As macrophages exhibit a huge functional plasticity under homeostasis and pathological conditions, they have become a therapeutic target for chronic inflammatory diseases. Hence, the identification of macrophage subset-specific markers is a requisite for the development of macrophage-directed therapeutic interventions. In this regard, the macrophage-specific Folate Receptor β (FRβ, encoded by the FOLR2 gene) has been already validated as a target for molecular delivery in cancer as well as in macrophage-targeting therapeutic strategies for chronic inflammatory pathologies. We now show that the transcriptome of human macrophages from healthy and inflamed tissues (tumor; rheumatoid arthritis, RA) share a significant over-representation of the “anti-inflammatory gene set”, which defines the gene profile of M-CSF-dependent IL-10-producing human macrophages (M-MØ). More specifically, FOLR2 expression has been found to strongly correlate with the expression of M-MØ-specific genes in tissue-resident macrophages, tumor-associated macrophages (TAM) and macrophages from inflamed synovium, and also correlates with the presence of the PU.1 transcription factor. In fact, PU.1-binding elements are found upstream of the first exon of FOLR2 and most M-MØ-specific- and TAM-specific genes. The functional relevance of PU.1 binding was demonstrated through analysis of the proximal regulatory region of the FOLR2 gene, whose activity was dependent on a cluster of PU.1-binding sequences. Further, siRNA-mediated knockdown established the importance of PU.1 for FOLR2 gene expression in myeloid cells. Therefore, we provide evidence that FRβ marks tissue-resident macrophages as well as macrophages within inflamed tissues, and its expression is dependent on PU.1.

The androgen receptor (AR) is essential for diverse aspects of prostate development and function. Molecular mechanisms by which prostate cancer (PC) cells redirect AR signaling to genes that primarily support growth are unclear. A systematic search for critical AR-tethering proteins led to ELK1, an ETS transcription factor of the ternary complex factor subfamily. Although genetically redundant, ELK1 was obligatory for AR-dependent growth and clonogenic survival in both hormone-dependent PC and castration-recurrent PC cells but not for AR-negative cell growth. AR required ELK1 to up-regulate a major subset of its target genes that was strongly and primarily enriched for cell growth functions. AR functioned as a coactivator of ELK1 by association through its A/B domain, bypassing the classical mechanism of ELK1 activation by phosphorylation and without inducing ternary complex target genes. The ELK1-AR synergy per se was ligand-independent, although it required ligand for nuclear localization of AR as targeting the AR A/B domain to the nucleus recapitulated the action of hormone; accordingly, Casodex was a poor antagonist of the synergy. ELK3, the closest substitute for ELK1 in structure/function and genome recognition, did not interact with AR. ELK1 thus directs selective and sustained gene induction that is a substantial and critical component of growth signaling by AR in PC cells. The ELK1-AR interaction offers a functionally tumor-selective drug target.

Distal metastasis of luminal breast cancer is frequent and incurable, yet the metastasis mechanisms are poorly understood. Estrogen, even at postmenopausal concentrations, suppresses invasiveness of luminal breast cancer cells through the estrogen receptor (ER). Invasive tumors overexpress the short progesterone receptor A (PR-A) isoform. Even at postmenopausal concentrations, progesterone activates PR-A, inducing invasiveness by counteracting estrogens effects, particularly when cells are hyper-sensitized to progesterone by PR-A overexpression. To interrogate the role of this crosstalk in metastasis, we investigated selective crosstalk mechanisms of PR-A with ER. We developed a quantitative PCR-based lymph node infiltration assay to address slowness of metastasis of tumor xenografts. We found that 15 microRNAs (miRNAs) are regulated by progesterone via PR-A, but not the longer PR-B isoform, with increased progesterone sensitivity when PR-A was overexpressed. Two of these miRNAs whose induction (miR-92a-3p) or repression (miR-26b-5p) by estrogen was suppressed by progesterone plus PR-A were critical for the PR-A-ER crosstalk causing a gene-regulatory pattern of invasiveness and metastasis and complete rescue of invasiveness in vitro. Constitutive expression of miR-92a-3p or inhibiting miR-26b-5p profoundly suppressed metastasis. Finally, in primary breast tumors, PR-A expression was correlated negatively with miR-92a-3p expression and positively with miR-26b-5p expression. Therefore, hormonal crosstalk of PR-A with ER is likely a fundamental mechanism that enables metastasis of luminal breast cancer. Moreover, miRNA biomarkers of hyperactive PR-A may help predict metastatic potential of luminal breast tumors. Further, miR-92a-3p and miR-26b-5p may reveal target pathways for selective intervention to suppress hormone-regulated metastasis, both pre- and post-menopause.

