TLR3 agonism augments CD47 inhibition in acute myeloid leukemia.

CD47-SIRPa is a myeloid check point pathway that promotes phagocytosis of cells lacking markers for self-recognition. Tumor cells can overexpress CD47 and bind to SIRPa on macrophages, preventing phagocytosis. CD47 expression is enhanced and correlated with a negative prognosis in acute myeloid leukemia (AML), with its blockade leading to cell clearance. ALX90 is an engineered fusion protein with high affinity for CD47. Composed of the N-terminal D1 domain of SIRPα genetically linked to an inactive Fc domain from human immunoglobulin (Ig) G, ALX90 is designed to avoid potential toxicity of CD47-expressing red blood cells. Venetoclax (VEN) is a specific B-cell lymphoma-2 (BCL-2) inhibitor that can restore apoptosis in malignant cells. In AML, VEN is combined with azanucleosides to induce superior remission rates, however treatment for refractory/relapse is an unmet need. We questioned whether the anti-tumor activity of a VENbased regimen can be augmented through CD47 inhibition (CD47i) in AML and how this triplet may be enhanced. Human AML cell lines were sensitive to ALX90 and its addition increased efficacy of a VEN plus azacitidin (VEN+AZA) regimen in vivo. However, CD47i failed to clear bone marrow tumor burden in PDX models. We hypothesized that the loss of resident macrophages in the bone marrow in AML reduced efficiency of CD47i. Therefore, we attempted to enhance this medullary macrophage population with agonism of TLR3 via polyinosinic:polycytidylic acid (poly(I:C)), which led to expansion and activation of medullary macrophages in in vivo AML PDX models and potentiated CD47i. In summary, the addition of poly(I:C) can enhance medullary macrophage populations to potentiate the phagocytosis merited by therapeutic inhibition of CD47.

Role of TGF-ß signaling in generation of CD39+CD73+ myeloid cells in tumors.

There is growing evidence that generation of adenosine from ATP, which is mediated by the CD39/CD73 enzyme pair, predetermines immunosuppressive and proangiogenic properties of myeloid cells. We have previously shown that the deletion of the TGF-ß type II receptor gene (Tgfbr2) expression in myeloid cells is associated with decreased tumor growth, suggesting protumorigenic effect of TGF-ß signaling. In this study, we tested the hypothesis that TGF-ß drives differentiation of myeloid-derived suppressor cells into protumorigenic terminally differentiated myeloid mononuclear cells (TDMMCs) characterized by high levels of cell-surface CD39/CD73 expression. We found that TDMMCs represent a major cell subpopulation expressing high levels of both CD39 and CD73 in the tumor microenvironment. In tumors isolated from mice with spontaneous tumor formation of mammary gland and conditional deletion of the type II TGF-ß receptor in mammary epithelium, an increased level of TGF-ß protein was associated with further increase in number of CD39(+)CD73(+) TDMMCs compared with MMTV-PyMT/TGFßRII(WT) control tumors with intact TGF-ß signaling. Using genetic and pharmacological approaches, we demonstrated that the TGF-ß signaling mediates maturation of myeloid-derived suppressor cells into TDMMCs with high levels of cell surface CD39/CD73 expression and adenosine-generating capacity. Disruption of TGF-ß signaling in myeloid cells resulted in decreased accumulation of TDMMCs, expressing CD39 and CD73, and was accompanied by increased infiltration of T lymphocytes, reduced density of blood vessels, and diminished progression of both Lewis lung carcinoma and spontaneous mammary carcinomas. We propose that TGF-ß signaling can directly induce the generation of CD39(+)CD73(+) TDMMCs, thus contributing to the immunosuppressive, proangiogenic, and tumor-promoting effects of this pleiotropic effector in the tumor microenvironment.

Abrogation of TGF beta signaling in mammary carcinomas recruits Gr-1+CD11b+ myeloid cells that promote metastasis.

Aberrant TGFbeta signaling is common in human cancers and contributes to tumor metastasis. Here, we demonstrate that Gr-1+CD11b+ myeloid cells are recruited into mammary carcinomas with type II TGF beta receptor gene (Tgfbr2) deletion and directly promote tumor metastasis. Gr-1+CD11b+ cells infiltrate into the invasive front of tumor tissues and facilitate tumor cell invasion and metastasis through a process involving metalloproteinase activity. This infiltration of Gr-1+CD11b+ cells also results in increased abundance of TGF beta 1 in tumors with Tgfbr2 deletion. The recruitment of Gr-1+CD11b+ cells into tumors with Tgfbr2 deletion involves two chemokine receptor axes, the SDF-1/CXCR4 and CXCL5/CXCR2 axes. Together, these data indicate that Gr-1+CD11b+ cells contribute to TGFbeta-mediated metastasis through enhancing tumor cell invasion and metastasis.

