Recent advances in retrometabolic design approaches

Loteprednol Etabonate for the Treatment of Dry Eye Disease

Dry eye disease (DED) is a common ocular condition that can impair vision and may adversely impact quality of life. Due to the inflammatory nature of this disorder, topical corticosteroids are an effective treatment option, particularly for moderate-to-severe DED when first-line treatments, such as ocular lubricants, are insufficient. Loteprednol etabonate (LE) is a retrometabolically designed corticosteroid with a low propensity to cause corticosteroid-related adverse effects, such as elevated intraocular pressure (IOP). This review was conducted to provide an assessment of published studies on the use of LE for treatment of inflammation associated with DED. Twelve prospective and 2 retrospective studies evaluating LE ophthalmic suspension 0.5% and 2 prospective studies evaluating LE ophthalmic gel 0.5% were identified. LE given as monotherapy or with artificial tears (AT) improved signs of DED, especially among patients with a more pronounced inflammatory component, and also improved DED symptoms compared to baseline and/or control. Treatment with LE before cyclosporine A (CsA) therapy reduced stinging upon CsA initiation and provided more rapid relief of DED signs and symptoms than CsA plus AT alone. In patients with meibomian gland dysfunction, LE alone, or in addition to eyelid scrubs/warm compresses, reduced clinical signs and symptoms, and tear proinflammatory cytokine levels. Overall, LE was safe and well tolerated, with minimal effects on IOP. While larger and longer-term studies are warranted, these data support the use of LE as a safe and effective treatment option for DED.

Risk assessment of volatile organic compounds (VOCs) detected in sanitary pads

Disposable sanitary pads are a necessity for women's health, but safety concerns regarding the use of these products have created anxiety. The aim of this study was to conduct a risk assessment of 74 volatile organic compounds (VOCs), which were expected to be contained within sanitary pads. Of the 74 VOCs, 50 were found in sanitary pads retailed in Korea at concentrations ranging from 0.025 to 3548.09 µg/pad. In order to undertake a risk assessment of the VOCs, the toxicological database of these compounds in the United States Environmental Protection Agency (USEPA), Agency for Toxic Substances and Disease Registry (ATSDR), National Toxicology Program (NTP) and World Health Organization (WHO) was searched. Ethanol was found to exhibit the highest reference dose (RfD) while 1,2-dibromo-3-chloro-propane displayed the lowest RfD. Consequently, a worst-case exposure scenario was applied in this study. It was assumed that there was the use of 7.5 sanitary napkins/day for 7 days/month. In the case of panty liners or overnight sanitary napkins, the utilization of 90 panty liners/month or 21 overnight sanitary napkins/month was assumed, respectively. In addition, 43 kg, the body weight of 12 to 13-year-old young women, and 100% VOCs skin absorption were employed for risk assessment. The systemic exposure dose (SED) values were calculated ranging from 1.74 (1,1,2-trichloroethane) ng/kg/day to 144.4 (ethanol, absolute) µg/kg/day. Uncertainty factors (UFs) were applied ranging from 10 to 100,000 in accordance with the robustness of animal or human experiments. The margin of exposure (MOE) of 34 VOCs was more than 1 (acceptable MOE > 1). Applicable carcinogenic references reported that the cancer risk of five VOCs was below 10^-6. Based on our findings, evidence indicates that the non-cancer and cancer risks associated with VOCs detected in sanitary pads currently used in South Korea do not pose an adverse health risk in women.

