Next-Generation CTC Technology
Commercially available since 2004, CellSearch has open-channel capabilities built into the technology that allow users to include additional antibodies for further phenotypic specification, or for targeting a therapy (such as the identification of HER2 receptors). Janssen Diagnostics is collaborating with Massachusetts General Hospital (MGH) on the development of next-generation CTC technology that will isolate CTCs based on both positive and negative selection.
The recently published results from the SWOG S0500 study demonstrated the predictive value of CTC enumeration in patients with metastatic breast cancer as an indicator of the response to first-line chemotherapy and to guide the decision to change to an alternative chemotherapeutic regimen with the aim of improving overall or progression-free survival (PFS). Patients with elevated CTC counts prior to the start of therapy who subsequently showed low CTC counts three weeks later had a significantly better PFS and overall survival (OS) than did patients whose CTC counts did not decrease after the start of therapy.
The latter patients, however, did not benefit from an early switch to an alternative chemotherapy. The authors concluded that for these patients, participation in clinical trials and access to experimental therapies should be considered instead of another line of chemotherapy.
Negative selection of CTCs has particular advantages when analyzing the mRNA content of tumor cells, as “binding of anything to the surface of a membrane initiates signal transduction and starts changing the expression of certain molecules in a cell,” explained Dr. McCormack. Negative-selection methods also allow for single-cell sorting for NGS applications. In addition, Janssen Diagnostics has had success culturing CTCs, which can then be used to test for drug susceptibility or resistance.
David Miyamoto, M.D., Ph.D., instructor in radiation oncology, Massachusetts General Hospital, described the successive generations of microfluidic devices a team of bioengineers, biologists, and clinicians at MGH have developed to isolate CTCs from blood samples. Through improvements and modifications in design and materials, the chip-based device has evolved to be able to capture single CTCs as well as clusters of CTCs and to provide enhanced adherence across the chip surface.
MGH has tested its second-generation “herringbone CTC chip” in several pilot studies in various cancers including prostate, breast, and melanoma. Prototypes of a third-generation chip, the CTC iChip (the “i” stands for “inertial focusing device”), is in development in collaboration with Johnson & Johnson. These prototypes have been engineered to facilitate downstream assays. Instead of the CTCs remaining trapped on the device, as with previous versions of the chip, the CTC iChip releases the CTCs into solution.
“This allows for a range of applications and enables single-cell analysis,” noted Dr. Miyamoto. “You can isolate single cells” for RNA expression analysis, DNA analysis, or mutation analysis, for example.
A key advantage of the third-generation device is its use of both positive and negative selection for CTC isolation, according to Dr. Miyamoto. Negative selection is achieved by coating all of the non-CTCs in a sample with magnetic beads, a procedure that targets the non-CTCs for removal, leaving the CTCs unperturbed. Dr. Miyamoto is studying the use of the device as a prognostic tool in prostate cancer, and in particular to isolate CTCs in blood samples from patients with metastatic castration-resistant prostate cancer to assay for androgen receptor signaling prior to treatment with second-generation androgen receptor targeting agents.
“I think CTC technology is going beyond the enumeration and examination of molecular pathways that are activated or turned off as a result of therapies,” projected Dr. Miyamoto. “[It is becoming] a tool to guide targeted therapies and advance personalized medicine.”