EBP1, an ErbB3-binding protein, is decreased in prostate cancer and implicated in hormone resistance

Aberrant activation of the androgen receptor (AR) by the ErbB2/ErbB3 heterodimer contributes to the development of hormone resistance in prostate cancer. EBP1, an ErbB3-binding protein, acts as an AR corepressor. As EBP1 is decreased in preclinical models of hormone-refractory prostate cancer, we studied the expression of EBP1 in human prostate cancer. We found that the expression of the EBP1 gene was significantly decreased in prostate cancer tissues compared with benign prostate at both mRNA and protein levels. Restoration of EBP1 expression in the hormone-refractory LNCaP C81 cell line led to an amelioration of the androgen-independent phenotype based on established biological criteria and a reduction in the expression of a cohort of AR target genes. The ability of the ErbB3 ligand heregulin (HRG) to stimulate growth and AKT phosphorylation of hormone-refractory prostate cancer cells was abolished. Abrogation of EBP1 expression by short hairpin RNA in hormone-dependent LNCaP cells, which undergo apoptosis in response to HRG, resulted in HRG-stimulated cell growth. Restoration of EBP1 expression decreased the tumorigenicity of C81 xenografts in female mice, whereas elimination of EBP1 expression enhanced the ability of LNCaP cells to grow in female mice. Our data support a role for EBP1 in the development of hormone-refractory prostate cancer via inhibition of both AR- and HRG-stimulated growth and present a novel strategy for treating androgen-refractory prostate cancer.     

Combined targeting of epidermal growth factor receptor and hedgehog signaling by gefitinib and cyclopamine cooperatively improves the cytotoxic effects of docetaxel on metastatic prostate cancer cells

The epidermal growth factor receptor (EGFR) and hedgehog cascades provide a critical role in prostate cancer progression and contribute to the resistance to clinical therapies and disease relapse. Therefore, we evaluated, for the first time, the antiproliferative and cytotoxic effects induced by a combination of selective inhibitors of EGFR tyrosine kinase and smoothened hedgehog signaling element, gefitinib and cyclopamine, with a current chemotherapeutic drug used in the clinics, docetaxel, on some metastatic prostate cancer cell lines. Immunohistochemical analyses revealed that sonic hedgehog (SHH) expression was enhanced in 39% of primary prostatic adenocarcinomas (Gleason scores 4-10) compared with the corresponding normal tissues of the same prostate gland from 32 prostate cancer patients. The confocal microscopy and Western blot analyses have also indicated the high expression levels of SHH and EGFR in metastatic LNCaP, DU145, and PC3 cells. Moreover, the results revealed that the drugs, alone or in combination, at lower concentrations inhibited the growth of EGF plus SHH-stimulated and serum-stimulated androgen-responsive LNCaP-C33 and androgen-independent LNCaP-C81, DU145, and PC3 cells. Importantly, the combined docetaxel, gefitinib, and cyclopamine also caused a higher rate of apoptotic death of prostate cancer cells compared with individual agents. The cytotoxic effects induced by these drugs in PC3 cells seem to be mediated in part through the cellular ceramide production and activation of caspase cascades via a mitochondrial pathway and the release of cytochrome c into the cytosol. Additionally, the combined agents were more effective at suppressing the invasiveness of PC3 cells through Matrigel in vitro than the single drugs. These findings indicate that the combined use of inhibitors of EGF-EGFR and hedgehog signaling with docetaxel could represent a more promising strategy for treatment in patients with metastatic and androgen-independent prostate cancer.     

Chemical ablation of androgen receptor in prostate cancer cells by the histone deacetylase inhibitor LAQ824

