Detection of circulating tumor DNA in patients with osteosarcoma

Identification and quantification of somatic alterations in plasma-derived, circulating tumor DNA (ctDNA) is gaining traction as a non-invasive and cost effective method of disease monitoring in cancer patients, particularly to evaluate response to treatment and monitor for disease recurrence. To our knowledge, genetic analysis of ctDNA in osteosarcoma has not yet been studied. To determine whether somatic alterations can be detected in ctDNA and perhaps applied to patient management in this disease, we collected germline, tumor, and serial plasma samples from pediatric, adolescent, and young adult patients with osteosarcoma and used targeted Next Generation Sequencing (NGS) to identify somatic single nucleotide variants (SNV), insertions and deletions (INDELS), and structural variants (SV) in 7 genes commonly mutated in osteosarcoma. We demonstrate that patient-specific somatic alterations identified through comparison of tumor-germline pairs can be detected and quantified in cell-free DNA of osteosarcoma patients.

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.

Abstract 2731: Identifying circulating tumor DNA in patients with osteosarcoma

Introduction:

Osteosarcoma (OS) is the most common primary malignant bone tumor and primarily affects children and adolescents. During and after treatment there is no non-invasive test to assess disease response and early relapse. We hypothesize that circulating tumor DNA (ctDNA) can be used to assess tumor burden, evaluate response to treatment, and monitor for recurrence in OS. We effectively tested this hypothesis on a mouse model and have utilized our methods on a first cohort of human patients.

Materials and Methods:

Twenty blood samples with matched primary tumor material were obtained from 10 patients with OS who were at various stages of treatment or post treatment. Cell free DNA was isolated from blood collected in Cell-Free DNA blood collection tubes using the QIamp Circulating Nucleic Acid kit. We performed massively parallel sequencing (MPS) with the Illumina HiSeq 2500 in the Epigenomics Shared Facility (ESF) to a depth of at least 800x using custom designed probes (Roche NimbleGen SeqCap EZ) capturing genes commonly altered in OS including TP53, RB1, ATRX, DLG2, MET, PTEN, and SLC19A1. We aligned the fastq files with BWA, called the variants using Varscan and GATK HaplotypeCaller, and annotated the variants with SnpEff.

Summary of Data:

Using an initial threshold of 2% of variants, ctDNA was identified in two of the patients in our study. The first patient’s sample, collected at the completion of therapy, contained a missense mutation in the coding exon of DLG2 at position chr11 84027990 (2.07% of reads). This patient has no radiographic evidence of recurrent disease 12 months after completion of treatment. In a second patient with 4 samples drawn, a mutation was found in the intron region of RB1 at position chr13 48986157. The variant was 0.17% of reads upon completion of therapy, undectable at 3 months, 2.16% of reads at 6 months, and 1.5% of reads at 9 months. The patient is at high-risk for recurrence but is currently disease-free. Sequencing and analysis of serially collected patient samples, including from 3 patients with recurrent disease, and primary tumor is ongoing.

Conclusions:

We have identified pathogenic variants in the cell free DNA of patients with no radiologic evidence of OS but who are at high risk for relapse. This is the first step to utilizing a non-invasive test to assess tumor burden, response to treatment, and likelihood of recurrence. As part of future work, we will lower the threshold for calling variants and quantify ctDNA abundance in serially collected samples from treatment and during surveillance, and correlate the findings with clinical outcome.

Citation Format: David M. Barris, Michael Fremed, Robert Durbin, Xusheng Zhang, Sajida Piperdi, Wendong Zhang, Shahina Maqbool, Jonathan Gill, Michael Roth, Bang Hoang, David Geller, Richard Gorlick, Daniel Weiser. Identifying circulating tumor DNA in patients with osteosarcoma [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 2731. doi:10.1158/1538-7445.AM2017-2731

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 697: Stage 1 in vivo evaluation of multi-receptor tyrosine-kinase inhibitor lenvatinib in osteosarcoma patient derived mouse xenograft models

Background: Osteosarcoma (OS) is the most common primary bone tumor in children and young adults. Over the past three decades improvement in outcomes for children with OS have remained stagnant. Novel therapies are needed to improve outcomes for these patients. Lenvatinib is an oral small-molecule tyrosine-kinase inhibitor (TKI), targeting multiple receptors including VEGFR1-3, FGFR 1-4, PDGFRα, RET, and c-kit. Prior studies have shown that PDGFR-VEGF/VEGFR and FGFR3 are overexpressed in human OS cell lines. Lenvatinib is FDA-approved for the treatment of differentiated thyroid cancer, and, in combination with mTOR inhibitor everolimus, for the treatment of renal cell carcinoma. The current study assessed the in vivo efficacy of lenvatinib in osteosarcoma xenograft models.

Materials and Methods: Single agent lenvatinib was tested against 5 well-established osteosarcoma patient derived mouse xenograft models. Lenvatinib was administered using a dose of 7.5mg/kg given by oral route daily (5/7 days) for 6 weeks or until study endpoints were met. Tumor volume and mouse body weight were measured bi-weekly. Tumor volume was compared to baseline tumor volume to calculate the relative tumor volume (RTV). The RTV was compared between the control and experimental groups utilizing the student t-test. P-values <0.05 were considered statistically significant. Additional statistical analyses were conducted as per the Pediatric Preclinical Testing Program analysis plan.

Results: Lenvatinib was generally well tolerated in vivo, without noted toxicity in any of the treated animals. Lenvatinib treatment led to delayed tumor progression in 4/5 models tested. Relative tumor volumes in the treatment group compared to the control group at week 3 in xenografts OS1, OS2, OS17, OS31, and OS33 were 0.77 (p=0.013), 0.88 (p=0.147), 0.49 (p<0.001), 0.66 (p<0.001), and 0.40 (p<0.001), respectively. Despite delayed progression observed in the OS xenografts treated with lenvatinib, all groups experienced progressive disease by the end of the study period.

Conclusions: Single agent lenvatinib demonstrates consistent anti-tumor activity in osteosarcoma patient derived mouse xenograft models. Preclinical studies, as well as clinical trials, have demonstrated the efficacy of tyrosine kinase inhibition in combination with inhibition of mTOR in a variety of malignancies. The current study, along with prior data, suggests that targeting receptor tyrosine kinases, in addition to mTOR, may lead to more effective inhibition of osteosarcoma cell growth. Ongoing studies are assessing the efficacy of lenvatinib, administered in combination with mTOR inhibitor, everolimus, in osteosarcoma patient derived mouse xenografts.

Citation Format: Wendong Zhang, Michael E. Roth, Jonathan Gill, Sajida Piperdi, E. Anders Kolb, David S. Geller, Bang Hoang, Rui Yang, Richard Gorlick. Stage 1 in vivo evaluation of multi-receptor tyrosine-kinase inhibitor lenvatinib in osteosarcoma patient derived mouse xenograft models [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 697. doi:10.1158/1538-7445.AM2017-697

Genetically transforming human osteoblasts to sarcoma: development of an osteosarcoma model

Osteosarcoma is the most common primary malignant bone tumor in children and young adults. Although histologically defined by the presence of malignant osteoid, the tumor possesses lineage multipotency suggesting it could be derived from a cell anywhere on the differentiation pathway between a mesenchymal stem cell (MSC) and a mature osteoblast. To determine if preosteoblasts (pOB) could be the cell of origin differentiated MSCs were transformed with defined genetic elements. MSCs and pOB differentiated from the same MSCs were serially transformed with the oncogenes hTERT, SV40 large T antigen and H-Ras. Assays were performed to determine their tumorigenic properties, differentiation capacity and histologic appearance. When subcutaneously implanted in immunocompromised mice, cell lines derived from transformed MSC and pOB formed tumors in 4 weeks. In contrast to the transformed MSC, the pOB tumors demonstrated a histological appearance characteristic of osteosarcoma. The cell lines derived from the transformed pOB only had osteogenic and chondrogenic differentiation potential, but not adipogenic ones. However, the transformed MSC cells and standard osteosarcoma cell lines maintained their tri-lineage differentiation capacity. The inability of the transformed pOB cell line to undergo adipogenic differentiation, may suggest that osteosarcoma is derived from a cell intermediate in differentiation between an MSC and a pOB, with partial commitment to the osteoblastic lineage.