Disruption of bone morphogenetic protein receptor 2 (BMPR2) in mammary tumors promotes metastases through cell autonomous and paracrine mediators.

Bone morphogenetic proteins (BMPs) are members of the TGF-ß superfamily of signaling molecules. BMPs can elicit a wide range of effects in many cell types and have previously been shown to induce growth inhibition in carcinoma cells as well as normal epithelia. Recently, it has been demonstrated that BMP4 and BMP7 are overexpressed in human breast cancers and may have tumor suppressive and promoting effects. We sought to determine whether disruption of the BMP receptor 2 (BMPR2) would alter mammary tumor progression in mice that express the Polyoma middle T antigen. Mice expressing Polyoma middle T antigen under the mouse mammary tumor virus promoter were combined with mice that have doxycycline-inducible expression of a dominant-negative (DN) BMPR2. We did not observe any differences in tumor latency. However, mice expressing the BMPR2-DN had a fivefold increase in lung metastases. We characterized several cell autonomous changes and found that BMPR2-DN-expressing tumor cells had higher rates of proliferation. We also identified unique changes in inflammatory cells and secreted chemokines/cytokines that accompanied BMPR2-DN-expressing tumors. By immunohistochemistry, it was found that BMPR2-DN primary tumors and metastases had an altered reactive stroma, indicating specific changes in the tumor microenvironment. Among the changes we discovered were increased myeloid derived suppressor cells and the chemokine CCL9. BMP was shown to directly regulate CCL9 expression. We conclude that BMPR2 has tumor-suppressive function in mammary epithelia and microenvironment and that disruption can accelerate mammary carcinoma metastases.

Transforming growth factor beta receptor type III is a tumor promoter in mesenchymal-stem like triple negative breast cancer.

INTRODUCTION: There is a major need to better understand the molecular basis of triple negative breast cancer (TNBC) in order to develop effective therapeutic strategies. Using gene expression data from 587 TNBC patients we previously identified six subtypes of the disease, among which a mesenchymal-stem like (MSL) subtype. The MSL subtype has significantly higher expression of the transforming growth factor beta (TGF-ß) pathway-associated genes relative to other subtypes, including the TGF-ß receptor type III (TßRIII). We hypothesize that TßRIII is tumor promoter in mesenchymal-stem like TNBC cells. METHODS: Representative MSL cell lines SUM159, MDA-MB-231 and MDA-MB-157 were used to study the roles of TßRIII in the MSL subtype. We stably expressed short hairpin RNAs specific to TßRIII (TßRIII-KD). These cells were then used for xenograft tumor studies in vivo; and migration, invasion, proliferation and three dimensional culture studies in vitro. Furthermore, we utilized human gene expression datasets to examine TßRIII expression patterns across all TNBC subtypes. RESULTS: TßRIII was the most differentially expressed TGF-ß signaling gene in the MSL subtype. Silencing TßRIII expression in MSL cell lines significantly decreased cell motility and invasion. In addition, when TßRIII-KD cells were grown in a three dimensional (3D) culture system or nude mice, there was a loss of invasive protrusions and a significant decrease in xenograft tumor growth, respectively. In pursuit of the mechanistic underpinnings for the observed TßRIII-dependent phenotypes, we discovered that integrin-α2 was expressed at higher level in MSL cells after TßRIII-KD. Stable knockdown of integrin-α2 in TßRIII-KD MSL cells rescued the ability of the MSL cells to migrate and invade at the same level as MSL control cells. CONCLUSIONS: We have found that TßRIII is required for migration and invasion in vitro and xenograft growth in vivo. We also show that TßRIII-KD elevates expression of integrin-α2, which is required for the reduced migration and invasion, as determined by siRNA knockdown studies of both TßRIII and integrin-α2. Overall, our results indicate a potential mechanism in which TßRIII modulates integrin-α2 expression to effect MSL cell migration, invasion, and tumorigenicity.

