We are speaking with Michael J. Powell, PhD, CChem, MRSC, the chief scientific officer of California-based DiaCarta Inc, a genomics and personalized diagnostics company. They are developing an assay called ColoScape, which can be used for early detection of colorectal cancer, as well as monitoring for disease recurrence. He presented data from a validation study conducted by DiaCarta on the ability of the assay to detect mutations in tumor biopsies and plasma from patients with colorectal cancer at the International Conference on Molecular Targets and Cancer Therapeutics, which was held in October in Philadelphia and sponsored by the American Association for Cancer Research.
—Interviewed by Anna Azvolinsky
Cancer Network: Can you describe the ColoScape test, how it works, and its potential use in the clinic?
Michael J. Powell: ColoScape is basically a real-time PCR assay for the detection of colorectal cancer driver and resistance mutations in DNA, obtained either from a patient’s tumor biopsy or in their biological fluids such as blood or stool. The initial indication for ColoScape is going to be for monitoring disease recurrence after diagnosis and treatment of colorectal cancer. We can use this assay to monitor for disease recurrence and for the development of any resistance mutations during therapy.
Cancer Network: Can you tell us about the study that you presented at this recent meeting? What were the results?
Michael J. Powell: Yes, the study was a validation study of the assay in tissue biopsy samples and plasma DNA taken from colorectal cancer patients. The study was an analytical validation of the sensitivity and the specificity of the assay for all of the mutations that we have. We found that both were high—greater than 95% sensitivity for detection of colorectal cancer—and we could even detect early adenomas as well, which is quite interesting. We could potentially use this assay as a screening assay, but our initial indication that we are developing is for monitoring after surgery or after therapy.
Cancer Network: How else has this assay been tested, other than the study you just discussed?
Michael J. Powell: The other studies were done with various other clinical samples we had obtained. An extensive study was conducted from the researchers that had developed the assay, who we licensed the assay from, in stool samples. More than 500 stool samples from patients have been analyzed. Then we did a test with tissue samples that we had obtained from various different clinical sites, and also some liquid biopsies and plasma samples.
Cancer Network: Are there upcoming trials with this assay that are in the works to validate it further?
Michael J. Powell: Yes. We have big plans for the assay. We have a couple of big trials going on in Europe. We have a big study that is going to be conducted in Florida. We are also looking at China to do a large study and to get Chinese approval.
Cancer Network: There are tests that are being developed to detect new mutations in circulating tumor DNA that may be a sign of disease resistance and/or recurrence. Can you talk about what differentiates ColoScape? How is it similar or different from other DNA-based assays?
Michael J. Powell: ColoScape is unique because it has special chemistry that we utilize that allows for high sensitivity and detection on standard machines that are already present in every laboratory. We have xeno nucleic acid, and these are modified probes—modified DNA molecules—that bind to and inhibit amplification of wild-type sequences, so that we only amplify mutant sequences. This is a very sensitive method for detecting mutant DNA in plasma samples. There is a large excess of wild-type DNA in blood samples, and we actually eliminate that by blocking the wild-type DNA from being amplified. It’s a very simple protocol. We don’t have to use any sophisticated instrumentation, we just take the sample and put in the xeno DNA, and block the wild-type DNA and amplify the mutant DNA. We can detect very low frequency mutations and that is why our sensitivity is so high.
Cancer Network: Thank you so much for joining us today, Michael.
Michael J. Powell: Thank you very much.