Cytotoxic Molecules from Natural Sources: Tapping the Brazilian Biodiversity

Abstract

The use of plant miscellaneous preparations as an alternative to the treatment of cancer is a reality today due to the massive marketing of natural medicines versus anticancer chemotherapy. Although this situation is controversial and has not led to any significant benefits to patients, plants may play a significant role in the treatment of cancer. Historically, natural leads have evolved to some of the outstanding medicines used nowadays against lung, breast, and ovarian cancers, and leukemia. Natural products are still some of the important sources of new anticancer drugs. The Brazilian flora is considered one of the most diverse in the world, although not many large-scale pharmacological and phytochemical studies have been conducted so far. We present the updated status and results of the research developed by Brazilian research centers on anticancer active substances derived from natural sources, mainly plants from the Brazilian Rain Forests, focusing on their potential effectiveness and difficulties.

Full text

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CYTOTOXIC MOLECULES FROM NATURAL SOURCES: TAPPING THE BRAZILIAN
BIODIVERSITY
I.B. Suffredini*
∗
, A.D. Varella, R.N. Younes
Laboratório de Extração da Universidade Paulista – UNIP
ABSTRACT: The use of plant miscellaneous preparations as an alternative to the treatment of cancer is a
reality today due to the massive marketing of natural medicines versus anticancer chemotherapy.
Although this situation is controversial and has not led to any significant benefits to patients, plants may
play a significant role in the treatment of cancer. Historically, natural leads have evolved to some of the
outstanding medicines used nowadays against lung, breast, and ovarian cancers, and leukemia. Natural
products are still some of the important sources of new anticancer drugs. The Brazilian flora is considered
one of the most diverse in the world, although not many large-scale pharmacological and phytochemical
studies have been conducted so far. We present the updated status and results of the research developed by
Brazilian research centers on anticancer active substances derived from natural sources, mainly plants
from the Brazilian Rain Forests, focusing on their potential effectiveness and difficulties.
KEYWORDS: biodiversity, screening, natural products, Amazon Rain Forest, Atlantic Forest.
∗
Corresponding address to IBS at the Laboratório de Extração – Uiversidade Paulista, Av. Paulista, 900, 1
andar, São Paulo, SP, Brazil, 01310-100. Phone 55 11 3170-3776, FAX: 55 11 3170-3978, Email:
extractlab@unip.br

2
The treatment of cancer has evolved
dramatically with the introduction of new
drugs and regimens, both for the treatment of
established systemic diseases, and as adjuvant
setting following surgery or radiation therapy
[1]. Several new molecules have been
developed into commercially available drugs
that originated from natural resources. The
traditional use of plants and teas by
indigenous people in different parts of the
world drew the attention of scientists to the
potential beneficial effect of those plants in
one or more diseases. The research with
natural products is focused in two different
approaches: (1) the identification of isolated
compounds with pharmacological activity and
(2) the research of complex mixtures as
remedies, including extracts, teas, a plant or
part of a plant. Both directions can start from
traditional information related to the use of
the plant as remedy or to its toxicity, as it is
going to be further discussed. The marketing
of complex mixtures, as extracts, as remedies
usually is deprived of a rigorous control of
quality, due to the natural difficulties found in
this kind of preparation, such as to obtain a
regular concentration of the active substances,
to control the stability of the active principle,
the lack of clinical trials in this kind of
preparation. Despite all the technical
difficulties to obtain a remedy composed by
extracts, there is a clear misunderstanding
related to the common phrase “plant is from
nature and for that reason it is not harmful”,
and we believe that all these factors support
the consumption of plants as remedies by
some groups of people. Cancer patients can
find themselves deprived of hope and
frequently are prone to attend any therapy,
including the consumption of toxic plants;
second, a new boom of “natural” remedies
marketed as less harmful than
chemotherapics; and third, every now and
then plant and derivatives are the only choice
for poor people, particularly in developing
countries. Occasionally, the toxic properties
overcome the therapeutic uses of these
traditional plants, as is the case of Euphorbia
tirucalli sp., known in Brazil as “avelos”. This
plant is told to cure cancer, but it is reported

