A comprehensive approach toward novel serum biomarkers for benign prostatic hyperplasia: the MPSA Consortium

Identifying possible biomarkers of lower urinary tract symptoms using metabolomics and partial least square regression

INTRODUCTION

The objective of this study was to explore potential novel biomarkers for moderate to severe lower urinary tract symptoms (LUTS) using a metabolomics-based approach, and statistical methods with significant different features than previous reported.

MATERIALS AND METHODS

The patients and the controls were selected to participate in the study according to inclusion/exclusion criteria (n = 82). We recorded the following variables: International prostatic symptom score (IPSS), prostate volume, comorbidities, PSA, height, weight, triglycerides, glycemia, HDL cholesterol, and blood pressure. The study of 41 plasma metabolites was done using the nuclear magnetic resonance spectroscopy technique. First, the correlations between the metabolites and the IPSS were done using Pearson. Second, significant biomarkers of LUTS from metabolites were further analysed using a multiple linear regression model. Finally, we validated the findings using partial least square regression (PLS).

RESULTS

Small to moderate correlations were found between IPSS and methionine (-0.301), threonine (-0.320), lactic acid (0.294), pyruvic acid (0.207) and 2-aminobutyric-acid (0.229). The multiple linear regression model revealed that only threonine (p = 0.022) was significantly associated with IPSS, whereas methionine (p = 0.103), lactic acid (p = 0.093), pyruvic acid (p = 0.847) and 2-aminobutyric-acid (p = 0.244) lost their significance. However, all metabolites lost their significance in the PLS model.

CONCLUSION

When using the robust PLS-regression method, none of the metabolites in our analysis had a significant association with lower urinary tract symptoms. This highlights the importance of using appropriate statistical methods when exploring new biomarkers in urology.

Personalized medicine for the management of benign prostatic hyperplasia

PURPOSE

Benign prostatic hyperplasia affects more than 50% of men by age 60 years, and is the cause of millions of dollars in health care expenditure for the treatment of lower urinary tract symptoms and urinary obstruction. Despite the widespread use of medical therapy, there is no universal therapy that treats all men with symptomatic benign prostatic hyperplasia. At least 30% of patients do not respond to medical management and a subset require surgery. Significant advances have been made in understanding the natural history and development of the prostate, such as elucidating the role of the enzyme 5α-reductase type 2, and advances in genomics and biomarker discovery offer the potential for a more targeted approach to therapy. We review the current understanding of benign prostatic hyperplasia progression as well as the key genes and signaling pathways implicated in the process such as 5α-reductase. We also explore the potential of biomarker screening and gene specific therapies as tools to risk stratify patients with benign prostatic hyperplasia and identify those with symptomatic or medically resistant forms.

MATERIALS AND METHODS

A PubMed® literature search of current and past peer reviewed literature on prostate development, lower urinary tract symptoms, benign prostatic hyperplasia pathogenesis, targeted therapy, biomarkers, epigenetics, 5α-reductase type 2 and personalized medicine was performed. An additional Google Scholar™ search was conducted to broaden the scope of the review. Relevant reviews and original research articles were examined, as were their cited references, and a synopsis of original data was generated with the goal of informing the practicing urologist of these advances and their implications.

RESULTS

Benign prostatic hyperplasia is associated with a state of hyperplasia of the stromal and epithelial compartments, with 5α-reductase type 2 and androgen signaling having key roles in the development and maintenance of the prostate. Chronic inflammation, multiple growth factor and hormonal signaling pathways, and medical comorbidities have complex roles in prostate tissue homeostasis as well as its evolution into the clinical state of benign prostatic hyperplasia. Resistance to medical therapy with finasteride may occur through silencing of the 5α-reductase type 2 gene by DNA methylation, leading to a state in which 30% of adult prostates do not express 5α-reductase type 2. Novel biomarkers such as single nucleotide polymorphisms may be used to risk stratify patients with symptomatic benign prostatic hyperplasia and identify those at risk for progression or failure of medical therapy. Several inhibitors of the androgen receptor and other signaling pathways have recently been identified which appear to attenuate benign prostatic hyperplasia progression and may offer alternative targets for medical therapy.

CONCLUSIONS

Progressive worsening of lower urinary tract symptoms and bladder outlet obstruction secondary to benign prostatic hyperplasia is the result of multiple pathways including androgen receptor signaling, proinflammatory cytokines and growth factor signals. New techniques in genomics, proteomics and epigenetics have led to the discovery of aberrant signaling pathways, novel biomarkers, DNA methylation signatures and potential gene specific targets. As personalized medicine continues to develop, the ability to risk stratify patients with symptomatic benign prostatic hyperplasia, identify those at higher risk for progression, and seek alternative therapies for those in whom conventional options are likely to fail will become the standard of targeted therapy.

Benign prostate specific antigen distribution and associations with urological outcomes in community dwelling black and white men

PURPOSE

We describe cross-sectional associations of benign prostate specific antigen with clinical urological measures and examined the risk of future urological outcomes in 2 population based cohorts of black and white men, respectively.

MATERIALS AND METHODS

Two population based cohort studies were established to characterize the natural history of and risk factors for prostate disease progression in white and black male residents of Olmsted County, Minnesota, and Genesee County, Michigan, respectively.

