Search

Antibodies targeting insulin-like growth factor 1 receptor (IGF-1R) induce objective responses in only 5% to 15% of children with sarcoma. Understanding the mechanisms of resistance may identify combination therapies that optimize efficacy of IGF-1R–targeted antibodies. Sensitivity to the IGF-1R–targeting antibody TZ-1 was determined in rhabdomyosarcoma and Ewing sarcoma cell lines. Acquired resistance to TZ-1 was developed and characterized in sensitive Rh41 cells. The BRD4 inhibitor, JQ1, was evaluated as an agent to prevent acquired TZ-1 resistance in Rh41 cells. The phosphorylation status of receptor tyrosine kinases (RTK) was assessed. Sensitivity to TZ-1 in vivo was determined in Rh41 parental and TZ-1–resistant xenografts. Of 20 sarcoma cell lines, only Rh41 was sensitive to TZ-1. Cells intrinsically resistant to TZ-1 expressed multiple (>10) activated RTKs or a relatively less complex set of activated RTKs (∼5). TZ-1 decreased the phosphorylation of IGF-1R but had little effect on other phosphorylated RTKs in all resistant lines. TZ-1 rapidly induced activation of RTKs in Rh41 that was partially abrogated by knockdown of SOX18 and JQ1. Rh41/TZ-1 cells selected for acquired resistance to TZ-1 constitutively expressed multiple activated RTKs. TZ-1 treatment caused complete regressions in Rh41 xenografts and was significantly less effective against the Rh41/TZ-1 xenograft. Intrinsic resistance is a consequence of redundant signaling in pediatric sarcoma cell lines. Acquired resistance in Rh41 cells is associated with rapid induction of multiple RTKs, indicating a dynamic response to IGF-1R blockade and rapid development of resistance. The TZ-1 antibody had greater antitumor activity against Rh41 xenografts compared with other IGF-1R–targeted antibodies tested against this model.

Stimulating the innate immune system has been explored as a therapeutic option for the treatment of gliomas. Inactivating mutations inATRX, defining molecular alterations inIDH-mutant astrocytomas, have been implicated in dysfunctional immune signaling. However, little is known about the interplay between ATRX loss andIDHmutation on innate immunity. To explore this, we generatedATRXknockout glioma models in the presence and absence of theIDH1R132Hmutation. ATRX-deficient glioma cells were sensitive to dsRNA-based innate immune agonism and exhibited impaired lethality and increased T-cell infiltrationin vivo. However, the presence ofIDH1R132Hdampened baseline expression of key innate immune genes and cytokines in a manner restored by genetic and pharmacological IDH1R132Hinhibition. IDH1R132Hco-expression did not interfere with theATRXKO-mediated sensitivity to dsRNA. Thus, ATRX loss primes cells for recognition of dsRNA, while IDH1R132Hreversibly masks this priming. This work reveals innate immunity as a therapeutic vulnerability of astrocytoma.

Supplemental data

Antibodies targeting insulin-like growth factor 1 receptor (IGF-1R) induce objective responses in only 5% to 15% of children with sarcoma. Understanding the mechanisms of resistance may identify combination therapies that optimize efficacy of IGF-1R–targeted antibodies. Sensitivity to the IGF-1R–targeting antibody TZ-1 was determined in rhabdomyosarcoma and Ewing sarcoma cell lines. Acquired resistance to TZ-1 was developed and characterized in sensitive Rh41 cells. The BRD4 inhibitor, JQ1, was evaluated as an agent to prevent acquired TZ-1 resistance in Rh41 cells. The phosphorylation status of receptor tyrosine kinases (RTK) was assessed. Sensitivity to TZ-1 in vivo was determined in Rh41 parental and TZ-1–resistant xenografts. Of 20 sarcoma cell lines, only Rh41 was sensitive to TZ-1. Cells intrinsically resistant to TZ-1 expressed multiple (>10) activated RTKs or a relatively less complex set of activated RTKs (∼5). TZ-1 decreased the phosphorylation of IGF-1R but had little effect on other phosphorylated RTKs in all resistant lines. TZ-1 rapidly induced activation of RTKs in Rh41 that was partially abrogated by knockdown of SOX18 and JQ1. Rh41/TZ-1 cells selected for acquired resistance to TZ-1 constitutively expressed multiple activated RTKs. TZ-1 treatment caused complete regressions in Rh41 xenografts and was significantly less effective against the Rh41/TZ-1 xenograft. Intrinsic resistance is a consequence of redundant signaling in pediatric sarcoma cell lines. Acquired resistance in Rh41 cells is associated with rapid induction of multiple RTKs, indicating a dynamic response to IGF-1R blockade and rapid development of resistance. The TZ-1 antibody had greater antitumor activity against Rh41 xenografts compared with other IGF-1R–targeted antibodies tested against this model.

