miR-143 and miR-145 inhibit stem cell characteristics of PC-3 prostate cancer cells

Emerging evidence demonstrates that cancer stem cells (CSCs) are the critical drivers of tumor progression and metastasis. The microRNAs (miRNAs) may play a crucial role in repressing/promoting metastasis of cancer by regulating CSCs. A previous study showed that miR-143 and miR-145 play an important role in regulating bone metastasis of prostate cancer (PCa), but the exact mechanism of regulation of bone metastasis of PCa is not fully understood. In this study, we found that overexpression of miR-143 and miR-145 inhibited the cell viability and colony formation of PC-3 cells from PCa bone metastasis. Furthermore, miR-143 and miR-145 suppressed tumor sphere formation and expression of CSC markers and 'stemness' factors including CD133, CD44, Oct4, c-Myc and Klf4 in PC-3 cells. The study further found that miR-143 and miR-145 inhibit bone invasion and tumorigenicity of PC-3 cells in vivo. Collectively, these findings demonstrate that miR-143 and miR-145 inhibit CSC properties of PC-3 cells and suggest that miR-143 and miR-145 may play a significant role in the bone metastasis progression of PCa by regulating CSC characteristics.     

Gamma‐tocotrienol as an effective agent in targeting prostate cancer stem cell‐like population

Emerging evidence supports that prostate cancer originates from a rare subpopulation of cells, namely prostate cancer stem cells (CSCs). Conventional therapies for prostate cancer are believed to mainly target the majority of differentiated tumor cells but spare CSCs, which may account for the subsequent disease relapse after treatment. Therefore, successful elimination of CSCs may be an effective strategy to achieve complete remission from this disease. Gamma‐tocotrienols (γ‐T3) is one of the vitamin‐E constituents, which have been shown to have anticancer effects against a wide range of human cancers. Recently, we have reported that γ‐T3 treatment not only inhibits prostate cancer cell invasion but also sensitizes the cells to docetaxel‐induced apoptosis, suggesting that γ‐T3 may be an effective therapeutic agent against advanced stage prostate cancer. Here, we demonstrate for the first time that γ‐T3 can downregulate the expression of prostate CSC markers (CD133/CD44) in androgen‐independent prostate cancer cell lines (PC‐3 and DU145), as evident from Western blotting analysis. Meanwhile, the spheroid formation ability of the prostate cancer cells was significantly hampered by γ‐T3 treatment. In addition, pretreatment of PC‐3 cells with γ‐T3 was found to suppress tumor initiation ability of the cells. More importantly, although CD133‐enriched PC‐3 cells were highly resistant to docetaxel treatment, these cells were as sensitive to γ‐T3 treatment as the CD133‐depleted population. Our data suggest that γ‐T3 may be an effective agent in targeting prostate CSCs, which may account for its anticancer and chemosensitizing effects reported in previous studies.     

Differential effect of grape seed extract and its active constituent procyanidin B2 3,3″‐di‐O‐gallate against prostate cancer stem cells

The present study aimed to determine whether grape seed extract (GSE) procyanidin mix, and its active constituent procyanidin B2 3,3″‐di‐O‐gallate (B2G2) have the potential to target cancer stem cells (CSCs) in prostate cancer (PCa). The CSC populations were isolated and purified based on CD44⁺‐α2β1^high surface markers in PCa cell lines LNCaP, C4‐2B, 22Rv1, PC3, and DU145, and then subjected to prostasphere formation assays in the absence or presence of GSE or B2G2. Results indicated that at lower doses (<15 μg) , the GSE procyanidin mix produced activity in unsorted prostate cancer antigen (PCA) cells, but not in sorted; however, multiple treatments with low dose GSE over a course of time inhibited sphere formation by sorted PCA CSCs. Importantly, B2G2 demonstrated significant potential to target both unsorted and sorted CSCs at lower doses. As formation of spheroids, under specific in vitro conditions, is a measure of stemness, these results indicated the potential of both GSE and B2G2 to target the self‐renewal of CSC in PCa cell lines, though B2G2 was more potent in its efficacy. Subsequent mechanistic studies revealed that both GSE procyanidins and B2G2 strongly decreased the constitutive as well as Jagged1 (Notch1 ligand)‐induced activated Notch1 pathway. In totality, these in vitro studies warrant extensive dose‐profiling‐based assessments in vivo settings to conclusively determine the impact on CSC pool kinetics on the efficacy of both GSE and B2G2 to target PCa growth as well as tumor relapse.     

