BET-inhibition by JQ1 promotes proliferation and self-renewal capacity of hematopoietic stem cells.

Although inhibitors of bromodomain and extra terminal domain (BET) proteins show promising clinical activity in different hematologic malignancies, a systematic analysis of the consequences of pharmacological BET inhibition on healthy hematopoietic (stem) cells is urgently needed. We found that JQ1 treatment decreases the numbers of pre-, immature and mature B cells while numbers of early pro-B cells remain constant. In addition, JQ1 treatment increases apoptosis in T cells, all together leading to reduced cellularity in thymus, bone marrow and spleen. Furthermore, JQ1 induces proliferation of long-term hematopoietic stem cells, thereby increasing stem cell numbers. Due to increased numbers, JQ1-treated hematopoietic stem cells engrafted better after stem cell transplantation and repopulated the hematopoietic system significantly faster after sublethal myeloablation. As quantity and functionality of hematopoietic stem cells determine the duration of life-threatening myelosuppression, BET inhibition might benefit patients in myelosuppressive conditions.

The HDL particle composition determines its antitumor activity in pancreatic cancer.

Despite enormous efforts to improve therapeutic options, pancreatic cancer remains a fatal disease and is expected to become the second leading cause of cancer-related deaths in the next decade. Previous research identified lipid metabolic pathways to be highly enriched in pancreatic ductal adenocarcinoma (PDAC) cells. Thereby, cholesterol uptake and synthesis promotes growth advantage to and chemotherapy resistance for PDAC tumor cells. Here, we demonstrate that high-density lipoprotein (HDL)-mediated efficient cholesterol removal from cancer cells results in PDAC cell growth reduction and induction of apoptosis in vitro. This effect is driven by an HDL particle composition-dependent interaction with SR-B1 and ABCA1 on cancer cells. AAV-mediated overexpression of APOA1 and rHDL injections decreased PDAC tumor development in vivo. Interestingly, plasma samples from pancreatic-cancer patients displayed a significantly reduced APOA1-to-SAA1 ratio and a reduced cholesterol efflux capacity compared with healthy donors. We conclude that efficient, HDL-mediated cholesterol depletion represents an interesting strategy to interfere with the aggressive growth characteristics of PDAC.

Chronic pancreatitis is associated with disease-specific regulatory T-cell responses.

BACKGROUND & AIMS: Chronic pancreatitis is characterized by alternating phases of acute inflammation and quiescent disease. Involvement of T-cell responses has been suggested, but pancreatitis-specific T cells have not been described. METHODS: We characterized T-cell responses against pancreatitis, pancreatic carcinoma-associated antigens, and tetanus toxoid in the bone marrow, blood, and/or pancreatitis lesions of patients with pancreatitis, pancreatic cancer, and healthy individuals. T cells were functionally characterized by antigen-dependent secretion of interferon (IFN)-gamma, interleukin (Il)-4, and IL-10, which indicate type 1, type 2, or regulatory T-cell responses, respectively. Regulatory T cells were characterized by multicolor flow cytometry. Isolated regulatory T cells were tested for their capacity to recognize pancreatitis-associated antigens and to suppress conventional T cells in an antigen-dependent manner. T cell-derived cytokines in tissue lesions were quantified by enzyme-linked immunosorbent assay. RESULTS: Chronic pancreatitis patients showed similar to pancreatic cancer patients and healthy individuals type 1 T-cell responses against tetanus toxoid; however, they exhibited strong IL-10-based T-cell responses against pancreatitis-associated but not pancreatic carcinoma-associated antigens. T cells from pancreatic cancer patients responded to pancreatic cancer-associated but not pancreatitis-associated antigens with IFN-gamma secretion. Pancreatitis-specific IL-10 responses were mediated by IL-10(+)IFN-gamma(-)FoxP3(+) regulatory T cells, which were expanded in the blood, bone marrow, and pancreatitis lesions and possessed the potential to suppress the proliferation of autologous conventional T cells in an antigen-specific manner. Pancreatitis lesions, in comparison with pancreatic carcinomas, contained increased concentrations of IL-10 and reduced levels of IFN-gamma, suggesting pancreatitis-specific activity of regulatory T cells in situ. CONCLUSIONS: Chronic pancreatitis is associated with disease-specific regulatory T-cell responses.

AXL Inhibition Represents a Novel Therapeutic Approach in BCR-ABL Negative Myeloproliferative Neoplasms.

