Plant-derived Epigenetic Modulators For Cancer Treatment And Prevention

Huma Qureshi10-Arid-1788

Ph. D. Botany (1st Semester)

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WHAT IS EPIGENETICS?

In the early 1940s, C. H. Waddington coined the term epigenetics to mean

“above or in addition to genetics” “genome information that is super-imposed on the DNA sequence”

How can identical twins have different hair colors?How do different adult stem cells know their fate?

Myoblasts can only form muscle cells Keratinocytes only form skin cells Hematopoetic cells only become blood cells But all have identical DNA sequences.

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Modern definition is non-sequence dependent inheritance.Epigenetic phenomena are reversibleEpigenetic phenomena are critical for the embryonic development, aging, and the process of many diseases including cancers. A bridge that connects environmental factors to our genes and bring the phenotype into being.

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EPIGENETIC MECHANISMS

Gene Expression

RNA Interference

Histone Modifications

DNA Methylation

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DNA METHYLATION

DNA methylation is a unique modification of DNA and the most common epigenetic phenomenon in eukaryotic cells.

DNA methyltransferases catalyze the transfer of methyl group from S-adenosylmethionine (AdoMet) to the carbon-5’ position of cytosine in CpG dinucleotides.

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HISTONE MODIFICATION

When histones are tagged, or acetylated, chromatin is open and genes are potentially active;

When histones are not chemically tagged, deacetylated, the chromatin condenses and genes silenced.

Levels of acetylation of the core histones result from the steady balance between HAT and HDAC.

HDAC

HAT

ActiveInactive

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Non coding RNAs

RNA which is not used for making proteins (non-coding RNA) can be cleaved and used to inhibit protein-coding RNAs

siRNAs, microRNAs (~22 Nucleotides; fine tune gene Expression)

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WHAT IS CANCER?

Carcinogenesis is a complex and multistep process that involves the accumulation of successive transformational events driven by genetic mutations and epigenetic alterations that affect major cellular processes and pathways such as proliferation, differentiation, invasion and survival

These alterations affect normal gene regulation and impede normal cellular processes including cell cycle, DNA repair, cell growth, differentiation and apoptosis.

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Abnormal accumulation of abnormal cells with a loss of control to grow and spread

Cell Proliferation Cell DeathHomeostasis

Regulation of Cell Cycle:Cell Cycle Check points

Control of Apoptosis

Cancer arises from both, epigenetic and genetic abnormalities, that cause deregulated gene expression and function

Regulation by genetics involves a change in the DNA sequence, whereas epigenetic regulation involves alteration in chromatin structure and

methylation of the promoter region

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The human body is prone to developing cancer, from a very early stage of life, until the end of life

The human genome has several built in tumour suppressor genes, whose protein products suppress the formation of tumours. It is important for these genes to continue expressing their tumour suppressor proteins as long as the person lives

To date, more than 600 genes, including tumor suppressor

genes, oncogenes, and cancer-associated viral genes, have been reported to be regulated by epigenetic mechanisms. For example, these genes include APC, ER, RAR, p15, p16, p73, DAPK1, E-cathedrin, GSTP1, LKB1, MGMT, TIMP3, and VHL

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EPIGENETICS AND CANCER

There is evidence that epigenetic deregulation can be a preliminary transforming event. Epigenetic changes such as global DNA hypomethylation and promoter-specific hypermethylation are commonly observed in early-stage tumors. This suggests that epigenetic alterations are early events in the loss of cellular homeostasis and may precede genetic mutations and genomic instability

Deregulated epigenetic mechanisms may initiate genetic instability, resulting in the acquisition of genetic mutations that inactivate tumor-suppressor genes and activate oncogenes

The most frequent epigenetic changes are increased methylation of CpG (phopshorylated cytosine-guanine) islands within gene promoters and deacetylation or methylation of histones

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DNA METHYLATION AND CANCER

Robertson, Nature Reviews Genetics, Vol6, 597

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PROGRESSIVE CHANGES IN PROMOTER METHYLATION AT CPG SITES DURING CANCER INITIATION AND

PROGRESSION

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THE POSSIBLE ROLE OF DNA METHYLATION IN CARCINOGENESIS

Mechanism

Initiation & early progression

Epigenetic gatekeeper gene silencing Activation of normally silenced allele by loss of imprinting Activation of oncogene and chromosomal instability Interrelationship with histone modifications

Mutation Inactivation of repair gene Spontaneous deamination at methylcytosine residue

Cancer progression

Epigenetic plasticity Spreading of aberrant methylation

Metastasis Epigenetic plasticity

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HISTONE MODIFICATIONS AND CANCER

