Electrostatic Coating of Viral Particles for Gene Delivery Applications in Muscular Dystrophies: Influence of Size on Stability and Antibody Protection

BACKGROUND

Duchenne Muscular Dystrophy (DMD) is one of the most common muscular dystrophies, caused by mutated forms of the dystrophin gene. Currently, the only treatment available is symptoms management. Novel approximations are trying to treat these patients with gene therapy, namely, using viral vectors. However, these vectors can be recognized by the immune system decreasing their therapeutic activity and making impossible a multidose treatment due to the induction of the humoral immunity following the first dose.

OBJECTIVE

Our objective is to demonstrate the feasibility of using a hybrid vector to avoid immune clearance, based on the electrostatic coating of adeno-associated virus (AAVs) vectors with our proprietary polymers.

METHODS

We coated model adeno-associated virus vectors by electrostatic interaction of our cationic poly (beta aminoester) polymers with the viral anionic capsid and characterized biophysical properties. Once the nanoformulations were designed, we studied their in vivo biodistribution by bioluminescence analysis and we finally studied the capacity of the polymers as potential coatings to avoid antibody neutralization.

RESULTS

We tested two polymer combinations and we demonstrated the need for poly(ethylene glycol) addition to avoid vector aggregation after coating. In vivo biodistribution studies demonstrated that viral particles are located in the liver (short times) and also in muscles (long times), the target organ. However, we did not achieve complete antibody neutralization shielding using this electrostatic coating.

CONCLUSIONS

The null hypothesis stands: although it is feasible to coat viral particles by electrostatic interaction with a proprietary polymer, this strategy is not appropriate for AAVs due to their small size, so other alternatives are required as a novel treatment for DMD patients.

Autoradioluminography, a powerful and reliable tool for drug development: Accelera's experience

A deeper understanding of the pharmacokinetic and pharmacodynamic properties of a drug candidate is a pivotal component of drug discovery and development. Autoradiography is an excellent technique allowing exploiting the advantages of the use of radioisotopes in the drug disscovery field. The introduction of phosphor imaging technology has revolutionized the handling of drug distribution studies providing high-resolution images. Specifically, quantitative whole-body autoradioluminography is employed for preclinical study where the aim is to obtain information about the route of elimination and tissue distribution of a drug candidate. Autoradioluminography is also the technique of choice pursued to deal with all the issue that it is possible to encounter in all stage of drug development (ie, site-specific drug localization and retention, drug-drug interactions, penetration into specific target, specific tissue binding, crossing of brain blood barrier, and placental transfer). The purpose of this review is to give a picture of how autoradiography is employed in our laboratory as a key tool for advances in the assessment of the drug disposition and to validate new experimental models.

Evaluation of New 99mTc(CO)3 + Radiolabeled Glycylglycine In Vivo

BACKGROUND

Peptide-based agents are used in molecular imaging due to their unique properties, such as rapid clearance from the circulation, high affinity and target selectivity. Many of the radiolabeled peptides have been clinically experienced with diagnostic accuracy. The aim of this study was to investigate in vivo biological behavior of [^99mTc(CO)₃(H₂O)₃]+ radiolabeled glycylglycine (GlyGly).

METHODS

Glycylglycine was radiolabeled with a high radiolabeling yield of 94.69±2%, and quality control of the radiolabeling process was performed by thin layer radiochromatography (TLRC) and High-Performance Liquid Radiochromatography (HPLRC). Lipophilicity study for radiolabeled complex (^99mTc(CO)₃-Gly-Gly) was carried out using solvent extraction. The in vivo evaluation was performed by both biodistribution and SPECT imaging.

RESULTS

The high radiolabelling yield of ^99mTc(CO)₃-GlyGly was obtained and verified by TLRC and HPLRC as well. According to the in vivo results, SPECT images and biodistribution data are in good accordance. The excretion route from the body was both hepatobiliary and renal.

