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Tracking metastasis tumor cell extravasation with quantum dot nanocrystals and fluorescence emission-scanning microscopyCentral Question : Can metastasis and extravasation be traced in-vivo with the use of quantum dot nanocrystals without causing toxicity upon prolonged exposure to quantum dots?Presented by(1) Bianca Reichart(2) Gayathri Janarthanam

Introduction : Metastasis: > Pathogenic agent's spread from an initial site to a different site within the host's body. > Lymphatic or hematogenous spread: circulating tumor cells acquire the ability to penetrate the walls of lymphatic or blood vessels. > Typical for a malignant tumor. Extravasation Cascade of events: > Tumor cell arrest on the endothelium > Formation of dynamic contacts > Significant cytoskeletal changes > Tumor cell transendothelial migration > Invasion into the surrounding matrix

Labeling tumor cells with QD > QD was packed in cationic lipids. > Can efficiently transduce negatively charged nucleic acids into the cytoplasm. Intracellular labeling of tumor cells by QDs permits in vivo imaging despite tissue autofluorescence.

Fluorescence emission spectroscopy: > Scans the surface of a sample with an electron beam. > High-resolution images.

IN-VIVO IMAGING : > QDs - good multiphoton absorption between 700 - 1000 nm. > QDs labeled with orange cell trackers were injected into the mice. > QDs -circles; orange trackers - diamonds; lectin - squares => distinguishable from tissue autofluorescence.

> QDs - Cadmium and selenium cores. > May cause toxicity upon prolonged stay in vivo. > If QDs aid in extravasation/ affected the survival of the tumor cells: Qd-labeled tumor cells in tissues < QD-labelled cells during injection. > QD - labeled tumor cells were quantified after 40 days - no significant difference; Did not interfere with the growth of the tumor cells or cause extravasation. > Comparison for 5 days vs 40 days - no unlabelled cells found; remained the same relatively in both cases - proof that QDs have no role in extravasation. > Black bars: in-vitro Grey bars: in-vivo

Multiphoton imaging of the QDs : > Thicker tissues - absorb and scatter visible light => infrared excitation is suitable in vivo. > Different colour emitting QDs ranging 510, 550, 570, 590, and 610 nm were identified using multiphoton emission-scanning microscopy. > Helps identify multiple populations of cells. > Image A: Different QDs excited at 820 nm after 5 h of injection. > Image B: Circles - 510 nm QDs ; Diamonds -570 nm QDs; > Image C: QDs under a coverslip excited at 680 nm.

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