The role of insulin-like growth factor binding protein-3 in the growth inhibitory actions of androgens in LNCaP human prostate cancer cells

Insulin-like growth factor binding protein-3 (IGFBP-3), an antiproliferative and proapoptotic protein, has been shown to be upregulated by growth inhibitory concentrations of androgens in LNCaP human prostate cancer (PCa) cells, but the mechanism of regulation and the role of IGFBP-3 in the modulation of PCa cell proliferation are unknown. In this study, we have examined the effects of a range of concentrations of the synthetic androgen R1881 on IGFBP-3 expression and cell growth in LNCaP cells. We have also investigated the role of androgen-stimulated IGFBP-3 in androgen-induced growth inhibition. We show that low doses of R1881 stimulate LNCaP cell proliferation, but do not induce IGFBP-3 expression, whereas high doses of R1881 that inhibit cell growth, significantly increase expression of IGFBP-3. Importantly, we demonstrate that the combination of calcitriol and androgens not only synergistically upregulates IGFBP-3 expression but also inhibits cell growth better than either hormone alone. siRNA knockdown of IGFBP-3 expression partially reverses the growth inhibition by calcitriol and by androgens. Furthermore, we find that the growth inhibitory dose of R1881 leads to increases in the cyclin dependent kinase inhibitors (CDKIs), p21 and p27 as well as to G1 arrest. These changes can be blocked or partially reversed by IGFBP-3 siRNA, indicating that the induction of CDKIs is downstream of IGFBP-3. Our data suggest, for the first time, that IGFBP-3 is involved in the antiproliferative action of high doses of androgens partly through p21 and p27 pathways and that IGFBP-3 may contribute significantly to androgen-induced changes in LNCaP cell growth.     

Effect of calcitriol on prostate-specific antigen in vitro and in humans.

BACKGROUND: Calcitriol, the natural ligand for the vitamin D receptor, has significant potential in prostate cancer treatment. Measurement of its antineoplastic activity in prostate cancer clinical trials may be complicated by effects of calcitriol on prostate-specific antigen (PSA) production. We examined the effects of calcitriol at similar concentration on cell proliferation, androgen receptor (AR) expression, and PSA production in vitro and on PSA concentrations in prostate cancer patients. EXPERIMENTAL DESIGN: LNCaP prostate cancer cell proliferation was examined by cell counts 6 days after exposure to a range of concentrations of calcitriol. AR and PSA protein was quantified in LNCaP cells over 96 hours after exposure to 1 nmol/L calcitriol. Serum PSA and free PSA was serially measured by immunoassay over a period of 8 days in patients with hormone-na?ve prostate cancer after a single dose of 0.5 microg/kg calcitriol. RESULTS: Calcitriol treatment resulted in dose-dependent growth inhibition of LNCaP with approximately 50% growth inhibition at the clinically achievable concentration of 1 nmol/L. Time-dependent up-regulation of AR expression and of PSA production in LNCaP cells was shown at the same concentration. No significant change in serum PSA or free PSA over 8 days was seen in eight subjects treated with a single dose of 0.5 microg/kg calcitriol. The analysis was powered to detect a 1.23-fold change between the baseline and day 8 serum PSA. CONCLUSIONS: At clinically achievable concentrations, calcitriol inhibits growth and induces AR and PSA expression in LNCaP cells. We did not detect similar changes in serum PSA or free PSA in patients exposed to similar concentrations of calcitriol. Thus, a PSA flare, predicted by preclinical systems, is unlikely to occur in patients and therefore unlikely to complicate interpretation of clinical trial outcomes.     