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.

Abstract 645: The effect of rhBMP-2 on in vitro osteosarcoma tumorigenesis and on pulmonary growth and development

Introduction: Complete surgical resection is a critical component of care for patients with osteosarcoma (OS). Limb-salvage surgery is performed in over 90% of cases. Non-union is a well-recognized complication of allograft reconstructions, frequently performed following tumor extirpation. Bone Morphogenetic Protein-2 (BMP-2) has been shown to be osteoinductive and could theoretically improve allograft-host bone union. The purpose of this investigation is to evaluate the effect of exogenous recombinant human BMP-2 (rhBMP-2) on osteosarcoma.

Methods: Functional assays were performed using five standard osteosarcoma cell lines and three patient derived xenograft cell lines. Random migration motility was measured via wound healing scratch assay. Migration (haptotaxis) was quantitatively measured using Boyden Chamber assay. Invasion was assessed using the Biocoat Matrigel Invasion Kit. Cell proliferation rate was measured by using MTT reagent. Metastatic disease was assessed using a xenograft murine model.

Results: Findings suggest that exogenous rhBMP-2 does not meaningfully affect osteosarcoma migration, invasion or proliferation across all tested lines. Average corrected lung weight in the single-dose rhBMP-2 experiment was 1.56 g in the experimental group versus 1.67 g in the control group (p = 0.69). Average corrected lung weight in the triple-dose rhBMP-2 experiment was 1.23 g in the experimental group versus 1.06 g in the control group (p = 0.07).

Conclusions and Future Directions: Results support the contention that exposure of osteosarcoma to exogenous rhBMP-2 does not increase either in vitro tumorigenesis or pulmonary disease growth and development within this experimental model. While results are compelling, additional characterization and confirmation of these findings are necessary safety prerequisites prior to proposing clinical application.

Citation Format: David S. Geller, So Hak Chung, Wendong Zhang, Sajida Piperdi, Carrie Freeman, Bang Hoang, Rui Yang, Michael Roth, Jonathan Gill, Richard Gorlick. The effect of rhBMP-2 on in vitro osteosarcoma tumorigenesis and on pulmonary growth and development. [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 645.

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.

Abstract 2221: HHLA2, a novel member of the B7 family of inhibitory ligands, is highly expressed in osteosarcoma

Purpose: Over the past four decades there have been minimal improvements in outcomes for patients with osteosarcoma (OS). New targets and novel therapies are needed to improve outcomes for these patients. In this study, we sought to evaluate the prevalence and prognostic utility of the immune checkpoint inhibitor HHLA2 in OS.

Experimental Design: HHLA2 expression was evaluated in two cohorts of OS patients using a tumor microarray (TMA) (n = 62) and whole slides (n = 48). HHLA2 expression was assessed in primary tumor specimens and metastatic disease, and correlated with the presence of tumor infiltrating lymphocytes (TILs), and event free survival.

Results: HHLA2 was expressed in 68% of OS tumors in the TMA and in 54% in the second cohort. 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).

Conclusions: HHLA2 is expressed in the majority of OS tumors, is associated with metastatic disease, and is associated with poorer survival. Further studies are needed assessing the effect of HHLA2 expression on the function of the immune microenvironment, as well as assessing the feasibility and utility of targeting HHLA2 in OS.

Citation Format: Pratistha Koirala, Michael Roth, Jonathan Gill, Jordan Chinai, Michelle Ewart, Sajida Piperdi, David Geller, Bang Hoang, Yekaterina Fatakhova, Maya Ghorpade, Xingxing Zang, Richard Gorlick. HHLA2, a novel member of the B7 family of inhibitory ligands, is highly expressed 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 2221.

Abstract 3133A: Circulating tumor DNA as “liquid biopsy” in pediatric osteosarcoma

BACKGROUND: Osteosarcoma (OS) is the most common primary malignant bone tumor and children and adolescents represent half of new cases diagnosed each year. During and after treatment there is no non-invasive test to assess disease response and early relapse, respectively. Monitoring of circulating tumor material as a “liquid biopsy” has potential to provide this critical information in OS, as it has proven useful in other solid tumors. We hypothesized that circulating tumor DNA (ctDNA) can be extracted from mouse plasma and identified using next generation sequencing. This could ultimately be used to assess tumor burden, evaluate response to treatment, and monitor for recurrence in OS. We overcome the challenge of identifying tumor DNA in a background of host DNA by first using primary tumor material to identify genomic aberrations in a targeted gene region known to be altered in >95% of patients with OS. We then use next generation sequencing to identify in circulation the rare tumor DNA based on known aberrations expected to be present when there is a tumor burden.

MATERIALS AND METHODS: Human osteosarcoma cell lines 143b and M17 were grown in culture and introduced into SCID mice via tail vein, subcutaneous flank, and tibial plateau injections. Terminal bleeds were performed 30 minutes after tail vein injection and at max tumor growth respectively. DNA was extracted from primary tumor cell lines as well as from the plasma of injected mice. We then performed next generation sequencing (NGS) with the Illumina HiSeq 2000 using custom designed probes capturing genes commonly altered in osteosarcoma including TP53, RB1, ATRX, DLG2, MET, PTEN, and SLC19A1. DNA extracted from the plasma of a SCID mouse that did not receive tumor cell injection was used as a negative control.

RESULTS: Gene coverage of approximately 80% was obtained for targeted genes to a depth ranging from 250x to 2000x coverage for tumor cell lines. Cell free circulating tumor DNA was identified in plasma of mice injected with 143b mice via tail vein and flank injections but not from tumor cell free plasma negative control. Over 1000 mutations were identified, most notably c.467G>C p.R156P, a well documented osteosarcoma mutation, which was present in the 143b cell line as well as the DNA extracted from the plasma of tail vein and flank injected mice.

CONCLUSIONS: Circulating cell free tumor DNA can be successfully extracted from SCID mouse plasma and identified using next generation sequencing of target genes. Based on these mouse findings, we anticipate that this will serve as a non-invasive biomarker of disease burden and response to therapy, as well as a biomarker to assess recurrence. The pilot work provides rationale to expand these findings into clinical trials that can prospectively validate our methods and findings. Our approach has the potential to improve outcomes for a childhood cancer frequently associated with poor survival.

Citation Format: Michael Fremed, Sajida Piperdi, Wendong Zhang, Shahina Maqbool, Brent Calder, Raquel Castellanos, Jonathan Gill, Michael Roth, Bang Hoang, David Geller, Richard Gorlick, Daniel Weiser. Circulating tumor DNA as “liquid biopsy” in pediatric 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 3133A.

