Deeper insights into hematological oncology disorders via single-cell phospho-signaling analysis

The Stat3/5 Signaling Biosignature in Hematopoietic Stem/Progenitor Cells Predicts Response and Outcome in Myelodysplastic Syndrome Patients Treated with Azacitidine

PURPOSE

Azacitidine is the mainstay of high-risk myelodysplastic syndromes (MDS) therapy, but molecular predictors of response and the mechanisms of resistance to azacitidine remain largely unidentified. Deregulation of signaling via Stat3 and Stat5 in acute myeloid leukemia (AML) is associated with aggressive disease. Numerous genes involved in cell signaling are aberrantly methylated in MDS, yet the alterations and the effect of azacitidine treatment on Stat3/5 signaling in high-risk MDS have not been explored.

EXPERIMENTAL DESIGN

We assessed longitudinally constitutive and ligand-induced phospho-Stat3/5 signaling responses by multiparametric flow cytometry in 74 patients with MDS and low blast count AML undergoing azacitidine therapy. Pretreatment Stat3/5 signaling profiles in CD34(+)cells were grouped by unsupervised clustering. The differentiation stage and the molecular properties of the CD34(+)G-CSF-inducible Stat3/5 double-positive subpopulation were performed by flow cytometry and quantitative real-time PCR in isolated MDS progenitors.

RESULTS

The pretreatment Stat3/5 signaling profiles in CD34(+)cells correlated strongly with response and cytogenetics and independently predicted event-free survival. We further identified a CD34(+)G-CSF-inducible Stat3/5 double-positive subpopulation (DP subset) whose pretreatment levels were inversely associated with treatment response and cytogenetics. The kinetics of the DP subset followed the response to azacitidine and the disease course, whereas its molecular characteristics and cellular hierarchy were consistent with a leukemia propagating cell phenotype.

CONCLUSIONS

Our findings provide a novel link among Stat3/5 signaling and MDS pathobiology and suggest that the Stat3/5 signaling biosignature may serve as both a response biomarker and treatment target.

Diverse phosphorylation patterns of B cell receptor-associated signaling in naïve and memory human B cells revealed by phosphoflow, a powerful technique to study signaling at the single cell level

Following interaction with cognate antigens, B cells undergo cell activation, proliferation, and differentiation. Ligation of the B cell receptor (BCR) leads to the phosphorylation of BCR-associated signaling proteins within minutes of antigen binding, a process with profound consequences for the fate of the cells and development of effector immunity. Phosphoflow allows a rapid evaluation of various signaling pathways in complex heterogenous cell subsets. This novel technique was used in combination with multi-chromatic flow cytometry (FC) and fluorescent-cell barcoding (FCB) to study phosphorylation of BCR-associated signaling pathways in naïve and memory human B cell subsets. Proteins of the initiation (Syk), propagation (Btk, Akt), and integration (p38MAPK and Erk1/2) signaling units were studied. Switched memory (Sm) CD27+ and Sm CD27- phosphorylation patterns were similar when stimulated with anti-IgA or -IgG. In contrast, naïve and unswitched memory (Um) cells showed significant differences following IgM stimulation. Enhanced phosphorylation of Syk was observed in Um cells, suggesting a lower activation threshold. This is likely the result of higher amounts of IgM on the cell surface, higher pan-Syk levels, and enhanced susceptibility to phosphatase inhibition. All other signaling proteins evaluated also showed some degree of enhanced phosphorylation in Um cells. Furthermore, both the phospholipase C-γ2 (PLC-γ2) and phosphatidylinositol 3-kinase (PI3K) pathways were activated in Um cells, while only the PI3K pathway was activated on naïve cells. Um cells were the only ones that activated signaling pathways when stimulated with fluorescently labeled S. Typhi and S. pneumoniae. Finally, simultaneous evaluation of signaling proteins at the single cell level (multiphosphorylated cells) revealed that interaction with gram positive and negative bacteria resulted in complex and diverse signaling patterns. Phosphoflow holds great potential to accelerate vaccine development by identifying signaling profiles in good/poor responders.

Multi-parameter phenotypic profiling: using cellular effects to characterize small-molecule compounds

Multi-parameter phenotypic profiling of small molecules provides important insights into their mechanisms of action, as well as a systems level understanding of biological pathways and their responses to small molecule treatments. It therefore deserves more attention at an early step in the drug discovery pipeline. Here, we summarize the technologies that are currently in use for phenotypic profiling--including mRNA-, protein- and imaging-based multi-parameter profiling--in the drug discovery context. We think that an earlier integration of phenotypic profiling technologies, combined with effective experimental and in silico target identification approaches, can improve success rates of lead selection and optimization in the drug discovery process.

A new biomarker for mitotic cells

Many epitopes are phosphorylated during mitosis. These epitopes are useful biomarkers for mitotic cells. The most commonly used are MPM-2 and serine 10 of histone H3. Here we investigated the use of an antibody generated against a phospho peptide matching residues 774-788 of the human retinoblastoma protein 1 (Rb) to detect mitotic cells. Human cell lines were stained with DNA dyes and antibodies reactive with epitopes defined by antibody MPM-2, phospho-S10-histone-H3, and the phospho-serine peptide, TRPPTLSPIPHIPRC (phospho-S780-Rb). Immunoreactivity and DNA content were measured by flow and image cytometry. Correlation and pattern recognition analyses were performed on list mode data. Western blots and immunoprecipitation were used to investigate the number of peptides reactive with phospho-S780-Rb and the relationship between reactivity with this antibody and MPM-2. Costaining for bromodeoxyuridine (BrdU) was used to determine acid resistance of the phospho-S780-Rb epitope. Cell cycle related phospho-S780-Rb immunofluorescence correlated strongly with that of MPM-2. Laser scanning cytometry showed that phospho-S780-Rb immunofluorescence is expressed at high levels on all stages of mitotic cells. Western blotting and immunoprecipitation showed that the epitope is expressed on several peptides including Rb protein. Costaining of BrdU showed that the epitope is stable to acid. Kinetic experiments showed utility in complex cell cycle analysis aimed at measuring cell cycle transition state timing. The phospho-S780-Rb epitope is a robust marker of mitosis that allows cytometric detection of mitotic cells beginning with chromatin condensation and ending after cytokinesis. Costaining of cells with DNA dyes allows discrimination and counting of mitotic cells and post-cytokinetic ("newborn") cells. To facilitate use without confusion about specificity, we suggest the trivial name, pS780 for this mitotic epitope.