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393
marketing approval and trading of herbal formulations. To solve these problems and
promote the worldwide usage of high-quality and less expensive herbal medicinal
products, countries should frame a treaty like “Free Trade Agreement,” which may
reduce regulatory barriers and facilitate easy commercial transactions by protecting
the rights of both countries.
Harmonizing activities have been started with the standardization of pharmaco-
peial specications and classication of herbal drugs to guarantee that the same
herbal medicines are of the same quality, safety, and efcacy among nations. Similar
herbal remedies are included in the pharmacopeias of China, Japan, and Korea, but
their details are varied. Although the original plant’s family is the same, different
species were mentioned, which create a confusion for scientists. Moreover, the
name of herbal medicine represented by the regulatory body is in regional character,
which may differ for the same plant in different countries. To aid in the promotion
of the commercialization of safe and effective herbal medicines across the world,
the Western Pacic Regional Forum for the “Harmonization of Herbal Medicine”
attempted to harmonize the herbal medicine monographs in the pharmacopeias of
six Asian countries, i.e., China, Hong Kong, Japan, Korea, Singapore, and Vietnam
(World Health Organization 2024b).
In 2000, American countries started to harmonize their procedural criteria for the
registration of herbal medicine and related products. Pan American Network of
Drug Regulatory Harmonization (PANDRH) is a working group on medicinal
plants, which share advanced knowledge of different categories of herbal products,
related terminologies, protocols, and minimal standards for herbal product registra-
tion. Another important institute for harmonizing herbal medicine worldwide is
WHO’s “International Standard Terminologies on Traditional Medicine in the
Western Pacic Region” (Working Group on “Access to Health Systems including
AYUSH” 2024). Overall, the WHO and governments of some countries have tried
to harmonize the regulatory framework to smooth the supply chain of herbal medi-
cines and related products worldwide; however still efforts are required to harmo-
nize the regulatory guidelines for herbal medicines, globally.
15.7 Conclusion
Researchers and scientists are actively focusing on natural compounds due to enor-
mous potential of pharmacologically active herbal medicine in the prevention and
treatment of human ailments. Researchers are trying to increase the efcacy and
lessen the regulatory restrictions of a therapeutic application of herbal medicine by
employing a nanodrug delivery method. Thus far, animal models have demonstrated
improved stability and sustained release capabilities of nanopreparations based on
natural products, together with optimal therapeutic effects at low dose, which raises
the system’s long-term safety margin. Some diseases need to be treated over an
extended period, which means that specially formulated nanodrugs must satisfy
several requirements, including stability in systemic circulation and the ability to
release therapeutic concentrations in the appropriate locations without harming
15 Herbal Formulations: Development, Challenges, Testing, Stability, and…
394
healthy tissues. It is important to remember that drug-delivery nanocarriers have the
ability to stimulate and suppress the immune system. For this reason, comprehen-
sive immunotoxicology study is necessary before bringing such herbal medications
to the clinic.
Simultaneously, researchers also face various issues in the identication of
desired species of herbal plants and extractions of herbal medicines. The scientic
innovations happened in analytical sciences made the identication and separation
of extraction components easy. However, there is an urgent need of streamlining the
extraction processes to maintain the uniformity in quality and efcacy of herbal
medicines and formulations. Overall, the researches performed in the past proved
the potential of herbal medicine in treatment of various diseases; however, there is
an immediate need of detailed regulatory guideline for easy clinical translation of
such herbal formulations.
Acknowledgments The authors are thankful to the Department of Pharmaceuticals, Ministry of
Chemicals and Fertilizers, Government of India, for providing facilities to carry out this research
work. The NIPER-R communication number for the manuscript is NIPER-R/Communication/610.
Conict of Interest
The authors declare that they have no known competing nancial interests or
personal relationships that could have appeared to inuence the work reported in this chapter.
