Introduction Oncogenic signaling in gastrointestinal stromal tumors (GIST) is sustained via PI3K/AKT pathway. We used a panel of six GIST xenograft models to assess efficacy of GDC-0941 as single agent or in combination with imatinib (IMA). Experimental design Nude mice (n=136) were grafted bilaterally with human GIST carrying divers KIT mutations. Mice were orally dosed over four weeks, grouped as follows: A) control; B) GDC-0941; C) IMA and D) GDC+IMA treatments. Xenografts re-growth after treatment discontinuation was assessed in group C and D for additional four weeks. Tumor response was assessed by volume measurements, micro-PET imaging, histopathology and immunoblotting. Moreover genomic alterations in PTEN/PI3K/AKT pathway were evaluated. Results In all models, GDC-0941 caused tumor growth stabilization, inhibiting tumor cells proliferation but did not induce apoptosis. Under GDC+IMA, profound tumor regression, superior to either treatment alone, was observed. This effect was associated with the best histologic response, a nearly complete proliferation arrest and increased apoptosis. Tumor re-growth assays confirmed superior activity of GDC+IMA over IMA; in three out of six models tumor volume remained reduced and stable even after treatment discontinuation. A positive correlation between response to GDC+IMA and PTEN loss, both on gene and protein levels, was found. Conclusion GDC+IMA has significant antitumor efficacy in GIST xenografts, inducing more substantial tumor regression, apoptosis and durable effects than IMA. Notably, after treatment withdrawal, tumor regression was sustained in tumors exposed to GDC+IMA, which was not observed under IMA. Assessment of PTEN status may represent a useful predictive biomarker for patient selection.

Purpose: KIT activity is crucial for gastrointestinal stromal tumors (GIST). Imatinib (IMA) and sunitinib (SUN) are very effective KIT-inhibitors in patients with advanced GIST but have no curative potential. We evaluated the efficacy of the novel HSP90 inhibitor IPI-493 alone, or in combination with IMA or SUN in GIST xenografts with KIT mutations.Experimental Design: Nude mice (n ¼ 98) were grafted bilaterally with human GIST carrying KIT exon 11 (GIST-PSW), KIT exon 9 (GIST-BOE), or double, KIT imatinib-sensitive exon 11 and imatinib-resistant exon 17 mutations (GIST-48). Mice were divided into six treatment groups and dosed orally for 15 days as follows: (i) control group, sterile water; (ii) IMA alone; (iii) SUN alone; (iv) IPI-493 alone; (v) IPI-493þIMA; and (vi) IPI-493þSUN.Results: Treatment with IPI-493 resulted in tumor growth stabilization, variable proliferation arrest, induction of apoptosis and necrosis, and downregulation of KIT and its signaling cascade, especially in the GIST-BOE model. Significant reduction of vessel density was observed with IPI-493 treatment, and was equal to SUN treatment in GIST-PSW and GIST-BOE xenografts. IPI-493 treatment effects were enhanced in combination with TKIs, especially with IPI-493þSUN. In our hands, IPI-493 showed dose-dependent liver damages.Conclusions: When administered as a single agent in a xenograft model, the HSP90 inhibitor IPI-493 has consistent antitumor activity and induces KIT downregulation in GISTs with heterogeneous KIT mutations. IPI-493 synergizes with TKIs that are commonly used for the treatment of advanced or IMAresistant GIST. The antitumor response of IPI-493 is particularly enhanced in combination with SUN.

Purpose: Gastrointestinal stromal tumors (GIST) are commonly treated with tyrosine kinase inhibitors (TKI). The majority of patients with advanced GIST ultimately become resistant to TKI due to acquisition of secondary KIT mutations, whereas primary resistance is mainly caused by PDGFRA p.D842V mutation. We tested the activity of avapritinib, a potent and highly selective inhibitor of mutated KIT and PDGFRA, in three patientderived xenograft (PDX) GIST models carrying different KIT mutations, with differential sensitivity to standard TKI.Experimental Design: NMRI nu/nu mice (n ¼ 93) were transplanted with human GIST xenografts with KIT exon 11þ17 (UZLX-GIST9 KIT 11þ17 ), exon 11 (UZLX-GIST3 KIT 11 ), or exon 9 (UZLX-GIST2B KIT 9 ) mutations, respectively. We compared avapritinib (10 and 30 mg/kg/once daily) versus vehicle, imatinib (50 mg/kg/bid) or regorafenib (30 mg/kg/once daily; UZLX-GIST9 KIT 11þ17 ); avapritinib (10, 30, 100 mg/kg/once daily) versus vehicle or imatinib [UZLX-GIST3 KIT11 ]; and avapritinib (10, 30, 60 mg/kg/once daily) versus vehicle, imatinib (50, 100 mg/kg/twice daily), or sunitinib (40 mg/kg/once daily; UZLX-GIST2B KIT9 ).Results: In all models, avapritinib resulted in reduction of tumor volume, significant inhibition of proliferation, and reduced KIT signaling. In two models, avapritinib led to remarkable histologic responses, increase in apoptosis, and inhibition of MAPK-phosphorylation. Avapritinib showed superior (UZLX-GIST9 KIT 11þ17 and -GIST2B KIT 9 ) or equal (UZLX-GIST3 KIT 11 ) antitumor activity to the standard dose of imatinib. In UZLX-GIST9 KIT 11þ17 , the antitumor effects of avapritinib were significantly better than with imatinib or regorafenib.Conclusions: Avapritinib has significant antitumor activity in GIST PDX models characterized by different KIT mutations and sensitivity to established TKI. These data provide strong support for the ongoing clinical trials with avapritinib in patients with GIST (NCT02508532, NCT03465722).

