Pratistha Koirala

Endocardial to Myocardial Notch-Wnt-Bmp Axis Regulates Early Heart Valve Development

Endocardial to mesenchymal transformation (EMT) is a fundamental cellular process required for heart valve formation. Notch, Wnt and Bmp pathways are known to regulate this process. To further address how these pathways coordinate in the process, we specifically disrupted Notch1 or Jagged1 in the endocardium of mouse embryonic hearts and showed that Jagged1-Notch1 signaling in the endocardium is essential for EMT and early valvular cushion formation. qPCR and RNA in situ hybridization assays reveal that endocardial Jagged1-Notch1 signaling regulates Wnt4 expression in the atrioventricular canal (AVC) endocardium and Bmp2 in the AVC myocardium. Whole embryo cultures treated with Wnt4 or Wnt inhibitory factor 1 (Wif1) show that Bmp2 expression in the AVC myocardium is dependent on Wnt activity; Wnt4 also reinstates Bmp2 expression in the AVC myocardium of endocardial Notch1 null embryos. Furthermore, while both Wnt4 and Bmp2 rescue the defective EMT resulting from Notch inhibition, Wnt4 requires Bmp for its action. These results demonstrate that Jagged1-Notch1 signaling in endocardial cells induces the expression of Wnt4, which subsequently acts as a paracrine factor to upregulate Bmp2 expression in the adjacent AVC myocardium to signal EMT.

Immune infiltration and PD-L1 expression in the tumor microenvironment are prognostic in osteosarcoma

Osteosarcoma patient survival has remained stagnant for 30 years. Novel therapeutic approaches are needed to improve outcomes. We examined the expression of Programmed Death Ligand 1 (PD-L1) and defined the tumor immune microenvironment to assess the prognostic utility in osteosarcoma. PD-L1 expression in osteosarcoma was examined in two patient cohorts using immunohistochemistry (IHC) (n = 48, n = 59) and expression was validated using quantitative real time PCR (n = 21) and western blotting (n = 9). IHC was used to determine the presence of tumor infiltrating lymphocytes and antigen-presenting cells (APCs) in the tumor. Expression of PD-L1 was correlated with immune cell infiltration and event-free-survival (EFS). The 25% of primary osteosarcoma tumors that express PD-L1 were more likely to contain cells that express PD-1 than PD-L1 negative tumors (91.7% vs 47.2%, p = 0.002). Expression of PD-L1 was significantly associated with the presence of T cells, dendritic cells, and natural killer cells. Although all immune cell types examined were present in osteosarcoma samples, only infiltration by dendritic cells (28.3% vs. 83.9%, p = 0.001) and macrophages (45.5% vs. 84.4%, p = 0.031) were associated with worse five-year-EFS. PD-L1 expression was significantly associated with poorer five-year-EFS (25.0%. vs. 69.4%, p = 0.014). Further studies in osteosarcoma are needed to determine if targeting the PD-L1:PD-1 axis improves survival.

HHLA2, a member of the B7 family, is expressed in human osteosarcoma and is associated with metastases and worse survival.

Over the past four decades there have been minimal improvements in outcomes for patients with osteosarcoma. New targets and novel therapies are needed to improve outcomes for these patients. We sought to evaluate the prevalence and clinical significance of the newest immune checkpoint, HHLA2, in osteosarcoma. HHLA2 protein expression was evaluated in primary tumor specimens and metastatic disease using an osteosarcoma tumor microarray (TMA) (n = 62). The association of HHLA2 with the presence of tumor infiltrating lymphocytes (TILs) and five-year-event-free-survival were examined. HHLA2 was expressed in 68% of osteosarcoma tumors. HHLA2 was expressed in almost all metastatic disease specimens and was more prevalent than in primary specimens without known metastases (93% vs 53%, p = 0.02). TILs were present in 75% of all osteosarcoma specimens. Patients whose tumors were ≥25% or ≥50% HHLA2 positive had significantly worse five-year event-free-survival (33% vs 64%, p = 0.03 and 14% vs 59%, p = 0.02). Overall, we have shown that HHLA2 is expressed in the majority of osteosarcoma tumors and its expression is associated with metastatic disease and poorer survival. Along with previously reported findings that HHLA2 is a T cell co-inhibitor, these results suggest that HHLA2 may be a novel immunosuppressive mechanism within the osteosarcoma tumor microenvironment.