Purpose: To investigate the antitumor activity of a mitochondrial-localized HSP90 inhibitor, Gamitrinib, in multiple glioma models, and to elucidate the antitumor mechanisms of Gamitrinib in gliomas. Experimental Design: A broad panel of primary and temozolomide (TMZ)-resistant human glioma cell lines were screened by cell viability assays, flow cytometry, and crystal violet assays to investigate the therapeutic efficacy of Gamitrinib. Seahorse assays were used to measure the mitochondrial respiration of glioma cells. Integrated analyses of RNA sequencing (RNAseq) and reverse phase protein array (RPPA) data were performed to reveal the potential antitumor mechanisms of Gamitrinib. Neurospheres, patient-derived organoids (PDO), cell line–derived xenografts (CDX), and patient-derived xenografts (PDX) models were generated to further evaluate the therapeutic efficacy of Gamitrinib. Results: Gamitrinib inhibited cell proliferation and induced cell apoptosis and death in 17 primary glioma cell lines, 6 TMZ-resistant glioma cell lines, 4 neurospheres, and 3 PDOs. Importantly, Gamitrinib significantly delayed the tumor growth and improved survival of mice in both CDX and PDX models in which tumors were either subcutaneously or intracranially implanted. Integrated computational analyses of RNAseq and RPPA data revealed that Gamitrinib exhibited its antitumor activity via (i) suppressing mitochondrial biogenesis, OXPHOS, and cell-cycle progression and (ii) activating the energy-sensing AMP-activated kinase, DNA damage, and stress response. Conclusions: These preclinical findings established the therapeutic role of Gamitrinib in gliomas and revealed the inhibition of mitochondrial biogenesis and tumor bioenergetics as the primary antitumor mechanisms in gliomas.

Supplementary Figure 1. (A-B) Successful labeling of CellTrace Violet for M059K and H4 cells. M059K and H4 cells were labeled with a cell membrane dye CellTrace Violet and verified the success of labeling by FACS. (C-D) Cell viability of M059K and H4 following THIO treatment. M059K and H4 cells were treated with control medium or THIO at 5µM and then determined the cell viability percentage via detecting PSVue643 and PI by FACS. (E-F) Western blot results of time-course and dose-titration experiments in M059K and H4. For the time-course experiment, cells were treated with THIO at 5µM and proteins were tested at 0, 24, 48 and 72 hours. For dose-titration experiments, cells were treated with serious doses of THIO for 72 hours. TMZ functions as control. Actin serves as a loading control. Supplementary Figure 2. (A) Crystal violet staining images for acquired TMZ-resistant (TR) cell lines after treatment. (B) The heatmap of quantification results of the crystal violet images of TR cells. % relative to control. (C) Senescence assay for DBTRG-05MG, M059K and H4 cells following THIO treatment at 1 µM for 7 days, and then fixed and stained using Senescence β-Galactosidase Staining Kit and taken images by microscope. (D-F) Quantification results of senescence assay for DBTRG-05MG, M059K and H4 cells. 7 fields were counted for each group. (G-J) Neurosphere growth curves for T98G, U87MG, 13.0302 and TS-603 treated with or without THIO at 5 µM.

Supplementary Tables

Supplementary Figure Legends

Purpose:To investigate the therapeutic role of a novel telomere-directed inhibitor, 6-thio-2′-deoxyguanosine (THIO) in gliomas both in vitro and in vivo.Experimental Design:A panel of human and mouse glioma cell lines was used to test therapeutic efficacy of THIO using cell viability assays, flow cytometric analyses, and immunofluorescence. Integrated analyses of RNA sequencing and reverse-phase protein array data revealed the potential antitumor mechanisms of THIO. Four patient-derived xenografts (PDX), two patient-derived organoids (PDO), and two xenografts of human glioma cell lines were used to further investigate the therapeutic efficacy of THIO.Results:THIO was effective in the majority of human and mouse glioma cell lines with no obvious toxicity against normal astrocytes. THIO as a monotherapy demonstrated efficacy in three glioma cell lines that had acquired resistance to temozolomide. In addition, THIO showed efficacy in four human glioma cell lines grown as neurospheres by inducing apoptotic cell death. Mechanistically, THIO induced telomeric DNA damage not only in glioma cell lines but also in PDX tumor specimens. Integrated computational analyses of transcriptomic and proteomic data indicated that THIO significantly inhibited cell invasion, stem cell, and proliferation pathways while triggering DNA damage and apoptosis. Importantly, THIO significantly decreased tumor proliferation in two PDO models and reduced the tumor size of a glioblastoma xenograft and a PDX model.Conclusions:The current study established the therapeutic role of THIO in primary and recurrent gliomas and revealed the acute induction of telomeric DNA damage as a primary antitumor mechanism of THIO in gliomas.

Supplementary Figure 1. (A-B) Successful labeling of CellTrace Violet for M059K and H4 cells. M059K and H4 cells were labeled with a cell membrane dye CellTrace Violet and verified the success of labeling by FACS. (C-D) Cell viability of M059K and H4 following THIO treatment. M059K and H4 cells were treated with control medium or THIO at 5µM and then determined the cell viability percentage via detecting PSVue643 and PI by FACS. (E-F) Western blot results of time-course and dose-titration experiments in M059K and H4. For the time-course experiment, cells were treated with THIO at 5µM and proteins were tested at 0, 24, 48 and 72 hours. For dose-titration experiments, cells were treated with serious doses of THIO for 72 hours. TMZ functions as control. Actin serves as a loading control.