Acetylation and methylation of lysine-rich histone tails are two major post-translational modifications involved in the regulation of chromatin structure and gene expression. Alteration of histone modification profiles causing TSG silencing is associated to carcinogenesis

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Genetic Mutations in Epigenetic Modifiers in Cancer

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Epigenetic alterations are reversible, unlike genetic ones and occur at the earliest steps of carcinogenesis, placing epigenetic drugs at the forefront of cancer therapy and represent opportunities not only for therapeutic but also for preventive interventions

“Epi-drugs", which are drugs targeting epigenetic mechanisms, show promise in cancer therapy. Natural products modulating epigenetic mechanisms constitute part of the hope offered by pharmaco-epigenomics in cancer prevention and treatment

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PLANT-DERIVED ANTICANCER DRUGS WITHEPIGENETIC ACTIVITIES

Plant-derived anticancer drugs with epigenetic tumor inhibitory mechanisms are divided into

major minor groups

based on the number of publications and the variety of targeted cancers.

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OHPOLY-PHENOLS

Polyphenols are plant secondary metabolites consisting of one or more (poly-) phenol unit(s). Their conjugated systems, and hence, electron delocalization properties enable them to efficiently quench free radicals. Additionally, phenols bear several hydroxyl groups making them excellent hydrogen bond donors which bind with high affinity to proteins and nucleic acids.

Flavonoids are the largest and best characterized polyphenols and include the flavonols, flavones, catechins, flavanones, anthocyanidins, and isoflavonoids. Several polyphenolics mediate their anticancer activities by modulating the acetylation pattern of crucial genes and inhibiting hypermethylation of tumor suppressor genes, which is a landmark in cancer development

Major plant-derived anticancer drugs as epigenetic modulators

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Anacardic acids are plant phenols extracted from traditional medicinal plants predominantly belonging to the Anacardiaceae family and have been shown to exhibit antitumor and anti-oxidant activity. Anacardic acid and analogues, such as benzamide derivatives, act as epigenetic modulators by inhibiting the HATs, p300, PCAF, and TBP interacting protein (TIP60) in cervical, breast, kidney, and prostate cancer cells and in lymphoid and myeloid leukemia cells

OH

R

OH

O

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Curcumin or diferuloylmethane is a naturally occurring flavonoid derived from the rhizome of Curcuma longa (Turmeric). Curcumin epigenetically inhibits cancer through modulation of histone acetylation by altering the activities of both, HATs and HDACs. Curcumin induces HDAC1 and HDAC2 or inhibits HAT activity leading to a decrease in global and in H3 and H4 histone acetylation in prostate, liver, brain, and lymphoid leukemia cancer cells

H3CO

OH

OCH3

OH

O OH

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ALKALOIDS

Alkaloids are naturally occurring compounds containing basic nitrogen atoms.

Procainamide shows promising anticancer properties particularly through epigenetic modulation of DNA methylation. It inhibits DNMT activity in myeloid leukemia cells and specifically DNMT1 in colon cancer cells. DNMT1’s affinity to its two substrates, hemimethylated DNA and SAM, was decreased by procainamide through partial competitive inhibition. The inhibition of DNMT activity by procainamide leads to decreased promoter methylation of several genes, thus, inducing their expression.

NH2

NH N

O

CH3

CH3

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TERPENOIDS

Terpenes are hydrocarbons derived from fivecarbon isoprene units they can be modified to terpenoids through addition of oxygen atoms or skeletal rearrangements.

Parthenolide, a 15-carbon terpenoid (sesquiterpene lactone), is commonly extracted from the European feverfew herb (Tanacetum parthenium) that specifically depletes HDAC1 proteins. Parthenolide also inhibits DNMT1 in lymphoid and myeloid leukemias

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Other plant-derived anticancer drugs have shown promise as epigenetic modulators but were classified as minor compounds as their epigenetic mechanisms are less established than the previously described major ones

Biochanin A and Daidzein from Glycine max (Soybean) Caffeic Acid and Chlorogenic Acid from Coffea arabica (Coffee) Catechin and Epicatechin from Uncaria rhynchophylla (Cat's claw

herb) Thymoquinone from Nigella sativa (Black seed)

