The role of the DNA damage response in zebrafish and cellular models of Diamond Blackfan anemia

Ribosomal biogenesis involves the processing of pre-ribosomal RNA. A deficiency of some ribosomal proteins (RPs) impairs processing and causes Diamond Blackfan anemia (DBA), which is associated with anemia, congenital malformations and cancer. p53 mediates many features of DBA, but the mechanism of p53 activation remains unclear. Another hallmark of DBA is the upregulation of adenosine deaminase (ADA), indicating changes in nucleotide metabolism. In RP-deficient zebrafish, we found activation of both nucleotide catabolism and biosynthesis, which is consistent with the need to break and replace the faulty ribosomal RNA. We also found upregulation of deoxynucleotide triphosphate (dNTP) synthesis - a typical response to replication stress and DNA damage. Both RP-deficient zebrafish and human hematopoietic cells showed activation of the ATR/ATM-CHK1/CHK2/p53 pathway. Other features of RP deficiency included an imbalanced dNTP pool, ATP depletion and AMPK activation. Replication stress and DNA damage in cultured cells in non-DBA models can be decreased by exogenous nucleosides. Therefore, we treated RP-deficient zebrafish embryos with exogenous nucleosides and observed decreased activation of p53 and AMPK, reduced apoptosis, and rescue of hematopoiesis. Our data suggest that the DNA damage response contributes to p53 activation in cellular and zebrafish models of DBA. Furthermore, the rescue of RP-deficient zebrafish with exogenous nucleosides suggests that nucleoside supplements could be beneficial in the treatment of DBA.

Single cell network profiling assay in bladder cancer

The aim of this study was to assess the feasibility of applying the single cell network profiling (SCNP) assay to the examination of signaling networks in epithelial cancer cells, using bladder washings from 29 bladder cancer (BC) and 15 nonbladder cancer (NC) subjects. This report describes the methods we developed to detect rare epithelial cells (within the cells we collected from bladder washings), distinguish cancer cells from normal epithelial cells, and reproducibly quantify signaling within these low frequency cancer cells. Specifically, antibodies against CD45, cytokeratin, EpCAM, and cleaved-PARP (cPARP) were used to differentiate nonapoptotic epithelial cells from leukocytes, while measurements of DNA content to determine aneuploidy (DAPI stain) allowed for distinction between tumor and normal epithelial cells. Signaling activity in the PI3K and MAPK pathways was assessed by measuring intracellular levels of p-AKT and p-ERK at baseline and in response to pathway modulation; 66% (N = 19) of BC samples and 27% (N = 4) of NC samples met the "evaluable" criteria, i.e., at least 400,000 total cells available upon sample receipt with >2% of cells showing an epithelial phenotype. The majority of epithelial cells detected in BC samples were nonapoptotic and all signaling data were generated from identified cPARP negative cells. In four of 19 BC samples but in none of the NC specimens, SCNP assay identified epithelial cancer cells with a quantifiable increase in epidermal growth factor-induced p-AKT and p-ERK levels. Furthermore, preincubation with the PI3K inhibitor GDC-0941 reduced or completely inhibited basal and epidermal growth factor-induced p-AKT but, as expected, had no effect on p-ERK levels. This study demonstrates the feasibility of applying SCNP assay using multiparametric flow cytometry to the functional characterization of rare, bladder cancer cells collected from bladder washing. Following assay standardization, this method could potentially serve as a tool for disease characterization and drug development in bladder cancer and other solid tumors.

Single cell network profiling (SCNP): mapping drug and target interactions

Measuring target coverage of small molecule inhibitors is paramount-first, for selection of molecules to progress through the drug development process and second, once a candidate drug moves to clinical testing, for guiding dose/schedule selection. Single cell network profiling (SCNP) using multiparameter flow cytometry can measure compound effects on multiple signaling cascades in a cell-type-specific manner. We applied SCNP to a panel of compounds with reported inhibitory effects on Jak/Stat signaling using a novel system where modulation of multiple signaling cascades are simultaneously measured in discrete cell subsets in whole (ie, unfractionated) blood. Jak2 vs. Jak3 selectivity as well as "off-target" effects on other cell signaling pathways were measured using a combination of cytokines that target different white blood cell subsets, namely GM-CSF (monocytes/granulocytes), IL-2 (T cells), and CD40L (B cells). The compounds were then rank-ordered by potency and selectivity against the different pathways tested. Notably, SCNP performed in whole unfractionated blood compared to fractionated peripheral blood mononuclear cells (PBMC) from the same donors revealed potency loss for all compounds, with one exception. These studies show that SCNP can be used to efficiently measure a drug candidate's potency and selectivity in a physiologically relevant environment (eg, whole blood) and that robust IC(50) are attainable from rare subpopulations (<100 cells). The ability to generate in vitro IC(50) measurements in whole blood can be used not only for the preclinical selection of lead molecules, but also to determine the target plasma concentration for clinical studies and to measure target coverage after drug administration in early phase clinical trials. Knowledge of the compound plasma concentration necessary to achieve biochemical coverage permits rational design of clinical trials based on biologically active dose vs. the traditional maximum tolerated dose (MTD) design, which is better suited for cytotoxic, nontargeted drugs.