Purpose:To investigate the antitumor activity of a mitochondrial-localized HSP90 inhibitor, Gamitrinib, in multiple glioma models, and to elucidate the antitumor mechanisms of Gamitrinib in gliomas.Experimental Design:A broad panel of primary and temozolomide (TMZ)-resistant human glioma cell lines were screened by cell viability assays, flow cytometry, and crystal violet assays to investigate the therapeutic efficacy of Gamitrinib. Seahorse assays were used to measure the mitochondrial respiration of glioma cells. Integrated analyses of RNA sequencing (RNAseq) and reverse phase protein array (RPPA) data were performed to reveal the potential antitumor mechanisms of Gamitrinib. Neurospheres, patient-derived organoids (PDO), cell line–derived xenografts (CDX), and patient-derived xenografts (PDX) models were generated to further evaluate the therapeutic efficacy of Gamitrinib.Results:Gamitrinib inhibited cell proliferation and induced cell apoptosis and death in 17 primary glioma cell lines, 6 TMZ-resistant glioma cell lines, 4 neurospheres, and 3 PDOs. Importantly, Gamitrinib significantly delayed the tumor growth and improved survival of mice in both CDX and PDX models in which tumors were either subcutaneously or intracranially implanted. Integrated computational analyses of RNAseq and RPPA data revealed that Gamitrinib exhibited its antitumor activity via (i) suppressing mitochondrial biogenesis, OXPHOS, and cell-cycle progression and (ii) activating the energy-sensing AMP-activated kinase, DNA damage, and stress response.Conclusions:These preclinical findings established the therapeutic role of Gamitrinib in gliomas and revealed the inhibition of mitochondrial biogenesis and tumor bioenergetics as the primary antitumor mechanisms in gliomas.

Supplementary Figure 3. (A) Relative initial telomere length of 17 glioma cell lines and NHA. (B) Correlation of IC50s of THIO and initial telomere length in 17 glioma cell lines. (C) Baseline relative expression of hTERT in 17 glioma cell lines and NHA. (D) RNAseq data of hTERT expression in 11 glioma cell lines obtained from CCLE. (E) Correlation of IC50s of THIO and baseline expression of hTERT in 17 glioma cell lines. (F) Correlation of IC50s of THIO and baseline expression of hTERT in 11 glioma cell lines from CCLE. (G) The heatmap of the enrichment scores of 5 telomere/telomerase-related gene signatures for 65 glioma cell lines from CCLE. (H-I) Relative telomere length of M059K and DBTRG-05MG cells following THIO treatment at 2.5 µM for 5 days. (J-K) Telomerase activity of M059K and DBTRG-05MG cells following THIO treatment at 5 µM for 72 hours. (L) Baseline telomerase activity of 10 glioma cell lines, including 5 cell lines that more sensitive to THIO and 5 cell lines that more resistant to THIO. (M) Correlation of baseline telomerase activity and cell viability (%) following THIO treatment. (N) Quantification of western blot of γH2AX expression in 8 glioma cell lines treated with THIO for 72 hours.

Supplementary Data from Antitumor Activity of a Mitochondrial-Targeted HSP90 Inhibitor in Gliomas

Supplementary Figure 5. (A-C) The heatmap of proteins changed by THIO in M059K, LN229 and U87MG cells from RPPA data. (D-F) Western blot was performed to confirm the change of these proteins in H4 (more sensitive to THIO) (D), U87MG (less sensitive to THIO) (E), and U251MG (more resistant to THIO) (F) after treatment with THIO at 5 µM. Actin serves as a loading control. (G) Heatmap of pathways regulated by THIO in M059K, LN229 and U87MG cells.

Supplementary Figure 4. (A-D) The heatmap of significantly expressed gene in M059K, H4, D2224MG and DBTRG-05MG cells treated with or without THIO for 72 hours. |Log2 FC|>2.5 and p

Supplementary Figure 6. (A) Creation of primary patient-derived glioblastoma organoids. (B) Quantification of tumor weight of U87MG xenograft model. (C) The curve of body weight of mice of U87MG xenograft model during THIO treatment. (D) Quantification of tumor weight of GBM PDX model. (E) The curve of body weight of mice of GBM PDX model during THIO treatment. (F) The curve of body weight of mice of U251MG xenograft model during THIO treatment.