Androgen receptor plays a critical role in the development of primary as well as advanced hormone-refractory prostate cancer. Therefore, ablation of androgen receptor from prostate cancer cells is an interesting concept for developing a new therapy not only for androgen-dependent prostate cancer but also for metastatic hormone-refractory prostate cancer, for which there is no effective treatment available. We report here that LAQ824, a cinnamyl hydroxamatic acid histone deacetylase inhibitor currently in human clinical trials, effectively depleted androgen receptor in prostate cancer cells at nanomolar concentrations. LAQ824 seemed capable of depleting both the mutant and wild-type androgen receptors in either androgen-dependent and androgen-independent prostate cancer cells. Although LAQ824 may exert its effect through multiple mechanisms, several lines of evidence suggest that inactivation of the heat shock protein-90 (Hsp90) molecular chaperone is involved in LAQ824-induced androgen receptor depletion. Besides androgen receptor, LAQ824 reduced the level of Hsp90 client proteins HER-2 (ErbB2), Akt/PKB, and Raf-1 in LNCaP cells. Another Hsp90 inhibitor, 17-allyamino-17-demethoxygeldanamycin (17-AAG), also induced androgen receptor diminution. LAQ824 induced Hsp90 acetylation in LNCaP cells, which resulted in inhibition of its ATP-binding activity, dissociation of Hsp90-androgen receptor complex, and proteasome-mediated degradation of androgen receptor. Consequently, LAQ824 blocked androgen-induced prostate-specific antigen production in LNCaP cells. LAQ824 effectively inhibited cell proliferation and induced apoptosis of these prostate cancer cells. These results reveal that LAQ824 is a potent agent for depletion of androgen receptor and a potential new drug for prostate cancer.     

Berberine, a natural product, induces G1-phase cell cycle arrest and caspase-3-dependent apoptosis in human prostate carcinoma cells

Berberine, a naturally occurring isoquinoline alkaloid, has been shown to possess anti-inflammatory and antitumor properties in some in vitro systems. Here, we report that in vitro treatment of androgen-insensitive (DU145 and PC-3) and androgen-sensitive (LNCaP) prostate cancer cells with berberine inhibited cell proliferation and induced cell death in a dose-dependent (10-100 micromol/L) and time-dependent (24-72 hours) manner. Treatment of nonneoplastic human prostate epithelial cells (PWR-1E) with berberine under identical conditions did not significantly affect their viability. The berberine-induced inhibition of proliferation of DU145, PC-3, and LNCaP cells was associated with G1-phase arrest, which in DU145 cells was associated with inhibition of expression of cyclins D1, D2, and E and cyclin-dependent kinase (Cdk) 2, Cdk4, and Cdk6 proteins, increased expression of the Cdk inhibitory proteins (Cip1/p21 and Kip1/p27), and enhanced binding of Cdk inhibitors to Cdk. Berberine also significantly (P < 0.05-0.001) enhanced apoptosis of DU145 and LNCaP cells with induction of a higher ratio of Bax/Bcl-2 proteins, disruption of mitochondrial membrane potential, and activation of caspase-9, caspase-3, and poly(ADP-ribose) polymerase. Pretreatment with the pan-caspase inhibitor z-VAD-fmk partially, but significantly, blocked the berberine-induced apoptosis, as also confirmed by the comet assay analysis of DNA fragmentation, suggesting that berberine-induced apoptosis of human prostate cancer cells is mediated primarily through the caspase-dependent pathway. The effectiveness of berberine in checking the growth of androgen-insensitive, as well as androgen-sensitive, prostate cancer cells without affecting the growth of normal prostate epithelial cells indicates that it may be a promising candidate for prostate cancer therapy.     

Targeting prostate cancer with conditionally replicative adenovirus using PSMA enhancer.

Prostate cancer is the second most commonly diagnosed cancer in men and accounts for significant mortality and morbidity in the United States. Initially androgen-dependent, prostate cancer ultimately becomes androgen-independent, which makes the disease extremely difficult to cure. In this study, we examined the use of conditionally replication-competent adenovirus for the treatment of hormone-independent prostate cancer. We utilized PSME, an enhancer element for prostate-specific PSMA expression, to control viral E1A protein expression and achieve exclusive virus replication in prostate. Western blotting confirmed that PSME mediated high E1A protein expression in PSMA-positive, androgen-independent prostate cancer cells (C4-2 and CWR22rv), but was much less active in PSMA-negative cancer cells (PC-3 and A549). Consistent with E1A protein expression, the recombinant adenovirus Ad5-PSME-E1a replicated in C4-2 and CWR22rv almost as efficiently as wild type with low levels of androgen, but its replication was significantly attenuated in PSMA-negative cells. In the in vitro killing assay, Ad5-PSME-E1a lysed all C4-2 and CWR22rv cells 5 days after infection, with minimal effect on PSMA-negative cells. In addition, injections of 1.7 x 10(8) plaque-forming units in a CWR22rv xenograft model in nude mice induced significant tumor growth delay, with a substantial necrotic area. These studies suggest that PSME-driven replication-competent adenovirus may be a new therapeutic modality for prostate cancer patients after hormone ablation therapy.     

