1.INTRODUCTION 1.1 Herbs for health Using herbs and plants for medicinal purposes has a long tradition. In India and China, these traditions date back thousands of years. Once thought of as "traditional medicine" used by native or ancient cultures, herbal medicine has emerged as a popular alternative or supplement to modern medicine. According to the World Health Organization, 4 billion people, almost 70 % of the world population, use herbal medicine for some aspect of primary health care (Abramov, 1996). It is estimated that in the United States alone, botanical dietary supplements exceed $3 billion per year (The U.S. Food and Drug Administration, 1999). Forty percent of Americans take dietary supplements. About half of these people take vitamin and mineral supplements, a third take some type of herbal product, and the rest take other ergogenic aids, such as amino acids or protein powders (Industry Overview, 1999). The herbal market is growing steadily at about 20 % in every year (The U.S. Food and Drug Administration, 1999). People take herbs for many reasons and many conditions. One of the biggest reasons is that herbs are considered natural and therefore healthier and gentler than conventional drugs (Ironically, many prescription drugs are of herbal origin). Some people take Page 1 of 177
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1. INTRODUCTION
1.1 Herbs for health
Using herbs and plants for medicinal purposes has a long tradition. In India and
China, these traditions date back thousands of years. Once thought of as "traditional
medicine" used by native or ancient cultures, herbal medicine has emerged as a popular
alternative or supplement to modern medicine. According to the World Health
Organization, 4 billion people, almost 70 % of the world population, use herbal medicine
for some aspect of primary health care (Abramov, 1996). It is estimated that in the United
States alone, botanical dietary supplements exceed $3 billion per year (The U.S. Food
and Drug Administration, 1999).
Forty percent of Americans take dietary supplements. About half of these people
take vitamin and mineral supplements, a third take some type of herbal product, and the
rest take other ergogenic aids, such as amino acids or protein powders (Industry
Overview, 1999). The herbal market is growing steadily at about 20 % in every year (The
U.S. Food and Drug Administration, 1999). People take herbs for many reasons and
many conditions. One of the biggest reasons is that herbs are considered natural and
therefore healthier and gentler than conventional drugs (Ironically, many prescription
drugs are of herbal origin). Some people take them for overall health and well-being, not
for any specific condition. For others, herbal use is grounded in traditions passed down
from generation to generation or recommended by folk healers.
Medicinal herbs are significant source of synthetic and herbal drugs. In the
commercial market, medicinal herbs are used as raw drug, extract or tincture. Isolated
active constituents are used for applied research. For the last few decades,
phytochemistry has been making rapid progress and herbal products are becoming
popular. Ayurveda, the ancient healing system of India, flourished in the Vedic Era in
India. According to historical facts, the classical texts of Ayurveda, Charaka Samhita and
Sushruta Samhita were written around 1000 B.C. The Ayurvedic Materia Medica
includes 600 medicinal plants along with therapeutics. Herbs like turmeric, fenugreek,
ginger, garlic and holy basil are integral part of Ayurvedic formulations. The
formulations incorporate single herb or more than two herbs (poly-herbal formulations).
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Medicinal herb is considered to be a chemical factory as it contains multitude of
chemical compounds like alkaloids, glycosides, saponins, resins, oleoresins,
sesquiterpene lactones and oils (essential and fixed). Today there is growing interest in
chemical composition of plant based medicines. Several bioactive constituents have been
isolated and studied for pharmacological activities.
1.2 Herbs as a Traditional medicine
The World Health Organization (WHO) defines traditional medicine (TM) as "the
total combination of knowledge and practices, where explicable or not, used in
diagnosing, preventing or eliminating physical, mental or social diseases which may rely
exclusively on past experience and observation handed down from generation to
generation, verbally or in writing" (WHO Africa, 2000). WHO also specifies traditional
African medicine as "the sum total of practices, measures, ingredients and procedures of
all kinds whether material or not which from time immemorial had enabled African to
guard against diseases, to alleviate his suffering and to cure himself" (WHO Geneva,
1978). TM has been utilized by the majority of the world population for thousands of
years. Until the beginning of the 19th century, all medicines were traditional. Yet, in
many developing countries, it is true that for the majority of rural population, TM is the
only primary or any other kind of health care available (Koita, 1990). For more than 80%
of the population in Africa, they are using traditional medicine. In recognition of this fact,
WHO underlined the potential role that TM may play in reinforcing the health care
through the primary health care approach in developing countries (WHO Geneva, 1978).
1.3 History of traditional medicine
Guided by taste and experience, early societies developed a means of healing by
using plants, animal products and minerals that were not mostly among their usual diet.
The physical evidence of herbal remedies goes back some 60,000 years to a burial site of
a Neanderthal man uncovered in 1960 in a cave in Northern Iraq. In this cave, scientists
found what appears to be the remains of an ordinary human bones, and analysis of the
soil around these revealed extraordinary quantities of pollen that could not have been
introduced accidentally at the burial site. Rather, it is assumed that someone from the
cave community had consciously made eight species of plants to surround the dead body,
seven of which are medicinal plants still used throughout the herbal world (Jin-Ming et
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al., 2003). One of the earliest records of the use of herbal medicine is that of
Chaulmoogra oil from species of Hydnocarpus gaertn, which was known to be effective
in the treatment of leprosy. Such use was recorded in pharmacopoeia of the Emperor
Shen Nung of China between 2730 and 3000 B.C. Similarly, seeds of opium poppy
(Papaver somniferum L.) and castor oil seeds (Ricinus communis L.) were excavated
from some ancient Egyptian tombs, which indicated their use in that part of Africa as far
back as 1500 B.C. Suffice it to say that some 5000 years back, man was well aware of
medicinal properties of some plants growing around him (Sofowora, 1982).
