Michael Roth

Eltrombopag inhibits the proliferation of leukemia cells via reduction of intracellular iron and induction of differentiation

Eltrombopag (EP) is a small-molecule, nonpeptide thrombopoietin receptor (TPO-R) agonist that has been approved recently for the treatment of thrombocytopenia in patients with chronic immune thrombocytopenic purpura. Prior studies have shown that EP stimulates megakaryopoiesis in BM cells from patients with acute myeloid leukemia and myelodysplastic syndrome, and the results also suggested that it may inhibit leukemia cell growth. In the present study, we studied the effects of EP on leukemia cell proliferation and the mechanism of its antiproliferative effects. We found that EP leads to a decreased cell division rate, a block in G(1) phase of cell cycle, and increased differentiation in human and murine leukemia cells. Because EP is species specific in that it can only bind TPO-R in human and primate cells, these findings further suggested that the antileukemic effect is independent of TPO-R. We found that treatment with EP leads to a reduction in free intracellular iron in leukemic cells in a dose-dependent manner. Experimental increase of intracellular iron abrogated the antiproliferative and differentiation-inducing effects of EP, demonstrating that its antileukemic effects are mediated through modulation of intracellular iron content. Finally, determination of EPs antileukemic activity in vivo demonstrated its ability to prolong survival in 2 mouse models of leukemia.

Satb1 regulates the self-renewal of hematopoietic stem cells by promoting quiescence and repressing differentiation commitment

How hematopoietic stem cells (HSCs) coordinate the regulation of opposing cellular mechanisms such as self-renewal and differentiation commitment remains unclear. Here we identified the transcription factor and chromatin remodeler Satb1 as a critical regulator of HSC fate. HSCs lacking Satb1 had defective self-renewal, were less quiescent and showed accelerated lineage commitment, which resulted in progressive depletion of functional HSCs. The enhanced commitment was caused by less symmetric self-renewal and more symmetric differentiation divisions of Satb1-deficient HSCs. Satb1 simultaneously repressed sets of genes encoding molecules involved in HSC activation and cellular polarity, including Numb and Myc, which encode two key factors for the specification of stem-cell fate. Thus, Satb1 is a regulator that promotes HSC quiescence and represses lineage commitment.

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

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.

Minimal PU.1 reduction induces a preleukemic state and promotes development of acute myeloid leukemia

Modest transcriptional changes caused by genetic or epigenetic mechanisms are frequent in human cancer. Although loss or near-complete loss of the hematopoietic transcription factor PU.1 induces acute myeloid leukemia (AML) in mice, a similar degree of PU.1 impairment is exceedingly rare in human AML; yet, moderate PU.1 inhibition is common in AML patients. We assessed functional consequences of modest reductions in PU.1 expression on leukemia development in mice harboring DNA lesions resembling those acquired during human stem cell aging. Heterozygous deletion of an enhancer of PU.1, which resulted in a 35% reduction of PU.1 expression, was sufficient to induce myeloid-biased preleukemic stem cells and their subsequent transformation to AML in a DNA mismatch repair–deficient background. AML progression was mediated by inhibition of expression of a PU.1-cooperating transcription factor, Irf8. Notably, we found marked molecular similarities between the disease in these mice and human myelodysplastic syndrome and AML. This study demonstrates that minimal reduction of a key lineage-specific transcription factor, which commonly occurs in human disease, is sufficient to initiate cancer development, and it provides mechanistic insight into the formation and progression of preleukemic stem cells in AML.

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.

Insulin-like growth factor 1 receptor and response to anti-IGF1R antibody therapy in osteosarcoma

Background Survival outcomes for patients with osteosarcoma (OS) have remained stagnant over the past three decades. Insulin-like growth factor 1 receptor (IGF1R) is over-expressed in a number of malignancies, and anti-IGF1R antibodies have and are currently being studied in clinical trials. Understanding the molecular aberrations which result in increased tumor response to anti-IGF1R therapy could allow for the selection of patients most likely to benefit from IGF1R targeted therapy. Methods IGF1R mRNA expression was assessed by RT PCR in OS patient primary tumors, cell lines, and xenograft tumors. IGF1R copy number was assessed by 3 approaches: PCR, FISH, and dot blot analysis. Exons 1–20 of IGF1R were sequenced in xenograft tumors and 87 primary OS tumors, and surface expression of IGF1R was assessed by flow cytometry. Levels of mRNA and protein expression, copy number, and mutation status were compared with tumor response to anti-IGF1R antibody therapy in 4 OS xenograft models. Results IGF1R mRNA is expressed in OS. Primary patient samples and xenograft samples had higher mRNA expression and copy number compared with corresponding cell lines. IGF1R mRNA expression, cell surface expression, copy number, and mutation status were not associated with tumor responsiveness to anti-IGF1R antibody therapy. Conclusions IGF1R is expressed in OS, however, no clear molecular markers predict response to IGF1R antibody-mediated therapy. Additional pre-clinical studies assessing potential predictive biomarkers and investigating targetable molecular pathways critical to the proliferation of OS cells are needed.

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

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.

Low Enrollment of Adolescents and Young Adults Onto Cancer Trials: Insights From the Community Clinical Oncology Program

PURPOSE Stagnant outcomes for adolescents and young adults (AYAs; 15 to 39 years old) with cancer are partly attributed to poor enrollment onto clinical trials. The National Cancer Institute (NCI) Community Clinical Oncology Program (CCOP) was developed to improve clinical trial participation in the community setting, where AYAs are most often treated. Further, many CCOP sites had pediatric and medical oncologists with collaborative potential for AYA recruitment and care. For these reasons, we hypothesized that CCOP sites enrolled proportionately more AYAs than non-CCOP sites onto Childrens Oncology Group (COG) trials. METHODS For the 10-year period 2004 through 2013, the NCI Division of Cancer Prevention database was queried to evaluate enrollments into relevant COG studies. The proportional enrollment of AYAs at CCOP and non-CCOP sites was compared and the change in AYA enrollment patterns assessed. All sites were COG member institutions. RESULTS Although CCOP sites enrolled a higher proportion of patients in cancer control studies than non-CCOP sites (3.5% v 1.8%; P < .001), they enrolled a lower proportion of AYAs (24.1% v 28.2%, respectively; P < .001). Proportional AYA enrollment at CCOP sites decreased during the intervals 2004 through 2008 and 2009 through 2013 (26.7% v 21.7%; P < .001). CONCLUSION Despite oncology practice settings that might be expected to achieve otherwise, CCOP sites did not enroll a larger proportion of AYAs in clinical trials than traditional COG institutions. Our findings suggest that the CCOP (now the NCI Community Oncology Research Program) can be leveraged for developing targeted interventions for overcoming AYA enrollment barriers.

Ganglioside GD2 expression is maintained upon recurrence in patients with osteosarcoma.

BackgroundOsteosarcoma 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.FindingsIn 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.ConclusionsGD2 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.

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.