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16
Drug Repurposing andVirtual Screening
RuchikaSharma, SwetaRoy, andAnoopKumar
Abstract
Drug repurposing is a promising strategy in which already approved drugs are
explored for their alternate indications. It saves time and money which is involved
in the development of new chemical entities as behaviour of a molecule in a large
number of populations is already known. Virtual screening could play a signi-
cant role in the identication of potential repurposing candidates using high-
performance computational techniques. A number of virtual methods like
molecular docking, molecular dynamics, quantitative structure activity relation-
ship (QSAR), etc. are available for the identication. Recently, researchers have
also used pharmacovigilance data to identify promising drug repurposing candi-
dates. This chapter starts with introduction to drug repurposing and its impor-
tance along with various approaches which are being used. The commonly used
databases/software along with steps involved are also discussed.
Keywords
Virtual screening · Drug repurposing · In silico · High-throughput screening ·
Protein database · Algorithms
R. Sharma
Centre for Precision Medicine and Pharmacy, Delhi Pharmaceutical Sciences and Research
University, New Delhi, India
S. Roy · A. Kumar (
*)
Department of Pharmacology, Delhi Institute of Pharmaceutical Sciences and Research
(DIPSAR), Delhi Pharmaceutical Sciences and Research University (DPSRU),
New Delhi, India
400
Abbreviations
ACE2 Angiotensin-converting enzyme 2
BBB Blood-brain barrier
CCLE Cancer Cell Line Encyclopaedia
CML Chronic myeloid leukaemia
CNS Central nervous system
COVID-19 Coronavirus disease 2019
DARS Division of Applied Regulatory Science
DR Drug repurposing
FDA Food and Drug Administration
FFT Fast Fourier transform
GEO Gene Expression Omnibus
GIST Gastrointestinal stromal tumours
GOLD Genomes Online Database
HTS/HCS High-throughput or high-content screening
IRAK-4 Interleukin-1 receptor-associated kinase
LBVS Ligand-based virtual screening
MD Molecular dynamics
MDDR MDL Drug Data Report
ML Machine learning
NCBI-GEO National Centre for Biotechnology Information-Gene
Expression Omnibus
PD Protein database
PHASE Public health assessment via structural evaluation
QSAR Quantitative structure-activity relationship
SARS Severe acute respiratory syndrome
SBVS Structure-based virtual screening
TBVS Target-based virtual screening
UCSF University of California, San Francisco
VS Virtual screening
16.1 Introduction
In the previous decade, the research and manufacturing methods for new pharma-
ceuticals have been constantly evolving, with benets and results directly tied to
improving the global population’s life quality (Sahoo etal. 2021). Production and
manufacturing tactics are becoming more effective, but the costs remain a hurdle.
The average cost of developing a new medicine is between $1 and $2 billion USD,
and the entire process can take 10–17years, from target selection to registration.
These costs indicate an expensive, time-consuming, and laborious process that
involves drugs with a high added value that are frequently out of reach for at least
one-third of the global population. Therefore, drug repurposing (DR), often referred
R. Sharma et al.
401
to as drug recycling, drug rescue, drug repositioning, drug reproling, and therapeu-
tic ipping, is a ground-breaking strategy for resolving this problem (Sahoo etal.
2021). Drug repurposing (DR) includes the exploration of novel applications or
indications for existing drugs, extending beyond their initial medical uses. Utilizing
drug repurposing has the potential to reduce the average time required for drug
development by 5–7 years. Numerous instances of successful drug repurposing
exist, such as imatinib, initially designed for chronic myeloid leukaemia (CML) and
later found effective in treating malignant gastrointestinal stromal tumours (GIST).
Another illustration is aspirin, a non-steroidal anti-inammatory drug taken orally
that is also used to prevent colorectal cancer and cardiovascular disease (Gan etal.
2023). It is predicted that the drug repositioning procedure will take approximately
5years only.
The traditional drug development process incurs an average cost of USD 1.24
billion to bring a new medicine for public use, while drug repurposing involves
approximately ≤60% of the expenditure associated with traditional methods
(Napolitano et al. 2013). The accessibility of earlier gathered data on structural
optimization, pharmacokinetics, toxicology, clinical effectiveness, and safety of
drugs in the traditional approach contributes to a saving in the time and cost of
medication development, along with a decreased risk of failure or a higher success
level in medicine repurposing (Wu etal. 2013).