Attenuated transforming growth factor beta signaling promotes metastasis in a model of HER2 mammary carcinogenesis.

INTRODUCTION: Transforming growth factor beta (TGFß) plays a major role in the regulation of tumor initiation, progression, and metastasis. It is depended on the type II TGFß receptor (TßRII) for signaling. Previously, we have shown that deletion of TßRII in mammary epithelial of MMTV-PyMT mice results in shortened tumor latency and increased lung metastases. However, active TGFß signaling increased the number of circulating tumor cells and metastases in MMTV-Neu mice. In the current study, we describe a newly discovered connection between attenuated TGFß signaling and human epidermal growth factor receptor 2 (HER2) signaling in mammary tumor progression. METHODS: All studies were performed on MMTV-Neu mice with and without dominant-negative TßRII (DNIIR) in mammary epithelium. Mammary tumors were analyzed by flow cytometry, immunohistochemistry, and immunofluorescence staining. The levels of secreted proteins were measured by enzyme-linked immunosorbent assay. Whole-lung mount staining was used to quantitate lung metastasis. The Cancer Genome Atlas (TCGA) datasets were used to determine the relevance of our findings to human breast cancer. RESULTS: Attenuated TGFß signaling led to a delay tumor onset, but increased the number of metastases in MMTVNeu/DNIIR mice. The DNIIR tumors were characterized by increased vasculogenesis, vessel leakage, and increased expression of vascular endothelial growth factor (VEGF). During DNIIR tumor progression, both the levels of CXCL1/5 and the number of CD11b+Gr1+ cells and T cells decreased. Analysis of TCGA datasets demonstrated a significant negative correlation between TGFBR2 and VEGF genes expression. Higher VEGFA expression correlated with shorter distant metastasis-free survival only in HER2+ patients with no differences in HER2-, estrogen receptor +/- or progesterone receptor +/- breast cancer patients. CONCLUSION: Our studies provide insights into a novel mechanism by which epithelial TGFß signaling modulates the tumor microenvironment, and by which it is involved in lung metastasis in HER2+ breast cancer patients. The effects of pharmacological targeting of the TGFß pathway in vivo during tumor progression remain controversial. The targeting of TGFß signaling should be a viable option, but because VEGF has a protumorigenic effect on HER2+ tumors, the targeting of this protein could be considered when it is associated with attenuated TGFß signaling.

Repair of leukemia-associated single nucleotide variants via interallelic gene conversion.

CRISPR-Cas9 is a useful tool for inserting precise genetic alterations through homology-directed repair (HDR), although current methods rely on provision of an exogenous repair template. Here, we tested the possibility of repairing heterozygous single nucleotide variants (SNVs) using the cell's own wild-type allele rather than an exogenous template. Using high-fidelity Cas9 to perform allele-specific CRISPR across multiple human leukemia cell lines as well as in primary hematopoietic cells from patients with leukemia, we find high levels of reversion to wild-type in the absence of exogenous template. Moreover, we demonstrate that bulk treatment to revert a truncating mutation in ASXL1 using CRISPR-mediated interallelic gene conversion (IGC) is sufficient to prolong survival in a human cell line-derived xenograft model (median survival 33 days vs 27.5 days; p = 0.0040). These results indicate that IGC can be applied to numerous types of leukemia and can meaningfully alter cellular phenotypes at scale. Because our method targets single-base mutations, rather than larger variants targeted by IGC in prior studies, it greatly expands the pool of risk-increasing genetic lesions which could potentially be targeted by IGC. This technique may reduce cost and complexity for experiments modeling phenotypic consequences of SNVs. The principles of SNV-specific IGC demonstrated in this proof-of-concept study could be applied to investigate the phenotypic effects of targeted clonal reduction of leukemogenic SNV driver mutations.

Lactate Utilization Enables Metabolic Escape to Confer Resistance to BET Inhibition in Acute Myeloid Leukemia.

