Evaluation and structure-activity relationship of synthesized cyclohexanol derivatives on percutaneous absorption of ketoprofen using artificial neural network

Model-Informed Drug Development: In Silico Assessment of Drug Bioperformance following Oral and Percutaneous Administration

The pharmaceutical industry has faced significant changes in recent years, primarily influenced by regulatory standards, market competition, and the need to accelerate drug development. Model-informed drug development (MIDD) leverages quantitative computational models to facilitate decision-making processes. This approach sheds light on the complex interplay between the influence of a drug's performance and the resulting clinical outcomes. This comprehensive review aims to explain the mechanisms that control the dissolution and/or release of drugs and their subsequent permeation through biological membranes. Furthermore, the importance of simulating these processes through a variety of in silico models is emphasized. Advanced compartmental absorption models provide an analytical framework to understand the kinetics of transit, dissolution, and absorption associated with orally administered drugs. In contrast, for topical and transdermal drug delivery systems, the prediction of drug permeation is predominantly based on quantitative structure-permeation relationships and molecular dynamics simulations. This review describes a variety of modeling strategies, ranging from mechanistic to empirical equations, and highlights the growing importance of state-of-the-art tools such as artificial intelligence, as well as advanced imaging and spectroscopic techniques.

Surging footprints of mathematical modeling for prediction of transdermal permeability

In vivo skin permeation studies are considered gold standard but are difficult to perform and evaluate due to ethical issues and complexity of process involved. In recent past, a useful tool has been developed by combining the computational modeling and experimental data for expounding biological complexity. Modeling of percutaneous permeation studies provides an ethical and viable alternative to laboratory experimentation. Scientists are exploring complex models in magnificent details with advancement in computational power and technology. Mathematical models of skin permeability are highly relevant with respect to transdermal drug delivery, assessment of dermal exposure to industrial and environmental hazards as well as in developing fundamental understanding of biotransport processes. Present review focuses on various mathematical models developed till now for the transdermal drug delivery along with their applications.

Formulation and biopharmaceutical evaluation of a transdermal patch containing letrozole

The purpose of this study was to formulate a drug-in-adhesive (DIA) transdermal patch containing letrozole, a third generation aromatase inhibitor for the treatment of breast cancer, using pressure-sensitive-adhesives (PSAs) and to evaluate the percutaneous penetration and pharmacokinetics of letrozole after transdermal administration, compared with that for the oral route. The formulation factors for such a patch, including the PSAs, enhancers and amount of drug loaded were investigated. Among the tested preparations, the formulation with DURO-TAK 87-4098, Azone and propylene glycol showed the highest letrozole permeation. The pharmacokinetic characteristics of an optimized DIA patch containing letrozole were determined using rats, while orally administered letrozole in solution was used as a control. The pharmacokinetic parameter, such as the mean residence time (MRT) was significantly (p<0.05) different following transdermal administration compared with oral administration. The in vivo results observed with the patches in rats were in good agreement with the plasma concentrations predicted from the in vitro penetration data. As a patient-friendly, convenient, high local drug concentration and sustained dosing therapeutic system, the transdermal patches incorporating letrozole provide a useful strategy for the prevention and treatment of breast cancer.

Percutaneous permeation enhancement by terpenes: mechanistic view

A popular approach for improving transdermal drug delivery involves the use of penetration enhancers (sorption promoters or accelerants) which penetrate into skin to reversibly reduce the barrier resistance. The potential mechanisms of action of penetration enhancers include disruption of intercellular lipid and/or keratin domains and tight junctions. This results in enhanced drug partitioning into tissue, altered thermodynamic activity/solubility of drug etc. Synthetic chemicals (solvents, azones, pyrrolidones, surfactants etc.) generally used for this purpose are rapidly losing their value in transdermal patches due to reports of their absorption into the systemic circulation and subsequent possible toxic effect upon long term application. Terpenes are included in the list of Generally Recognized As Safe (GRAS) substances and have low irritancy potential. Their mechanism of percutaneous permeation enhancement involves increasing the solubility of drugs in skin lipids, disruption of lipid/protein organization and/or extraction of skin micro constituents that are responsible for maintenance of barrier status. Hence, they appear to offer great promise for use in transdermal formulations. This article is aimed at reviewing the mechanisms responsible for percutaneous permeation enhancement activity of terpenes, which shall foster their rational use in transdermal formulations.