The Arab medicine known as Unani system of medicine had its origin in the fifth
and fourth centuries B.C under the patronage of Hippocrates in Greece and later
expanded by the great teachers such as Aristotle, Theophrastus, Dioscorides, and Galen,
etc. Then, this body of knowledge moved to Rome, Alexandria and to the Arab countries
and got the name "The Arab (Unani) or Greco-Arab system of medicine". In the
Ayruvedic medical system that is believed to have been in practice for 2000 years mainly
in India, 582 herbs and 600 remedies were described in the early book on internal
medicine and in the book of surgery, respectively.
According to medical history, Hippocrates born in 460 B.C. was the first Greek to
regard medicine as a science and he is now referred to as the father of medicine. His
material medica consisted essentially of herbal recipes, some 400 simple remedies having
been combined and 4 described by him. Theophrastus of Athens was another famous
Greek, who was born in 370 B.C. produced a number of manuscripts including the
famous Historic plantarium. Both these early doctors administered various vegetable
drugs including myrrh and frankincense. At that time preparation of aromatic roots and
flowers were also used for treating many ailments (Jin-Ming et al., 2003; Sofowora,
1982). In the middle ages, the writings of Galen (Born in 131 A.D.) became popular. He
is considered today to be the most distinguished physician of antiquity after Hippocrates.
He treated diseases essentially by the use of herbs, and those who followed his methods
eventually developed the sect known as "Eclectics" who employed herbal as well as
mineral substances in treating the sick. Allopathic as well as homeopathic systems of
medicine today are based on doctrines expatiated by Galen (Sofowora, 1982). The use of
many medicinal plants in Europe in the 14th century was based on the doctrine of
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signature or similars developed by Paracelsus (1490-1541), a Swiss alchemist and
physician. According to this doctrine, healing herbs have features made by God
identifying the plant with specific disease or part of the body. For example, plants with
heart shaped leaves were good for treating heart disease (Sofowora, 1982).
1.4 Global perspectives of traditional medicine
Trends in the use of traditional and complementary medicine are on the increase
in many developed and developing countries. In the USA, it was estimated that 42.5
million visits were made to herbalists in 1990, contrasting with the 388 million actual
visits to primary health care physicians. In 1992, 20 million patients in Germany used
homeopathy (Jin-Ming et al., 2003), acupuncture as well as chiropractic and herbal
medicine as the most popular forms of complementary medicine. In Australia in 1998,
about 60% of the population used complementary medicine, 17,000 herbal products had
already been registered and a total of US $650 million was spent on complementary
medicine (WHO Africa, 2000).
The herbal medicine market has expanded tremendously in the last 15 years and
the total annual sale of herbal medicines is still growing over the counter sales of herbal
medicines in the USA and Canada during which it showed growth rate of 15%. In
Europe, the sales of herbal products have been referred as "Europe's growth market"
which amounted to USD 1.4 billion in 1992. In Malaysia, it is estimated that about US
$500 million is spent every year on traditional medicine, compared to only about US
$300 million on modern medicine. In 1996 the total annual sale of herbal medicines
reached US $14 billion worldwide (WHO Africa, 2000).
In China traditional medicines account for 30 – 50% of total medicinal
consumption and the total sales of their herbal medicines amounted to USD 2.5 billion in
1993. In addition, China exported medicinal herbs in 1993 with an estimated value of
USD 40 million. Within China the traditional systems of health care are incorporated into
the formal component of national health care. In 1991, there were 530,000 medical and
technical personnel in traditional Chinese medicinal field. There were more than 2,000
hospitals of traditional Chinese medicine, and 170,000 beds within the hospitals. Also,
there were more than 160 scientific research institutions of traditional Chinese Materia
Medica, forming a scientific research system. There were more than 2,000 factories of
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manufacturing medicinal herbs, producing more than 4,000 kinds of ready-made Chinese
herbal medicine every year (Xiang, 1990).
In India, where 75% of the populations depend on herbal preparations in 1991,
540 plant species were reported to be used in different formulations (Bhat, 1990). In
1995, there were 250,000 registered traditional medicine practitioners, the majority
having received training in degree graduating college.
1.5 Ethnopharmacology in drug discovery
Ethnopharmacology as a specifically designated field of research has had a
relatively short history. The term was used in 1967 as a title of a book on hallucinogens
“Ethnopharmacologic search for psychoactive drugs” and is nowadays much more
broadly defined: “The observation, identification, description, and experimental
investigation of the ingredients and the effects of the ingredients and the effects of such
indigenous drugs is a truly interdisciplinary field of research which is very important in
the study of traditional medicine. Ethnopharmacology is thus defined as the
interdisciplinary scientific exploration of biologically active agents traditionally
employed or observed by man”. This definition draws attention to the evaluation of
indigenous uses and does not explicitly address the issue of searching for new bioactive
drugs (drug discovery). Here we look at different processes involved in drug discovery.
The discovery process is composed of several stages. The first stage must be the reported
use of a naturally occurring material for some purpose, which can be related to a
medicinal use. Consideration of the cultural practice associated with it is important in
deciding possible bases of the reputed activity. If there is an indication of genuine effect,
then the material needs to be identified and characterized according to scientific
nomenclature. It can then be collected for experimental studies, usually comprising some
tests for relevant biological activity linked with isolation and structure determination of
any chemicals present, which might be responsible for the observed activity.
