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Fighting cancer while saving the mayapple


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The genes required for synthesizing a plant-derived anticancer compound are identified [Also see Report by Lau and Sattely ]
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11 SEPTEMBER 2015 • VOL 349 ISSUE 6253 1167SCIENCE
cGAS-mediated detection, suggesting that
the viral particles that emerge from an in-
fected cell would likely not incorporate
cGAMP ( 10). However, Gentili et al. and
Bridgeman et al. show that a poxvirus and
a herpesvirus (both double-stranded DNA
viruses) can take up cGAMP into viral par-
ticles. Perhaps the stowaway mechanism is
restricted to certain classes of DNA viruses
or retroviruses that lack sophisticated eva-
sion tactics.
Another question is whether cGAMP in-
corporation into virions is a host-directed
strategy or simply a consequence of stochas-
tic fluid-phase uptake of cytosolic material
into viral particles. By necessity, enveloped
viruses must use host membranes to com-
plete the virus assembly and maturation
process. Viruses incorporate a variety of
host molecules into their virions such as
histocompatibility proteins, tetraspanins,
or even antiviral molecules like apolipo-
protein B messenger RNA editing enzyme,
catalytic polypeptide-like 3G (APOBEC3G)
in the case of HIV-1 ( 11). Yet, it is not clear
if this process is regulated by the host. It
is tantalizing to speculate that the host is
as wily an adversary as the virus, with the
ability to sneak an antiviral molecule into
outbound viral particles.
What are the biological implications of
cGAMP incorporation into viral particles?
The host might benefit on multiple levels.
A virus carrying cGAMP may promote long-
distance transmission of antiviral signals to
cells and tissues located far from the initial
site of infection. Similarly, a cGAMP-loaded
virion could serve as a sentinel of innate im-
mune signaling during transmission of the
virus from one host to another, potentially
even crossing species barriers. The main
benefit to the host could be rapid initia-
tion of cGAMP-mediated signaling, even in
cells that cannot mount antiviral responses
due to poor cGAS expression. It is not yet
clear, however, whether cGAMP loading is
a propagating mechanism. Further studies
will be needed to determine whether cells
activated into an antiviral state by incoming
virus carrying cGAMP also produce virions
that carry cGAMP.
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(2013 ).
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Plants synthesize an abundance of
metabolites that can be exploited for
pharmacological purposes ( 1). The
pool of plant metabolites that can be
considered medicinally important
is greatly expanded when consider-
ing that many plant natural products can
be used as a scaffold for derivatization, with
the resulting unnatural analogs often having
either improved or novel medicinal activity.
Typically, unnatural analogs are made semi-
synthetically by chemically modifying natu-
ral biosynthetic intermediates. However, on
page 1224 of this issue, Lau and Sattely ( 2)
report the discovery of a set of biosynthetic
enzymes in mayapple (Podophyllum) plants
that can produce a compound that is a di-
rect precursor to etoposide, an “unnatural”
anticancer agent. Moreover, Lau and Sattely
show that the genes encoding these enzymes
can be expressed in a different plant species
to produce this etoposide precursor. The
study clearly demonstrates the power of met-
abolic pathway discovery and genetic engi-
neering to make not only naturally occurring
compounds, but also natural product analogs
with enhanced pharmacological value.
Derivatizing unnatural analogs from
natural plant compounds has had success-
ful outcomes in the development of anti-
cancer drugs. For example, camptothecin,
which is produced by the Chinese “happy
tree” (Camptotheca), is a potent inhibitor
of topoisomerase, an enzyme that controls
DNA integrity during the cell division cycle.
However, camptothecin is too insoluble for
clinical use. Its derivatization with an amino
group yields topotecan, an anticancer agent
currently used in the clinic to treat ovarian,
cervical, and small-cell lung cancer ( 3). Even
when natural compounds are clinically im-
portant, chemical derivatization can broaden
the spectrum of applications or mitigate side
By Sarah E. O’Connor
John Innes Centre, Department of Biological Chemistry,
Norwich NR4 7UK, UK. E-mail: sarah.o’
Fighting cancer while
saving the mayapple
The genes required for synthesizing a plant-derived
anticancer compound are identified
Plant precursor. Epotoside is a
commonly used chemotherapy
drug that is derived from a natural
compound in mayapple plants.