3
to be toxic to the skin and to mollusks [2].
Aloe sp. has been recently promoted as an
antitumoral natural remedy in Brazil. The
anthraquinones contained in the leaves of Aloe
species have been reported to be cathartic by
in vitro and in vivo pharmacological
investigations on its antitumoral activity
against a neuroectodermal tumor [3], with
positive results due to the apoptosis caused by
aloe-emodin [4,5].
The same applies to infectious
diseases. Infections are still considered one of
the main causes of human and animal deaths.
Controlling resistant bacteria is an ever-
growing endeavor, mainly in patients admitted
to hospitals. The development of multi-
resistant strains of bacteria has been a major
concern of microbiologists around the world
[6, 7, 8, 9]. The introduction of new
antibiotics became a matter of public health.
Fortunately, the research in this area is
widespread, and, as for cancer, natural
products can be considered one of the main
sources of new drugs. Data published in 1997
show that new antibiotics came in toto from
natural sources, or were natural product
copies [10]. In addition, the period of 1970-
1980 was particularly productive in terms of
natural product drug discovery programs,
when new chemical entities were natural
products, semi-synthesized or synthesized
based on natural products, totalizing almost
49% [11].
The study of anticancer and
antibacterial substances should continue to
include natural products. The effectiveness of
drugs such as paclitaxel, docetaxel, etoposide,
and the vinca alkaloids [12], along with
important antibiotics as vancomycin and
penicillin is an evidence of the importance of
natural products. Nonetheless, difficulties
found in the research of natural products can
be listed: (1) the time between the discovery
of a hit and the release of a drug –
approximately 10 years in developing
countries –; (2) the difficulty to access the
biodiversity to put together plant, animal or
microorganisms extract libraries after the
1992 Rio Convention on Biodiversity; (3) the
introduction of cancer target models

4
supported by high-throughput screening allied
to combinatorial chemistry used by
pharmaceutical industries make these libraries
contain up to a million different molecules
[13].
Time
The interest of humans in natural
products is as old as history. Ancient
communities, like the Egyptian, Indian,
Chinese, and others, have been using plant
remedies for thousands of years. In the 19th
century, morphine was the first molecule to be
isolated and identified. Since then, thousands
of active compounds have been identified,
particularly after the second half of the 20
th
century due to the technology that became
available. The role of natural products in
cancer therapy was evidenced by the
discovery of the vinca alkaloids [14], and after
that, many molecules were found to inhibit
cell growth.
The isolation of natural products is
time-consuming, from extraction and drug
release. Over the decades, new technical
apparatus minimized this problem, especially
the equipment used to elucidate new chemical
entities, as nuclear magnetic resonance, mass
spectrometers [13], and the enrichment of
extraction procedures. The problem becomes
significant when pre-clinical and clinical trials
are to be done, due to the amount of drug
needed to run in vivo assays. In this moment,
one of two procedures may be adopted: the
molecule may be synthesized and follow the
traditional medicinal chemistry studies or it
can be extracted from nature, which is not
considered the right choice due conservation
issues.
Access to biodiversity
Another important issue in natural
product drug discovery programs in Brazil is
the restrictive laws based on the 1992 Rio
Convention on Biodiversity. The law
basically regulates the access to the Brazilian
genetic patrimony and its bioprospection. That
means that any Brazilian citizen or foreigner
who desires to bioprospect in Brazil must
apply for a license to access the biodiversity
and collect material, and have a Brazilian