Impairing the BET family coactivator BRD4 with small-molecule inhibitors (BETi) showed encouraging preclinical activity in treating acute myeloid leukemia (AML). However, dose-limiting toxicities and limited clinical activity dampened the enthusiasm for BETi as a single agent. BETi resistance in AML myeloblasts was found to correlate with maintaining mitochondrial respiration, suggesting that identifying the metabolic pathway sustaining mitochondrial integrity could help develop approaches to improve BETi efficacy. Herein, we demonstrated that mitochondria-associated lactate dehydrogenase allows AML myeloblasts to utilize lactate as a metabolic bypass to fuel mitochondrial respiration and maintain cellular viability. Pharmacologically and genetically impairing lactate utilization rendered resistant myeloblasts susceptible to BET inhibition. Low-dose combinations of BETi and oxamate, a lactate dehydrogenase inhibitor, reduced in vivo expansion of BETi-resistant AML in cell line and patient-derived murine models. These results elucidate how AML myeloblasts metabolically adapt to BETi by consuming lactate and demonstrate that combining BETi with inhibitors of lactate utilization may be useful in AML treatment. SIGNIFICANCE: Lactate utilization allows AML myeloblasts to maintain metabolic integrity and circumvent antileukemic therapy, which supports testing of lactate utilization inhibitors in clinical settings to overcome BET inhibitor resistance in AML. See related commentary by Boët and Sarry, p. 950.

LAIR-1 agonism as a therapy for acute myeloid leukemia.

Effective eradication of leukemic stem cells (LSCs) remains the greatest challenge in treating acute myeloid leukemia (AML). The immune receptor LAIR-1 has been shown to regulate LSC survival; however, the therapeutic potential of this pathway remains unexplored. We developed a therapeutic LAIR-1 agonist antibody, NC525, that induced cell death of LSCs, but not healthy hematopoietic stem cells in vitro, and killed LSCs and AML blasts in both cell- and patient-derived xenograft models. We showed that LAIR-1 agonism drives a unique apoptotic signaling program in leukemic cells that was enhanced in the presence of collagen. NC525 also significantly improved the activity of azacitidine and venetoclax to establish LAIR-1 targeting as a therapeutic strategy for AML that may synergize with standard-of-care therapies.

Lack of transforming growth factor-ß signaling promotes collective cancer cell invasion through tumor-stromal crosstalk.

INTRODUCTION: Transforming growth factor beta (TGF-ß) has a dual role during tumor progression, initially as a suppressor and then as a promoter. Epithelial TGF-ß signaling regulates fibroblast recruitment and activation. Concurrently, TGF-ß signaling in stromal fibroblasts suppresses tumorigenesis in adjacent epithelia, while its ablation potentiates tumor formation. Much is known about the contribution of TGF-ß signaling to tumorigenesis, yet the role of TGF-ß in epithelial-stromal migration during tumor progression is poorly understood. We hypothesize that TGF-ß is a critical regulator of tumor-stromal interactions that promote mammary tumor cell migration and invasion. METHODS: Fluorescently labeled murine mammary carcinoma cells, isolated from either MMTV-PyVmT transforming growth factor-beta receptor II knockout (TßRII KO) or TßRIIfl/fl control mice, were combined with mammary fibroblasts and xenografted onto the chicken embryo chorioallantoic membrane. These combinatorial xenografts were used as a model to study epithelial-stromal crosstalk. Intravital imaging of migration was monitored ex ovo, and metastasis was investigated in ovo. Epithelial RNA from in ovo tumors was isolated by laser capture microdissection and analyzed to identify gene expression changes in response to TGF-ß signaling loss. RESULTS: Intravital microscopy of xenografts revealed that mammary fibroblasts promoted two migratory phenotypes dependent on epithelial TGF-ß signaling: single cell/strand migration or collective migration. At epithelial-stromal boundaries, single cell/strand migration of TßRIIfl/fl carcinoma cells was characterized by expression of α-smooth muscle actin and vimentin, while collective migration of TßRII KO carcinoma cells was identified by E-cadherin+/p120+/ß-catenin+ clusters. TßRII KO tumors also exhibited a twofold greater metastasis than TßRIIfl/fl tumors, attributed to enhanced extravasation ability. In TßRII KO tumor epithelium compared with TßRIIfl/fl epithelium, Igfbp4 and Tspan13 expression was upregulated while Col1α2, Bmp7, Gng11, Vcan, Tmeff1, and Dsc2 expression was downregulated. Immunoblotting and quantitative PCR analyses on cultured cells validated these targets and correlated Tmeff1 expression with disease progression of TGF-ß-insensitive mammary cancer. CONCLUSION: Fibroblast-stimulated carcinoma cells utilize TGF-ß signaling to drive single cell/strand migration but migrate collectively in the absence of TGF-ß signaling. These migration patterns involve the signaling regulation of several epithelial-to-mesenchymal transition pathways. Our findings concerning TGF-ß signaling in epithelial-stromal interactions are important in identifying migratory mechanisms that can be targeted as recourse for breast cancer treatment.

