Prostate cancer patients have increased levels of stress and anxiety. Conversely, men who take beta blockers, which interfere with signaling from the stress hormones adrenaline and noradrenaline, have a lower incidence of prostate cancer; however, the mechanisms underlying stress-prostate cancer interactions are unknown. Here, we report that stress promotes prostate carcinogenesis in mice in an adrenaline-dependent manner. Behavioral stress inhibited apoptosis and delayed prostate tumor involution both in phosphatase and tensin homolog-deficient (PTEN-deficient) prostate cancer xenografts treated with PI3K inhibitor and in prostate tumors of mice with prostate-restricted expression of c-MYC (Hi-Myc mice) subjected to androgen ablation therapy with bicalutamide. Additionally, stress accelerated prostate cancer development in Hi-Myc mice. The effects of stress were prevented by treatment with the selective β 2 -adrenergic receptor (ADRB2) antagonist ICI118,551 or by inducible expression of PKA inhibitor (PKI) or of BCL2-associated death promoter (BAD) with a mutated PKA phosphorylation site (BAD S112A ) in xenograft tumors. Effects of stress were also blocked in Hi-Myc mice expressing phosphorylation-deficient BAD (BAD 3SA ). These results demonstrate interactions between prostate tumors and the psychosocial environment mediated by activation of an adrenaline/ADRB2/ PKA/BAD antiapoptotic signaling pathway. Our findings could be used to identify prostate cancer patients who could benefit from stress reduction or from pharmacological inhibition of stress-induced signaling.
PTEN loss and constitutive activation of the PI3K signaling pathway have been associated with advanced androgen-independent prostate cancer. PTEN-deficient prostate cancer C42Luc cells survive in serum-free media and show relative resistance to apoptosis even in the presence of the PI3K inhibitor ZSTK474. Yet, when ZSTK474 is combined with the translation inhibitor cycloheximide, C42Luc cells undergo apoptosis within 6 hours. We identified dephosphorylation of BAD (Bcl2-associated death promoter) as a main apoptosis-regulatory molecule downstream from PI3K, and loss of MCL-1 (Myeloid cell leukemia -1) as a major target of cycloheximide. The combination of MCL-1 knockdown and expression of phosphorylation-deficient mutant BAD2SA is sufficient to trigger rapid apoptosis in prostate cancer cells. These results establish the mechanism for the synergistic induction of apoptosis by the combination of a PI3K inhibitor and of a protein synthesis inhibitor in PTEN-deficient prostate cancer cells.
The phosphoinositide 3-kinase (PI3K) pathway is activated in most advanced prostate cancers, yet so far treatments with PI3K inhibitors have been at best tumorostatic in preclinical cancer models and do not show significant antitumor efficacy in clinical trials. Results from tissue culture experiments in prostate cancer cells suggest that PI3K inhibitors should be combined with other cytotoxic agents; however, the general toxicity of such combinations prevents translating these experimental data into preclinical and clinical models. We investigated the emerging concept of tumor-targeted synthetic lethality in prostate cancer cells by using the pan-PI3K inhibitor ZSTK474 and the immunotoxin J591PE, a protein chimera between the single-chain variable fragment of the monoclonal antibody J591 against the prostate-specific membrane antigen (PSMA) and the truncated form of the Pseudomonas aeruginosa exotoxin A (PE38QQR). The combination of ZSTK474 and J591PE increased apoptosis within 6 hours and cell death (monitored at 24-48 hours) in the PSMA-expressing cells LNCaP, C4-2, and C4-2Luc but not in control cells that do not express PSMA (PC3 and BT549 cells). Mechanistic analysis suggested that induction of apoptosis requires Bcl-2-associated death promoter (BAD) dephosphorylation and decreased expression of myeloid leukemia cell differentiation protein 1 (MCL-1). A single injection of ZSTK474 and J591PE into engrafted prostate cancer C4-2Luc cells led to consistent and stable reduction of luminescence within 6 days. These results suggest that the combination of a PI3K inhibitor and a PSMA-targeted protein synthesis inhibitor toxin represents a promising novel strategy for advanced prostate cancer therapy that should be further investigated.