A) Information sources
The most reliable type of information arises from in-depth studies carried out by
field workers living in that particular community of a particular ethnic group on the use
of local plants and other materials. This usually comprises frequent communication with
the local population, preferably in their own language. It should be noted, however, that
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an extensive knowledge of TM may reside with only a few people and a focus on this
group would yield greater results. Before such knowledge can be investigated
scientifically, the information provided will often need clarification and translation into
scientific terms of particular importance. The correct identification of the species used
can be very difficult due to a lack of or poor quality sample specimens. Illustrations as
well as language difficulties can also be additional barriers. However, data on the part
used, time of collection, method of preparation of formulation and methods of application
are also necessary since they all affect the nature and amount of any biologically active
compounds. Any restriction on use due to time of year may be important since they may
indicate low levels or high levels of active compounds. Similarly, any type of individuals
excluded from being treated may indicate groups at risk due to age, gender or occupation
(Cox et al., 1994; Heinrich et al., 2001).
B) Extraction
The extract used for testing should approximate as closely as possible to that
obtained from the traditional process. In many cases, this will be simple extraction with
hot water. But a variety of other solvents as well as various additives may be used in the
treatment of materials before use. In most instances however, it is likely that fairly polar
compounds will be extracted, although the solubility of less polar substances may be
increased considerably due to solubilizing compounds (Cox et al., 1994; Heinrich et al.,
2001).
In most instances of modern drug discovery carried out by industrial and
academic research groups, a particular assay, or series of in vitro bioassays, designed on
the basis of the biochemistry or molecular biology of the disease, is used to test the
extract. In these situations, the ethnopharmacology has little relevance to the tests used
except that it provides a number of screening samples selected on the basis of their
traditional use for the disease in question (Cox et al., 1994; Heinrich et al., 2001).
C) Chemical examination
Chemical examination should be linked with tests for biological activity and it is
probably only a happy accident of history that the many alkaloidal drugs were developed
from traditional medicines, without the need for bioassay guided fractionation because
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the alkaloids were present in fairly high amounts and they were relatively easy to obtain
in a purified state.
For many other traditional medicines, where activity is not due to alkaloids, it has
been much more difficult to separate the activities from all the other compounds
(Heinrich et al., 2001). Chemotaxonomic approach increases the proportion of plants that
screen positively, thus saving research time and money. Specific secondary metabolites,
such as flavonoids, are often restricted in distribution, being found only in groups of
related plants. For example, isoflavnoids are common in species of the Fabaceae, but are
found in few other plant families. Of the over 5500 types of alkaloids known, many are
confined to a single genus or subfamily. Only a single alkaloid has been found in the
many species of Bombacaceae tested so far, but the Solanaceae, Rubiacea and
Ranunculaceae are the source of hundreds of distnict forms (Martin, 1995).
The presence of different secondary metabolites in a plant can be screened by the
use of appropriate chromogenic reagents after separation (Heinrich et al., 2001). A
typical example of success reported in drug discovery based on ethnopharmacological
approach is the discovery of artemisinin. Artemisia annua is a plant which was recorded
during 281-340 AD for treating malaria (Samuelsson, 1987). In 1976, artemisinin
compounds were identified and their mechanism of action elucidated. Artemisnin acts
against malarial parasite in a very different way from quinine and most of the synthetic
quinoline antimalarials. Several large trial studies have shown the efficacy of artemisinin
but the more soluble analogue artemether and artesunates are now widely used and are
recommended by WHO as antimalarias in chloroquine resistant areas (WHO China,
2001; WHO Geneva, 2001). The principles underlying herbal medicines are relatively
simple, although they are quite distinct from conventional medicine and herbal medicine.
Often overlooked distinction exists between herbal medicine (the practice) and the plant
based remedies used in the practice of herbal medicine. India is a rich source of medicinal
plants and a number of plant extracts are used against diseases in various systems of
medicine such as ayurveda, unani and siddha. Only a few of them have been scientifically
explored. Plant derived natural products such as flavanoids, terpenes, and alkaloids and
soon has received considerable attention in recent years, due to their diverse
pharmacological properties including cytotoxic and cancer chemo preventive effects.
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Plants have a long history of use in the treatment of cancer (Ramakrishna et al.,
1984). Extensive research at Sandoz laboratories in Switzerland in the 1960s and 1970s
led to the development of etoposide and teniposide as clinically effective agents which
are used in the treatment of lymphomas, bronchial and testicular cancer (Bholin et al.,
1999). Of 2069 anticancer trials recorded by the NCI as being in progress as of July 2004,
over 150 are drug combinations including etoposide against a range of cancers (National
Cancer Institute, 2009).
1.6 General overview of cancer and its treatment
The human adult is comprised of about 1015 cells, many of which are required to
divide and differentiate in order to repopulate organs and tissues which require cell
turnover (Bertram, 2001). The ability of the body to control cell multiplicity is achieved
by a network of overlapping molecular mechanisms which direct cell proliferation and
death. Any alteration in this balance (birth and death of cells), has a potential, if
uncorrected, to alter the number of cells in an organ or tissue. Such changes may result in
cancer, a disease that is manifested in many forms depending primarily on the organ from
which it evolves. Characteristically, cancer is defined as the uncontrolled proliferation of
cells which become structurally abnormal and possess the ability to detach themselves
from a tumor and establish a new tumor at a remote site within the host (National Cancer
Institute, 2009). Globally, cancer is one of the leading causes of death. According to the
American Cancer Society (ACS), an estimation of about 1,500,000 new cases and over
500,000 deaths are expected to be recorded in the US in 2009. South Africa experiences
one of the highest incidence rates of cancer in Africa (Mqoqi et al., 2004). Every one in
four males and six females have the potential of developing cancer. The current statistics
by the National Cancer Registry of South Africa indicate that cancers of the bladder,
colon, breast, cervix, lungs and melanoma are among the most common (Mqoqi et al.,
2004).
