Metastatic castrate-resistant prostate cancer: dawn of a new age of management

MLL5, a histone modifying enzyme, regulates androgen receptor activity in prostate cancer cells by recruiting co-regulators, HCF1 and SET1

In prostate cancer, the androgen receptor (AR) transcription factor is a major regulator of cell proliferation and metastasis. To identify new AR regulators, we focused on Mixed lineage leukemia 5 (MLL5), a histone-regulating enzyme, because significantly higher MLL5 expression was detected in prostate cancer tissues than in matching normal tissues. When we expressed shRNAs targeting MLL5 gene in prostate cancer cell line, the growth rate and AR activity were reduced compared to those in control cells, and migration ability of the knockdown cells was reduced significantly. To determine the molecular mechanisms of MLL5 on AR activity, we proved that AR physically interacted with MLL5 and other co-factors, including SET-1 and HCF-1, using an immunoprecipitation method. The chromatin immunoprecipitation analysis showed reduced binding of MLL5, co-factors, and AR enzymes to AR target gene promoters in MLL5 shRNA-expressing cells. Histone H3K4 methylation on the AR target gene promoters was reduced, and H3K9 methylation at the same site was increased in MLL5 knockdown cells. Finally, xenograft tumor formation revealed that reduction of MLL5 in prostate cancer cells retarded tumor growth. Our results thus demonstrate the important role of MLL5 as a new epigenetic regulator of AR in prostate cancer.

Silencing circSLC19A1 Inhibits Prostate Cancer Cell Proliferation, Migration and Invasion Through Regulating miR-326/MAPK1 Axis

Background

Emerging evidence indicates that circular RNAs (circRNAs), which form as covalently closed loops, play a regulatory role in various types of cancer, including prostate cancer (PCa). CircSLC19A1, one kind of circRNA, was subjected to the study and its role in PCa was explored.

Methods

Expressions of circSLC19A1, miR-326 and MAPK1 in PCa tissues and cells were assessed by qRT-PCR. CircSLC19A1 was identified by RNase R treatment. The binding relations between circSLC19A1 and miR-326 and between miR-326 and MAPK1 were predicted by RegRNA2.0 or Targetscan7.2 and further confirmed by dual-luciferase reporter assay. Pearson correlation analysis of the correlation among circSLC19A1, miR-326 and MAPK1 was performed. CCK-8, cell colony formation, wound healing and Transwell assays were used to assess PCa cell viability, proliferation, migration and invasion, respectively.

Results

CircSLC19A1 expression was up-regulated in PCa tissue and cell cytoplasm. Silencing circSLC19A1 inhibited PCa cell viability, proliferation, migration, invasion and miR-326 expression. MiR-326 inhibitor promoted the luciferase activities of circSLC19A1 and MAPK1, increased MAPK1 expression and facilitated PCa cell progression. MiR-326 expression was down-regulated in PCa tissue and there was a negative correlation between miR-326 and circSLC19A1 expressions. MAPK1 expression was up-regulated in PCa tissue. There was a negative correlation between MAPK1 and miR-326 expressions as well as a positive correlation between MAPK1 and circSLC19A1 expressions. Silencing MAPK1 promoted the viability, proliferation, migration, and invasion of PCa cells co-transfected with siRNA-circSLC19A1a and miR-326 inhibitor.

Conclusion

CircSLC19A1 silencing inhibited PCa cell proliferation, migration and invasion through regulating miR-326/MAPK1 axis.

Downregulation of class II phosphoinositide 3-kinase PI3K-C2β delays cell division and potentiates the effect of docetaxel on cancer cell growth

Background

Alteration of signalling pathways regulating cell cycle progression is a common feature of cancer cells. Several drugs targeting distinct phases of the cell cycle have been developed but the inability of many of them to discriminate between normal and cancer cells has strongly limited their clinical potential because of their reduced efficacy at the concentrations used to limit adverse side effects. Mechanisms of resistance have also been described, further affecting their efficacy. Identification of novel targets that can potentiate the effect of these drugs or overcome drug resistance can provide a useful strategy to exploit the anti-cancer properties of these agents to their fullest.