5
counterpart. After setting up the extract
library, the group has to apply for a license to
submit the extracts to all biological assays.
Local authorities are trying to establish more
effective systems to support the demand,
allowing more widespread, and at the same
time controlled bioprospection. Foreign
support to develop whole steps involved in
finding new drugs is a necessity, as the
Brazilian industry does not have the tradition
of investing in basic or applied research.
Cancer targeted research and
combinatorial chemistry
Today the focus of new anticancer
drugs is concentrated in specific cancer targets
that evolved from the rapid advances in the
understanding of the molecular basis of cancer
development and progress, such as the
behavior of oncogenes, tumor suppressor
genes, protein kinases involved in deregulated
signaling pathways [15], angiogenesis and the
apoptosis cascade [16]. The design of new
anticancer drugs has entered in a new era
since then, especially because these recent
biological tools are used to analyze thousands
of compounds obtained from combinatorial
chemistry, and both techniques together
became impressive tools for the introduction
of new drugs in the market. However, the
chemical diversity found in natural products
shows a differential in relation to the
thousands of products obtained from
combinatorial chemistry. Compounds isolated
from plants, especially small molecules,
frequently show biological activity as the
inhibition of macromolecular targets or
proteins, for instance. Thus, synthetic
products, sometimes a whole library, may not
show activity, because they were conceived to
be huge other than to have biological activity
[17].
Why natural products and why in
Brazil
Bioprospection of natural resources
using screening procedures was used for some
decades to achieve new molecules and some
techniques were implemented in Brazil in the
past decade. The US/NIH National Cancer

6
Institute (NCI) had a large screening program
capable of testing 10,000 compounds/extracts
per year. More than 114,000 extracts obtained
from 35,000 plant species have already been
tested in the program, and only 4% have
shown reproductive activity [18]. Nowadays,
the NCI bank of extracts has more than
200,000 extracts from marine and terrestrial
plant and animal extracts and isolated
compounds. This program led to the discovery
of some important anticancer drugs, as
paclitaxel (from Taxus brevifolia Nutt.),
camptothecin (Camptotheca acuminata
Decne) and podophyllotoxin/etoposide (semi-
synthetically obtained from Podophyllum
peltatum L.) [19]. All drugs listed above were
discovered based on bioguide-fractionation
techniques.
Research in the area of natural
products has been undertaken for decades,
mainly with terrestrial or marine plants or
animals found in North America, Europe,
China and India, but little is known about the
pharmacology or the phytochemistry of plants
and animals that compose the biodiversity
found in countries located in the Southern
Hemisphere, as Brazil.
Only a small amount of superior plants
has been pharmacologically or
phytochemically analyzed, especially those
found in the tropics. The number of superior
plants is estimated to be between 200,000 and
250,000 species [20] and only approximately
20% of these plants have been
pharmacologically evaluated [10]. Brazil
concentrates 20% of the world’s biodiversity
[21], and 17% of the Brazilian biodiversity
can be found in the Amazon Rain Forest [22].
The Atlantic Forest contains approximately
35% of the world's Angiospermae, and more
than 8% of the Pteridophytae [23]. The
Amazon Rain Forest has 6,000,000 km
2
, and
60% of this area is located within Brazilian
territory. The remaining 8% of the Atlantic
Forest has 100,000 km
2
[24]. In view of this
species richness, and considering that the
Atlantic Forest is one of the world's foci for
conservation [25], Brazilian forests are a
potential source to discover new hits. Setting
up an extract library, then, is essential to

