Abstract 3781: Expression of neuroendocrine markers in circulating tumor cells from patients with prostate cancer visceral metastases
Authors: Sperger Jamie M. , Singh Anupama , Niles David , Stahlfeld Charlotte N. , Beebe David J. , Lang Joshua M. 
Published: July 2017

Abstract
Purpose: Therapeutic resistance to Androgen Receptor (AR) targeted therapies in patients with Castration Resistant Prostate Cancer (CRPC) is complex and originates from a wide range of molecular alterations including AR point mutations, gene rearrangements and splice variant expression. An aggressive subtype of CRPC involves neuroendocrine de-differentiation that is often found in patients with visceral metastases. To evaluate neuroendocrine signatures in patients progressing on AR targeted therapies, we measured gene expression in circulating tumor cells (CTCs) as a minimally-invasive approach to examine putative resistance mechanisms to AR targeted therapies.
Methods: We utilized the VERSA platform, an integrated CTC capture and analysis technology, to capture CTCs using antibodies for EpCAM or TROP2 in parallel. mRNA was extracted on chip from live cells for comparison of gene expression profiles for markers of neuroendocrine de-differentiation (SYP, CHGA, GHGB, MYCN, NCAM) and the AR signaling pathway. Fixed PBMC were stained and imaged with fluorescence microscopy and CTCs were enumerated by defining CTCs as EpCAM or TROP2 captured, intact nuclei, negative for CD45/CD11b/CD14/CD34 and cytokeratin positive. Synaptophysin or Chromogranin A protein expression was quantified in individual CTCs and compared to tumor biopsy results where available.
Results: Expression of the Synaptophysin (SYP) gene was found in 39% of the patients in our initial 18 patient cohort. These patients could be split into two groups. Group 1 patients had low AR expression with minimal detection of AR target genes. Of these four patients, three had visceral metastases. Group 2 patients had high levels of AR expression including expression of the splice variants ARV7 and ARV9, and robust expression of KLK3 (PSA) and PSMA. Of these three patients, two had visceral metastases. Subsets of the patients in both groups also exhibited expression of genes identified in neuroendocrine prostate cancer including Chromogranin B, MYCN, and NCAM. A subset of the patients tested for gene expression are being screened for CTC detection of protein markers of neuroendocrine phenotypes including Chromogranin A and Synaptophysin.
Conclusions: We report the first identification of neuroendocrine gene expression signatures in CTCs from patients with CRPC experiencing disease progression on advanced AR targeted therapies. These signatures may serve as predictive biomarkers of resistance to AR targeted therapies. Future studies will evaluate these signatures in prospective clinical trials.
Citation Format: Jamie M. Sperger, Anupama Singh, David Niles, Charlotte N. Stahlfeld, David J. Beebe, Joshua M. Lang. Expression of neuroendocrine markers in circulating tumor cells from patients with prostate cancer visceral metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3781. doi:10.1158/1538-7445.AM2017-3781