Cancer nanotechnology: drug encapsulated nanoparticle-aptamer bioconjugates for targeted delivery to prostate cancer cells - Aptamers

Cancer nanotechnology: drug encapsulated nanoparticle-aptamer bioconjugates for targeted delivery to prostate cancer cells
November 2005
O.C. Farokhzad12, J. Cheng2, B. Teply2, A. Khademhosseini2, S. Jon3, E. Levy-Nissenbaum12, R. Langer2
European Cancer Conference
Introduction: Nucleic acid ligands (aptamers) are potentially well suited for the therapeutic targeting of drug encapsulated controlled release polymer nanoparticles in a cell- or tissue-specific manner. We used Prostate Cancer (PCa) cells as a model to test this hypothesis.
Methods: We synthesized poly(lactic acid)-block-poly(ethylene glycol) controlled release copolymer with a terminal carboxylic acid functional group (PLA-PEG-COOH), and encapsulated rhodamine-labeled dextran (as a model drug) within PLA-PEG-COOH nanoparticles using the double emulsion method. We generated nanoparticle-aptamer bioconjugates using nuclease stabilized RNA aptamers that bind to the Prostate Specific Membrane Antigen (PSMA), a well known PCa tumor-marker which is over-expressed on prostate acinar epithelial cells. These bioconjugates were examined for targeted delivery and uptake by LNCaP (PSMA+) and PC3 (PSMA-) model PCa cells under a range of physiologic shear stress conditions using microfluidic channels.
Results: Nanoparticles had the following desirable characteristics: 1) negative surface charge (-50 mV ? 3 mV, Mean ? SD, N = 3), which may minimize non-specific interaction with the negatively charged nucleic acid aptamers, 2) carboxylic acid groups on the particle surface for potential modification and covalent conjugation to amine-modified aptamers, 3) presence of PEG on particle surface which enhances circulating half-life while contributing to decreased uptake in non-targeted cells. Nanoparticles were conjugated to PSMA aptamers to develop the first example of a nanoparticle-aptamer bioconjugate. Nanoparticle-aptamer bioconjugates selectively adhered to LNCaP but not PC3 cells at static and low shear (<1 dyne/cm2) but not higher shear (~4.5 dynes/cm2) conditions. Using z-axis fluorescent microscopy and 3-D image reconstruction (figure 1), we studied the localization of the nanoparticle-aptamer bioconjugates (red dots) after incubation with LNCaP cells, and confirmed that even at 2 hrs, the particles were largely internalized into cells. In contrast to LNCaP cells, the uptake of these particles is not enhanced in PC3 cells which do not express the PSMA protein.