Resolution of Cellular Heterogeneity in Human Prostate Cancers: Implications for Diagnosis and Treatment.

Prostate cancers have a justified reputation as one of the most heterogeneous human tumours. Indeed, there are some who consider that advanced and castration-resistant prostate cancers are incurable, as a direct result of this heterogeneity. However, tumour heterogeneity can be defined in different ways. To a clinician, prostate cancer is a number of different diseases, the treatments for which remain equally heterogeneous and uncertain. To the pathologist, the histopathological appearances of the tumours are notoriously heterogeneous. Indeed, the genius of Donald Gleason in the 1960s was to devise a classification system designed to take into account the heterogeneity of the tumours both individually and in the whole prostate context. To the cell biologist, a prostate tumour consists of multiple epithelial cell types, inter-mingled with various fibroblasts, neuroendocrine cells, endothelial cells, macrophages and lymphocytes, all of which interact to influence treatment responses in a patient-specific manner. Finally, genetic analyses of prostate cancers have been compromised by the variable gene rearrangements and paucity of activating mutations observed, even in large numbers of patient tumours with consistent clinical diagnoses and/or outcomes. Research into familial susceptibility has even generated the least tractable outcome of such studies: the genetic loci are of low penetrance and are of course heterogeneous. By fractionating the tumour (and patient-matched non-malignant tissues) heterogeneity can be resolved, revealing homogeneous markers of patient outcomes.

Construction of therapeutically relevant human prostate epithelial fate map by utilising miRNA and mRNA microarray expression data.

BACKGROUND: Objective identification of key miRNAs from transcriptomic data is difficult owing to the inherent inconsistencies within miRNA target-prediction algorithms and the promiscuous nature of miRNA-mRNA target relationship. METHODS: An integrated database of miRNAs and their 'relevant' mRNA targets was generated from validated miRNA and mRNA microarray data sets generated from patient-derived prostate epithelial normal and cancer stem-like cells (SCs) and committed basal (CB) cells. The effect of miR-542-5p inhibition was studied to provide proof-of-principle for database utility. RESULTS: Integration of miRNA-mRNA databases showed that signalling pathways and processes can be regulated by a single or relatively few miRNAs, for example, DNA repair/Notch pathway by miR-542-5p, P=0.008. Inhibition of miR-542-5p in CB cells (thereby achieving miR-542-5p expression levels similar to SCs) promoted efficient DNA repair and activated expression of Notch reporters, HES1 and Survivin, without inducing dedifferentiation into SCs. CONCLUSIONS: Our novel framework impartially identifies therapeutically relevant miRNA candidates from transcriptomic data sets.

Clonal Evolution in Healthy and Premalignant Tissues: Implications for Early Cancer Interception Strategies.

Histologically normal human tissues accumulate significant mutational burden with age. The extent and spectra of mutagenesis are comparable both in rapidly proliferating and post-mitotic tissues and in stem cells compared with their differentiated progeny. Some of these mutations provide increased fitness, giving rise to clones which, at times, can replace the entire surface area of tissues. Compared with cancer, somatic mutations in histologically normal tissues are primarily single-nucleotide variations. Interestingly though, the presence of these mutations and positive clonal selection in isolation remains a poor indicator of potential future cancer transformation in solid tissues. Common clonally expanded mutations in histologically normal tissues also do not always represent the most frequent early mutations in cancers of corresponding tissues, indicating differences in selection pressures. Preliminary evidence implies that stroma and immune system co-evolve with age, which may impact selection dynamics. In this review, we will explore the mutational landscape of histologically normal and premalignant human somatic tissues in detail and discuss cell-intrinsic and environmental factors that can determine the fate of positively selected mutations within them. Precisely pinpointing these determinants of cancer transformation would aid development of early cancer interventional and prevention strategies.

Efficacy and Cardiotoxic Safety Profile of Raltitrexed in Fluoropyrimidines-Pretreated or High-Risk Cardiac Patients With GI Malignancies: Large Single-Center Experience.

