Magneto-aerotactic bacteria deliver drug-containing nanoliposomes to tumour hypoxic regions.

Oxygen-depleted hypoxic regions in the tumour are generally resistant to therapies. Although nanocarriers have been used to deliver drugs, the targeting ratios have been very low. Here, we show that the magneto-aerotactic migration behaviour of magnetotactic bacteria, Magnetococcus marinus strain MC-1 (ref. 4), can be used to transport drug-loaded nanoliposomes into hypoxic regions of the tumour. In their natural environment, MC-1 cells, each containing a chain of magnetic iron-oxide nanocrystals, tend to swim along local magnetic field lines and towards low oxygen concentrations based on a two-state aerotactic sensing system. We show that when MC-1 cells bearing covalently bound drug-containing nanoliposomes were injected near the tumour in severe combined immunodeficient beige mice and magnetically guided, up to 55% of MC-1 cells penetrated into hypoxic regions of HCT116 colorectal xenografts. Approximately 70 drug-loaded nanoliposomes were attached to each MC-1 cell. Our results suggest that harnessing swarms of microorganisms exhibiting magneto-aerotactic behaviour can significantly improve the therapeutic index of various nanocarriers in tumour hypoxic regions.

SN-38 active loading in poly(lactic-co-glycolic acid) nanoparticles and assessment of their anticancer properties on COLO-205 human colon adenocarcinoma cells.

SN-38 is a highly effective drug against many cancers. The development of an optimal delivery system for SN-38 is extremely challenging due to its low solubility and labile lactone ring. Herein, SN-38 encapsulated in poly(D,L-lactide-co-glycolide) nanoparticles (NPs) is introduced to enhance its solubility, stability and cellular uptake. SN-38-loaded NPs prepared by spontaneous emulsification solvent diffusion (SESD) method had an average diameter of 310 nm, a zeta potential of -9.69 mV and a loading efficiency of 71%. They were able to protect the active lactone ring of SN-38 against inactivation under physiological condition. A colorectal adenocarcinoma cell line (COLO-205) was used to assess the NPs effects on cytotoxicity and cellular uptake. Result showed a significant decreased cell proliferation and cell apoptosis. These results suggest that these SN-38-loaded NPs can be an effective delivery system for the treatment of colon cancer and potentially for other types of cancers.

Improved antifungal activity of itraconazole-loaded PEG/PLA nanoparticles.

Poly(ethylene glycol)/polylactic acid (PEG/PLA) nanoparticles (NPs) containing the hydrophobic antifungal itraconazole (ITZ) were developed to provide a controlled release pattern of ITZ as well as to improve its aqueous dispersibility and hence enhance its antifungal action. Two PEG/PLA copolymers (PEGylated PLA polymers) were used in this study; branched PEGylated polymer in which PEG was grafted on PLA backbone at 7% (mol/mol of lactic acid monomer), PEG7%-g-PLA, and multiblock copolymer of PLA and PEG, (PLA-PEG-PLA)n with nearly similar PEG insertion ratio and similar PEG chain length. ITZ-loaded PLA NPs were also prepared and included in this study as a control. ITZ-NPs were prepared from a 1 : 1 w/w blend of PLA and each PEGylated polymer either PEG7%-g-PLA or (PLA-PEG-PLA)n using an oil-in-water emulsion evaporation method. The NPs morphology, size and size distribution, zeta potential, loading efficiency, release profile and antifungal activity were characterized. All ITZ-NPs were nearly spherical with smooth surface and showed less aggregating tendency with a size range of 185-285 nm. All ITZ-NPs measured nearly neutral zeta potential values close to 0 mV. The % LE of ITZ was ∼94% for PEG7%-g-PLA NPs and ∼83% for (PLA-PEG-PLA)n at 15.3% w/w theoretical loading. PEG/PLA NPs were stable over time regarding size and size distribution and % ITZ loading efficiency (% LE). ITZ release showed an initial burst followed by a gradual release profile for ITZ-NPs over 5 days. (PLA-PEG-PLA)n NPs exhibited faster release rates than PEG7%-g-PLA NPs particularly at the last 2 days. Differential scanning calorimetry and powder X-ray diffractometry data confirmed that ITZ exists in an amorphous state or a solid solution state into the NPs matrix. Fourier transform infrared revealed the possibility of chemical interaction between ITZ and the NPs matrix polymer indicating the successful entrapment of ITZ inside the particles. In haemolysis test, ITZ-NPs caused mild haemolysis over the concentration range (5-20 µg/mL) compared to free ITZ, indicating better safety profile of ITZ-NPs. ITZ-loaded PEG/PLA NPs inhibited fungal growth more efficiently than either free ITZ or ITZ-loaded PLA NPs. Our results suggest that PEG/PLA-ITZ could be used efficiently as a nanocarrier to improve the aqueous dispersibility of ITZ, control its release over time and, thereby, enhance its antifungal efficacy.