雷公藤红素对人前列腺癌细胞凋亡及SENP1基因表达的影响

目的：研究雷公藤红素对人前列腺癌（PCa）细胞生长、凋亡及SUMO特异蛋白酶1（SUMO-specificproteases 1,SENP1）基因表达的影响。方法：对前列腺癌细胞PC-3和LNCaP进行雷公藤红素处理,通过测定细胞生长曲线,荧光染色,荧光显微镜观察,流式细胞仪分析和实时定量PCR,检测雷公藤红素对前列腺癌细胞生长、凋亡及SENP1 mRNA表达水平的影响。结果：雷公藤红素能够显著抑制PCa细胞的生长,并且抑制作用呈剂量依赖性;雷公藤红素能够诱导PCa细胞凋亡,1μmol/L雷公藤红素处理24h诱导14.8%的PC-3细胞和23.2%的LNCaP细胞发生凋亡或死亡;雷公藤红素还能够降低PCa细胞中SENP1 mRNA水平,尤其是PC-3细胞。结论：雷公藤红素能够显著抑制PCa细胞的生长并诱导细胞凋亡,表明雷公藤红素具有抗前列腺癌作用,雷公藤红素能够降低PCa细胞中SENP1 mRNA水平,揭示雷公藤红素可能通过SENP1相关信号通路达到抗前列腺癌作用。     

The therapeutic and preventive effect of RRR-alpha-vitamin E succinate on prostate cancer via induction of insulin-like growth factor binding protein-3.

PURPOSE: Insulin-like growth factor binding protein-3 (IGFBP-3) is a well-known antiproliferative and proapoptotic molecule in prostate cancer, suggesting that targeting IGFBP-3 might produce clinical benefits. In prostate cancer cells, RRR-alpha-vitamin E succinate (VES) inhibits cell proliferation and induces apoptosis, yet the mechanisms remain to be elucidated. We hypothesize that the protective effects of VES in prostate cancer are mediated by IGFBP-3 up-regulation. Using prostate cancer models, the involvement of IGFBP-3 in the anticancer effect of VES was investigated. EXPERIMENTAL DESIGN: IGFBP-3 mRNA and protein were determined by real-time PCR and Western blotting in prostate cancer cells, xenografted tumors of nude mice, and prostate tumors of transgenic adenocarcinoma mouse prostate (TRAMP) mice. The serum levels of IGFBP-3 were assessed by ELISA. The importance of IGFBP-3 in VES-mediated antitumor effects was confirmed by small interfering RNA knockdown strategy. RESULTS: We found that VES induced IGFBP-3 mRNA and protein levels in human prostate cancer cell lines. Knockdown of IGFBP-3 by small interfering RNA attenuated VES-induced IGFBP-3 expression and VES-mediated antiproliferative and proapoptotic functions. Furthermore, administration of VES resulted in a significant therapeutic effect on LNCaP and PC3 xenografts and a preventive effect on tumorigenic progression in the TRAMP model without overt toxicity. Notably, the therapeutic and preventive efficacy of VES correlated with increased accumulation of IGFBP-3 in mouse serum as well as in the xenograft tumors and TRAMP prostate samples. Consequently, reduced proliferation and induced apoptosis were witnessed. CONCLUSIONS: VES mediates its therapeutic and preventive effects against prostate cancer at least partially through up-regulating IGFBP-3, which inhibits cell proliferation and promotes cell apoptosis.     

Insulin-like growth factor binding protein-6 inhibits prostate cancer cell proliferation: implication for anticancer effect of diethylstilbestrol in hormone refractory prostate cancer

Diethylstilbestrol (DES) is a synthetic oestrogen, and its anticancer effects are exerted in androgen-dependent prostate cancer. The administration of DES decreases serum testosterone to castration levels. However, in androgen-independent prostate cancer patients, who are already orchiectomised, the administration of DES improves symptoms and decreases prostate-specific antigen (PSA). The mechanisms responsible for these direct inhibitory effects have been explained as biological actions not mediated by oestrogen receptors. We assessed the gene expression profiles of prostate cancer cells treated with DES, and investigated direct inhibitory effects of DES. DES inhibited the proliferation of LNCaP and PC-3 cells. cDNA microarray analysis showed that expression of many genes was downregulated by DES. However, insulin-like growth factor binding protein 6 (IGFBP-6) gene expression levels were upregulated in PC-3 cells. IGFBP-6 gene expression and protein levels significantly increased after DES treatment. Recombinant IGFBP-6 inhibited cell proliferation, and the inhibitory effect of DES was neutralised by anti-IGFBP-6 antibody. From the immunohistochemical analysis of IGFBP-6 using biopsy samples from androgen-independent prostate cancer, we found IGFBP-6 expression in androgen independent prostate cancer, and that DES treatment increased the IGFBP-6 staining intensity of the cancer cells in one sample. These findings suggested that DES induces IGFBP-6, which inhibits cell proliferation in an androgen-independent prostate cancer cell line, PC-3. IGFBP-6 therefore might be involved in the direct effects of DES in androgen-independent prostate cancer.     

