Metabolite 'fingerprints' linked to aggressive prostate cancer

In a paper published in Nature (2009; 457:910-4), senior author Arul M. Chinnaiyan, MD, PhD, and colleagues reported findings from research in which they used high-throughput mass spectrometry to develop metabolomic profiles for 262 clinical samples obtained from men with benign prostate disease and clinically localized or metastatic prostate cancer.

They quantified 1,126 metabolites. Focusing first on prostate tissue specimens, Dr. Chinnaiyan and colleagues were able to identify a metabolomic signature of prostate cancer progression. The analysis found 60 compounds that were present in cancer specimens, but not in benign prostate, and six metabolites-sarcosine, uracil, kynurenine, glycerol-3-phosphate, leucine, and proline-that were present in significantly higher levels in the metastatic prostate cancer samples compared with those from men with clinically localized disease.

Focusing on sarcosine because it was consistently elevated across the spectrum from benign to metastatic disease and because it is a participant in biochemical pathways known to be enriched in prostate cancer development, researchers conducted a series of additional experiments analyzing levels of sarcosine in biospecimens and investigating its role in cancer biology. The results provide consistent support for further evaluation of sarcosine as a biomarker for prostate cancer detection, disease prognostication and as a novel therapeutic target.

"There is a need for new biomarkers for prostate cancer that can supplement PSA for diagnosis and, more importantly, that can predict disease aggressiveness and help guide treatment decisions," said Dr. Chinnaiyan, director of the Michigan Center for Translational Pathology and professor of pathology, University of Michigan Medical School, Ann Arbor. "Our laboratory and others have been looking for genomic, proteomic, and transcriptomic alterations as strategies to identify such biomarkers. Analyzing differences in metabolite profiles in a global fashion complements these 'omic' studies by concentrating on the small molecules that are generated in the context of their alterations.

"Our study provides proof of principle that metabolomic profiling can be used to measure metabolites in clinical samples in an unbiased fashion, and we believe the findings demonstrate that it has significant potential to contribute toward improved understanding of tumor biology, identification of novel biomarkers, and even advances in therapy," he told Urology Times.

Analysis of an initial set of prostate tissue samples showed sarcosine was markedly elevated in 79% of 14 metastatic prostate cancer specimens and in 42% of 12 clinically localized prostate cancer samples, but was undetectable in all 16 benign prostate tissue specimens, which represented adjacent tissue in men with biopsy-positive cancer. These findings were validated in an independent set of 89 prostate specimens in which the sarcosine level was found to be significantly higher in cancerous versus benign prostate samples and higher in the metastatic prostate cancer samples than in those from men with clinically localized prostate cancer.

With interest in exploring the potential of sarcosine as a noninvasive biomarker, researchers subsequently investigated whether their intriguing findings could be replicated using urine samples. Comparing biopsy-positive and -negative men, most of whom had a PSA level >4.0 ng/mL, they found the sarcosine level was significantly higher in the samples from the biopsy-positive patients. Considering men with a PSA in the range of 2.0 to 10.0 ng/mL, sarcosine was better able to discriminate the positive and negative biopsy groups than PSA.

In vitro studies were also undertaken to investigate the biological relevance of elevated sarcosine levels in prostate cancer. The results showed sarcosine was present in significantly higher levels in prostate cancer cell lines compared to benign prostate epithelial cells and correlated with cell invasiveness. Further, both the addition of exogenous sarcosine and blocking enzymes mediating sarcosine degradation in benign prostate epithelial cells induced a cancer-invasive phenotype. Conversely, invasiveness of prostate cancer cells was decreased by blocking enzymes involved in sarcosine generation.

"These findings indicate that sarcosine may be directly involved in cancer cell invasiveness and suggest that in addition to being a potential biomarker, sarcosine may be a target for the development of new therapeutic strategies," Dr. Chinnaiyan noted.

He and colleagues are working to validate their findings about sarcosine in independent sets of clinical samples provided by outside institutions. In addition, they will investigate other metabolites identified in their initial profiling with the hope of developing a panel of urinary biomarkers.

"Ideally, we would like to rely not only on sarcosine as we try to develop a clinically useful biomarker assay. Based on our research so far, it seems realistic to think we may be able to identify up to 10 compounds that can be used together to optimize prediction of prostate cancer aggressiveness," Dr. Chinnaiyan said.