Importance
• It has the potential to enter directly into the phase II clinical trials.
• Reduce the attrition rate.
• Pharmacokinetic prole is already known.
• Safety prole is already known.
The extensive studies are not required for the repurposed candidates; however
few studies need to be conducted for the following reasons: need to make sure the
drug works in alternate indication, biology of diseases is different, required dose
may be different from the approved dose, and can interfere with current treatment
regimen. Therefore, few studies need to be done for the repurposing candidates.
16.2 A Prime Candidate forRepurposing
A pharmaceutical product, having completed clinical medicine development and
positioned as an excellent applicant for repurposing, may bypass additional clinical
trials if it possesses robust safety and toxicity data from prior clinical studies and if
it has received regulatory approval. The selected drug’s mechanism of action must
be clearly dened (Dinić etal. 2020).
Medicines that have progressed through various levels of clinical development
but were failed due to reasons unrelated to safety are well-suited for repurposing.
16 Drug Repurposing andVirtual Screening
402
Some instances of DR have occurred even within the course of clinical trials, exem-
plied by the renowned case of viagra (sildenal). Originally designed for hyper-
tension and angina, its novel application for treating erectile dysfunction was
discovered during clinical trials (Kulkarni etal. 2023).
16.3 Approaches
The primary challenge in drug repositioning involves identifying new associations
between drugs and diseases. Two general categories for systematic drug repurpos-
ing are in silico methods and experimental screening techniques. While the latter
strategy employs current data and new computational techniques that are substan-
tially less expensive than the former, the former approach depends on specially
developed high-throughput trials. Virtual screening is one such technology that can
be used in drug development to quickly search compound libraries using computer-
aided drug design (CADD). To tackle this challenge, various strategies have been
devised, encompassing computational methods, biological experiments, and hybrid
approaches (Fig.16.1).
A number of databases including information on medicine and diseases have
emerged as a result of the rapid development of biological microarray techniques,
including DrugBank (Wishart etal. 2018), ChemBank (Seiler etal. 2008), OMIM
(Hamosh etal. 2005), KEGG (Ogata etal. 1999), and PubMed (2024). Large-scale
genomic databases have also been constructed at the same time, including MIPS
(Mewes et al. 1998), PDB (Bank RPD 2024), GEO (Barrett et al. 2013), and
GenBank (Benson etal. 2013). The expansion of various computing techniques has
been greatly expedited by this abundance of information and data. Computational
methodologies are characterized by cheaper costs and fewer restrictions than bio-
logical experimental methods (Oprea and Overington 2015). A number of methods
are available for the identication of repurposing drugs. The details about the avail-
able methods are explained below.
16.3.1 Phenotypic Screening
The approach of phenotypic screening was employed in the identication of com-
pounds and biologics sanctioned by regulatory authorities. These techniques lack
pharmaceutical or biological data, making it less probable for them to unveil the
mechanisms of drug action. Typically, they rely on fortuitous identication through
tests targeting specic disease and medications. The notable benet of these
approaches, specically off-label use and phenotypic screening, lies in their height-
ened potential for applicability across various drugs or conditions (Jin and
Wong 2014).
R. Sharma et al.
403
16.3.2 Target-Based Methods
This approach necessitates specialized information concerning targets, like 3D pro-
tein type of structures. Knowledge-driven approaches rely on information about
medicine or diseases, encompassing adverse effects, governing approval labels,
clinical trial documents, and available biomarkers (potential targets) or pathways
associated with diseases. Scientists can quickly screen a large number of pharmaco-
logical compounds with known chemical structures using these techniques (e.g.
simplied molecular response line-entry system (SMILES)). These strategies fall
under the category of target-based DR techniques.
Conducting high-throughput or high-content screening (HTS/HCS) of drugs
in vitro and animal studies for a specic protein/biomarker, along with in silico
selection using methods like ligand-based screening or docking, constitutes the
Fig. 16.1 The computational approaches for drug repositioning
16 Drug Repurposing andVirtual Screening