ERK inhibitor PD98059 enhances docetaxel-induced apoptosis of androgen-independent human prostate cancer cells

Anticancer drugs docetaxel and vinorelbine suppress cell growth by altering microtubule assembly and activating the proapoptotic signal pathway. Vinorelbine and docetaxel have been approved for treating several advanced cancers. However, their efficacy in the management of advanced hormone-refractory prostate cancer remains to be clarified. Microtubule damage by some anticancer drugs can activate the ERK survival pathway, which conversely compromises chemotherapeutic efficacy. We analyzed the effect of ERK inhibitors PD98059 and U0126 on vinorelbine- and docetaxel-induced cell growth suppression of androgen-independent prostate cancer cells. In androgen-independent C-81 LNCaP cells, inhibition of ERK by PD98059, but not U0126, plus docetaxel resulted in enhanced growth suppression by an additional 20% compared to the sum of each agent alone (p < 0.02). The combination treatment of docetaxel plus PD98059 also increased cellular apoptosis, which was in part due to the inactivation of Bcl-2 by increasing phosphorylated Bcl-2 by more than 6-fold and Bax expression by 3-fold over each agent alone. At these dosages, docetaxel alone caused only marginal phosphorylation of Bcl-2 (10%). Docetaxel plus U0126 had only 20% added effect on Bcl-2 phosphorylation compared to docetaxel alone. Nevertheless, both U0126 and PD98059 exhibited an enhanced effect on docetaxel-induced growth suppression in PC-3 cells. No enhanced effect was observed for vinorelbine plus PD98059 or U0126. Thus, the combination therapy of docetaxel plus PD98059 may represent a new anticancer strategy, requiring lower drug dosages compared to docetaxel monotherapy. This may lower the cytotoxicity and enhance tumor suppression in vivo. This finding of a combination effect could be of potential clinical importance in treating hormone-refractory prostate cancer.     

Prostate tumor progression is mediated by a paracrine TGF-beta/Wnt3a signaling axis

Transforming growth factor (TGF)-beta is an important paracrine factor in tumorigenesis. Ligand binding of the type I and II TGF-beta receptors initiate downstream signaling. The role of stromal TGF-beta signaling in prostate cancer progression is unknown. In mice, the conditional stromal knockout of the TGF-beta type II receptor expression (Tgfbr2(fspKO)) resulted in the development of prostatic intraepithelial neoplasia and progression to adenocarcinoma within 7 months. Clinically, we observed a loss of TGF-beta receptor type II expression in 69% of human prostate cancer-associated stroma, compared to 15% of stroma associated with benign tissues (n=140, P-value <0.0001). To investigate the mechanism of paracrine TGF-beta signaling in prostate cancer progression, we compared the effect of the prostatic stromal cells from Tgfbr2(fspKO) and floxed TGF-beta type II receptor Tgfbr2(floxE2/floxE2) mice on LNCaP human prostate cancer cells in vitro and tissue recombination xenografts. Induction of LNCaP cell proliferation and tumorigenesis was observed by Tgfbr2(fspKO) prostate stroma as a result of elevated Wnt3a expression. Neutralizing antibodies to Wnt3a reversed LNCaP tumorigenesis. The TGF-beta inhibition of Wnt3a expression was in part through the suppression of Stat3 activity on the Wnt3a promoter. In conclusion, the frequent loss of stromal TGF-beta type II receptor expression in human prostate cancer can relieve the paracrine suppression of Wnt3a expression.     

