(721a) Response of Breast Tumor Cells to Hybrid Polymer-Peptide Self-Assembled Nanoparticles

Introduction: A novel strategy to circumvent the short half-life, limited solubility, and improve uptake of anti-cancer drugs is encapsulation in colloidal self-assembled nanoparticles (NPs). Hybrid polymer-peptide NPs can selectively target the tumor over normal cells while enhancing intracellular uptake of the drug. The objective of this work was to investigate the effect of charged head-group of the peptide Cys-Val₆-Y₂ (CY₆Y₂), where Y is arginine or lysine, conjugated to acrylated poly(L-lactide) (PLAA-CV6Y2) on uptake and migration of tumor cells when loaded with Doxorubicin (Dox) chemotherapeutic agent.

Methods: PLA was conjugated to CY₆Y₂ peptide, where Y was lysine (CV₆K₂) or arginine (CV₆R₂), and the polymer-peptide conjugate was self-assembled into NPs as described [1]. Control PLAA NPs (without charged peptide) stabilized with poly(ethylene oxide) (PLAA-EO) were synthesized as described [1]. Size and distribution of the NPs were measured with light scattering. For cell uptake experiment 4T1 (mouse breast tumor) cells were incubated with NPs encapsulating FITC (2 mg/mL, 2% loading) for 24 hours. At every time point, the supernatant and cells were collected and analyzed by a fluorescent plate reader. For invasion and migrations studies, 4T1 cells at a density of 1.5×10⁴ cells/well in 24-well Transwell plates were exposed to empty and Dox-loaded NPs (5 μM Dox for loaded particles, 5% loading). Free Dox was used as a positive control. The cells were allowed to migrate through the transwell membrane in the absence (migration) or presence (invasion, 5% wt gel in media) of Matrigel in the upper chamber. After 24 h, the membranes were fixed, stained with eosin-Y and azure dyes, imaged, and the number of migrating cells were counted with an inverted microscope.

Results and Conclusions: NPs had a narrow size distribution between 50-150 nm. Release kinetics showed sustained Dox delivery for 25-35 days.  After 24 h incubation of 4T1 tumor cells with self-assembled PLAA-CV₆R₂ and PLAA-CV₆K₂ NPs, 60 and 50% of the NPs were taken up by the cells, respectively, compared with only 30% for PLAA-EO NPs. Migration experiments indicated that Dox-loaded PLAA-CV₆R₂ NPs were more effective in retarding the migration of 4T1 cells than PLAA-CV₆K₂, PLAA-EO, or the free Dox. Our results demonstrate that the arginine head group was more effective with respect to NPs uptake and retarding the migration of tumor cells than the lysine head group