Stable Formulations of Peptide-Based Nanogels

Abstract

Recently, nanogels have been identified as innovative formulations for enlarging the application of hydrogels (HGs) in the area of drug delivery or in diagnostic imaging. Nanogels are HGs-based aggregates with sizes in the range of nanometers and formulated in order to obtain injectable preparations. Regardless of the advantages offered by peptides in a hydrogel preparation, until now, only a few examples of peptide-based nanogels (PBNs) have been developed. Here, we describe the preparation of stable PBNs based on Fmoc-Phe-Phe-OH using three different methods, namely water/oil emulsion (W/O), top-down, and nanogelling in water. The effect of the hydrophilic-lipophilic balance (HLB) in the formulation was also evaluated in terms of size and stability. The resulting nanogels were found to encapsulate the anticancer drug doxorubicin, chosen as the model drug, with a drug loading comparable with those of the liposomes.

Keywords: diagnostic imaging; doxorubicin; hydrogel nanoparticles; inverse emulsion; nanogel formulation; peptide aggregates; peptide-based nanogels.

Figure 1

Icons graphical representation of the three different strategies for the nanogel formulation. (A) Water-in-oil emulsion methodology; (B) Top-down method; and (C) Nanogelling in water approach. Each step is identified using an icon of which the legend is reported too.

Figure 2

Chemical formulas of components used for the peptide-based nanogel formulation. Internal core (red) is formed by Fmoc-Phe-Phe-OH (Fmoc-FF). External surfactants shell (green) was formulated using d-α-tocopherol polyethylene glycol 1000 succinate (E-TPGS-PEG1000) or mixing SPAN^® 60 (sorbitan monostearate) and TWEEN^® 60 (polyethylene glycol sorbitan monostearate) in different ratios.

Figure 3

Intensity correlation functions for Fmoc-FF nanogels prepared according to the inverse emulsion at three different HLB values (4.7, 10, and 14.9). On the right, the dynamic light scattering (DLS) profiles for these formulations freshly prepared and after one month.

Figure 4

DLS profiles. (A) For Fmoc-FF/SPAN^®60 (HLB = 4.7) and Fmoc-FF/TWEEN^®60 (HLB = 14.9) as compared with the corresponding aggregates lacking the dipeptide; (B) For Fmoc-FF nanogels prepared according to W/O emulsion, top-down, and nanogelling in water methods (HLB = 10).

Figure 5

Structural characterization of nanogels prepared by inverse emulsion method. Fluorescence spectrum (A) and circular dichroism (CD) spectrum (B) of Fmoc-FF nanogel formulation as compared with fluorescence and CD spectra of Fmoc-FF hydrogel.

Figure 6

Doxorubicin release profile by Fmoc-FF PBNs. The amount of Dox released was estimated by fluorescence spectroscopy at 590 nm.