Interactions of Renal-Clearable Gold Nanoparticles with Tumor Microenvironments: Vasculature and Acidity Effects

Abstract

The success of nanomedicines in the clinic depends on our comprehensive understanding of nano-bio interactions in tumor microenvironments, which are characterized by dense leaky microvasculature and acidic extracellular pH (pH_e ) values. Herein, we investigated the accumulation of ultrasmall renal-clearable gold NPs (AuNPs) with and without acidity targeting in xenograft mouse models of two prostate cancer types, PC-3 and LNCaP, with distinct microenvironments. Our results show that both sets of AuNPs could easily penetrate into the tumors but their uptake and retention were mainly dictated by the tumor microvasculature and the enhanced permeability and retention effect over the entire targeting process. On the other hand, increased tumor acidity indeed enhanced the uptake of AuNPs with acidity targeting, but only for a limited period of time. By making use of simple surface chemistry, these two effects can be synchronized in time for high tumor targeting, opening new possibilities to further improve the targeting efficiencies of nanomedicines.

Keywords: microvascular density; nanoparticles; renal clearance; tumor acidity; tumor targeting.

Figure 1

Renal-clearable AuNPs coated with both glutathione and cysteamine (GC-AuNPs) were designed for targeting tumor acidity. A) TEM image (scale bar: 5 nm) and core size and hydrodynamic diameter (HD) distributions of the GC-AuNPs. Core size: 2.3 ± 0.4 nm; HD: 2.9 ± 0.3 nm. B) Absorption, excitation, and emission spectra of GC-AuNPs in aqueous solution. C) Bright-field and fluorescence images of live HeLa cells incubated with GC-AuNPs at pH 7.4 and 6.5 in PBS at 25°C for 10 min (scale bar: 20 μm). D) Luminescence intensity of cell membranes incubated with GC-AuNPs at different pH values in PBS.

Figure 2

The two prostate cancer models PC-3 and LNCaP differ in both tumor vasculature and acidity. A) Densities and B) diameters of intratumoral vasculatures in the tumor periphery and tumor center quantified by analyzing CD31-antibody-stained tumor sections. C) Intensity of the CD31 expression measured in six fields that were selected from the tumor periphery and center. D) Extracellular pH (pH_e) values of tumors determined by ³¹P magnetic resonance spectroscopy (MRS). The standard ³¹P MRS titration curve is shown in gray. N=4 for PC-3, N=8 for LNCaP. *P < 0.05.

Figure 3

Analysis of the tumor targeting of GS-AuNPs and GC-AuNPs in PC-3 and LNCaP models at 1, 24, 72 h p.i. A) Tumor-to-blood ratios at 1 h p.i. Tumor accumulation of GS-AuNPs at 1 h p.i.: 2.48 ± 0.34%IDg⁻¹ in PC-3, 2.43 ± 0.83%IDg⁻¹ in LNCaP; GC-AuNPs at 1 h p.i.: 3.71 ± 0.43%IDg⁻¹ in PC-3, 4.01 ± 0.83%IDg⁻¹ in LNCaP. B) Blood pharmacokinetics of GS-AuNPs and GC-AuNPs. C) Tumor targeting efficiencies of GS-AuNPs at 24 and 72 h p.i. D) Tumor-to-blood ratios of GS-AuNPs at 24 and 72 h p.i. E) Tumor targeting efficiencies of GC-AuNPs at 24 and 72 h p.i. F) The (TA_LNCaP/TA_PC-3)_GC-AuNPs to (TA_LNCaP/TA_PC-3)_GS-AuNPs ratio at 1, 24, and 72 h p.i. TA =Tumor accumulation of the NPs. *P < 0.05, **P <0.01, ***P< 0.001, ns= no significant difference (P >0.05).