Targeted therapy of osteosarcoma with radiolabeled monoclonal antibody to an insulin-like growth factor-2 receptor (IGF2R)

INTRODUCTION Osteosarcoma overall survival has plateaued around 70%, without meaningful improvements in over 30years. Outcomes for patients with overt metastatic disease at presentation or who relapse are dismal. In this study we investigated a novel osteosarcoma therapy utilizing radioimmunotherapy (RIT) targeted to IGF2R, which is widely expressed in OS. METHODS Binding efficiency of the Rhenium-188(188Re)-labeled IGF2R-specific monoclonal antibody (mAb) to IGF2R on OS17 OS cells was assessed with Scatchard plot analysis. Biodistribution studies were performed in heterotopic murine osteosarcoma xenografts. Tumor growth was compared over a 24-day period post-treatment between mice randomized to receive 188Re-labeled IGF2R-specific murine mAb MEM-238 (188Re-MEM-238) or one of three controls: 188Re-labeled isotype control mAb, unlabeled MEM-238, or no treatment. RESULTS Results demonstrate that the radioimmunoconjugate had a high binding constant to IGF2R. Both 188Re-MEM-238 and the isotype control had similar initial distribution in normal tissue. After 48h 188Re-MEM-238 exhibited a 1.8 fold selective uptake within tumor compared to the isotype control (p=0.057). Over 24days, the tumor growth ratio was suppressed in animals treated with RIT compared to unlabeled and untreated controls (p=0.005) as demonstrated by a 38% reduction of IGF2R expressing osteosarcoma cells in the RIT group (p=0.002). CONCLUSIONS In conclusion, given the lack of new effective therapies in osteosarcoma, additional investigation into this target is warranted. ADVANCES IN KNOWLEDGE High expression of IGF2R on osteosarcoma tumors, paired with the specificity and in vivo anti-cancer activity of 188Re-labeled IGF2R-specific mAb suggests that IGF2R may represent a novel therapeutic target in the treatment of osteosarcoma. IMPLICATIONS FOR PATIENT CARE This targeted approach offers the benefits of being independent of a specific pathway, a resistance mechanism, and/or an inherent biologic tumor trait and therefore is relevant to all OS tumors that express IGF2R.

CD49b inhibits osteogenic differentiation and plays an important role in osteosarcoma progression

Osteosarcoma is a cancer whose cell of origin lies in the differentiation pathway between the mesenchymal stem cell (MSC) and the osteoblast (OB). In this study, we sought to determine if surface markers associated with osteoblastic differentiation are involved in osteosarcoma progression. cDNA expression arrays were performed on MSCs and osteoblasts to identify differentially expressed genes. The specificity of candidate genes for osteoblast differentiation was assessed through time course experiments in differentiation media with confirmation utilizing CD49b transfected MSCs. In addition, CD49b was transfected into osteosarcoma cell lines to determine its impact on cell proliferation, motility, and invasion. Finally, the expression of CD49b was assessed in osteosarcoma patient samples and correlated with survival outcomes. cDNA expression arrays identified a list of genes differentially expressed between MSCs and osteoblasts with a subset of those genes encoding cell surface proteins. Three genes were selected for further analysis, based on qPCR validation, but only CD49b was selective for osteoblastic differentiation. Forced expression of CD49b in MSCs led to delayed osteoblastic differentiation. Down-regulation of CD49b expression in osteosarcoma cell lines resulted in inhibition of their migration and invasion capacity. CD49b expression in osteosarcoma patients was associated with presence of metastases and inferior 5 year overall survival (31.4% vs. 57.4%, p=0.03). Surface proteins involved in osteosarcoma cell differentiation, such as CD49b, have the potential to serve as prognostic biomarkers, and may lead to the identification of new therapeutic targets.