CONCLUSION

This study shows that ^99mTc(CO)₃-GlyGly has the potential to be used as a peptide-based imaging agent. Further studies, ^99mTc(CO)₃-GlyGly can be performed on tumor-bearing animals.

Adefovir dipivoxil loaded proliposomal powders with improved hepatoprotective activity: formulation, optimization, pharmacokinetic, and biodistribution studies

The present study aimed to prepare proliposomal formulae for improving the oral bioavailability of adefovir dipivoxil (AD), a nucleoside reverse transcriptase inhibitor effective against hepatitis B virus (HBV). The prepared proliposomal formulae were characterized for entrapment efficiency (E.E.%), vesicle size and in vitro drug release after reconstitution to conventional liposomes. The optimized formula (F9) with a maximum desirability value of 0.858 was selected having E.E.% of 71 ± 3.3% with an average vesicle size of 164.6 ± 5 nm. Moreover, the crystallization of AD within the optimized formula investigated via powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) confirmed the presence of the drug in an amorphous state within the lipid vesicles with enhanced stability over a storage period of 12 months. Thioacetamide-induced liver damage in rats evidenced by elevated liver enzymes was significantly improved after treatment with the optimum formula. Pharmacokinetic and biodistribution studies of formula F9 showed a higher accumulation of AD in the liver with enhanced bioavailability compared to AD suspension which highlights its potential advantage for an effective treatment of chronic HBV. Hence, proliposomal drug delivery is considered as a better choice for the oral delivery of AD.

Biodistribution and scintigraphic evaluation of 99mTc-Mannan complex

Technetium-99m (99mTc) is extensively used in nuclear medicine, mostly used to label radiopharmaceuticals and in radio diagnostics. In the present study, we directly radiolabeled mannan with 99mTc by using Tin(II) Chloride Dihydrate (SnCl2·2H2O) as a reducing agent. Mannan, a TLR agonist is a complex carbohydrate identified as a potential modulator of biological effects of ionizing radiation, both in vitro and in vivo, in our laboratory. Under in vivo conditions mannan modulates radiation response when administered through either oral or parenteral routes. The present study aims to understand the pharmacologic biodistribution of the 99mTc-mannan complex in mice (via oral, i.p. and i.v. routes) using non-invasive scintigraphic imaging and invasive radiometry. Qualitative and quantitative analysis of 99mTc-mannan complex was performed by ITLC-SG, ascending paper chromatography. Radio-complexation efficiency of >98% was consistently achieved with hydrolyzed reduced Tc-99m being 1-2%. We confirmed stability of complex in saline and serum up to 24 h at room temperature. Biodistribution studies were performed using the above radiocomplex in BALB/c mice and 99mTc-mannan complex was administered though oral, i.p. and i.v. routes. To our expectations, most of the radioactivity accumulated in stomach and small intestine in mice with oral administration, along with insignificant activity in the remaining studied organs. It suggests that 99mTc-mannan complex did not get absorbed from the gut and was removed as such in the fecal material. On the contrary, i.p. and i.v administration of mannan resulted in significant accumulation of the 99mTc-mannan complex in kidney, liver, intestine, lungs, spleen, bone marrow, blood and heart, at both 1 h and 4 h after i.v. administration. The remaining organs (stomach, testis and muscles) showed lower accumulation of the 99mTc-mannan complex. 99mTc-mannan complex was adminstered (i.v.) in New Zealand white rabbits and it was evident from the scintigraphic images that mannan cleared very rapidly from the administration site and reached into systemic circulation. No activity in the thyroid, salivary gland, or gastric mucosa suggests an insignificant amount of free pertechnetate in the 99mTc-complex preparation, further confirming the in vivo stability of the radiolabeled mannan complex. Significant amount of radioactivity in liver, intestine and kidneys suggests hepatobiliary as well as renal routes of clearance. The bio-availability of the complex varies with the route of administration. An entirely different biodistribution pattern exists when the same molecule is administered through oral or parenteral route. Our study is the first step towards a better understanding of the mechanisms involved in radiation modulation offered by mannan administration, in vivo.