Lipid modified aptamers as vehicles for ophthalmic drug delivery

Abstract

Purpose : Low efficiency of topical drug delivery formulations is an acknowledged problem in ophthalmology. To address this, we introduce lipid modified aptamers (lApts) as a new class of vehicles for ophthalmic drug delivery. The lApt design comprises the introduction of a lipid modification in an aptamer that has been selected for the target drug. This makes the aptamer strand amphiphilic, resulting in spontaneous formation of nanoparticles (NPs). At the same time, the aptameric corona of the NP ensures highly controlled drug loading.

Methods : The generality of the approach was demonstrated employing 3 different aptamers selected for Travoprost, Brimonidin and Kanamycin. Cytotoxicity of the lApt-NP was evaluated using primary corneal cells via MTS and caspase3/7 assay. For adherence studies fluorescently labeled lApt-NP solution was applied on rats. After the designated time-point the rat were sacrificed and eyes were enucleated and evaluated. Kanamycin loaded lApt-NP (lApt^Kan) and free kanamycin itself were used for minimum inhibitory concentration test (MIC) using E.coli. For further evaluation of lApt^Kan activity, porcine eyes from an abattoir were employed. Infectious P. aeruginosa were applied on corneas for 15 min. After 24 h, the treatment with lApt^Kan and free kanamycin was started. 2 days later different dilutions of the homogenized cornea were incubated on PIA plates and the colonies forming units (c.f.u.) were calculated.

Results : The lipid aptamers exhibit an increased corneal adherence compared with unmodified aptamers as they were still detectable 60 min after application. No toxic effects were measured for the tested lApt-NPs concentrations. The MIC tests showed that under in vitro conditions, lApt^Kan NPs exhibited comparable level of activity to the free drug, which proved that the drug was liberated from the NPs.
The efficacy study revealed that lApt delivered kanamycin reduces bacterial growth on corneas much better than free kanamycin. In the untreated control, a growth of 5.3*10⁹ c.f.u. was noted while free kanamycin reduced the c.f.u. to 3.7*10⁹. A significant effect was observed with lApt^Kan, here only 0.4*10⁹ c.f.u (p>0.001) were found.

Conclusions : The functionality of our lApt carrier system was proven in-vitro and ex vivo on corneal tissue. It can be concluded that due to the long residence time of lApt on the cornea, the efficacy of NP-formulated kanamycin is significantly higher when compared to free drug.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.