Self-Assembled Quantum Dot−Peptide Bioconjugates for Selective Intracellular Delivery

Abstract

We demonstrate the use of self-assembled luminescent semiconductor quantum dot (QD) -peptide bioconjugates for the selective intracellular labeling of several eukaryotic cell lines. A bifunctional oligoarginine cell penetrating peptide (based on the HIV-1 Tat protein motif) bearing a terminal polyhistidine tract was synthesized and used to facilitate the transmembrane delivery of the QD bioconjugates. The polyhistidine sequence allows the peptide to self-assemble onto the QD surface via metal-affinity interactions while the oligoarginine sequence allows specific QD delivery across the cellular membrane and intracellular labeling as compared to non-conjugated QDs. This peptidedriven delivery is concentration-dependent and thus can be titrated. Upon internalization, QDs display a punctate-like staining pattern in which some, but not all, of the QD signal is co-localized within endosomes. The effects of constant versus limited exposure to QD-peptide conjugates on cellular viability are evaluated by a metabolic specific assay and clear differences in cytotoxicity are observed. The efficacy of using peptides for selective intracellular delivery is highlighted by performing a multicolor QD labeling, where we found that the presence or absence of peptide on the QD surface controls cellular uptake.

Cell-penetrating peptides for nanomedicine – how to choose the right peptide

“…This modification also allowed active targeting of the nucleus in spite of the increased size of the particles (14.1-18 nm in diameter) [36]. We should mention that the cellular uptake can be influenced not only by the conjugation of CPPs, but also by the number of QD-associated CPPs and the cell-type, which has been confirmed by Delehanty et al [88] The functionalization of QDs with CPPs can facilitate their transport across the plasma membrane, and thus enable these particles to cross the blood-brain barrier (BBB). Tat-modified QDs, for example, were successfully used by Santra et al to fluorescently label brain tissue of rodents (SD adult rats, Sprague-Dawley rats) [89].…”

Entrapment in phospholipid vesicles quenches photoactivity of quantum dots

“…69 Bioconjugation of QDs with cell-penetrating polyargininetype peptide has resulted in partial colocalization of the QDs within endosomes. 70 Furthermore, coating with hyperbranched copolymer ligands has demonstrated an endosomedisrupting effect (endosomolysis). 71 The osmotic-imbalance strategy can also be employed by dipeptides that are cleaved by lysosomal dipeptidase.…”

Potential clinical applications of quantum dots

“…QDs capped with compact carboxylated ligands have shown reasonable rates of nonspecifi c endocytosis (Jaiswal et al 2003), however receptor-mediated uptake has demonstrated better effi ciency by specifi cally targeting receptors displayed on the cell surface (Chan and Nie 1998;Lidke et al 2004;Bharali et al 2005). As expected, ligands previously identifi ed to cue and facilitate receptormediated endocytosis continue to function effectively when attached to QD surfaces resulting in effi cient delivery of the modifi ed nanoparticle assembly within cells, but with the potential drawback of the cargoes remaining largely confi ned inside the endosomes (Delehanty et al 2006). If the intended destination of a QD bioconjugate is a specifi c organelle or general release into the cytosol, this perpetual confi nement presents a signifi cant obstacle.…”

“…The authors found negligible toxicity in these model cells and attribute this result to appropriate sequestration of the core-shell material and the biocompatibility of the surface-bound PEG. Mattoussi's group has reported on the dosage effects of QDs on different cell lines (Delehanty et al 2006). They found that acute (1 hour) versus chronic (continuous) exposure and labeling of different concentrations of QDs to two cell lines resulted in a signifi cantly different impact on subsequent cellular viability.…”