A calcitriol analogue, EB1089, inhibits the growth of LNCaP tumors in nude mice

Limited options for the treatment of prostate cancer have spurred the search for new therapies. One innovative approach is the use of 1alpha,25-dihydroxyvitamin D3 (calcitriol) analogues to inhibit cancer growth. We demonstrate here that the calcitriol analogue, EB1089, extensively inhibits the growth of LNCaP prostate cancer cells in culture and causes the cells to both accumulate in G0-G1 and undergo apoptosis. Importantly, we found that EB1089 inhibits the growth of LNCaP tumor xenografts in nude mice. Because of these antiproliferative properties in vivo, EB1089 is a potential new therapeutic agent for the treatment of prostate cancer.     

Prohibitin and cofilin are intracellular effectors of transforming growth factor beta signaling in human prostate cancer cells

A proteomic analysis was pursued to identify new signaling effectors of transforming growth factor beta1 (TGF-beta1) that serve as potential intracellular effectors of its apoptotic action in human prostate cancer cells. The androgen-sensitive and TGF-beta-responsive human prostate cancer cells, LNCaP T beta RII, were used as in vitro model. In response to TGF-beta, significant posttranslational changes in two proteins temporally preceded apoptotic cell death. TGF-beta mediated the nuclear export of prohibitin, a protein involved in androgen-regulated prostate growth, to the cytosol in the LNCaP T beta RII cells. Cofilin, a protein involved in actin depolymerization, cell motility, and apoptosis, was found to undergo mitochondrial translocation in response to TGF-beta before cytochrome c release. Loss-of-function approaches (small interfering RNA) to silence prohibitin expression revealed a modest decrease in the apoptotic response to TGF-beta and a significant suppression in TGF-beta-induced cell migration. Silencing Smad4 showed that the cellular localization changes associated with prohibitin and cofilin action in response to TGF-beta are independent of Smad4 intracellular signaling.     

Flavokawain B,a kava chalcone,induces apoptosis via up‐regulation of death‐receptor 5 and Bim expression in androgen receptor negative,hormonal refractory prostate cancer cell lines and reduces tumor growth

Limited success has been achieved in extending the survival of patients with metastatic and hormone‐refractory prostate cancer (HRPC). There is a strong need for novel agents in the treatment and prevention of HRPC. We have shown that flavokawain B (FKB), a kava chalcone, is about 4‐ to 12‐fold more effective in reducing the cell viabilities of androgen receptor (AR)‐negative, HRPC cell lines DU145 and PC‐3 than AR‐positive, hormone‐sensitive prostate cancer cell lines LAPC4 and LNCaP, with minimal effect on normal prostatic epithelial and stromal cells. FKB induces apoptosis with an associated increased expression of proapoptotic proteins: death receptor‐5, Bim and Puma and a decreased expression of inhibitors of apoptosis protein: XIAP and survivin. Among them, Bim expression was significantly induced by FKB as early as 4 hr of the treatment. Knockdown of Bim expression by short‐hairpin RNAs attenuates the inhibitory effect on anchorage‐dependent and ‐independent growth and caspase cleavages induced by FKB. These findings suggest that the effect of FKB, at least in part, requires Bim expression. In addition, FKB synergizes with TRAIL for markedly enhanced induction of apoptosis. Furthermore, FKB treatment of mice bearing DU145 xenograft tumors results in tumor growth inhibition and increases Bim expression in tumor tissues. Together, these results suggest robust mechanisms for FKB induction of apoptosis preferentially for HRPC and the potential usefulness of FKB for prevention and treatment of HRPC in an adjuvant setting.     