Co-Expression of Putative Cancer Stem Cell Markers CD44 and CD133 in Prostate Carcinomas

Cancer stem cells (CSCs) are the main players of prostate tumorigenesis thus; characterization of CSCs can pave the way for understanding the early detection, drug resistance, metastasis and relapse. The current study was conducted to evaluate the expression level and clinical significance of the potential CSC markers CD44 and CD133 in a series of prostate tissues. One hundred and forty eight prostate tissues composed of prostate cancer (PCa), high-grade prostatic intraepithelial neoplasia (HGPIN), and benign prostate hyperplasia (BPH) were immunostained for the putative CSC markers CD44 and CD133. Subsequently, the correlation between the expression of these markers and the clinicopathological variables was examined. A higher level of CD44 expression was observed in 42% of PCa, 57% of HGPIN, and 42% BPH tissues. In the case of CD133 expression PCa, HGPIN, and BPH samples demonstrated high immunoreactivity in 46%, 43%, and 42% of cells, respectively. Statistical analysis showed an inverse significant correlation between CD44 expression with Gleason score of PCa (P = 0.02), while no significant correlation was observed between CD133 expression and clinicopathological parameters. A significant reciprocal correlation was observed between the expression of two putative CSC markers CD44 and CD133 in PCa specimens while not indicating clinical significance. Further clinical investigation is required to consider these markers as targets of new therapeutic strategies for PCa     

BRCA1 and EZH2 cooperate in regulation of prostate cancer stem cell phenotype

Prostate cancer (PCa) is the second most common malignancy and the sixth leading cause of cancer-related death among men worldwide. Prostate carcinogenesis is driven by the accumulation of genetic and epigenetic aberrations, which regulate cancer cell transition between a stem- and nonstem-cell state and accelerate tumor evolution. Elevated expression of enhancer of zeste homolog 2 (EZH2) histone methyltransferase, a core member of the polycomb repressive complex 2 (PRC2), results in cancer progression through histone methylation-driven tumor cells dedifferentiation. Previous studies demonstrated that tumor suppressor breast cancer 1 (BRCA1) is a negative regulator of PRC2-dependent H3K27 methylation. Our recent studies revealed that inhibition of EZH2-mediated histone methylation radiosensitizes prostate cancer stem cells (CSCs) population. However, the link between BRCA1 and EZH2 in regulation of prostate CSCs remains elusive. Present study demonstrated that BRCA1 and EZH2 are coregulated in patients’ tumors and PCa cell lines, and cooperate in regulation of CSC phenotype and properties. Knockdown of BRCA1 expression significantly increases the number and the size of tumor spheres. Inhibition of BRCA1 and EZH2 expression leads to an increase of aldehyde dehydrogenase (ALDH)-positive cell population that is, at least partially, attributed to the upregulation of ALDH1A3 protein. Treatment with a global histone methylation inhibitor 3-Deazaneplanocin A abrogates this regulation, downregulates BRCA1 and EZH2 expression and has an inhibitory effect on the tumorigenic properties of radioresistant PCa cells in vivo. We found that EZH2/BRCA1 signaling mechanisms play an important role in the maintenance of prostate CSC properties and may be a promising target for tumor treatment.     

