Abstract 3634: Molecular determinants of taxane activity using CTCs from CRPC patients
Authors: Sung Matthew S. , Gjyrezi Ada , Loftus Matthew , Lee Guang Yu , Diamond Elan , Mason Christopher , Bander Neil , Tagawa Scott , Nanus David , Kirby Brian , Giannakakou Paraskevi 
Published: August 2012

Abstract
Androgen receptor (AR) signaling drives castration resistant prostate cancer (CRPC) disease progression. The taxanes (TXN) represent the only class of chemotherapy agents that improve survival in CRPC. Our recent work revealed that TXNs work by blocking AR nuclear accumulation and signaling downstream of microtubule (MT) stabilization. Moreover, we showed that AR cytoplasmic sequestration in CRPC patients’ circulating tumor cells (CTCs) significantly correlated with clinical response to TXN therapy. Our data, suggest that TXN-induced blockade of AR nuclear accumulation partly underlies the clinical activity of TXNs in CRPC. Recently several AR splice variants, lacking the ligand binding domain, have been identified in CRPC. These variants are constitutively active in the nucleus and likely to be insensitive to current therapies targeting either ligand biosynthesis or ligand-receptor interactions. Currently, the role of AR splice variants on TXN chemotherapy response in CRPC is unknown. Our preliminary data in preclinical PC models suggest that certain AR variants depend on MTs for nuclear accumulation and are TXN sensitive while others are MT-independent and TXN-insensitive. In this study we are prospectively evaluating whether the presence of AR splice variants and the integrity of the MT-AR axis in CTCs can predict clinical response to TXN chemotherapy in CRPC. CTCs are captured by the geometrically enhanced differential immunocapture (GEDI) microfluidic device that uses PSMA-based immunocapture and size-selective cell transport for maximum specificity of CRPC-derived CTCs. We captured viable CTCs from CRPC patients (median 54 CTC/ml) and performed molecular and functional analyses. Comparison of CTCs captured by CellSearch or GEDI, using same day blood draw from 30 CRPC patients, revealed a 2-400 fold increase in CTC numbers with the GEDI. GEDI-capture of live CTCs allowed us to evaluate ex-vivo TXN sensitivity and determine drug-target-engagement (DTE) by MT bundling. CTCs isolated from docetaxel (DTX)-resistant CRPC patients did not show any evidence of DTX activity in this assay suggesting that it can be used to monitor patient's response in real time. In addition, we have miniaturized RNA sequencing (RNA-Seq) to enable molecular analyses of GEDI-captured CTCs. RNA-Seq of 50 GEDI-captured LNCap 86.2 cells spiked into 1 ml healthy donor blood, detected both the T868A AR point mutation and ARv567 splice variant. In an ongoing prospective clinical study, we are capturing CTCs from CRPC patients treated with TXNs and are evaluating the integrity of the MT-AR signaling axis, in relation to clinical response to therapy. Our CTC analyses include RNA-Seq for the detection of AR splice variants, alterations in tubulin isotypes and MT related proteins, and multiplex confocal microscopy of DTE and AR localization. These analyses are performed longitudinally and may identify biomarkers predictive of clinical TXN efficacy.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3634. doi:1538-7445.AM2012-3634