Rheological Properties, Dissolution Kinetics, and Ocular Pharmacokinetics of Loteprednol Etabonate (Submicron) Ophthalmic Gel 0.38

Purpose: To evaluate rheological properties, in vitro dissolution, and in vivo ocular pharmacokinetics of loteprednol etabonate (LE) (submicron) ophthalmic gel 0.38%. Methods: The viscosity of the LE gel 0.38% formulation was measured with a controlled stress rheometer. Dissolution kinetics were evaluated in a fixed-volume and flow-through assay. Rabbits received a single instillation of LE (submicron) gel 0.38% (both eyes), and concentrations of LE in ocular tissues were determined through 24 h by liquid chromatography with tandem mass spectrometry. Where indicated, comparators included micronized LE gel 0.38%, 0.5% (Lotemax® gel), and 0.75%. Results: LE (submicron) gel 0.38% exhibited shear-thinning characteristics similar to LE gel 0.5% with nearly identical yield stress. LE (submicron) gel 0.38% released 2.6-fold more LE into the dissolution medium than micronized LE gel 0.5% over 30 s in the fixed-volume dissolution assay, and submicron LE attained higher concentrations of dissolved LE than micronized LE gel 0.38% in the flow-through dissolution assay. In rabbits, the maximal concentration and area-under-the-curve over 24 h for LE in aqueous humor were 2.5- and 1.8-fold higher, respectively, for LE (submicron) gel 0.38% versus micronized LE gel 0.5% (both P < 0.001). Pharmacokinetic parameters were similar for most other tissues. Conclusions: LE (submicron) gel 0.38% demonstrated similar rheological properties to micronized LE gel 0.5% but faster dissolution, thus providing similar or higher LE concentrations in the aqueous humor, cornea, and iris-ciliary body after ocular dosing in rabbits despite a lowered concentration of drug in the formulation.

Prolonged exposure to loteprednol etabonate in human tear fluid and rabbit ocular tissues following topical ocular administration of Lotemax gel, 0.5%

PURPOSE

A new gel formulation containing loteprednol etabonate (LE), a C-20 ester corticosteroid used to treat ocular inflammation, was developed to provide increased retention on the ocular surface for improved drug delivery to intraocular tissues. This investigation evaluated concentrations of LE in tear fluid following topical instillation of LE gel to humans and the ocular and systemic pharmacokinetics of LE following administration to rabbits.

METHODS

LE ophthalmic gel 0.5% was administered as a single topical dose to human volunteers (n=12) and Dutch Belted rabbits (n=40). In the human study, tear sampling was performed at 6, 9, 12, and 24 h after instillation. In the rabbit study, tears and ocular tissues were collected from 5 min through 24 h postdose. Serial blood samples were collected from one cohort of rabbits for plasma analysis. Concentrations of LE were determined by high performance liquid chromatography tandem mass spectrometry.

RESULTS

In humans, LE was detected in tears at all the time points assessed with mean concentrations of 114 μg/g at 6 h declining to 2.41 μg/g at 24 h postdose. In rabbits, LE was detected in all ocular tissues within 5 min after dosing. Maximum concentrations of LE were achieved within 0.5 h and were highest in tear fluid (1560 μg/g), followed by bulbar conjunctiva (4.03 μg/g), cornea, (2.18 μg/g), iris/ciliary body (0.162 μg/g), and aqueous humor (0.0138 μg/mL). LE remained measurable in all ocular tissues through 24 h with the exception of aqueous humor. In contrast, plasma levels of LE were low with no detectable levels after 4 h.

CONCLUSIONS

The gel formulation of LE provided prolonged exposure to LE on the ocular surface, with measurable levels in tears through 24 h in both humans and rabbits, for delivery of LE to anterior segment tissues, as evidenced by sustained levels of LE in rabbit conjunctiva, cornea, and iris/ciliary body.

Application of computational toxicological approaches in human health risk assessment. I. A tiered surrogate approach

Hazard identification and dose-response assessment for chemicals of concern found in various environmental media are typically based on epidemiological and/or animal toxicity data. However, human health risk assessments are often requested for many compounds found at contaminated sites throughout the US that have limited or no available toxicity information from either humans or animals. To address this issue, recent efforts have focused on expanding the use of structure-activity relationships (SAR) approaches to identify appropriate surrogates and/or predict toxicological phenotype(s) and associated adverse effect levels. A tiered surrogate approach (i.e., decision tree) based on three main types of surrogates (structural, metabolic, and toxicity-like) has been developed. To select the final surrogate chemical and its surrogate toxicity value(s), a weight-of-evidence approach based on the proposed decision tree is applied. In addition, a case study with actual toxicity data serves as the evaluation to support our tiered surrogate approach. Future work will include case studies demonstrating the utility of the surrogate approach under different scenarios for data-poor chemicals. In conclusion, our surrogate approach provides a reasonable starting point for identifying potential toxic effects, target organs, and/or modes-of-action, and for selecting surrogate chemicals from which to derive either reference or risk values.

