Medically Translatable Quantum Dots and Cancer Microenvironment Sensitive Molecular Probes

Abstract

Fluorescence imaging is a powerful tool for screening of cancer with superior sensitivity, non-invasion, real-time visualization with relatively simple and potable instrumentation and multiplexing ability of the targets of interest. The detection of colon cancer using endoscopy is widely used but the interpretation of the diagnosis is based on the clinician's naked eye. This is subjective and can lead to false detection. A rapid and accurate molecular fluorescence imaging technique was developed using antibody-coated quantum dots (Ab-QDs) sprayed and washed simultaneously on colon tumor tissues inside live animals, subsequently excited and imaged by endoscopy. QDs were conjugated to matrix metalloproteinases (MMP) 9, MMP 14 or carcinoembryonic antigen (CEA) Abs with zwitterionic surface coating to reduce non-specific bindings. The Ab-QD probes can diagnose tumors on sectioned mouse tissues, fresh mouse colons stained ex vivo and also in vivo as well as fresh human colon adenoma tissues in 30 minutes and can be imaged with a depth of 100 μm. The probes successfully detected not only cancers that are readily discernible by bare eyes but also hyperplasia and adenoma regions. Sum and cross signal operations provided post-processed images that can show complementary information or regions of high priority. This multiplexed quantum dot, spray-and-wash, and endoscopy approach provides a significant advantage for detecting small or flat tumors that may be missed by conventional endoscopic examinations and bestows a strategy for the improvement of cancer diagnosis. To improve accuracy of detection, ratiometric probe based on fluorescent molecular dye are developed which can be activated by λ-glutamyltranspeptidase(GGT), overexpressed in many cancers including colorectal cancer. Ratiometric probes were synthesized with cresyl violet (CV) and glutamic acid (Glu) through peptide bond thus they can be shifted their optical properties by GGT activity. CV-Glu probe applied to human colon cancer cells, flesh mouse colon tissue and human colon adenoma tissues. Ratiometric imaging of CV-Glu probes showed tumor regions rapidly and accurately within 10 min. Single administration of CV-Glu probes and MMP14Ab-AgInS2/ZnS QD probes respectively can be missed tumor due to cancer inhomogeneity but sequential applying of each probe was complementary and more accurate. It could be due to that each probe work in different ways to their targeted proteins respectively. It was also demonstrated that each probe showed unsimilar distribution originated from the specific locations of expression in macroscopic view. Toxicity evaluation showed topical “spray and wash” method of MMP14 Ab-QD probes and CV-Glu probes is suitable for clinical application.