Suppresses Prostate Cancer Metastasis Research Articles

The study of a novel CDK8 inhibitor E966-0530–45418 that inhibits prostate cancer metastasis in vitro and in vivo

Prostate cancer is a prevalent malignancy among men globally, and androgen deprivation therapy is the conventional first-line treatment for metastatic prostate cancer. While androgen deprivation therapy is efficacious in castration-sensitive prostate cancer, it remains less effective in castration-resistant cases. Transcriptional dysregulation is a well-established hallmark of cancer, and targeting proteins involved in transcriptional regulation, such as cyclin-dependent kinase 8 (CDK8), has become an attractive therapeutic strategy. CDK8, a nuclear serine-threonine kinase, is a key component of the mediator complex and plays a critical role in transcriptional regulation. Recent studies have highlighted the promising role of CDK8 as a target in the treatment of metastatic prostate cancer. Our study assessed the efficacy of a novel CDK8 inhibitor, E966–0530–45418, which exhibited potent CDK8 inhibition (IC50 of 129 nM) and high CDK8 selectivity. Treatment with E966–0530–45418 significantly inhibited prostate cancer cell migration and epithelial-to-mesenchymal transition (EMT) at both the RNA and protein levels. Further mechanistic analysis indicated that E966–0530–45418 suppresses prostate cancer metastasis by decreasing CDK8 activity and inhibiting TGF-β1-mediated Smad3/RNA polymerase II linker phosphorylation and Akt/GSK3β/β-catenin signaling. The results in animal model also showed that E966–0530–45418 exhibited anti-metastatic properties in vivo. Our study demonstrated that E966–0530–45418 has great therapeutic potential in the treatment of metastatic prostate cancer.

CircPHF16 suppresses prostate cancer metastasis via modulating miR-581/RNF128/Wnt/β-catenin pathway

Circular RNAs (circRNAs) have been recognized as important regulators in tumorigenesis. However, the specific role of circRNAs in prostate cancer is still largely unknown. Here, we identified that circPHF16 was downregulated in prostate cancer (PCa) tissues compared with normal tissues. Functionally, circPHF16 restrained prostate cancer metastasis both in vivo and in vitro. Mechanistically, circPHF16 directly interacted with miR-581, leading to the downregulation of ring finger protein 128 (RNF128) and inhibiting the metastatic ability of PCa. Furthermore, circPHF16-dependent upregulation of RNF128 inactivated Wnt/β-catenin signaling. In total, our findings revealed that circPHF16 suppressed prostate cancer metastasis through the circPHF16/miR-581/Wnt/β-catenin pathways.

Abstract 5836: SMC4 promotes prostate cancer organ-specific metastasis by modifying cancer cell metabolism

Abstract Structural maintenance of chromosomes 4 (SMC4), one subunit of condensin complexes, is a key structural component of mitotic chromosomes. Accumulating evidence has suggested that SMC4 regulates prostate carcinogenesis. However, its roles on regulation of prostate cancer development remain unclear. Our previous studies showed that the expression of SMC4 is increased in highly lung-metastatic prostate cancer cells, RM1-LM, an organ-specific metastasis cell line that we developed. To investigate the function of SMC4, SMC4 gene was knockdown in RM1-LM cells by CRISPR/Cas9 system. Knockdown of SMC4 significantly diminished the cancer cell growth in RM1-LM. In addition, transwell assay results showed that SMC4 knockdown in RM1-LM suppressed the cell migration and invasion. Furthermore, we observed that SMC4 protein is important in the non-dividing phase of the cell cycle. In particular, cell cycle flow cytometry analysis indicated that SMC4 knockdown leaded to cell arrest in S phase. Finally, RM1-LM cells showed increased lung metastases compared with RM1-SMC4+/- cells in a murine model. The H&E and IHC results confirmed that RM1-LM cells induced greater number of lung metastases and colonization than RM1-SMC4+/-cells, suggesting the loss of SMC4 suppressed prostate cancer metastasis. The interactome of SMC4 was uncovered through IP-MS and revealed that SMC4 may interacted with GLUT1, a key protein in glycolysis pathway. The ATP rate assay and Glycolysis rate assay illustrated a significantly metabolic switch existing in RM1-SMC4+/-cells compared with their parental cells. Collectively, our study suggested that the interaction between SMC4 and GLUT1, confirmed by Co-IP, promotes prostate cancer cells metastasis via modifying the cell metabolism. This work was supported by NSFC projects 81802949, 81773146, 81972766, 81972420, 82173336; Shenzhen Science and Technology Commission Project JCYJ20190809161811237, JCYJ2021032410424040; Guangdong Provincial Key Laboratory of Cell Microenvironment and Disease Research (2017B030301018);and College students' innovative entrepreneurial training program (S202114325028) Citation Format: Wei Zhang, Xin Huang, yueming Li, yingxuan Gong, xiuzhi Li. SMC4 promotes prostate cancer organ-specific metastasis by modifying cancer cell metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5836.

