Semifluorinated Alkanes as New Drug Carriers-An Overview of Potential Medical and Clinical Applications

Fluorinated compounds have been used in clinical and biomedical applications for years. The newer class of semifluorinated alkanes (SFAs) has very interesting physicochemical properties including high gas solubility (e.g., for oxygen) and low surface tensions, such as the well-known perfluorocarbons (PFC). Due to their high propensity to assemble to interfaces, they can be used to formulate a variety of multiphase colloidal systems, including direct and reverse fluorocarbon emulsions, microbubbles and nanoemulsions, gels, dispersions, suspensions and aerosols. In addition, SFAs can dissolve lipophilic drugs and thus be used as new drug carriers or in new formulations. In vitreoretinal surgery and as eye drops, SFAs have become part of daily clinical practice. This review provides brief background information on the fluorinated compounds used in medicine and discusses the physicochemical properties and biocompatibility of SFAs. The clinically established use in vitreoretinal surgery and new developments in drug delivery as eye drops are described. The potential clinical applications for oxygen transport by SFAs as pure fluids into the lungs or as intravenous applications of SFA emulsions are presented. Finally, aspects of drug delivery with SFAs as topical, oral, intravenous (systemic) and pulmonary applications as well as protein delivery are covered. This manuscript provides an overview of the (potential) medical applications of semifluorinated alkanes. The databases of PubMed and Medline were searched until January 2023.

VEGF TrapR1R2 Suspended in the Semifluorinated Alkane F6H8 Inhibits Inflammatory Corneal Hem- and Lymphangiogenesis

Purpose

Semifluorinated alkanes (SFAs) are used at the ocular surface as lubricants or vehicles for drugs. The purpose of this study was to test the effect of vascular endothelial growth factor (VEGF) Trap_R1R2 suspended in the SFA perfluorohexyloctane (Trap/F6H8) on corneal neovascularization.

Methods

Suture placement was used to induce inflammatory corneal neovascularization in mice. Treatment groups were: Trap/F6H8, VEGF Trap_R1R2 as aqueous formulation dissolved in phosphate buffer (Trap), F6H8, and phosphate buffer (controls). Eye drops were applied 3×/daily for 2 weeks. Afterward, corneas were stained with CD31 and LYVE-1 to analyze corneal hem- and lymphangiogenesis. To investigate the effect of on inflammatory cell recruitment, corneal CD45+ cells were quantified. In addition, epithelial wound closure after debridement was assessed by corneal fluorescein staining.

Results

Trap/F6H8 was as effective as Trap in inhibiting corneal hemangiogenesis and lymphangiogenesis after 2 weeks of treatment. After 3 days of treatment, Trap/F6H8 was even more effective than Trap in inhibiting corneal hemangiogenesis. Both treatment groups (Trap/F6H8 and Trap) significantly reduced corneal CD45+ cell recruitment. Epithelial closure after debridement was unaffected by Trap/F6H8 or Trap.

Conclusions

In this study, we demonstrate that F6H8 is a potential carrier for VEGF Trap_R1R2 to topically treat corneal neovascularization. Our findings might open new treatment avenues for local anti-angiogenic therapy at the cornea, as F6H8 is already approved for the usage at the ocular surface.

Translational Relevance

With this study we show for the first time that SFAs can serve as carriers for anti-angiogenic drugs at the ocular surface.

Semifluorinated Alkane Eye Drops for Treatment of Dry Eye Disease Due to Meibomian Gland Disease

Purpose: Meibomian gland disease is generally accepted as the leading cause for evaporative dry eye disease (DED). In a previous study, perfluorohexyloctane, a semifluorinated alkane, has been demonstrated to significantly increase tear film breakup time and to reduce corneal fluorescein staining in patients with evaporative DED, thereby vastly reducing dry eye-related symptoms. This study was set up to evaluate perfluorohexyloctane in a larger population of patients with Meibomian gland dysfunction.

Methods: Seventy-two patients with Meibomian gland disease and associated dry eye received 1 drop of perfluorohexyloctane 4 times daily during an observational, prospective, multicenter, 6–8-week study. Clinical assessment included best-corrected visual acuity, intraocular pressure, Schirmer test I, tear film breakup time, anterior and posterior blepharitis assessment, number of expressible Meibomian glands, meibum quality and quantity, ocular surface fluorescein staining, lid margin and symptom assessment, and Ocular Surface Disease Index (OSDI^©).

Results: From the 72 patients recruited, 61 completed the trial per protocol. Nine patients did not apply the medication as recommended and 2 patients were lost to follow-up. Tear film breakup time, corneal and conjunctival fluorescein staining, number of expressible Meibomian glands, and severity of anterior and posterior blepharitis significantly improved after 6–8 weeks of perfluorohexyloctane application. In addition, symptoms improved as demonstrated by a significant decrease of OSDI-values from 37 (±13) to 26 (±16).

Conclusions: In concordance with previous findings, 6–8 weeks of topical application of perfluorohexyloctane significantly improves clinical signs of Meibomian gland disease and associated mild to moderate DED.

19F Oximetry with semifluorinated alkanes

This work examines the variation of longitudinal relaxation rate R1(= 1/T1) of the ¹⁹F-CF₃-resonance of semifluorinated alkanes (SFAs) with oxygen tension (pO₂), temperature (T) and pH in vitro. Contrary to their related perfluorocarbons (PFCs), SFA are amphiphilic and facilitate stable emulsions, a prerequisite for clinical use. A linear relationship between R1 and pO₂ was confirmed for the observed SFAs at different temperatures. Using a standard saturation recovery sequence, T1 has been successfully measured using fluorine ¹⁹F-MRI with a self-constructed birdcage resonator at 9.4 T. A calibration curve to calculate pO₂ depending on T and R1 was found for each SFA used. In contrast to the commonly used PFC, SFAs are less sensitive to changes in pO₂, but more sensitive to changes in temperature. The influence of pH to R1 was found to be negligible.