BACKGROUND: Gastrointestinal (GI) cancer patients may not be considered for therapy with fluoropyrimidines (FPs) because of previous cardiovascular (CV) toxicity or preexisting risk factors; such patients may benefit from raltitrexed-based therapy. PATIENTS AND METHODS: Patient, tumor, and treatment characteristics, as well as clinical outcomes of all consecutively treated patients with raltitrexed at the Royal Marsden Hospital between October 1998 and July 2011 were examined. GI cancer patients who developed CV toxicity as a result of FPs and those with significant CV risk factors receiving raltitrexed were included in this analysis. RESULTS: A total of 247 patients (155 and 92 with CV FP-related CV toxicities and significant CV risk factors, respectively) treated with raltitrexed alone or in combination were examined after a median follow-up of 47.1 months. CV toxicity profiles of patients receiving capecitabine (n = 110) and 5-fluorouracil (n = 45) were largely similar. Of raltitrexed-treated patients, 13 (5%) experienced CV toxicities and 1 (< 0.1%) died as a result of myocardial infarction. The median progression-free survival (PFS) and overall survival (OS) were 36.0 months (95% confidence interval [CI], 26.5-48.6) and 44.3 months (95% CI, 33.1-56.8), respectively. The 5-year survival for early stage GI malignancies (n = 140) was 62.0% (95% CI, 50.1-71.9). Median PFS and OS were not reached in this group (interquartile range = 38.4 months to NR); median PFS and OS for advanced GI malignancies (n = 107) were 18.8 (95% CI, 11.9-25.7) and 23.7 months (95% CI, 17.0-26.9), respectively. CONCLUSION: A raltitrexed-based regimen is well-tolerated therapy with comparable efficacy to FPs in patients with GI malignancies with significant CV toxicities or risk factors.

Evolutionary analysis indicates that DNA alkylation damage is a byproduct of cytosine DNA methyltransferase activity.

Methylation at the 5 position of cytosine in DNA (5meC) is a key epigenetic mark in eukaryotes. Once introduced, 5meC can be maintained through DNA replication by the activity of 'maintenance' DNA methyltransferases (DNMTs). Despite their ancient origin, DNA methylation pathways differ widely across animals, such that 5meC is either confined to transcribed genes or lost altogether in several lineages. We used comparative epigenomics to investigate the evolution of DNA methylation. Although the model nematode Caenorhabditis elegans lacks DNA methylation, more basal nematodes retain cytosine DNA methylation, which is targeted to repeat loci. We found that DNA methylation coevolved with the DNA alkylation repair enzyme ALKB2 across eukaryotes. In addition, we found that DNMTs introduced the toxic lesion 3-methylcytosine into DNA both in vitro and in vivo. Alkylation damage is therefore intrinsically associated with DNMT activity, and this may promote the loss of DNA methylation in many species.

Telomerase Activity and Telomere Length in Human Benign Prostatic Hyperplasia Stem-like Cells and Their Progeny Implies the Existence of Distinct Basal and Luminal Cell Lineages.

UNLABELLED: Benign prostatic hyperplasia (BPH) treatments have changed little over many years and do not directly address the underlying cause. Because BPH is characterised by uncontrolled cell growth, the chromosomal telomeres should be eroded in the reported absence or low levels of telomerase activity, but this is not observed. We investigated the telomere biology of cell subpopulations from BPH patients undergoing transurethral resection of prostate (TURP). Measurement of TERC, TERT, and telomerase activity revealed that only the epithelial stem-like and progenitor fractions expressed high levels of telomerase activity (p<0.01) and individual enzyme components (p<0.01). Telomerase activity and TERT expression were not detected in stromal cells. Telomere length measurements reflected this activity, although the average telomere length of (telomerase-negative) luminal cells was equivalent to that of telomerase-expressing stem/progenitor cells. Immunohistochemical analysis of patient-derived BPH arrays identified distinct areas of luminal hyperproliferation, basal hyperproliferation, and basal-luminal hyperproliferation, suggesting that basal and luminal cells can proliferate independently of each other. We propose a separate lineage for the luminal and basal cell components in BPH. PATIENT SUMMARY: We unexpectedly found an enzyme called telomerase in the cells that maintain benign prostatic hyperplasia (BPH), suggesting that telomerase inhibitors could be used to alleviate BPH symptoms.

Inhibition of the glucocorticoid receptor results in an enhanced miR-99a/100-mediated radiation response in stem-like cells from human prostate cancers.

Radiation therapy is a major primary treatment option for both localized early stage prostate cancer, and for advanced, regionally un-resectable, cancer. However, around 30% of patients still experience biochemical recurrence after radiation therapy within 10 years. Thus, identification of better biomarkers and new targets are urgently required to improve current therapeutic strategies. The miR-99 family has been shown to play an important role in the regulation of the DNA damage response, via targeting of the SWI/SNF chromatin remodeling factors, SMARCA5 and SMARCD1 in cell line models. In the present study, we have demonstrated that low expression of miR-99a and miR-100 is present in cell populations which are relatively radiation insensitive, for example in prostate cancer stem cells and in castration-resistant prostate cancer. Additionally, treatment of cells with the synthetic glucocorticoid, Dexamethasone resulted in decreased miR-99a and 100 expression, suggesting a new mechanism of miR-99a and 100 regulation in androgen-independent prostate cells. Strikingly, treatment of prostate cells with the glucocorticoid receptor inhibitor, Mifepristone was found to sensitize prostate cells to radiation by increasing the levels of miR-99a and miR-100. These results qualify the miR99 family as markers of radiation sensitivity and as potential therapeutic targets to improve efficiency of radiotherapy.

