On The Horizon – Detecting the Undetectable In Prostate Cancer Recurrence – A New Zero for PSA Tests
ByA team of Northwestern University researchers, lead by Chad A. Mirkin, PhD, George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences, professor of medicine, professor of materials science and engineering and a member of President Obama’s Science and Technology Advisory Council has found that an extremely sensitive tool based on nanotechnology can detect previously undetectable levels of prostate-specific antigen (PSA) in men who have undergone a radical prostatectomy.
After the surgical removal of the prostate gland, men typically have PSA levels that are undetectable when measured using current conventional diagnostic tools. According to Mirkin, this new tool which they just developed, is 300 times more sensitive than current commercially available PSA tests. This new technology will allow doctors to easily and quickly detect very low levels of PSA, even immediately after surgery. It is thought that this ability to will enable doctors to diagnose men with a prostate cancer recurrence years earlier than is currently possible, allowing earlier treatment of the recurrence before the cancer spreads.
Mirkin said, “We have defined a new zero for PSA,” “This level of sensitivity in detecting low concentrations of PSA will take the blinders off the medical community, especially when it comes to tracking residual disease.”
William J. Catalona, MD, professor of urology at the Feinberg School and director of the Clinical Prostate Cancer Program at the Lurie Cancer Center, who was the first researcher to demonstrate that the PSA test, a simple blood test, could be used as a screening tool for prostate cancer said about this new technology, “This new PSA assay may alter the management of patients who have been treated with surgery for prostate cancer. Studies have shown that postoperative radiation therapy given early to patients with adverse pathology, called adjuvant radiation, reduces the recurrence rate and improves survival. Because the ‘nano-PSA assay’ is more sensitive than the current commercially available PSA tests, it may allow physicians to target adjuvant radiation for patients destined to have a life-threatening tumor recurrence.”
In the case of prostate cancer recurrence following primary surgical treatment, men with detectable but non-rising PSA levels could be given the reassurance that their cancer will not recur, eliminating the type of secondary damage (increased worry) that many critics of early PSA testing use as a reason to suspend screening. And, more importantly, for those men with increasing levels of PSA post surgery early detection allows earlier treatment and saved life.
It is also possible that this type of tool can be used to evaluate the effectiveness of post-operative treatments (radiation, hormone therapy or chemotherapy) by more accurately monitoring the PSA levels.
“The first route to a new therapeutic is a good diagnostic tool, and that’s what we have here,” said Mirkin. This bio-barcode assay, or a variant of it, could be a commercial tool in as little as 18 months. The technology is there. Now it’s a business decision.”
This study was only a pilot study that looked at serum samples from 18 post-prostatectomy patients collected over the course of a number of years. The researchers were able to reliably and accurately quantify PSA values at less than 0.1 nanograms per milliliter, the current clinical limit of detection for commercial assays. The lower limit of detection for PSA using this new tool, a bio-barcode assay is approximately 300 times lower than the 0.1 nanograms per milliliter level.
The Northwestern team is now conducting a similar retrospective study of 260 patients and eventually plans to do a large prospective study.
Their new tool is based on gold nanoparticle probes, decorated with DNA and antibodies that can recognize and bind to PSA when present at extremely low levels in a blood sample. A magnetic microparticle, outfitted with a second antibody for PSA, also is used in the assay. When in solution, the antibody-functionalized particles “recognize” and bind to PSA, sandwiching the protein between the two particles.
It is conceivable that this new technology can also be an effective on-going tool in evaluating the effectiveness of the post primary treatments, radiation, hormone therapy and chemotherapy in a man as he undergoes the treatment process. Additionally, there has also been a suggestion that this type of technology might also be used to improve medical diagnostics and early cancer detection in many other cancer types, not just in prostate cancer.
The study was published in the Proceedings of the National Academy of Sciences (PNAS). Mirkin and C. Shad Thaxton, MD, PhD, assistant professor of urology in the Feinberg School of Medicine.
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