Abstract 454: Transferrin receptor identifies a novel circulating tumor cell population in patients with pancreatic cancer with a unique metastasis-associated molecular signature
Authors: Halima Ahmed , Zhang Jiaren , Galletti Giuseppe , Ocean Allyson J. , Giannakakou Paraskevi 
Published: August 2019

Abstract
Pancreatic Ductal Adenocarcinomas (PDAC) is the fourth most common cancer, expected to be the second leading cause of cancer mortality by 2030. Most PDAC patients are diagnosed with metastatic disease, with dismal prognosis of less than 1% 5-year survival. A major challenge in PDAC treatment is the absence of actionable molecular targets and the scarcity of available tumor tissue impeding molecular understanding of PDAC progression. Circulating Tumor Cells (CTCs) provide an easily accessible source for tumor tissue. CellSearchTM is the only FDA-cleared platform for CTC isolation based on positive selection of EpCAM+ cells. However, this method performs poorly in PDAC failing to show any prognostic relevance, likely due to EpCAM down-regulation during epithelial-to-mesenchymal transition (EMT), which precedes metastasis. To overcome this limitation, we tested Transferrin Receptor 1 (TfR) in the identification and isolation of CTCs from PDAC patients. TfR is a cell surface protein that mediates iron uptake, is overexpressed in multiple tumors with sustained expression throughout EMT, making it a suitable candidate for CTC isolation. To test this hypothesis, we first assessed TfR expression in a panel of 9 human PDAC cell lines, and we observed that TfR was expressed in 9/9 (100%) in contrast to 6/9 (66.7%) being EpCAM positive. No TfR expression was detected in healthy donor and PDAC patients’ PBMCs. To assess the performance of TfR in CTC identification and isolation from the peripheral blood of PDAC patients, we collected samples from 37 PDAC patients with stage 4 disease, enriched CTCs by negative CD45 depletion (RossetteSepTM) and subsequently stained live CTCs with TfR, EpCAM, and CD45. CTCs were defined as CD45- cells, positive for TfR+ or EpCAM+. We observed that the number of TfR+ CTCs (median: 148, range 2-4182) was significantly higher than EpCAM+ CTCs (median: 68, range 0-1552) within the same patient and across different patients (P-value 0.007). In addition, serial sampling at baseline (chemotherapy-naïve) and at disease progression from 5 PDAC patients revealed that TfR+CTC enumeration correlated with disease progression radiologically and/or CA19-9 (PDAC tumor marker) levels. In contrast, there was no correlation between the number of EpCAM+CTCs and clinical outcomes.
RNA-Sequencing of isolated pools of TfR+ or EpCAM+ CTCs, followed by gene set enrichment analysis, revealed significant enrichment in oncogenic pathways, such as EMT, G2M, MYC and KRAS in TfR+ CTCs as compared with EpCAM+ CTCs. Taken together, our results reveal that TfR identifies a clinically relevant CTC subpopulation which correlates with disease progression and is molecularly distinct. Ongoing studies are focused on the function of TfR in disease progression and the potential use of TfR+ CTC molecular profiles in personalized PDAC treatment.
Citation Format: Ahmed Halima, Jiaren Zhang, Giuseppe Galletti, Allyson J. Ocean, Paraskevi Giannakakou. Transferrin receptor identifies a novel circulating tumor cell population in patients with pancreatic cancer with a unique metastasis-associated molecular signature [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 454.