Shikonin enhances the antitumor effect of cabazitaxel in prostate cancer stem cells and reverses cabazitaxel resistance by inhibiting ABCG2 and ALDH3A1

Cancer stem cells (CSCs) are a small population among cancer cells, defined as capable of self-renewal, and driving tumor growth, metastasis, and therapeutic relapse. The development of therapeutic strategies to target CSCs is of great importance to prevent tumor metastasis and relapse. Increasing evidence shows that shikonin has inhibiting effects on CSCs. This study was to determine the effect of shikonin on prostate CSCs, and on drug resistant cells. Sphere formation assay was used to enrich prostate CSCs. The effect of shikonin on viability, proliferation, migration, and invasion was studied. Typical CSCs markers were analyzed by flow cytometry and RT-qPCR. The cytotoxic mechanism of shikonin was analyzed by staining for annexin V, reactive oxygen species (ROS) and mitochondrial membrane potential. To study the effect of shikonin on drug-resistant cells a cabazitaxel resistant cell line was established. Shikonin inhibited the viability, proliferation, migration, and invasion of prostate CSCs. Shikonin enhanced the antitumor effect of cabazitaxel, which is a second-line chemotherapeutic drug in advanced prostate cancer. Shikonin induced apoptosis through generating ROS and disrupting the mitochondrial membrane potential. Furthermore, shikonin suppressed the expression of ALDH3A1 and ABCG2 in prostate CSCs, which are two markers related to drug-resistance. When inhibiting the expression of ABCG2 and ALDH3A1, the cabazitaxel resistant cells acquired more sensibility to cabazitaxel. Shikonin enhances the cytotoxic activity of cabazitaxel in prostate CSCs and reverses the cabazitaxel-resistant state.     

A TARBP2-dependent miRNA expression profile underlies cancer stem cell properties and provides candidate therapeutic reagents in Ewing sarcoma

We have recently demonstrated that human pediatric mesenchymal stem cells can be reprogrammed toward a Ewing sarcoma family tumor (ESFT) cancer stem cell (CSC) phenotype by mechanisms that implicate microRNAs (miRNAs). Here, we show that the miRNA profile of ESFT CSCs is shared by embryonic stem cells and CSCs from divergent tumor types. We also provide evidence that the miRNA profile of ESFT CSCs is the result of reversible disruption of TARBP2-dependent miRNA maturation. Restoration of TARBP2 activity and systemic delivery of synthetic forms of either of two of its targets, miRNA-143 or miRNA-145, inhibited ESFT CSC clonogenicity and tumor growth in vivo. Our observations suggest that CSC self-renewal and tumor maintenance may depend on deregulation of TARBP2-dependent miRNA expression.     

Prostate cancer stem/progenitor cells: identification, characterization, and implications

Several solid tumors have now been shown to contain stem cell-like cells called cancer stem cells (CSC). These cells, although generally rare, appear to be highly tumorigenic and may be the cells that drive tumor formation, maintain tumor homeostasis, and mediate tumor metastasis. In this Perspective, we first provide our insight on how a CSC should be defined. We then summarize our current knowledge of stem/progenitor cells in the normal human prostate (NHP), an organ highly susceptible to hyperproliferative diseases such as benign prostate hyperplasia (BPH) and prostate cancer (PCa). We further review the evidence that cultured PCa cells, xenograft prostate tumors, and patient tumors may contain stem/progenitor cells. Along with our discussion, we present several methodologies that can be potentially used to identify putative tumor-reinitiating CSC. Finally, we present a hypothetical model for the hierarchical organization of human PCa cells and discuss the implications of this model in helping understand prostate carcinogenesis and design novel diagnostic, prognostic, and therapeutic approaches.     