Supplementary Figure from Antitumor Activity of a Mitochondrial-Targeted HSP90 Inhibitor in Gliomas

Purpose: To investigate the therapeutic role of a novel telomere-directed inhibitor, 6-thio-2′-deoxyguanosine (THIO) in gliomas both in vitro and in vivo. Experimental Design: A panel of human and mouse glioma cell lines was used to test therapeutic efficacy of THIO using cell viability assays, flow cytometric analyses, and immunofluorescence. Integrated analyses of RNA sequencing and reverse-phase protein array data revealed the potential antitumor mechanisms of THIO. Four patient-derived xenografts (PDX), two patient-derived organoids (PDO), and two xenografts of human glioma cell lines were used to further investigate the therapeutic efficacy of THIO. Results: THIO was effective in the majority of human and mouse glioma cell lines with no obvious toxicity against normal astrocytes. THIO as a monotherapy demonstrated efficacy in three glioma cell lines that had acquired resistance to temozolomide. In addition, THIO showed efficacy in four human glioma cell lines grown as neurospheres by inducing apoptotic cell death. Mechanistically, THIO induced telomeric DNA damage not only in glioma cell lines but also in PDX tumor specimens. Integrated computational analyses of transcriptomic and proteomic data indicated that THIO significantly inhibited cell invasion, stem cell, and proliferation pathways while triggering DNA damage and apoptosis. Importantly, THIO significantly decreased tumor proliferation in two PDO models and reduced the tumor size of a glioblastoma xenograft and a PDX model. Conclusions: The current study established the therapeutic role of THIO in primary and recurrent gliomas and revealed the acute induction of telomeric DNA damage as a primary antitumor mechanism of THIO in gliomas.

Innate-based immunotherapies are becoming increasingly important for treating brain tumor patients. About 50% of WHO grade II and III gliomas carry mutations in IDH1 and ATRX genes. Mutant IDH1 results in the production of 2-hydroxyglutarate, an oncometabolite that promotes global metabolic and epigenetic alterations. ATRX is a SWI-SNF chromatin remodeling protein that is involved in cell cycle regulation and maintenance of genomic stability. Both IDH1 and ATRX mutations have been implicated in dysfunctional immune signaling in cancer cells. However, the interplay between these mutations in mediating innate immune responses has not been investigated in gliomas. We have derived human and mouse glioma cell lines carrying mutations in IDH1 (IDH1R132H) and/or ATRX, which we then used to generate both immune competent and nude mice models. Treating the ATRX knockout (KO) cell lines with dsRNA-based innate stimuli led to an early induction in phospho-IRF3, and late induction in phospho-STAT1 and ISG15, suggesting that ATRX deletion may enable a potent activation of type I interferon production and sensitize glioma cells to dsRNA-based innate stimuli. Our syngeneic murine glioma models confirm a survival advantage for mice carrying ATRX-KO tumors. These tumors also exhibit enhanced infiltration of T-cells and expression of activated macrophage markers. On the other hand, presence of IDH1R132H led to a suppression in baseline expression of key innate immune players, which could be rescued by the mutant IDH1 inhibitor, BAY-1436032. Cells harboring IDH1R132H and ATRX-KO retained sensitivity to dsRNA indicating that IDH1R132H does not dampen the ATRX KO-mediated sensitivity to dsRNA. Our models are under evaluation with a combination of BAY-1436032 and clinically relevant dsRNA-based innate therapies. Our data indicates the presence of an interplay between IDH1 and ATRX mutations that may regulate innate signaling in gliomas. Understanding the mechanisms governing this interplay may aid in designing therapies that exploit this interplay.

STING (Stimulator of interferon genes) is an initiator of endogenous antitumor immunity. Loss of STING expression has been observed in various cancer types. Here we describe a mechanism of STING suppression that is common to brain tumors, occurring through regional promoter hypermethylation (RPH) near its transcriptional start site. The RPH-mediated suppression of STING expression is selective to normal brain and neuroectoderm-derived tumors, but not present in most other tumor types and cells in the brain tumor microenvironment. A pan-cancer comparison revealed that STING RPH levels in tumors correlate with the respective tissue of origin, including tumors metastasizing to the brain. We demonstrate that STING RPH suppression in glioma cells may be reversed by treatment with decitabine, a DNA methyltransferase inhibitor that is used in the treatment of hematologic malignancies. Collectively, our results suggest that the epigenetic silencing of STING occurs early in brain development and may provide an immunosuppressive context for the genesis of brain tumors. Furthermore, our findings that STING suppression in brain tumor cells can be reversed by epigenetic modulation have significant therapeutic implications for the treatment of glioblastoma and potentially other STING-silenced, immunologically-cold cancers.

