Jacqueline Martinez

Crosstalk between KIT and FGFR3 Promotes Gastrointestinal Stromal Tumor Cell Growth and Drug Resistance

Kinase inhibitors such as imatinib have dramatically improved outcomes for patients with gastrointestinal stromal tumor (GIST), but many patients develop resistance to these treatments. Although in some patients this event corresponds with mutations in the GIST driver oncogenic kinase KIT, other patients develop resistance without KIT mutations. In this study, we address this patient subset in reporting a functional dependence of GIST on the FGF receptor FGFR3 and its crosstalk with KIT in GIST cells. Addition of the FGFR3 ligand FGF2 to GIST cells restored KIT phosphorylation during imatinib treatment, allowing sensitive cells to proliferate in the presence of the drug. FGF2 expression was increased in imatinib-resistant GIST cells, the growth of which was blocked by RNAi-mediated silencing of FGFR3. Moreover, combining KIT and FGFR3 inhibitors synergized to block the growth of imatinib-resistant cells. Signaling crosstalk between KIT and FGFR3 activated the MAPK pathway to promote resistance to imatinib. Clinically, an IHC analysis of tumor specimens from imatinib-resistant GIST patients revealed a relative increase in FGF2 levels, with a trend toward increased expression in imatinib-naïve samples consistent with possible involvement in drug resistance. Our findings provide a mechanistic rationale to evaluate existing FGFR inhibitors and multikinase inhibitors that target FGFR3 as promising strategies to improve treatment of patients with GIST with de novo or acquired resistance to imatinib.

Ponatinib overcomes FGF2-mediated resistance in CML patients without kinase domain mutations

Development of resistance to kinase inhibitors remains a clinical challenge. Kinase domain mutations are a common mechanism of resistance in chronic myeloid leukemia (CML), yet the mechanism of resistance in the absence of mutations remains unclear. We tested proteins from the bone marrow microenvironment and found that FGF2 promotes resistance to imatinib in vitro. Fibroblast growth factor 2 (FGF2) was uniquely capable of promoting growth in both short- and long-term assays through the FGF receptor 3/RAS/c-RAF/mitogen-activated protein kinase pathway. Resistance could be overcome with ponatinib, a multikinase inhibitor that targets BCR-ABL and FGF receptor. Clinically, we identified CML patients without kinase domain mutations who were resistant to multiple ABL kinase inhibitors and responded to ponatinib treatment. In comparison to CML patients with kinase domain mutations, these patients had increased FGF2 in their bone marrow when analyzed by immunohistochemistry. Moreover, FGF2 in the marrow decreased concurrently with response to ponatinib, further suggesting that FGF2-mediated resistance is interrupted by FGF receptor inhibition. These results illustrate the clinical importance of ligand-induced resistance to kinase inhibitors and support an approach of developing rational inhibitor combinations to circumvent resistance.

FGF2 from Marrow Microenvironment Promotes Resistance to FLT3 Inhibitors in Acute Myeloid Leukemia

Potent FLT3 inhibitors, such as quizartinib (AC220), have shown promise in treating acute myeloid leukemia (AML) containing FLT3 internal tandem duplication (ITD) mutations. However, responses are not durable and resistance develops within months. In this study, we outline a two-step model of resistance whereby extrinsic microenvironmental proteins FLT3 ligand (FL) and fibroblast growth factor 2 (FGF2) protect FLT3-ITD+ MOLM14 cells from AC220, providing time for subsequent accumulation of ligand-independent resistance mechanisms. FL directly attenuated AC220 inhibition of FLT3, consistent with previous reports. Conversely, FGF2 promoted resistance through activation of FGFR1 and downstream MAPK effectors; these resistant cells responded synergistically to combinatorial inhibition of FGFR1 and FLT3. Removing FL or FGF2 from ligand-dependent resistant cultures transiently restored sensitivity to AC220, but accelerated acquisition of secondary resistance via reactivation of FLT3 and RAS/MAPK signaling. FLT3-ITD AML patients treated with AC220 developed increased FGF2 expression in marrow stromal cells, which peaked prior to overt clinical relapse and detection of resistance mutations. Overall, these results support a strategy of early combination therapy to target early survival signals from the bone marrow microenvironment, in particular FGF2, to improve the depth of response in FLT3-ITD AML. Cancer Res; 76(22); 6471-82. ©2016 AACR.