High dose acetaminophen inhibits STAT3 and has free radical independent anti-cancer stem cell activity

High-dose acetaminophen (AAP) with delayed rescue using n-acetylcysteine (NAC), the FDA-approved antidote to AAP overdose, has demonstrated promising antitumor efficacy in early phase clinical trials. However, the mechanism of action (MOA) of AAP''s anticancer effects remains elusive. Using clinically relevant AAP concentrations, we evaluated cancer stem cell (CSC) phenotype in vitro and in vivo in lung cancer and melanoma cells with diverse driver mutations. Associated mechanisms were also studied. Our results demonstrated that AAP inhibited 3D spheroid formation, self-renewal, and expression of CSC markers when human cancer cells were grown in serum-free CSC media. Similarly, anti-CSC activity was demonstrated in vivo in xenograft models - tumor formation following in vitro treatment and ex-vivo spheroid formation following in vivo treatment. Intriguingly, NAC, used to mitigate AAP''s liver toxicity, did not rescue cells from AAP''s anti-CSC effects, and AAP failed to reduce glutathione levels in tumor xenograft in contrast to mice liver tissue suggesting nonglutathione-related MOA. In fact, AAP mediates its anti-CSC effect via inhibition of STAT3. AAP directly binds to STAT3 with an affinity in the low micromolar range and a high degree of specificity for STAT3 relative to STAT1. These findings have high immediate translational significance concerning advancing AAP with NAC rescue to selectively rescue hepatotoxicity while inhibiting CSCs. The novel mechanism of selective STAT3 inhibition has implications for developing rational anticancer combinations and better patient selection (predictive biomarkers) for clinical studies and developing novel selective STAT3 inhibitors using AAP''s molecular scaffold.     

Targeting of pancreatic and prostate cancer stem cell characteristics by Crambe crambe marine sponge extract

Cancer stem cells (CSCs) are suggested as reason for resistance of tumors toward conventional tumor therapy including pancreatic and advanced prostate cancer. New therapeutic agents are urgently needed for targeting of CSCs. Marine sponges harbor novel and undefined compounds with antineoplastic activity but their potential to eliminate CSC characteristics is not examined so far. We collected 10 marine sponges and one freshwater sponge by diving at the seaside and prepared crude methanolic extracts. The effect to established pancreatic and prostate CSC lines was evaluated by analysis of apoptosis, cell cycle, side population, colony and spheroid formation, migratory potential in vitro and tumorigenicity in vivo. While each sponge extract at a 1:10 dilution efficiently diminished viability, Crambe crambe marine sponge extract (CR) still strongly reduced viability of tumor cells at a dilution of 1:1,000 but was less toxic to normal fibroblasts and endothelial cells. CR inhibited self-renewal capacity, apoptosis resistance, and proliferation even in gemcitabine-selected pancreatic cancer cells with acquired therapy resistance and enhanced CSC characteristics. CR pretreatment of tumor cells diminished tumorigenicity of gemcitabine-resistant tumor cells in mice and totally abolished tumor take upon combination with gemcitabine. Our data suggest that CR contains substances, which render standard cancer therapy more effective by targeting of CSC characteristics. Isolation of bioactive metabolites from CR and evaluation in mice are required for development of new CSC-specific chemotherapeutic drugs from a marine sponge.     

QKI impairs self-renewal and tumorigenicity of oral cancer cells via repression of SOX2

Cancer stem cells (CSCs) may contribute to tumor initiation, distant metastasis and chemo-resistance. One of RNA-binding proteins, Quaking (QKI), was reported to be a tumor suppressor. Here we showed that reduced QKI levels were observed in many human oral cancer samples. Moreover further reduction of QKI expression in CSCs was detected compared with non-CSCs in oral cancer cell lines. Overexpressing QKI in oral cancer cells significantly reduced CSC sphere formation and stem cell-associated genes. In tumor implanting nude mice model, QKI significantly impeded tumor initiation rates, tumor sizes and lung metastasis rates. As a contrast, knocking down QKI enhanced the above effects. Among the putative CSC target genes, SOX2 expression was negatively affected by QKI, mechanism study revealed that QKI may directly regulate SOX2 expression via specific binding with its 3′UTR in a cis element-dependent way. Loss of SOX2 even completely reversed the sphere forming ability in QKI knockdown cell line. Taken together, these data demonstrated that SOX2 is an important CSC regulator in oral cancer. QKI is a novel CSC inhibitor and impaired multiple oral CSC properties via partial repression of SOX2. Therefore, reduced expression of QKI may provide a novel diagnostic marker for oral cancer.     