7
provide a large number of extracts to be tested
in as many in vitro biological tests as possible.
Terrestrial versus marine natural
products
In the past two decades, the interest in
looking for new drugs from marine natural
products increased significantly [26].
Research in the area of marine natural
products is quite recent, and found a peak in
the period spanning from the late 1990’s to
2000, when there was an increase in the
number of new molecules discovered,
especially from sponges, coelenterates and
microorganisms including phytoplankton
[27]. The number of new molecules
discovered from marine sources increased
very fast over the past two decades, if
compared to the new hits discovered from
plant sources. This happened due to the boom
in the research on marine natural products that
occurred in a period favored by high
technological support in molecular
characterization, such as HPLC coupled to
mass spectrometer and the techniques related
to nuclear magnetic resonance spectroscopy.
Now, the discovery of new hits from both
marine and terrestrial natural sources is at a
plateau, although pre-clinical and clinical
trials are still being performed with both
marine [28] and terrestrial products
discovered some years ago, as well as are
being clinically used (podophyllotoxins,
taxanes, vinca alkaloids and camptothecins)
[29]. In Brazil, the research in marine natural
products is challenging and relatively new.
The size of the coast, more than 8,000 km
long, is attractive. This is not our main focus
here, but there are Brazilian groups exploring
marine natural products [26].
TAPPING THE BRAZILIAN
BIODIVERSITY FOR ANTITUMOR
AND ANTIBACTERIAL ACTIVITY
Our group, UNIP (Universidade
Paulista), São Paulo, São Paulo, concentrates
its efforts on collecting plants from the
Amazon rain forest (Manaus, AM) and from
the Atlantic Forest. The University provides
the local facilities, including laboratories,

8
boats, and personnel in both regions, and an
infrastructure with capacity for testing
approximately 500 extracts a year, in the main
laboratory, in São Paulo, SP.
The establishment of a bank of
extracts was a priority to our group since the
beginning of the project. Special attention,
investment and technical support were spent
in selecting and processing plant material. For
that reason, today we have one of the most
standardized banks of extracts composed by
plants native to the Amazon and Atlantic
Forests.
One of the main strategies to create a
well-established bank of extracts is to
determine which plants will be collected, and
how collection should be performed. Plant
collection strategies can be:
- based on traditional knowledge,
- based on chemotaxonomic
information,
- random.
Traditional knowledge
The use of plants as medicines by
traditional communities is still a widespread
practice in developing countries [30],
including Brazil. The selection of the plants
used as medicines by traditional communities
has been done by centuries of trial and error
approach. Such plants have an enormous
possibility of presenting active compounds.
Many groups decide to work with those plants
because they may be a fast track to get to a
positive result, i.e., pharmacologically active
extracts or isolated compounds. Usually the
research approach is to confirm a traditional
use by submitting extracts or compounds to in
vitro or in vivo assays. Today, in Brazil, there
are strict laws that regulate the relationships
between the community, the university and
industry. Hardly ever will a foreign institution
get a license without a Brazilian counterpart
being part of the research team or without
providing clear benefits to the community.
According to the Brazilian law, the access to
traditional knowledge involves not only the
direct contact with a healer or a shaman, but
also all the information that has already been

9
published in scientific papers or any written or
electronic media that describe the use of the
plant by a community.
Chemotaxonomy as a tool in Brazil
The collection of plants to be extracted
based on the chemotaxonomic approach is
based on the collection of plants
taxonomically related to those whose active
chemicals have already been isolated and
described in the literature. This approach
certainly expands the number of plants to be
collected and there is an increased likelihood
that a plant from the same group will present
an active substance as well. A taxonomy
library and technical support provided by
botanists are strongly required if this strategy
is chosen .
The random approach is easier to be
taken in the field, where plants are collected.
Special attention is given to plants in the
reproductive cycle so as to facilitate
taxonomic identification. There are
advantages and disadvantages in this
approach. The advantage is that collecting a
good variety of species certainly adds value to
the bank of extracts, because a large number
of plants may lead to a wide variety of
pharmacological activity and phytochemicals,
once the random collection contains both the
plants used as medicines by traditional
communities and the plants that are not
traditionally used, but which may still present
active compounds. The downside is the higher
investment needed to run random collections,
once there is a larger number of plants to be
collected, more material is necessary to
process the plants, and more expeditions are
needed so as to follow the flowering of plants
on a regular basis. The high number of species
to be identified, processed and tested requires
a well-established group of technical people.
UNIP’s bank of extracts is has approximately
2,000 aqueous and organic extracts obtained
from different parts of plants or whole plants,
depending on biomass availability. Most of
them were collected in the Amazon Rain
Forest, and a small part of them was collected
in the Atlantic Forest.