Abstract 2182: Flavokawain A and B from kava extract exhibits low toxicity and up-regulates tumor suppressor miRNAs in human osteosarcoma cells

Objective: Osteosarcoma (OS) is the most common primary bone malignancy with a high propensity for local invasion and distant metastasis. Flavokawain A and B (FKA and FKB) from kava extract have been reported to have significant anti-tumoral effects on human cancer cells. The consumption of kava-containing beverage has been associated with a low cancer incidence. The objective of this study is to investigate the anti-tumoral effects of flavokawains in OS. In a previous report, mice treated with high-dose FKA did not demonstrate any significant major organ toxicity. MicroRNAs (miRNA), endogenous, non-coding RNA, are associated with cell-cycle regulation, differentiation, proliferation, apoptosis, and migration. There remains a paucity of literature on the effects of flavokawains on the expression of miRNA in OS. As such, we hypothesize that flavokawains will up-regulate tumor-suppressive miRNA in OS cell lines.

Methods: Human OS cell lines from American Type Culture Collection (ATCC), patient-derived OS cell lines, human mesenchymal stem cells, human intestinal epithelial cells, and mouse bone marrow cells were cultured. Cell lines were divided into control and treatment groups with increasing doses of FKA or FKB. Cell viability was determined by MTT proliferation assays and cytotoxicity to bone marrow cells was examined by colony formation. Effects of flavokawain on intestinal cells were examined by fluorescent cytotoxicity and flow cytometry. Apoptotic assays were performed following flavokawain treatments. The expression of miRNA after FKA and FKB treatment was examined by qRT-PCR. SCID mice were injected with OS 143B cells in the tibia and treated with either vehicle control or FKA (200 mg/kg) by oral gavage.

Results: By flow cytometry, FKB increases apoptosis of OS 143B cells while sparing intestinal FHs 74 intestinal cells. Mouse bone marrow cells treated with FKB showed no significant difference in colony forming units compared to control cells. Exposure of OS cell lines to FKA or FKB resulted in a loss of cell viability in a dose-dependent manner. In all cell lines tested a dose-dependent expression of miRNA was observed after exposure to FKA or FKB. Flavokawain B induced miR-26a while FKA induced miR-26a, miR-34, and miR-203 expression in OS cell lines. Mice bearing 143B xenograft tumors treated with FKA did not exhibit weight loss compared to control animals. Animals treated with FKA sustained less lung metastasis than animals treated with vehicle control.

Conclusions: Taken together, the evidence suggests flavokawains up-regulate tumor suppressive miRNAs in OS cells. In vivo experiments suggest that FKA exerts anti-metastatic effects in OS. Given their low toxicity profile, flavokawains may be useful as a chemopreventive strategy for OS and thus warrant further investigations.

Citation Format: Wendong Zhang, Jonathan Morris, Sajida Piperdi, Yi Guo, Tao Ji, Rui Yang, Michael Roth, Jonathan Gill, David S. Geller, Richard Gorlick, Kevin Jones, Xiaolin Zi, Bang H. Hoang. Flavokawain A and B from kava extract exhibits low toxicity and up-regulates tumor suppressor miRNAs in human osteosarcoma cells. [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 2182.

A RUNX2-Mediated Epigenetic Regulation of the Survival of p53 Defective Cancer Cells

The inactivation of p53 creates a major challenge for inducing apoptosis in cancer cells. An attractive strategy is to identify and subsequently target the survival signals in p53 defective cancer cells. Here we uncover a RUNX2-mediated survival signal in p53 defective cancer cells. The inhibition of this signal induces apoptosis in cancer cells but not non-transformed cells. Using the CRISPR technology, we demonstrate that p53 loss enhances the apoptosis caused by RUNX2 knockdown. Mechanistically, RUNX2 provides the survival signal partially through inducing MYC transcription. Cancer cells have high levels of activating histone marks on the MYC locus and concomitant high MYC expression. RUNX2 knockdown decreases the levels of these histone modifications and the recruitment of the Menin/MLL1 (mixed lineage leukemia 1) complex to the MYC locus. Two inhibitors of the Menin/MLL1 complex induce apoptosis in p53 defective cancer cells. Together, we identify a RUNX2-mediated epigenetic mechanism of the survival of p53 defective cancer cells and provide a proof-of-principle that the inhibition of this epigenetic axis is a promising strategy to kill p53 defective cancer cells.

Because activated p53 is a potent inducer of apoptosis, several approaches centering on p53 activation are designed for killing cancer cells. However, more than half of human tumors have p53 inactivation, which renders these p53-activating approaches less effective in killing cancer cells. Targeting the survival signals specific to p53 defective cancer cells offers an opportunity to circumvent the challenge of p53 inactivation. In this study, we showed that one such survival signal is the RUNX2 signaling pathway. To investigate the mechanism underlying this survival signal, we used biochemical, genetic, and genomic approaches. The MYC gene was identified as a novel mediator of the pro-survival function of RUNX2. We further studied the regulatory mechanism of MYC by RUNX2 and found that RUNX2 recruits the Menin/MLL1 epigenetic complex to induce the expression of MYC. Using small molecule inhibitors of the Menin/MLL1 complex, we showed that targeting RUNX2/Menin/MLL1/MYC axis is a feasible strategy for killing p53 defective cancer cells. Our study paves the road for the future development of targeted therapies for OS.

Targeting Glycoprotein NMB With Antibody-Drug Conjugate, Glembatumumab Vedotin, for the Treatment of Osteosarcoma

BACKGROUND

Cure rates for children and young adults with osteosarcoma have remained stagnant over the past three decades. Targeting glycoprotein non-metastatic b (GPNMB) with the antibody-drug conjugate glembatumumab vedotin has improved outcomes for patients with melanoma and breast cancer. The potential utility of targeting GPNMB in osteosarcoma was explored.

METHODS

GPNMB protein expression was evaluated by immunohistochemistry in human osteosarcoma tumor samples and by enzyme-linked immunosorbent assay (ELISA) in osteosarcoma cell lines. mRNA expression was measured by quantitative PCR in primary osteosarcoma samples and cell lines. Surface GPNMB expression was evaluated by flow cytometry and correlated with in vitro and in vivo cytotoxicity of glembatumumab vedotin.

RESULTS

Sixty seven human osteosarcoma samples were evaluated by immunohistochemistry, including 12 samples from initial biopsy, 38 samples from definitive surgery, and 17 from the time of disease recurrence. GPNMB was expressed in 92.5% (62/67) of osteosarcoma samples. All primary osteosarcoma samples expressed high levels of GPNMB mRNA. Glembatumumab induced cytotoxic effects in 74% (14/19) of osteosarcoma cell lines, and GPNMB protein levels correlated with glembatumumab in vitro cytotoxicity (r = -0.46, P = 0.04). All osteosarcoma cell lines demonstrated surface GPNMB expression.

CONCLUSIONS

GPNMB is expressed in osteosarcoma and targeting GPNMB with the antibody-drug conjugate glembatumumab vedotin demonstrates osteosarcoma cytotoxic activity. Clinical trials are indicated to assess the efficacy of targeting GPNMB in patients with osteosarcoma.

Abstract 1412: Utilizing cell surface markers to define osteosarcoma and the stages of osteoblast differentiation

Background

Osteosarcoma (OS) is the most common primary malignant bone tumor in children. Despite advances in OS treatment, survival rates have remained stagnant over the past three decades. This may in part be reflective of the complex nature of OS—although all OS’ are pleomorphic, spindle shaped cells that are capable of producing osteoid, this is often where the similarities between tumors ends. Tumor phenotypes can be used to classify OS into multiple groups including the most common form, conventional, which can be further subdivided into osteoblastic, chondroblastic, or fibroblastic OS. Although these tumors display unique phenotypes, they have similar response rates to standard treatments such as chemotherapy and surgery suggesting that they may have a common progenitor, which we seek to identify.