The existing strategy of eradicating cancer after detection has resulted in mortality
that may have been preventable if caution was taken against the causative agents (Doll et
al., 1981). Although, the etiology of cancer remains unknown to an extent, epidemiology
has suggested the hypotheses that multiple causative factors may be operating. These
factors (exogenous and endogenous) exert their specific effects at different times in the
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life of the patient. The impact of such effects might be cumulative or synergistic. The
main predictors of the incidence of cancer fall largely into two broad categories:
environmental and positive family history (Parkin et al., 2005). A number of other risk
factors exist from a wide range of studies in various populations and geographic
locations.
The progress in research on the etiology of cancer has revealed the evidence that
dietary patterns, nutrients and food constituents are closely associated with the risk of
several types of cancer (Doll et al., 1981). Fats have been the focus of nutritional studies
on cancers of the prostate, breast and colon more than any other dietary component
(National Research Council, 1989). Several studies in countries consuming high fat diets
have consistently shown higher incidence and mortality rates for breast, colon and
prostate cancers (National Research Council, 1989; Hursting et al., 1990). Studies of
specific environmental influences have suggested an increased risk of developing various
forms of cancer with exposure to particulate air pollutants and fertilizers. Substances such
as asbestos, aniline dye, uranium and nickel have been implicated as environmental
carcinogens (Monson et al., 1997).
A) The role of inflammation in the initiation of cancer
The association between inflammation and tumor has long been known (Balkwill
et al., 2001). Since then, inflammation is increasingly recognized as an important
component of several cancers, although the mechanisms involved are not fully
understood (Ben, 2006). A vast body of evidence has indicated that inflammatory
leucocytes contribute to cancer development either directly by the release of vesicle
stored growth and survival factors and diverse proteolytic enzymes, or indirectly via the
activation of cell signaling cascades as a result of altered pericellular matrix remodelling
activity (Van Kempen et al., 2006). Products of inflammation such as growth factors,
cytokines and transcription factors, like nuclear factorkappa B (NF-κB), control the
expression of cancer genes and key inflammatory enzymes such as inducible nitric oxide
(iNOS) and cyclooxygenase-2 (COX-2) (Hofseth et al., 2006).
Bacterial, viral and parasitic infections, chemical irritants and non-digestible
particles are some of the causes of chronic inflammation. The longer this inflammation
persists, the higher the risk of associated carcinogenesis (Shacter et al., 2002). Chronic
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inflammation occurs due to environmental stress around the tumor, thus generating a
shield protecting the tumor from the immune system (Assenat et al., 2006). Recent
demonstrations have shown that microenvironment of tumors highly resemble an
inflammation site, with a significant tendency for tumor progression (Assenat et al.,
2006). In addition, this micro-environment apart from its significant role in cancer
progression and protection has a considerable adverse effect on the success of the various
current cancer treatments (Assenat et al., 2006). The pro-cancerous outcome of chronic
inflammation are increased DNA damage, increased DNA synthesis, cellular
proliferation, the disruption of DNA repair pathways and cellular milieu, the inhibition of
apoptosis, the promotion of angiogenesis and invasion (Hofseth et al., 2007). Therefore,
inflammation plays a major role in the initiation and progression of cancers.
Inflammatory-related ailments are treated mainly with non-steroidal anti-inflammatory
drugs (NSAIDs). These drugs are used to reduce the consequences of inflammation
(Vane et al., 1996). Indomethacin, an NSAID, for example has been found to block
carcinogenesis in animals by reducing the production of inflammatory cytokines
(Federico et al., 2007). A lower risk of cancer incidence has also been found in people
regularly taking NSAIDs (Fosslien, 2000).
B) Treatment options for cancer
The treatment option for cancer is influenced by several factors, such as the
specific nature of the cancer; the status of the patient (age and health); and whether the
goal of treatment is eradication of the tumor, control of the local tumor growth,
prolongation of survival or palliation of cancer symptoms (National Cancer Institute,
2009). Depending on these factors, treatment options such as surgery, chemotherapy,
radiation and hormonal therapy could be used. More than half of all people diagnosed
with cancer are treated with chemotherapy because it is considered a systemic treatment.
The cancer-fighting drugs circulate in the blood to parts of the body where the cancer
may have spread and can kill or eliminate cancers cells at sites of great distances from the
original cancer. The side effects observed with these treatments may be severe, thus
reducing the quality of life, compromising treatment and sometimes limiting the chance
for an optimal outcome from treatment. Common side effects includes anaemia,
depression, fatigue, hair loss, infections, low blood counts, nausea and vomiting and long
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term effects such as cardiac toxicity, growth problems and sterility (National Cancer
Institute, 2009).