Published by AAAS
on September 4, 2017 from
1168 11 SEPTEMBER 2015 • VOL 349 ISSUE 6253 SCIENCE
effects. Derivatives of the plant-derived anti-
cancer agent taxol [isolated from the Pacific
yew tree (Taxus brevifolia)] and vinblastine
[isolated from the Madagascar periwinkle
(Catharanthus roseus)] are used in the clinic
in addition to the natural compounds ( 4, 5).
Etoposide is chemically synthesized from
the natural metabolite podophyllotoxin, a
liganin that is produced in mayapple plants
( 6). The potent cytotoxic activity of podophyl-
lotoxin suggested that it could be developed
into an anticancer drug, but in practice, the
compound proved to be too toxic for clinical
use. In the 1950s, a program was launched
to synthesize and screen semisynthetic podo-
phyllotoxin derivatives that exhibited less
toxic side effects. Etoposide, which was even-
tually discovered from this effort, showed
excellent results in clinical trials and was
introduced to the United States drug market
in 1983 ( 6). Etoposide has a different mode
of cytotoxicity compared to the podophyllo-
toxin precursor. Chemical derivatization is
typically used to enhance pharmacological
properties such as water solubility, but eto-
poside reflects how subtle chemical modifi-
cations can also dramatically change the
biological mode of action.
Medicinally useful plant metabolites, in-
cluding podophyllotoxin, are usually iso-
lated from the producer plant and are often
produced in low yields. Furthermore, many
medicinal plants are difficult to grow or are
endangered, as is the case for a number of
Podophyllum species ( 7). Development of a
renewable plant cell culture that generates
sufficient yields of podophyllotoxin has been
unsuccessful ( 8). An emerging approach for
sustainable production of plant-derived com-
pounds is reconstitution of the biosynthetic
genes in a heterologous host to recreate a
functional pathway. Many challenges must be
overcome to reconstitute these complex bio-
synthesis pathways, but perhaps the largest
hurdle is finding the relevant genes within a
large, uncharacterized plant genome.
Lau and Sattely identified missing steps in
podophyllotoxin biosynthesis by tracking the
expression levels of mayapple genes. Because
podophyllotoxin increases in response to leaf
wounding, comparison of RNA sequence
data sets from wounded and unwounded
leaf tissue pinpointed appropriately upregu-
lated genes. Lau and Sattely filtered the pool
of gene candidates by considering only up-
regulated genes that encode four enzyme
classes that are predicted to carry out spe-
cific types of chemical reactions required
for podophyllotoxin biosynthesis. Once this
set of candidates was identified, the genes
could be transformed into the heterologous
host Nicotiana benthamiana, a fast-growing
relative of tobacco for which a robust pro-
tein expression system has been developed
( 9). Lau and Sattely expressed multiple gene
candidates at once in this host plant and
identified the resulting compounds in leaf
tissue by mass spectrometry. This untargeted
metabolite profiling approach, in which all
compounds resulting from candidate gene
expression are identified, proved critical for
characterizing unexpected, but highly valu-
able, chemical reactions that are catalyzed
by these candidate gene products. Expres-
sion of one candidate gene consumed the
biosynthetic intermediate (–)-deoxypodo-
phyllotoxin, but the expected hydroxylated
product was not detected, and instead, a
demethylated product was observed. A sec-
ond candidate gene did hydroxylate (–)-de-
oxypodophyllotoxin in the predicted position
but yielded unexpected stereochemistry. Lau
and Sattely realized that these unpredicted
enzymatic reactions could be used to pro-
duce a more direct precursor for etoposide.