Sequential combination of flavopiridol and docetaxel reduces the levels of X-linked inhibitor of apoptosis and AKT proteins and stimulates apoptosis in human LNCaP prostate cancer cells

Clinical trials have shown that chemotherapy with docetaxel combined with prednisone can improve survival of patients with androgen-independent prostate cancer. It is likely that the combination of docetaxel with other novel chemotherapeutic agents would also improve the survival of androgen-independent prostate cancer patients. We investigated whether the combination of docetaxel and flavopiridol, a broad cyclin-dependent kinase inhibitor, can increase apoptotic cell death in prostate cancer cells. Treatment of DU 145 prostate cancer cells with 500 nmol/L flavopiridol and 10 nmol/L docetaxel inhibited apoptosis probably because of their opposing effects on cyclin B1-dependent kinase activity. In contrast, when LNCaP prostate cancer cells were treated with flavopiridol for 24 hours followed by docetaxel for another 24 hours (FD), there was a maximal induction of apoptosis. However, there was greater induction of apoptosis in DU 145 cells when docetaxel was followed by flavopiridol or docetaxel. These findings indicate a heterogeneous response depending on the type of prostate cancer cell. Substantial decreases in X-linked inhibitor of apoptosis (XIAP) protein but not survivin, both being members of the IAP family, were required for FD enhanced apoptosis in LNCaP cells. Androgen ablation in androgen-independent LNCaP cells increased activated AKT and chemoresistance to apoptosis after treatment with FD. The proteasome inhibitor MG-132 blocked FD-mediated reduction of XIAP and AKT and antagonized apoptosis, suggesting that the activation of the proteasome pathway is one of the mechanisms involved. Overall, our data suggest that the docetaxel and flavopiridol combination requires a maximal effect on cyclin B1-dependent kinase activity and a reduction of XIAP and AKT prosurvival proteins for augmentation of apoptosis in LNCaP cells.     

CircRNA-100395 基因通过启动子区甲基化调控miRNA-136-5p/Smad3 轴促进前列腺癌细胞增殖及侵袭的机制研究

目的　检测前列腺癌细胞中环状核糖核酸（circular RNAs, CircRNA）100395 基因启动子区甲基化状态及其表达水平,研究CircRNA-100395 基因去甲基化对前列腺癌细胞增殖、侵袭的影响及作用机制。方法　选择人正常前列腺上皮细胞（RWPE）和前列腺癌细胞系（LNCap,PC3 和DU145）进行研究。采用甲基化特异性聚合酶链式反应(methylationspecific polymerase chain reaction, MSP) 检测CircRNA-100395 基因启动子区甲基化状态。采用实时荧光定量聚合酶链反应(qRT-PCR) 法检测上述细胞中CircRNA-100395 mRNA 表达水平。应用去甲基药物5- 氮杂-2'- 脱氧胞苷（AZA）处理LNCap 细胞,检测AZA 去甲基化处理前后细胞中CircRNA-100395 表达水平。采用CCK-8 和Transwell 实验检测CircRNA-100395 基因去甲基化前后LNCap 细胞增殖和侵袭能力。构建CircRNA-100395 野生型和突变型质粒,通过双荧光素酶报告分析CircRNA-10039 与miRNA-136-5p 之间的靶向关系;利用qRT-PCR 检测CircRNA-10039 与miRNA-136-5p 表达水平,验证其调控关系。采用Westernblot 法检测AZA 去甲基化和miRNA-136-5p 过表达对Smad3,p-Smad3 蛋白表达的影响。结果　前列腺癌细胞中CircRNA-100395 呈高甲基化状态;LNCap,PC3 及DU145 细胞中CircRNA-100395 相对表达水平分别为0.39±0.08,0.65±0.14,0.62±0.10,显著低于RWPE（1.12±0.15）细胞中表达水平,差异有统计学意义（F=42.076,P ＜ 0.001）。经AZA 去甲基化处理后,LNCap 细胞中CircRNA-100395 表达水平为1.02±0.17,较未处理LNCap 细胞（0.42±0.05）明显升高,差异有统计学意义（t=5.808,P ＜ 0.01）。AZA 去甲基化处理显著抑制了LNCap 细胞的增殖能力（t=8.764~12.970,均P ＜ 0.001）、迁移能力（t=6.092,P ＜ 0.01）。miRNA-136-5 可能是CircRNA-100395 的下游靶基因。未经AZA 处理前LNCap 细胞中CircRNA-100395,miRNA-136-5p 表达水平分别为0.39±0.08,0.87±0.15,AZA 处理后两者表达水平分别为1.02±0.17,0.35±0.08,差异有统计学意义（t=5.808,5.298,均P ＜ 0.01）。AZA 处理后Smad3 和p-Smad3 蛋白表达明显升高,差异有统计学意义（t=7.394,11.889,均P ＜ 0.01）;miRNA-136-5p 过表达抑制了Smad3 和p-Smad3 蛋白表达,差异有统计学意义（t=4.996,5.422,均P ＜ 0.01）。结论　CircRNA-100395 基因启动子区的高甲基化状态可以抑制CircRNA-100395 在前列腺癌细胞中的表达水平,去甲基化处理后CircRNA-100395 表达恢复,并抑制前列腺癌细胞增殖和侵袭,其作用机制可能与CircRNA-100395 靶向调控miRNA-136-5p/Smad3 轴有关。     

