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Single-Cell Proteomic Analysis Points to Role of Rare Cell Populations in Localized Prostate Cancer

NEW YORK — Individuals with localized prostate cancer may already have rare cell subpopulations typically linked to metastatic disease, a new single-cell proteomic analysis has found.

Prostate cancer affects about 12.6 percent of men over the course of their lives, according to the US Centers for Disease Control and Prevention. While most individuals with localized disease can be cured, disease does recur in a small number of patients.

As part of an effort to identify prognostic biomarkers for prostate cancer, researchers from Germany and Switzerland analyzed millions of cells from nearly five dozen men with localized prostate cancer. They analyzed those cells using single-cell mass cytometry and a clustering pipeline to identify different cell subpopulations within both tumor and adjacent normal tissue. As they reported Tuesday in Cell Reports Medicine, this analysis highlighted changes that occur in tumor tissue and high-grade disease as well as identified rare subpopulations linked to disease progress that may be present in localized disease.

"Of note is the fact that most prostate cancer patients differed mainly in rare cell types," co-senior author Peter Wild from University Hospital Frankfurt and colleagues wrote in their paper. "Based on our results, we hypothesize that cellular phenotypes associated with resistance to hormone ablation therapy are also found in treatment-naïve prostate cancer patients."

The researchers collected samples from a cohort of 58 prostate cancer patients that included 24 patients with grade II disease, 22 with grade III, and 12 with grade V disease. For 17 patients, they also collected and analyzed adjacent benign prostatic tissue. The single-cell mass cytometry analysis the researchers used relied on a panel of 36 metal-tagged antibodies that recognized surface markers, enzymes, transcription factors, and markers of functional readouts. In all, they analyzed more than 1.67 million cells.

The researchers then fed their data into the Franken computational pipeline, an unsupervised, single-cell clustering approach they developed. Franken identified 55 different cell clusters, which the researchers organized in a set of 33 metaclusters, consisting of 14 epithelial, 16 immune, one stromal, and one endothelial cell clusters as well as a cluster lacking most markers in the panel.

This set, the researchers said, reflects the main cell-type compartments in the prostate. Luminal cells, for instance, were the most abundant cell type, followed by T cells.

There was, the researchers noted, overlap in the cell phenotypes found among tumor and associated benign tissue, though they diverged in their immune landscape and in rare phenotypes present. Two T cell clusters — dubbed TC03 and TC04, representing apoptotic and proliferating T cells, respectively — were enriched among tumor samples, as were two macrophage clusters.

However, they also uncovered differences. For instance, prostein-high phenotypes were depleted in tumor regions, particularly in high-grade tumors even as compared to intermediate-grade ones. They additionally noted that intermediate-grade and high-grade tumors are more similar to each other than to their associated benign tissue, suggesting that high-grade tumors develop from intermediate-grade ones.

They additionally noted that two phenotypes enriched in high-grade patients express CD15, which is involved in cell adhesion and migration and has been implicated in other tumor types as having stem-like potential, suggesting it could be a marker of aggressive disease.

Meanwhile, both AR-high/PSA-low cells and AR-low/PSA-low cells — phenotypes previously associated with castration-resistant disease after ADT or metastatic diseases — were present among patients with localized, hormone-naïve disease. This suggested to the researchers that these rare cells may be present even before treatment.

"The alterations to the epithelium and microenvironment should be further explored to guide development of new diagnostic and treatment paradigms for prostate cancer and to understand which cellular phenotypes in primary prostate cancer need to be detected and may change treatment decisions," the researchers added.