Down-regulation of Skp2 expression inhibits invasion and lung metastasis in osteosarcoma

Osteosarcoma (OS), the most common primary cancer of bone, exhibits a high propensity for local invasion and distant metastasis. This study sought to elucidate the role of S phase kinase-associated protein (Skp2) in osteosarcoma invasion and metastasis and to explore flavokawain A (FKA), a natural chalcone from kava extract, as a potential Skp2 targeting agent for preventing osteosarcoma progression. Skp2 was found to be overexpressed in multiple osteosarcoma cell lines, including 5 standard and 8 primary patient-derived cell lines. Patients whose tumors expressed high levels of Skp2 sustained a significantly worse metastasis-free (p = 0.0095) and overall survival (p = 0.0013) than those with low Skp2. Skp2 knockdown markedly reduced in vitro cellular invasion and in vivo lung metastasis in an orthotopic mouse model of osteosarcoma. Similar to Skp2 knockdown, treatment with FKA also reduced Skp2 expression in osteosarcoma cell lines and blocked the invasion of osteosarcoma cells in vitro and lung metastasis in vivo. Together, our findings suggest that Skp2 is a promising therapeutic target in osteosarcoma, and that FKA may be an effective Skp2-targeted therapy to reduce osteosarcoma metastasis.

Abstract 920: ICAM-1(CD54) is involved in the osteogenic differentiation of mesenchymal stem cells and affects the progression of osteosarcoma cells

Purpose: The aim of this study is to validate the relationship between the expression of ICAM-1(CD54), a cell surface glycoprotein, and osteogenic differentiation of mesenchymal stem cells (MSCs) and the role of ICAM-1 in the progression of osteosarcoma (OS) cells. Experimental Design: To compare the gene expression profiles between MSCs and MSCs after osteogenic induction, a microarray analysis was first performed. The differences in expression of specific genes including ICAM-1 were confirmed using western blot and flow cytometry. MSCs were sorted into two groups of cells by CD105+CD44+CD54+ and CD105+C44+CD54- and properties of these cells were compared. Expression of ICAM-1 among tumor cell lines and xenograft OS cells were tested at the protein level. ICAM-1 was stably, constitutively overexpressed in multiple cell types. Differences in osteogenic differentiation potential between normal cell lines and transformed cell lines were studied using alizarin red S staining. Motility, proliferation and invasion as well as the metastatic potential of the transformed and normal cells were evaluated. Results: The initial microarray analysis revealed that ICAM-1 expression was significantly increased in MSCs after osteogenic induction for 15 days (p=0.042). Consistent results were achieved in western blot and flow cytometry analysis. Further microarray analysis between CD105+CD44+CD54+ and CD105+C44+CD54- groups determined that NF-kB signaling pathway was differentially activated. As for OS cells, ICAM-1 is not expressed at high level among OS tumor cell lines and is inconsistently expressed in xenograft OS cells. Enhanced osteogenic differentiation potential was observed in ICAM-1 overexpressing cells. Although there were no major difference in in vitro motility, proliferation or invasion tests, substantially less lung nodules occurred with transformation as compared to the normal control. Conclusions: ICAM-1 is involved in the osteogenic differentiation of mesenchymal stem cells and its down regulation may be involved in the progression of osteosarcoma cells. Citation Format: Yidan Zhang, Sajida Piperdi, Nikolas Zaphiros, Pratistha Koirala, Tingting Ren, Michael Roth, Jonathan Gill, Bang Hoang, David Geller, Rui Yang, Wendong Zhang, Xiuquan Du, Jinghang Zhang, Richard Gorlick. ICAM-1(CD54) is involved in the osteogenic differentiation of mesenchymal stem cells and affects the progression of osteosarcoma cells [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 920. doi:10.1158/1538-7445.AM2017-920