C) Phytotherapy for cancer treatment
Despite the major scientific and technological progress in the treatment and
management of cancer, no reliable and definitive cure has been found (Richardson et al.,
1999). This has led to an increase in the dependence of patients on unconventional
medical therapies (Alschuler et al., 1997). All over the world, the traditional use of plants
in the treatment of ailments has been on the increase especially in developing countries
where there is invariably poor availability of primary health care (Alschuler et al., 1997).
Plants are a viable source of biologically active natural products which have served as
commercial drugs or as lead structures for the development of modified derivatives
possessing enhanced activity (Cordell et al., 1991). Extracts of plants have a long history
of use in the treatment of cancer (Hartwell, 1969). Over 60% of the currently used
anticancer agents are derived in one way or the other from natural sources including
plants and marine organisms (Cragg et al., 2005a). For example, the breakthrough for
cancer treatment was achieved by the discovery and development of the vinca alkaloids,
vincristine and vinblastine isolated from Catharanthus roseus in the early 1950’s
(Chadwick et al., 1994). The discovery of these chemicals led to other research where
compounds such as podophyllotoxin derivatives, etoposide and teniposide from the root
of various Podophyllum species (Gurib-Fakim, 2006) and paclitaxel from the bark of
Taxus brevifolia (Cragg et al., 2005b) were isolated. Other examples include the
camptothecin derivatives (topotecan, irinotecan and 9- aminocamptothecin) isolated from
Camptotheca acuminata, homoharringtonine from Cephalotaxus harringtonia var
drupaceae and elliptinium from several genera in the Apocyanaceae family (Wall, 1998;
Tingali, 2001). Since then, various studies have been undertaken to discover more natural
sources of drugs for the treatment of cancer.
D) Efficacy and safety of medicinal plants in cancer treatment
The traditional use of plants in the treatment of ailments has been on the increase
both in developing countries, where there is poor availability of primary health care, and
also in the developed world. Herbal medicines are in great demand in the developing
world for primary health care not only because they are inexpensive but also for better
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cultural acceptability, better compatibility with the human body and minimal side effects.
This is primarily due to the general belief that herbal medicines are relatively safe
because they are natural (Gesler, 1992). The knowledge of the healing virtues of
medicinal plants has been passed on from ancient times. History tells of medicinal plants
such as Catharanthus roseus G. Don, Digitalis purpurea Linn, Rauwolfia serpentina
Plum ex Linn, Willow (Salix species), Physostigma venenosum Balf. and a host of other
plants which have been used for centuries for the treatment of diseases such as cancer,
cardiovascular diseases, hypertension, depression, pain, glaucoma and an array of other
diseases that have plagued the world. Since then, plants have served as viable sources of
biologically active natural products which are either used as commercial drugs or as lead
structures for the development of modified derivatives possessing enhanced activity
(Alschuler et al., 1997). Modern medicine as a result of civilization led to the reduced
importance of medicinal plants to human survival. This was not because these plants
were ineffective but because they were not economically profitable as the newer synthetic
drugs (Tyler, 1999). However, in recent times, the concerns over the serious adverse
effect of conventional drugs and the movement towards a more natural living has brought
about a resurgence in the use of herbal products (Pal et al., 2003).
The number of patients seeking herbal approaches for therapy has grown
exponentially (Cordell et al., 1991). In France and Germany, the medical doctors
regularly prescribe herbal medicine to 70% of their patients. Available records have
illustrated the growth of the herbal medicine market in the European Union countries. In
1991, sales were about $ US 6 billion, with Germany accounting for $ US3 billion,
France $ US 1.6 billion and Italy $ US 0.6 billion while in the US, herbal medicine
market was about $ 4 billion in 1996 (Pal et al., 2003). India boasts about $ US 80
million for the exportation of herbal crude extracts (Kamboj, 2000). The resurgence and
popularity of herbal medicines have led to an increase in the number of medicinal plant
products in the market (Gupta et al., 1998). Unfortunately, the increased dependence on
phytotherapy, without concern for efficacy and safety has resulted in preventable serious
adverse effects (Gurib-Fakim, 2006).
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a) Efficacy of medicinal plants
With the slight increase in the randomized controlled trials to evaluate the
efficacy of herbal medicines, an estimate of about 39% of all 520 new approved drugs
were natural products or derived from natural products in 1983-1994 (Cragg et al., 1997).
The study of Harvey (1999), reported that 60-80% of antibacterial and anticancer drugs
were derived from natural products (Harvey, 1999). The antimalaria quinine from
Cinchona officinalis, analgesics codeine and morphine from Papaver somnifera,
antihypertensive reserpine from Rauwolfia serpentina and cardiac glycoside digoxin from
Digitalis pupurea are some of the many drugs derived from medicinal plants that have
been in use. The fact remains that plant substances constitute the basis for a very large
proportion of medications used today for the treatment of diseases of the liver and heart,
cancer, hypertension, depression and other ailments. This is the result of an increase in
the scientific studies carried out to validate the traditional claims of these plants (Gurib-
Fakim, 2006).
b) Safety of medicinal plants
Recent findings indicate that herbal medicines may not be safe and severe
consequences have arisen from the use of certain products (Gurib-Fakim, 2006; Bush et
al., 2007). Information obtained from health centres and hospital emergency rooms have
shown that 5 % of patients receiving complementary therapies report side effects
(Molassiotis et al., 2005). The true frequency of the incidence of side effects from herbal
remedies may be several folds higher than this, (Ernst, 2004) because the lack of
surveillance systems which are less extensive than for conventional drugs have limited
these reports (Bent et al., 2004). For example, acute poisoning as a result of herbal
medicines is estimated to cause anywhere from 8,000 to 20,000 deaths annually in South
Africa (Thomson et al., 2000). These side effects may occur through several different
mechanisms, including direct toxic effects of the herbs, effects of contaminants, and
interactions with drugs or other herbs (Ernst, 2004; Bent et al., 2004; Niggemann et al.,
2003). The risk of herbal remedies producing side effects depends not only on the herb
and the dose consumed, but also on the health status and age of the patient and the
concurrent use of other drugs (De Smet et al., 1995).