TGF-beta signaling is essential for joint morphogenesis.

Despite its clinical significance, joint morphogenesis is still an obscure process. In this study, we determine the role of transforming growth factor beta (TGF-beta) signaling in mice lacking the TGF-beta type II receptor gene (Tgfbr2) in their limbs (Tgfbr2(PRX-1KO)). In Tgfbr2(PRX-1KO) mice, the loss of TGF-beta responsiveness resulted in the absence of interphalangeal joints. The Tgfbr2(Prx1KO) joint phenotype is similar to that in patients with symphalangism (SYM1-OMIM185800). By generating a Tgfbr2-green fluorescent protein-beta-GEO-bacterial artificial chromosome beta-galactosidase reporter transgenic mouse and by in situ hybridization and immunofluorescence, we determined that Tgfbr2 is highly and specifically expressed in developing joints. We demonstrated that in Tgfbr2(PRX-1KO) mice, the failure of joint interzone development resulted from an aberrant persistence of differentiated chondrocytes and failure of Jagged-1 expression. We found that TGF-beta receptor II signaling regulates Noggin, Wnt9a, and growth and differentiation factor-5 joint morphogenic gene expressions. In Tgfbr2(PRX-1KO) growth plates adjacent to interphalangeal joints, Indian hedgehog expression is increased, whereas Collagen 10 expression decreased. We propose a model for joint development in which TGF-beta signaling represents a means of entry to initiate the process.

The delta isoform of phosphatidylinositol-3-kinase predominates in chronic myelomonocytic leukemia and can be targeted effectively with umbralisib and ruxolitinib.

Chronic myelomonocytic leukemia (CMML) is a myelodysplastic syndrome/myeloproliferative neoplasm overlap syndrome characterized by monocytic proliferation in the presence of dysplastic bone marrow changes, inflammatory symptoms, and propensity for transformation to acute myeloid leukemia (AML), with a poor prognosis and limited treatment options. Unlike the α and ß isoforms, the phosphatidylinositol-3-kinase (PI3K)-δ signaling protein is predominantly expressed by hematopoietic cells and therefore has garnered interest as a potential target for the treatment of lymphomas and leukemias. We revealed a pattern of increased PIK3CD:PIK3CA ratio in monocytic M5 AML patients and cell lines, and this ratio correlated with responsiveness to pharmacological PI3K-δ inhibition in vitro. Because CMML is a disease defined by monocytic clonal proliferation, we tested the PI3K-δ inhibitor umbralisib as a single agent and in combination with the JAK1/2 inhibitor ruxolitinib, in CMML. Our ex vivo experiments with primary CMML patient samples revealed synergistic inhibition of viability and clonogenicity with this combination. Phospho-specific flow cytometry revealed that dual inhibition had the unique ability to decrease STAT5, ERK, AKT, and S6 phosphorylation simultaneously, which offers a mechanistic hypothesis for the enhanced efficacy of the combination treatment. These preclinical data indicate promising activity by co-inhibition of PI3K-δ and JAK1/2 and support the use of ruxolitinib + umbralisib combination therapy in CMML under active clinical investigation.

BET Inhibition Enhances the Antileukemic Activity of Low-dose Venetoclax in Acute Myeloid Leukemia.

PURPOSE: The BCL2 inhibitor, venetoclax, has transformed clinical care in acute myeloid leukemia (AML). However, subsets of patients do not respond or eventually acquire resistance. Venetoclax-based regimens can lead to considerable marrow suppression in some patients. Bromodomain and extraterminal inhibitors (BETi) are potential treatments for AML, as regulators of critical AML oncogenes. We tested the efficacy of novel BET inhibitor INCB054329, and its synergy with venetoclax to reduce AML without induction of hematopoietic toxicity. EXPERIMENTAL DESIGN: INCB054329 efficacy was assessed by changes in cell cycle and apoptosis in treated AML cell lines. In vivo efficacy was assessed by tumor reduction in MV-4-11 cell line-derived xenografts. Precision run-on and sequencing (PRO-seq) evaluated effects of INCB054329. Synergy between low-dose BETi and venetoclax was assessed in cell lines and patient samples in vitro and in vivo while efficacy and toxicity was assessed in patient-derived xenograft (PDX) models. RESULTS: INCB054329 induced dose-dependent apoptosis and quiescence in AML cell lines. PRO-seq analysis evaluated the effects of INCB054329 on transcription and confirmed reduced transcriptional elongation of key oncogenes, MYC and BCL2, and genes involved in the cell cycle and metabolism. Combinations of BETi and venetoclax led to reduced cell viability in cell lines and patient samples. Low-dose combinations of INCB054329 and venetoclax in cell line and PDX models reduced AML burden, regardless of the sensitivity to monotherapy without development of toxicity. CONCLUSIONS: Our findings suggest low dose combinations of venetoclax and BETi may be more efficacious for patients with AML than either monotherapy, potentially providing a longer, more tolerable dosing regimen.