Phellinus linteus sensitises apoptosis induced by doxorubicin in prostate cancer

It has been demonstrated that the Phellinus linteus (PL) mushroom, which mainly consists of polysaccharides, possesses antitumour activity. The mechanisms of PL against malignant growth remain unknown. The anticancer drug doxorubicin (Dox) has been shown to induce apoptosis via initiating a caspase cascade. In this investigation, we tested the effect of PL on Dox-induced apoptosis in prostate cancer LNCaP cells. We showed that PL or Dox, at relatively low doses, does not induce apoptosis in the cells. However, combination treatment with low doses of PL and Dox results in a synergistic effect on the induction of apoptosis. In this apoptotic process, caspases 8, 3 and BID are cleaved, and the addition of caspase inhibitor z-VADfmk completely blocks apoptosis. In addition, JNK is activated in response to PL or the combination treatment in LNCaP cells. The suppression of JNK partially inhibits the induction of apoptosis elicited by the co-treatment. These findings indicate that PL has a synergistic effect with Dox to activate caspases in prostate cancer LNCaP cells. Our study also suggests that PL has therapeutic potential to augment the magnitude of apoptosis induced by antiprostate cancer drugs.     

Interleukin-6 inhibits the growth of prostate cancer xenografts in mice by the process of neuroendocrine differentiation

In vitro, the human prostate cancer (PCA) cell line LNCaP can be permanently transdifferentiated into a quiescent neuroendocrine (NE) phenotype by the cytokine interleukin-6 (IL-6). Recently, we have shown that the growth of prostate cancer cells is significantly suppressed when cocultured with NE cells. In order to explore the inhibitory activity of IL-6 on prostate tumor growth, nude mice bearing xenografts of the PCA cell lines LNCaP and DU-145 (a line that is incapable of NE transdifferentiation by IL-6 in vitro) were treated with IL-6 for 3 weeks, either injected around the tumor or systematically released from implanted minipumps. Both administration forms of IL-6 inhibited the growth of LNCaP xenografts by more than 75% compared to the control group. In contrast, there was no difference in DU-145 tumor growth between IL-6-treated animals and controls. In comparison to control and DU-145 tumors, both IL-6 injected and pump-infused LNCaP tumors exhibited a significant increase in the expression of the NE markers neuron-specific enolase (NSE) and betaIII tubulin. Serum NSE levels were also significantly elevated in both IL-6-treated LNCaP tumor groups when compared to controls. IL-6 treatment resulted in G(0) cell cycle accumulation as evidenced by a loss of Ki-67 expression in > 90% of LNCaP tumor cells. These combined results demonstrate that IL-6-induced NE transdifferentiation of PCA cells has a significant inhibitory effect on tumor growth in mice. Agents, like IL-6, capable of NE transdifferentiation of PCA cells, should be considered as a new therapeutic approach for the treatment of prostate cancer.     

Enhanced antiproliferative and proapoptotic effects on prostate cancer cells by simultaneously inhibiting androgen receptor and cAMP‐dependent protein kinase A

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 (RIα) 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 RIα was sufficient to inhibit PKA signaling and interestingly also impaired AR expression and activation. Vice versa, AR knockdown induced a decline in PKA RIα, associated with reduced PKA activity. This mutual influence on expression level was specific, because siRNAs against the AR did not affect expression of PKA RIα 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 RIα also potentiated the antiproliferative effect of the antiandrogen bicalutamide in androgen‐sensitive LNCaP. We therefore concluded that combined inhibition of PKA RIα and AR may be a promising new therapeutic option for prostate cancer patients and might be superior to solely preventing AR expression.     