Minor plant-derived anticancer drugs as epigenetic modulators

Compound Source Molecular targets Anti-caner properties

3,3′-Diindolylmethane

Digestive product of indole-3-carbinol found in cruciferous vegetables

inhibitory effect on HDAC activity by inducing proteasome-mediated down-regulation of several HDAC iso-enzymes

decrease of proliferation and promotion of tumor cell death

Butyrate and its derivatives

generated during gutflora-mediated fermentation of dietary fibers

Inhibit HDAC activity, induce DNA demethylation

cell cycle arrest, inhibition of proliferation, inflammation and oxidative stress, modulation of detoxification potential, and induction of differentiation and apoptotic cell death

Examples of Plant derived epigenetic modulators for cancer treatment

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Compound Source Molecular targets Anti-caner properties

Curcumin Naturally occurring flavonoid derived from the rhizome of Curcuma longa

decrease DNA methylation, decreases HAT activities and histone acetylation or reduces the expression of several HDAC isoenzymes accompanied by increased histone acetylation

Anti-oxidant, anti-angiogenic, antiproliferativeand pro-apoptotic activities

(−)-Epigallocatechin-3-gallate

polyphenol of green tea

DNA demethylatingagent by inhibiting DNMT1 and to decrease promoter methylation ofvarious TSGs leading to gene reactivation

anti-oxidant,anti-proliferative, anti-invasive, anti-angiogenic andpro-apoptotic effects

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Compound Source Molecular targets Anti-caner properties

Genistein and daidzein

polyphenols found in soybean

inhibit DNMT1 activity, decrease methylation of promotermethylation of TSGs, induce histone acetylation by inhibiting HDACs and activatingHATs

Inhibit oxidative stress,angiogenesis,modulation of cell cycle regulation, and induction of apoptosis

Quercetin polyphenol largely present in the plant kingdom

Decrease DNMT activity leading to p16 promoter demethylation and gene reactivation

Inhibit oxidative stress

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Compound Source Molecular targets Anti-caner properties

Resveratrol polyphenol found in grape and grape productssuch as red wine

reduces DNMT1expression and methylation of RARβ and PTEN genes

inhibition of cell proliferation, induction of anti-angiogenic response, and increased rate of apoptosis

Sulforaphane isothiocyanate found in cruciferous vegetables

HDACi increasingtotal and promoter-specific histone acetylation in cancer cells

Decreased proliferation and induction of apoptosis

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PLANT EXTRACTS WITH ANTICANCER ANDEPIGENETIC ACTIVITES

Polyphenols possess potent anti-oxidant and anticancer properties. Recently, polyphenol rich plant extracts have shown epigenetic activities in a variety of cancer types by modulating promoter methylation of critical tumor genes.

Green tea rich polyphenol extract was found to decrease CDX2 and p16 promoter methylation in colon and gastric cancer cells, as well as in primary gastric carcinoma cells

The Japanese rose (Rosa rugosa), allspice (Pimenta dioica) and pineapple guava (Feijoa sellowiana) crude extracts were shown to modulate histone acetylation in prostate cancer cells.

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Most of the major plant-derived compounds are in cancer clinical trials, namely, curcumin, which entered Phase III.

Among the minor plant-derived compounds, lycopene and thymoquinone are in cancer clinical trials

Many epidemiological studies and research data suggest that a diet rich in fruit and vegetables may reduce cancer incidence by mediating multiple biological activities and conferring the ability to counteract cell signaling cascades and mechanisms leading to genotoxic damage, redox imbalances and other forms of stresses associated or leading to a deregulation of cellular homeostasis

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CRITICAL ASSESSMENT

During decades, the best way to fight against cancer was to destroy pathologically altered cells with cytotoxic anti-neoplastic drugs, which is still the standardized regimen for chemotherapy. However, it is now considered that chemoprevention, the use of natural dietary agents and/or synthetic compounds in healthy individuals without signs of malignancy, may represent a better chance to avoid the burden of cancer by delaying, preventing, or even reversing the development of tumor cells

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CONCLUSIONS

Many plant-derived compounds have been identified for their anti-cancer properties with an emerging field regarding the modulation of epigenetic events. Most compounds are evaluated regarding histone modifications (mainly acetylation) and DNA methylation

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FUTURE DIRECTIONS

We need to consider the long-term and eventually trans-generational effects of sustained preventive interventions. Furthermore, there is the necessity to identify biomarkers to monitor the efficiency of preventive interventions by epigenetic modulators and eventually to predict the need of such interventions, which is going towards a personalized medical approach.

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REFERENCE

SCHNEKENBURGER, M., M. DICATO AND M. DIEDERICH. 2014. PLANT-DERIVED EPIGENETIC MODULATORS FOR CANCER TREATMENTAND PREVENTION. BIOTECHNOLOGY ADVANCES, 32: 1123–1132.

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