Targeting Aberrant Epigenetic Networks Mediated by PRMT1 and KDM4C in Acute Myeloid Leukemia.

Transcriptional deregulation plays a major role in acute myeloid leukemia, and therefore identification of epigenetic modifying enzymes essential for the maintenance of oncogenic transcription programs holds the key to better understanding of the biology and designing effective therapeutic strategies for the disease. Here we provide experimental evidence for the functional involvement and therapeutic potential of targeting PRMT1, an H4R3 methyltransferase, in various MLL and non-MLL leukemias. PRMT1 is necessary but not sufficient for leukemic transformation, which requires co-recruitment of KDM4C, an H3K9 demethylase, by chimeric transcription factors to mediate epigenetic reprogramming. Pharmacological inhibition of KDM4C/PRMT1 suppresses transcription and transformation ability of MLL fusions and MOZ-TIF2, revealing a tractable aberrant epigenetic circuitry mediated by KDM4C and PRMT1 in acute leukemia.

Synthetic lethal targeting of oncogenic transcription factors in acute leukemia by PARP inhibitors.

Acute myeloid leukemia (AML) is mostly driven by oncogenic transcription factors, which have been classically viewed as intractable targets using small-molecule inhibitor approaches. Here we demonstrate that AML driven by repressive transcription factors, including AML1-ETO (encoded by the fusion oncogene RUNX1-RUNX1T1) and PML-RARα fusion oncoproteins (encoded by PML-RARA) are extremely sensitive to poly (ADP-ribose) polymerase (PARP) inhibition, in part owing to their suppressed expression of key homologous recombination (HR)-associated genes and their compromised DNA-damage response (DDR). In contrast, leukemia driven by mixed-lineage leukemia (MLL, encoded by KMT2A) fusions with dominant transactivation ability is proficient in DDR and insensitive to PARP inhibition. Intriguingly, genetic or pharmacological inhibition of an MLL downstream target, HOXA9, which activates expression of various HR-associated genes, impairs DDR and sensitizes MLL leukemia to PARP inhibitors (PARPis). Conversely, HOXA9 overexpression confers PARPi resistance to AML1-ETO and PML-RARα transformed cells. Together, these studies describe a potential utility of PARPi-induced synthetic lethality for leukemia treatment and reveal a novel molecular mechanism governing PARPi sensitivity in AML.

MicroRNA expression profile of primary prostate cancer stem cells as a source of biomarkers and therapeutic targets.

UNLABELLED: MicroRNA (miRNA) expression profiles were generated from prostate epithelial subpopulations enriched from patient-derived benign prostatic hyperplasia (n=5), Gleason 7 treatment-naive prostate cancer (PCa) (n=5), and castration-resistant PCa (CRPC) (n=3). Microarray expression was validated in an independent patient cohort (n=10). Principal component analysis showed that miRNA expression is clustered by epithelial cell phenotype, regardless of pathologic status. We also discovered concordance between the miRNA expression profiles of unfractionated epithelial cells from CRPCs, human embryonic stem cells (SCs), and prostate epithelial SCs (both benign and malignant). MiR-548c-3p was chosen as a candidate miRNA from this group to explore its usefulness as a CRPC biomarker and/or therapeutic target. Overexpression of miR-548c-3p was confirmed in SCs (fivefold, p<0.05) and in unfractionated CRPCs (1.8-fold, p<0.05). Enforced overexpression of miR-548c-3p in differentiated cells induced stemlike properties (p<0.01) and radioresistance (p<0.01). Reanalyses of published studies further revealed that miR-548c-3p is significantly overexpressed in CRPC (p<0.05) and is associated with poor recurrence-free survival (p<0.05), suggesting that miR-548c-3p is a functional biomarker for PCa aggressiveness. Our results validate the prognostic and therapeutic relevance of miRNAs for PCa management while demonstrating that resolving cell-type and differentiation-specific differences is essential to obtain clinically relevant miRNA expression profiles. PATIENT SUMMARY: We report microRNA (miRNA) expression profiles of epithelial cell fractions from the human prostate, including stem cells. miR-548c-3p was revealed as a functional biomarker for prostate cancer progression. The evaluation of miR-548c-3p in a larger patient cohort should yield information on its clinical usefulness.

CIP2A is a candidate therapeutic target in clinically challenging prostate cancer cell populations.

