Clinical Application: Identification of folate receptor alpha (FRA) positive CTCs for patient stratification
Key Words: CTCs, ApoStream®, patient stratification, protein expression, NSCLC
Background: This study was initiated to explore the utility of using biomarker expression levels in CTCs as a means of patient selection for treatment in a clinical trial. The drug being examined is a monoclonal antibody that binds to folate receptor alpha (FRA), which is estimated to be present in up to three-quarters of patients with adenocarcinoma of the lung, a form of non-small cell lung cancer (NSCLC). ApoCell was contacted to develop an assay using our proprietary antibody-independent CTC capture device, ApoStream®, which will be used as a screening mechanism for inclusion into an ongoing trial with this drug – patients who strongly express the drug’s target represent an ideal test group.
Methods: Blood was collected from 14 NSCLC patients and processed for CTC enrichment by ApoStream®. For the first 9 patients, CTCs were also enriched by the CellSearch® CTC kit, and CK+/CD45-/DAPI+ cell counts from the two systems compared. For the remaining five patients and 15 healthy donors, CTCs were enriched by ApoStream® alone. The cells enriched by ApoStream® were placed on glass slides and stained for cytokeratin (CK), CD45, DAPI, and FRA. The stained cells were then analyzed using Laser
Scanning Cytometry (LSC) for the following: total number of CTCs (cells exhibiting a DAPI+/CK+/CD45- phenotype) that are positive for FRA, the total number of CD45+ cells expressing FRA, and the mean fluorescence intensity (MFI) of the biomarker in both CTCs and CD45+ cells.
Results:
 |
 |
 |
| Figure 1. Head to Head Comparison. CellSearch® enrichment and identification of CTCs from NSCLC patients was low (mean: 1.56, median: 0); ApoStream enriched significantly higher counts (mean: 163, median: 81). |
Figure 2. FRA Analysis. ApoStream® enriched CTCs from all 5 additional NSCLC patients, and no CTCs from 15 tested healthy donors. FRA was found to be expressed on a subset of CTCs (range: 8.1% – 32.8%) from each patient, but not in the CD45+ leukocyte population, indicating FRA may serve as a suitable cancer specific marker for targeted therapies. | Figure 3. Representative LSC Images of CTCs. ApoStream® enriched CTCs stained with CTC phenotype markers and FRA. Yellow arrows in each channel indicate identified CTCs (cells possessing a CK+CD45-DAPI+ phenotype) that are expressing FRA. |
Impact: : ApoCell has demonstrated the feasibility of using folate receptor alpha expression (or the expression of other similar targets) on ApoStream®-enriched CTCs to inform patient selection strategies in a clinical trial.
Reference: Davis DW, et al. “Antibody-Independent ApoStream™ Technology Isolates Folate Receptor Alpha (FRA) ApoCell, Inc.
Positive Circulating Tumor Cells from Blood of Non-Small Cell Lung Adenocarcinoma Patients.” ePub Abstract, ASC0 2012.
Precision for Medicine is part of the Precision Medicine Group, an integrated team of experts that extends Precision for Medicine’s therapeutic development capabilities beyond approval and into launch strategies, marketing communication, and payer insights. As one company, the Precision Medicine Group helps pharmaceutical and life-sciences clients conquer product development and commercialization challenges in a rapidly evolving environment.