Methods

The class II PI3K isoform PI3K-C2β was downregulated in prostate cancer PC3 cells and cervical cancer HeLa cells using selective siRNAs and the effect on cell growth was determined in the absence or presence of the microtubule-stabilizing agent/anti-cancer drug docetaxel. Mitosis progression was monitored by time-lapse microscopy. Clonogenic assays were performed to determine the ability of PC3 and HeLa cells to form colonies upon PI3K-C2β downregulation in the absence or presence of docetaxel. Cell multi-nucleation was assessed by immunofluorescence. Tumour growth in vivo was assessed using a xenograft model of PC3 cells upon PI3K-C2β downregulation and in combination with docetaxel.

Results

Downregulation of PI3K-C2β delays mitosis progression in PC3 and HeLa cells, resulting in reduced ability to form colonies in clonogenic assays in vitro. Compared to control cells, PC3 cells lacking PI3K-C2β form smaller and more compact colonies in vitro and they form tumours more slowly in vivo in the first weeks after cells implant. Stable and transient PI3K-C2β downregulation potentiates the effect of low concentrations of docetaxel on cancer cell growth. Combination of PI3K-C2β downregulation and docetaxel almost completely prevents colonies formation in clonogenic assays in vitro and strongly inhibits tumour growth in vivo.

Conclusions

These data reveal a novel role for the class II PI3K PI3K-C2β during mitosis progression. Furthermore, data indicate that blockade of PI3K-C2β might represent a novel strategy to potentiate the effect of docetaxel on cancer cell growth.

MicroRNAs in prostate cancer: From function to biomarker discovery

MicroRNAs (miRNAs) are a small functional non-coding RNAs that post-transcriptionally regulate gene expression through mRNA degradation or translational repression. miRNAs are key regulatory components of various cellular networks. Current evidence support that multiple mammalian genome-encoded miRNAs impact the cellular biology, including proliferation, apoptosis, differentiation, and tumorigenesis, by targeting specific subsets of mRNAs. This minireview is focused on the current themes underlying the interactions between miRNAs and their mRNA targets and pathways in prostate tumorigenesis and progression, and their potential clinical utility as biomarkers for prostate cancer. Impact statement The primary goal of this article was to review recent literature on miRNA biogenesis and further elaborate on the identity of newly discovered miRNAs and their potential functional significance in the complex biological network associated with prostate tumorigenesis and disease progression and as biomarkers for prostate cancer.

Epigenomic Regulation of Androgen Receptor Signaling: Potential Role in Prostate Cancer Therapy

Androgen receptor (AR) signaling remains the major oncogenic pathway in prostate cancer (PCa). Androgen-deprivation therapy (ADT) is the principle treatment for locally advanced and metastatic disease. However, a significant number of patients acquire treatment resistance leading to castration resistant prostate cancer (CRPC). Epigenetics, the study of heritable and reversible changes in gene expression without alterations in DNA sequences, is a crucial regulatory step in AR signaling. We and others, recently described the technological advance Chem-seq, a method to identify the interaction between a drug and the genome. This has permitted better understanding of the underlying regulatory mechanisms of AR during carcinogenesis and revealed the importance of epigenetic modifiers. In screening for new epigenomic modifiying drugs, we identified SD-70, and found that this demethylase inhibitor is effective in CRPC cells in combination with current therapies. The aim of this review is to explore the role of epigenetic modifications as biomarkers for detection, prognosis, and risk evaluation of PCa. Furthermore, we also provide an update of the recent findings on the epigenetic key processes (DNA methylation, chromatin modifications and alterations in noncoding RNA profiles) involved in AR expression and their possible role as therapeutic targets.

