'Quantum Dots' enhance tumor imaging capabilities

Research published in the journal Nature Communications offers a proof-of-concept nanosystem that can markedly improve visualization of tumors. Results showed a five-fold increase over current tumor-specific imaging methods.

This new approach generates bright tumor signals by delivering “quantum dots” to cancer cells without any toxic effects. It was created by scientists at the Sanford Burnham Prebys Medical Discovery Institute (SBP). It was developed by Xiangyou Liu, PhD, and Gary Braun, PhD, in the laboratories of Kazuki Sugahara, MD, PhD, Adjunct Assistant Professor at SBP and Adjunct Associate Research Scientist at Columbia University, and Erkki Ruoslahti, MD, PhD, Distinguished Professor at SBP.

“Tumor imaging is an integral part of cancer detection, treatment, and tracking the progress of patients after treatment,” said Dr. Sugahara. “Although significant progress has been made in the last two decades, better and more sensitive detection, such as the method we are developing, will contribute to more personalized and potentially more effective interventions to improve the clinical outcomes of cancer patients.”

The new method utilizes intravenously administered quantum dots, or QDs, which are tiny particles that emit intense fluorescent signals when exposed to light. It also deploys an “etchant” to eliminate background signals.

After administration, some of the QDs exit the bloodstream, cross membranes, and enter cancer cells. Fluorescent signals emitted from the QDs that remain in the bloodstream are then rendered “invisible” by injecting the etchant.

“The novelty of our nanosystem is how the etchant works,” explained Dr. Braun.

The etchant and the QDs undergo a “cation exchange” when zinc in the QDs is swapped for silver in the etchant. Silver-containing QDs lose their fluorescent capabilities. Since the etchant cannot cross membranes to reach tumor cells, the QDs that have reached the tumor remain fluorescent. This process eliminates background fluorescence while preserving tumor-specific signals.

To develop the approach, researchers used mice that harbored human breast, prostate, and gastric tumors. QDs were actively delivered to tumors using a tumor penetrating peptide called iRGD, which activates a transport pathway that drives the peptide along with bystander molecules—in this case fluorescent QDs—into cancer cells. iRGD methodology was originally developed in Dr. Ruoslahti’s lab.

“To our knowledge, this is the first in vivo example of a background-destroying etchant being used to enhance the specificity of imaging,” said Dr. Sugahara. “We are encouraged that we were able to achieve a tumor-specific contrast index (CI) between five- and ten-fold greater than the general cut-off for optical imaging, which is 2.5.”

A new company is in the process of being formed to further develop the platform for human use.

“Moving forward, we will focus on developing our novel nanosystem to work with routine imaging tests like PET scans and MRIs,” Dr. Sugahara explained. “In our studies with mice, we use optical imaging, which isn’t always practical for humans.”

To read more about this study, click here.