Selective Inhibition of JAK1 Primes STAT5-Driven Human Leukemia Cells for ATRA-Induced Differentiation.

BACKGROUND: All-trans retinoic acid (ATRA), a derivate of vitamin A, has been successfully used as a therapy to induce differentiation in M3 acute promyelocytic leukemia (APML), and has led to marked improvement in outcomes. Previously, attempts to use ATRA in non-APML in the clinic, however, have been underwhelming, likely due to persistent signaling through other oncogenic drivers. Dysregulated JAK/STAT signaling is known to drive several hematologic malignancies, and targeting JAK1 and JAK2 with the JAK1/JAK2 inhibitor ruxolitinib has led to improvement in survival in primary myelofibrosis and alleviation of vasomotor symptoms and splenomegaly in polycythemia vera and myelofibrosis. OBJECTIVE: While dose-dependent anemia and thrombocytopenia limit the use of JAK2 inhibition, selectively targeting JAK1 has been explored as a means to suppress inflammation and STAT-associated pathologies related to neoplastogenesis. The objective of this study is to employ JAK1 inhibition (JAK1i) in the presence of ATRA as a potential therapy in non-M3 acute myeloid leukemia (AML). METHODS: Efficacy of JAK1i using INCB52793 was assessed by changes in cell cycle and apoptosis in treated AML cell lines. Transcriptomic and proteomic analysis evaluated effects of JAK1i. Synergy between JAK1i+ ATRA was assessed in cell lines in vitro while efficacy in vivo was assessed by tumor reduction in MV-4-11 cell line-derived xenografts. RESULTS: Here we describe novel synergistic activity between JAK1i inhibition and ATRA in non-M3 leukemia. Transcriptomic and proteomic analysis confirmed structural and functional changes related to maturation while in vivo combinatory studies revealed significant decreases in leukemic expansion. CONCLUSIONS: JAK1i+ ATRA lead to decreases in cell cycle followed by myeloid differentiation and cell death in human leukemias. These findings highlight potential uses of ATRA-based differentiation therapy of non-M3 human leukemia.

Oral Azacitidine and Cedazuridine Approximate Parenteral Azacitidine Efficacy in Murine Model.

BACKGROUND: DNA methyltransferase inhibitors (DNMTis) improve survival for patients with myelodysplastic syndromes (MDS) and those with acute myeloid leukemia (AML) unable to receive standard cytotoxic chemotherapy and are, accordingly, the backbone of standard-of-care treatment for these conditions. Standard regimens with DNMTIs, decitabine (DEC) or azacitidine (AZA) include daily subcutaneous (s.c.) or intravenous (i.v.) administration for 5-7 consecutive days. Attempts to provide the therapy orally have been limited given rapid clearance of the agents by the enzyme cytidine deaminase (CDA), which is ubiquitous in the gut and liver as part of first-pass metabolism. Recently, cedazuridine (CDZ), an oral inhibitor of CDA, was successfully combined with DEC to approximate the pharmacokinetics of i.v. DEC in patients. OBJECTIVE: To determine if an oral dosing strategy might be feasible in the clinic with AZA, we attempted to increase the bioavailability of oral AZA through the use of CDZ, in a murine model. METHODS: Following pharmacokinetic and pharmacodynamic assessment of oral AZA dosed with CDZ in murine and monkey models, we tested this regimen in vivo with a human cell line-derived xenograft transplantation experiment (CDX). Following this we combined the regimen with venetoclax (VEN) to test the efficacy of an all-oral regimen in a patient-derived xenograft (PDX) model. RESULTS: Parenteral AZA and oral AZA + CDZ exhibited similar pharmacokinetic profiles, and efficacy against human AML cells. Tumor regression was seen with AZA + CDZ in MOLM-13 CDX and PDX models. CONCLUSIONS: We conclude that oral AZA when combined with CDZ achieves successful tumor regression in both CDX and PDX models. Furthermore, the combination of AZA + CDZ with VEN in a PDX model emulated responses seen with VEN + AZA in the clinic, implying a potential all-oral VEN-based therapy opportunity in myeloid diseases.