2. AIM AND OBJECTIVES Page 13 of 113
Researchers are constantly making efforts to discover new drugs and design better
protocols for cancer. Synthetic anticancer drugs kill the cancer cells but they are also
harmful to the normal cells. Since, increase in the use of these drugs in cancer therapy
leads to many side effects and undesirable hazards, there is a worldwide trend to go back
to natural resources, i.e., traditional plant preparations which are not only therapeutically
effective but are actually acceptable and economically within the reach of even the
neediest people. An alternative solution of this problem is the use of medicinal plant
preparation to arrest the insidious character of the disease. Therefore it is imperative that
more attention is focused to control the carcinogenesis. It may be easier to control the
spread of cancer, if appropriate steps are taken before the initiation of the disease. The
most important imaginative approach to reduce the cancer cases worldwide could be the
inhibition of induction of carcinogenesis or cancer by the use of herbal technology. Many
naturally occurring substances have been tested for anticancer activity on experimental
animals resulting in the presence availability of some 30 effective anticancer drugs
(Ramakrishna et al., 1984). Cytotoxicity screening models provide important
preliminary data to help select plant extracts with potential antineoplastic properties for
future work (Bohlin et al., 1999).
Both ancient experience from traditional Chinese herbal medicine and modern
studies have demonstrated that herbal medicine could be effective remedy for cancer
treatment and to improve outcome of chemotherapy. Hence, the present study is
undertaken to evaluate the anticancer activity of Madhuca longifolia, Adina cordifolia,
Sida veronicaefolia in mice.
3. REVIEW OF LITERATURE
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3.1 Anti-Cancer plants – A Review
Natural Products, especially plants, have been used for the treatment of various
diseases for thousands of years. Terrestrial plants have been used as medicines in Egypt,
China, India and Greece from ancient time and an impressive number of modern drugs
have been developed from them. The first written records on the medicinal uses of plants
appeared in about 2600 BC from the Sumerians and Akkaidians. The “Ebers Papyrus”,
the best known Egyptian pharmaceutical record, which documented over 700 drugs,
represents the history of Egyptian medicine dated from 1500 BC. The Chinese Materia
Medica, which describes more than 600 medicinal plants, has been well documented with
the first record dating from about 1100 BC (Cragg et al., 1997). Documentation of the
Ayurvedic system recorded in Susruta and Charaka dates from about 1000 BC (Kappor,
1990). The Greeks also contributed substantially to the rational development of the herbal
drugs. Dioscorides, the Greek physician (100 A.D.), described in his work “De Materia
Medica” more than 600 medicinal plants. Phytochemicals have been proposed to offer
protection against a variety of chronic ailments including cardiovascular diseases,
obesity, diabetes, and cancer. As for cancer protection, it has been estimated that diets
rich in phytochemicals can reduce cancer risk by 20%.The compounds that are
responsible for medicinal property of the drug are usually secondary metabolites. Plant
natural product chemistry has played an active role in generating a significant number of
drug candidate compounds in a drug discovery program. Recently, it has been reported in
the literature that approximately 49 % of 877 small molecules that were introduced as
new pharmaceuticals between 1981 and 2002 by New Chemicals Entities were either
natural products or semi-synthetic analogs or synthetic products based on natural product
models.
Plants have a long history of use in the treatment of cancer. Hartwell, in his
review of plants used against cancer, lists more than 3000 plant species that have
reportedly been used in the treatment of cancer. It is significant that over 60% of
currently used anticancer agents are derived in one way or another from natural sources,
including plants, marine organisms and micro-organisms. Indeed, molecules derived from
natural sources (so called natural products), including plants, marine organisms and
micro-organisms have played and continue to play, a dominant role in the discovery of
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leads for the development of conventional drugs for the treatment of most human
diseases. The search for anti-cancer agents from plant sources started in earnest in the
1950s with the discovery and development of the vinca alkaloids, vinblastine and
vincristine, and the isolation of the cytotoxic podophyllotoxins. These discoveries
prompted the United States National Cancer Institute (NCI) to initiate an extensive plant
collection program in 1960. This led to the discovery of many novel chemotypes showing
a range of cytotoxic activities, including the taxanes and camptothecins (Cragg et al.,
2005a).
More than 50% of all modern drugs in clinical use are natural products, many of
which have the ability to control cancer cells. A recent survey shows that more than 60%
of cancer patients use vitamins or herbs as therapy (Sivalokanathan et al., 2005; Creemer
et al., 1996).
Many of these medicinal plants have been found effective in experimental and
clinical cases of cancers. Attempts are being made to isolate active constituents from
natural sources that could be used to treat this very serious illness. The first agents to
advance into clinical use were the isolation of the vinca alkaloids, vinblastine and
vincristine from the Madagascar periwinkle, Catharanthus roseus (Apo-cynaceae)
introduced a new era of the use of plant material as anticancer agents (Cassady et al.,
1981). They were the first agents to advance into clinical use for the treatment of cancer.