Regulation of gene expression and inhibition of experimental prostate cancer bone metastasis by dietary genistein

Prostate cancer frequently metastasizes to the bone, and the treatment outcome for metastatic prostate cancer has been disappointing so far. Dietary genistein, derived primarily from soy product, has been proposed to be partly responsible for the low rate of prostate cancer in Asians. Our previous studies have shown that genistein elicits pleiotropic effects on prostate cancer cells, but there are no studies documenting comprehensive gene expression profiles and antitumor effects of dietary genistein on human prostate cancer grown in human bone environment. In this study, we investigated the effects of genistein on PC3 prostate cancer cells and experimental PC3 bone tumors created by injecting PC3 cells into human bone fragments previously implanted in severe combined immunodeficient (SCID) mice (SCID human model). We found that genistein significantly inhibited PC3 bone tumor growth using both prevention and intervention strategies. By using microarray and real-time polymerase chain reaction technology, we found that genistein regulated the expression of multiple genes involved in the control of cell growth, apoptosis, and metastasis both in vitro and in vivo. For example, the expression of various metalloproteinases (MMPs) in PC3 bone tumors was inhibited by genistein treatment, whereas osteoprotegerin was upregulated. MMP immunostaining and transfection experiments also demonstrated that MMP-9 expression was inhibited in PC3 cells in vitro and PC3 bone tumors in vivo after genistein treatment. These results, particularly the in vivo results, demonstrate that dietary genistein may inhibit prostate cancer bone metastasis by regulating metastasis-related genes. Genistein may thus be a promising agent for the prevention and/or treatment of prostate cancer.     

4EGI-1 targets breast cancer stem cells by selective inhibition of translation that persists in CSC maintenance,proliferation and metastasis

Cancer death is a leading cause of global mortality. An estimated 14.1 million new cancer cases and 8.2 million cancer deaths occurred worldwide in 2012 alone. Cancer stem cells (CSCs) within tumors are essential for tumor metastasis and reoccurrence, the key factors of cancer lethality. Here we report that 4EGI-1, an inhibitor of the interaction between translation initiation factors eIF4E1 and eIF4G1 effectively inhibits breast CSCs through selectively reducing translation persistent in breast CSCs. Translation initiation factor eIF4E1 is significantly enhanced in breast CSCs in comparison to non-CSC breast cancer cells. 4EGI-1 presents increased cytotoxicity to breast CSCs compared to non-CSC breast cancer cells. 4EGI-1 promotes breast CSC differentiation and represses breast CSC induced tube-like structure formation of human umbilical vein endothelial cells (HUVECs). 4EGI-1 isomers suppress breast CSC tumorangiogenesis and tumor growth in vivo. In addition, 4EGI-1 decreases proliferation in and induces apoptosis into breast CSC tumor cells. Furthermore, 4EGI-1 selectively inhibits translation of mRNAs encoding NANOG, OCT4, CXCR4, c-MYC and VEGF in breast CSC tumors. Our study demonstrated that 4EGI-1 targets breast CSCs through selective inhibition of translation critical for breast CSCs, suggesting that selective translation initiation interference might be an avenue targeting CSCs within tumors.     

Ras activation contributes to the maintenance and expansion of Sca-1 cells in a mouse model of breast cancer

The cancer stem cell (CSC) hypothesis proposes that CSCs are the root of cancer and cause cancer metastasis and recurrence. In this study, we examined whether Ras signaling is associated with stemness of the CSCs population characterized by the stem cell antigen (Sca-1) phenotype in a 4T1 syngeneic mouse model of breast cancer. The Sca-1^pos putative CSCs had high levels of activated Ras and phosphorylated MEK (p-MEK), compared with counterparts. The Ras farnesylation inhibitor (FTI-277) suppressed the maintenance and expansion of CSCs. Therefore, selective inhibition of Ras activation may be useful for stem-specific cancer therapy.     