10
After collection, the initial plant
processing, such as cleaning the material from
insects and other species, separating the
organs (leaves, stem, fruits, flowers, wood,
roots, barks, etc.), is conducted inside the
boat, as well as the initial taxonomic
identifications, up to the level of gender, if
possible.
The crude plant material is brought to
São Paulo, where an organic extract is
obtained through maceration in equal volumes
of dichloromethane and methanol; the same
plant material is then macerated with water ,
resulting in two extracts from each plant.
The antitumoral screening performed
at UNIP’s Laboratório de Extração is directed
against six human cancer cell lines provided
to us by the National Cancer Institute
(DTP/NCI/NIH/USA). The cancer cells were
chosen according to the most prevalent
malignant diseases occurring in Brazil [31].
Breast, prostate, lung, colon, central nervous
system, and leukemia cell lines are cultured in
vitro [32] and the extracts are evaluated
initially at a single dose of 100 µg/mL, and
after determination of the LD
50
, the active
extracts are submitted to fractionation. The
fractions are re-evaluated against the cancer
cell lines so the active ones are identified and
submitted to further fractionation. This
procedure continues until the active
substances are isolated. The isolated substance
is identified using traditional techniques, such
as UV, NMR, MS and IR spectrometer
analysis, in a collaborative basis.
Fractionation and structure elucidation are
being done now with some of the active
extracts, but one of the current limitations of
the process is the great number of extracts to
be processed and chemically analyzed or
fingerprinted.
A similar analysis is made against four
strains of bacteria, obtained from American
Type Culture Collection. The initial screening
is made against Staphylococcus aureus,
Enterococcus faecalis, Escherichia coli and
Pseudomonas aeruginosa at a single dose of
100 µg/mL [33], and the active extracts are
submitted to the analysis of minimal
inhibitory concentration (MIC) and minimal

11
bactericidal concentration (MBC). Both
antibacterial and antitumoral active extracts
are bioguide-fractionated so that their active
compounds can be isolated. Today, our group
has full autonomy to collect the plants,
process the material to obtain standardized
extracts, screen them for both antibacterial
and antitumoral activities, fractionate active
extracts applying usual techniques of
partition, and finally re-test fractions. Further
phytochemical analyses on the active fractions
need collaborative work.
Step by step
An example of how research in natural
products begins is given based on our own
experience. The UNIP’s Laboratório de
Extração has now screened up to 1,220 plant
extracts against the six human cancer cell
lines and against the four bacteria. From the
initial screening, we eventually obtained 72
extracts that showed activity against at least
one of the cancer cell lines and 50 extracts
that showed antibacterial activity against one
or both gram-positive bacteria used in the
assay, at a dose of 100 µg/mL. The plants
which yielded active extracts are listed in
Table 1.
The discovery of new anticancer drugs
is traditionally performed in vitro or in vivo
and cytotoxic models prevailed in the 1980’s
and 1990’s. The approach adopted by our
group [32] is based on the ability the extracts
have to prevent cancer cell lines from growing
in vitro, using a spectrophotometer reader to
detect a color reaction between the
macromolecules of the cancer cell line and
sulforhodamine B, and shows the pros and
cons that are discussed further.
Recent comprehension of the
physiological and biochemical basis of cancer
pathologies favored the development of
cancer target models and is a basis for high-
throughput screening assays. These assays
have recently been introduced in the research
of natural products. Although the advantages
of analyzing plant extracts against a wide
range of cancer targets are evident, it is too
budget-consuming for small laboratories. So,
the alternative is to implement a traditional