KMT2C methyltransferase domain regulated INK4A expression suppresses prostate cancer metastasis

BackgroundFrequent truncation mutations of the histone lysine N-methyltransferase KMT2C have been detected by whole exome sequencing studies in various cancers, including malignancies of the prostate. However, the biological consequences of these alterations in prostate cancer have not yet been elucidated.MethodsTo investigate the functional effects of these mutations, we deleted the C-terminal catalytic core motif of Kmt2c specifically in mouse prostate epithelium. We analysed the effect of Kmt2c SET domain deletion in a Pten-deficient PCa mouse model in vivo and of truncation mutations of KMT2C in a large number of prostate cancer patients.ResultsWe show here for the first time that impaired KMT2C methyltransferase activity drives proliferation and PIN formation and, when combined with loss of the tumour suppressor PTEN, triggers loss of senescence, metastatic dissemination and dramatically reduces life expectancy. In Kmt2c-mutated tumours we show enrichment of proliferative MYC gene signatures and loss of expression of the cell cycle repressor p16INK4A. In addition, we observe a striking reduction in disease-free survival of patients with KMT2C-mutated prostate cancer.ConclusionsWe identified truncating events of KMT2C as drivers of proliferation and PIN formation. Loss of PTEN and KMT2C in prostate cancer results in loss of senescence, metastatic dissemination and reduced life expectancy. Our data demonstrate the prognostic significance of KMT2C mutation status in prostate cancer patients. Inhibition of the MYC signalling axis may be a viable treatment option for patients with KMT2C truncations and therefore poor prognosis.

HOXD13 suppresses prostate cancer metastasis and BMP4-induced epithelial-mesenchymal transition by inhibiting SMAD1.

The HOX genes are a group of highly conserved Homeobox-containing genes that control the body plan organization during development. However, their contributions to tumorigenesis and tumor progression remain uncertain and controversial. Here we provided evidence of tumor-suppressive activity of HOXD13 in prostate cancer. HOXD13 depletion contributes to more aggressiveness of prostate cancer cells in vitro and in vivo. These effects were corroborated in a metastatic mice model, where we observed more bone metastatic lesions formed by prostate cancer cells with HOXD13 ablation. Mechanistically, HOXD13 prevents BMP4-induced epithelial-mesenchymal transition (EMT) by inhibiting mothers against decapentaplegic homolog 1 (SMAD1) transcription. Both bioinformation and our tissue microarray cohort data show that HOXD13 expression inversely correlated in advanced prostate cancer patient specimens. Our findings establish HOXD13 as a negative regulator of prostate cancer progression and metastasis by preventing BMP4/SMAD1 signaling, and potentially suggest new strategies for targeting metastatic prostate cancer.

Stromal CAVIN1 Controls Prostate Cancer Microenvironment and Metastasis by Modulating Lipid Distribution and Inflammatory Signaling.

