Selective biophysical interactions of surface modified nanoparticles with cancer cell lipids improve tumor targeting and gene therapy

Abstract

Targeting gene- or drug-loaded nanoparticles (NPs) to tumors and ensuring their intratumoral retention after systemic administration remain key challenges to improving the efficacy of NP-based therapeutics. Here, we investigate a novel targeting approach that exploits changes in lipid metabolism and cell membrane biophysics that occur during malignancy. We hypothesized that modifications to the surface of NPs that preferentially increase their biophysical interaction with the membrane lipids of cancer cells will improve intratumoral retention and in vivo efficacy upon delivery of NPs loaded with a therapeutic gene. We have demonstrated that different surfactants, incorporated onto the NPs' surface, affect the biophysical interactions of NPs with the lipids of cancer cells and normal endothelial cells. NPs surface modified with didodecyldimethylammoniumbromide (DMAB) demonstrated greater interaction with cancer cell lipids, which was 6.7-fold greater than with unmodified NPs and 5.5-fold greater than with endothelial cell lipids. This correlated with increased uptake of DMAB-modified NPs with incubation time by cancer cells compared to other formulations of NPs and to uptake by endothelial cells. Upon systemic injection, DMAB-NPs demonstrated a 4.6-fold increase in tumor accumulation compared to unmodified NPs which also correlated to improved efficacy of p53 gene therapy. Characterization of the biophysical interactions between NPs and lipid membranes of tumors or other diseased tissues/organs may hold promise for engineering targeted delivery of therapeutics.

Figure 1. NP-Lipid biophysical interaction studies

The different surfactants used in PLGA NP formulation (a). Unmodified NPs were formulated with PVA alone; surface-modified NPs were formulated with PVA and either DMAB or CTAB. To study NP-lipid interactions, representative lipid monolayers were created over a buffer subphase into which NPs were injected (b). The change in surface pressure (ΔSP) was monitored over time for PC-3 lipids (c) and HUVEC lipids (d). Curves represent the median result. The positive ΔSP at 20 min after NP injection demonstrates quantitatively that DMAB-NPs had greater interaction with PC-3 lipids than did CTAB- and unmodified NPs and that DMAB-NPs also had greater interaction with PC-3 cells than with HUVECs (e). Data are shown as mean ± standard deviation; n = 3;*p< 0.05.

Figure 2. Cell uptake of NPs

Uptake of NPs by HUVECs and PC-3 cells after 15 min (a) and 30 min (b) of incubation. Data are shown as mean ± standard deviation; n = 3. Brackets indicate p< 0.05 between groups. Confocal microscopy (c) shows NP (green) uptake in PC-3 and HUVEC cells after 30 min of incubation (cell membranes labeled red).

Figure 3. Biodistribution of surface-modified NPs

In vivo NIR signal from the tumor and from a skin region further away from the tumor (background tissue signal) was monitored over 4 days after injection of NIR-dye loaded unmodified NPs (a), DMAB-NPs (b), and CTAB-NPs (c); n = 3–4. Statistical analysis was performed on tumor signal with skin signal subtracted (*p<0.05). Quantification of NPs in tumor and liver for each group was also performed ex vivo 48 hrs post-injection (d, *p< 0.05).

Figure 4. Efficacy of p53-gene therapy by surface-modified NPs in prostate tumors

Tumor-bearing mice were treated with two doses of unmodified p53NPs, CTAB-p53NPs, and DMAB-p53NPs, with each dose equivalent to 60 μg of p53 plasmid DNA. Controls included saline and DMAB-CNPs made with control plasmid. Tumor volume was monitored over time (a). Tumor volume is shown up to the time point when most animals were still alive. The area under the curve (calculated 0 through day 17, the day the first animal died) demonstrated significantly greater reduction in overall tumor growth in the DMAB-p53NP group vs. all other treated and control groups (*p< 0.05) (b). This Kaplan-Meier plot shows improvement in animal survival after treatment with DMAB-p53NPs vs. other treatment and control groups. Log-rank test of DMAB-p53NP and each group yields *p ≤ 0.05 (c).