Methods

In order to determine the OS cell of origin, we first performed flow cytometry analysis using cell surface markers that are differentially expressed on mesenchymal stem cells (MSC) and osteoblasts (OB)—CD44, CD105, CD54, CD49b, CD325, and GD2. MSCs were differentiated into OBs using induction media and cells were collected for analysis at multiple time points in differentiation; day (d)0, d3, d5, d10, d15, and d20. MSCs became fully differentiated OBs by d20, as determined by alizarin red staining. Similar flow cytometry analysis was performed on four OS standard cell lines, SaOS, U2OS, HOS, and HOS-143B, and marker profiles were compared to MSC to OB differentiation.

Results

CD44 and CD105 expression, both of which are known MSC markers, was high in MSCs and immediately dropped off during differentiation, while decrease in CD325 expression was more gradual. CD49b expression increased over time and GD2 expression varied greatly. CD54 expression peaked at d10 and decreased as differentiation continued. Expression of these markers was varied in the OS standard cell lines. These markers can be used to sort out specific populations of cells at different time points during differentiation.

Conclusions and Future Directions

In this study we have identified potential markers of OB progenitor populations and compared their expression to OS standard cell lines. We will use these prospective makers to sort progenitor populations and drive their differentiation into OBs, chondroblasts, and fibroblasts in order to determine branch points in MSC differentiation. Finally, in order to assess the potential of these cells to form OS, we plan to transform candidate progenitor cells with human telomerase reverse transcriptase, simian virus 40 large T antigen, and lentivirus containing oncogenic H-Ras serially.

Citation Format: Pratistha Koirala, Vincent Poon, Sajida Piperdi, Amy Park, Michael Fremed, Michael Roth, Jonathan Gill, Richard Gorlick. Utilizing cell surface markers to define osteosarcoma and the stages of osteoblast differentiation. [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 1412. doi:10.1158/1538-7445.AM2015-1412

Abstract 1630: Effects of rhBMP-2 on osteosarcoma tumorigenesis

Introduction: Osteosarcoma (OS) is the most common primary bone malignancy in children and young adults. Complete surgical extirpation of bulk tumor is essential to successful treatment of OS. While historically ablative surgery such as amputations were the mainstay of treatment, wide excision has been shown to provide equivalent survival results, permitting for limb-salvage surgery in over 90% of cases. Following tumor resection, structural allograft bone is often employed to reconstruct the involved extremity. Bone Morphogenetic Protein-2 (BMP-2), a member of the TGF beta superfamily, possesses tremendous osteoinductive potential and could theoretically be used to promote bone healing but has been historically contraindicated due to concern it may stimulate residual tumor. To date, the role of BMP-2 in OS remains unclear and its effect on OS remains controversial. The purpose of this investigation is to evaluate the effect of exogenous recombinant human BMP-2 (rhBMP-2) on osteosarcoma. We hypothesize that exposure of osteosarcoma to rhBMP-2 will not stimulate tumor growth or development.

Methods: Functional assays were performed using five standard osteosarcoma cell lines (143B, MG-63, SaOS-2, U20S, and HOS) and three patient derived xenograft cell lines (OS17, OS31, LM7). The concentration of rhBMP-2 utilized varied between 0.5 to 2 μg/ml. Motility (random migration) was measured by wound healing scratch assay. Migration (both haptotaxis and chemotaxis) was quantitatively measured using Boyden Chamber assay. Invasion was also measured using Boyden chamber over which a thin layer of extracellular matrix is applied. Comparison between different concentrations of rhBMP-2 upon different time points on osteosarcoma cell lines and characterizations are completed and underway.

Results: Preliminary findings suggest that exogenous rhBMP-2 does not increase the ability of osteosarcoma cells to migrate and invade in all tested lines (143B, MG-63, OS17). Quantitative migration decreases with increasing concentration of rhBMP-2 over a 5-hour time course in all tested lines (143B, SaOS-2, MG-63, OS17). Invasion did not increase with increasing rhBMP-2 concentration in any tested line (143B, SaOS-2, OS17).

Conclusions and Future Directions: Preliminary results support the contention that exposure of osteosarcoma to exogenous rhBMP-2 does not increase in vitro tumorigenesis. In fact, findings suggest that rhBMP-2 may have a protective effect in that tumor migration decreases following exposure. Continued characterization using additional tumor lines is ongoing.

Citation Format: Sajida Piperdi, David Geller, Amy Park, So Hak Chung, Richard Gorlick. Effects of rhBMP-2 on osteosarcoma tumorigenesis. [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 1630. doi:10.1158/1538-7445.AM2015-1630

Abstract 2344: The PD-1:PD-L1 pathway in the context of the osteosarcoma tumor microenvironment

Background

PD-1 is a transmembrane protein found on immune cells including T cells, B cells, natural killer (NK) T cells, activated monocytes, and dendritic cells. Its interaction with its ligand, PD-L1, plays a role in the suppression of the immune system and is important in many processes such as autoimmunity and both central and peripheral tolerance. Cancer cells can hijack the PD-1:PD-L1 pathway in order to evade clearance by the immune system—a mechanism that is evident in many solid tumors, including breast, ovarian, renal cell carcinoma, colorectal, and lung cancers. Inhibition of the PD-1:PD-L1 pathway with both PD-1 and PD-L1 inhibitors have shown varying levels of efficacy, and provide proof of concept—that modulating the PD- 1:PD-L1 pathway can tip the balance of immune response in favor of the patient, working to eliminate the tumor. We seek to determine the expression of PD-L1 in osteosarcoma (OS), specifically in relation to the prescience of tumor infiltrating lymphocytes (TILs). By displaying expression of PD-L1 and the presence of TILs we hope to subsequently target the PD-1:PD-L1 pathway in OS.

Methods

Paraffin imbedded and sectioned patient primary OS tumor samples were provided by IRB approved protocols at Montefiore Medical Center and Memorial Sloan Kettering Cancer Center. Antibodies to identify various immune cells were first validated and optimized using immune tissues and subsequently used to stain tumor sample. Next, RNA was extracted from patient OS tumor samples and used to generate cDNA. PD-L1 expression was determined using quantitative real time PCR. Protein was also extracted and will be used to confirm PD-L1 expression using western blotting.

Results

A variety of TILs are found in OS patient tumor samples. We see expression of T cells (CD3) and T cell subsets—helper (CD4), cytotoxic (CD8), and natural killer (CD56) T cells. There is also robust expression of B cells (CD20) and macrophages (CD68). Furthermore, the OS tumors displayed varying degrees of PD-L1 positivity, with some tumors displaying greatly increased expression, some showing moderate elevation, and others showing low to no changes in PD-L1 expression.

Conclusions and Future Directions

OS tumors display varying levels of PD-L1 positivity, suggesting that the PD-1:PD-L1 pathway can be modulated for immunotherapeutic purposes. Importantly, we also demonstrated that a subset of immune cells, potentially expressing PD-1, is present in some tumors. Cell lines derived from tumors expressing low, moderate, and high levels of PD-L1 are being cultured. These cell lines will be used to test inhibition of the PD-1:PD-L1 pathway and its impact on their tumorigenic properties.