Lipid uptake occurs through caveolae, plasma membrane invaginations formed by caveolins (CAV) and caveolae-associated protein 1 (CAVIN1). Genetic alterations of CAV1N1 and CAV1 modify lipid metabolism and underpin lipodystrophy syndromes. Lipids contribute to tumorigenesis by providing fuel to cancer metabolism and supporting growth and signaling. Tumor stroma promotes tumor proliferation, invasion, and metastasis, but how stromal lipids influence these processes remain to be defined. Here, we show that stromal CAVIN1 regulates lipid abundance in the prostate cancer microenvironment and suppresses metastasis. We show that depletion of CAVIN1 in prostate stromal cells markedly reduces their lipid droplet accumulation and increases inflammation. Stromal cells lacking CAVIN1 enhance prostate cancer cell migration and invasion. Remarkably, they increase lipid uptake and M2 inflammatory macrophage infiltration in the primary tumors and metastasis to distant sites. Our data support the concept that stromal cells contribute to prostate cancer aggressiveness by modulating lipid content and inflammation in the tumor microenvironment. IMPLICATIONS: This study showed that stromal CAVIN1 suppresses prostate cancer metastasis by modulating tumor microenvironment, lipid content, and inflammatory response.

WFDC2 suppresses prostate cancer metastasis by modulating EGFR signaling inactivation

WAP four-disulfide core domain 2 (WFDC2) is a small secretory protein that has been widely studied in ovarian cancer. It has been proven that WFDC2 promotes proliferation and metastasis in ovarian cancer, and serves as a diagnostic biomarker. However, the specific function of WFDC2 in prostate cancer has not been reported. Here, we first screened the diagnostic marker and favorable prognostic factor WFDC2 in prostate cancer by bioinformatics. WFDC2 expression was negatively correlated with Gleason score and metastasis in prostate cancer. Then, we revealed that overexpression of WFDC2, and addition of recombinant protein HE4 can significantly inhibit prostate cancer metastasis in vivo and in vitro. By co-immunoprecipitation and co-localization assays, we proved that WFDC2 binds to the extracellular domain of epidermal growth factor receptor (EGFR). Immunoblot showed that WFDC2 overexpression and recombinant protein HE4 addition inactivated the EGFR/AKT/GSK3B/Snail signaling pathway, and then restrained the progression of epithelial–mesenchymal transition. In conclusion, our study identified that the tumor suppressor WFDC2 can suppress prostate cancer metastasis by inactivating EGFR signaling.

ROR2 suppresses metastasis of prostate cancer via regulation of miR-199a-5p\u2013PIAS3\u2013AKT2 signaling axis

Bones are the most common metastatic sites for prostate cancer (PCa). Receptor tyrosine kinase-like orphan receptor 2 (ROR2), a noncanonical Wnt receptor, plays crucial roles in skeletal morphogenesis, osteoblast differentiation, and bone formation. The role of ROR2 in PCa metastasis is unclear. We analyzed online datasets from Oncomine as well as using IHC staining on tissue array to determine the relationship between ROR2 expression level and disease outcome of PCa. To investigate how ROR2 regulates migration and invasion of PCa cells, we performed transwell assay and orthotopic xenograft model in nude mice. We then applied the Micro-Western Array (MWA), a high-throughput western blotting platform to analyze the downstream signaling pathways being regulated by ROR2. Compared with nonmalignant PZ-HPV-7 and RWPE-1 cells, PCa cell lines express lower level of ROR2 protein. Constitutive expression of ROR2 in PC-3, DU-145, or C4-2B PCa cells significantly suppressed the cell migration, invasion, and epithelial–mesenchymal transition (EMT) proteins. MWA, western blotting, and microRNA analysis showed that elevation of ROR2 suppressed the expression of miR-199a-5p, which in turn increased the expression of PIAS3. The upregulation of PIAS3 then decreased AKT2 and the phosphorylation of AKT, resulting in the inhibition of migration and invasion of PCa cells both in vitro and in orthotopic xenograft mice model. IHC staining of tissue array and Oncomine datasets analysis indicated that the gene and protein level of ROR2 is much lower in metastatic prostate tumors as compared with primary tumors or adjacent normal prostate tissues. Low level of ROR2 correlated to poor survival and high recurrent frequency in PCa patients. In conclusion, we discovered that ROR2 suppresses PCa metastasis via regulation of PIAS3–PI3K–AKT2 signaling axis.