BACKGROUND Innate based immunotherapies are becoming increasingly important for treating brain tumor patients. Gliomas carry recurrent mutations in regulatory genes that control innate immune signaling responses. About 71% of adult WHO grade II and III gliomas and 57% of secondary glioblastomas also carry a loss-of-function mutation in the ATRX gene. ATRX is a SWI-SNF chromatin remodeling protein that has major roles in processes such as cell cycle regulation and maintenance of genomic stability. Recent studies have implicated ATRX in dysfunctional innate immune signaling in cancer cells. However, the role of ATRX in mediating innate immune responses has not been investigated in gliomas. METHODS AND RESULTS Human and mouse glioma cell lines from a variety of genetic contexts have been examined including models which carry IDH/ATRX mutations, IDH 1p-/19q- and ATRX -/- status. Additionally, using Crispr-Cas9 technology and cloning cell lines with ATRX deletions, we have derived a series of immune competent and nude mice models. Treating these cell lines with double-stranded RNA based innate stimuli led to an enhanced early induction in phospho-interferon regulatory factor 3 (IRF3) and late induction in phospho-STAT1 in the ATRX knockout (KO) cell lines. A differential increase in interferon-stimulated gene 15 (ISG15) release was also noted in the ATRX KO cell lines, further suggesting that ATRX deletion may enable a potent activation of type I interferon production. A combination of patient-derived glioma cell lines in xenograft models and syngeneic murine glioma models derived from ATRX KO cell lines and controls confirm a survival advantage in both immuno-competent mice and xenografts. Our models are under evaluation with PVSRIPO and other innate based RNA therapies. CONCLUSION Our data suggests that ATRX mutations may confer sensitivity to RNA-based innate immune signaling agonists in gliomas. This potential vulnerability can be targeted in future therapies.

BACKGROUND Atypical teratoid/rhabdoid tumors (AT/RT) are highly aggressive brain tumors affecting early childhood and are characterized by bi-allelic inactivation of the SMARCB1 gene. Though patients benefit from multimodal therapy, there is no improvement in overall survival necessitating exploration of alternative approaches including innate-based immune therapy and epigenetic therapy, which have shown promise in treating adult brain tumors and other cancers. Though reconstitution of SMARCB1 in SMARCB1-deficient cells leads to activation of interferon-stimulated genes, the role of innate immune signaling has not been investigated in AT/RTs. METHODS Our data from a panel of AT/RT cell lines indicates loss of expression of key innate signaling components, like RIG-I, MDA-5, cGAS and STING that are required for sensing extracellular dsRNA and dsDNA. These cell lines also do not respond to dsDNA-based or dsRNA-based innate agonists. However, co-treatment of the BT-16 cell line with two epigenetic drugs, panobinostat and 5-azacytidine leads to re-expression of STING and RIG-I. Panobinostat/5-azacytidine co-treatment followed by either genomic DNA (dsDNA agonist) or poly(I:C) (dsRNA agonist) treatment results in induction of innate responses, measured by STAT1 phosphorylation and production of ISG-15 and IFIT-1. CONCLUSION Our data suggests that AT/RT cell lines are unresponsive to innate agonists possibly due to the loss of expression of key innate immune components. However, these pathways can be reactivated by epigenetic drugs and further potentiated by dsDNA/dsRNA-based innate agonists. Combined epigenetic reprogramming and innate pathway stimulation may serve as a potential therapy option for treating AT/RT.

The Stimulator of interferon genes (STING) protein is a critical component of the innate immune response to pathogenic and cytosolic self DNA. The importance of STING signalling has recently been demonstrated in a number of tumor types, including glioblastoma (GBM), and its activation through STING agonism is a promising antitumor therapeutic avenue. Recent studies have shown a loss of STING expression in cancer and an overall dysregulation of the CGAS/STING pathway. A potential mechanism of STING silencing is the methylation of its promoter. Using bulk methylation array data from patient samples, we explore epigenetic control of the TMEM173 gene that encodes STING. We find that the STING promoter is highly methylated in glioblastoma and that STING RNA expression is correspondingly low. Methylation data from normal brain and non-cancer cerebral diseases reveal a consistent pattern of STING promoter hypermethylation in these diverse states. The degree of bulk STING methylation in GBM samples inversely correlates with tumor purity and markers of immune infiltration. Single-cell transcriptome sequencing reveals that STING is expressed specifically in immune cells and endothelial cells, but not glioma cells. Collectively these results suggest that STING signalling is disrupted in GBM, that STING is epigenetically silenced by DNA methylation in the tumor, and that STING expression in bulk GBM tumor samples arises from infiltrating immune cells in the tumor microenvironment. Therapeutic approaches stimulating the innate STING signalling pathway are therefore likely to be effective on infiltrating immune cells rather than tumor cells themselves. This work motivates further study into mechanisms of STING activation in the broader GBM tumor microenvironment.