Expression of these two genes, plus an addi-
tional eight biosynthetic genes and a small-
molecule precursor, in the N. benthamiana
host produced (–)-4-desmethylepipodophyl-
lotoxin, a compound that can be converted
to etoposide in fewer chemical steps than are
required for the podophyllotoxin precursor.
Although discovery of biosynthetic genes
from plant metabolic pathways remains a
challenging prospect, the elucidation of
this pathway by Lau and Sattely demon-
strates how far the field has come. The use
of a heterologous host as a gene discovery
tool ensures that gene candidates can be
examined in the context of other pathway
enzymes, which in this case was critical for
revealing unexpected chemistry carried out
by biosynthetic enzyme candidates. Rather
than produce podophyllotoxin, Lau and
Sattely used a specific combination of en-
zymes to synthesize a molecule more valu-
able than the initial target.
1. J. D. McChesney et al., Phytochemistry 68, 2015 (2007).
2. W. Lau, E . S. Satte ly, Science 349, 1224 (2015).
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(2014 ).
…biosynthetic enzymes
in mayapple…produce a…
precursor to…an ‘unnatural’
anticancer agent.
When de Broglie predicted that we
need to associate a periodic phe-
nomenon with any isolated portion
of matter or energy ( 1), this idea
became the basis of Schrödinger’s
wave equation and modern matter-
wave interferometry. It has stood the test of
time and inspired intriguing discussions on
the relation between quantum physics, classi-
cality ( 2), and general relativity theory (GRT)
( 35). It also inspired the recent work on page
1205 of this issue by Margalit et al. ( 6), who
demonstrated that the internal clock of a de-
localized atom can be used as a witness of the
atom’s path through a matter-wave interfer-
ometer. The study shows Bohr’s complemen-
tarity principle in action and how dephasing
in an external potential may mimic “classi-
cality” even though the underlying quantum
correlations can be erased and reversed.
In 1908, Einstein predicted that the proper
time of any clock on Earth will change with
the local gravitational potential by one part
in 1016 per meter height difference. This ef-
fect is tiny, but it already needed to account
for the comparison of optical clocks with a
height separation of 5 cm ( 7). If we take de
Broglie’s idea of a periodic phenomenon in
any lump of matter literally, does that imply
that even “a rock is a clock?” Could this boost
precision measurements of gravitational time
dilation in an atom interferometer where the
center-of-mass wave function of an atom is
delocalized over a certain height ( 3)?
Although it has been argued that time
dilation will remain unobservable in experi-
ments with simple “rocks” as probe particles
( 4), interesting effects are expected ( 5) when
the rock is replaced by a clock, i.e., a particle
with internal dynamics (see the figure, panel
A). Even if the two center-of-mass wave func-
tions of the same atom are perfectly in phase
and suitable for high-contrast matter-wave
interference, the internal atomic clocks may
still tick at different rates in each arm.
By Markus Arndt and Christian Brand
University of Vienna, Faculty of Physics, VCQ and
QuNaBioS, Boltzmanngasse 5, 1090 Vienna, Austria.
Interference of
atomic clocks
The time dilation of gravity
is mimicked with atomic
clocks in magnetic fields
Published by AAAS
on September 4, 2017 from
Fighting cancer while saving the mayapple
Sarah E. O'Connor
DOI: 10.1126/science.aad1801
(6253), 1167-1168.349Science
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... These substances are also able to relieve pain in the process of treatment. However, the efficacy of numerous cancer inhibitor components in plants is much lower compared with synthetic drugs (11). Therefore, a combination of different natural substances can increase the inhibitory and therapeutic effects (11). ...
... However, the efficacy of numerous cancer inhibitor components in plants is much lower compared with synthetic drugs (11). Therefore, a combination of different natural substances can increase the inhibitory and therapeutic effects (11). ...
