Metal-NHC complexes: a survey of anti-cancer properties.

New weapons to fight cancer are constantly needed. Among chemotherapeutics, anti-cancer metal-drugs have enjoyed a long and successful history since the discovery of the benchmark cisplatin. Advances in metal-drug discovery have motivated chemists to build plethora of complex structures. Among them, a novel area is emerging. This article presents a survey of the metal-N-Heterocyclic Carbenes (Ag(I), Au(I), Pd(II) and Cu(I)-NHCs) as potential anti-cancer agents. Most of the metal-NHCs considered display higher cytotoxicities than the reference metallo-drug cisplatin. Some of them are even selective for particular cell lines. Their mechanisms of action at the cellular level are further discussed, showing that the nature of the metal is of great importance. All these promising results demonstrate that this approach deserves more attention and work.

Prostaglandin F2alpha synthase activities of aldo-keto reductase 1B1, 1B3 and 1B7.

Here, we show that three enzymes belonging to the 1B group of the aldo-keto reductase (AKR) superfamily, i.e., human placental aldose reductase (AKR1B1), mouse kidney aldose reductase (AKR1B3) and mouse vas deferens protein (AKR1B7), catalyse the reduction of prostaglandin (PG) H(2), a common intermediate of various prostanoids, to form PGF(2alpha) in the presence of NADPH. AKR1B1, AKR1B3 and AKR1B7 displayed higher affinities for PGH(2) (K(m) = 1.9, 9.3 and 3.8 microM, respectively) and V(max) values (26, 53 and 44 nmol/min/mg protein, respectively) than did the human lung PGF(2alpha) synthase (AKR1C3; 18 microM and 4 nmol/min/mg protein, respectively). The PGF(2alpha) synthase activity of AKR1B1 and AKR1B3 was efficiently inhibited by two AKR inhibitors, tolrestat (K(i) = 3.6 and 0.26 microM, respectively) and sorbinil (K(i) = 21.7 and 0.89 microM, respectively), in a non-competitive or mixed-type manner, whereas that of AKR1B7 was not sensitive to these inhibitors (K(i) = 9.2 and 18 mM, respectively). These data provide a molecular basis for investigating novel functional roles for AKR1B members and PGF(2alpha) as mediators of physiological and pathological processes in mammalian organisms.

Aldo keto reductase 1B7 and prostaglandin F2alpha are regulators of adrenal endocrine functions.

Prostaglandin F(2alpha) (PGF(2alpha)), represses ovarian steroidogenesis and initiates parturition in mammals but its impact on adrenal gland is unknown. Prostaglandins biosynthesis depends on the sequential action of upstream cyclooxygenases (COX) and terminal synthases but no PGF(2alpha) synthases (PGFS) were functionally identified in mammalian cells. In vitro, the most efficient mammalian PGFS belong to aldo-keto reductase 1B (AKR1B) family. The adrenal gland is a major site of AKR1B expression in both human (AKR1B1) and mouse (AKR1B3, AKR1B7). Thus, we examined the PGF(2alpha) biosynthetic pathway and its functional impact on both cortical and medullary zones. Both compartments produced PGF(2alpha) but expressed different biosynthetic isozymes. In chromaffin cells, PGF(2alpha) secretion appeared constitutive and correlated to continuous expression of COX1 and AKR1B3. In steroidogenic cells, PGF(2alpha) secretion was stimulated by adrenocorticotropic hormone (ACTH) and correlated to ACTH-responsiveness of both COX2 and AKR1B7/B1. The pivotal role of AKR1B7 in ACTH-induced PGF(2alpha) release and functional coupling with COX2 was demonstrated using over- and down-expression in cell lines. PGF(2alpha) receptor was only detected in chromaffin cells, making medulla the primary target of PGF(2alpha) action. By comparing PGF(2alpha)-responsiveness of isolated cells and whole adrenal cultures, we demonstrated that PGF(2alpha) repressed glucocorticoid secretion by an indirect mechanism involving a decrease in catecholamine release which in turn decreased adrenal steroidogenesis. PGF(2alpha) may be regarded as a negative autocrine/paracrine regulator within a novel intra-adrenal feedback loop. The coordinated cell-specific regulation of COX2 and AKR1B7 ensures the generation of this stress-induced corticostatic signal.

Crosstalk between androgen receptor and epidermal growth factor receptor-signalling pathways: a molecular switch for epithelial cell differentiation.

In the male, androgens promote growth and differentiation of sex reproductive organs through ligand activation of the androgen receptor (AR). Here, we show that androgens are not major actors of the cell cycle arrest associated with the differentiation process, and that the epidermal growth factor (EGF)-mediated signalling interferes with AR activities to regulate androgen response when epithelial cells are differentiated. Higher AR expression and enhanced androgen responsiveness correlate with reduction of phosphorylated ERK1/2 over differentiation. These modifications are associated with recruitment of cells in phase G(0)/G(1), up-regulation of p27(kip1), down-regulation of p21(Cip1) and p53 proteins, and accumulation of hypo-phosphorylated Rb. Exposure to EGF reduces AR expression levels and blocks androgen-dependent transcription in differentiated cells. It also restores p53 and p21(Cip1) levels, Rb hyper-phosphorylation, ERK1/2 activation and promotes cell cycle re-entry as p27(kip1) protein levels are decreased. Treatment with a MEK inhibitor reverses the EGF-mediated AR down-regulation in differentiated cells, thus suggesting the existence of an inverse correlation between EGF and androgen signalling in non-tumoural epithelia. Interestingly, when androgen signalling is set in differentiated cells, dihydrotestosterone exerts an inhibitory effect on ERK activity but paradoxically does not modify EGFR (ErbB1) phosphorylation, indicating that androgens are able to disrupt the EGFR-ERK cascade. Overall, our data demonstrate the existence of a balance between AR and mitogen-activated protein kinase activities that favours either the maintenance of differentiated conditions or the enhancement of cell proliferation capacities.