Introduction: Pemetrexed is an S-phase targeted drug in front-line or maintenance therapy of advanced nonsquamous non–small-cell lung cancer (NSCLC) but methods are needed for predicting the drug response. Dexamethasone is typically administered the day before, the day of, and the day after pemetrexed. As dexamethasone strongly regulates many genes including p53 through the glucocorticoid receptor (GR), we hypothesized that dexamethasone influences tumor response to pemetrexed. Methods: Eight nonsquamous NSCLC cell line models with varied p53 and GRα/GRβ status were used for gene expression and cell-cycle analyses and for loss- or gain-of-function experiments. Results: In three cell lines dexamethasone profoundly, but reversibly, suppressed the fraction of S-phase cells. Dexamethasone also reversibly repressed expression of thymidylate synthase and dihydrofolate reductase, which are primary targets of pemetrexed but are also quintessential S-phase enzymes as well as the S-phase–dependent expression of thymidine kinase 1. Dexamethasone also decreased expression of the major pemetrexed transporters, the reduced folate carrier and the proton coupled folate transporter. Only cells expressing relatively high GRα showed these dexamethasone effects, regardless of p53 status. In cells expressing low GRα, the dexamethasone response was rescued by ectopic GRα. Further, depletion of p53 did not attenuate the dexamethasone effects. The presence of dexamethasone during pemetrexed treatment protected against pemetrexed cytotoxicity in only the dexamethasone responsive cells. Conclusions: The results predict that in nonsquamous NSCLC tumors, reversible S-phase suppression by dexamethasone, possibly combined with a reduction in the drug transporters, attenuates responsiveness to pemetrexed and that GR status is a principal determinant of tumor variability of this response.

Dexamethasone (Dex), co-administered to lung adenocarcinoma patients with pemetrexed chemotherapy, protects against pemetrexed cytotoxicity by inducing reversible G1 arrest, reflected by the effect of Dex on FLT-PET images of patient tumors. However, perioperative Dex treatment increases survival but the mechanism is unknown. In cells with glucocorticoid receptor-α (GR) expression corresponding to higher clinical tumor levels, Dex-induced growth arrest was followed by marked cell expansion, beta-galactosidase expression and Ki67 negativity, despite variable p53 and K-RAS status. Dex induced a transient early surge in p21^Cip1. However, a progressive, irreversible loss of clonogenic growth, whose time of onset was dependent on GR level and Dex dose, was independent of p21^Cip1and caused by gradual accumulation of p27^Kip1 due to transcriptional activation of p27^Kip1 by Dex. This effect was independent of canonical pathways of senescence or p27^Kip1 regulation. The in vitro observations were reflected by growth suppression and P27^Kip1 induction in GR-overexpressing tumor xenografts compared with isogenic low-GR tumors. Extended Dex treatment induces irreversible cell cycle blockade and a senescence phenotype through chronic activation of the p27^Kip1 gene in GR overexpressing lung tumor cell populations and hence could improve outcome of surgery/pemetrexed chemotherapy and sensitize tumors to immunotherapy.

Histone deacetylase inhibitors (HDACIs) can disrupt the viability of prostate cancer (PCa) cells through modulation of the cytosolic androgen receptor (AR) chaperone protein heat shock protein 90 (HSP90). However, toxicities associated with their pleiotropic effects could contribute to the ineffectiveness of HDACIs in PCa treatment. We designed hybrid molecules containing partial chemical scaffolds of enzalutamide and suberoylanilide hydroxamic acid (SAHA), with weakened intrinsic pan-HDACI activities, to target HSP90 and AR in enzalutamide-resistant PCa cells. The potency of the new molecules, compounds 2-75 [4-(3-(4-cyano-3-(trifluoromethyl)phenyl)-5,5-dimethyl-4-oxo-2-thioxoimidazolidin-1-yl)-2-fluoro-N-(7-(hydroxyamino)-7-oxoheptyl)benzamide] and 1005 [(E)-3-(4-(3-(4-cyano-3-(trifluoromethyl)phenyl)-5,5-dimethyl-4-oxo-2-thioxoimidazolidin-1-yl)-2-fluorophenyl)-N-hydroxyacrylamide], as inhibitors of nuclear and cytosolic histone deacetylases was substantially lower than that of SAHA in cell-free and in situ assays. Compounds 2-75 and 1005 antagonized gene activation by androgen without inducing chromatin association of AR. Enzalutamide had no effect on the levels of AR or HSP90, whereas the hybrid compounds induced degradation of both AR and HSP90, similar to (compound 1005) or more potently than (compound 2-75) SAHA. Similar to SAHA, compounds 2-75 and 1005 decreased the level of HSP90 and induced acetylation in a predicted approximately 55 kDa HSP90 fragment. Compared with SAHA, compound 2-75 induced greater hyperacetylation of the HDAC6 substrate α-tubulin. In contrast with SAHA, neither hybrid molecule caused substantial hyperacetylation of histones H3 and H4. Compounds 2-75 and 1005 induced p21 and caused loss of viability in the enzalutamide-resistant C4-2 cells, with efficacies that were comparable to or better than SAHA. The results suggest the potential of the new compounds as prototype antitumor drugs that would downregulate HSP90 and AR in enzalutamide-resistant PCa cells with weakened effects on nuclear HDACI targets.