Tissue biopsies to diagnose prostate cancer are invasive and they often miss cancer cells, which limits their utility for diagnosis. Scientists from The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University, Baltimore, Maryland, got closer to reaching the goal of a noninvasive urine biopsy that detects cancer-specific changes in RNA and metabolites using RNA deep sequencing and mass spectrometry. The results of their study appeared in February 2020 in the journal Scientific Reports.1
“[This work] certainly is provocative in trying to discern different metabolic pathways that can be used to demonstrate cancer [vs] no cancer,” said Neal Shore, MD, medical director for the Carolina Urologic Research Center, Myrtle Beach, South Carolina, who was not involved in the study. “We could potentially use these types of metabolic pathways to test responses to [prostate cancer] therapeutics.” He thinks this test could also lead to personalized treatments for prostate cancer if particular gene alteration profiles are detected in urine samples.
Levels of prostate-specific antigen (PSA) have been used for more than 30 years for prostate cancer screening and diagnosis.2 However, PSA levels are not very specific. “PSA may not be the right way to detect whether a patient has prostate cancer because patients may have other diseases, such as prostatitis and benign prostate hyperplasia, where PSA levels are also elevated,” explained Ranjan Perera, PhD, associate professor in the department of oncology at Johns Hopkins University School of Medicine, and senior author of the study. “We wanted to take a different approach and look at urine,” he told Cancer Therapy Advisor.
Dr Perera said the research team’s idea was to use urine to capture the cells that shed from the prostate to the urethra. They collected 50 ml of urine in patients with prostate cancer and used samples collected from those with or without benign prostatic disease as controls.
They looked for cancer-specific gene signatures in the cells from each sample and found that 37 genes were upregulated in the prostate cancer samples. Known markers of prostate cancer, such as KLK3, PQBP1, TRIM22, and PSMA3 were increased in urine samples from prostate cancer patients relative to controls.
The cells in the tumor samples had higher expression of cancer pathways, including PI3K/AKT and NF-kB. Gene enrichment analysis showed that several other pathways were upregulated in urine from patients with prostate cancer, including pyruvate metabolism and the TCA cycle, which cancer cells use as a source of energy to divide rapidly.
The observed urine signature closely matched what can be found in prostate cancer tissue. The researchers used RNA-Seq data from 65 prostate cancer patients and healthy controls to compare the gene-expression profile of the exfoliated urine cells to the profile of cells in prostate tissue. They found that 34 of the 37 genes that were upregulated in urine cells were also increased in the prostate cancer samples.
“The major discovery here is that [we were] able to check for the presence or absence [of cancer],” said Dr Perera. The metabolite profile of the prostate cancer samples was largely distinct from profiles from both the normal tissues and those derived from patients with prostatitis and benign prostate hyperplasia — indicating that this urine biopsy could distinguish between those 2 conditions and prostate cancer.
This urine analysis might also be able to detect advanced prostate tumors. The researchers found that the subset of 37 upregulated genes could divide the cancerous samples into 2 distinct groups: A and B, with group B expressing significantly higher levels of PCA3. Higher expression of this marker has been linked to higher tumor aggressiveness,3 and its upregulation occurred despite similarities in tumor stage, Gleason score, and metastasis status between the 2 groups.
The urine analysis also revealed possible novel drug targets for prostate cancer. One of the metabolites that was highly increased in cancerous urine samples was glutamate oxaloacetate transaminase 1 (GOT1), an enzyme the authors found to be the main metabolite influencing alanine, aspartic acid, and glutamic acid metabolism, as well as the TCA cycle — both of which are critical for rapid division in cancer cells.
GOT1 was highly expressed in malignant prostate tumors. The authors also found abnormal levels of glutamate, the product of GOT1, in primary and metastatic prostate cancer samples compared with levels found in normal tissues. When the researchers knocked down GOT1 in the cancer cell lines LNCaP and PC3 using siRNA, they observed increased cell death in both, indicating that GOT1 could be a molecular target that could be manipulated in efforts to eliminate prostate cancer cells.
The results are encouraging, as they show the promise of unveiling cancer-specific changes using a noninvasive approach and identify pathways researchers can pursue to try to stop tumor growth — but a larger study is needed. “Further validation is always requisite in these types of analyses,” Dr Shore said. “If [the researchers are] able to further correlate and reproduce their findings, that would be of great value clinically.” Dr Perera emphasized that this is just the beginning: “If we wanted to use this as a test, we have to do large-scale clinical trials. That’s something that we are thinking about doing.”
Jeffrey R. Smith, MD, PhD, professor of medicine at Vanderbilt Medical University, Nashville, Tennessee, who was not involved in the study, agreed that the study results need to be reproducible. “This study nominates a biomarker signature using 2 powerful research approaches, but independent replication of the observations is a key next step,” he said. He pointed out that although the test seems to accurately distinguish between normal and prostate cancer samples, the authors must be able to replicate those findings in entirely independent data — for example, in the context of a prospective clinical screening trial. “Validation and establishment of sensitivity and specificity within a very well-powered independent sample is a logical next step,” Smith added.
The results of this study have been met with enthusiasm from patients who could possibly benefit from the use of such a test. “There are a lot of inquiries I’m getting right now of people telling me that they have prostate cancer, and they want to know when this test is going to be available,” said Dr Perera. “When I say that we have to do a bigger study, they ask if they can enroll in it.” But for now, the major barrier is study funding. Dr Perera is currently exploring industry collaborations to initiate a larger clinical trial.
- Lee B, Mahmud I, Marchica J, et al. Integrated RNA and metabolite profiling of urine liquid biopsies for prostate cancer biomarker discovery. Sci Rep. 2020;10(1):3716.
- Truong M, Yang B, Jarrard DF. Toward the detection of prostate cancer in urine: a critical analysis. J Urol. 2013;189(2):422-429.
- Merola R, Tomao L, Antenucci A, et al. PCA3 in prostate cancer and tumor aggressiveness detection on 407 high-risk patients: a National Cancer Institute experience. J Exp Clin Cancer Res. 2015;34:15.
This article originally appeared on Cancer Therapy Advisor