A nanosystem that enhances the visualization of tumors was described today in Nature Communications. According to scientists from Sanford Burnham Prebys Medical Discovery Institute (SBP), the platform achieves a fivefold increase over existing tumor-specific optical imaging methods.
The nanosystem utilizes quantum dots (QDs) and an "etchant" that eliminates background signals. The QDs are delivered intravenously, and some of them leave the bloodstream and cross membranes, entering cancer cells. Fluorescent signals emitted from excess QDs that remain in the bloodstream are then made invisible by injecting the etchant.
Xiangyou Liu, Ph.D., and Gary Braun, Ph.D., developed the method in the laboratories of Kazuki Sugahara, M.D., Ph.D., adjunct assistant professor at SBP and adjunct associate research scientist at Columbia University, and Erkki Ruoslahti, M.D., Ph.D., distinguished professor at SBP.
"The novelty of our nanosystem is how the etchant works," explains Braun. The etchant and the QDs undergo a cation exchange that occurs when zinc in the QDs is swapped for silver in the etchant. Silver-containing QDs lose their fluorescent capabilities, and because the etchant can't cross membranes to reach tumor cells, the QDs that have reached the tumor remain fluorescent. Thus, the entire process eliminates background fluorescence while preserving tumor-specific signals.
The method was developed using mice harboring human breast, prostate, and gastric tumors. QDs were actively delivered to tumors using iRGD, a tumor-penetrating peptide that 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 Ruoslahti's lab.
"Moving forward we will focus on developing our novel nanosystem to work with routine imaging tests like PET scans and MRIs. In our studies with mice, we use optical imaging, which isn't always practical for humans," Sugahara explains.