Progenitor Hierarchy of Chronic Myelomonocytic Leukemia Identifies Inflammatory Monocytic-Biased Trajectory Linked to Worse Outcomes

Myeloblast expansion is a hallmark of disease progression and comprises CD34+ hematopoietic stem and progenitor cells (HSPC). How this compartment evolves during disease progression in chronic myeloid neoplasms is unknown. Using single-cell RNA sequencing and high-parameter flow cytometry, we show that chronic myelomonocytic leukemia (CMML) CD34+ HSPC can be classified into three differentiation trajectories: monocytic, megakaryocyte-erythroid progenitor (MEP), and normal-like. Hallmarks of monocytic-biased trajectory were enrichment of CD120b+ inflammatory granulocyte-macrophage progenitor (GMP)-like cells, activated cytokine receptor signaling, phenotypic hematopoietic stem cell (HSC) depletion, and adverse outcomes. Cytokine receptor diversity was generally an adverse feature and elevated in CD120b+ GMPs. Hypomethylating agents decreased monocytic-biased cells in CMML patients. Given the enrichment of RAS pathway mutations in monocytic-biased cells, NRAS-competitive transplants and LPS-treated xenograft models recapitulated monocytic-biased CMML, suggesting that hematopoietic stress precipitates the monocytic-biased state. Deconvolution of HSPC compartments in other myeloid neoplasms and identifying therapeutic strategies to mitigate the monocytic-biased differentiation trajectory should be explored.

SIGNIFICANCE

Our findings establish that multiple differentiation states underlie CMML disease progression. These states are negatively augmented by inflammation and positively affected by hypomethylating agents. Furthermore, we identify HSC depletion and expansion of GMP-like cells with increased cytokine receptor diversity as a feature of myeloblast expansion in inflammatory chronic myeloid neoplasms. This article is highlighted in the In This Issue feature, p. 476.

TGF-β-mediated silencing of genomic organizer SATB1 promotes Tfh cell differentiation and formation of intra-tumoral tertiary lymphoid structures

The immune checkpoint receptor PD-1 on T follicular helper (Tfh) cells promotes Tfh:B cell interactions and appropriate positioning within tissues. Here, we examined the impact of regulation of PD-1 expression by the genomic organizer SATB1 on Tfh cell differentiation. Vaccination of CD4^CreSatb1^f/f mice enriched for antigen-specific Tfh cells, and TGF-β-mediated repression of SATB1 enhanced Tfh differentiation of human T cells. Mechanistically, high Icos expression in Satb1^-/- CD4⁺ T cells promoted Tfh cell differentiation by preventing T follicular regulatory cell skewing and resulted in increased isotype-switched B cell responses in vivo. Ovarian tumors in CD4^CreSatb1^f/f mice accumulated tumor antigen-specific, LIGHT⁺CXCL13⁺IL-21⁺ Tfh cells and tertiary lymphoid structures (TLS). TLS formation decreased tumor growth in a CD4⁺ T cell and CXCL13-dependent manner. The transfer of Tfh cells, but not naive CD4⁺ T cells, induced TLS at tumor beds and decreased tumor growth. Thus, TGF-β-mediated silencing of Satb1 licenses Tfh cell differentiation, providing insight into the genesis of TLS within tumors.

Introduction to Multiparametric Flow Cytometry and Analysis of High-Dimensional Data

Multiparametric flow cytometry is a technique utilized in translational experiments that utilizes fluorescently tagged antibodies and functional fluorescent dyes to measure proteins on the surface or in the cytoplasm of cells and to measure processes occurring within cells themselves. These fluorescent molecules, or fluorophores, can be tagged to antibodies to measure specific biological molecules such as proteins inside or on the surface of cells. Small organic compounds such as the nucleic acid binding dye propidium iodide (PI) can permeate compromised cell membranes when cells are no longer viable or used to measure DNA content of cycling cells. Successful completion of flow cytometry experiments requires expertise in both the preparation of the samples, acquisition of the samples on instruments, and analyses of the results. This chapter describes the principles needed to conduct a successful multiparameter flow cytometry experiment needed for drug development with references to well established internet resources that are useful to those less experienced in the field. In addition, we provide a brief introduction to data analysis including complex analysis of 10+ parameters simultaneously. These high-dimensional datasets require novel methods for analysis due to the volume of data collected, which are also introduced in this chapter.

