The Various Types Of Cancer

Published Date: 02 Nov 2017

Cancer is a dreadful disease which is evolved after multi- steps involving, oncogenes, tumour suppressor genes and many molecules and signalling pathways that are leading to cell division, growth, differentiation and apoptosis. The abnormalities happening to these genes, molecules and signalling pathways cause abnormal cell progression and leads to cancer. Genes and molecules that control these processes are the prime targets of research to elucidate the markable differences in controlling genes expression between normal and cancerous cells and to find new answers to treat cancer.

Mutations and alterations in the oncogenes and tumour suppressor genes, leading to the alterations in its signalling pathways have been found to make cell cycle, take a deviation and keep its normal regulatory parameters at distance. Some genes determine the fate of cell allowing them either to survive or to undergo apoptosis. Alterations to such genes can also lead to the formation of predisposition to cancer (Kinzler and Vogelstein., 1997). There are many genes that control the cell growth, progression, apoptosis, inflammation, stress response and many other physiological processes (Rahman et al . , 2004, Tsuji et al . , 2004).

Types of cancer

Cancer can be classified into 5 broad groups like i) carcinomas, characterised by cells that cover internal and external part of the body such as lung, breast and colon cancer, ii) sarcomas, characterized by cells that are located in the bone, fat, cartilage, connective tissue, muscle and other supportive tissues, iii) lymphomas i.e., cancers that begin in the lymph nodes and immune system tissues, iv) leukemias which is the cancer that begin in the bone marrow and often accumulate in the bloodstream, v) adenomas, cancer that arise in the thyroid, pituitary gland, adrenal gland and other glandular tissues.

Some cancers have the property of metastasizing to other sites of the body. Every cancer has its own preferences for the site to which it gets metastasized. Metastasis involves many steps like invasion, angiogenesis, and intravastation, trafficking through blood vessels, extravastations and growth (Chambers AF, Matrisian LM . , 1997 ; Edward KL, Jeffery RM . , 2000). Bone is the main metastasis site of human breast cancer (Coleman RE, Rubens RD . , 1987). This property increases the severity of the disease.

Breast cancer status

Lung cancer is the most common type of cancer worldwide followed by breast cancer, according to WHO. Breast cancer is the primary cause of death in women. Reports from Times of India in 2012, states that, 1,00,000- 1,25,000 new breast cancer cases are reported in India every year.

Breast cancer is the most common cancer in the women worldwide. According to some surveys, there are 1.6 million new cases of breast cancer reported in women worldwide in 2010 ( Forouzanfar et al . , 2011). In U.S. alone, it is estimated that 232, 340 new cases of invasive breast cancer and 39, 620 cancer deaths among women and 2, 240 new cases of breast cancer and 410 breast cancer death among men are reported.

Causes of breast cancer

There are many factors that cause breast cancer. The chance of getting breast cancer increases as the age increases. Breast cancer risk is high for the women whose close blood relatives have the disease. Also a woman who had cancer on one breast, also has increased chance of breast cancer on her other breast. Women above the age of 50 years have more chances of getting breast cancer. Women whose menstruation started before age of 12 and women who had late menopause will have more chance of breast cancer. This is because estrogen production will start only after menstruation starts. Those women who had early menstruation and late menopause will be more exposed to estrogen. This increases the risk of cancer. Obese menopausal women have more amount of estrogen in their body. This acts as risk factor for cancer. Undergoing X-ray, CT- Scan etc for chest area cause more risk of cancer for such women. Women who had undergone hormone replacement therapy have higher risk of getting cancer.

Breast cancer is most common among African American women. Preceding lung cancer, breast cancer is the second most common cause of cancer death among African American women than in white women as reported by American Cancer Society. BRCA1 and BRCA2 are two genes which get mutated to form breast cancer in women. Those women who have inherited mutations in these genes are more prone to breast cancer ( Thorlacius et al . , 1998, Antoniou et al . , 2003, King et al . , 2003, Risch et al . , 2006). Some genes which belongs to the family of inhibitors of apoptosis proteins (IAP), like survivin, plays a very important role in the tumor growth, development of cancer, cell invasion, metastasis and chemoresistance ( Ikeguchi et al . , 2001, Orlowski et al . , 2002). Many studies have shown that survivin, considered as, anti apoptotic protein, is over expressed in the many human carcinomas, including breast cancer ( Wu J et al . , 2005). It is also reported that the survivin expression can be associated with cancer cell viability and drug resistance (Haefiner B et al ., 2002).

