Prospective analysis of prostate cancer (PC) circulating tumor cells (CTCs) to predict response to docetaxel (DOC) chemotherapy.

Abstract

100 Background: Taxane chemotherapy induces cellular microtubule stabilization (bundling) leading to mitotic arrest and apoptotic cell death. We recently reported that in castration-resistant PC, stabilizing of microtubules by taxanes inhibits ligand-induced androgen receptor (AR) nuclear translocation and activation of ARE-gene transcription (Cancer Res 2011;71:6019). This suggests the clinical activity of DOC results from inhibition of AR signaling. A pilot analysis of CTCs from 14 CRPC pts receiving taxanes revealed that predominant cytoplasmic AR and decreased total AR intensity each was associated with increased odds of response (P<0.001). We initiated a prospective trial to determine if CTC analysis could predict DOC response. Methods: Eligibility: Patients (pts) receiving DOC q21 days for CRPC with >5 CTCs determined by CellSearch. On cycle 1 d1 + d8, CTCs are isolated by ficoll tube separation and by CellSearch enrichment. Cells are stained for expression of prostate specific membrane antigen (PSMA), CD45, AR and acetylated tubulin (AcTub) as a marker of microtubule stabilization. AR localization and total fluorescence intensity, and AcTub intensity are quantitated by confocal microscopy and correlated with response to DOC using PCWG2 criteria. 72 pts are planned to provide 80% power to detect an association. Results: 28 of 72 pts have been prospectively enrolled to assess AR and AcTub as a biomarker of response. 20 pts have discontinued DOC. Day 1 samples were obtained from 27 pts and day 8 on 22 (5 pts on days 9 to 21). Immunofluorescence staining and evaluation of PSMA, CD45, and acetylated tubulin was performed successfully in 8 pts analyzed to date. CTCs can be identified in all pts. Cells are scored for AR and AcTub intensity (scale 1- 4) and AR nuclear vs cytoplasmic localization. Conclusions: Our results to date indicate that PC CTCs can be readily isolated from men receiving DOC chemotherapy in a multicenter fashion and assayed for AR localization and AcTub. Preliminary results suggest that monitoring AR subcellular localization and microtubule bundling in CTCs may predict clinical responses to DOC chemotherapy, warranting further study, including our prospective trial.