h-89 and bicalutamide

The androgen-signaling pathway with the androgen receptor (AR) as its key molecule is widely understood to influence prostate tumor growth significantly even after androgen ablation. Under androgen-deprived conditions, the AR may be activated inappropriately through interaction with other molecules, including cyclic AMP-dependent protein kinase A (PKA). In a previous study, we have shown that knocking down the AR significantly inhibits prostate tumor growth. In this study, we show that combined inhibition of the AR and the regulatory subunit I alpha of PKA (RIalpha) with small interference RNAs significantly increased the growth-inhibitory and proapoptotic effects of AR knockdown. This treatment strategy was effective in androgen-sensitive and in androgen ablation-resistant prostate cancer cells. In addition, we report that downregulating PKA RIalpha was sufficient to inhibit PKA signaling and interestingly also impaired AR expression and activation. Vice versa, AR knockdown induced a decline in PKA RIalpha, associated with reduced PKA activity. This mutual influence on expression level was specific, because siRNAs against the AR did not affect expression of PKA RIalpha in AR negative DU-145 cells and a siRNA control did not affect protein expression. Another important finding of our study was that depletion of PKA RIalpha also potentiated the antiproliferative effect of the antiandrogen bicalutamide in androgen-sensitive LNCaP. We therefore concluded that combined inhibition of PKA RIalpha and AR may be a promising new therapeutic option for prostate cancer patients and might be superior to solely preventing AR expression.

Topics: Adenocarcinoma; Androgen Antagonists; Androgen Receptor Antagonists; Androgens; Anilides; Animals; Apoptosis; Bucladesine; Cell Division; Colforsin; Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; Enzyme Induction; Gene Knockdown Techniques; Humans; Isoquinolines; Male; Metribolone; Neoplasm Proteins; Neoplasms, Hormone-Dependent; Nitriles; Prostatic Neoplasms; Receptors, Androgen; RNA, Small Interfering; Signal Transduction; Sulfonamides; Tosyl Compounds

The nicotinamide adenine dinucleotide-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH) catalyzes the oxidation of 15 (S)-hydroxyl group of prostaglandins and lipoxins and participates along with cyclooxygenases and lipoxygenases in controlling the cellular levels of prostaglandins and lipoxins. 15-PGDH could be induced by IL-6 and forskolin in addition to androgens in a time- and dose-dependent manner but not by other cytokines and growth factors in LNCaP cells. Concurrent addition of IL-6 and forskolin showed additive effect in the induction of 15-PGDH activity. However, combined addition of dihydrotestosterone (DHT) and IL-6 or DHT plus forskolin exhibited synergistic induction of 15-PGDH activity. The increase in enzyme activity was correlated with the expression of the enzyme protein as shown by Western blot analysis. The induction by DHT or IL-6 or forskolin or their combinations was inhibited by antiandrogen, casodex, in a dose-dependent manner, indicating that a functional androgen receptor was required for the action of any of these three agents. The induction by forskolin plus DHT or by either agent or by IL-6 alone was greatly inhibited by H-89, indicating the involvement of protein kinase A in the actions of forskolin, DHT, and IL-6. The induction of 15-PGDH by IL-6 was also blocked by some other protein kinase inhibitors, indicating the participation of MAPK, MAPK/ERK kinase, and STAT3 in the signaling pathway of IL-6. These results indicate that the induction of 15-PGDH by DHT, IL-6, and forskolin in LNCaP cells may involve a functional androgen receptor and phosphorylation-dependent multiple signaling pathways.

Topics: Androgen Antagonists; Anilides; Blotting, Western; Colforsin; Cyclic AMP-Dependent Protein Kinases; Dihydrotestosterone; DNA-Binding Proteins; Dose-Response Relationship, Drug; Drug Synergism; Enzyme Induction; Enzyme Inhibitors; Humans; Hydroxyprostaglandin Dehydrogenases; Interleukin-6; Isoquinolines; Kinetics; Male; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases; Nitriles; Phosphorylation; Prostatic Neoplasms; Receptors, Androgen; Signal Transduction; STAT3 Transcription Factor; Sulfonamides; Tosyl Compounds; Trans-Activators; Tumor Cells, Cultured