12
and economical technique, as the cytotoxic
model cited previously, to pre-screen plant
extracts before submitting the extracts to
specific cell division targets, such as the
checkpoint 1 p53 protein dependant [34],
tubulin and microtubule polymerization and
depolymerization [35, 36, 37, 38, 39], DNA
(40) and RNA (41, 42), and topoisomerases
[43, 44]. There are major inconveniences
generated by the adoption of this strategy: (1)
the range of targeted analyses to be made with
the cytotoxic extracts is limited to cell
division, (2) the analysis of complex mixtures
such as plant extracts or fractions can interfere
with high-throughput screening and (3) the
amount of pure compounds needed to be
tested in a wide range of assays, despite the
low amounts of the natural product in the
plant.
Even though Brazil is the richest
country in the world in terms of biodiversity,
the research in natural products does not occur
as fast as expected. Research laboratories
depend upon public funding, which
sometimes is hard to be obtained due to the
high cost of the basic equipment needed to run
both biological and chemical assays in he
same institution. In spite of that, there are
many laboratories in Brazil able to identify
isolated molecules, and usually cooperative
work is done.
Natural products are usually classified
as cytotoxic agents and their mechanisms of
action are related to targets located in the cell
cycle, which can be considered a limitation of
the technique when compared to the current
new cancer target assays. Nonetheless, taxol-
related drugs provide a strong support to
continue the search of new cytotoxic agents,
due to the particular way paclitaxel and
docetaxel stabilize the microtubules inhibiting
the depolymerization to tubulin [45], differing
from the way vinca alkaloids bind to tubulin
impeding the polymerization to microtubules,
in mitosis [38]. The biological models related
to cytotoxicity used in the isolation and
pharmacological analysis of taxol certainly
contributed to its identification as a new agent
that inhibits microtubules in mitosis. The
history of taxol and the results obtained in the

13
treatment of breast, ovarian and lung cancer
patients [46] gives us support to continue the
search for new plant-derived cytotoxic
anticancer agents.
There are two ways of analyzing the
ability of the 72 extracts to kill cancer cell
lines. The first one is to test those active
extracts against all of the cell lines. We found
Amphirrox sp. to be active against the six cell
lines and Macoubea sprucei to be active
against five cell lines. Probably widely active
extracts contain a cytotoxic substance that
binds with a common pharmacological or
toxicological site, located in normal cells. The
use of this extract, or isolated substance, as an
anticancer drug would be strongly dependant
on modifying the molecule structure so as to
diminish toxicity, without losing
pharmacological potential. The second
approach is to analyze the extracts whose
activity was verified against only one cell line.
Forty-nine out of the 72 extracts were active
against just one cell line out of six. That could
mean a specific activity, maybe related to a
single protein or site in a specific cancer cell
line, although tests were conducted to monitor
cell cycle sites. Further elucidation on the
mechanism of action of those extracts has to
be done.
The antibacterial screening resulted in
50 active aqueous and organic extracts or 4.10
% yield. Interestingly, none of the extracts
showed activity against any of the Gram-
negative E. coli and P. aeruginosa, at the dose
of 100 µg/mL, determined as the cutoff point
to select extracts that are going to have their
MIC and MBC obtained. When MIC and
MBC were obtained, we considered that the
extracts whose MIC and MBC were ≤ 200
µg/mL would be fractionated and the active
compounds isolated. We obtained 50 aqueous
and organic extracts from different organs
from the plants listed in Table 1.
As none of the extracts was active
against the Gram-negative bacteria we
studied, we decided to evaluate at what dose
these extracts would kill both microbes. Then
we tested a group of 27 extracts against the
bacteria and decided to change the cutoff
point to 1000 µg/mL. We obtained 14 extracts

