Fluorescent contrast agent efficacious for detecting prostate cancer

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A contrast agent that conjugates to receptors on prostate cancer cells, exhibits greater fluorescence when applied to cancerous prostate tissue as opposed to normal prostate tissue, according to researchers at the Institute for Ultrafast Spectroscopy and Lasers (IUSL) at The City College of New York (CCNY).

According to the study published in the April issue of Applied Optics, CCNY researchers conducted time-resolved fluorescence measurement and optical imaging studies that demonstrate the efficacy of the contrast agent Cytate as a fluorescence marker to detect prostate cancer.

“There is a need to develop a noninvasive technique for early detection of prostate cancer with higher accuracy and resolution,” said Robert R. Alfano, MD, distinguished professor of science and engineering and director of IUSL. Current noninvasive detection methods, which include digital exams, blood tests and ultrasound, have limited accuracy.

Cytate is dye-peptide conjugate consisting of Indocyanine Green, an FDA-approved near-infrared dye and a somatostatin receptor ligand. Somatostatin is a small cyclic neuropeptide that is believed to regulate the production of other hormones and perform an important role in cancer development. Previous studies had shown that Cytate could target somatostatin receptor-rich pancreas tumors in animal models because of its high affinity for the receptors, according to Alfano.

The researchers performed ultrafast time-resolved fluorescence polarization measurements on Cytate solution as well as on cancerous and normal prostate tissue sample that were stained with Cytate. In addition, they conducted fluorescence imaging of two small pieces of Cytate-stained normal and cancerous prostate tissue sandwiched between larger pieces of normal prostate tissue.

While the latter technique reveals which sections of tissue indicate presence of cancer, the former shows how the molecules of Cytate around the stained areas are behaving, explained Wubao Wang, MD, a senior researcher and project leader at IUSL.

The time-resolved fluorescence polarization study found the ratio for peak fluorescence intensity between the cancerous and normal tissue was around 3.57.

“Somatostatin receptors are over-expressed on cancerous cells relative to normal cells, so they absorb more of the Cytate,” Alfano noted. “Cytate essentially is a smart reagent that attaches to cancerous cells. It is an excellent contrast agent because its absorption and fluorescence spectra line the near-infrared tissue optical window (800 nanometers – 1 micron).”

Alfano added that the next step in the investigation is development of an optical probe called the “photonic finger” that can perform imaging of the prostate from inside the body. The project’s ultimate goal is to develop reliable cancer detection techniques based on imaging as an alternative to biopsies, he concluded.

The U.S. Army Medical Research and Material Command funded part of the study. A new grant awarded to Wang supports development of the “photonic finger” near-infrared scanning polarization imaging unit, according to a CCNY press release.