Introduction: The PI3K signaling pathway drives tumor cell proliferation and survival in gastrointestinal stromal tumor (GIST). We tested the in vivo efficacy of three PI3K inhibitors (PI3Ki) in patient-derived GIST xenograft models.Experimental Design: One hundred and sixty-eight nude mice were grafted with human GIST carrying diverse KIT genotypes and PTEN genomic status. Animals were dosed orally for two weeks as follows: control group (untreated); imatinib (IMA); PI3Ki (BKM120-buparlisib, BEZ235, or BYL719) or combinations of imatinib with a PI3Ki. Western blotting, histopathology, and tumor volume evolution were used for the assessment of treatment efficacy. Furthermore, tumor regrowth was evaluated for three weeks after treatment cessation.Results: PI3Ki monotherapy showed a significant antitumor effect, reflected in tumor volume reduction or stabilization, inhibitory effects on mitotic activity, and PI3K signaling inhibition. The IMAþPI3Ki combination remarkably improved the efficacy of either single-agent treatment with more pronounced tumor volume reduction and enhanced proapoptotic effects over either single agent. Response to IMAþPI3Ki was found to depend on the KIT genotype and specific model-related molecular characteristics.Conclusion: IMAþPI3Ki has significant antitumor efficacy in GIST xenografts as compared with singleagent treatment, resulting in more prominent tumor volume reduction and enhanced induction of apoptosis. Categorization of GIST based on KIT genotype and PI3K/PTEN genomic status combined with dose optimization is suggested for patient selection for clinical trials exploring such combinations. Clin Cancer Res; 20(23); 6071-82. Ó2014 AACR.

INTRODUCTION: The rarity of dedifferentiated liposarcoma (DDLPS) and the lack of experimental DDLPS models limit the development of novel therapeutic strategies. Pazopanib (PAZ) is a tyrosine kinase inhibitor that is approved for the treatment of non-adipocytic advanced soft tissue sarcoma. The activity of this agent has not yet been properly explored in preclinical liposarcoma models nor in a randomized phase Ш clinical trial in this entity. The aim of the present study was to investigate whether PAZ had antitumor activity in DDLPS models in vivo. MATERIAL AND METHODS: We established two patient-derived DDLPS xenograft models (UZLX-STS3 and UZLX-STS5) through implantation of tumor material from sarcoma patients in athymic nude NMRI mice. An animal model of the SW872 liposarcoma cell line was also used. To investigate the efficacy of PAZ in vivo, mice bearing tumors were treated for 2 weeks with sterile water, doxorubicin (1.2 mg/kg, intraperitoneally, twice per week), PAZ [40 mg/kg, orally (p.o.), twice per day], or PAZ plus doxorubicin (same schedules as for single treatments). RESULTS: Patient-derived xenografts retained the histologic and molecular features of DDLPS. PAZ significantly delayed tumor growth by decreasing proliferation and inhibited angiogenesis in all models tested. Combining the angiogenesis inhibitor with an anthracycline did not show superior efficacy. CONCLUSION: These results suggest that PAZ has potential antitumor activity in DDLPS primarily through antiangiogenic effects and therefore should be explored in clinical trials.

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.

In the majority of gastrointestinal stromal tumors (GIST), oncogenic signaling is driven by KIT mutations. Advanced GIST is treated with tyrosine kinase inhibitors (TKI) such as imatinib. Acquired resistance to TKI is mainly caused by secondary KIT mutations, but can also be attributed to a switch of KIT dependency to another receptor tyrosine kinase (RTK). We tested the efficacy of cabozantinib, a novel TKI targeting KIT, MET, AXL, and vascular endothelial growth factor receptors (VEGFR), in patient-derived xenograft (PDX) models of GIST, carrying different KIT mutations. NMRI nu/nu mice (n ¼ 52) were bilaterally transplanted with human GIST: UZLX-GIST4 (KIT exon 11 mutation, imatinib sensitive), UZLX-GIST2 (KIT exon 9, imatinib dose-dependent resistance), or UZLX-GIST9 (KIT exon 11 and 17 mutations, imatinib resistant). Mice were grouped as control (untreated), imatinib (50 mg/kg/bid), and cabozantinib (30 mg/kg/qd) and treated orally for 15 days. Cabozantinib resulted in significant tumor regression in UZLX-GIST4 and -GIST2 and delayed tumor growth in -GIST9. In all three models, cabozantinib inhibited the proliferative activity, which was completely absent in UZLX-GIST4 and significantly reduced in -GIST2 and -GIST9. Increased apoptotic activity was observed only in UZLX-GIST4. Cabozantinib inhibited the KIT signaling pathway in UZLX-GIST4 and -GIST2. In addition, compared with both control and imatinib, cabozantinib significantly reduced microvessel density in all models. In conclusion, cabozantinib showed antitumor activity in GIST PDX models through inhibition of tumor growth, proliferation, and angiogenesis, in both imatinib-sensitive and imatinib-resistant models. Mol Cancer Ther; 15(12); 2845-52. Ó2016 AACR.

Magnesium is an essential transmembrane and intracellular modulator of the electrical activity of cardiac cells. This review provides an up-to-date consideration of the cellular and clinical electrophysiological role of magnesium. This ubiquitous element seems to be important from both the theoretical and clinical point of view, because magnesium salts (MgSO4, MgCl2) administered intravenously are particularly effective in those arrhythmias in which the mechanism involves early or delayed after depolarization-induced triggered activity. The authors share the view that I.V. magnesium is the drug of choice in "torsade de pointes" ventricular tachycardia accompanying acquired long QT/QTU syndrome. It is complementary therapeutic agent in digitalis-induced tachycardias. Further studies are needed to elucidate magnesium's mode of action and efficacy in other types of clinical tachyarrhythmias.