Off-target based drug repurposing opportunities for tivantinib in acute myeloid leukemia

GSK3α has been identified as a new target in the treatment of acute myeloid leukemia (AML). However, most GSK3 inhibitors lack specificity for GSK3α over GSK3β and other kinases. We have previously shown in lung cancer cells that GSK3α and to a lesser extent GSK3β are inhibited by the advanced clinical candidate tivantinib (ARQ197), which was designed as a MET inhibitor. Thus, we hypothesized that tivantinib would be an effective therapy for the treatment of AML. Here, we show that tivantinib has potent anticancer activity across several AML cell lines and primary patient cells. Tivantinib strongly induced apoptosis, differentiation and G2/M cell cycle arrest and caused less undesirable stabilization of β-catenin compared to the pan-GSK3 inhibitor LiCl. Subsequent drug combination studies identified the BCL-2 inhibitor ABT-199 to synergize with tivantinib while cytarabine combination with tivantinib was antagonistic. Interestingly, the addition of ABT-199 to tivantinib completely abrogated tivantinib induced β-catenin stabilization. Tivantinib alone, or in combination with ABT-199, downregulated anti-apoptotic MCL-1 and BCL-XL levels, which likely contribute to the observed synergy. Importantly, tivantinib as single agent or in combination with ABT-199 significantly inhibited the colony forming capacity of primary patient AML bone marrow mononuclear cells. In summary, tivantinib is a novel GSK3α/β inhibitor that potently kills AML cells and tivantinib single agent or combination therapy with ABT-199 may represent attractive new therapeutic opportunities for AML.

PAXIP1 Potentiates the Combination of WEE1 Inhibitor AZD1775 and Platinum Agents in Lung Cancer

The DNA damage response (DDR) involves a complex network of signaling events mediated by modular protein domains such as the BRCA1 C-terminal (BRCT) domain. Thus, proteins that interact with BRCT domains and are a part of the DDR constitute potential targets for sensitization to DNA-damaging chemotherapy agents. We performed a pharmacologic screen to evaluate 17 kinases, identified in a BRCT-mediated interaction network as targets to enhance platinum-based chemotherapy in lung cancer. Inhibition of mitotic kinase WEE1 was found to have the most effective response in combination with platinum compounds in lung cancer cell lines. In the BRCT-mediated interaction network, WEE1 was found in complex with PAXIP1, a protein containing six BRCT domains involved in transcription and in the cellular response to DNA damage. We show that PAXIP1 BRCT domains regulate WEE1-mediated phosphorylation of CDK1. Furthermore, ectopic expression of PAXIP1 promotes enhanced caspase-3-mediated apoptosis in cells treated with WEE1 inhibitor AZD1775 (formerly, MK-1775) and cisplatin compared with cells treated with AZD1775 alone. Cell lines and patient-derived xenograft models expressing both PAXIP1 and WEE1 exhibited synergistic effects of AZD1775 and cisplatin. In summary, PAXIP1 is involved in sensitizing lung cancer cells to the WEE1 inhibitor AZD1775 in combination with platinum-based treatment. We propose that WEE1 and PAXIP1 levels may be used as mechanism-based biomarkers of response when WEE1 inhibitor AZD1775 is combined with DNA-damaging agents. Mol Cancer Ther; 15(7); 1669-81. ©2016 AACR.