14
active against both Gram-negative bacteria
(obtained from Duguetia uniflora,
Calophyllum brasiliense, Clusia sp., Tovomita
longifolia, Garcinia madruno, Croton
cuneatus, Mabea subsessilis, Rapanea
parvifolia and Ruizterania retusa), six
extracts active only against E. coli (obtained
from Annona sp., Annona hypoglauca, Vismia
guianensis, Amanoa gracillima, Smilax
rufescens and Bytneria sp.), and seven
extracts (obtained from Calophyllum
brasiliense, Vismia guianensis, Tovomita sp.
and Vismia schultesii) that showed activity
neither against E. coli or P. aeruginosa. None
of the 27 extracts was active against P.
aeruginosa and inactive against E. coli at the
same time. In most of the extracts, both the
MIC’s and MBC’s obtained against E. coli
and P. aeruginosa were clearly higher if
compared to those obtained in the Gram-
positive assays. This may occur due to the
physiological structure of the Gram-negative
bacteria membrane. These extracts can still be
considered for further studies regarding a
specific activity against Gram-negative
bacteria, even if the doses approximate 500
µg/mL. Once the active compounds are
identified and retested, an increase in the
antibacterial activity may occur.
The pharmacological strategy adopted
by our group starts with the general biological
assay used to select extracts that inhibit cell
cycle from happening. After the extracts were
selected, their mechanisms of action were
identified, so a fine selection of extracts could
be conducted. For that purpose, specific
cancer target bioassays should be used, but it
would be too budget-consuming for our
capacity to test large amount of extracts. Such
analysis would be best if done with isolated
compounds. Now, the active anticancer
extracts are being studied in relation to their
antioxidant and radical scavenging properties
using b-carotene and dyphenyl-picryl-hydrazil
(DPPH) and their capacity of inhibiting
Saccharomyces cerevisiaea from growing as a
pre-screening to further mechanistic analysis
related to mitosis.
Fractionation of the 122 active extracts
and the identification of the active compounds

15
are the next steps to be followed now. The
efficiency and time spent in the process are
important issues to be considered. The
bioguide-fractionation is clearly the fastest
strategy to identify active fractions and
substances, and obtaining a large number of
fractions to be retested is the key to the
identification of active compounds.
Traditional partition techniques are more
affordable, but the loss of extract and fraction
mass is significant, and can compromise the
final identification spectrometric analyses. On
the other hand, using equipment such as diode
array HPLC to obtain fractions is too
expensive to an ordinary laboratory. An
intermediate technique as flash
chromatography or vacuum-coupled column
chromatography certainly works properly and
is less budget-consuming, and results in a
good number of fractions with a relatively low
loss of extract or fraction. Our laboratory is
now working on fractionation of the active
plant extracts and next year we intend to
isolate cytotoxic compounds .
The discovery of a new anticancer
natural product often emerges from screening
cytotoxic methodologies. An extensive list of
natural products that were isolated from
terrestrial and marine organisms has been
published before [47]. Frequently, toxicity
appears to be a major concern with cytotoxic
anticancer agents due to their unspecific
mechanism of action, which does not
distinguish cancer cells from normal ones.
Studies involving the analysis of the structure-
activity relationship and molecular modeling
of these natural candidates to cancer drugs
should follow the traditional medicinal
chemistry steps, as was done with
podophyllotoxin and etoposide [48].
Conclusions
The starting point is the Brazilian
biodiversity, which certainly plays an
important role in the identification of new hits
in cancer treatment. Obtaining the permission
to access the Brazilian genetic patrimony is a
victory by itself. Our group has just renewed
the license to collect plant material and