Venetoclax response is enhanced by selective inhibitor of nuclear export compounds in hematologic malignancies.

The selective inhibitor of nuclear export (SINE) compounds selinexor (KPT-330) and eltanexor (KPT-8602) are from a novel class of small molecules that target exportin-1 (XPO1 [CRM1]), an essential nucleo-cytoplasmic transport protein responsible for the nuclear export of major tumor suppressor proteins and growth regulators such as p53, p21, and p27. XPO1 also affects the translation of messenger RNAs for critical oncogenes, including MYC, BCL2, MCL1, and BCL6, by blocking the export of the translation initiation factor eIF4E. Early trials with venetoclax (ABT-199), a potent, selective inhibitor of BCL2, have revealed responses across a variety of hematologic malignancies. However, many tumors are not responsive to venetoclax. We used models of acute myeloid leukemia (AML) and diffuse large B-cell lymphoma (DLBCL) to determine in vitro and in vivo responses to treatment with venetoclax and SINE compounds combined. Cotreatment with venetoclax and SINE compounds demonstrated loss of viability in multiple cell lines. Further in vitro analyses showed that this enhanced cell death was the result of an increase in apoptosis that led to a loss of clonogenicity in methylcellulose assays, coinciding with activation of p53 and loss of MCL1. Treatment with SINE compounds and venetoclax combined led to a reduction in tumor growth in both AML and DLBCL xenografts. Immunohistochemical analysis of tissue sections revealed that the reduction in tumor cells was partly the result of an induction of apoptosis. The enhanced effects of this combination were validated in primary AML and DLBCL patient cells. Our studies reveal synergy with SINE compounds and venetoclax in aggressive hematologic malignancies and provide a rationale for pursuing this approach in a clinical trial.

TGF-beta promotes cell death and suppresses lactation during the second stage of mammary involution.

Transforming growth factor beta (TGF-beta) ligands are known to regulate virgin mammary development and contribute to initiation of post-lactation involution. However, the role for TGF-beta during the second phase of mammary involution has not been addressed. Previously, we have used an MMTV-Cre transgene to delete exon 2 from the Tgfbr2 gene in mammary epithelium, however we observed a gradual loss of T beta RII deficient epithelial cells that precluded an accurate study of the role for TGF-beta signaling during involution timepoints. Therefore, in order to determine the role for TGF-beta during the second phase of mammary involution we have now targeted T beta RII ablation within mammary epithelium using the WAP-Cre transgene [T beta RII(WKO)Rosa26R]. Our results demonstrated that TGF-beta regulates commitment to cell death during the second phase of mammary involution. Importantly, at day 3 of mammary involution the Na-Pi type IIb co-transporter (Npt2b), a selective marker for active lactation in luminal lobular alveolar epithelium, was completely silenced in the WAP-Cre control and T beta RII(WKO)Rosa26R tissues. However, by day 7 of involution the T beta RII(WKO)Rosa26R tissues had distended lobular alveoli and regained a robust Npt2b signal that was detected at the apical luminal surface. The Npt2b abundance and localization positively correlated with elevated WAP mRNA expression, suggesting that the distended alveoli were the result of an active lactation program rather than residual milk protein and lipid accumulation. In summary, the results suggest that an epithelial cell response to TGF-beta signaling regulates commitment to cell death and suppression of lactation during the second phase of mammary involution.

Transcriptional cooperation between the transforming growth factor-beta and Wnt pathways in mammary and intestinal tumorigenesis.