Residual androgen receptor (AR)-signaling and presence of cancer stem-like cells (SCs) are the two emerging paradigms for clinically challenging castration-resistant prostate cancer (CRPC). Therefore, identification of AR-target proteins that are also overexpressed in the cancer SC population would be an attractive therapeutic approach.Our analysis of over three hundred clinical samples and patient-derived prostate epithelial cultures (PPECs), revealed Cancerous inhibitor of protein phosphatase 2A (CIP2A) as one such target. CIP2A is significantly overexpressed in both hormone-naïve prostate cancer (HN-PC) and CRPC patients . CIP2A is also overexpressed, by 3- and 30-fold, in HN-PC and CRPC SCs respectively. In vivo binding of the AR to the intronic region of CIP2A and its functionality in the AR-moderate and AR-high expressing LNCaP cell-model systems is also demonstrated. Further, we show that AR positively regulates CIP2A expression, both at the mRNA and protein level. Finally, CIP2A depletion reduced cell viability and colony forming efficiency of AR-independent PPECs as well as AR-responsive LNCaP cells, in which anchorage-independent growth is also impaired.These findings identify CIP2A as a common denominator for AR-signaling and cancer SC functionality, highlighting its potential therapeutic significance in the most clinically challenging prostate pathology: castration-resistant prostate cancer.

Mechanistic rationale for MCL1 inhibition during androgen deprivation therapy.

Androgen deprivation therapy induces apoptosis or cell cycle arrest in prostate cancer (PCa) cells. Here we set out to analyze whether MCL1, a known mediator of chemotherapy resistance regulates the cellular response to androgen withdrawal. Analysis of MCL1 protein and mRNA expression in PCa tissue and primary cell culture specimens of luminal and basal origin, respectively, reveals higher expression in cancerous tissue compared to benign origin. Using PCa cellular models in vitro and in vivo we show that MCL1 expression is upregulated in androgen-deprived PCa cells. Regulation of MCL1 through the AR signaling axis is indirectly mediated via a cell cycle-dependent mechanism. Using constructs downregulating or overexpressing MCL1 we demonstrate that expression of MCL1 prevents induction of apoptosis when PCa cells are grown under steroid-deprived conditions. The BH3-mimetic Obatoclax induces apoptosis and decreases MCL1 expression in androgen-sensitive PCa cells, while castration-resistant PCa cells are less sensitive and react with an upregulation of MCL1 expression. Synergistic effects of Obatoclax with androgen receptor inactivation can be observed. Moreover, clonogenicity of primary basal PCa cells is efficiently inhibited by Obatoclax. Altogether, our results suggest that MCL1 is a key molecule deciding over the fate of PCa cells upon inactivation of androgen receptor signaling.

Conserved two-step regulatory mechanism of human epithelial differentiation.

Human epithelia are organized in a hierarchical structure, where stem cells generate terminally differentiated cells via intermediate progenitors. This two-step differentiation process is conserved in all tissues, but it is not known whether a common gene set contributes to its regulation. Here, we show that retinoic acid (RA) regulates early human prostate epithelial differentiation by activating a tightly coexpressed set of 80 genes (e.g., TMPRSS2). Response kinetics suggested that some of these genes could be direct RA targets, whereas others are probably responding indirectly to RA stimulation. Comparative bioinformatic analyses of published tissue-specific microarrays and a large-scale transcriptomic data set revealed that these 80 genes are not only RA responsive but also significantly coexpressed in many human cell systems. The same gene set preferentially responds to androgens during terminal prostate epithelial differentiation, implying a cell-type-dependent interplay between RA and tissue-specific transcription factor-mediated signaling in regulating the two steps of epithelial differentiation.

Advanced prostate cancer--a case for adjuvant differentiation therapy.

The development of novel therapies such as abiraterone acetate and sipuleucel-T has improved the outlook for patients with advanced-stage and castration-resistant prostate cancer. However, the beneficial effects of these drugs are only measured in months. Moreover, the National Institute for Health and Clinical Excellence in the UK had ruled that the use of abiraterone acetate was not cost-effective before cost revision by the manufacturers. The FDA statement asserting that the use of 5α-reductase inhibitors for prostate cancer chemoprevention could increase the risk of developing high-grade prostate cancer also indirectly questions the value of direct androgen response manipulation for long-term benefit. These reports illustrate the need for a fresh and comprehensive analysis of advanced prostate cancer pathology to promote the next generation of effective adjuvant therapies. One such avenue is that of differentiation therapy, which seeks to promote the differentiation of cancer stem cells into a phenotype more sensitive to anticancer therapy than their parents. Using differentiation therapy with current antiandrogen therapies should augment our armoury of treatment for the management of advanced prostate cancer.