Characterization of rhodamine loaded PEG-g-PLA nanoparticles (NPs): effect of poly(ethylene glycol) grafting density.

In our previous study, PEG-g-PLA nanoparticles were developed and characterized. The aim of the present work is to investigate the effect of PEG grafting density (% PEG inserted onto poly(d, l)-lactide, PLA backbone) on both physicochemical and biological properties (mainly plasma protein binding and in vitro macrophage uptake) of PEG-g-PLA NPs. Rhodamine B (RHO) loaded NPs were prepared from a 1:1 (wt/wt) blend of PLA and PEG-g-PLA copolymer of varying PEG grafting density (1, 7, or 20% mol/mol of lactic acid monomer) by an o/w emulsion solvent evaporation method. These NPs were characterized with regard to their morphology, size, surface charge, loading efficiency, and rhodamine release. The extent of protein adsorption to the surface of different NPs was qualitatively investigated by dynamic light scattering technique. Additionally, the in vitro macrophage uptake following incubation of RAW 264.7 cells with rhodamine loaded PEG-g-PLA and PLA particles was investigated by confocal laser scanning microscopy (CLSM). The amount of NPs phagocytosed following incubation of RAW 264.7 cells with different concentrations of rhodamine loaded PLA or pegylated NPs for 24h at 37 °C was also determined by fluorescence spectroscopy. ALL lyophilized NPs showed larger diameter in the range of 300-400 nm compared to freshly prepared NPs suspension indicating particle aggregation upon lyophilization. % EE of rhodamine was found to be between 10% and 68% wt/wt depending on PEG grafting density. The higher the grafting density of PEG over PLA backbone, the more the entrapment efficiency. All pegylated NPs showed low zeta potential (close to zero) values. In vitro release analysis revealed that rhodamine leaked from all nanoparticles at a very slow rate at physiological pH, thus making it suitable for both imaging and uptake studies with RAW 264.7 cells. All PEG-g-PLA NPs of different PEG grafting density were well tolerated and exhibited no toxicity to RAW 264.7 cells as seen by cell proliferation assays. Cellular uptake of NPs was mainly dependent on polymer type as well as PEG grafting density. Grafted copolymer NPs resulted in lower degree of macrophage uptake compared to PLA NPs in macrophages cell lines. The higher the PEG grafting density, the lower the uptake of NPs by macrophage cells. Minimum NPs uptake for all the investigated concentrations was achieved when the PEG grafting density was 7% mol/mol of lactic acid. When increasing the PEG grafting density in the nanoparticles above 7%, no significant reduction in NPs phagocytosis was achieved. Thus, this study shows that the optimal PEG density required for designing stealth PEG-g-PLA NPs suitable for drug delivery applications might vary from 4 to 7%.

Effect of polyethylene glycol (PEG) chain organization on the physicochemical properties of poly(D, L-lactide) (PLA) based nanoparticles.

