Abstract 4961: Molecular heterogeneity in diverse prostate cancer circulating tumor cell subsets

Purpose: Circulating tumor cell (CTC) enumeration or Androgen Receptor (AR) splice variant 7 expression from Epithelial Cell Adhesion Molecule (EpCAM) positive CTCs are predictive biomarkers for patients with prostate cancer. Recent reports suggest subpopulations of CTCs with decreased EpCAM expression may have greater invasive capacity or drug-resistant potential. These include cells with mesenchymal phenotypes that express N-cadherin, or MUC1, or stem cell populations that express CD133. Integrated molecular analysis across different CTC subpopulations has not been performed. We sought to compare the molecular profile of different populations of CTCs from the blood of patients with prostate cancer. Methods: A multiparametric flow cytometry assay was used to identify different populations of CTCs from patients with prostate cancer. We then employed an integrated CTC capture and analysis technology known as the VERSA (Versatile Exclusion-based Rare Sample Analysis) platform to in parallel or sequentially capture CTC subsets based on differential cell surface marker expression. Target populations of CTCs include those expressing EpCAM, N-Cadherin, MUC1 or CD133. mRNA was extracted on chip for comparison of gene expression profiles for the AR, multiple AR splice variants, downstream targets in the canonical AR signaling pathway Results Flow cytometry results showed both intra- and inter-patient heterogeneity in populations of CTCs from patients with prostate cancer. Using flow cytometry we are able to identify CTCs at numbers comparable.to those isolated in the VERSA. We identified putative tumor cells (AR+Cytokeratin+CD45-) that co-expressed Epcam with mesenchymal or stem cells markers. Patients differed in cell surface marker compositon with ranges of 0-40% Epcam+/N-Cad+, 10-27% Epcam-/Ncad+ and 5-10% Epcam +/Ncad-. Based on this data, we captured CTCs using both parallel and serial capture from the same blood sample iwth different capture antibodies including EpCAM, N-Cadherin and CD133. We identified full length androgen receptor gene expression from CTCs captured with EpCAM and N-Cadherin from the same patient sample. The gene expression patterns of the Epcam-/N-cadherin+ CTCs varies across patients with differential expression of PSMA, PAP and PSA. Conclusions Prior reports have identified different populations of CTCs in patients with advanced prostate cancer. Using flow cytometry and a CTC capture methodology, we identified significant heterogeneity in CTC sub-populations. We confirmed expression of the full length Androgen Receptor with gene expression analysis across subtypes. This heterogeneity in CTCs may represent populations of cells from different metastatic sites or with different invasive potential. Citation Format: Jamie M. Sperger, Erika Heninger, Jennifer L. Schehr, Haley E.F. Allen, Anupama Singh, Joshua M. Lang. Molecular heterogeneity in diverse prostate cancer circulating tumor cell subsets. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4961.