted animals were randomly assigned to three treatment groups: 1) vehicle (20% hydroxypropyl β-cyclodextrin) 6.4 ml/kg intravenously (i.v.) once weekly (QW), 2) DOX 3.0 mg/kg i.v. QW, or 3) PLO 16 mg/kg i.v. QW. All treatments lasted 22 days. Antitumor activity was assessed by tumor volume analysis, histopathology and Western blotting. Mitotic count, phospho-histone H3 and Ki-67 were analyzed for proliferative activity. Apoptotic count, and cleaved poly-(ADP-ribose)-polymerase were analyzed for apoptotic activity. CD31 immunostains were used to evaluate the tumor vasculature. The Kruskal-Wallis test with Dunn's multiple comparisons (DMC) test was used to compare non-parametric variables between groups. Statistical significance was defined as p <0.05. Results: PLO treatment resulted in tumor shrinkage in UZLX-STS134CRS (to 40% of baseline volume) and UZLX-STS22_2FLMS (to 27%), and tumor volume stabilization in UZLX-STS124DDLPS and UZLX-STS122FIS. Vehicle-treated tumors of UZLX-STS134CRS, UZLX-STS22_2FLMS and UZLX-STS124DDLPS reached 363%, 287% and 261% of baseline volume, respectively. DOX did not affect tumor volume. All DOX-treated mice of UZLX-STS122FIS were lost before the end of the experiment: one mouse was sacrificed on day 16 due to body weight loss, the remaining five were found dead on day 19. Despite this, relative tumor volumes already differed significantly between the vehicle-PLO and DOX-PLO groups on day 16 for this model (p<0.001 and p=0.002, respectively, DMC). PLO-treated tumors of UZLX-STS134CRS and UZLX-STS22_2FLMS were necrotic and degenerated to such an extent that histological analysis could not be performed in full. In the PLO-treated tumors of UZLX-STS122FIS, we demonstrated a significant decrease in the total vascular area, consistent with the drug's vascular disrupting capacity. No effects on proliferation or apoptosis were observed. The experimental drug was well tolerated throughout the experiment at the administered dose. Conclusion: PLO is a novel anti-tubulin agent showing potent antitumor activity in a variety of PDX modes of STS. The drug induces cytotoxicity mainly through necrosis and is more active than DOX. This study provides strong arguments to study PLO further in STS and to explore the compound in clinical trials involving mesenchymal malignancies. Citation Format: Yannick Wang, Agnieszka Wozniak, Jasmien Cornillie, Che-Jui Lee, María José Guillén, Pablo Avilés, Maria Debiec-Rychter, Raf Sciot, Patrick Schöffski. Plocabulin, a novel tubulin inhibitor, has antitumor activity in various patient-derived xenograft models of soft tissue sarcoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1676.

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.

<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>