In January 2016, Exosome Diagnostics, Inc. of Cambridge, Massachusetts launched the ExoDx™ Lung(ALK) test which is considered the first CLIA-validated exosome-based clinical liquid biopsy test. The test isolates and analyzes exosomal RNA (exoRNA) contained in a blood specimen. The test detects EML4-ALK fusion transcripts in the plasma of lung cancer patients (NSCLC) whose primary tumors carry this type of mutation.
The ExoDx™ Lung(ALK) assay is considered an important milestone in the application of exosome-based biomarkers to precision medicine, especially in the areas of companion diagnostics and targeted therapies. The test is designed to identify the echinoderm microtubule-associated protein-like 4 (EML4)- anaplastic lymphoma kinase (ALK) gene fusion, which can predict response to ALK inhibitor therapies.
The EML4-ALK gene contains an abnormal configuration of DNA, whereby the EML4 gene is fused to the ALK gene. This abnormal gene fusion leads to the production of a protein (called EML4-ALK) which often appears to promote and maintain the malignant behavior of the cancer cell. The EML4-ALK fusion has been found in a small minority of NSCLC patients. These patients with the EML4-ALK fusion often respond to ALK inhibitor drugs, like crizotinib, which is an FDA-approved drug therapy that targets the EML4-ALK fusion gene.
Exosome Diagnostics has developed an innovative technology to isolate in a single step both exosomal RNA, which represents the living cellular process and cell-free DNA (cfDNA), which comes exclusively from dying cells. Using exoRNA analysis enhances the diagnostic sensitivity over using cfDNA alone and also provides a comprehensive insight into the biology of a tumor.
Summary of the ExoDx™ Lung(ALK) assay procedure
- Plasma specimen is collected from the patient.
- Plasma is spun in the exoRNeasy system (disposable spin columns). The columns serve to concentrate and purify the exoRNA from the extracellular vesicles (exosomes) contained in the plasma.
- The exoRNA bound to the RNeasy column is eluted from the column.
- The exoRNA transcripts in the eluate are quantified via reverse transcription, quantitative polymerase chain reaction (RT-qPCR). This process converts the RNA into DNA for identification and quantification of the EML4-ALK fusion transcripts. The test can detect five distinct EML4-ALK fusion transcripts.
The detection of the mutations for five distinct EML4-ALK fusion transcripts has been shown to account for up to 85% of the known EML4-ALK fusions.
Comments on the assay
The exoRNeasy System: This system used in the ExoDx™ Lung(ALK) test is made available by Qiagen as the exoRNeasy serum/plasma Maxi Kit. These kits use a simple spin-column method to isolate exosomes and other extracellular vesicles out of serum, plasma, cell culture supernatant, and other biological fluids. This procedure allows for concentrating the extracellular RNA derived from the exosomes contained in plasma, serum, or other biological fluids.