Citation Format: Pratistha Koirala, Jonathan Gill, Michael Roth, Sajida Piperdi, Amy Park, Vincent Poon, Michael Fremed, Bang Hoang, Richard Gorlick. The PD-1:PD-L1 pathway in the context of the osteosarcoma tumor microenvironment. [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 2344. doi:10.1158/1538-7445.AM2015-2344

Ganglioside GD2 expression is maintained upon recurrence in patients with osteosarcoma

BACKGROUND

Osteosarcoma is the most common primary malignant bone tumor in children and young adults. Ganglioside GD2 has been previously found on the cell surface in various tumor types, including osteosarcomas.

FINDINGS

In this study, forty-nine additional osteosarcoma samples from 14 individual patients were assessed for GD2 expression via immunohistochemistry, of which 47 samples were found to express GD2. In matched samples from patients, GD2 expression seen at initial biopsy was found to persist in 100% of tissues taken at recurrence.

CONCLUSIONS

GD2 expression was found to persist upon recurrence. These results suggest a phase 2 trial in children with recurrent osteosarcoma should provide an appropriate read out on the efficacy of anti-GD2 antibody.

Development of a Model System to Evaluate Local Recurrence in Osteosarcoma and Assessment of the Effects of Bone Morphogenetic Protein-2

PURPOSE

It is increasingly relevant to better define what constitutes an adequate surgical margin in an effort to improve reconstructive longevity and functional outcomes following osteosarcoma surgery. In addition, nonunion remains a challenging problem in some patients following allograft reconstruction. Bone morphogenetic protein-2 (BMP-2) could enhance osseous union, but has been historically avoided due to concerns that it may promote tumor recurrence.

EXPERIMENTAL DESIGN

An orthotopic xenograft murine model was utilized to describe the natural temporal course of osteosarcoma growth. Tumors were treated either with surgery alone, surgery and single-agent chemotherapy, or surgery and dual-agent chemotherapy to assess the relationship between surgical margin and local recurrence. The effect of BMP-2 on local recurrence was similarly assessed.

RESULTS

Osteosarcoma tumor growth was categorized into reproducible phases. Margins greater than 997 μm resulted in local control following surgery alone. Margins greater than 36 μm resulted in local control following surgery and single-agent chemotherapy. Margins greater than 12 μm resulted in local control following surgery and dual-agent chemotherapy. The application of exogenous BMP-2 does not confer an increased risk of local recurrence.

CONCLUSIONS

This model reliably reproduces the clinical, radiographic, and surgical conditions encountered in human osteosarcoma. It successfully incorporates relevant chemotherapy, further paralleling the human experience. Surgical margins required to achieve local control in osteosarcoma can be reduced using single-agent chemotherapy and further decreased using dual-agent chemotherapy. The application of BMP-2 does not increase local recurrence in this model.

Abstract 3984: Elucidating expression patterns of GPNMB and potential anti-tumor effects of the antibody-drug conjugate, glembatumumab vedotin (CDX-011) in human osteosarcoma primary samples and cell lines

Despite numerous clinical trials to improve outcomes for osteosarcoma treatment, there has been no significant improvement in cure rates over the last three decades. Glycoprotein NMB (GPNMB), also known as osteoactivin, is a transmembrane glycoprotein that is expressed in various normal cell types including osteoclasts and osteoblasts, and plays a role in development and differentiation, respectively. Studies have also shown that GPNMB is highly expressed in cancers including breast cancers and melanomas.

CDX-011 is an antibody-drug conjugate that targets the GPNMB protein. A human monoclonal antibody glembatumumab is linked to monomethyl auristatin E, an antimitotic agent. Recent studies have shown the drug is effective in treating patients with metastatic triple- negative GPNMB-expressing breast cancer, and melanoma. The pediatric preclinical testing program (PPTP) has recently shown the drug is efficacious in xenograft models of osteosarcoma. In this study, we explore the feasibility of GPNMB as a target for antibody-mediated therapy in osteosarcoma and assess the anti-tumor effects of CDX-011.

Since CDX-011 activity appears to correlate with GPNMB protein expression, a cohort of osteosarcoma tissue sections from patients at the time of initial biopsy, definitive surgery, and recurrence was stained immunohistochemically to determine the presence or absence of GPNMB protein. The majority of samples show positive staining suggesting further that osteosarcoma might be a candidate for CDX-011 treatment. Flow cytometry was performed on human osteosarcoma xenografts and cell lines to determine the surface expression level of GPNMB prior to treatment with CDX-011. Of the 9 cell lines studied, 5 lines showed high surface expression of GPNMB protein. Cytotoxicity assays were performed on the same 9 cell lines representing both high and low GPNMB surface expression patterns to determine the in vitro effectiveness of CDX-011 in osteosarcoma cell lines and its correlation with GPNMB expression. IC50 on those cell lines ranged from 3.5- 56 µM. Three out of 5 cell lines, which showed high GPNMB surface expression pattern, demonstrated lower IC50 (3- 14 µM) compared to the others. These findings suggest that CDX-011 may be a potential targeted treatment in osteosarcoma patients with elevated GPNMB expression patterns. In addition, further studies are ongoing, including quantitative PCR for GPNMB gene expression, and ELISA to further validate expression of GPNMB protein to better understand the mechanism of CDX-011 in osteosarcoma.

Citation Format: Sajida Piperdi, Vicky Kuo, Amy Park, Michael Roth, Richard Gorlick. Elucidating expression patterns of GPNMB and potential anti-tumor effects of the antibody-drug conjugate, glembatumumab vedotin (CDX-011) in human osteosarcoma primary samples and cell lines. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3984. doi:10.1158/1538-7445.AM2014-3984

HER-2 expression is not prognostic in osteosarcoma; a Children's Oncology Group prospective biology study

BACKGROUND

Since the initial reports of human epidermal growth factor receptor 2 (HER-2) expression as being prognostic in osteosarcoma, numerous small studies varying in the interpretation of the immunohistochemical (IHC) staining patterns have produced conflicting results. The Children's Oncology Group therefore embarked on a prospective biology study in a larger sample of patients to define in osteosarcoma the prognostic value of HER-2 expression using the methodology employed in the initial North American study describing an association between HER-2 expression and outcome.

PROCEDURE

The analytic patient population was comprised of 149 patients with newly diagnosed osteosarcoma, 135 with localized disease and 14 with metastatic disease, all of whom had follow up clinical data. Paraffin embedded material from the diagnostic biopsy was stained with CB11 antibody and scored by two independent observers. Correlation of HER-2 IHC score and demographic variables was analyzed using a Fisher's exact test and correlation with survival using a Kaplan-Meier analysis.

RESULTS

No association was found with HER-2 status and any of the demographic variables tested including the presence or absence of metastatic disease at diagnosis. No association was found between HER-2 status and either event free survival or overall survival in the patients with localized disease.

CONCLUSION

HER-2 expression is not prognostic in osteosarcoma in the context of this large prospective study. HER-2 expression cannot be used as a basis for stratification of therapy. Identification of potential prognostic factors should occur in the context of large multi-institutional biology studies.

Ganglioside GD2 as a therapeutic target for antibody-mediated therapy in patients with osteosarcoma

BACKGROUND

Survival outcomes for patients with osteosarcoma have remained stagnant over the past 30 years. Targeting of ganglioside GD2, a glycosphingolipid on the cell surface of some tumors, with immunotherapy has resulted in improved outcomes for patients with neuroblastoma. In the current study, the expression pattern of GD2 was examined in osteosarcoma.

METHODS

Immunohistochemistry was performed on osteosarcoma samples from patients at the time of initial biopsy, definitive surgery, and disease recurrence. The intensity and location of staining were scored. Cell-based enzyme-linked immunoadsorbent assay was performed on osteosarcoma cell lines to quantitate the level of GD2 expression.