Crosstalk Between Prostate Cancer Cells and Tumor-Associated Fibroblasts Enhances the Malignancy by Inhibiting the Tumor Suppressor PLZF.

Although prostate cancer is clinically manageable during the early stages of progression, metastatic progression severely compromises the prognosis and leads to mortality. Constitutive activation of STAT3 has been connected to prostate cancer malignancy, and abolishing the STAT3 activity may diminish tumor growth and metastasis. However, its suppressor genes and pathways have not been well established. In this study, we show that promyelocytic leukemia zinc finger (PLZF) has a putative tumor-suppressor function in prostate cancer by inhibiting phosphorylation of STAT3. Compared with a benign prostate, high-grade prostate cancer patient tissue was negatively correlated with PLZF expression. PLZF depletion accelerated proliferation and survival, migration, and invasion in human prostate cancer cells. Mechanistically, we demonstrated a novel role of PLZF as the transcriptional regulator of the tyrosine phosphatase SHP-1 that inhibits the oncogenic JAKs–STAT3 pathway. These results suggest that the collapse of PLZF expression by the CCL3 derived from fibroblasts accelerates the cell migration and invasion properties of prostate cancer cells. Our results suggest that increasing PLZF could be an attractive strategy for suppressing prostate cancer metastasis as well as for tumor growth.

Androgen receptor suppresses prostate cancer metastasis but promotes bladder cancer metastasis via differentially altering miRNA525-5p/SLPI-mediated vasculogenic mimicry formation.

Early studies suggest that the androgen receptor (AR) may play differential roles in influencing prostate cancer (PCa) and bladder cancer (BCa) metastasis, but the underlying mechanisms remain unclear. Here, we found that the AR might function via differentially altering vasculogenic mimicry (VM) formation to either decrease PCa metastasis or increase BCa metastasis. Mechanism dissection showed that the AR could differentially alter the expression of the VM marker SLPI through miR-525-5p to regulate SLPI; moreover, it could either increase miR-525-5p transcription in PCa or decrease it in BCa via binding to different androgen-response-elements (AREs) located at different positions in the miR-525 precursor promoter. Further, results from liquid chromatography-mass spectrometry (LC-MS) showed that the co-factors of AR in PCa and BCa are NFIX and HDAC2, respectively. Together, these results provide the first detailed mechanism of how the AR can differentially alter PCa and BCa metastasis; thus, targeting the newly identified AR-miR-525-5p-SLPI axis may help suppress metastasis.

P34 - Androgen receptor (AR) suppresses prostate cancer metastasis yet promotes bladder cancer metastasis via differential altering the miRNA525-5p/SLPI-mediated vasculogenic mimicry (VM) formation

P34 - Androgen receptor (AR) suppresses prostate cancer metastasis yet promotes bladder cancer metastasis via differential altering the miRNA525-5p/SLPI-mediated vasculogenic mimicry (VM) formation

Abstract 5084: Epigenetic modifications involving reactivation of RECK inhibiting MMP-9 and MMP-2 in prostate cancer