The aim of the present study was to investigate whether oridonin is able to increase the effects of lentinan (LNT) in HepG2 human hepatoblastoma cells by MTT, flow cytometry, reverse transcription-quantitative polymerase chain reaction and western blot analysis. The in vitro results demonstrated that 20 μg/ml of oridonin was a nontoxic concentration for L02 normal liver cells and HepG2 liver cancer cells. Furthermore, treatment with 0-200 μg/ml LNT was only able to decrease the viability of HepG2 liver cancer cells. The growth inhibitory rate of the LNT-L (100 μg/ml) treatment group was 20.7% and the rate of the LNT-H (200 μg/ml) treatment group was 54.8%. Notably, the growth inhibitory rate of the oridonin + LNT-H group was 84.3%. The highest percentage of apoptotic cells was observed in the oridonin + LNT-H group (20 μg/ml oridonin and 200 μg/ml LNT). The percentage of apoptotic cells in the oridonin + LNT-H group was significantly different from the percentage of apoptotic cells in the LNT-H (26.1%) and the LNT-L (16.8%) groups. Treatment with LNT produced an increase in caspase-3, caspase-9, Bcl-2-like protein 4, p53, p21, nuclear factor κB inhibitor-α mRNA and protein expression and a decrease in B-cell lymphoma 2 and nuclear factor-κB expression in HepG2 cells compared with untreated control cells. Treatment with a combination of oridonin and LNT-H induced a further increase in expression with the biggest differences in expression observed between the oridonin + LNT-H group and control. It was observed that treatment with oridonin was able to increase the anticancer effects of LNT in HepG2 cells. Therefore, oridonin may be used to sensitize cells to LNT.
... Cancer inhibitors exist in various plants naturally, and have very good effects on human cancer prevention. These cancer inhibitors that occur naturally have low toxicity, as well as can reduce the pain of patients during the treatment [17]. But the activity of many cancer inhibitors existing in natural plants is lower than that of synthetic drugs, and the combination of different natural cancer inhibitors can substantially improves the treatment effect of cancer, so finding out a reasonable combination becomes the most important thing to improve and enhance the anti-cancer effects resources that occurs naturally. ...
Full-text available
Background The aim of this in vitro study was to measure the enhanced anticancer effects of Res (resveratrol) on PA (paclitaxel) in HepG2 human liver cancer cells. Methods The MTT (thiazolyl blue tetrazolium bromide, 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide), flow cytometry, qPCR (real-time quantitative polymerase chain reaction) and western blot assay were used for cells growth inhibitory effects, cells apoptosis (DNA content of sub-G1), mRNA and protein expressions, respectively. Results The 10 μg/mL of Res had no growth inhibitory effect on Nthy-ori 3–1 normal cells or HepG2 cancer cells meanwhile the 5 or 10 μg/mL of PA also had no growth inhibitory effect on Nthy-ori 3–1 normal cells. Where as PA-L (5 μg/mL) and PA-H (10 μg/mL) had the growth inhibitory effects in HepG2 cancer cells, and Res increase these growth inhibitory effects. By flow cytometry experiment, after Res (5 μg/mL) + PA-H (10 μg/mL) treatment, the HepG2 cells showed the most apoptosis in cells as compared to other treatments groups, and after additionally treated with Res, both the apoptosis cells of two concentrations PA were raised. As PA raised it also raised the mRNA and protein expressions of caspase-3, caspase-8, caspase-9, Bax (Bcl-2 assaciated X protein), p53, p21, IκB-α (inhibitor of NF-κB alpha), Fas (factor associated suicide), FasL (factor associated suicide ligand), TIMP-1 (tissue inhibitor of metalloproteinases 1), TIMP-2 (tissue inhibitor of metalloproteinases 2) and decrease Bcl-2 (B cell leukemia 2), Bcl-xL (B cell leukemia extra large), HIAP-1 (cIAP-1, cellular inhibitor of apoptosis 1), HIAP-2 (cIAP-2, cellular inhibitor of apoptosis 2), NF-κB (nuclear factor kappa B), COX-2 (cyclooxygenase 2), iNOS (inducible nitric oxide synthase), MMP-2 (metalloproteinase 2), MMP-9 (metalloproteinase 9), EGF (epidermal growth factor), EGFR (epidermal growth factor receptor), VEGF (vascular endothelial growth factor), Fit-1 (VEGFR-1, vascular endothelial growth factor receptor 1). Meanwhile, the 5 μg/mL of Res could enhance these mRNA expressions changes as compared to the control cells. Conclusion From these results, we can conclude that Res could raise the anticancer effects of PA in HepG2 cells, Res could be used as a good sensitizing agent for PA.