Background STAT3 is a transcription factor involved in cytokine and receptor kinase signal transduction that is aberrantly activated in a variety of sarcomas, promoting metastasis and chemotherapy resistance. The purpose of this work was to develop and test a novel putative STAT3 inhibitor, LY5. Methods and findings An in silico fragment-based drug design strategy was used to create LY5, a small molecule inhibitor that blocks the STAT3 SH2 domain phosphotyrosine binding site, inhibiting homodimerization. LY5 was evaluated in vitro demonstrating good biologic activity against rhabdomyosarcoma, osteosarcoma and Ewing’s sarcoma cell lines at high nanomolar/low micromolar concentrations, as well as specific inhibition of STAT3 phosphorylation without effects on other STAT3 family members. LY5 exhibited excellent oral bioavailability in both mice and healthy dogs, and drug absorption was enhanced in the fasted state with tolerable dosing in mice at 40 mg/kg BID. However, RNAi-mediated knockdown of STAT3 did not phenocopy the biologic effects of LY5 in sarcoma cell lines. Moreover, concentrations needed to inhibit ex vivo metastasis growth using the PuMA assay were significantly higher than those needed to inhibit STAT3 phosphorylation in vitro. Lastly, LY5 treatment did not inhibit the growth of sarcoma xenografts or prevent pulmonary metastasis in mice. Conclusions LY5 is a novel small molecule inhibitor that effectively inhibits STAT3 phosphorylation and cell proliferation at nanomolar concentrations. LY5 demonstrates good oral bioavailability in mice and dogs. However LY5 did not decrease tumor growth in xenograft mouse models and STAT3 knockdown did not induce concordant biologic effects. These data suggest that the anti-cancer effects of LY5 identified in vitro were not mediated through STAT3 inhibition.

Myofibroblast differentiation is required for wound healing and accompanied by activation of smooth muscle α-actin (SMαA) gene expression. The stress-response protein, Y-box binding protein-1 (YB-1) binds SMαA mRNA and regulates its translational activity. Activation of SMαA gene expression in human pulmonary myofibroblasts by TGFβ1 was associated with formation of denaturation-resistant YB-1 oligomers with selective affinity for a known translation-silencer sequence in SMαA mRNA. We have determined that YB-1 is a substrate for the protein-crosslinking enzyme transglutaminase 2 (TG2) that catalyzes calcium-dependent formation of covalent γ-glutamyl-isopeptide linkages in response to reactive oxygen signaling. TG2 transamidation reactions using intact cells, cell lysates, and recombinant YB-1 revealed covalent crosslinking of the 50 kDa YB-1 polypeptide into protein oligomers that were distributed during SDS-PAGE over a 75-250 kDa size range. In vitro YB-1 transamidation required nanomolar levels of calcium and was enhanced by the presence of SMαA mRNA. In human pulmonary fibroblasts, YB-1 crosslinking was inhibited by (a) anti-oxidant cystamine, (b) the reactive-oxygen antagonist, diphenyleneiodonium, (c) competitive inhibition of TG2 transamidation using the aminyl-surrogate substrate, monodansylcadaverine, and (d) transfection with small-interfering RNA specific for human TG2 mRNA. YB-1 crosslinking was partially reversible as a function of oligomer-substrate availability and TG2 enzyme concentration. Intracellular calcium accumulation and peroxidative stress in injury-activated myofibroblasts may govern SMαA mRNA translational activity during wound healing via TG2-mediated crosslinking of the YB-1 mRNA-binding protein.

Background: Pediatric bone and soft tissue sarcomas are heavily dependent on the Type 1 insulin-like growth factor receptor (IGF-1R) signaling axis, which promotes tumorigenic properties such as proliferation, survival, angiogenesis and metastasis. While a substantial proportion of patients demonstrate intrinsic resistance to monoclonal antibodies targeting IGF-1R, a strong and sustained response is seen in a limited number of patients, and disease stabilization in about 30% of patients. Understanding these resistance mechanisms may identify combinations of targeted therapies that optimize therapeutic efficiency of IGF-1R-targeted antibodies. Methods: For intrinsic resistance, we used a panel of Ewing sarcoma (ES; n=10) and rhabdomyosarcoma (RMS; n=10) cell lines that, with the exception of Rh41, are all intrinsically resistant to TZ-1, a monoclonal antibody that targets IGF-1R. For acquired resistance, we developed a TZ-1 resistant RMS cell line, Rh41/TZ-1. We utilized Receptor Tyrosine Kinase (RTK) Arrays to analyze the phosphorylation status of 49 RTKs. The cell lines were treated with TZ-1 and changes in RTK expression were assessed by quantitative PCR. Results: RMS cells intrinsically resistant to TZ-1 treatment expressed multiple activated RTKs including EGFR family of receptors, IGF-1R, IR, PDGFR, FGFR4, HGFR4, RYK, ALK, DDR1, AXL, DTK. Interestingly, ES cells (n=5) had either a complex pattern of activated RTK expression similar to RMS cells or a relatively less complex set (n=5) of activated RTKs (IGF-1R, IR, HGFR, ERBB4, AXL, DTK). TZ-1 treatment of these cell lines with intrinsic resistance demonstrated decreased phosphorylation of IGF-1R, but had little effect on other RTKs. In contrast TZ-1 treatment of Rh41 cells rapidly induced activation of several RTKs including: AXL, PDGFRB, FGFR4 and ALK. Increased expression of these receptors was confirmed by qPCR. In contrast, Rh41/TZ-1 cells selected for acquired resistance to TZ-1 constitutively expressed activated RTKs (PDGFRB, FGFR4, AXL, DTK, VEGFR1). In Rh41 cells treated with TZ-1, the BRD4 inhibitor, JQ1 (500 nM, 24 Hr), blocked the induction of IGF-1R, IRB, AXL, PDGFR-A/-B, VEGFR1 and ALK. However, it had less effect on the induction of FGFR 2/3/4 receptors. Further, combined treatment of TZ-1 and JQ1 reduced cellular proliferation of Rh41 cells more than TZ-1 treatment alone. Conclusions: We demonstrate that intrinsic resistance to the IGF-1R targeted antibody TZ-1 is characterized by constitutive activation of multiple RTKs. In response to TZ-1 treatment in a sensitive cell line there is rapid induction of multiple RTKs indicating a dynamic response to inhibition of IGF-1R. Our data suggests that BRD4 is involved in induction of these signaling molecules and that combined inhibition of BRD4 along with the IGF-1R targeted therapy can overcome this resistance and warrants further investigation. Support: US Public Health Service Grant CA165995. Citation Format: Terry J. Shackleford, Seethalakshmi Hariharan, Doris Phelps, Hemant Bid, Hiahong Zhong, Peter Houghton. Mechanisms of intrinsic and acquired resistance to antibodies targeting IGF-1R in pediatric sarcoma cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5825. doi:10.1158/1538-7445.AM2017-5825

