ß3-Adrenoceptors as Putative Regulator of Immune Tolerance in Cancer and Pregnancy.

Understanding the mechanisms of immune tolerance is currently one of the most important challenges of scientific research. Pregnancy affects the immune system balance, leading the host to tolerate embryo alloantigens. Previous reports demonstrated that ß-adrenergic receptor (ß-AR) signaling promotes immune tolerance by modulation of NK and Treg, mainly through the activation of ß2-ARs, but recently we have demonstrated that also ß3-ARs induce an immune-tolerant phenotype in mice bearing melanoma. In this report, we demonstrate that ß3-ARs support host immune tolerance in the maternal microenvironment by modulating the same immune cells populations as recently demonstrated in cancer. Considering that ß3-ARs are modulated by oxygen levels, we hypothesize that hypoxia, through the upregulation of ß3-AR, promotes the biological shift toward a tolerant immunophenotype and that this is the same trick that embryo and cancer use to create an aura of immune-tolerance in a competent immune environment. This study confirms the analogies between fetal development and tumor progression and suggests that the expression of ß3-ARs represents one of the strategies to induce fetal and tumor immune tolerance.

ß3-Adrenoreceptor Blockade Reduces Hypoxic Myeloid Leukemic Cells Survival and Chemoresistance.

ß-adrenergic signaling is known to be involved in cancer progression; in particular, beta3-adrenoreceptor (ß3-AR) is associated with different tumor conditions. Currently, there are few data concerning ß3-AR in myeloid malignancies. Here, we evaluated ß3-AR in myeloid leukemia cell lines and the effect of ß3-AR antagonist SR59230A. In addition, we investigated the potential role of ß3-AR blockade in doxorubicin resistance. Using flow cytometry, we assessed cell death in different in vitro myeloid leukemia cell lines (K562, KCL22, HEL, HL60) treated with SR59230A in hypoxia and normoxia; furthermore, we analyzed ß3-AR expression. We used healthy bone marrow cells (BMCs), peripheral blood mononuclear cells (PBMCs) and cord blood as control samples. Finally, we evaluated the effect of SR59230A plus doxorubicin on K562 and K562/DOX cell lines; K562/DOX cells are resistant to doxorubicin and show P-glycoprotein (P-gp) overexpression. We found that SR59230A increased cancer cell lines apoptosis especially in hypoxia, resulting in selective activity for cancer cells; moreover, ß3-AR expression was higher in malignancies, particularly under hypoxic condition. Finally, we observed that SR59230A plus doxorubicin increased doxorubicin resistance reversion mainly in hypoxia, probably acting on P-gp. Together, these data point to ß3-AR as a new target and ß3-AR blockade as a potential approach in myeloid leukemias.

ß3-Adrenoreceptor Blockade Induces Stem Cells Differentiation in Melanoma Microenvironment.

Although there is an increasing evidence that cancer stem cell (CSC) niches in the tumor microenvironment (TME) plays a crucial role in sustaining solid tumors progression, several molecular players involved in this regulation still remain unknown. The role of ß-adrenergic signaling in enhancing tumor growth through ß2-adrenoreceptors (ß2-ARs) has been confirmed in different cancer models, but the role played by the ß3-adrenergic receptor (ß3-AR) has recently emerged. Previous studies showed that ß3-AR promotes cancer growth through the activation of different stromal cells in the TME, and leads to melanoma malignancy progression through inflammation, angiogenesis, and immunotolerance. Here we show that in B16 melanoma-bearing mice, the pharmacological ß3-AR blockade is able to reduce the expression of CSC markers, and to induce a differentiated phenotype of hematopoietic subpopulations in TME. In particular, cytofluorimetric analysis (FACS) of the tumor mass shows that ß3-AR antagonist SR59230A promotes hematopoietic differentiation as indicated by increased ratios of lymphoid/hematopoietic stem cells (HSCs) and of myeloid progenitor cells/HSCs, and increases the number of Ter119 and natural killer (NK) precursor cells, and of granulocyte precursors, indicating active hematopoiesis within the tumor tissue. Moreover, pharmacological antagonism of ß3-AR induces mesenchymal stem cell (MSC) differentiation into adipocytes subtracting a potential renewal of the stem compartment by these cells. Here we demonstrate that ß3-AR blockade in the TME by inducing the differentiation of different stromal cells at the expense of stemness traits could possibly have a favorable effect on the control of melanoma progression.

ß3-Adrenoreceptor Activity Limits Apigenin Efficacy in Ewing Sarcoma Cells: A Dual Approach to Prevent Cell Survival.

Ewing Sarcoma (ES) is an aggressive paediatric tumour where oxidative stress and antioxidants play a central role in cancer therapy response. Inhibiting antioxidants expression, while at the same time elevating intracellular reactive oxygen species (ROS) levels, have been proposed as a valid strategy to overcome ES cancer progression. Flavonoid intake can affect free radical and nutritional status in children receiving cancer treatment, but it is not clear if it can arrest cancer progression. In particular, apigenin may enhance the effect of cytotoxic chemotherapy by inducing cell growth arrest, apoptosis, and by altering the redox state of the cells. Little is known about the use of apigenin in paediatric cancer. Recently, ß3-adrenergic receptor (ß3-AR) antagonism has been proposed as a possible strategy in cancer therapy for its ability to induce apoptosis by increasing intracellular levels of ROS. In this study we show that apigenin induces cell death in ES cells by modulating apoptosis, but not increasing ROS content. Since ES cells are susceptible to an increased oxidative stress to reduce cell viability, here we demonstrate that administration of ß3-ARs antagonist, SR59230A, improves the apigenin effect on cell death, identifying ß3-AR as a potential discriminating factor that could address the use of apigenin in ES.