Antibody-independent ApoStream technology isolates folate receptor alpha (FRA)–positive circulating tumor cells from blood of non-small cell lung adenocarcinoma patients.

e21028 Background: The ability to enrich and interrogate circulating tumor cells (CTCs) from blood may allow for the analysis of metastatic dissemination and potential use of CTCs as surrogates for monitoring drug efficacy. We developed ApoStream, a dieletrophoresis field-flow fractionation based platform, for antibody-independent CTC isolation. We demonstrated that ApoStream successfully isolates non-small cell lung adenocarcinoma (NSCLC) CTCs that express Folate Receptor alpha (FRA), a GPI-anchored receptor, which has emerged as a cancer biomarker and potential therapeutic target in multiple cancer types. Methods: ApoStream technology was used to enrich CTCs from NSCLC patients’ blood. CTC enrichment by ApoStream was compared to that of the FDA cleared CellSearch CTC kit. A multiplexed immunofluorescent assay was developed to enable CTC enumeration (Cytokeratin+/CD45-/DAPI+ cells) and analysis of FRA expression (detection by murine antibody clone 26B3) using single cell quantitative laser scanning cytometry (LSC). Results: In a side-by-side comparison with the CellSearch CTC kit, ApoStream isolated significantly higher numbers of CTCs in 9 metastatic adenocarcinoma NSCLC patients (Apostream: mean =139, range 3-487 per 7.5 mL of blood, versus CellSearch kit: mean =2, range 0-8 per 7.5 mL of blood, n= 9, p=0.041). All patients were found to be CTC-positive by ApoStream, while only 3 of 9 (33%) patients were CTC-positive based on the CellSearch kit. LSC analysis demonstrated that 8-33% of all CTCs isolated expressed FRA and that FRA expression was confined to CTCs only. No false positive CTCs and no FRA-expressing cells were isolated by ApoStream from normal donor blood (n=15). Conclusions: All NSCLC adenocarcinoma patients analyzed had FRA-positive CTCs, suggesting that FRA may play a key role in metastasis and that screening of patients with the ApoStream CTC isolation system may identify patients who could benefit from FRA-targeted therapy.