Adeno-associated virus 2-mediated intratumoral prostate cancer gene therapy: long-term maspin expression efficiently suppresses tumor growth

Maspin is a member of the serine protease inhibitors and the maspin gene, a tumor suppressor gene, is down-regulated in a large fraction of prostate cancers. We evaluated the use of adeno-associated virus (AAV, serotype 2) vector encoding maspin as a means for in vivo gene therapy for human prostate cancer. TUNEL assay of subcutaneously formed LNCaP or DU145 tumors in nude mice showed that intratumoral AAV-mediated maspin expression significantly upregulated the number of apoptotic cells compared with AAV-LacZ treatment. Immunofluorescence double staining for maspin protein and apoptosis in LNCaP tumors showed that the percentage of apoptotic cells in AAV-maspin-mediated maspin-expressing cells was significantly high compared with that in AAV-GFP-mediated GFP-expressing cells. Moreover, significantly fewer CD31-positive microvessels were observed in AAV-maspin-treated tumors compared with the control tumors. These therapeutic responses were highly correlated to persistent maspin expression in tumors, confirmed by Western blot analysis until at least day 56 after treatment. Finally, intratumoral delivery of AAV-maspin significantly suppressed growth of LNCaP and DU145 tumors and improved survival of mice. We conclude that AAV-mediated prolonged maspin expression efficiently suppresses human prostate tumor growth in vivo by apoptosis induction and inhibition of angiogenesis.     

Accumulation of Trans-1-Amino-3-[18F]Fluorocyclobutanecarboxylic Acid in Prostate Cancer due to Androgen-Induced Expression of Amino Acid Transporters

Purpose

Androgens play a crucial role in prostate cancer progression, and trans-1-amino-3-[¹⁸F]fluorocyclobutanecarboxylic acid (anti-[¹⁸?F]FACBC) are used for visualization of prostate cancer. We examined the effect of androgen on the expression of amino acid transporters related to anti-[¹⁸F]FACBC transport and uptake of trans-1-amino-3-fluoro-[1-¹⁴C]cyclobutanecarboxylic acid (anti-[¹⁴C]FACBC).

Procedures

Expression of amino acid transporters and uptake of anti-[¹⁴C]FACBC in androgen receptor (AR)-positive LNCaP and AR-negative DU145 human prostate cancer cells cultured with/without 5α-dihydrotestosterone (DHT) and the effect of bicalutamide, an AR antagonist, on DHT-associated changes were investigated.

Results

DHT stimulated the expression of amino acid transporters ASCT2, SNAT5, 4F2 heavy chain, and LAT3 in LNCaP but not in DU145 cells. Anti-[¹⁴C]FACBC uptake was enhanced, in a DHT-dependent manner, in LNCaP cells only.

Conclusions

DHT enhanced the expression of ASCT2, the transporter responsible for anti-[¹⁸F]FACBC uptake, thereby increasing anti-[¹⁴C]FACBC uptake in AR-positive LNCaP cells. Androgen-mediated induction may contribute to the distinct anti-[¹⁸F]FACBC accumulation pattern in prostate cancer.     