Advanced androgen-independent prostate cancer is notoriously resistant to conventional systemic therapies, and at the moment there is no effective protocol for hormone-refractory advanced prostate cancer affected patients. One of possible mechanisms of such resistance is activation of the anti-apoptotic signaling PI3K/Akt pathway that is constitutively active in the 60% of advanced prostate cancers. However, multiple inhibitors of PI3K are just well studied and some have just gone on to clinical trials, but unfortunately they showed limited efficacy against prostate cancer alone. Our recent experiments has shown remarkable synergy in inducing rapid and massive apoptosis when PI3K inhibitor ZSTK474 is used in combination with Pseudomonas aeruginosa exotoxin A fragment fused with Transforming Growth Factor Alpha (TGFα-PE38). Time lapse video microscopy of prostate cancer C4-2 cell line has shown the substantial cell death within 4-6 hours with combined administration, compared to limited cell death in single agents-treated cells. Analysis of PARP and cleaved-caspase 3 fragment by Western blotting confirmed that cell death occurs via apoptosis. Quantitation of caspase 3 and 7 activity with luminescent AFC-DEVD substrate confirmed synergy in apoptosis activation by combination of TGFα-PE38 and ZSTK474, while single agents even in higher concentration did not induce substantial apoptosis within 6 hours time period. Analysis of the mechanisms underlying this synergy has shown that PI3K inhibitor ZSTK474 triggers Bad dephosphorylation, while TGFα-PE38 reduces expression levels of Mcl-1. A slight increase of Bim protein was detected and related with ZSTK474 administration. No major variations were detected in the expression levels of pro- and anti-apoptotic proteins Bax, Bcl-2 and Bcl-XL. To address the role of Bad phosphorylation and Mcl-1 expression in apoptosis induction by PI3K inhibitor ZSTK474 and TGFα-PE38, we examined apoptosis in C4-2 cells that express phosphorylation-deficient mutant Bad (BAD2SA). Results indicated that the expression of BAD2SA sensitized C4-2 cells to apoptosis induced by TGFα-PE38. Experiments that address the role of Mcl-1 loss in apoptosis induced by TGFα-PE38 are ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 183. doi:10.1158/1538-7445.AM2011-183
Prostate cancer remains the second leading cause of cancer-related death in men in the United States, as at present there are no effective treatments for advanced stage-affected patients. Recurrence usually involves hormonal androgen suppression, which typically translates into androgen-ablation insensitivity with accompanied limited or transient response to systemic chemotherapy. Our preliminary experiments have shown that it is possible to induce massive and rapid apoptosis in the hormone-refractory prostate cancer cells in vitro and in vivo, by using the PI3K inhibitor ZSTK474 in combination with a prostate cancer-selective cytotoxin J591PE38, a fusion protein between two fragments: one from the J591 antibody (that recognizes the Prostate-Specific Membrane Antigen, expressed in nearly all prostate cancers with the highest rate in poorly differentiated, metastatic and hormone-refractory cases), and the other from the Pseudomonas aeruginosa exotoxin A (PE38, that ADP-ribosylates and inhibits the Eukaryotic Elongation Factor 2). The PI3K inhibitor ZSTK474 in combination with the cytotoxin J591PE38 induces massive cell death (around 100%) in prostate cancer C4-2tetLuc and C4-2 cells monitored by Time-Lapse Video Microscopy during 24 hours, when compared to controls. Combined agents at 6 hours synergistically increases Caspase 3 activity, as confirmed by DEVD-Afc enzymatic assay (about 25 and 30 folds in C4-2tetLuc and C4-2 cells respectively, compared to control) and Western blotting (3.28 and 2.45 folds in C4-2tetLuc and C4-2 cells respectively, compared to control). Apoptosis activation was confirmed by detecting the cleaved fragments of Caspase 7 and PARP (compared to control respectively: 4.12 and 3.58 folds for C4-2tetLuc; 5.38 and 13.38 folds for C4-2 cells). No any major effects were found in the PSMA-negative prostate cancer PC-3 and breast cancer BT-549 cells treated with both agents when compared to controls, confirming the specificity of the cytotoxin J591PE38. PI3 Kinase inhibition by ZSTK474 was confirmed in all cell lines used by monitoring the phosphorylation levels of Akt (Thr308) by Western blotting. Prostate cancer C4-2tetLuc xenografts in nude mice showed a potent reduction of luminescence (around 95% at day 7) in tumors treated with a single local injection of both agents, when compared to controls. Apoptosis activation and PI3 Kinase inhibition at 6 hours were confirmed by monitoring the protein levels of cleaved-PARP and the phosphorylation levels of Akt by Western blotting. In summary, in this study we demonstrated the efficacy of a potential combinatorial approach using a specific PI3 Kinase and de novo protein synthesis inhibitor to treat hormone-refractory prostate cancer with constitutive active PI3K/Akt pathway, by generating massive and rapid apoptosis in vitro and in vivo (This work is supported by NIH/NCI grant 3R01 CA 118329 02S2). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2748. doi:1538-7445.AM2012-2748
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.