Abstract B182: Single cell network profiling (SCNP) by flow cytometry as a tool to measure potency and selectivity of JAK/STAT inhibitors in PBMC and whole blood discrete cell subsets

Background: With the development of targeted therapeutics aimed at modulating signal transduction networks, there is a need for measuring the pharmacodynamic impact of these agents in relevant complex tissues at the single cell level. The ability to assess target coverage and selectivity is paramount - first, for selection of candidate molecules to progress through the drug development process and second, once a candidate drug moves into clinical testing, for guiding dose and schedule selection.

Objectives: This study tested the ability to use single cell network profiling (SCNP), in which cells are perturbed with extracellular modulators and their response ascertained by multiparametric flow cytometry, to 1) measure the potency and selectivity of a panel of compounds with reported inhibitory effects on JAK/STAT signaling in whole blood versus fractionated peripheral blood mononuclear cells (PBMC) and 2) test the ability of SCNP to capture rare cells amid a heterogeneous population of cells.

Methods: We measured modulation of JAK/STAT, MAPK and NFkB signaling pathways in cell subsets after in vitro exposure of whole blood and PBMC to GM-CSF (monocytes/neutrophils), IL-2 (T-cells), and CD40L (B-cells) in the presence and absence of known JAK inhibitors. For evaluation of SCNP in rare cells, phosphorylation of STAT proteins in response to IL-27 was examined on CD34+ CD11b− CD33− progenitors in healthy PBMCs.

Results: The relative selectivity of JAK3 versus JAK2 inhibition was simultaneously measured by plotting p-Stat-5 inhibition curves from gated T cells (JAK3 mediated) and monocytes (JAK2 mediated). Notably, CP-690550, currently in clinical trials for a variety of autoimmune diseases, was 36-fold more potent at inhibiting JAK3 compared to JAK2 activity, which is consistent with published reports. In addition, off-target signaling effects outside the JAK/STAT pathway were observed (eg, Cucurbitacin I induced a dose-dependent increase in p-ERK in the monocyte subset and “Stat3 Inhibitor VII” blocked CD40L stimulated p-ERK and pNFkB p65 in B cells). Importantly, a significant decrease in potency in all compounds except CP-690550 was observed when studies were performed in whole blood, the clinically relevant tissue, versus fractionated PBMC. Notably, SCNP technology captured IL-27 induced p-Stat-1 and p-Stat-3 responses and inhibition by Pyridone 6 in CD34+ CD11b− CD33− progenitor cells, a very rare (&lt;40 cells; 0.11% of the total live cells) cell population in PBMC.

Conclusions: SCNP technology allowed for the evaluation of 1) compound activity in primary cells in a physiologically relevant environment (whole blood), 2) signal transduction target and off-target effects in relevant cell populations, and 3) robust IC50 determination from rare subpopulations (&lt;100 cells). Therefore, this technology is well suited for application in oncology drug development where assessment of candidate drug effects on rare cell populations (eg, cancer stem cells, minimal residual disease, and circulating tumor cells) is crucial and permits the rational design of clinical trials based on biologically active dose rather than the traditional maximum tolerated dose (MTD) design, which is better suited for cytotoxic, non-targeted drugs.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B182.

Akt activation by arachidonic acid metabolism occurs via oxidation and inactivation of PTEN tumor suppressor

Cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) enzymes are overexpressed during inflammation and multistage tumor progression in many neoplastic disorders including lung, breast and pancreatic cancers. Here we report that the tumor suppressor phosphatase and tensin homolog (PTEN) is oxidized and inactivated during arachidonic acid (AA) metabolism in pancreatic cancer cell lines expressing COX-2 or 5-LOX. Oxidation of PTEN decreases its phosphatase activity, favoring increased phosphatidylinositol 3,4,5-triphosphate production, activation of Akt and phosphorylation of downstream Akt targets including GSK-3beta and S6K. These effects are recapitulated with pancreatic phospholipase A(2), which hydrolyses the release of membrane-bound AA. Interference with PTEN's physiological antagonism of signals from growth factors, insulin and oncogenes may confer risk for hypertrophic or neoplastic diseases associated with chronic inflammation or unwarranted oxidative metabolism of essential fatty acids.

The IL-27 receptor (WSX-1) is an inhibitor of innate and adaptive elements of type 2 immunity

Although previous studies have investigated the role of IL-27/WSX-1 interactions in the regulation of Th1 responses, little is known about their role in regulating Th2-type responses. Studies presented in this work identify a direct role for IL-27/WSX-1 interactions in the negative regulation of type 2 responses independent of effects on type 1 cytokines. WSX-1-/- mice infected with the gastrointestinal helminth Trichuris muris displayed accelerated expulsion of parasites and the development of exaggerated goblet cell hyperplasia and mastocytosis in the gut due to increased production of Th2 cytokines. Enhanced mast cell activity in the absence of WSX-1 was consistent with the ability of wild-type mast cells to express this receptor. In addition, IL-27 directly suppressed CD4+ T cell proliferation and Th2 cytokine production. Together, these studies identify a novel role for IL-27/WSX-1 in limiting innate and adaptive components of type 2 immunity at mucosal sites.