RESULTS

The benign prostate specific antigen distribution was similar in black men at a median of 32.9 pg/ml (25th, 75th percentiles 17.3, 68.0) and white men at a median of 32.2 pg/ml (25th, 75th percentiles 16.6, 68.9, respectively). However, it was much lower than in previous reports. For Olmsted County men in the upper quartile of benign prostate specific antigen there was a fifteenfold increased risk of prostate cancer (HR 14.6, 95% CI 3.1-68.6) and a twofold higher risk of treatment for benign prostatic hyperplasia (HR 2.2, 95% CI 1.2-4.2) after adjusting for age. After additional adjustment for baseline prostate specific antigen the association between benign prostate specific antigen and prostate cancer risk was attenuated but remained almost ninefold higher for men in the upper quartile of benign prostate specific antigen (HR 8.7, 95% CI 1.8-42.4). The twofold higher risk of treatment for benign prostatic hyperplasia also remained after adjusting for baseline prostate specific antigen for men in the upper benign prostate specific antigen quartile (HR 1.9, 95% CI 0.9-4.0).

CONCLUSIONS

Results suggest that increased benign prostate specific antigen may help identify men with prostate cancer and those at risk for benign prostatic hyperplasia treatment.

What is a biomarker? Research investments and lack of clinical integration necessitate a review of biomarker terminology and validation schema

A continual trend of annual growth can be seen within research devoted to the discovery and validation of disease biomarkers within both the natural and clinical sciences. This expansion of intellectual endeavours was quantified through database searches of (a) research grant awards provided by the various branches of the National Institutes of Health (NIH) and (b) academic publications. A search of awards presented between 1986 and 2009 revealed a total of 28,856 grants awarded by the NIH containing the term "biomarker". The total funds for these awards in 2008 and 2009 alone were over $2.5 billion. During the same respective time frames, searches of "biomarker" and either "discovery", "genomics", "proteomics" or "metabolomics" yielded a total of 4,928 NIH grants whose combined funding exceeded $1.2 billion. The derived trend in NIH awards paralleled the annual expansion in "biomarker" literature. A PubMed search for the term, between 1990 and 2009, revealed a total of 441,510 published articles, with 38,457 published in 2008. These enormous investments and academic outputs however have not translated into the expected integration of new biomarkers for patient care. For example no proteomics derived biomarkers are currently being utilized in routine clinical management. This translational chasm necessitates a review of the previously proposed biomarker definitions and evaluation schema. A subsequent discussion of both the analytical and pre-analytical considerations for such research is also presented within. This required knowledge should aid scientists in their pursuit and validation of new biological markers of disease.

Gene expression down-regulation in CD90+ prostate tumor-associated stromal cells involves potential organ-specific genes

Background

The prostate stroma is a key mediator of epithelial differentiation and development, and potentially plays a role in the initiation and progression of prostate cancer. The tumor-associated stroma is marked by increased expression of CD90/THY1. Isolation and characterization of these stromal cells could provide valuable insight into the biology of the tumor microenvironment.

Methods

Prostate CD90⁺ stromal fibromuscular cells from tumor specimens were isolated by cell-sorting and analyzed by DNA microarray. Dataset analysis was used to compare gene expression between histologically normal and tumor-associated stromal cells. For comparison, stromal cells were also isolated and analyzed from the urinary bladder.

Results

The tumor-associated stromal cells were found to have decreased expression of genes involved in smooth muscle differentiation, and those detected in prostate but not bladder. Other differential expression between the stromal cell types included that of the CXC-chemokine genes.

Conclusion

CD90⁺ prostate tumor-associated stromal cells differed from their normal counterpart in expression of multiple genes, some of which are potentially involved in organ development.

Review of diagnostic markers for prostate cancer

This review concentrates mainly on currently available markers for prostate cancer and cannot cover the multiple marker substances which are now in experimental and clinical development. Prostate-specific antigen (PSA) is still the main diagnostic tool despite its serious limitations, which will be addressed. Studies of new diagnostic markers and also most studies of PSA are subject to attribution or assignment bias, which limits the accuracy of the resulting information. Usually a more or less arbitrarily chosen cut-off value is used as a "gold standard" to determine the indication for the decisive test, a prostatic biopsy, and the assumption is made that no cancers are present below that cut-off value. This assumption has been proved wrong by findings in the control arm of the Prostate Cancer Prevention Trial (PCPT), where more than 5,000 men were biopsied independent of their PSA status. As an example: a PSA cut-off value of4.0 ng/ml, a commonly used biopsy indicator, missed about 75% of all biopsy-detectable cancers. On the other hand, sextant biopsies in all men led to a detection rate of 21.9%, evidence of the diagnosis of many cases in men who otherwise would never have had any clinical signs of prostate cancer (overdiagnosis). The only way out of this dilemma is a better understanding of the natural history of those cases with low PSA values that would not be considered suspicious with the use of currently available risk indicator nomograms. The European Randomised Study of Screening for Prostate Cancer (ERSPC) offers such an opportunity. Results are summarised in this chapter. Evidence is provided that men diagnosed in the low PSA ranges (< 3.0 ng/ml) usually present with more favourable cancers which, when identified, are often eligible for active surveillance after application of the appropriate nomogram. In addition, the data in the setting of the ERSPC study show that biopsy in such men can safely be delayed until PSA rises to above a cut-off value of 3.0 ng/ml. The limitations of PSA discussed herein clearly point to the need to find better diagnostic and prognostic markers for prostate cancer.