Androgen receptor mediates non-genomic activation of phosphatidylinositol 3-OH kinase in androgen-sensitive epithelial cells.

Androgens are known to modulate many cellular processes such as cell growth and survival by binding to the androgen receptor (AR) and activating the transcription of target genes. Recent data suggested that AR can also mediate non-transcriptional actions outside the nucleus in addition to its ligand-inducible transcription factor function. Here, we describe a transcription-independent activation of the phosphatidylinositol 3-OH kinase (PI3-K) signaling pathway by androgens. Using non-transformed androgen-sensitive epithelial cells, we show that androgens enhance the PI3-K activity by promoting accumulation of phosphoinositide-3-P phospholipids in vitro. This activation is found in conjunction with an increased time-dependent phosphorylation of the downstream kinase AKT/protein kinase B on both Ser(473) and Thr(308) residues. Hormone-stimulated phosphorylation of AKT requires AR since incubation with the anti-androgen bicalutamide completely abolishes the androgen-stimulated AKT phosphorylation. Accordingly, we show that androgens increase AKT phosphorylation level in prostatic carcinoma PC3 cells only once they have been transfected with AR. Downstream, androgens enhance phosphorylation of transcription factor FKHR (Forkhead in rhabdomyosarcoma)-L1 and proapoptotic Bad protein and promote cell survival as they can counteract an apoptotic process. We also report that non-genomic effects of androgens are based on direct interaction between AR and the p85alpha regulatory subunit of class I(A) PI3-K. Together, these novel findings point out an important and physiologically relevant link between androgens and the PI3-K/AKT signaling pathway in governing cell survival.

Both retinoids and androgens are required to maintain or promote functional differentiation in reaggregation cultures of human prostate epithelial cells.

BACKGROUND: Primary cultures and subcultures of prostate epithelial cells (PEC) proliferate markedly, but rapidly loose secretory differentiated function and androgen responsiveness. Here, we investigated whether differentiation could be restored or preserved by using three-dimensional reaggregation cultures treated with retinoids and/or androgens. METHODS: PEC were cultured as monolayers or as reaggregation cultures on a rotatory shaker. Reaggregation cultures were also developed from freshly isolated cells. Morphology was evaluated microscopically. Expression of cytokeratins (CKbasal for basal cells and CK18 for luminal cells), E-cadherin, alpha- and beta-catenin, androgen receptor (AR), and prostate specific antigen (PSA) was evaluated by immunohistochemistry and/or Western blotting. Differentiated function was further evaluated by measurements of PSA in the medium and by reverse transcriptase-polymerase chain reactions for AR, PSA, prostate specific membrane antigen, beta-microseminoprotein, and zinc-alpha 2-glycoprotein. Proliferation was evaluated by immunohistochemical staining for Ki-67. RESULTS: Monolayer cultures of PEC expressed CKbasal as well as CK18, a combination compatible with an intermediary amplifying population of epithelial cells. No expression of PSA could be detected, and all attempts to re-induce differentiation of PEC in classic two-dimensional culture systems failed. In reaggregation cultures of subcultured PEC, retinoids proved essential to maintain a compact three-dimensional structure. This effect was accompanied by increased levels of E-cadherin and of the catenins and by a shift in the cytokeratin expression pattern toward that typical for secretory differentiated cells (CK18 only). Even in the presence of androgens, however, PSA remained undetectable. Similar effects of retinoids were observed in reaggregation cultures of freshly prepared PEC, and in the latter cultures, the combination of androgens and retinoids maintained a low level of PSA secretion for at least 40 days. CONCLUSIONS: A combination of retinoids and androgens is able to preserve, for a prolonged period of time, some degree of secretory differentiation in freshly isolated PEC maintained in reaggregation culture. The same combination is unable to restore secretory differentiation in subcultured PEC.

Androgen receptor expression is regulated by the phosphoinositide 3-kinase/Akt pathway in normal and tumoral epithelial cells.

The androgen receptor (AR) is a ligand-responsive transcription factor known to play a central role in the pathogenesis of prostate cancer. However, the regulation of AR gene expression in the normal and pathological prostate remains poorly understood. This study focuses on the effect of the phosphoinositide 3-kinase (PI 3-kinase)/Akt axis on AR expression in vas deferens epithelial cells (VDEC), a suitable model to study androgen regulation of gene expression, and LNCaP cells (derived from a metastasis at the left supraclavicular lymph node from a 50-year-old patient with a confirmed diagnosis of metastatic prostate carcinoma). Taken together, our data show for the first time that the PI 3-kinase/Akt pathway is required for basal and dihydrotestosterone-induced AR protein expression in both VDEC and LNCaP. Inhibition of the PI 3-kinase/Akt pathway reduced AR expression and the decline in AR protein level correlated with a decrease in AR mRNA in VDEC but not in LNCaP. Since PI 3-kinase/Akt axis is active in prostate cancer, cross-talk between PI 3-kinase/Akt and AR signalling pathways may have implications for endocrine therapy.