RESULTS

Forty-four osteosarcoma samples were evaluated by immunohistochemistry, including 8 samples from the initial biopsy, 28 samples from the definitive surgery, and 8 samples from the time of disease recurrence. GD2 was expressed on all 44 osteosarcoma samples. Osteosarcoma tissue obtained at the time of disease recurrence demonstrated a higher intensity of staining compared with samples obtained at initial biopsy and definitive surgery (P = .016). The majority of osteosarcoma cell lines expressed GD2 at higher levels than the neuroblastoma cell line BE(2)-C.

CONCLUSIONS

Ganglioside GD2 is highly expressed on osteosarcomas. Clinical trials are needed to assess the efficacy of targeting GD2 in patients with osteosarcoma.

Abstract 5034: Quantification of required surgical margins in a xenograft osteosarcoma model with and without single-agent chemotherapy

In addition to systemic therapy, complete surgical excision is essential for successful treatment of osteosarcoma. Currently, the gold standard is to perform a "wide excision," however the definition of a wide excision is descriptive only. There is no current clear consensus on what constitutes an adequate "wide excision." The purpose of this project is to quantify an adequate "wide excision," defined by lack of local and/or distant recurrence using a xenograft murine model both with and without single agent chemotherapy. Patient-derived osteosarcoma tumor cells (OS17 and 187) were cultured and surgically implanted into the proximal metaphyseal tibia of female SCID mice. Once tumors were papable, amputations were performed under general anesthesia in either an intralesional, marginal, or wide manner. Histological sectioning was conducted in a standardized fashion to obtain measurements of bone and soft tissue margins. Mice were followed for six weeks, after which amputation stumps were evaluated for local recurrence while both the lungs and livers were assessed for metastatic dissemination. Thereafter, a second group of mice underwent implantation and amputation as previously described. They were thereafter treated with either cisplatin or doxorubicin over a course 4 weeks and followed for an additional 6 weeks to identify local and distant recurrence. In mice implanted with either OS17 or 187 and treated without chemotherapy, surgical bone margins lower than 100μm reliably resulted in local recurrence while margins greater than 700μm showed no recurrence. A variable recurrence rate was found between margins of 100μm and 700 μm. Similarly, soft-tissue margins below 50μm reliably resulted in local recurrence while margins greater then 600μm showed no recurrence. In mice implanted with OS17 and thereafter treated with chemotherapy, no recurrence was seen above bone or soft-tissue margins of 14μm while mice implanted with 187 showed no recurrence above bone margins of 25μm or soft tissue margins above 10μm. Metastatic disease did not overtly develop and may require a longer period of observation. In conclusion, single agent chemotherapy appears to reliably decrease the surgical margin required to obtain adequate local control in this xenograft model. Combination chemotherapy may prove to further decrease necessary margins, which ultimately may have ramifications on surgical morbidity and long-term reconstructive and functional outcome for patients with localized high-grade osteosarcoma.

Citation Format: David S. Geller, Michael Singh, Wendong Zhang, Esperanza Vilanueva-Siles, Amy Park, Sajida Piperdi, Richard Gorlick. Quantification of required surgical margins in a xenograft osteosarcoma model with and without single-agent chemotherapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5034. doi:10.1158/1538-7445.AM2013-5034

Cell surface receptor expression patterns in osteosarcoma

BACKGROUND

Although the presence of numerous cell signaling receptors in osteosarcoma is known, their simultaneous characterization has not been performed to date. The current study sought to characterize and quantify the expression of cell surface receptors across a variety of osteosarcoma cell lines.

METHODS

Standard (n = 4) and patient-derived (n = 10) osteosarcoma cell lines were cultured and labeled with antibodies to epidermal growth factor receptor, human epidermal growth factor receptor (HER)-2, HER-3, HER-4, insulin-like growth factor 1 receptor (IGF-1R), IGF-2R, insulin receptor (IR), vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, VEGFR-3, c-Met, fibroblast growth factor receptor (FGFR)-2, FGFR-3, and platelet-derived growth factor receptor (PDGFR)-β. Cell surface examination was performed using flow cytometry, and the geometric fluorescent mean for each receptor was calculated and compared against a positive control.

RESULTS

Significant overexpression of IGF-2R was shown in all cell lines, with an average geometric mean above the upper expression quartile. A variable expression pattern was seen for c-Met, PDGFR-β, IR, IGFR-1, HER-2, and VEGFR-3 with expression values for the remaining receptors mainly in the lower quartile. An apparent association between the expression of IGF-1R and HER-2 and between the expression of PDGFR-β and IR was demonstrated.

CONCLUSION

IGF-2R was consistently overexpressed on the cell surface across all tested osteosarcoma cell lines. Substantial, although variable, expression of c-Met, HER-2, IGF-1R, VEGFR-3, IR, and PDGFR-β was demonstrated as well, suggesting that these receptors may contribute to osteosarcoma aggressiveness and biological heterogeneity and may serve as potential targets within a subset of tumors. Associated receptor expression may provide new insight into common regulatory factors or pathways. Targeting either common factors or targeting multiple specific receptors may have therapeutic relevance.

Abstract 5332: Evaluation of GD2 expression in patients with osteosarcoma

GD2 is a disialoganglioside that is expressed on the cell surface in specific normal and malignant human tissues. Tumor specific cell surface antigens serve as important targets in cancer therapy. Anti-GD2 therapy using antibodies targeted to the cell surface antigen GD2 to induce antibody-dependent cellular cytotoxicity has been proven effective in treating GD2 expressing tumors like neuroblastoma and melanoma. Prior studies of osteosarcoma have shown GD2 to be expressed in malignant cells of osteosarcoma patients. In this study, the expression of GD2 in osteosarcoma will be evaluated further. A previously created and described tissue microarray was stained with 14.G2a, a murine monoclonal anti-GD2 antibody that was obtained from the National Cancer Institute. The intensity and location of tissue staining were assessed by a comparison between the positive and negative control slides. To evaluate GD2 expression quantitatively a cell-based ELISA was performed on different osteosarcoma patient derived cell cultures. The results of the tissue microarray showed that 34.8% of patient samples stained positive for GD2 while 60.9% of samples showed intermediate staining and only 4.3% of samples showed negative staining for GD2 (n=88). Nearly all of the osteosarcoma cell lines (n=24) showed levels of GD2 expression comparable to the neuroblastoma and fibrosarcoma cell lines and in some cases GD2 expression was significantly greater. Anti-GD2 therapy has been proven effective in treating patients with neuroblastoma and melanoma. The findings in this paper indicate that osteosarcomas express GD2 to a similar extent as neuroblastomas. These results would suggest clinical trials are worthwhile to further evaluate the benefit of anti-GD2 therapy in patients with osteosarcoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5332. doi:10.1158/1538-7445.AM2011-5332

Abstract 1581: Determination of the cellular origin of stroma in osteosarcoma

Introduction- Solid tumors like osteosarcoma have a distinct structure that is comprised of two interdependent compartments, the parenchyma (neoplastic cells) and the stroma that the neoplastic cells induce or produce and in which they are dispersed. The stroma may be induced as a result of tumor cell-host interactions or alternatively tumors may undergo different patterns of programmed differentiation to perform the necessary stromal support functions. Since stroma development is critical to the growth of tumor, identification of origin and mechanism of development of stroma can help target potential therapies against the tumor. Therefore we performed this study to elucidate the origin of stroma in a osteoarcoma xenograft, with a hypothesis that, the stroma of osteosarcoma is host (mouse) derived.