Functional genomic landscape of acute myeloid leukaemia.

The implementation of targeted therapies for acute myeloid leukaemia (AML) has been challenging because of the complex mutational patterns within and across patients as well as a dearth of pharmacologic agents for most mutational events. Here we report initial findings from the Beat AML programme on a cohort of 672 tumour specimens collected from 562 patients. We assessed these specimens using whole-exome sequencing, RNA sequencing and analyses of ex vivo drug sensitivity. Our data reveal mutational events that have not previously been detected in AML. We show that the response to drugs is associated with mutational status, including instances of drug sensitivity that are specific to combinatorial mutational events. Integration with RNA sequencing also revealed gene expression signatures, which predict a role for specific gene networks in the drug response. Collectively, we have generated a dataset—accessible through the Beat AML data viewer (Vizome)—that can be leveraged to address clinical, genomic, transcriptomic and functional analyses of the biology of AML.Analyses of samples from patients with acute myeloid leukaemia reveal that drug response is associated with mutational status and gene expression; the generated dataset provides a basis for future clinical and functional studies of this disease.

Kinase profiling of liposarcomas using RNAi and drug screening assays identified druggable targets

BackgroundLiposarcoma, the most common soft tissue tumor, is understudied cancer, and limited progress has been made in the treatment of metastatic disease. The Achilles heel of cancer often is their kinases that are excellent therapeutic targets. However, very limited knowledge exists of therapeutic critical kinase targets in liposarcoma that could be potentially used in disease management.MethodsLarge RNAi and small-molecule tyrosine kinase inhibitor screens were performed against the proliferative capacity of liposarcoma cell lines of different subtypes. Each small molecule inhibitor was either FDA approved or in a clinical trial.ResultsScreening assays identified several previously unrecognized targets including PTK2 and KIT in liposarcoma. We also observed that ponatinib, multi-targeted tyrosine kinase inhibitor, was the most effective drug with anti-growth effects against all cell lines. In vitro assays showed that ponatinib inhibited the clonogenic proliferation of liposarcoma, and this anti-growth effect was associated with apoptosis and cell cycle arrest at the G0/G1 phase as well as a decrease in the KIT signaling pathway. In addition, ponatinib inhibited in vivo growth of liposarcoma in a xenograft model.ConclusionsTwo large-scale kinase screenings identified novel liposarcoma targets and a FDA-approved inhibitor, ponatinib with clear anti-liposarcoma activity highlighting its potential therapy for treatment of this deadly tumor.

Abstract 1631: FGF2 activation of FGFR1 in head and neck squamous cell carcinoma is associated with more invasive disease and can be attenuated by FGFR inhibition