Vinblastine and vincristine are primarily used in combination with other cancer
chemotherapeutic drugs for the treatment of a variety of cancers, including leukemias,
lymphomas, advanced testicular cancer, breast and lung cancers, and Kaposi’s sarcoma
(Cassady et al., 1981).
The discovery of paclitaxel from the bark of the Pacific Yew, Taxus brevifolia
Nutt. (Taxaceae), is another evidence of the success in natural product drug discovery.
Various parts of Taxus brevifolia and other Taxus species (e.g., Taxus Canadensis, Taxus
baccata ) have been used by several Native American Tribes for the treatment of some
noncancerous cases (Cragg et al., 2005a). Taxus baccata was reported to use in the Indian
Ayurvedic medicine for the treatment of cancer. Paclitaxel is significantly active against
ovarian cancer, advanced breast cancer, small and non-small cell lung cancer.
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Camptothecin, isolated from the Chinese ornamental tree Camptotheca acuminate
(Nyssaceae), was advanced to clinical trials by NCI in the 1970s but was dropped
because of severe bladder toxicity. Topotecan and irinotecan are semi-synthetic
derivatives of camptothecin and are used for the treatment of ovarian and small cell lung
cancers, and colorectal cancers, respectively (Harvey, 1999; Bertino, 1997).
Epipodophyllotoxin is an isomer of podophyllotoxin which was isolated as the
active antitumor agent from the roots of Podophyllum species, Podophyllum peltatum and
Podophyllum emodi (Berberidaceae).Etoposide and teniposide are two semi-synthetic
derivatives of epipodophyllotoxin and are used in the treatment of lymphomas and
bronchial and testicular cancers (Cragg et al., 2005b).
Combretastatins were isolated from the bark of the South African tree Combretum
caffrum (Combretaceae). Combretastatin is active against colon, lung and leukemia
cancers and it is expected that this molecule is the most cytotoxic phytomolecule isolated
so far (Ohsumi et al., 1998; Petit et al., 1987).
Betulinic acid, a pentacyclic triterpene, is a common secondary metabolite of
plants, primarily from Betula species (Betulaceae) (Cichewitz et al., 2004). Betulinic acid
was isolated from Zizyphus species, e.g. Zizyphus mauritiana, Zizyphus rugosa and
Zizyphus oenoplia and displayed selective cytotoxicity against human melanoma cell
lines (Pisha E et al., 1995).
The Podophyllum species (Podophyllaceae), Podophyllum peltatum (commonly
known as the American mandrake or Mayapple), and Podophyllum emodii from the
Indian subcontinent, have a long history of medicinal use, including the treatment of skin
cancers and warts. Podophyllum peltatum was used by the Penobscot Native Americans
of Maine for the treatment of cancer (Cragg et al., 2002).
Camptothecin isolated from Camptotheca acuminata (Nyssaceae), also known as
tree of joy in China is a possible source of steroidal precursors for the production of
cortisone. The extract of Camptotheca acuminata was the only one of 1000 of the plant
extracts tested for anti-tumor activity which showed efficacy and camptothecin was
isolated as an active constituent (Cragg et al., 2002).
Other plant derived agents in clinical use are homoharringtonine isolated from the
Chinese tree, Cephalotaxus harringtonia (Cephalotaxaceae), and elliptinium, a derivative
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of ellipticine isolated from species of several genera of the Apocynaceae family including
Bleekeria vitensis, a Fijian medicinal plant with reputed anti-cancer properties. Several
Terminalia species have reportedly been used in the treatment of cancer. The
combretastatins are a family of stilbenes which act as anti-angiogenic agents causing
vascular shutdown in tumors and resulting in tumor necrosis (Cragg et al., 2002).
Dragon's blood is the popular name for a dark red viscous sap produced by
Croton lechleri. This herb is used in folk medicine as an anti-inflammatory, antimicrobial
and anticancer (Pieters et al., 1993; Hartwell, 1969; Lopes, 2004). Crude extracts from
plants like Colubrina macrocarpa, Hemiangium excelsum and Acacia pennatula have
been shown to possess a selective cytotoxic activity against human tumor cells (Popoca et
al., 1998).
In Saudi Arabia, aerial parts of Commiphora opobalsamum are commonly used to
treat various diseases. However, its potential use in stomach problems and cancer has
been reported only recently (Howiriny et al., 2005).
Some Astragalus species are used to treat leukemia and promote wound healing
(Calis et al., 1997). Salvia officinalis is the most popular herbal remedy in the Middle
East to treat common health complications. Salvia species (Labiatae) are known for their
antitumor effects (Liu et al., 2000).
Phytochemically, the whole plant contains several antioxidants that protect
against cellular peroxidative damage. Lantana camara possesses several medicinal
properties and is commonly used in folk medicine for its antipyretic, antimicrobial and
antimutagenic properties (Fernanda et al., 2005).
Solanum nigrum is a common herb that grows wildly and abundantly in open
fields. It has been used in traditional folk medicine because of its diuretic and antipyretic
effects. More specifically, it has been used for a long time in oriental medicine to cure
inflammation, edema, mastitis and hepatic cancer (Lee et al., 2003).
Evaluation of the in-vitro anticancer effects of bioflavonoids, viz. quercelon,
catechin, luteolin and rutin against human carcinoma of larynx (Hep-2) and sacroma 180
(S-180) cell lines showed that only luteolin and quercelon inhibited the proliferation of
the cells. Luteolin caused depletion of glutathione in the cells and a decline in DNA
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synthesis, as seen by 3H thymidine uptake studies, thus demonstrating its anticancer
potential (Elangovan et al., 1994).
