Abstract 1713: Transferrin receptor 1 (TfR) as marker for circulating tumor cells (CTCs) identification in NSCLC
Authors: Galletti Giuseppe , Kallergi Galatea , Saxena Ashish , Aggouraki Despoina , Stournaras Christos , Georgoulias Vassilis , McGraw Timothy E. , Altorki Nasser , Giannakakou Paraskevi 
Published: July 2017

CTCs are used as a surrogate source of tumor material in solid tumors. Clinical applications of CTCs as liquid biopsy comprise the monitoring of molecular alterations during tumor progression and dynamic evaluation of molecular markers of treatment response. The FDA-cleared method to isolate CTCs in cancer patients (Cell Search) is based on positive selection of EpCAM expressing cells. However, this approach performs poorly in non-small cell lung cancer (NSCLC) as it identifies CTCs in only 7% of the subjects, failing to show any prognostic relevance.

Down-regulation/loss of epithelial markers to isolate (EpCAM) and identify (cytokeratin, CK) CTCs could in part explain the low CTC yield obtained in NSCLC with approaches based on epithelial markers expression. To overcome this challenge we used size-based CTC enrichment (ISET filters) from NSCLC patients’ peripheral blood. As a positive identifier of CTCs we used transferrin receptor 1 (TfR) which is a cell membrane-associated protein, that mediates intracellular iron uptake, and which is expressed at low levels in many normal tissues but over-expressed in cancer cells.

We first analyzed TfR protein expression by immunofluorescence in a panel of NSCLC cell lines and in healthy donor leukocytes. While all NSCLC cells lines analyzed were positive for TfR expression, none of the leukocyte expressed the receptor. Moreover, TfR expression was detected also in EpCAM negative NSCLC cell lines. To determine the clinical applicability of this novel CTC identifier, we determined TfR expression in CTCs isolated from peripheral blood of 35 metastatic NSCLC patients using the ISET filter technology. The isolated CTCs were stained for TfR, CK, CD45 and DAPI. For each patient, one additional ISET filter was stained with Giemsa for morphologic analysis by a pathologist. By using the classic panel of CTC identifiers markers (CK+/CD45-/DAPI+), CTCs were identified in 4/34 (11%) patients, while by using TfR as positive identifier (TfR+/CD45-/DAPI+) CTCs were identified in 31/35 (88%) subjects. The morphologic review of Giemsa stained filters confirmed the presence of tumor cells in 28/34 (82%) samples [0-217 CTCs/sample]. Interestingly, patients with &gt; 6 TfR+ CTCs had a worse overall survival (OS) than patients with &lt; 6 TfR+ CTCs [p=0.048 Log Rank (Mantel-Cox)]. OS did not significantly differ using the same cutoff with CTCs defined based on CK or Giemsa staining.

Overall, our data indicate that TfR is a promising biomarker for the detection of CTCs in NSCLC CTCs, superior to CK or EpCAM. Our data also suggest that TfR may potentially identify CTCs subpopulations with a significant prognostic role in NSCLC. We are currently isolating TfR+ CTCs from early stage and metastatic NSCLC patients for further molecular characterization and determination of clinical significance.

Citation Format: Giuseppe Galletti, Galatea Kallergi, Ashish Saxena, Despoina Aggouraki, Christos Stournaras, Vassilis Georgoulias, Timothy E. McGraw, Nasser Altorki, Paraskevi Giannakakou. Transferrin receptor 1 (TfR) as marker for circulating tumor cells (CTCs) identification in NSCLC [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 1713. doi:10.1158/1538-7445.AM2017-1713