**1. Introduction**

In the early years of this century, it was expected that revolutionary development in industry and technology will allow an unprecedented opportunities for drug discovery and development; however, the disappointing rate of drug approval in the last 20 years shed the light on the urgent need to reassess the efficiency of current strategies of drug discovery.

Despite the large amount of investment that has been put in drug development, several drug candidates fail to pass due to pharmacokinetic issues or severe side effects that mainly are not demonstrated until clinical phases, which lead to extreme economic loss to pharmaceutical companies that might spend more than billion dollars in the process.

These facts were not overlooked by pharmaceutical industries or academia; so, they started to apply a new strategy that embraces new application of approved drugs rather than starting from scratch, which is known as drug repositioning. While the term was first coined in 2004, the approach has already led to the discovery of several therapeutic agents in the last century; however, serendipity, trials, and errors were the main players in most of these cases.

This means that harnessing our highly advanced tools of molecular biology and computational techniques would guarantee the rediscovery of new indications for already approved drugs, which will not only increase our arsenal of therapeutic agents but also will drastically decrease the time and costs of the whole process.

Moreover, this approach could help for finding therapeutic solutions for orphan diseases or clinical conditions that affects low number of population which are usually neglected by pharmaceutical corps as in the case of dermatologic therapeutics due to the low prevalence of many dermatoses and the inappropriate estimation of the burden of psychological and physical impact of skin disorders on the quality of life.

Indeed, the field of dermatology covers wide range of disorders, but this means that drug repurposing strategy may be uniquely successful, hence the broad variety of pathophysiological process affecting the skin. In that aspect, the liver research laboratory (FAB-Lab, Faculty of Pharmacy, Mansoura University, Mansoura, Egypt) has utilized several approaches for not only optimization and enhancing the therapeutic effect of commonly available natural products but also recognizing novel application for them so that one therapeutic agent could be used for treatment of several or complex conditions (**Table 1**). In this chapter, we will review different strategies for drug repositioning and their application in dermatological and cosmeceutical field.


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**Figure 1.**

*Drug Repurposing in Dermatology: Molecular Biology and Omics Approach*

the associated pathways, and change in disease phenotypes.

approach and its application in drug repositioning.

Drug repositioning is achieved by understanding of molecular mechanisms of drug action and by identification of the interacting proteins of the drug. In many cases, molecular mechanism of drug action is poorly understood or completely unknown. The drug action can be observed by identification of drug targets and their specific interactions, drug-induced change in expression of a specific gene and

Current approaches for drug repositioning come from the so-called "drug action spectrum" concept as shown in **Figure 1**, which is based on three paradigms, namely, target-centric, drug-centric, and disease-centric repositioning. The first and second modules are closely related and usually applied interchangeably; the target-centric module focuses on finding new indication for the already established target; for example, the discovery of the role of androgenic receptor in hair loss allowed the repurposing of finasteride for treatment of androgenic alopecia.

Drug-centric module aims in finding a new target for therapeutic agent, experimental or abandoned drugs; for example, the notorious thalidomide, which was firstly indicated for treatment of nausea and caused the phocomelia crisis, has been repurposed for treatment of myeloma and several dermatological conditions related

These types of repositioning use computational ligand- and structure-based techniques [12, 13], chemical proteomics [16, 17], and off-target screening to identify potential therapeutic applications; so, we will explain the theory behind its

In the third module, the repurposing depends on the similarity of pathophysiological nature of diseases; for example, different types of cancers or different autoimmune diseases which allow the expansion of drug to a closely related indication so that extensive analysis of the associated molecular targets may not be required. Nevertheless, this type of repositioning strategy is the most observed type

*The concept of drug action spectrum in drug repositioning is based on three paradigms, namely, drug-centric, target-centric, and disease-centric repositioning. In the first and second approaches, computational approaches are used extensively to identify novel targets for compounds that were used for different applications. Omics, data mining, and meta-analysis of clinical trials could also be used to analyze the relationship between diseases* 

*and novel molecular targets that was previously investigated in different diseases.*

*DOI: http://dx.doi.org/10.5772/intechopen.93344*

**2. Drug repositioning strategies**

to immune diseases.

**Table 1.**

*Studies of natural product repositioning in FAB-Lab.*

*Drug Repurposing in Dermatology: Molecular Biology and Omics Approach DOI: http://dx.doi.org/10.5772/intechopen.93344*
