PURPOSE: Developing and testing of microbicides for pre-exposure prophylaxis and post-exposure protection from HIV are on the list of major HIV/AIDS research priorities. To improve solubility and bioavailability of highly potent anti-retroviral drugs, we explored the use of a nanoparticle (NP) for formulating a combination of two water-insoluble HIV inhibitors. METHODS: The combination of a non-nucleoside HIV reverse transcriptase inhibitor (NNRTI), Efavirenz (EFV), and an inhibitor of HIV integrase, Elvitegravir (ELV) was stabilized with a graft copolymer of methoxypolyethylene glycol-polylysine with a hydrophobic core (HC) composed of fatty acids (HC-PGC). Formulations were tested in TZM-bl cells infected either with wild-type HIV-1IIIB, or drug-resistant HIV-1 strains. In vivo testing of double-labeled NP formulations was performed in female rats after a topical intravaginal administration using SPECT/CT imaging and fluorescence microscopy. RESULTS: We observed a formation of stable 23-30 nm NP with very low cytotoxicity when EFV and ELV were combined with HC-PGC at a 1:10 weight ratio. For NP containing ELV and EFV (at 1:1 by weight) we observed a remarkable improvement of EC50 of EFV by 20 times in the case of A17 strain. In vivo imaging and biodistribution showed in vivo presence of NP components at 24 and 48 h after administration, respectively. CONCLUSIONS: insoluble orthogonal inhibitors of HIV-1 life cycle may be formulated into the non-aggregating ultrasmall NP which are highly efficient against NNRTI-resistant HIV-1 variant.

Initially developed in 1992 as an MR imaging agent, the family of protected graft copolymers (PGC) is based on a conjugate of polylysine backbone to which methoxypoly(ethylene glycol) (MPEG) chains are covalently linked in a random fasion via N-epsilon-amino groups. While PGC is relatively simple in terms of its chemcial composition and structure, it has proved to be a versatile platform for in vivo drug delivery. The advantages of poly amino acid backbone grafting include multiple available linking sites for drug and adaptor molecules. The grafting of PEG chains to PGC does not compromise biodegradability and does not result in measurable toxicity or immunogenicity. In fact, the biocompatablility of PGC has resulted in its being one of the few 100% synthetic non-proteinaceous macromolecules that has suceeded in passing the initial safety phase of clinical trials. PGC is capable of long circulation times after injection into the blood stream and as such found use early on as a carrier system for delivery of paramagnetic imaging compounds for angiography. Other PGC types were later developed for use in nuclear medicine and optical imaging applications in vivo. Recent developments in PGC-based drug carrier formulations include the use of zinc as a bridge between the PGC carrier and zinc-binding proteins and re-engineering of the PGC carrier as a covalent amphiphile that is capabe of binding to hydrophobic residues of small proteins and peptides. At present, PGC-based formulations have been developed and tested in various disease models for: 1) MR imaging local blood circulation in stroke, cancer and diabetes; 2) MR and nuclear imaging of blood volume and vascular permeability in inflammation; 3) optical imaging of proteolytic activity in cancer and inflammation; 4) delivery of platinum(II) compounds for treating cancer; 5) delivery of small proteins and peptides for treating diabetes, obesity and myocardial infarction. This review summarizes the experience accumulated by various research groups that chose to use PGC as a drug delivery platform.

BACKGROUND: Vascular parameters, such as vascular volume, flow, and permeability, are important disease biomarkers for both type 1 and type 2 diabetes. Therefore, it is essential to develop approaches to monitor the changes in pancreatic microvasculature non-invasively. METHODS: Here, we describe the application of the long-circulating, paramagnetic T1 contrast agent, protected Graft Copolymer bearing covalently linked gadolinium diethylenetriaminepentaacetic acid residues and labelled with fluorescein (PGC-GdDTPA-F) for the non-invasive semi-quantitative evaluation of vascular changes in diabetic models using magnetic resonance imaging. RESULTS: We observed a significantly higher accumulation of protected graft copolymer bearing covalently linked gadolinium diethylenetriaminepentaacetic acid residues and labelled with fluorescein in the pancreata of BBDR rats induced to develop diabetes, as compared to non-diabetic controls at 1 h post-injection. No differences were seen in the blood pool, kidney, or muscle, indicating that the effect is specific to the diabetic pancreas. Fluorescence microscopy revealed a marked increase in contrast agent availability in the pancreas with the development of the pathology. Similar changes were noted in the homozygous Leprdb mouse model of type 2 diabetes. This effect appeared to result both from the increase of vascular volume and permeability. CONCLUSIONS: High-molecular weight paramagnetic blood volume contrast agents are valuable for the in vivo definition of pancreatic microvasculature dynamics by magnetic resonance imaging. The increase in vascular volume and permeability, associated with diabetic inflammation, can be monitored non-invasively and semi-quantitatively by magnetic resonance imaging in diabetic BBDR rats. This imaging strategy represents a valuable research tool for better understanding of the pathologic process.