Toxicity testing in the 21st century: a vision and a strategy

With the release of the landmark report Toxicity Testing in the 21st Century: A Vision and a Strategy, the U.S. National Academy of Sciences, in 2007, precipitated a major change in the way toxicity testing is conducted. It envisions increased efficiency in toxicity testing and decreased animal usage by transitioning from current expensive and lengthy in vivo testing with qualitative endpoints to in vitro toxicity pathway assays on human cells or cell lines using robotic high-throughput screening with mechanistic quantitative parameters. Risk assessment in the exposed human population would focus on avoiding significant perturbations in these toxicity pathways. Computational systems biology models would be implemented to determine the dose-response models of perturbations of pathway function. Extrapolation of in vitro results to in vivo human blood and tissue concentrations would be based on pharmacokinetic models for the given exposure condition. This practice would enhance human relevance of test results, and would cover several test agents, compared to traditional toxicological testing strategies. As all the tools that are necessary to implement the vision are currently available or in an advanced stage of development, the key prerequisites to achieving this paradigm shift are a commitment to change in the scientific community, which could be facilitated by a broad discussion of the vision, and obtaining necessary resources to enhance current knowledge of pathway perturbations and pathway assays in humans and to implement computational systems biology models. Implementation of these strategies would result in a new toxicity testing paradigm firmly based on human biology.

New and improved glucocorticoid receptor ligands

The therapeutic and prophylactic use of glucocorticoids is widespread due to their powerful anti-inflammatory, antiproliferative and immunomodulatory activity. However, long-term use of these drugs can result in severe dose-limiting side effects. One of the most critical and debilitating side effects is osteoporosis, which leads to increased risk of fractures. Glucocorticoids damage bone through several different mechanisms. The search for novel glucocorticoids that have reduced side effects in bone and other tissues is being driven by the identification of new mechanisms of action of the glucocorticoid receptor. This may facilitate the detection of new, safer therapies with efficacies equivalent to currently prescribed steroids.

QUANTITATIVE STRUCTURE-METABOLISM RELATIONSHIP MODELING OF METABOLICN-DEALKYLATION REACTION RATES

It is widely recognized that preclinical drug discovery can be improved via the parallel assessment of bioactivity, absorption, distribution, metabolism, excretion, and toxicity properties of molecules. High-throughput computational methods may enable such assessment at the earliest, least expensive discovery stages, such as during screening compound libraries and the hit-to-lead process. As an attempt to predict drug metabolism and toxicity, we have developed an approach for evaluation of the rate of N-dealkylation mediated by two of the most important human cytochrome P450s (P450), namely CYP3A4 and CYP2D6. We have taken a novel approach by using descriptors generated for the whole molecule, the reaction centroid, and the leaving group, and then applying neural network computations and sensitivity analysis to generate quantitative structure-metabolism relationship models. The quality of these models was assessed by using the cross-validated correlation coefficients of 0.82 for CYP3A4 and 0.79 for CYP2D6 as well as external test molecules for each enzyme. The relative performance of different neural networks was also compared, and modular neural networks with two hidden layers provided the best predictive ability. Functional dependencies between the neural network input and output variables, generalization ability, and limitations of the described approach are also discussed. These models represent an initial approach to predicting the rate of P450-mediated metabolism and may be applied and integrated with other models for P450 binding to produce a systems-based approach for predicting drug metabolism.