miR-30c对前列腺癌的功能调控作用

目的研究mi R-30c在前列腺癌中的功能调控作用,获得其调控前列腺癌侵袭及转移的可靠证据,进而揭示其在前列腺癌中可能的调控机制。方法从mi RNA芯片检测结果中获得前列腺癌相关的差异表达的mi R-30c分子,进一步通过mi R-30c过表达质粒转染前列腺癌细胞,运用Transwell检测细胞侵袭变化,划痕实验检测细胞转移变化。结果 LNCa P/DU145转染质粒后,mi R-30c的表达水平显著高于阴性对照组(LNCa P:倍数=3.87,P<0.001;Du145:倍数=4.32,P<0.001)。Transwell侵袭实验表明,mi R-30c转染组的LNCa P/DU145细胞侵袭的数量显著低于对照组(LNCa P:67 vs.120个/视野,P<0.001;DU145:130 vs.220个/视野,P<0.001)。划痕实验结果发现mi R-30c转染后,LNCa P/DU145细胞实验组转移的数量显著低于对照组(LNCa P:241 vs.520个/视野,P<0.001;DU145:490 vs.660个/视野,P<0.001)。结论 mi R-30c可抑制前列腺癌细胞的侵袭及转移,这说明mi R-30c在前列腺中确实起着抑癌的作用,其可能通过KRAS-MAPK信号通路抑制前列腺癌的侵袭及转移。     

薄荷醇抑制前列腺癌DU145细胞的增殖和迁移

目的探讨薄荷醇对雄激素非依赖性前列腺癌DU145细胞增殖和迁移能力的影响。方法通过RT-PCR、免疫组织化学和Western blot方法检测TRPM8和TRPA1的表达;MTT和划痕试验检测薄荷醇对DU145细胞的增殖和迁移能力的影响;流式细胞术检测TRPM8对DU145细胞周期和凋亡的影响。结果 RT-PCR、免疫组织化学和Western blot提示TRPM8在DU145细胞中高表达而TRPA1在DU145细胞中不表达;薄荷醇能诱导细胞周期阻滞于G0/G1期,与未经薄荷醇处理的细胞相比,经100μmol/L薄荷醇处理的细胞培养24、48和72h后,G0/G1期细胞显著增加（49.12%±1.92%vs61.71%±2.70%、77.65%±1.63%、71.81%±2.46%,P〈0.05,P〈0.01）,进而抑制细胞增殖（P〈0.05）,并抑制细胞迁移（P〈0.05）,流式细胞术检测显示薄荷醇并不引起细胞凋亡。结论 TRPM8可能成为前列腺癌治疗的一个新靶点,对于高表达TRPM8的雄激素非依赖性前列腺癌针对TRPM8通道的药物治疗可能比TRPM8基因治疗更为实用,因此,薄荷醇作为一个潜在的抗肿瘤药物也拥有很大的发展前景。     

低频低功率超声联合微泡对DU145细胞及PC3细胞早期凋亡的影响

目的比较低频低功率超声联合微泡造影剂对人前列腺癌DU145细胞与PC3细胞早期凋亡率的不同影响。方法使用低频低功率超声连续波辐照人前列腺癌DU145细胞和PC3细胞悬液60 s,实验中两种细胞系各分为4组:空白对照组(A组)、单纯微泡组(B组)、单纯超声组(C组)和超声联合微泡组(D组),辐照后细胞继续培养24 h,流式细胞仪检测细胞早期凋亡情况,透射电镜观察细胞形态改变。结果两种细胞D组的早期细胞凋亡率明显高于其余各组(P﹤0.01),C组亦均高于A组(P﹤0.05),A、B组之间差异无统计学意义;两种细胞经相同处理后,C、D组PC3细胞的早期细胞凋亡率均高于DU145细胞(P﹤0.01)。透射电镜下两种细胞D组可见癌细胞体积变小变圆,空泡增多,有明显的凋亡小体形成,PC3细胞内还可见大量的自噬体出现。结论低频低功率超声联合微泡造影剂能明显诱导人前列腺癌细胞的早期凋亡,且对PC3细胞早期细胞凋亡作用强于DU145细胞。     

Modulation of protein phosphatase 2A activity alters androgen-independent growth of prostate cancer cells: therapeutic implications