BCR-ABL negative myeloproliferative neoplasms (MPNs) consist of essential thrombocythemia, polycythemia vera, and myelofibrosis. The majority of patients harbor the JAK2-activating mutation V617F. JAK2 inhibitors were shown to reduce symptom burden and splenomegaly in MPN patients. However, treatment options are limited after failure of JAK2 inhibitors. AXL, a member of the TAM family of receptor tyrosine kinases, mediates survival and therapy resistance of different myeloid cancers including acute myeloid leukemia and chronic myeloid leukemia. We studied the relevance of AXL as a target in MPN using primary patient cells and preclinical disease models. We found that AXL is abundantly activated in MPN cells and that its ligand growth arrest-specific gene 6 is upregulated in MPN patients. Pharmacologic and genetic blockade of AXL impaired viability, decreased proliferation and increased apoptosis of MPN cells. Interestingly, ruxolitinib treatment induced increased phosphorylation of AXL indicating that activation of AXL might mediate resistance to ruxolitinib. Consistently, the AXL inhibitor bemcentinib exerted additive effects with ruxolitinib via impaired STAT3, STAT5, and AKT signaling. Both agents had activity when employed alone and exerted an additive effect on survival and splenomegaly in vivo. Moreover, bemcentinib treatment normalized red blood cell count and hemoglobin levels in vivo. Thus, our data indicate that AXL inhibition represents a novel treatment option in MPN warranting clinical investigation.

Blockade of Myeloid-Derived Suppressor Cell Expansion with All-Trans Retinoic Acid Increases the Efficacy of Antiangiogenic Therapy.

Intrinsic and adaptive resistance hampers the success of antiangiogenic therapies (AAT), especially in breast cancer where this treatment modality has proven largely ineffective. Therefore, novel strategies to improve the efficacy of AAT are warranted. Solid tumors such as breast cancer are characterized by a high infiltration of myeloid-derived suppressor cells (MDSC), which are key drivers of resistance to AAT. Therefore, we hypothesized that all-trans retinoic acid (ATRA), which induces differentiation of MDSC into mature cells, could improve the therapeutic effect of AAT. ATRA increased the efficacy of anti-VEGFR2 antibodies alone and in combination with chemotherapy in preclinical breast cancer models. ATRA reverted the anti-VEGFR2-induced accumulation of intratumoral MDSC, alleviated hypoxia, and counteracted the disorganization of tumor microvessels. Mechanistic studies indicate that ATRA treatment blocked the AAT-induced expansion of MDSC secreting high levels of vessel-destabilizing S100A8. Thus, concomitant treatment with ATRA holds the potential to improve AAT in breast cancer and possibly other tumor types.Significance: Increasing the therapeutic efficiency of antiangiogenic drugs by reducing resistance-conferring myeloid-derived suppressor cells might improve breast cancer treatment.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/12/3220/F1.large.jpg Cancer Res; 78(12); 3220-32. ©2018 AACR.

Cyclooxygenase-2 blockade can improve efficacy of VEGF-targeting drugs.

Anti-angiogenic therapies were approved for different cancers. However, significant primary and secondary resistance hampers efficacy in several tumor types including breast cancer. Thus, we need to develop clinically applicable strategies to enhance efficacy of anti-angiogenic drugs.We report that anti-angiogenic therapies can induce upregulation of cyclooxygenase-2 (Cox-2) and of its product prostaglandin E2 (PGE2) in breast cancer models. Upon Cox-2 inhibition PGE2 levels were normalized and efficacy of anti-vascular endothelial growth factor receptor 2 (anti-VEGFR-2) antibodies and sunitinib was enhanced. Interestingly, both treatments exerted additive anti-angiogenic effects. Following Cox-2 inhibition, we observed reduced infiltration of tumors with cancer-associated fibroblasts (CAFs) and lower levels of pro-angiogenic factors active besides the VEGF axis including hepatocyte growth factor (HGF) and basic fibroblast growth factor (FGF2). Mechanistic studies indicated that Cox-2 inhibition reduced PGE2-induced migration and proliferation of CAFs via inhibiting phosphorylation of Akt.Hence, Cox-2 inhibition can increase efficacy of anti-angiogenic treatments and our findings might pave the road for clinical investigations of concomitant blockade of Cox-2 and VEGF-signaling.