Soft steroids: a new approach to the treatment of inflammatory airways diseases

Inhaled synthetic glucocorticosteroids are widely used in the treatment of bronchial asthma where they provide very effective first line treatment. However, a range of unwanted side effects and the often complex dosing schedules associated with these drugs frequently result in poor patient compliance. The soft drug approach has been utilised as a means of delivering these potent anti-inflammatory agents close to their site of action while reducing the degree of systemic exposure and thus limiting or eliminating the associated systemic and local side effects. A further target for pharmaceutical companies is to deliver these new treatments in a once daily formulation thus further enhancing patient compliance. While many soft steroids have failed to progress into the clinic two are meeting with some degree of success. Loteprednol etabonate, an inactive metabolite soft steroid, has been accepted for the treatment of ophthalmic disorders and is being examined in clinical trials for its effects on airway inflammation. Ciclesonide, a pro-drug soft steroid, has demonstrated efficacy without side effects in a once daily formulation in asthma patients and is being developed for the treatment of both asthma and chronic obstructive pulmonary disease with launches of a once daily inhaler formulation expected in 2003. These drugs may represent a significant step forward in the treatment of inflammatory diseases of the airways.

Pharmacology of airway inflammation in asthma and COPD

The current asthma therapies are not cures and symptoms return soon after treatment is stopped even after long term treatment. Although inhaled glucocorticoids are highly effective in controlling airway inflammation in asthma, they are ineffective in the small group of patients with glucocorticoid-dependent and -resistant asthma. With very few exceptions, COPD is caused by tobacco smoking, and smoking cessation is the only truly effective treatment of COPD available. Current pharmacological treatment of COPD is unsatisfactory, as it does not significantly influence the severity of the disease or its natural course. Glucocorticoids are scarcely effective in COPD patients without concomitant asthma. Bronchodilators improves symptoms and quality of life, in COPD patients, but, with the exception of tiotropium, they do not significantly influence the natural course of the disease. Theophylline is the only drug which has been demonstrated to have a significant effect on airway inflammation in patients with COPD. Here we review the pharmacology of currently used antiinflammatory therapies for asthma and COPD and their proposed mechanisms of action. Recent understanding of disease mechanisms in severe steroid-dependent and -resistant asthma and in COPD, has lead to the development of novel compounds, which are in various stages of clinical development. We review the current status of some of these new potential drugs.

Potency and specificity of the pharmacological action of a new, antiasthmatic, topically administered soft steroid, etiprednol dicloacetate (BNP-166)

In the present study, the pharmacological effects of etiprednol dicloacetate (BNP-166; ethyl-17alpha-dichloroacetoxy-11beta-hydroxyandrosta-1,4-diene-3-one-17beta-carboxylate), a new soft steroid, intended to use for the treatment of asthma, were investigated in an animal model of allergen sensitized and challenged Brown Norway rats using local treatment. The examinations involved the determination of the effect of the compound on the extent of allergen induced broncho-alveolar fluid and lung tissue eosinophilia, goblet cell hyperplasia and mucus production, perivascular edema formation, and airways hyperresponsiveness. The activity of etiprednol dicloacetate was compared with that of budesonide. Using in vitro methods, the soft character of etiprednol dicloacetate was investigated together with its capability to dissociate transrepressing and transactivating properties. We found that combining all the examined parameters etiprednol dicloacetate was at least equipotent with budesonide in the animal model, but in several investigated variables it surpassed the activity of budesonide. The effect of etiprednol dicloacetate in vitro was shown to be the function of the quantity of the serum, present in the assay, it was also strongly affected by the incubation time and decreased significantly when it was preincubated with human plasma. These features are characteristics of a soft drug that is quickly inactivated in the systemic circulation. In addition, it was revealed that while the transrepressing potential of etiprednol dicloacetate remained high, its transactivating activity was greatly reduced. These data indicate that the strong local effect of the compound will very likely be accompanied with a significantly reduced systemic activity predicting favorable selectivity in the pharmacological action of etiprednol dicloacetate.