Methods- (1) Frozen sections from xenograft osteosarcomas, were stained with vWF and CD31 (endothelial marker antigens) to identify the blood vessels. (2) The endothelial cells were laser capture dissected from frozen sections by pattern recognition. The Human and mice vWF and CD31 gene expression was quantified by real time PCR. (3) Detection of human and mice vWF gene by F.I.S.H. (4) Double immunofluorescent staining used to further delineate the mouse or human origin of the blood vessels. Anti Human Vimentin used to stain all human tissues, and anti vWF(Human and mice) to stain blood vessels of human and mice, fluorophore labeled secondary antibodies used to identify the bound primary antibodies.

Results-The Immuno staining for vWF (reactive for both human and mice) and CD 31 (reactive only for human) revealed deficient staining for CD31, implying that the blood vessels were mostly murine. The gene expression assays on the microdissected samples for human and mouse VWF and CD 31, showed that there is expression of both human and murine vWF and CD31 in the xenografts, with more mouse genes than human in the microdissected blood vessels.

The findings were confirmed by F.I.S.H for vWF probes for human and mice, whose initial results show that 95% of the tumors is human but at least 5% of the xenograft section stained for the mouse vWF probes. Double immunofluorescent studies are still in progress but preliminary results show, predominant human blood vessels with interspread murine blood vessels.

Conclusions – Although confirmatory experiments are still in progress, initial suggestions in the context of human heterotopic osteosarcoma xenografts, show that most of blood vessels are murine derived. Further studies will be undertaken to determine whether the blood vessels in human osteosarcomas are tumor derived or a result of vascular in-growth as is the case in the murine system.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1581. doi:10.1158/1538-7445.AM2011-1581

Abstract 1208: Elucidating possible functional implications of osteosarcoma risk-associated genetic level alterations in IGF2R

To address the need for novel osteosarcoma (OS) treatment regimens with greater efficacy and less toxicity, attention has been focused on developing antibodies that target components of the insulin-like growth factor (IGF) pathway, particularly insulin-like growth factor 1 receptor tyrosine kinase (IGF1R). IGF1R and its two ligands, insulin-like growth factor 1 (IGF1) and insulin-like growth factor 2 (IGF2), are known to be over-expressed in several cancers including OS and have roles in regulating cellular growth and proliferation. Clinical trials of IGF1R-inhibiting antibody therapies in OS, however, have returned mixed results. Studies aimed at elucidating the biologic basis of this differential clinical sensitivity to IGF1R-targeting therapeutic agents are currently underway. Interestingly, recent studies from our lab show that IGF2R is consistently over-expressed, relative to other known transmembrane receptors, on the cell surface, across 4 standard and 10 patient-derived OS cell lines. Coupled with results from concurrent experiments suggesting a lack of IGF1R copy number amplification in the majority of tested patient-derived OS samples and xenograft models, we chose to focus our next set of studies on IGF2R_aiming to characterize significant genetic variations within this gene and any functional implications, thereby elucidating the link, if any, between IGF2R's mutational status and its cell surface expression in OS. Relative quantification studies, done via real-time PCR, demonstrated variable IGF2R gene expression across 27 patient-derived OS samples, 4 xenograft models, and 4 standard cell culture (serum-starved) lines. Using the CaCo-2 cell line as the calibrator, 12 out of 27 patient-derived OS samples showed increased IGF2R gene expression, while none of the xenograft models or the standard OS cell lines did. Ongoing studies will examine the relationship between genetic level alterations in IGF2R and its patterns of expression; common IGF2R SNPs will be genotyped, first in the four available OS xenograft models. Findings will be correlated with known patterns of clinical response/sensitivity to IGF1R-targeted therapy tested on these models. The same SNPs will then be genotyped in the patient-derived OS samples and standard cell culture lines. Depending on the results obtained from these initial studies, further experiments can be designed to sequence/genotype other suspect coding regions on the IGF2R gene that may contain functionally significant mutations.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1208. doi:10.1158/1538-7445.AM2011-1208

Abstract 489: The origin of osteosarcoma

Introduction: Osteosarcoma is the most prevalent primary malignant bone tumour in children and young adults, with poor survival in 40% of patients. Theoretically, osteosarcoma could potentially be derived from a cell anywhere on the differentiation pathway between human mesenchymal stem cell (hMSC) and a mature osteoblast (OB). To identify the cell of origin and the genetic alterations involved in osteosarcomagenesis, hMSCs and the OBs derived from the same hMSCs were serially transformed with viral constructs containing oncogenes.

Methods: Bone-marrow-derived hMSCs were characterized through FACS analysis, and were induced to osteogenic differentiation for 4-6 weeks. OBs derived from hMSCs were identified with alkaline phosphatase activity and alizarin red staining. The hMSCs and the OBs were serially transformed with retrovirus containing human telomerase reverse transcriptase (hTERT), simian virus 40 large t antigen (SV40 TAg) and lentivirus containing oncogenic H-Ras. Genome-wide expression profiles, karyotype, and multilineage differentiation capacity were tested in all genetically transformed cell lines. Orthotopic tumorigenicity assays and soft agar assay were used to compare the biologic behavior between hMSC and the derivatives.

Results: OBs differentiated from hMSCs showed a diffused positive staining for alkaline phosphatase activity and alizarin red. Levels of osteocalcin secretion from differentiated OBs in osteogenic medium were significantly higher than hMSCs. All genetically transformed cell lines were identified by RT-PCR and Western-Blot. In tumorigenicity assays, tumors formed with sarcomatous cell lines derived from hMSC and osteoblasts in either subcutaneously injected or orthotopic-injected mice 4 weeks after the implantation. In osteoblasts group, tumor showed a typical osteosarcoma appearance. All transforming cell lines derived from osteoblasts lost the adipogenic differentiation capacity.

Conclusion: Our previous study showed that two sarcomatous cell lines were established by introducing genetic alterations serially to transform hMSC into a malignant phenotype, but there was no osteoid production or osteoblast-like features observed in the neoplastic cells. In this study, we have successfully developed a human osteosarcoma model by introducing the same genetic alterations into preosteoblasts derived from hMSC by osteogenic differentiation. The neoplastic cells transformed from preosteoblasts, which only have bilineage (osteogenic and chondrogenic) differentiation potential, were apparently different from the derivatives of hMSCs. The gene expression profiles revealed some significant pathways involved in osteosarcomagenesis, in which losing adipogenic differentiation capacity may be a crucial step.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 489. doi:10.1158/1538-7445.AM2011-489

