Biocompatible Surface Coated Nano-Particles for Live-Cell Imaging and
Early Cancer Detection, 10-R9536

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Principal Investigators
Jian Ling
Hong Dixon

Inclusive Dates:  04/01/05 – 08/01/06

Background - Quantum dots (Qdots) are human-made semiconductor CdSe-ZnS fluorescence nanoparticles, which are currently being developed for live-cell and in vivo imaging. Qdots are brighter, more stable, and more spectrally distinct than traditional organic fluorescent dyes. These properties make Qdots especially suitable for long-term live-cell imaging. The challenge is how to deliver the quantum-dot-conjugated antibodies into cells and further allow the conjugated antibodies to move freely inside cells so they can bind their target molecules. This study investigated the feasibility of using a cell-penetrating peptide to facilitate the internalization of quantum-dot-conjugated antibodies for the labeling of two intracellular cervical cancer biomarkers.

Approach - Commercially available water-soluble and biocompatible Qdots were directly conjugated with antibodies of two biomarkers. They were successfully tested to stain fixed cells and shown to be able to differentiate biomarker positive and negative cells. The conjugates were further modified with a cell-penetrating peptide and then delivered to live biomarker-positive HeLa and biomarker-negative UM-UC-3 cells. Long-term time-lapse, multicolor fluorescence images were recorded before, during, and after the cells being exposed to the Qdot conjugated antibodies.

Accomplishments - A temperature-controlled chamber was integrated into the Nikon 2000E microscope system for long-term live-cell imaging (see video of cell mitosis. The imaging data indicate that the quantum-dot-conjugated antibodies were partially internalized through cell endocytosis. Some conjugates were secreted from the cells after incubation (see video of cellular internalization of quantum dots. The remaining conjugates were distributed in the nucleus, cytoplasm, and concentrated in perinuclear regions of the biomarker-positive HeLa cells. In the biomarker-negative Um-Uc-3 cells, however, the conjugates finally concentrated in the juxtanuclear region after approximately 18 hours of incubation. Cells labeled with quantum dots still go through a normal mitosis process and transfer the quantum dots into the daughter cells. The study showed that the use of cell-penetration peptide is a promising method for the intracellular labeling of living cell molecules using quantum dots.

Fluorescence images of Quantum dot labeled antibody (red) and FITC-labeled dextran (green) in live cervical cancer cells: HeLa. Quantum dots are partially co-localized (yellow) with endocytotic vesicles labeled with dextran.

A sequence of time-lapse images illustrates the mitosis of HeLa cells labeled with yellow quantum dot conjugated antibody.

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