Identification of microRNA signature and potential pathway targets in prostate cancer

Prostate cancer (PC) is the most common and the second leading cause of cancer-related death among American men. Early diagnosis is a prerequisite to improving therapeutic benefits. However, the current clinical biomarkers for PC do not reliably decipher indolent PC from other urogenital disorders. Thus, effective clinical intervention necessitates development of new biomarkers for early detection of PC. The present study aimed to identify the miRNA signature in organ-confined (Gleason Score 6) prostate tumors. MicroRNA (miRNA/miR) array analysis identified 118 upregulated and 73 downregulated miRNAs in microdissected tumors in comparison to matched neighboring normal prostate epithelium. The miRs-Plus-A1083, -92b-5p, -18a-3p, -19a-3p, -639, -3622b-3p, -3189-3p, -155-3p, -410, -1179, 548b-5p, and -4469 are predominantly expressed (7-11-fold), whereas miRs-595, 4490, -3120-5p, -1299, -21-5p, -3677-3, -let-7b-5p, -5189, 3-121-5p, -4518, -200a-5p, -3682-5p, -3689d, -3149 represent the most downregulated (12-113-fold) miRNAs in microdissected prostate tumors. The array expression profile of selected miRNA signature and their potential mRNA targets was validated by qRT-PCR analysis in PC cell lines. Integrated in silico and computational prediction analyses demonstrated that the dysregulated miRNA signature map to key regulatory factors involved in tumorigenesis, including cell cycle, apoptosis, and p53 pathways. The newly identified miRNA signature has potential clinical utility as biomarkers, prognostic indicators, and therapeutic targets for early detection of PC. Further studies are needed to assess the functional significance and clinical usefulness of the identified miRNAs. Impact Statement To our knowledge his is the first study of identifying miRNA signatures in microdissected indolent (Gleason score 6) prostate cancer in comparison to matched normal prostate epithelium. By employing in silico and computational prediction analysis, the study provides a landscape of potential miRNA targets and key cellular pathways involved in prostate tumorigenesis. Identification if miRNAs and their relevant targets and pathways pave the way for underpinning their mechanistic role of miRNAs in human prostate tumorigenesis, and possibly other human cancers. Importantly, the outcome of the study has important clinical implications for the management of prostate cancer, including the use of miRNA(s) as biomarkers for early detection of prostate cancer.

Prostate cancer epigenetic biomarkers: next-generation technologies

Cancer is caused by a combination of genetic alterations and gross changes to the epigenetic landscape that together result in aberrant cancer gene regulation. Therefore, we need to fully sequence both the cancer genome and the matching cancer epigenomes before we can fully integrate the suite of molecular mechanisms involved in initiation and progression of cancer. A further understanding of epigenetic aberrations has a great potential in the next era of molecular genomic pathology in cancer detection and treatment in all types of cancer, including prostate cancer. In this review, we discuss the most common epigenetic aberrations identified in prostate cancer with the biomarker potential. We also describe the innovative and current epigenomic technologies used for the identification of epigenetic-associated changes in prostate cancer and future translational applications in molecular pathology for cancer detection and prognosis.

[Cabazitaxel after docetaxel: a new option in metastatic castration-resistant prostate cancer]

The management of patients with metastatic castration-resistant prostate cancer is a real challenge. Indeed, after a first line chemotherapy with docetaxel, there was no standard because the treatments were ineffective. Today, several therapeutic options are available with the development of new therapies. Among them, cabazitaxel, semi-synthetic derivative of a natural taxoid, has been developed to its low recognition by the MDR system and power distribution including brain. This new chemotherapy was assessed in patients with metastatic castration-resistant prostate cancer whose disease has progressed during or after docetaxel-based therapy. Treatment with cabazitaxel plus prednisone has improved overall survival of 2.4 months compared to mitoxantrone in the TROPIC phase III. However, hematologic toxicity may be limiting with a risk of febrile neutropenia; hematopoietic growth factors are advised in case of significant neutropenia. The cabazitaxel, Jevtana(®), has been approved in second line after docetaxel. Its position in relation to new types of hormone therapy, as abiraterone acetate, in the same indication requires further investigations, including predictive factors of response. Studies are on going in first line indication (compared to docetaxel) and associated to other new hormone therapies.