Expression of smooth muscle alpha-actin (SMαA) is essential for myofibroblast-mediated wound contraction following tissue injury. The Pur α/β and YB-1 transcriptional repressors govern the DNA-binding activity of serum response factor (SRF) and phosphorylated Smad3 (pSmad3) transcriptional activators during induction of SMαA gene expression in human pulmonary myofibroblasts. In quiescent fibroblasts, Pur α exhibited a novel function in enhancing stability of pre-existing SRF complexes with SMαA core promoter DNA, whereas Pur β was more effective in disrupting SRF-DNA interaction. Pur proteins were less efficient competitors of pre-existing, core-promoter complexes containing both SRF and pSmad3 in nuclear extracts from TGFβ1-activated myofibroblasts. TGFβ1 signaling dissociated a SRF/Pur protein complex with concurrent formation of a transient pSmad3/MRTF-A/Pur β complex during early phase myofibroblast differentiation. Pur β was replaced by Pur α in the pSmad3/MRTF-A complex in mature myofibroblasts. Combining all three repressors potently inhibited SRF and pSmad3 binding to promoter DNA in quiescent fibroblasts and TGFβ1-activated myofibroblasts, respectively. The results point to dynamic interplay between transcriptional activators and repressors in regulating SMαA gene output during myofibroblast differentiation. Therapeutic targeting of nucleoprotein complexes regulating the SMαA promoter may prevent excessive myofibroblast accumulation associated with chronic cardiopulmonary fibrosis and dysfunctional tissue remodeling.

Myofibroblast differentiation is required for wound healing and accompanied by activation of smooth muscle α-actin (SMαA) gene expression. The stress-response protein, Y-box binding protein-1 (YB-1) binds SMαA mRNA and regulates its translational activity. Activation of SMαA gene expression in human pulmonary myofibroblasts by TGFβ1 was associated with formation of denaturation-resistant YB-1 oligomers with selective affinity for a known translation-silencer sequence in SMαA mRNA. We have determined that YB-1 is a substrate for the protein-crosslinking enzyme transglutaminase 2 (TG2) that catalyzes calcium-dependent formation of covalent γ-glutamyl-isopeptide linkages in response to reactive oxygen signaling. TG2 transamidation reactions using intact cells, cell lysates, and recombinant YB-1 revealed covalent crosslinking of the 50 kDa YB-1 polypeptide into protein oligomers that were distributed during SDS-PAGE over a 75-250 kDa size range. In vitro YB-1 transamidation required nanomolar levels of calcium and was enhanced by the presence of SMαA mRNA. In human pulmonary fibroblasts, YB-1 crosslinking was inhibited by (a) anti-oxidant cystamine, (b) the reactive-oxygen antagonist, diphenyleneiodonium, (c) competitive inhibition of TG2 transamidation using the aminyl-surrogate substrate, monodansylcadaverine, and (d) transfection with small-interfering RNA specific for human TG2 mRNA. YB-1 crosslinking was partially reversible as a function of oligomer-substrate availability and TG2 enzyme concentration. Intracellular calcium accumulation and peroxidative stress in injury-activated myofibroblasts may govern SMαA mRNA translational activity during wound healing via TG2-mediated crosslinking of the YB-1 mRNA-binding protein.