The anti-tumor effect of the crude extract of Centella asiatica as well as its
partially purified fraction was studied in both, In-vitro short and long term
chemosensitivity test systems and in vivo tumor models. The purified fraction inhibited
the proliferation of transformed cell lines of Ehrlich ascites tumor cells and Dalton’s
lymphoma ascites tumor cells more significantly than the crude extract. It also
significantly suppressed the multiplication of mouse lung fibroblast cells in long term
culture. In-vivo administration of both extracts retarded the development of solid and
ascites tumors and increased the lifespan of the tumor bearing mice. Triturated thymidine,
uridine and leucine incorporation assays suggest that the purified fraction acts directly on
DNA synthesis (Babu et al., 1995).
Fresh root suspension of Janakia arayalpathra exhibited strong anti-tumor effects
in mice challenged with Ehrlich ascites carcinoma (EAC) cells. It prolonged the survival
of all mice and protected a number of mice from tumor growth, probably by enhancing
the activity of the immune system (Subramanian et al., 1996).
Withaferin A, a steroidal lactone isolated from the roots of Withania somnifera,
reduced survival of V79 cells in a dose-dependent manner. The applicability of this drug
as a radiosensitizer in cancer therapy needs to be explored (Devi et al., 1996).
Banerjee et al., 1996, have studied the modulatory influence of the alcoholic
extract of leaves of Ocimum sanctum on various enzyme levels in the liver, lung and
stomach of mouse. Oral treatment with the extract significantly elevated the activities of
cytochrome P450, cytochrome b5, arylhydrocarbon hydroxylase and glutathione S-
transferase enzyme, all of which are important in the detoxification of carcinogens as
well as mutagens. Moreover, it also significantly elevated extra-hepatic glutathione S-
transferase and reduced glutathione levels in the lever, lung, and stomach. These
observations suggest that the leaf extract or its active principles may have a potential role
in the chemoprevention of chemical carcinogenesis (Banerjee et al., 1996).
Petroleum ether extract of Hygrophilic spinosa exhibited anti-tumor activity in
Ehlrich ascites carcinoma and sacroma 180 bearing mice (Mazumdar et al., 1997).
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Aqueous extract of Podophyllum hexandrum, a herb from the Himalayas,
demonstrated significant antitumor effects when drug was tested in strain ‘A’ mice
carrying solid tumors developed by transplanting Ehlrich ascites tumor cells.
Radioprotective effects were also seen when the drug was administrated to mice before
whole body lethal irradiation of 10 Gy (Goel et al., 1998).
The chemopreventive efficacy of Trianthema portulacastrum L. Aizoaceae was
tested in male Sprague-Dawley rats. Hepatocarcinogenesis was induced by the potent
carcinogen diethylnitrosoamine (DENA). Treatment of the rats with aqueous, ethanolic
and chloroform fractions of the plant extract at a dose of 100 mg/kg once daily reduced
the incidence, numerical preponderance, multiplicity and size distribution of visible
neoplastic nodules. Morphometric evaluation of focal lesions showed a reduction in
number of altered liver cell foci per square centimeter as well as of average area of
individual lesion. A decrease in the percentage of liver parenchyma occupied by foci
seems to suggest the anticarcinogenic potential of the plant extract in DENA-induced
hepatocarcinogenesis (Bhattacharya et al., 1998).
Pretreatment with Ocimum sanctum leaf extract followed by the addition of 7, 12-
dimethylbenz[a]anthracene (DMBA) significantly blocked the formation of DMBA-DNA
adducts in primary cultures of rat hepatocytes invitro. The viability of the cells was not
adversely affected by the extract (Prashar et al., 1998).
Table 3.1: List of plants reported for their anticancer activity
Species Family Part used Reference
Allium sativum Liliaceae Bulbs Hirsh et al., 2000
Aristolochia triangularis Aristolochiaceae Bark Mongelli et al., 2000
Barringtonia racemosa Lecythidaceae Bark MacKeen et al., 1997
Betula platyphylla Cupuliferae Whole plant Ju et al., 2004
Boscia senegalensis Capparidaceae Leaves Ali et al.,2002
Catalpa bignonioides Bignoniaceae Seeds Muñoz et al., 2003
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Celastrus orbiculatus Celestraceae Root Jin et al.,, 2002
Clerodendrum
myricoidesVerbenaceae Root bark
Kamuhabwa et al .,
2000
Clematis chinensis Ranunculaceae Whole plant Qiu et al ., 1999
Crocus sativus Iridaceae Stigma Nair et al ., 1995
Croton palanostigma Euphorbiaceae Sap Sandoval et al ., 2002
Cunuria spruceane EuphorbiaceaeRoot, Root
bark
Gunasekera et
al ., 1979
Cupressus lusitanica Cupressaceae Leaves Lopéz et al ., 2002
Dendrostellera lessertii Thymelaeaceae Leaves Sadeghi et al ., 2003
Dioscorea birmanica Dioscoriaceae Whole plantWoerdnbeg et al.,
1986
Emblica officinalis Euphorbiaceae Fruits Jose et al., 2001
Emilia sonchifolia Compositae Whole plant Shylesh, et al., 2000
Eurycoma longifolia Simaroubaceae Leaves Jiwajinda et al ., 2002
Garcinia atroviridis Guttiferae Stem bark Mackeen et al., 2000