Development and validation of a standardized CELLSEARCH® assay for real-time monitoring of prostate-specific membrane antigen (PSMA) expression on circulating tumor cells
Presenter: Zoltan Simandi, PhD Session: Circulating Tumor Cells, Metastasis, and Dissemination Biology 1 Time: 4/19/2026 2:00:00 PM → 4/19/2026 5:00:00 PM
Authors
Steven M. Jones , Thai Bui , Damodara Gullipalli , Shemeeakah Powell , Margaret LaCava , Zoltan Simandi Menarini Silicon Biosystems, Huntingdon Valley, PA, PA
Abstract
BACKGROUND: Prostate-Specific Membrane Antigen (PSMA) is a critical biomarker whose dynamic expression dictates the clinical utility of emerging PSMA-targeted radioligand therapies. A major clinical challenge remains the lack of a standardized, highly sensitive, and minimally invasive method for PSMA expression monitoring. We addressed this by developing and validating a novel PSMA-specific assay integrated into the CELLSEARCH® platform, the only FDA-cleared system for CTC enumeration. METHODS: The PSMA assay utilizes the CELLSEARCH® platform’s immunomagnetic enrichment of EpCAM+ CTCs, followed by staining with fluorescently labeled anti-cytokeratin, anti-CD45, DAPI, and a high-affinity anti-PSMA antibody. Analytical validation was conducted using PSMA-positive (LNCaP, 22Rv1) and PSMA-negative (PC-3.9) cell lines spiked into healthy donor blood, assessing assay sensitivity, specificity, and recovery over a 96-hour sample preservation time in CellSave™ tubes. Captured CTCs are suitable for both platform imaging and subsequent molecular analysis. RESULTS: The customized PSMA assay demonstrated exceptional analytical performance, meeting all pre-defined criteria. The linear relationship between spiked and recovered PSMA-positive LNCaP cells was robust, achieving R^2 values >0.999 across all tested donors. High accuracy was confirmed by mean percent recovery for PSMA-positive cells, which ranged from 83.3% to 93.3% for spike levels of 10 to 1000 cells. Assay precision was also confirmed, with a Coefficient of Variation (CV) of 6.97% at the 10-cell spike level. In a preliminary clinical cohort (N=20) of PCa patients, the assay successfully detected PSMA+ CTCs. Enriched patient samples were then subjected to orthogonal flow cytometry analysis and cell sorting to provide independent confirmation of PSMA protein expression. Downstream molecular analysis of the sorted cells confirmed the presence of PCa-specific genomic alterations, providing molecular verification of the PSMA-positive CTC population. CONCLUSIONS: This novel, fully validated PSMA CTC assay provides a highly specific, and standardized liquid biopsy tool for PSMA detection. Its robust analytical performance establishes the utility of the platform in monitoring PSMA expression dynamics to inform therapeutic decisions in metastatic prostate cancer patients.
Disclosure
S. M. Jones, Menarini Silicon Biosystems Employment. T. Bui, Menarini Silicon Biosystems Employment. D. Gullipalli, Menarini Silicon Biosystems Employment. S. Powell, Menarini Silicon Biosystems Employment. M. LaCava, Menarini Silicon Biosystems Employment. Z. Simandi, Menarini Silicon Biosystems, Inc. Employment.
Cited in
Control: 4349 · Presentation Id: 10262 · Meeting 21436