Abstract 2125: Flavokawain A, a kava chalcone, inhibits growth and invasion of human osteosarcoma cells by targeting Skp2

Purpose: Osteosarcoma (OS) is the most common primary bone malignancy with a high propensity for local invasion and distant metastasis. Flavokawain A (FKA), a major chalcone from kava extract, has been reported to have antitumor effects on multiple cancer cell lines. The consumption of kava-containing beverage has been associated with a low cancer incidence. In a previous report, mice treated with high-dose FKA did not demonstrate any significant major organ toxicity. However, the efficacy and anticancer mechanisms of FKA in OS is still to be elucidated. Experimental Design: OS cell lines were treated with increasing dosage of FKA and tested for cell motility, proliferation, and invasion by MTT assay and Matrigel invasion assay. Cell cycle analysis was performed using flow cytometry. We examined Skp2 expression in several OS cell lines using western blot and in patient tissue array by immunostaining. Kaplan-meier analysis and log rank test were used to compare overall survival. Both Skp2-dependent cell cycle progression and Skp2-related RhoA expression were also examined after FKA treatment. The effects of FKA on lung metastasis were evaluated after orthotopic injection of OS cells into the tibia. Results: We show that FKA inhibits the growth and motility of multiple OS cell lines in vitro. Flow cytometry analysis confirms cellular apoptosis and arrest in G2/M phase after FKA treatment, whereas cellular invasion is also inhibited in a dose-dependent manner. Skp2 is expressed in several OS cell lines and is associated with a poor prognosis in OS patients. Skp2 levels in OS cell lines decreased after FKA treatment. The expression of cell cycle regulators including p21 and p27, which are downstream of Skp2, was upregulated. Moreover, Skp2-related RhoA expression is inhibited by FKA and confirmed at protein level. Conclusions: Taken together, the evidence suggests FKA exerts anti-invasive effects in association with Skp2-dependent cell cycle progression and Skp2-related RhoA expression. Since Skp2 is a negative prognostic factor for OS patients, FKA should be investigated further as an anti-Skp2 therapeutic strategy for OS. Citation Format: Yidan Zhang, Wendong Zhang, Nikolas Zaphiros, Xiuquan Du, Pratistha Koirala, Michael Roth, Jonathan Gill, Sajida Piperdi, David Geller, Rui Yang, Jinghang Zhang, Richard Gorlick, Xiaolin Zi, Tao Ji, Bang H. Hoang. Flavokawain A, a kava chalcone, inhibits growth and invasion of human osteosarcoma cells by targeting Skp2 [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 2125. doi:10.1158/1538-7445.AM2017-2125

Abstract 4134: Immune infiltration and PD-L1 expression in the tumor microenvironment are prognostic in osteosarcoma

Purpose: Over the past four decades, osteosarcoma (OS) survival rates have remained stagnant. There is a need to identify novel therapies to target OS. In this study we examined the expression of Programed Death Ligand 1 (PD-L1) and defined the tumor microenvironment in OS in order to assess the feasibility of utilizing immune checkpoint inhibitors as a treatment modality. Experimental Design: PD-L1 expression in OS was examined in two patient cohorts using immunohistochemistry (IHC) (n = 48, n = 59) and expression was validated using quantitative real time PCR (qRT-PCR) (n = 21) and western blotting (n = 9). IHC was used to determine presence of tumor infiltrating lymphocytes and antigen presenting cells (APCs) in the tumor. Expression of PD-L1 was correlated with the presence of immune cells and with event free survival in OS. Results: PD-L1 is expressed in up to 25% of primary OS tumors. Of the PD-L1 positive tumors the majority were also PD-1 positive (92% vs 8%, p = 0.002). In addition, the presence of immune cells in the tumor mass was significantly associated with PD-L1 expression. Although all immune cell types examined were present in OS, only infiltration by APCs, specifically CD1a positive dendritic cells (48.6% vs. 51.4%, p = 0.0010) and CD68 positive macrophages (70.3% vs. 29.7%, p = 0.0316), was associated with worse outcomes. PD-L1 expression was significantly associated with worsened survival (21.6% pos. vs. 78.4% neg., p = 0.0146). Conclusions: For the first time we have identified PD-L1 expression or presence of CD1a or CD68 positive antigen presenting cells as prognostic markers for worsened outcome in OS. Furthermore, we show that IHC is a valid detection method for PD-L1 in OS. With up to 25% of OS patients expressing PD-L1, this study provides rational for targeting the PD-L1:PD-1 axis for immunotherapy in OS. Citation Format: Pratistha Koirala, Michael Roth, Jonathan Gill, Jordan Chinai, Sajida Piperdi, David Geller, Bang Hoang, Vincent Poon, Xingxing Zang, Richard Gorlick. Immune infiltration and PD-L1 expression in the tumor microenvironment are prognostic in osteosarcoma. [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 4134.