Combined effects of ethanol and l-menthol on hairless rat stratum corneum investigated by synchrotron X-ray diffraction

Synchrotron X-ray diffraction was employed to evaluate the effect of ethanol and l-menthol on lipid arrangements in the stratum corneum of hairless rats. Two sharp diffractions (S=2.40 and S=2.67, corresponding to spacing of 0.417 nm and 0.374 nm respectively) were observed on the broad hump peak derived from soft keratin. To assist in understanding the effects of treatment with ethanol and l-menthol, an abundance ration of lipid hydrocarbon chain packing index (R(H/O)) was defined as R(H/O)=(Peak area at S=2.40 nm(-1))/(Peak area at S=2.67 nm(-1)). When ethanol was applied to the stratum corneum the intensities of diffraction peaks declined slightly. The R(H/O) values observed were not affected by variations in ethanol concentrations in the range 0-40% (w/w). The R(H/O) values did not change even when treatment with ethanol (40%, w/w) was extended to 8 h. These results suggested that lipid arrangements in the stratum corneum were not affected by ethanol. On the other hand, exposure of the stratum corneum to 2% (w/w) L-menthol caused a significant decrease in R(H/O) value. It was shown that L-menthol was dispersed through the stratum corneum, intruded mainly into hexagonal hydrocarbon chain packing, and disrupted the regular organization of these structures.

The mode of promoting activity of O-ethylmenthol as a transdermal absorption enhancer

PURPOSE

The mode of action of O-ethylmenthol (MET), a promising compound to enhance transdermal drug delivery, was elucidated. Morphology of the skin treated with MET was investigated employing a laser scanning confocal microscopy.

METHODS

Confocal scanning laser microscope and laser scanning microscope were employed for the morphological evaluation of the stratum corneum. To evaluate the fluidity of intercellular lipids by treatment with MET, liposomes composed of the stratum corneum lipids were prepared.

RESULTS

Distribution amounts of the fluorescent probes greatly increased in the intercellular regions of the stratum corneum treated with 40% ethanol containing MET. Based on the skin surface observations, the difference in relative height between keratinocytes and intercellular regions was defined as DeltaH = DeltaH(keratinocytes) - DeltaH(intercellular space), where DeltaH is the difference in relative height, DeltaH(keratinocytes) is the height of center region in the keratinocytes, and DeltaH(intercellular space) is the height of the intercellular space. DeltaH values became negative in the skin surface treated with 40% ethanol containing MET because of the swelling in the intercellular regions. DeltaH values changed from positive to negative 15-30 min after the administration of MET. A very short period of application of MET was sufficient to induce its promoting activity.

CONCLUSIONS

MET was able to change the structure of the intercellular lipids, thereby enhancing both the partitioning and diffusion of drugs through the skin.

The effect of penetration enhancers on drug delivery through skin: a QSAR study

Skin penetration enhancers are used to allow formulation of transdermal delivery systems for drugs that are otherwise insufficiently skin-permeable. A full understanding of the mode of action could be beneficial for the design of potent enhancers and for the choice of the enhancer to be used in the topical formulation of a special drug. In this study, the structural requirements of penetration enhancers have been investigated using the Quantitative Structure-Activity Relationship (QSAR) technique. Activities of naturally occurring terpenes, pyrrolidinone and N-acetylprolinate derivatives on the skin penetration of 5-fluorouracil, diclofenac sodium (DFS), hydrocortisone (HC), estradiol and benazepril have been considered. The resulting QSARs indicated that for 5-fluorouracil and diclofenac sodium, less hydrophobic enhancers were the most active. More precisely, molecular descriptors in the corresponding QSARs indicated the possible involvement of intermolecular electron donor-acceptor interactions. This was in contrast to the skin permeation promotion of hydrocortisone, estradiol and benazepril by enhancers, where a linear relationship between enhancement activity and n-octanol/water partition coefficients of enhancers was evident. The possible mechanisms of penetration enhancement as suggested by the QSARs will be discussed.

