Previously, we obtained gene expression profiles of primary prostate tumors resected from 33 African-American and 36 European-American patients. Analyzing the resulting datasets, we identified gene expression differences between African-American and European-American patients that portray the existence of a distinct tumor microenvironment for these two patient groups. Many of the differently expressed genes were immune-regulatory. Perhaps most unexpected was the presence of a distinct interferon signature in many of the African-American tumors. As now discovered by us, this signature is closely related to an interferon-related DNA damage resistance signature (IRDS) that predicts resistance to chemotherapy and radiation. The presence of IRDS in African-American tumors was confirmed in another patient cohort and is consistent with other publications that observed overexpression of STAT1 in tumors of African-American patients, a key gene of IRDS. Interestingly, IRDS has also been linked to the pro-metastatic epithelial to mesenchymal transition of cancer cells. Thus, IRDS may promote the metastatic process in certain circumstances. To further understand the possible origin of the detected immunobiological differences in tumors of African-American and European-American prostate cancer patients, we started with the evaluation of blood-based immune cell profiles of African-American and European-American prostate cancer patients and age-matched population-based controls with a focus of immune cell subpopulations that have immune-regulatory functions in cancer biology. It was the hypothesis of this project that immune cell subpopulations that have immune-regulatory functions in cancer biology are different in abundance in these two population groups. This project did not find that any of the investigated immune cell subpopulations (myeloid-derived suppressor cells, T- and B-cell-derived suppressor cells, dendritic cell subpopulations and polarized macrophages) was different in abundance comparing the blood samples from African-American and European-American prostate cancer patients. Currently we are investigating whether the development of this signature could be functionally linked to a germline variation that frequently occurs in men of African ancestry but is rather uncommon in men of European ancestry and encodes a novel interferon termed interferon lambda 4. The presence of an interferon gene signature in prostate tumors suggests a possible involvement of either a viral infection in disease pathology or the reactivation of endogenous retroviruses in the tumor microenvironment. This hypothesis was further supported by our finding that the interferon signature in prostate tumors coincides with a gene signature of retroviral activation. Thus, we started a project exploring the presence of viral infections and the reactivation of endogenous retroviruses in tumors from African-American and European-American patients. Aberrant expression of subgroup k human endogenous retroviruses (HERV-K) has been previously observed in prostate cancer. This subgroup is unique because it encodes sequences in the human genome containing open reading frames for near intact retroviruses. We hypothesized that HERV-K reactivation could serve as a non-invasive early disease detection marker for prostate cancer. We evaluated HERV-K gag mRNA expression in blood samples of African-American and European-American men using a case-control design via quantitative real-time PCR. Additionally, we examined HERV-K envelope protein expression in prostate tumors by immunohistochemistry. HERV-K envelope protein was commonly up-regulated in prostate tumors, but more so in tumors of African-American than European-American patients (61% versus 40%, P 0.01). Examining HERV-K gag expression in peripheral blood mononuclear cells (PBMC) from 294 cases and 135 healthy men, we found that the abundance of HERV-K gag message was significantly higher in cases than controls and was associated with increased plasma interferon gamma. Men with gag expression in the highest quartile had greater 12-fold increased odds (odds ratio = 12.87 [95% confidence interval 6.3-26.25]) of being diagnosed with prostate cancer than those in the lowest quartile. Moreover, our results showed that HERV-K expression may perform better as a disease biomarker in older than younger men (whereas the sensitivity of prostate-specific antigen (PSA) testing decreases with age) and in men with a smoking history compared with never smokers. We conclude that combining non-invasive HERV-K testing with PSA testing may improve the efficacy of prostate cancer detection specifically among older men and smokers who tend to develop a more aggressive disease. Future work will include RNAseq analysis of tumors from African-American and European-American patients using formalin-fixed paraffin-embedded tumor samples. These patients will have long-term follow up, allowing linkage of gene expression data to disease outcome (e.g., disease recurrence, survival). The work will be pursued in collaboration with Kevin Gardner, NCI/NIMHD. Additionally, we are profiling blood samples of African-American and European-American men in our NCI Case Control study for immune and inflammation markers and will test whether disease-associated inflammation marker are linked to exposure data that are collected through our survey. Recently, metabolomics emerged as a new discovery tool with the promise of identifying druggable metabolic dependencies of cancer cells. Novel and essential metabolomic pathways for tumor growth have been described for various human cancers and somatic mutations in metabolic enzymes were recently discovered. Research has also shown that resistance to chemotherapy can be metabolite-based. To date, very few studies have examined the prostate cancer metabolome. Arun Sreekumar, our collaborator, was the first to describe a metabolite signature for the disease. Because of our interest in the tumor biological differences between African-American and European-American prostate cancer patients, we started studying the metabolome of prostate tumors. In a pilot study, 12 tumors and 12 non-tumor tissues from African-American patients and the same number of tissues from European-American patients were analyzed. A total of 600 metabolites were identified. A pathway analysis of the metabolite-based differences between tumor and adjacent non-cancerous tissue revealed that cAMP signaling could be particularly important in the tumor biology of African-American patients. This finding is of interest because cAMP-dependent mechanisms can activate the androgen receptor in the absence of a ligand. Future research will include efforts to validate and refine the metabolome profiles of prostate cancer in African-American and European-American men using additional prostate tumors. The tumor metabolome data will allow us to select the metabolites that should be prioritized for its detection in body fluids. Our laboratory provided the Sreekumar laboratory at Baylor College of Medicine with 260 urine samples from 80 AA patients & 80 EA patients (each 1:1 low/high grade disease), 50 AA controls and 50 EA controls. These samples have been collected through the NCI Maryland Prostate Cancer Case-Control study. This biomarker discovery project is supported by a UO1 health disparity grant (PI: Sreekumar). All sample analyses are being conducted at the Sreekumar laboratory.
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