Abstract 2471: Evaluation of CD47 expression and effects of CD47-SIRPα fusion protein in patients with osteosarcoma

CD47 is a commonly expressed trans-membrane protein which binds to signal regulatory protein α (SIRPα) expressed on the surface of the macrophages resulting in inhibition of phagocytosis and cell clearance. Several malignancies demonstrate high expression of CD47 and recent studies suggest interfering with the CD47-macrophage interaction may be therapeutic. A prior expression analysis performed on osteosarcoma (OS) patient samples reported marked expression of CD47. The current study evaluated the utility of targeting CD47 in Osteosarcoma by determining the prevalence of CD47 expression and the prognostic value of CD47 expression in patients with Osteosarcoma. An immunofluorescence phagocytosis assay is being performed to directly assess the therapeutic potential of the CD47-SIRPα fusion protein. A previously created and described tissue microarray (TMA) was stained with a murine monoclonal anti-CD47 (B6H12) antibody. The intensity and location of tissue staining were assessed by a comparison between the positive and negative control slides. 81 specimens were evaluated on the TMA. Overall, CD47 was expressed in 87.7% of specimens, with 28.4%, 27.2%, and 32.1% demonstrating high, intermediate, and low expression, respectively. Almost all metastatic tumor specimens (85.7%) expressed CD47. To evaluate CD47 expression quantitatively, a real time PCR was performed on OS patient-derived primary samples, and cell lines. 71.4% of patient derived cell lines (n = 15) showed higher level of CD47 expression compared to that of mesenchymal stem cells and an osteoblast cell line. Furthermore, flow cytometry was performed on human OS xenografts and cell lines to determine the surface expression level of CD47 prior to treatment with CD47-SIRPα fusion protein. 85% of the OS cell lines (n = 13) showed levels of CD47 expression comparable to that of the positive control, leukemia cell line HL60. Survival analyses suggested that increased expression of CD47 may be associated with poorer 5 year event free survival (69.3% vs 42.4%, p = 0.6 and 49.5% vs. 33.6%, p = 0.16) when using thresholds of intermediate/high expression of CD47 and high expression of CD47, respectively. Results of an in-vitro phagocytosis assay assessing cytotoxicity of a CD47-SIRPα fusion protein on OS cell lines using laser scanning cytometry at present show some inhibition of phagocytosis upon adding 500 ug/ml of CD47-SIRPα fusion protein, but it does not reach the statistical significance. These findings demonstrate that CD47 is highly prevalent in Osteosarcoma and suggest CD47 has potential utility as a novel target for anti-cancer therapy in Osteosarcoma. Although the immunofluorescence assays have not demonstrated marked augmentation of activity with the CD47-SIRPα fusion protein, this may be attributable to limitations of the method with clinical trials necessary to define its true level of activity in treating patients with Osteosarcoma. Citation Format: Sajida Piperdi, Michael Roth, Nick Morriss, Christian Zinone, Wendong Zhang, Pratistha Koirala, David Geller, Bang Hoang, Rui Yang, Jonathan Gill, Richard Gorlick. Evaluation of CD47 expression and effects of CD47-SIRPα fusion protein in patients with osteosarcoma. [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 2471.