Transforming growth factor-beta (TGF-beta) and Wnt ligands function in numerous developmental processes, and alterations of both signaling pathways are associated with common pathologic conditions, including cancer. To obtain insight into the extent of interdependence of the two signaling cascades in regulating biological responses, we used an oligonucleotide microarray approach to identify Wnt and TGF-beta target genes using normal murine mammary gland epithelial cells as a model. Combination treatment of TGF-beta and Wnt revealed a novel transcriptional program that could not have been predicted from single ligand treatments and included a cohort of genes that were cooperatively induced by both pathways. These included both novel and known components or modulators of TGF-beta and Wnt pathways, suggesting that mutual feedback is a feature of the coordinated activities of the ligands. The majority of the cooperative targets display increased expression in tumors derived from either Min (many intestinal neoplasia) or mouse mammary tumor virus (MMTV)-Wnt1 mice, two models of Wnt-induced tumors, with nine of these genes (Ankrd1, Ccnd1, Ctgf, Gpc1, Hs6st2, IL11, Inhba, Mmp14, and Robo1) showing increases in both. Reduction of TGF-beta signaling by expression of a dominant-negative TGF-beta type II receptor in bigenic MMTV-Wnt1/DNIIR mice increased mammary tumor latency and was correlated with a decrease in expression of Gpc1, Inhba, and Robo1, three of the TGF-beta/Wnt cooperative targets. Our results indicate that the TGF-beta and Wnt/beta-catenin pathways are firmly intertwined and generate a unique gene expression pattern that can contribute to tumor progression.

A Novel MCL1 Inhibitor Combined with Venetoclax Rescues Venetoclax-Resistant Acute Myelogenous Leukemia.

Suppression of apoptosis by expression of antiapoptotic BCL2 family members is a hallmark of acute myeloblastic leukemia (AML). Induced myeloid leukemia cell differentiation protein (MCL1), an antiapoptotic BCL2 family member, is commonly upregulated in AML cells and is often a primary mode of resistance to treatment with the BCL2 inhibitor venetoclax. Here, we describe VU661013, a novel, potent, selective MCL1 inhibitor that destabilizes BIM/MCL1 association, leads to apoptosis in AML, and is active in venetoclax-resistant cells and patient-derived xenografts. In addition, VU661013 was safely combined with venetoclax for synergy in murine models of AML. Importantly, BH3 profiling of patient samples and drug-sensitivity testing ex vivo accurately predicted cellular responses to selective inhibitors of MCL1 or BCL2 and showed benefit of the combination. Taken together, these data suggest a strategy of rationally using BCL2 and MCL1 inhibitors in sequence or in combination in AML clinical trials. SIGNIFICANCE: Targeting antiapoptotic proteins in AML is a key therapeutic strategy, and MCL1 is a critical antiapoptotic oncoprotein. Armed with novel MCL1 inhibitors and the potent BCL2 inhibitor venetoclax, it may be possible to selectively induce apoptosis by combining or thoughtfully sequencing these inhibitors based on a rational evaluation of AML.See related commentary by Leber et al., p. 1511.This article is highlighted in the In This Issue feature, p. 1494.

Increased malignancy of Neu-induced mammary tumors overexpressing active transforming growth factor beta1.

To determine if Neu is dominant over transforming growth factor beta (TGF-beta), we crossed mouse mammary tumor virus (MMTV)-Neu mice with MMTV-TGF-beta1(S223/225) mice expressing active TGF-beta1 in the mammary gland. Bigenic (NT) and Neu-induced mammary tumors developed with a similar latency. The bigenic tumors and their metastases were less proliferative than those occurring in MMTV-Neu mice. However, NT tumors exhibited less apoptosis and were more locally invasive and of higher histological grade. NT mice exhibited more circulating tumor cells and lung metastases than Neu mice, while NT tumors contained higher levels of phosphorylated (active) Smad2, Akt, mitogen-activated protein kinase (MAPK), and p38, as well as vimentin content and Rac1 activity in situ than tumors expressing Neu alone. Ex vivo, NT cells exhibited higher levels of P-Akt and P-MAPK than Neu cells. These were inhibited by the TGF-beta inhibitor-soluble TGF-beta type II receptor (TbetaRII:Fc), suggesting they were activated by autocrine TGF-beta. TGF-beta stimulated migration of Neu cells into surrounding matrix, while the soluble TGF-beta inhibitor abrogated motility and invasiveness of NT cells. These data suggest that (i) the antimitogenic and prometastatic effects of TGF-beta can exist simultaneously and (ii) Neu does not abrogate TGF-beta-mediated antiproliferative action but can synergize with TGF-beta in accelerating metastatic tumor progression.