Peptide dendrimer-conjugates of ketoprofen: Synthesis andex vivoandin vivoevaluations of passive diffusion, sonophoresis and iontophoresis for skin delivery
The aim of this study was to evaluate skin delivery of ketoprofen when covalently tethered to mildly cationic (2+ or 4+) peptide dendrimers prepared wholly by solid phase peptide synthesis. The amino acids glycine, arginine and lysine formed the dendrimer with ketoprofen tethered either to the lysine side-arm (Nε) or periphery of dendrimeric branches. Passive diffusion, sonophoresis- and iontophoresis-assisted permeation of each peptide dendrimer-drug conjugate (D1–D4) was studied across mouse skin, both in vitro and in vivo. In addition, skin toxicity of dendrimeric conjugates when trialed with iontophoresis or sonophoresis was also evaluated. All dendrimeric conjugates improved aqueous solubility at least 5-fold, compared to ketoprofen alone, while also exhibiting appreciable lipophilicity. In vitro passive diffusion studies revealed that ketoprofen in its native form was delivered to a greater extent, compared with a dendrimer-conjugated form at the end of 24 h (Q24 h (μg/cm2): ketoprofen (68.06 ± 3.62) > D2 (49.62 ± 2.92) > D4 (19.20 ± 0.89) > D1 (6.45 ± 0.40) > D3 (2.21 ± 0.19). However, sonophoresis substantially increased the skin permeation of ketoprofen-dendrimer conjugates in 30 min (Q30 min (μg/cm2): D4 (122.19 ± 7.14) > D2 (66.74 ± 3.86) > D1 (52.10 ± 3.22) > D3 (41.66 ± 3.22)) although ketoprofen alone again proved superior (Q30 min: 167.99 ± 9.11 μg/cm2). Next, application of iontophoresis was trialed and shown to considerably increase permeation of dendrimeric ketoprofen in 6 h (Q6 h (μg/cm2): D2 (711.49 ± 39.14) > D4 (341.23 ± 16.43) > D3 (89.50 ± 4.99) > D1 (50.91 ± 2.98), with a Q6 h value of 96.60 ± 5.12 μg/cm2 for ketoprofen alone). In vivo studies indicated that therapeutically relevant concentrations of ketoprofen could be delivered transdermally when iontophoresis was paired with D2 (985.49 ± 43.25 ng/mL). Further, histopathological analysis showed that the dendrimeric approach was a safe mode as ketoprofen alone. The present study successfully demonstrates that peptide dendrimer conjugates of ketoprofen, when combined with non-invasive modalities, such as iontophoresis can enhance skin permeation with clinically relevant concentrations achieved transdermally.