Altered glucuronidation deregulates androgen dependent response profiles and signifies castration resistance in prostate cancer

Glucuronidation controls androgen levels in the prostate and the dysregulation of enzymes in this pathway is associated with castration resistant prostate cancer. UDP-glucose dehydrogenase (UGDH) produces UDP-glucuronate, the essential precursor for glucuronidation, and its expression is elevated in prostate cancer. We compared protein and metabolite levels relevant to the glucuronidation pathway in five prostate cancer patient-derived xenograft models paired with their isogenic counterparts that were selected in vivo for castration resistant (CR) recurrence. All pairs showed changes in UGDH and associated enzymes and metabolites that were consistent with those we found in an isogenic androgen dependent (AD) and CR LNCaP prostate cancer model. Ectopic overexpression of UGDH in LNCaP AD cells blunted androgen-dependent gene expression, increased proteoglycan synthesis, significantly increased cell growth compared to controls, and eliminated dose responsive growth suppression with enzalutamide treatment. In contrast, the knockdown of UGDH diminished proteoglycans, suppressed androgen dependent growth irrespective of androgens, and restored androgen sensitivity in CR cells. Importantly, the knockdown of UGDH in both LNCaP AD and CR cells dramatically sensitized these cells to enzalutamide. These results support a role for UGDH in androgen responsiveness and a target for therapeutic strategies in advanced prostate cancer.     

Equol inhibits prostate cancer growth through degradation of androgen receptor by S‐phase kinase‐associated protein 2

Chemopreventive and potential therapeutic effects of soy isoflavones have been shown to be effective in numerous preclinical studies as well as clinical studies in prostate cancer. Although the inhibition of androgen receptor signaling has been supposed as one mechanism underlying their effects, the precise mechanism of androgen receptor inhibition remains unclear. Thus, this study aimed to clarify their mechanism. Among soy isoflavones, equol suppressed androgen receptor as well as prostate‐specific antigen expression most potently in androgen‐dependent LNCaP cells. However, the inhibitory effect on androgen receptor expression and activity was less prominent in castration‐resistant CxR and 22Rv1 cells. Consistently, cell proliferation was suppressed and cellular apoptosis was induced by equol in LNCaP cells, but less so in CxR and 22Rv1 cells. We revealed that the proteasome pathway through S‐phase kinase‐associated protein 2 (Skp2) was responsible for androgen receptor suppression. Taken together, soy isoflavones, especially equol, appear to be promising as chemopreventive and therapeutic agents for prostate cancer based on the fact that equol augments Skp2‐mediated androgen receptor degradation. Moreover, because Skp2 expression was indicated to be crucial for the effect of soy isoflavones, soy isoflavones may be applicable for precancerous and cancerous prostates.     

PCOTH, a novel gene overexpressed in prostate cancers, promotes prostate cancer cell growth through phosphorylation of oncoprotein TAF-Ibeta/SET

Through genome-wide cDNA microarray analysis coupled with microdissection of prostate cancer cells, we identified a novel gene, prostate collagen triple helix (PCOTH), showing overexpression in prostate cancer cells and its precursor cells, prostatic intraepithelial neoplasia (PIN). Immunohistochemical analysis using polyclonal anti-PCOTH antibody confirmed elevated expression of PCOTH, a 100-amino-acid protein containing collagen triple-helix repeats, in prostate cancer cells and PINs. Knocking down PCOTH expression by small interfering RNA (siRNA) resulted in drastic attenuation of prostate cancer cell growth, and concordantly, LNCaP derivative cells that were designed to constitutively express exogenous PCOTH showed higher growth rate than LNCaP cells transfected with mock vector, suggesting the growth-promoting effect of PCOTH on prostate cancer cell. To investigate the biological mechanisms of this growth-promoting effect, we applied two-dimensional differential gel electrophoresis (2D-DIGE) to analyze the phospho-protein fractions in LNCaP cells transfected with PCOTH. We found that the phosphorylation level of oncoprotein TAF-Ibeta/SET was significantly elevated in LNCaP cells transfected with PCOTH than control LNCaP cells, and these findings were confirmed by Western blotting and in-gel kinase assay. Furthermore, knockdown of endogenous TAF-Ibeta expression by siRNA also attenuated viability of prostate cancer cells as well. These findings suggest that PCOTH is involved in growth and survival of prostate cancer cells thorough, in parts, the TAF-Ibeta pathway, and that this molecule should be a promising target for development of new therapeutic strategies for prostate cancers.