Abstract Metastasis is responsible for more than 90% of prostate cancer-associated mortality in the United States. One of the distinctive reason for metastasis has been the imbalance of matrix metalloproteinases (MMPs) as a result of reduced expression of RECK (reversion-inducing-cysteine-rich protein with Kazal motifs) a novel tumor suppressor. RECK has been shown to be a potent inhibitor of MMP-2 and MMP-9. Loss of RECK has been frequently identified in clinical prostate cancer specimens and prostate cancer cell lines, therefore mechanistic understanding of its loss and approaches to restore its expression would facilitate inhibition of metastasis. Green tea polyphenols (GTP) and its major constituent, epigallocatechin-3-gallate (EGCG) has been shown to suppress prostate cancer metastasis, however the mechanism has not been fully elucidated. We determined whether treatment with GTP has ability to restore induction of RECK and play a key role in suppressing invasiveness in prostate cancer. Human prostate cancer LNCaP tumor were implanted in the ventral prostate of athymic nude mice for 2 weeks followed by per-oral intake of GTP at 7.5 and 15.0 mg/kg body weight freshly prepared in 100µl PBS. Other groups were treated with DNA methyltransferase inhibitor-5-aza-2'-deoxycytidine (AZA), histone deacetylase inhibitor-trichostatin A (TSA) and histone methyltransferase inhibitor-3-Deazaneplanocin A (DZNep) individually at 0.1 mg/kg body weight intraperitoneally at alternate days/week; and combination of AZA+TSA and DZNep+TSA at similar doses and times. Treatment of mice with GTP resulted in marked decrease in tumor growth and its local invasion in dose dependent manner, compared to treatment with epigenetic inhibitors and their combination after 8 weeks of intervention. GTP treatment significantly reduced serum levels of MMP-2, MMP-9 and VEGF, compared to treatment with epigenetic inhibitors alone. Combination of AZA+TSA exhibited similar effect which was equivalent to the lower dose of GTP treatment. Furthermore, GTP treatment significantly reduced EZH2 and H3K27me3 and class I HDAC protein levels in tumors. GTP partially reversed RECK hypermethylation and significantly enhanced its expression in the tumor tissue. Similar findings were noted in cell culture where treatment of PC-3 and LNCaP cells with 20µM EGCG and 10µg/mL GTP for 72 h significantly induced RECK expression at mRNA and protein levels along with decrease invasiveness in these cells. Our findings suggest that induction of RECK is a key epigenetic event reactivated by GTP/EGCG that results in suppression of MMP-2/MMP-9, matrix degradation and angiogenesis to delay prostate cancer invasion and its subsequent progression. Citation Format: Eswar Shankar, Omair Iqbal, Natarajan Bhaskaran, Gauri Deb, Gregory T. MacLennan, Pingfu Fu, Sanjay Gupta. Epigenetic modifications involving reactivation of RECK inhibiting MMP-9 and MMP-2 in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5084.

MiR-451 suppresses the growth, migration, and invasion of prostate cancer cells by targeting macrophage migration inhibitory factor

Background: Metastasis is the most common cause of death of prostate cancer patients. Identification of key regulators in prostate cancer metastasis is essential for improved management of the disease. Accumulation of evidence suggests that miRNAs play important roles in cancer metastasis. Here, we investigated the role of miR-451 in prostate cancer progression and metastasis. Methods: In this study, we performed reverse transcription-quantitative PCR analysis to examine the expression of miR-451 in clinical prostate cancer samples and cell lines. TargetScan Release 7.0 programs, luciferase reporter assay, and a rescue experiment were used to validate the direct target of miR-451. The protein expression of the miR-451 target was detected by Western blot. MTS cell viability assay, transwell migration assay, and modified Boyden chamber invasion assay were used to demonstrate the effects of increased miR-451 expression on prostate cancer cell growth, migration and invasiveness. Results: We identified the decreased expression of miR-451 in clinical metastatic prostate cancer compared to localized primary prostate cancer and benign prostate. Consistently, we also observed the decreased expression of miR-451 in highly metastatic prostate cancer cell lines (C4-2 and PC3M) compared to their low metastatic counterparts (LNCaP and PC3). Furthermore, we confirmed the macrophage migration inhibitory factor (MIF) is a direct target of miR-451 in prostate cancer and demonstrated a negative correlation between miR-451 and MIF expression in clinical prostate cancer samples. Functional studies showed increased miR-451 expression significantly suppressed cell growth, migration and invasiveness via targeting MIF. The effect of increased miR-451 expression can be reversed by overexpressing MIF in prostate cancer cells. Conclusions: These findings suggest that miR-451 suppresses prostate cancer cell growth, migration and metastasis, which provides insight into the development of novel therapeutic approaches for prostate cancer treatment.

