Drug tracking marks scientific "first"

By ELLEN GOLDBAUM
News Services Editor

Scientists at UB and Tulane University have, for the first time, optically tracked in real-time the pathway of one of the most widely used cancer drugs linked to a peptide hormone carrier as it is being taken up by a human breast-cancer cell.

The research, published in the current issue of Proceedings of the National Academy of Sciences, demonstrates the power and utility of new photonic materials developed at UB that have allowed scientists this first-ever, bird's-eye view of the cellular pathway of the chemotherapeutic agent.

The compound used was AN-152, a combination of the commonly prescribed chemotherapeutic agent doxorubicin, which is linked to an LH-RH (luteinizing hormone-release hormone) analog that targets only cells with LH-RH receptors on them. This makes the compound specific to cancers of the ovary, breast, cervix and prostate, and possibly others as well.

AN-152, now in animal trials, was first synthesized by Andrew V. Schally, 1977 Nobel laureate in medicine and director of the Endocrine, Polypeptide and Cancer Institute of the Veterans Affairs Medical Center in New Orleans, and Attila Nagy, associate professor of medicine at Tulane University School of Medicine. Both are co-authors on the paper.

The UB researchers were able to track this compound through a human breast-cancer cell by combining it with a fluorescent probe (C625) synthesized in the laboratory of Paras Prasad, SUNY Distinguished Professor in the Department of Chemistry in the College of Arts and Sciences. Prasad also is executive director of UB's new Institute for Lasers, Photonics and Biophotonics, where the experimental work was done.

These findings provide researchers with evidence that AN-152 directly enters cancer cells, accumulates in the nucleus and associates with the cell's chromosomes, which had been suspected but never proven.

According to the researchers, this significantly increases the safety margin of doxorubicin, potentially allowing for much lower doses to be used and greatly reducing the risk of side effects in patients.

"While the mechanism of action of many cytotoxic compounds is known, we have never been able to optically track a compound to a particular tumor site," said Schally. "The UB researchers specifically followed the track of this cytotoxic radical in the cell, which is very important."

The research paves the way for similar studies with other fluorescent probes to determine how cancer cells take up other chemotherapeutic agents.

"Eventually, we will be able to quantify exactly how much of a particular drug is being taken up by a cancer cell," said Prasad.

"This was a tremendous step forward," said Charles Liebow, co-author and professor of oral and maxillofacial surgery. "The C625 allowed us to follow the agent and to see exactly where and how it is working."

C625 is just one of many new photonic materials that have been developed at the institute. These materials exhibit strong two-photon absorption, an unusual phenomenon where a molecule absorbs two photons of light simultaneously if pumped with light of sufficiently high intensity. Until recently, most two-photon materials have been capable only of a very weak absorption of two photons, making them inadequate for most applications.

The materials developed by Prasad's team over the past four years have exhibited strong multiphoton absorption, as well as strong fluorescence emission.

For this research, the UB scientists custom-designed C625, which absorbs two photons of light at 800 nanometers, so that it can be used with the laser-scanning microscope.

The material's two-photon capabilities allow the scientists to use infrared light-not damaging ultraviolet light-to cause C625 to fluoresce.

"The advantage of using two-photon laser-scanning microscopy is that the short pulsed near-infrared light used to excite the C625 avoids injury to the cell, thus allowing repeated examination of living cells," explained E.J. Bergey, research assistant professor of chemistry and a member of Prasad's team.

Generation of the image is done by optical sectioning of cells treated with AN-152-C625, where a beam of light from the microscope is focused on different planes of the cell, one at a time.

"When the AN-152-C625 is outside of the cell, we do not see it because the concentration is too low," said Prasad. "But you begin to see it accumulate on the cell, then in the cytoplasm and finally in the nucleus, with the whole process taking about half an hour."

Other co-authors are Xiopeng Wang, doctoral candidate; Mohammed Al-Nuri, postdoctoral researcher, and Haridas E. Pudavar, postdoctoral researcher, all in the Department of Chemistry; Linda J. Krebs, a doctoral student in the Department of Physiology and Biophysics in the School of Medicine and Biomedical Sciences and the Department of Oral Biology in the School of Dental Medicine, and Saswati Ghosal of Laser Photonics Technologies, Inc.