16
received the license to bioprospect the
extracts. The challenges of starting to run a
natural product laboratory in the present are
huge, due to the basic technological needs to
complete the whole sequence from plant
collection to the identification of an active
compound. For that reason, collaborative
work is the alternative. Collaboration provides
a chance of optimizing the analyses of the
extracts against a wide range of biological
models and to determine the structure of the
active compounds.
Recently, the introduction of new
models to evaluate cancer targets made the
search for new anticancer drugs more precise
and less time-consuming. Natural product
research accompanies this tendency, although
little has been done in Brazil so far. Our
current interest is to pre-screen plant extracts
in order to select the active ones, test them in
terms of their active chemical constituents,
and then identify the mechanism of action by
means of collaborative work. Meanwhile,
tapping the Brazilian biodiversity is a slow
and painstaking endeavor, and the results are
slowly showing their potential.
Acknowledgements
The authors thank FAPESP
(grant#99/05904-6) and NCI/NIH/USA for
the human cancer cell lines.
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20
Table 1. List of plants whose extracts showed cytotoxic and antibacterial activities in doses of 100 µg/mL.
SPECIES MCF-7
1
PC-3
2
NCI-H460
3
KM-12
4
SF-268
5
RPMI-8226
6
ANTIBACTERIA
L
Abarema cf. jupunba X X
Adiscanthus fusciflorus X X X
Aldina cf. reticulata X
Aldina sp.2 X
Amanoa cf. gracilima X
Amphirrox sp. X X X X X X X
Annona hypoglauca X X X
Banisteriopsis sp. X
Blastomanthus sp. X
Byrsonima cf. duckeana X
Byrsonima cf. sericea, X
Calophyllum brasiliense X X
Caraipa grandifolia X
Caryocar microcarpum X
Cassipourea guianensis X
Chaunochiton loranthoides X X
Cimeria sp. X
Combretum laurifolium, X
Commelina diffusa X
Connarus perrottetii X
Cordia cf. exaltata X
Crataeva tapia X X
Croton cuneatus X
Cynometra spruceana X
Dioclea violacea X
Diospyros cf. guianensis X

21
Distictella magnoliifolia X X
Doliocarpus guianensis, X
Garcinia madruno X
Gnetum leyboldii X X
Guatteria riparia X X X X
Guatteria schomburgkiana X
Gustavia augusta X
Haploclathra paniculata, X
Hasseltia sp. X
Heliconia acuminata X
Homalium racemosum X X
Hymenaea courbaril X
Laetia corymbulosa X
Laetia suaveolens X X X
Macoubea sprucei X X X X X
Macrolobium acaciifolium X
Macrolobium multijugum X X
Malouetia tamaquarina X
Mora paraensis X
Ocotea amazonica X
Ocotea myriantha X
Ocotea sp. X
Pagamea coriacea X
Palicourea guianensis X
Parahancornia surrogata, X
Passiflora acuminata X X X X
Paullinia cf. fissistipula X
Pentaclethra macroloba X X X
Philodendron solimoesense X X X X

22
Picrolemma sprucei X
Piper arboretum X
Pithecellobium sp. X X
Pouteria sp. X
Pseudoconnarus macrophyllus X
Psidium densicomum X X
Psittacanthus cucularis X
Psychotria sp. X
Rapanea parvifolia X
Roucheria punctata X
Roupala sp. X
Simaba cf. paraenesis X
Simaba polyphylla X
Siparuna guianensis X
Smilax sp. X
Stryphnodendron pulcherrimum X
Swartzia laevicarpa X X
Swartzia sericea var. sericea X X
Tapirira guianensis X
Taralea oppositifolia X
Toulicia cf. pulvinata X X
Tournefortia aff. candidula X
Tovomita brasiliensis X
Trichilia cf. pleeana X
Trigonia cf. sericea X
Unonopsis guatterioides X
Virola theiodora X X
Vismia guianensis X X
Vitex sp. X

23
Xylopia aromatica X
Zanthoxylum sp. X
(1) Breast cancer percentage of lethality ranged from -14.89 % to -80.73 %. (2) Prostate carcinoma cell percentage of
lethality spanned from -15.95 to -35.48 %. (3) Non-small cell lung cancer cell line percentage of lethality
spanned from -16.03 to -36.53 %. (4) The colorectal adenocarcinoma cell line activity spanned from -15.22 to -
100.00 %. (5) The central nervous system cancer cell line percentage of lethality spanning from -18.13 to -76.97
%. (6) The peripheral blood multiple myeloma leukemia cell line percentage of lethality spanned from -14.96 to -
94.40 %.