MiR-582-3p and miR-582-5p Suppress Prostate Cancer Metastasis to Bone by Repressing TGF-β Signaling

A number of studies have reported that aberrant expression of microRNAs (miRNAs) closely correlates with the bone metastasis of prostate cancer (PCa). However, clinical significance and functional roles of both strands of a single miRNA in bone metastasis of PCa remain undefined. Here, we reported that miR-582-3p and miR-582-5p expression were simultaneously reduced in bone metastatic PCa tissues compared with non-bone metastatic PCa tissues. Downexpression of miR-582-3p and miR-582-5p strongly and positively correlated with advanced clinicopathological characteristics and shorter bone metastasis-free survival in PCa patients. Upregulating miR-582-3p and miR-582-5p inhibited invasion and migration abilities of PCa cells in vitro, as well as repressed bone metastasis in vivo. Our results further revealed that miR-582-3p and miR-582-5p attenuated bone metastasis of PCa via inhibiting transforming growth factor β (TGF-β) signaling by simultaneously targeting several components of TGF-β signaling, including SMAD2, SMAD4, TGF-β receptor I (TGFBRI), and TGFBRII. Moreover, deletion contributes to miR-582-3p and miR-582-5p downexpression in PCa tissues. Finally, clinical negative correlations of miR-582-3p and miR-582-5p with SMAD2, SMAD4, TGFBRI, and TGFBRII were demonstrated in PCa tissues. Thus, our findings explore a novel tumor-suppressive miRNA with its both strands implicated in bone metastasis of PCa, suggesting its potential therapeutic value in treatment of PCa bone metastasis.

Aberrant expression of CITED2 promotes prostate cancer metastasis by activating the nucleolin-AKT pathway

Despite many efforts to develop hormone therapy and chemotherapy, no effective strategy to suppress prostate cancer metastasis has been established because the metastasis is not well understood. We here investigate a role of CBP/p300-interacting transactivator with E/D-rich carboxy-terminal domain-2 (CITED2) in prostate cancer metastasis. CITED2 is highly expressed in metastatic prostate cancer, and its expression is correlated with poor survival. The CITED2 gene is highly activated by ETS-related gene that is overexpressed due to chromosomal translocation. CITED2 acts as a molecular chaperone to guide PRMT5 and p300 to nucleolin, thereby activating nucleolin. Informatics and experimental data suggest that the CITED2–nucleolin axis is involved in prostate cancer metastasis. This axis stimulates cell migration through the epithelial–mesenchymal transition and promotes cancer metastasis in a xenograft mouse model. Our results suggest that CITED2 plays a metastasis-promoting role in prostate cancer and thus could be a target for preventing prostate cancer metastasis.

Reduced Arginyltransferase 1 is a driver and a potential prognostic indicator of prostate cancer metastasis.

Most prostate cancer cases remain indolent for long periods of time, but metastatic progression quickly worsens the prognosis and leads to mortality. However, little is known about what promotes the metastasis of prostate cancer and there is a lack of effective prognostic indicators, making it immensely difficult to manage options for treatment or surveillance. Arginyltransferase 1 (Ate1) is the enzyme mediating post-translational protein arginylation, which has recently been identified as a master regulator affecting many cancer-relevant pathways including stress response, cell cycle checkpoints, and cell migration/adhesion. However, the precise role of Ate1 in cancer remains unknown. In this study, we found the occurrence of metastasis of prostate cancer is inversely correlated with the levels of Ate1 protein and mRNA in the primary tumor. We also found that metastatic prostate cancer cell lines have a reduced level of Ate1 protein compared to non-metastatic cell lines, and that a depletion of Ate1 drives prostate cancer cells towards more aggressive pro-metastatic phenotypes without affecting proliferation rates. Furthermore, we demonstrated that a reduction of Ate1 can result from chronic stress, and that shRNA-reduced Ate1 increases cellular resistance to stress, and drives spontaneous and stress-induced genomic mutations. Finally, by using a prostate orthotropic xenograft mouse model, we found that a reduction of Ate1 was sufficient to enhance the metastatic phenotypes of prostate cancer cell line PC-3 in vivo. Our study revealed a novel role of Ate1 in suppressing prostate cancer metastasis, which has a profound significance for establishing metastatic indicators for prostate cancer, and for finding potential treatments to prevent its metastasis.