The synthetic retinoid ST1926 attenuates prostate cancer growth and potentially targets prostate cancer stem‐like cells

Retinoids are vitamin A derivatives that regulate crucial biological processes such as cellular proliferation, apoptosis, and differentiation. The use of natural retinoids in cancer therapy is limited due to their toxicity and the acquired resistance by cancer cells. Therefore, synthetic retinoids were developed, such as the atypical adamantyl retinoid ST1926 that provides enhanced bioavailability and reduced toxicity. We have assessed the in vitro and in vivo antitumor properties and mechanism of action of ST1926 in targeting cancer stem‐like cells population of human prostate cancer (PCa) cell lines, DU145 and PC3, and mouse PCa cell lines, PLum‐AD and PLum‐AI. We demonstrated that ST1926 substantially reduced proliferation of PCa cells and induced cell cycle arrest, p53‐independent apoptosis, and early DNA damage. It also decreased migration and invasion of PCa cells and significantly reduced prostate spheres formation ability in vitro denoting sufficient eradication of the self‐renewal ability of the highly androgen‐resistant cancer stem cells. Importantly, ST1926 potently inhibited PCa tumor growth and progression in vivo. Our results highlight the potential of ST1926 in PCa therapy and warrant its clinical development.     

High metabolic rate and stem cell characteristics of esophageal cancer stem-like cells depend on the Hsp27–AKT–HK2 pathway

Tumor progression with chemoresistance and local recurrence is commonly happened during treatment of esophageal squamous cell carcinoma (ESCC). Cancer stem cells (CSC) may respond for tumor progression. However, there are few reports regarding metabolism of esophageal CSCs with clinical correlation. In this work, we demonstrated that ESCC cell lines in spheroid culture display CSC phenotypes, including increased ALDH activity, chemoresistance and tumor initiation, which are dependent on Hsp27 activation. Esophageal CSCs also exhibit reprogrammed metabolic features particularly higher glycolysis and oxidative phosphorylation, which are regulated via the Hsp27–AKT–HK2 pathway. Moreover, HK2 is required for maintenance of CSC phenotypes. Inhibition of CSC metabolism reduces cell growth and tumor formation. Clinically, patients who underwent surgical resection for esophageal cancer, and displayed overexpression of both Hsp27 and HK2, had the worst prognosis of all expression types. In conclusion, stem cells features and aberrant metabolic reprogramming of esophageal CSCs depend on the Hsp27–AKT–HK2 pathway. Targeting Hsp27 and HK2 could be novel therapeutic strategy for treating esophageal cancer and warrants further investigation.     

Human kallikrein 2 (KLK2) promotes prostate cancer cell growth via function as a modulator to promote the ARA70-enhanced androgen receptor transactivation

Recent data suggested that tissue human kallikrein 2 (KLK2) might be involved in the carcinogenesis and tumor metastasis of prostate cancer (PCa). However, the detailed pathophysiological roles of KLK2 in PCa remain unclear. We report here that KLK2 may be treated as a potential therapeutic target in castration-resistant PCa (CRPC). Histologic analyses show that the increased KLK2 expression is correlated with higher cell proliferation rate and lower cell apoptosis index in CRPC specimens. Adding functional KLK2 cDNA into high passage LNCaP cells led to increased cell growth, and knockdown of KLK2 expression with KLK2-siRNA in LNCaP cells resulted in increased cell apoptosis with cell growth arrest at the G1 phase. Results from in vitro colony formation assay and in vivo xenografted PCa tissues also demonstrated that targeting KLK2 led to suppressed growth of PCa in the castration-resistant stage. Further mechanism dissection shows that KLK2 may cooperate with the AR coregulator, ARA70, to enhance AR transactivation that may result in alteration of PCa formation. Together, these results suggested KLK2 might become a new therapeutic target to battle the CRPC and KLK2-siRNA may be developed as an alternative approach to suppress PCa growth.