... Certain substances with cancer cell apoptosis-inducing effects that were extracted from plants have low toxicity and are safe to use, which enhances the quality of life of patients during treatment. While numerous natural anticancer drugs contained in plants have a lower efficacy than certain synthetic drugs, the combination of various natural products may have an improved therapeutic effect (9). Identification of a reasonable combination has become an important task in the field of natural product-based as anticancer treatments. ...
The aim of the present study was to determine the ability of oridonin to enhance the anticancer activity of lentinan (LNT) in SMMC-7721 human hepatoma cells in vitro by using various techniques, including MTT, flow cytometry, quantitative PCR and western blot assays. The results demonstrated that 20 μg/ml was a non-toxic concentration of oridonin for L02 normal liver cells and SMMC-7721 cells, while 0-200 μg/ml of LNT only had anti-proliferative effects on SMMC-7721 cells. LNT at 100 and 200 μg/ml inhibited the growth of SMMC-7721 cells by 22.8 and 60.0%, respectively, and after addition of 20 μg/ml oridonin, the inhibitory rate of 100 and 200 μg/ml LNT was increased to 47.2 and 80.7%, respectively. Oridonin (20 μg/ml) + LNT (200 μg/ml)-treated SMMC-7721 cells showed the highest apoptotic rate, which was 40.5±2.5%, which was higher than that of cells treated with LNT only. LNT raised the mRNA and protein expression of caspase-3, -8 and -9 as well as B-cell lymphoma 2 (Bcl-2)-associated X protein, p53 and p21, while reducing the expression of Bcl-2, Bcl extra large protein, epidermal growth factor (EGF) and EGF receptor expression in SMMC-7721 cells as compared to that in control cells. Treatment with 20 μg/ml oridonin and 200 μg/ml LNT increased these changes of gene expression. From the obtained results, it may be concluded that oridonin raised the in vitro anti-cancer effects of LNT in SMMC-7721 cells. Oridonin may also be used as a sensitizing agent to increase the anticancer activity of LNT in vivo.
... This study holds significance as it can play a significant role in reducing the burden on first plant species in addition to providing a shorter route for the chemical synthesis of etoposide. [159] The presence of the biosynthetic pathway for podophyllotoxin was also reported in Anthriscus, Linum and Forsythia. [160] With the availability of genomic data for species accumulating podophyllotoxin, elucidation of unknown steps in the biosynthetic pathway is a major challenge. ...
Full-text available
Podophyllotoxin is an aryltetralin lignan synthesized in several plant species, which is used in chemotherapies for cancers and tumor treatment. More potent semisynthetic derivatives of podophyllotoxin such as etoposide and teniposide are being developed and evaluated for their efficacy. To meet the ever increasing pharmaceutical needs, species having podophyllotoxin are uprooted extensively leading to the endangered status of selective species mainly Sinopodophyllum hexandrum. This has necessitated bioprospection of podophyllotoxin from different plant species to escalate the strain on this endangered species. The conventional and non-conventional mode of propagation and bioprospection with the integration of biotechnological interventions could contribute to sustainable supply of podophyllotoxin from the available plant resources. This review article is focused on the understanding of different means of propagation, development of genomic information, and its implications for elucidating podophyllotoxin biosynthesis and metabolic engineering of pathways. In addition, various strategies for sustainable production of this valuable metabolite are also discussed, besides a critical evaluation of future challenges and opportunities for the commercialization of podophyllotoxin.
Small family farms in the United States are looking to the future toward sustainability. It is suggested that biopharming for nutritional improvement, vaccines, therapeutics, chemical precursors for manufacturing by using genetically modified crop plants could provide a niche market to increase their profits margins.
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Cancer has become the second leading cause of death worldwide. The incidences of cancer are rising at an alarming rate but it can be reduced and controlled by evidence-based strategies for cancer prevention, early detection, and management of patients with cancer. Historically, it is proven that plants and their metabolites have great potential in the treatment of various acute diseases as well as chronic disorders. The novel bioactive compounds from many plants are being studied as potential therapeutic agents because of their high activity and low toxicity. This review gives a comprehensive description of such medicinal plants which have been studied as potentially effective against cancer.
Full-text available
Intraspecific genetic variation in natural populations governs their potential to overcome challenging ecological and environmental conditions. In addition, knowledge of this variation is critical for the conservation and management of endangered plant taxa. Found in the Himalayas, Podophyllum hexandrum is an endangered high-elevation plant species that has great medicinal importance. Here we report on the genetic diversity analysis of 24 P. hexandrum populations (209 individuals), representing the whole of the Indian Himalayas. In the present study, seven amplified fragment length polymorphism (AFLP) primer pairs generated 1677 fragments, of which 866 were found to be polymorphic. NJ clustering, PCoA and STRUCTURE analysis clustered 209 individuals from 24 populations of the Indian Himalayan mountains into two major groups with a significant amount of geneflow (Nm=2.13) and moderate genetic differentiation Fst(0.196), G'st(0.20). This suggests that, regardless of geographic location, all of the populations from the Indian Himalayas are intermixed and are composed broadly of two types of genetic populations. High variance partitioned within populations (80%) suggests that the most of the diversity is restricted to the within-population level. These results suggest two possibilities about the ancient population structure of P. hexandrum: either all of the populations in the geographical region of Indian Himalayas are remnants of a once-widespread ancient population, or they originated from two types of genetic populations, which coexisted a long time ago, but subsequently separated as a result of long-distance dispersal and natural selection. High variance partitioned within the populations indicates that these populations have evolved in response to their respective environments over time, but low levels of heterozygosity suggest the presence of historical population bottlenecks. Published by Oxford University Press on behalf of the Annals of Botany Company.
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Recent developments in transient expression methods have enabled the efficient delivery and expression of multiple genes within the same plant cell over a timescale of days. In some cases, the vectors deployed can be fine-tuned to allow differential expression of the various genes. This has opened the way to the deployment of transient expression for such applications as the production of macromolecular complexes and the analysis and manipulation of metabolic pathways. The ability to observe the effect of gene expression in a matter of days means that transient expression is becoming the method of choice for many plant-based synthetic biology applications.
Full-text available
The synthetic investigation of biologically active natural compounds serves two main purposes: (i) the total synthesis of alkaloids and their analogues; (ii) modification of the structures for producing more selective, more effective, or less toxic derivatives. In the chemistry of dimeric Vinca alkaloids enormous efforts have been directed towards synthesizing new derivatives of the antitumor agents vinblastine and vincristine so as to obtain novel compounds with improved therapeutic properties.
Transplanting the wisdom of the mayapple Etoposide, a topoisomerase inhibitor, is used to treat various cancers. However, etoposide isn't that easy to get. Its precursor comes from the very slow-growing mayapple plant. Lau and Sattely used bioinformatics, heterologous enzyme expression, and kinetic characterization, to work out the pathway that makes the precursor in mayapple (see the Perspective by O'Connor). They then successfully transplanted the full biosynthetic pathway into tobacco plants. Science , this issue p. 1224 ; see also p. 1167
Infected cells generate a factor that is incorporated into viruses and transferred to other cells [Also see Reports by Bridgeman et al. and Gentili et al. ]
Camptothecin (CPT) and its derivatives comprise an important group of heterocyclic compounds that are well recognized for their anticancer activities. Efforts have been made over the years aiming to develop new CPT analogs with better clinical efficacy, improved pharmacokinetic profile and lower toxicity. First generation of analogs, irinotecan (CPT-11) and topotecan (TPT) was approved for use by FDA in 1996 for the treatment of colorectal (CPT-11) and cervical, ovarian and small lung cancers (TPT). Other analogs of CPT are currently in different phases of clinical trials. As CPT represents an important lead compound in the field of antitumor- research, in this review we will highlight some recent discoveries (2008-2013) on the development of novel camptothecin-based compounds as potential anticancer agents.
Paclitaxel belongs to the most successful anticancer drugs developed and utilised during the past two decades. Nevertheless, the development of resistance of tumor cells and severe side effects in the patients require further improvement of the drug. In this review, we provide a detailed overview of the state-of-the-art in the medicinal chemistry of paclitaxel and its analogues. A number of strategies have been explored to obtain sufficient amounts of paclitaxel for clinical use from natural resources. Semi-synthesis from its precursor, 10-deacetylbaccatin III, which can be extracted from Taxus leavesturned out as the most appropriate method for commercial production. So far, many paclitaxel derivatives have been synthesized, and their effect on microtubules stabilization and cytotoxicity were investigated in terms of structure-activity relationships (SAR). One of them, docetaxel, was approved as a more potent anticancer agent than paclitaxel towards a variety of tumor types. This review summarizes current possibilities to harvest sufficient amount of drugs from natural sources, including the production of taxanes in bioreactors and synthetic approaches for paclitaxel and its analogues, their mechanism of action and structure-activity relationships. In addition, future developments and perspectives for this class of compounds are outlined.
The natural lignan podophyllotoxin, a dimerized product of two phenylpropanoid moieties which occurs in a few plant species, is a pharmacologically important compound for its anticancer activities. It is used as a precursor for the chemical synthesis of the anticancer drugs etoposide, teniposide and etopophose. The availability of this lignan is becoming increasingly limited because of the scarce occurrence of its natural sources and also because synthetic approaches for its production are still commercially unacceptable. Biotechnological production using cell culture may be considered as an alternative source. Selection of the best performing cell line, its maintenance and stabilization are necessary prerequisites for its production in bioreactors and subsequent scale-up of the cultivation process to the industrial level. Scale-up of growth and product yield depends on a multitude of factors, such as growth medium, physicochemical conditions, seed inoculum, type of reactor and processing conditions. The composition of the growth medium, elicitors and precursors, etc. can markedly influence the production. Optimum levels of parameters that facilitate high growth and product response in cell suspensions of Podophyllum hexandrum have already been determined by statistical design. P. hexandrum cells have successfully been cultivated in a 3-l stirred-tank bioreactor under low shear conditions in batch and fed-batch modes of operation. The batch kinetic data were used to identify the mathematical model which was then used to develop nutrient-feeding strategies for fed-batch cultivation to prolong the productive log phase of cultivation. An improvement in the production of podophyllotoxin to 48.8 mg l(-1) in a cell culture of P. hexandrum was achieved, with a corresponding volumetric productivity of 0.80 mg l(-1) day(-1), when the reactor was operated in continuous cell-retention mode. Efforts are being made to further enhance its production levels by the development of hairy root culture or by varying the channeling of precursors towards the desired biosynthetic pathway by molecular approaches.
Natural product substances have historically served as the most significant source of new leads for pharmaceutical development. However, with the advent of robotics, bioinformatics, high throughput screening (HTS), molecular biology-biotechnology, combinatorial chemistry, in silico (molecular modeling) and other methodologies, the pharmaceutical industry has largely moved away from plant derived natural products as a source for leads and prospective drug candidates. Can, or will, natural products ever recapture the preeminent position they once held as a foundation for drug discovery and development? The challenges associated with development of natural products as pharmaceuticals are illustrated by the Taxol story. Several misconceptions, which constrain utilization of plant natural products, for discovery and development of pharmaceuticals, are addressed to return natural products to the forefront.