NF-κB is found to up- regulate and express the IAP molecule, survivin, which causes the survival of cancer cells ( Li F et al . , 1998). NF-κB is a transcription factor that plays an important role in cell proliferation, differentiation, immune response and in blocking apoptosis (Hayden MS and Ghosh S . , 2004 ; Schmitz et al . , 2004). In the cells which are not stimulated, NF-κB will be seen in the cytoplasm as an inactive complex with the interaction of IκB inhibitor protein. When some stimulations by TNF (Tumor Necrosis Factor), Interleukin (IL), lipopolysaccharides (Wei H et al . , 2003), genotoxic agents like radiation, doxorubicin ( Ahmed KM and Li JJ . , 2007; Gangadharan C, Thoh M, Manna SK . , 2009) occurs, the IκBα gets phosphorylated and then degrades by proteolysis. This proteolysis causes the release of NF-κB. This NF-κB will be translocated into the nucleus and cause the transcription. When some genes related to NF-κB gets over expressed, rearranged or amplified, it causes tumour growth. This has been noted and reported in many studies (Rayet B, Gelinas C., 1999). Down regulation of NF-κB has found to reduce cancer in many studies, both in vivo and in vitro ( Duffey DC I et al. , 1999).

Breast cancer is also sensitive to hormones, mainly, estrogen, progesterone and HER- 2/neu and has receptors for these hormones on it. Hence most of the treatments available for breast cancer are based on this receptor status.

Symptoms of breast cancer

During the initial period, the breast cancer will not show any symptoms. The first symptom can be a small lump on the breast which can be felt. But at times, this lump will not be big and cannot be felt also. The lump can be hard, painless and with uneven edges. At times, the lump will be soft and rounded. As the lump progresses in the size or metastasize, a swelling can be seen in the full breast or a part of it. There may be redness, skin irritation, breast pain associated with a discharge from the nipples. Sometimes a lump can be seen in the under arms. These are main symptoms of the breast cancer.

Therapies and their side effects

Therapies available for the treatment of cancer include surgery, radiation therapy, chemotherapy, targeted therapy etc. Surgery is done to remove the cancer as much as possible. It can also be done to check whether the cancer has spread to other parts through the lymph. In surgery, either a part of the breast or lump or the entire breast will be removed based on the size, place of tumour and other factors.

Side effects: Apart from change in the shape of breast, pain, swelling, bleeding and infection are also some side effects of surgery.

Radiation therapy is done to shrink or kill cancer cells. High energy radiation like, X-ray etc are used in this treatment. This can be done even after the surgery to avoid relapse of cancer in the breast.

Side effects: This treatment can cause swelling, heaviness in the breast, lymphedema, weak and sun- burn like changes on the skin.

Chemotherapy uses cyto toxic drugs that kill cancer cells. These drugs can be taken as pills or shots, liquids or as injections. This treatment will help in killing even the cancer cells that has metastasized.

Side effects: Chemotherapy can also affect the normal cells and it leads to hair loss, nausea, vomiting, mouth sores, tired etc.

Hormonal therapy is used for the cancer cells that are sensitive to hormones. This therapy will not have any effect on cancers that are not sensitive to hormones.

Side effects: This can cause mood swings, night sweating, vaginal dryness blood clotting etc.

Targeted therapy is targeted against the changes occurring in the genes. Targeted therapy includes drugs made out of monoclonal antibody.

Side effects: Side effects include, mouth sore, tired, low blood count, shortness of breath etc.

Even though chemotherapy has an important role in treating breast cancer, the number of people not responding to the treatment and number of cases of failures after initial responses, highlights the role of drug resistance mechanism in breast cancer management ( Chintamani et al . , 2011).

Chemoresistance

Chemoresistance is major problem faced during treating cancer ( Higgins CF . , 2007). Prolonged activation of AKT and NF-κB have been reported as a cause of chemoresistance, which leads to failure of chemotherapy for treating cancer ( Liotta . , 2001, Liotta LA, Kohn EC . , 2001). The mechanism of chemoresistance in tumor cells can be of two ways, either intrinsic, where the cells are resistant before the treatment or, acquired, where the cells acquire the resistance during the treatment.

Causes of chemoresistance

The anti tumor drugs prescribed, have to reach the cells in a sufficient quantity to exert its effect on the cells. Any change in the uptake of the drug can cause the chemoresistance ( