Retina-Targeted Delivery of 17β-Estradiol by the Topically Applied DHED Prodrug

Effect of estradiol replacement on hippocampal concentrations of estrogens in aged rhesus macaques maintained on an obesogenic diet

Replacement involving estrogens has proven efficacy at treating a wide range of disorders that develop with menopause or after surgical removal of the ovaries. Here, we tested whether an estradiol (E2) replacement paradigm that recapitulates physiological E2 levels in the circulation also recapitulates physiological E2 levels within the hippocampus. E2 was delivered continuously to old ovariectomized (OVX) rhesus macaques, maintained on a high-fat, high-sugar Western-style diet (WSD) for ∼30 months, via subcutaneous implants; this resulted in physiological concentrations of both estrone (E1) and E2 in the circulation (determined by LC-MS/MS). Surprisingly, however, hippocampal concentrations of E2 were markedly (P < 0.01) higher than in ovary-intact animals maintained on a regular chow diet. The data suggest that E2 replacement paradigms that appear to recapitulate physiological E2 concentrations in the circulation may produce hyper-physiological E2 levels within some brain areas, especially when individuals are maintained on a WSD.

A Green Blue LED-Driven Two-Liquid-Phase One-Pot Procedure for the Synthesis of Estrogen-Related Quinol Prodrugs

Quinol derivatives of estrogens are effective pro-drugs in steroid replacement therapy. Here, we report that these compounds can be synthesized in one-pot conditions and high yield by blue LED-driven photo-oxygenation of parent estrogens. The oxidation was performed in buffer and eco-certified 2-methyltetrahydrofuran as the two-liquid-phase reaction solvent, and in the presence of meso-tetraphenyl porphyrin as the photosensitizer. Two steroidal prodrugs 10β, 17β-dihydroxyestra-1,4-dien-3-one (DHED) and 10β-Hydroxyestra-1,4-diene-3,17-dione (HEDD) were obtained with high yield and selectivity.

Novel Eye Drop Delivery Systems: Advance on Formulation Design Strategies Targeting Anterior and Posterior Segments of the Eye

Eye drops are the most common and convenient route of topical administration and the first choice of treatment for many ocular diseases. However, the ocular bioavailability of traditional eye drops (i.e., solutions, suspensions, and ointments) is very low because of ophthalmic physiology and barriers, which greatly limits their therapeutic effect. Over the past few decades, many novel eye drop delivery systems, such as prodrugs, cyclodextrins, in situ gels, and nanoparticles, have been developed to improve ophthalmic bioavailability. These novel eye drop delivery systems have good biocompatibility, adhesion, and propermeation properties and have shown superior performance and efficacy over traditional eye drops. Therefore, the purpose of this review was to systematically present the research progress on novel eye drop delivery systems and provide a reference for the development of dosage form, clinical application, and commercial transformation of eye drops.

Topical drug delivery to the retina: obstacles and routes to success

INTRODUCTION

Retinal diseases are one of the main reasons for vision loss where all available drug treatments are based on invasive drug administration such as intravitreal injections. Despite huge efforts and some promising results in animal models, almost all delivery technologies tested have failed in human trials. There are however examples of clinically effective topical delivery systems such as fast dissolving aqueous eye drop suspensions.

AREAS COVERED

Six obstacles to topical drug delivery to the eye have been identified and discussed in some details. These obstacles consist of static membrane barriers to drug permeation into the eye, dynamic barriers such as the lacrimal drainage and physiochemical barriers such as low thermodynamic activity. It is explained how and why these obstacles hamper drug permeation and how different technologies, both those that are applied in marketed drug products and those that are under investigation, have addressed these obstacles.

EXPERT OPINION

The reason that most topical drug delivery systems have failed to deliver therapeutic drug concentrations to the retina is that they do not address physiochemical barriers such as the thermodynamic activity of the permeating drug molecules. Topical drug delivery to the retina has only been successful when the static, dynamic, and physiochemical barriers are addressed simultaneously.

Proteomics-Based Retinal Target Engagement Analysis and Retina-Targeted Delivery of 17β-Estradiol by the DHED Prodrug for Ocular Neurotherapy in Males

We examined the impact of 17β-estradiol (E2) eye drops on the modulation of the proteome profile in the male rat retina. With discovery-driven proteomics, we have identified proteins that were regulated by our treatment. These proteins were assembled to several bioinformatics-based networks implicating E2's beneficial effects on the male rat retina in a broad context of ocular neuroprotection including the maintenance of retinal homeostasis, facilitation of efficient disposal of damaged proteins, and mitochondrial respiratory chain biogenesis. We have also shown for the first time that the hormone's beneficial effects on the male retina can be constrained to this target site by treatment with the bioprecursor prodrug, DHED. A large concentration of E2 was produced after DHED eye drops not only in male rat retinae but also in those of rabbits. However, DHED treatment did not increase circulating E2 levels, thereby ensuring therapeutic safety in males. Targeted proteomics focusing on selected biomarkers of E2's target engagement further confirmed the prodrug's metabolism to E2 in the male retina and indicated that the retinal impact of DHED treatment was identical to that of the direct E2 treatment. Altogether, our study shows the potential of topical DHED therapy for an efficacious and safe protection of the male retina without the unwanted hormonal side-effects associated with current estrogen therapies.

Brain-Selective Estrogen Therapy Prevents Androgen Deprivation-Associated Hot Flushes in a Rat Model

Hot flushes are best-known for affecting menopausal women, but men who undergo life-saving castration due to androgen-sensitive prostate cancer also suffer from these vasomotor symptoms. Estrogen deficiency in these patients is a direct consequence of androgen deprivation, because estrogens (notably 17β-estradiol, E2) are produced from testosterone. Although estrogens alleviate hot flushes in these patients, they also cause adverse systemic side effects. Because only estrogens can provide mitigation of hot flushes on the basis of current clinical practices, there is an unmet need for an effective and safe pharmacotherapeutic intervention that would also greatly enhance patient adherence. To this end, we evaluated treatment of orchidectomized (ORDX) rats with 10β, 17β-dihydroxyestra-1,4-dien-3-one (DHED), a brain-selective bioprecursor prodrug of E2. A pilot pharmacokinetic study using oral administration of DHED to these animals revealed the formation of E2 in the brain without the appearance of the hormone in the circulation. Therefore, DHED treatment alleviated androgen deprivation-associated hot flushes without peripheral impact in the ORDX rat model. Concomitantly, we showed that DHED-derived E2 induced progesterone receptor gene expression in the hypothalamus without stimulating galanin expression in the anterior pituitary, further indicating the lack of systemic estrogen exposure upon oral treatment with DHED.