Cholesterol Esterification Inhibition Suppresses Prostate Cancer Metastasis by Impairing the Wnt/β-catenin Pathway.

Dysregulation of cholesterol is a common characteristic of human cancers including prostate cancer. This study observed an aberrant accumulation of cholesteryl ester in metastatic lesions using Raman spectroscopic analysis of lipid droplets in human prostate cancer patient tissues. Inhibition of cholesterol esterification in prostate cancer cells significantly suppresses the development and growth of metastatic cancer lesions in both orthotopic and intracardiac injection mouse models. Gene expression profiling reveals that cholesteryl ester depletion suppresses the metastatic potential through upregulation of multiple regulators that negatively impact metastasis. In addition, Wnt/β-catenin, a vital pathway for metastasis, is downregulated upon cholesteryl ester depletion. Mechanistically, inhibition of cholesterol esterification significantly blocks secretion of Wnt3a through reduction of monounsaturated fatty acid levels, which limits Wnt3a acylation. These results collectively validate cholesterol esterification as a novel metabolic target for treating metastatic prostate cancer. Mol Cancer Res; 16(6); 974-85. ©2018 AACR.

Aphthous ulcer drug inhibits prostate tumor metastasis by targeting IKKɛ/TBK1/NF-κB signaling.

Tumor metastasis is the major cause of death for prostate cancer (PCa) patients. However, the treatment options for metastatic PCa are very limited. Epithelial-mesenchymal transition (EMT) has been reported to be an indispensable step for tumor metastasis and is suggested to associate with acquisition of cancer stem cell (CSC) attributes. We propose that small-molecule compounds that can reverse EMT or induce mesenchymal-epithelial transition (MET) of PCa cells may serve as drug candidates for anti-metastasis therapy.Methods: The promoters of CDH1 and VIM genes were sub-cloned to drive the expression of firefly and renilla luciferase reporter in a lentiviral vector. Mesenchymal-like PCa cells were infected with the luciferase reporter lentivirus and subjected to drug screening from a 1274 approved small-molecule drug library for the identification of agents to reverse EMT. The dosage-dependent effect of candidate compounds was confirmed by luciferase reporter assay and immunoblotting. Wound-healing assay, sphere formation, transwell migration assay, and in vivo intracardiac and orthotopic tumor xenograft experiments were used to evaluate the mobility, metastasis and tumor initiating capacity of PCa cells upon treatment. Possible downstream signaling pathways affected by the candidate compound treatment were analyzed by RNA sequencing and immunoblotting.Results: Drug screening identified Amlexanox, a drug used for recurrent aphthous ulcers, as a strong agent to reverse EMT. Amlexanox induced significant suppression of cell mobility, invasion, serial sphere formation and in vivo metastasis and tumor initiating capacity of PCa cells. Amlexanox treatment led to downregulation of the IKK-ɛ/ TBK1/ NF-κB signaling pathway. The effect of Amlexanox on EMT reversion and cell mobility inhibition can be mimicked by other IKK-ɛ/TBK1 inhibitors and rescued by reconstitution of dominant active NF-κB.Conclusions: Amlexanox can sufficiently suppress PCa metastasis by reversing EMT through downregulating the IKK-ɛ/TBK1/NF-κB signaling axis.