Introduction. Head and neck squamous cell carcinomas (HNSCCs) account for nearly 600,000 deaths worldwide annually and have limited treatment options. Approximately 20% of HNSCCs harbor amplifications of fibroblast growth factor receptor 1 (FGFR1) on chromosome 8p, however FGFR1 amplification by itself does not predict clinical response to FGFR inhibitors. We hypothesized that FGF2, or basic FGF, ligand expression is a better marker of FGFR activation and predictor of response to FGFR inhibitors. Results. A tissue micro array (TMA) of HNSCC patient biopsies was stained and quantitated for FGF2 expression by Aperio ImageScope software. FGF2 was significantly increased in recurrent tissue samples (p = 0.04). We examined a number of immortalized HNSCC cell lines and found that overexpression of both FGF2 and FGFR1 predicted response to the selective FGFR inhibitor PD173074. FGFR inhibition did not cause apoptosis, but rather induced a G0/G1 arrest and growth inhibition. FGFR inhibition also induced a change in cell morphology, with a significant increase in cell size and adherence. The expression of epithelial-to‐mesenchymal transition (EMT) proteins was examined and FGF2-FGFR1 activation was associated with a more mesenchymal phenotype. Accordingly, FGFR inhibition reversed invasiveness as measured using the Incucyte WoundMaker scratch assay, suggesting that HNSCCs with FGF2-FGFR1 activation have more metastatic potential. Invasiveness of these cells in vivo was confirmed using orthotopic injection into the buccal pad of NSG mice. Once primary tumors reached 0.8 cm in size, mice were sacrificed and buccal mucosa, lung, liver, and neck tissue were examined post-mortem. All of the injected animals developed local invasion, and distant metastases in the lungs. 5/7 mice also had metastases in the liver and this model is being used to test the ability of FGFR inhibition to prevent metastasis. The mechanism of autocrine FGF2-FGFR1 activation was further explored and FGF2 was found to be secreted in association with extracellular vesicles (ECVs). Interestingly, inhibition of FGFR reduced secretion of ECVs and FGF2, providing a novel approach to target autocrine and paracrine FGFR1 activation within the tumor. We further tested a number of small molecule inhibitors in combination with PD173074 to look for synergistic combinations of kinase inhibitors and found significant synergy between EGFR and FGFR inhibitors suggesting this combination may be most effective in patients with HNSCC. Conclusions. Increased FGF2 in HNSCC patient samples is correlated with recurrent disease. FGF2-FGFR1 activation increases invasiveness through activation of EMT genes both in vitro, and in an orthotopic model. Inhibition of FGF2-FGFR1 reversed the invasive phenotype in vitro and may be an effective therapeutic strategy to reduce metastases in HNSCC patients. Citation Format: Isabel A. English, Jacqueline Martinez, Edward El Rassi, Mark Schmidt, Ellen Langer, Sophia Bornstein, John Gleysteen, Melissa Wong, Brian Druker, Elie Traer. FGF2 activation of FGFR1 in head and neck squamous cell carcinoma is associated with more invasive disease and can be attenuated by FGFR inhibition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1631.

Abstract 984: FGF2 from the bone marrow promotes resistance to FLT3 inhibitors in AML

Introduction: Activating mutations in the FLT3 kinase are present in ∼25% of newly diagnosed acute myeloid leukemia (FLT3+ AML) patients and confer a poor prognosis. Treatment with FLT3 inhibitors is initially effective, but residual leukemia cells survive in the bone marrow microenvironment and clinical resistance develops within months. We tested proteins from the bone marrow microenvironment for their ability to protect FLT3-ITD+ MOLM14 cells from AC220, and found that FLT3 ligand (FL) and fibroblast growth factor 2 (FGF2) were among the most protective. Results: Consistent with previous reports, FL restored downstream FLT3 phosphorylation and signaling in the presence of the FLT3 inhibitor quizartinib (AC220). In contrast, FGF2 activated FGFR1 and the MAPK pathway, circumventing the effects of AC220 on MOLM14 cells and increasing cell survival. To model the effect of prolonged contact with the bone marrow microenvironment, MOLM14 cells were cultured continuously in FGF2 and AC220. Under these conditions, 4/4 cultures developed AC220 resistance and resumed exponential growth after 7 weeks. Development of FGF2-mediated resistance was accelerated compared to MOLM14 cultured continuously in AC220 alone (only 2/4 resistant cultures,12 weeks). Long-term resistant cultures grown in FGF2 were protected from AC220 across a wide range of concentrations, but concurrent treatment with the FGFR inhibitor PD173074 synergistically overcame FGF2-mediated protection. Serial bone marrow biopsies of patients on the AC220 phase II clinical trial were analyzed by immunohistochemistry. Quantification of FGF2 revealed a significant increase in AC220 during treatment (34% to 51% after one month, p Conclusions: FGF2 ligand-induced activation of the FGFR1/MAPK pathway leads to protection from AC220 in vitro and eventual development of resistance. FGF2-mediated resistance can be overcome by concurrent FLT3 and FGFR inhibition. Consistent with our in vitro model, patients treated with AC220 had increasing FGF2 in their bone marrow, which peaked prior to resistance and relapse, suggesting that combined FLT3 and FGFR inhibitors may improve the durability of response. Our results provide an approach to develop rational inhibitor combinations that cirucumvent ligand-mediated pathways of resistance. Citation Format: Jacqueline Martinez, Elie Traer, Nathalie Javidi-Sharifi, Anupriya Agarwal, Jennifer Dunlap, Isabel English, Tibor Kovacsovics, Jeffrey Tyner, Melissa Wong, Brian Druker. FGF2 from the bone marrow promotes resistance to FLT3 inhibitors in AML. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 984. doi:10.1158/1538-7445.AM2015-984