To design and synthesize prodrugs of gatifloxacin targeting OCT, MCT, and ATB (0, +) transporters and to identify a prodrug with enhanced delivery to the back of the eye.
Dimethylamino-propyl, carboxy-propyl, and amino-propyl(2-methyl) derivatives of gatifloxacin (GFX), DMAP-GFX, CP-GFX, and APM-GFX, were designed and synthesized to target OCT, MCT, and ATB (0, +) transporters, respectively. LC-MS method was developed to analyze drug and prodrug levels in various studies. Solubility and Log D (pH 7.4) were measured for prodrugs and the parent drug. Permeability of the prodrugs was determined in cornea, conjunctiva, and sclera-choroidretinal pigment epitheluim (SCRPE) and compared with gatifloxacin using Ussing chamber assembly. Permeability mechanisms were elucidated by determining the transport in the presence of transporter specific inhibitors. 1-Methyl-4-phenylpyridinium iodide (MPP+), nicotinic acid sodium salt, and α-methyl-DL-tryptophan were used to inhibit OCT, MCT, and ATB (0, +) transporters, respectively. A prodrug selected based on in vitro studies was administered as an eye drop to pigmented rabbits and the delivery to various eye tissues including vitreous humor was compared with gatifloxacin dosing.
DMAP-GFX exhibited 12.8-fold greater solubility than GFX. All prodrugs were more lipophilic, with the measured Log D (pH 7.4) values ranging from 0.05 to 1.04, when compared to GFX (Log D: -1.15). DMAP-GFX showed 1.4-, 1.8-, and 1.9-fold improvement in permeability across cornea, conjunctiva, as well as SCRPE when compared to GFX. Moreover, it exhibited reduced permeability in the presence of MPP+ (competitive inhibitor of OCT), indicating OCT-mediated transport. CP-GFX showed 1.2-, 2.3- and 2.5-fold improvement in permeability across cornea, conjunctiva and SCRPE, respectively. In the presence of nicotinic acid (competitive inhibitor of MCT), permeability of CP-GFX was reduced across conjunctiva. However, cornea and SCRPE permeability of CP-GFX was not affected by nicotinic acid. APM-GFX did not show any improvement in permeability when compared to GFX across cornea, conjunctiva, and SCRPE. Based on solubility and permeability, DMAP-GFX was selected for in vivo studies. DMAP-GFX showed 3.6- and 1.95-fold higher levels in vitreous humor and CRPE compared to that of GFX at 1 hour after topical dosing. In vivo conversion of DMAP-GFX prodrug to GFX was quantified in tissues isolated at 1 hour after dosing. Prodrug-to-parent drug ratio was 8, 70, 24, 21, 29, 13, 55, and 60 % in cornea, conjunctiva, iris-ciliary body, aqueous humor, sclera, CRPE, retina, and vitreous humor, respectively.
DMAP-GFX prodrug enhanced solubility, Log D, as well as OCT mediated delivery of gatifloxacin to the back of the eye.