SEC-induced activation of ANXA7 GTPase suppresses prostate cancer metastasis

Annexin A7 (ANXA7) is a suppressor of tumorigenesis and metastasis in prostate cancer. Activated ANXA7 GTPase promotes prostate cancer cell apoptosis. However, the role and underlying mechanism of ANXA7 GTPase in prostate cancer metastasis have not been established. RKIP is a metastatic suppressor and downregulated in prostate cancer metastases. The binding of RKIP and its target proteins could inhibit the activation of its interactive partners. However, the effect of RKIP on ANXA7 GTPase activation is not clear. Here, we report that activation of ANXA7 GTPase by a small molecule SEC ((S)-ethyl 1-(3-(4-chlorophenoxy)-2-hydroxypropyl)-3- (4-methoxyphenyl)-1H-pyrazole-5-carboxylate) effectively inhibited prostate cancer metastasis. Mechanistically, activated ANXA7 promoted AMPK phosphorylation, leading to decreased mTORC1 activity, suppressed STAT3 nuclear translocation, and downregulation of pro-metastatic genes, including CCL2, APLN, and IL6ST. Conversely, RKIP interacted with ANXA7 and impaired activation of ANXA7 GTPase by SEC and its downstream signaling pathway. Notably, SEC treatment suppressed metastasis of prostate cancer cells in in vivo orthotopic analysis. Together, our findings provide a novel insight into how metastasis of prostate cancer with low RKIP expression is suppressed by SEC-induced activation of ANXA7 GTPase via the AMPK/mTORC1/STAT3 signaling pathway.

Abstract 2170: Rb1 suppresses prostate cancer metastasis and lineage plasticity underlying castration resistance

Abstract Androgen deprivation therapy (ADT) is an effective treatment for metastatic prostate cancer (mPCa), but patients eventually relapse with ADT resistant disease. Well-characterized mechanisms of ADT resistance include AR amplification, intra-tumoral androgen synthesis, AR splice variants, and growth receptor bypass. All of these mechanisms function to maintain sufficient AR signaling for tumor growth and survival. Improved ADT like abiraterone acetate (AA) and enzalutamide (Enza) were developed to combat such resistance mechanisms associated with alterations in androgen receptor or androgen metabolism. While AA and Enza extend survival, clinical benefits are short-lived. A new form of resistance is increasingly appreciated in patients relapsing from AA or Enza, histologic transformation of prostate adenocarcinoma (PADC) to neuroendocrine prostate cancer (NEPC) variants. NEPC is lethal and the survival time is less than a year as effective targeted therapy is unavailable. NEPC typically exhibits reduced AR expression, increased expression of neuroendocrine markers, and visceral metastasis in the absence of rising PSA. Of note, NEPC possesses the similar genome rearrangements with adjacent PADC cells, indicating they share clonal origin. Thus, NEPC may arise by histologic transformation of PADC. Underlying mechanisms of histologic transformation are not understood and experimental models are limited, hindering development of effective remedies. RB1 loss is common in NEPC, but rare in PADC; genetic profiling shows human NEPC exhibit elevated levels of several epigenetic modifiers. We hypothesize that transdifferentiation from PADC to NEPC in the context of RB1 loss is due to epigenetic alterations and can be reversed or blocked by epigenetic targeted therapies. We established several genetically engineered mouse models (GEMMs) to test the role of Rb1, and we find Rb1 loss causes metastatic progression of PADC initiated by Pten deficiency. This Rb1/Pten deficient (DKO) PADC exhibits expression markers for both PADC and NEPC as seen in human patients. Yet, these tumors are sensitive to ADT but relapse with low AR expression and acquired Trp53 mutations. RNA profiling demonstrates the phenotype of DKO tumors is similar to human NEPC. Both human and mouse NEPC is accompanied by increased expression of epigenetic reprogramming factors like Sox2 and Ezh2. Clinically relevant Ezh2 inhibitors GSK126 and EPZ6438 can restore Enza sensitivity by reversing neuroendocrine transformation. This finding has been genetically validated using short-hairpin RNA(shRNA) in vitro. These results uncover genetic mutations driving prostate cancer lineage plasticity and suggest an epigenetic approach for extending the clinical benefits of ADT. Citation Format: Sheng-Yu Ku, Spencer Rosario, Yanqing Wang, Ping Mu, Mukund Seshadri, Zachary Goodrich, Maxwell Goodrich, David P. Labbé, Eduardo Cortez Gomez, Jianmin Wang, Henry W. Long, Bo Xu, Myles Brown, Massimo Loda, Charles L. Sawyers, Leigh Ellis, David G. Goodrich. Rb1 suppresses prostate cancer metastasis and lineage plasticity underlying castration resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2170. doi:10.1158/1538-7445.AM2017-2170