Earlier we identified PPP2CA, which encodes for the α-isoform of protein phosphatase 2A (PP2A) catalytic subunit, as one of the downregulated genes in androgen-independent prostate cancer. PP2A is a serine/threonine phosphatase and a potent tumor suppressor involved in broad cellular functions; however, its role in prostate cancer has not yet been determined. Here, we have investigated the effect of PP2A activity modulation on the androgen-independent growth of prostate cancer cells. Our data show that the PPP2CA expression and PP2A activity is downregulated in androgen-independent (C4-2) prostate cancer cells as compared with androgen-dependent (LNCaP) cells. Downregulation of PP2A activity by pharmacologic inhibition or short interfering RNA-mediated PPP2CA silencing sustains the growth of LNCaP cells under an androgen-deprived condition by relieving the androgen deprivation-induced cell-cycle arrest and preventing apoptosis. Immunoblot analyses reveal enhanced phosphorylation of Akt, extracellular signal-regulated kinase (ERK), BAD, increased expression of cyclins (A1/D1), and decreased expression of cyclin inhibitor (p27) on PP2A downregulation. Furthermore, our data show that androgen receptor (AR) signaling is partially maintained in PP2A-inhibited cells through increased AR expression and ligand-independent phosphorylation. Pharmacologic inhibition of Akt, ERK, and AR suggest a role of these signaling pathways in facilitating the androgen-independent growth of LNCaP cells. These observations are supported by the effect of ceramide, a PP2A activator, on androgen-independent C4-2 cells. Ceramide inhibited the growth of C4-2 cells on androgen deprivation, an effect that could be abrogated by PP2A downregulation. Altogether, our findings suggest that modulation of PP2A activity may represent an alternative therapeutic approach for the treatment of advanced androgen-independent prostate cancer.     

Development of a prostate-specific promoter for gene therapy against androgen-independent prostate cancer

Androgen ablation has been the standard treatment for metastasized prostate cancer. In most cases, however, prostate cancer cells eventually lose androgen dependency and become refractory to the conventional endocrine therapy. Androgen-independent prostate cancer is characterized by a heterogeneous loss of androgen receptor (AR) expression among tumor cells. Prostate-specific promoters such as prostate-specific antigen and rat probasin (rPB) promoters have been examined in the development of gene therapy targeted to prostate cancer. However, those promoters require binding of the androgen–AR complex to the androgen-response element and are active only in the androgen-dependent prostate cancer cell lines and not in the androgen-independent cell lines. To target transgene expression in androgen-independent prostate cancer, we designed a prostate-specific promoter that is activated by the retinoids–retinoid receptor complex instead of the androgen–AR complex. The modified rPB promoters expressed transgenes in response to retinoid in both androgen-dependent and androgen-independent prostate cancer cells and not in other cancer cell lines or in human normal cells, in vitro and in vivo. Furthermore, the combination of retinoid treatment and adenovirus-mediated gene transfer of the modified rPB-driven HSV-tk gene resulted in a significant growth suppression of the androgen-independent prostate cancer cells in the presence of the prodrug ganciclovir. This study suggests that tailoring of the hormone-responsive elements may offer a new therapeutic opportunity against the hormone-refractory stage of prostate cancer.     

The radiosensitization effect of parthenolide in prostate cancer cells is mediated by nuclear factor-kappaB inhibition and enhanced by the presence of PTEN

Parthenolide has been shown to have anti-inflammatory and antitumor properties. However, whether and how parthenolide enhances tumor sensitivity to radiation therapy are unknown. In this study, we show that inhibition of the nuclear factor-kappaB (NF-kappaB) pathway is a common mechanism for the radiosensitization effect of parthenolide in prostate cancer cells LNCaP, DU 145, and PC3. Parthenolide inhibits radiation-induced NF-kappaB DNA-binding activity and the expression of its downstream target sod2, the gene coding for an important antiapoptotic and antioxidant enzyme (manganese superoxide dismutase) in the three prostate cancer cells. Different susceptibilities to parthenolide's effect are observed in two radioresistant cancer cells, DU 145 and PC3, with DU 145 cells showing higher sensitivity. This differential susceptibility to parthenolide is due, in part, to the fact that in addition to NF-kappaB inhibition, parthenolide activates the phosphatidylinositol-3-kinase/Akt prosurvival pathway in both cell lines. However, the activated Akt in DU 145 cells is kept at a relatively low level compared with that in PC3 cells due to the presence of functional PTEN. Transfection of wild-type PTEN into PTEN-null cells, PC3, confers the enhanced radiosensitization effect of parthenolide in PTEN-expressing cells. When PTEN expression is knocked down in DU 145 cells, the cells become more resistant to parthenolide's effect. Taken together, these results suggest that parthenolide inhibits the NF-kappaB pathway and activates the phosphatidylinositol-3-kinase/Akt pathway in prostate cancer cells. The radiosensitization effect of parthenolide is due, in part, to the inhibition of the NF-kappaB pathway. The presence of PTEN enhances the radiosensitization effect of parthenolide, in part, by suppressing the absolute amount of activated p-Akt.