The aim of the present study is to evaluate the effect of polyethylene glycol (PEG) chain organization on various physicochemical aspects of drug delivery from poly(D, L-lactide) (PLA) based nanoparticles (NPs). To reach that goal, two different pegylated polymers of poly(D, L-lactide) (PLA) were synthesized. Polymers used in this study are grafted ones in which PEG was grafted on PLA backbone at 7% (mol/mol of lactic acid monomer), PEG7%-g-PLA, and multiblock copolymer of both PLA and PEG, (PLA-PEG-PLA)n with nearly similar PEG insertion ratio and the same PEG chain length. Blank and ibuprofen-loaded NPs were prepared from both polymers and their properties were compared to PLA homopolymer NPs as a control. Encapsulation efficiency of ibuprofen was found to be approximately 25% for (PLA-PEG-PLA)n NPs and approximately 80% for PEG7%-g-PLA NPs. (PLA-PEG-PLA)n NPs either blank or loaded showed larger hydrodynamic diameter (approximately 200 nm) than PEG7%-g-PLA NPs (approximately 135 nm). A significant difference was observed in the amount of PVA associated with the surface of both NPs where 3.6% and 0.4% (wt/wt) were found on the surface of PEG7%-g-PLA and (PLA-PEG-PLA)n NPs, respectively. No observed difference in zeta potential values for both NPs formulations was found. DSC showed the existence of the drug in a crystalline state inside NPs matrix irrespective of the type of polymer used with either shifting or/and broadening of the drug melting endotherm. Both AFM phase imaging and XPS studies revealed the possibility of existence of more PEG chains at the surface of grafted polymer NPs than (PLA-PEG-PLA)n during NPs formation. The in vitro release behavior showed that (PLA-PEG-PLA)n NPs exhibited faster release rates than PEG7%-g-PLA NPs. The physicochemical differences obtained between both polymers were probably due to different chain organization during NPs formulation. Such pegylated NPs made from these two different polymers might find many applications, being able to convert poorly soluble, poorly absorbed substances into promising drugs, improving their therapeutic performance, and helping them reach adequately their target area. Our results suggest that the properties of pegylated PLA-based NPs can be tuned by proper selection of both polymer composition and polymer architecture.

Effect of aqueous solubility of grafted moiety on the physicochemical properties of poly(d,l-lactide) (PLA) based nanoparticles.

In order to evaluate the solubility effect of grafted moiety on the physicochemical properties of poly(d,l-lactide) (PLA) based nanoparticles (NPs), two materials of completely different aqueous solubility, polyethylene glycol (PEG) and palmitic acid were grafted on PLA backbone at nearly the same grafting density, 2.5% (mol of grafted moiety/mol of lactic acid monomer). Blank and ibuprofen-loaded NPs were fabricated from both polymers and their properties were compared to PLA homopolymer NPs as a control. NPs were analyzed for major physicochemical parameters such as encapsulation efficiency, size and size distribution, surface charge, thermal properties, surface chemistry, % poly(vinyl alcohol) (PVA) adsorbed at the surface of NPs, and drug release pattern. Encapsulation efficiency of ibuprofen was found to be nearly the same for both polymers approximately 36% and 39% for PEG2.5%-g-PLA and palmitic acid2.5%-g-PLA NPs, respectively. Lyophilized NPs of palmitic acid2.5%-g-PLA either blank or loaded showed larger hydrodynamic diameter ( approximately 180nm) than PEG2.5%-g-PLA NPs ( approximately 135nm). PEG2.5%-g-PLA NPs showed lower % of PVA adsorbed at their surface ( approximately 5%, w/w) than palmitic acid2.5%-g-PLA NPs ( approximately 10%, w/w). Surface charge of palmitic acid2.5%-g-PLA NPs seems to be influenced by the large amount of PVA remains associated within their matrix. Thermal analysis using DSC revealed possible drug crystallization inside NPs. Both AFM phase imaging and XPS studies revealed the tendency of PEG chains to migrate towards the surface of PEG2.5%-g-PLA NPs. While, XPS analysis of palmitic acid2.5%-g-PLA NPs showed the tendency of palmitate chains to position themselves into the inner core of the forming particle avoiding facing the aqueous phase during NPs preparation using O/W emulsion method. The in vitro release pattern showed that PEG2.5%-g-PLA NPs exhibited faster release rates than palmitic acid2.5%-g-PLA NPs. PEG and palmitate chains when grafted onto PLA backbone, different modes of chain organization during NPs formation were obtained, affecting the physicochemical properties of the obtained NPs. The obtained results suggest that the properties of PLA-based NPs can be tuned by judicious selection of both chemistry and solubility profile of grafted material over PLA backbone.