Myofibroblasts (MFBs) are smooth muscle-like cells that provide contractile force required for tissue repair during wound healing. The leading agonist for MFB differentiation is transforming growth factor β1 (TGFβ1) that induces transcription of genes encoding smooth muscle α-actin (SMαA) and interstitial collagen that are markers for MFB differentiation. TGFβ1 augments activation of Smad transcription factors, pro-survival Akt kinase, and p38 MAP kinase as well as Wingless/int (Wnt) developmental signaling. These actions conspire to activate β-catenin needed for expression of cyclin D, laminin, fibronectin, and metalloproteinases that aid in repairing epithelial cells and their associated basement membranes. Importantly, β-catenin also provides a feed-forward stimulus that amplifies local TGFβ1 autocrine/paracrine signaling causing transition of mesenchymal stromal cells, pericytes, and epithelial cells into contractile MFBs. Complex, mutually interactive mechanisms have evolved that permit several mammalian cell types to activate the SMαA promoter and undergo MFB differentiation. These molecular controls will be reviewed with an emphasis on the dynamic interplay between serum response factor, TGFβ1-activated Smads, Wnt-activated β-catenin, p38/calcium-activated NFAT protein, and the RNA-binding proteins, Purα, Purβ, and YB-1, in governing transcriptional and translational control of the SMαA gene in injury-activated MFBs.

Background: Insulin-like growth factor-I receptor (IGFR) signaling promotes tumorigenic properties which makes targeting IGFR an attractive therapeutic target. IGF signaling has been linked to proliferation, survival, angiogenesis, metastasis and resistance to anticancer therapies, and contributes to pediatric malignancies including Ewing sarcoma and rhabdomyosarcoma. Recently, monoclonal antibodies targeting IGFR have shown promise in a limited number of sarcoma patients. A substantial proportion of patients demonstrate intrinsic resistance, and those that do respond will often lose clinical benefit (acquired resistance). Intrinsic and acquired resistance ultimately results in failure to respond to treatment and continued growth of the tumor. Understanding these resistance mechanisms will identify combinations of targeted therapy to optimize therapeutic efficiency of this targeted agent. Methods: To test intrinsic and acquired mechanisms of resistance, we utilized Receptor Tyrosine Kinase (RTK) Arrays to analyze the phosphorylation status of 49 RTKs. For intrinsic resistance, we used a panel of Ewing Sarcoma (EWS) cell lines that are unresponsive to TZ1, a monoclonal antibody that targets IGFR. For acquired resistance, we developed a TZ1 resistant rhabdomyosarcoma (RMS) cell line from TZ1 sensitive RH41 cells. The cell lines were treated with TZ1, an anti-IGFR monoclonal antibody. Signaling changes were assessed by comparing phosphorylation status of the RTKs in the untreated versus treated cells in the inherent resistance model and in the parental versus resistant cells in the acquired resistance model. Results: TZ-1 treatment of the EWS cell lines with intrinsic resistance decreased pIGFR, but these cells were characterized by expression of multiple phosphorylated RTKs. In the Rh41 acquired resistance model, increased activation of signaling pathways was detected in the resistance cells including: AXL, PDGFR, FGFR4 and ALK. Treatment of parental Rh41 cells with TZ1 also rapidly induced several activated RTKs. In TZ1-resistant Rh41 cells combined treatment of TZ1 with the PDGFR inhibitor, crenolanib, and the pan-FGFR inhibitor LY2874455 resulted in significant decrease in cellular proliferation. Conclusions: Intrinsic resistance to TZ1 in EWS cell lines appears to be due to redundancy through multiple alternative activated RTKs. Systematic knockdown to determine which activated RTKs confer resistance is being undertaken. In Rh41 RMS cells acquired resistance to TZ1 is characterized by induction of several alternative activated RTKs, some of which are induced rapidly after TZ1 exposure. Combined treatment with TZ1 and drugs targeting PDGFR and FGFR was effective at overcoming resistance. These results suggest that identification of signaling pathways that compensate for IGFR inhibition can lead to effective potent multi-target combination therapy. Supported by USPHS Grant CA165995. Citation Format: Terry J. Shackleford, Seethalakshmi Hariharan, Hemant K. Bid, Peter J. Houghton. Mechanisms of resistance to IGFR-targeted therapy in pediatric sarcomas. [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 2472.

Bimolecular fluorescence complementation assays allow the visualization of the homotypic and heterotypic GTPase interactions in vivo. The Rsr1 homotypic interaction involves its polybasic region and depends on its GDP-GTP exchange factor. Dimerization of GTPases may be an efficient mechanism to set up cellular asymmetry., Cell polarization occurs along a single axis that is generally determined in response to spatial cues. In budding yeast, the Rsr1 GTPase and its regulators direct the establishment of cell polarity at the proper cortical location in response to cell type–specific cues. Here we use a combination of in vivo and in vitro approaches to understand how Rsr1 polarization is established. We find that Rsr1 associates with itself in a spatially and temporally controlled manner. The homotypic interaction and localization of Rsr1 to the mother-bud neck and to the subsequent division site are dependent on its GDP-GTP exchange factor Bud5. Analyses of rsr1 mutants suggest that Bud5 recruits Rsr1 to these sites and promotes the homodimer formation. Rsr1 also exhibits heterotypic interaction with the Cdc42 GTPase in vivo. We show that the polybasic region of Rsr1 is necessary for the efficient homotypic and heterotypic interactions, selection of a proper growth site, and polarity establishment. Our findings thus suggest that dimerization of GTPases may be an efficient mechanism to set up cellular asymmetry.