Ferritin-based drug delivery systems: Hybrid nanocarriers for vascular immunotargeting

Abstract

Ferritin subunits of heavy and light polypeptide chains self-assemble into a spherical nanocage that serves as a natural transport vehicle for metals but can include diverse cargoes. Ferritin nanoparticles are characterized by remarkable stability, small and uniform size. Chemical modifications and molecular re-engineering of ferritin yield a versatile platform of nanocarriers capable of delivering a broad range of therapeutic and imaging agents. Targeting moieties conjugated to the ferritin external surface provide multivalent anchoring of biological targets. Here, we highlight some of the current work on ferritin as well as examine potential strategies that could be used to functionalize ferritin via chemical and genetic means to enable its utility in vascular drug delivery.

Fig. 1

Illustration of drug loading strategies and modular ferritin platforms. a) Different routes for ferritin drug loading such as 1) chemical conjugation of drugs to ferritin surface, 2) pH- or salt-based assembly and disassembly of drugs inside ferritin, and 3) diffusion of small molecules through the surface pores of ferritin. b) Examples of modular ferritin platforms such as 1) ferritin incorporating Fc-binding peptide for binding targeting antibodies[39], 2) incorporation of unnatural azide-bearing amino acid in ferritin for click coupling to targeting ligands or antibodies (unpublished internal study), 3) ferritin surface conjugated with β-cyclodextrins for rapid drug loading[40], 4) ferritin incorporating protein G and 6X-His tag for antibody or cargo binding[41], and 5) engineered ferritin displaying functional peptides for siRNA delivery[42].

Fig. 2

Distribution and anti-tumor efficacy of FTn/FTn–PEG particles in mouse lung and proximal lung cancer model. a) in vivo distribution of FTn or FTn/FTn–PEGx (PEG sizes = 2, 5, and 10 kDa) labeled with Cy5 in large airways. Red (particles) DAPI (cell nuclei), b) quantification of labeled nanoparticles. Mice were administered intratracheally with particles and harvested at 10 minutes, and c) quantification of total fluorescence intensity throughout mouse trachea. FTn/FTn–PEG2k/DOX were administered intratracheally in an orthotopic mouse model of proximal lung cancer. d) IVIS imaging of 3LL lung tumor tissue bioluminescence signal over time, e) quantification of bioluminescence signal, and f) survival study of mice treated with and without treatment. Reprinted with permission from reference[45].

Fig. 3

Copper sulfide-ferritin nanocages in cancer theranostics a) Schematic for synthesis of CuS–ferritin nanocarriers. b) Positron-emission tomography (PET) imaging of tumor-bearing mice I.V. injected with of 50 μCi ⁶⁴CuS–ferritin nanocages at 2, 4, 8, 20, and 24 h. c) Tumor targeting of ⁶⁴CuS–ferritin nanocages vs. free copper. d) Tissue biodistribution of ⁶⁴CuS–ferritin nanocarriers 24 h after injection. Reprinted with permission from reference[54].

Fig. 4

Illustration of various potential chemical and bioconjugation strategies available for attachment of cargo or targeting moieties to ferritin.

Fig. 5

Pulmonary targeting of ICAM-1 and PECAM-1 directed nanoparticles. Targeting efficiency indicates % injected dose per gram tissue. mAb - isolated monoclonal antibody, FNP - ferritin nanoparticles, PVP - 100-nm polyvinylphenol particles, liposomes – 150-nm PEGylated immunoliposomes[–103].