Mechanistic and empirical modeling of skin permeation of drugs

The skin forms a barrier to the external environment, maintaining body fluids within our system and excluding harmful substances, while the skin is a site of administration of drugs for topical and systemic chemotherapy. It is an important issue to predict the rate at which drugs or other xenobiotics penetrate the skin. In this article, we review modeling approaches for predicting skin permeation of compounds, including both mechanistic and empirical approaches. Mechanistic approaches can give us much information on understanding of skin permeation of the compounds, such as structure-permeability relationship, contribution of each barrier step, mechanism of penetration enhancers, and in vivo-in vitro relationship. On the other hand, empirical modeling can overcome any inaccuracies of mechanistic models caused by the existence of uncertainties and, therefore, give us better predictions from the practical point of view. Artificial neural networks are being available for empirical modeling of complex skin transport phenomenon.

Neural network based optimization of drug formulations

A pharmaceutical formulation is composed of several formulation factors and process variables. Several responses relating to the effectiveness, usefulness, stability, as well as safety must be optimized simultaneously. Consequently, expertise and experience are required to design acceptable pharmaceutical formulations. A response surface method (RSM) has widely been used for selecting acceptable pharmaceutical formulations. However, prediction of pharmaceutical responses based on the second-order polynomial equation commonly used in an RSM, is often limited to low levels, resulting in poor estimations of optimal formulations. The purpose of this review is to describe the basic concept of the multi-objective simultaneous optimization technique, in which an artificial neural network (ANN) is incorporated. ANNs are being increasingly used in pharmaceutical research to predict the nonlinear relationship between causal factors and response variables. Superior function of the ANN approach was demonstrated by the optimization for typical numerical examples.

Effect of 1-O-ethyl-3-butylcyclohexanol on the skin permeation of drugs with different physicochemical characteristics

The effects of 1-O-ethyl-3-butylcyclohexanol (OEBC) on the in vitro skin permeation of ten model drugs with different physicochemical properties across excised rat skin were evaluated. The results showed that the addition of OEBC significantly improved the in vitro skin permeation of the model drugs compared with the control (without OEBC). To clarify the promoting mechanism of OEBC, a multiple regression analysis was employed. When the permeation study was performed without OEBC, the permeability coefficient was quantitatively predicted as a linear function of molecular weight (log MW) and their lipophilicity (partition coefficient of drugs between octanol and water (log K(o/w)) with a sufficiently high correlation coefficient (r=0.842). It was suggested that skin permeation of drugs without OEBC was explained as a function of diffusion of drugs through the skin and partitioning of drugs to the skin. Although OEBC was administered, the permeability coefficient of drugs cannot be predicted as a linear function of log MW and log K(o/w) (r=0.572).

Influence of molecular dipoles on human skin permeability: Use of 6-ketocholestanol to enhance the transdermal delivery of bacitracin

In the present work, we report the possibility of modifying the electrostatic properties of the skin by treating human epidermis with compounds whose structures possess a large molecular dipole moment. Data are presented showing that such a modification can be used to enhance dermal drug delivery. Inclusion of such compounds in biological membranes affects the so-called membrane dipole potential, an electrical potential originating from molecular dipoles present on the lipid molecules. Modifications in the magnitude of this potential are known to affect the interaction of hydrophobic ions and peptides with model membranes. Using fluorescein-labeled bacitracin and confocal microscopy, we show that the penetration of the antibiotic peptide bacitracin into the epidermis is enhanced when the skin has been pretreated with liposomes loaded with 30 mol % 6-ketocholestanol, a compound known to increase the magnitude of the membrane dipole potential. Studies using the fluorescent indicators fluoresceinphosphatidylethanolamine and 1-(3-sulfonatopropyl)-4-[beta [2-(di-n-octylamino)-6-naphthyl] vinyl] pyridinium betaine show that the interaction of bacitracin with model membranes is also enhanced by the presence of 6-ketocholestanol in the bilayer and offers some indication to the mechanism of penetration enhancement.

Predictive non-linear modeling of complex data by artificial neural networks

An artificial neural network (ANN) is an artificial intelligence tool that identifies arbitrary nonlinear multiparametric discriminant functions directly from experimental data. The use of ANNs has gained increasing popularity for applications where a mechanistic description of the dependency between dependent and independent variables is either unknown or very complex. This machine learning technique can be roughly described as a universal algebraic function that will distinguish signal from noise directly from experimental data. The application of ANNs to complex relationships makes them highly attractive for the study of biological systems. Recent applications include the analysis of expression profiles and genomic and proteomic sequences.