Abstract 675: Off-target based drug repurposing opportunities for tivantinib in acute myeloid leukemia

GSK3 alpha has been shown to be a new target in the treatment of acute myeloid leukemia (AML); however current GSK3 inhibitors are unselective and target both GSK3 alpha and GSK3 beta. Interestingly, a known pan-GSK3 inhibitor LiCl has been previously investigated for the treatment of AML yet has met limited clinical success. This could be partly due to the fact that pan-GSK3 inhibition results in beta-catenin stabilization, which has been shown to mediate hematopoietic self-renewal and leukemogenesis. As beta-catenin stabilization requires inhibition of both kinases and most GSK3 inhibitors target GSK3 alpha and GSK3 beta with equal potency, these compounds may possess some significant limitations. We have previously shown GSK3 alpha to be a prominent target of the intended MET inhibitor tivantinib (ARQ197) and that tivantinib shows some specificity for GSK3 alpha over GSK3 beta. We thus hypothesized that tivantinib would be an effective therapy for the treatment of AML. Consistently, tivantinib potently inhibited cellular viability across several AML cell lines. Using an unbiased, mass-spectrometry based chemical proteomics approach; we confirmed GSK3 alpha (and to a slightly lesser extent GSK3 beta) to be targeted by tivantinib in AML. Tivantinib strongly induced apoptosis as compared to the pan-GSK3 inhibitor LiCl in these cells while LiCl showed larger effects on cell differentiation. Interestingly tivantinib caused less stabilization of beta-catenin as compared to LiCl. Subsequent drug combination studies identified the Bcl-2 inhibitor ABT-199 to synergize with tivantinib and to amplify apoptosis as seen by PARP1 cleavage. Furthermore, the combination of tivantinib with ABT-199 completely abrogated beta-catenin stabilization. Tivantinib was able to significantly inhibit colony formation of primary AML patient bone marrow mononuclear cells (BMNCs) and ABT-199 combination showed significant benefit over tivantinib or ABT-199 alone. In summary, tivantinib has potent anticancer activity in AML based on targeting GSK3 alpha; and tivantinib single agent or combination with ABT-199 may represent a novel and exciting opportunity for the treatment of AML.

Citation Format: Brent M. Kuenzi, Lily L. Remsing Rix, Sateesh S. Kunigal, Fumi Kinose, Claire E. Knezevic, Gabriela Wright, Jodi L. Kroeger, Jeffrey E. Lancet, Eric Padron, Uwe Rix. Off-target based drug repurposing opportunities for tivantinib in acute myeloid leukemia. [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 675. doi:10.1158/1538-7445.AM2015-675

Lipid Accumulation and Dendritic Cell Function in Cancer (49.10)

Immune cell dysfunction in cancer is an area of intense study, with particular focus on dendritic cell (DC) abnormalities. The mechanism of these abnormalities remains unclear. We examined the potential role of lipid metabolism in defective DC function in cancer. Different mouse tumor models (CT26, MC38, or EL4) were used for in vivo studies. Tumors grew for up to 3w and then spleens were harvested for DC analysis. Phenotypic analysis by flow cytometry included CD11c, CD11b, MHCII, CD40, CD80, and CD86. Lipid levels were determined using Bodipy 493/503. For the analysis of DC function, cells with high and normal lipid content were sorted and used in allogenic mixed leukocyte reaction. For in vitro studies, DCs were harvested from spleen and cultured overnight with a variety of stimulants (LPS, tumor supernatant, GM-CSF, or IL-4). The control level of lipids in DCs was established in naïve tumor-free mice. 30–40% of freshly isolated splenic DCs from tumor-bearing mice had increased levels of intracellular lipid compared to naïve mice, and this accumulation was time dependent. Phenotypically, DCs with increased amounts of lipid had increased levels of MHCII and co-stimulatory molecules. However, despite that increase, DCs with high lipid content had substantially reduced ability to stimulate T cells in allogenic mixed leukocyte reaction than DCs with normal lipid amount. These results indicate a role for lipid accumulation in dendritic cell dysfunction. The data also indicate that the tumor microenvironment is necessary to induce the lipid accumulation and dysfunction.