Abstract 3195: Genomic amplification of IGF-1R in osteosarcoma

Osteosarcoma (OS) is the most common primary malignant bone tumor in children and young adults. Even though the current treatment regimen has increased event-free survival to 70%, there still exists a poor prognosis for patients with unresectable primary tumors and those with clinically evident metastases. Insulin like growth factor-1 (IGF-1) and its receptor are thought to have a role in the pathogenesis, invasion, and distant metastasis of many human solid tumors. Our previous preclinical data using an IGF-1R antibody against xenograft models of OS demonstrated responses in four out of six OS xenografts suggesting this as a potential therapeutic target. It may be hypothesized that IGF-1R is selected for genomic amplification in some OS due to its proliferative and anti-apoptotic effects. Real time RT-PCR was performed on the primary patient samples, xenografts, and 143B, a standard cell line, to see the expression of IGF-1R. Only 3 of 20 patient samples, and 1 of 4 xenografts have shown higher level of expression of IGF-1R in reference to GAPDH. Genomic DNA was isolated from the same samples, and quantitative PCR was performed to detect gene copy numbers. 11 of 19 (58%)samples were shown to have more than 2 copies of IGF-1R (2 samples have >10 copies, 1 has 7, 2 have 5, 6 have 33), whereas 37% have 2 copies. Two OS xenografts, which respond to IGF-1R antibody in preclinical testing, showed increases in the copy number of IGF-1R. Fluorescence in situ hybridization (FISH) was used to detect the amplification of IGF-1R gene in both patient derived and xenograft OS cell lines. FISH was performed on metaphase slides of fixed cultured cells. Three BAC probes spanning the IGF-1R gene locus in 15q26.3 were produced by isolating BAC DNA, and labeling with AlexaFluor 488 by nick translation. Metaphase prep slides were then hybridized with IGF-1R probes and Texas Red-labeled chromosome 15 centromere probes, counter stained with DAPI, and viewed under fluorescence microscope. Copy number was counted in cells showing a full metaphase spread. Based on initial FISH results, it seems that in the majority of OS the IGF-1R gene is not amplified. This does not imply that IGF1R overamplification does not play a role in IGF-IR overexpression in OS: given the heterogeneity of these tumors and the limited sample size of the experiments thus far IGF-1R amplification may be a rare phenomenon in OS. As responses to IGF-1R are not observed in the majority, it remains possible that amplification correlates with therapeutic response to IGF-1R antibody. FISH on more patient cell lines and xenografts are underway, and even if no amplification is demonstrated, increased IGF-IR activity could still be explained by GOF mutation, or other mechanisms. Additional experiments including FISH in a larger pool of samples, comparing amplification results to clinical data and responsiveness of the cell lines to anti-IGF-IR therapy, and looking for other abnormalities in the IGF-I system, among others are underway.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3195.

Activation of the RAF/mitogen-activated protein/extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase pathway mediates apoptosis induced by chelerythrine in osteosarcoma

PURPOSE

Chelerythrine, a widely used broad-range protein kinase C inhibitor, induces apoptosis in many cell types. In this study, the mechanism of chelerythrine-induced apoptosis in osteosarcoma was investigated.

EXPERIMENTAL DESIGN

Signaling pathways activated by chelerythrine in osteosarcoma were detected by Western blots. Impacts of RAF/mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK MAPK on apoptosis and cell survival were studied using genetic approaches and pharmacologic pathway-specific inhibitors.

RESULTS

Osteosarcoma cells underwent apoptosis rapidly after treatment with chelerythrine. Three parallel MAPKs pathways, including the ERKs, c-Jun NH(2) kinases, and p38, were activated by chelerythrine in a dose-dependent and time-dependent fashion. For the ERKs, the activation was evident at the earliest time point tested (2 minutes) and sustained for >4 hours. Introduction of a dominant-negative H-RAS mutant (17N) partially attenuated ERK activation and delayed the onset of apoptosis induced by chelerythrine. The ERK activation and apoptotic effects of chelerythrine were greatly abrogated by the pharmaceutical inhibitors of MEK, but not by those of c-Jun NH(2) kinase or p38. Moreover, osteosarcoma cells were sensitized to chelerythrine by transient transfection with wild-type MEK1 or constitutively active MEK1 and became resistant with dominant-negative MEK1. Other protein kinase C inhibitors, including GF109203X or Gö6976, did not cause ERK activation or apoptosis in the same timeframe tested.

CONCLUSION

In osteosarcoma, chelerythrine-induced apoptosis is mediated through activation of the RAF/MEK/ERK pathway. These findings suggest that activating the ERK MAPK, as opposed to inhibiting it, may be a therapeutic strategy in osteosarcoma.

Platelet-derived growth factor receptor as a prognostic marker and a therapeutic target for imatinib mesylate therapy in osteosarcoma

The purpose of this review was to determine whether imatinib mesylate (STI571, Gleevec) has a role in the treatment of osteosarcoma. The expression of platelet-derived growth factor (PDGF) receptor and its ligand was examined in a panel of surgical specimens obtained from 54 osteosarcoma patients, and then the expression was compared with prognosis. The effects of imatinib mesylate on growth and molecular events in 10 patient-derived osteosarcoma cell cultures were investigated. Immunohistochemical studies demonstrated frequent expression of PDGF-AA (80.4%) and PDGF-alpha receptor (79.6%) and their correlation with inferior event-free survival (P < .05). PDGF-B-B and PDGF-beta-receptor expressions were also frequent (75.4% and 86%, respectively); however, statistically significant inferior event-free survival was not demonstrated (P = .15). In vitro studies demonstrated that imatinib mesylate had a variable cytotoxic effect on various osteosarcoma primary cultures, with an IC(50) of 5.6 microM to 9.5 microM, and blocked the PDGF-induced intracellular signal transduction as well as inhibition of downstream Akt phosphorylation. Mitogen-activated protein kinase (MAPK) was constitutively activated despite PDGF stimulation and imatinib mesylate treatment in 7 of 10 osteosarcoma cultures, perhaps explaining uncontrolled proliferation and relative unresponsiveness to imatinib. Imatinib mesylate could not be viewed as having a role as a single agent at current conventional doses for the treatment of osteosarcoma. These findings predicted activity in osteosarcoma clinical trials and suggested that in vitro model systems predict clinical behavior and that PDGF and its receptor expression could potentially be used for determining prognosis of osteosarcoma.

Monoclonal antibodies to Mycobacterium tuberculosis CDC 1551 reveal subcellular localization of MPT51

Mycobacterium tuberculosis CDC 1551, a highly immunogenic outbreak strain, previously reported to have unique surface distribution of capsular polysaccharide, was used to generate novel monoclonal antibodies (mabs) to surface mycobacterial targets. Two immunoglobulin G1 (IgG1) mAbs, 16a1 and 16a6 were generated. The mAbs originated from the same B cell, bound strongly to whole cell M. tuberculosis CDC1551 and to its cell wall, membrane and cytosol fractions recognizing a 90kDa protein. Immunoprecipitation using mAb 16a1 isolated a protein with amino acid peptide sequences matching MPT51 from the cytosol. This immunogenic protein of unknown function was previously reported only in culture filtrates of M. tuberculosis. Our findings suggest for the first time that this protein is found within the M. tuberculosis cell.

Antigenic evidence of prevalence and diversity of Mycobacterium tuberculosis arabinomannan

Arabinomannan (AM) is a polysaccharide of the mycobacterial capsule. The capsular polysaccharides of various microorganisms are diverse, and this diversity is important for classification of organisms into serotypes and vaccine development. In the present study we examined the prevalence and diversity of AM among Mycobacterium tuberculosis strains using four AM-binding monoclonal antibodies (MAbs). One of these MAbs, MAb 9d8, is known to bind to AM specifically. By whole-cell enzyme-linked immunosorbent assay (ELISA), the AM recognized by MAb 9d8 was detected on the surfaces of 9 of 11 strains, while 2 strains showed no reactivity with MAb 9d8. However, the AM recognized by MAb 9d8 was found in the culture supernatants of all 11 M. tuberculosis strains tested, as demonstrated by capture ELISA. Other AM-binding MAbs reacted both with the surfaces and with the culture supernatants of all 11 strains. Mice immunized with an experimental AM-recombinant Pseudomonas aeruginosa exoprotein A (rEPA) conjugate vaccine had an increased antibody response to AM and a moderate reduction in the numbers of CFU in their organs 7 days after challenge. Our results indicate that AM was detected in all M. tuberculosis strains tested, with differences in epitope distributions of certain strains. In addition, our results suggest that an experimental AM-rEPA vaccine has a moderate effect on the numbers of CFU in organs early after infection.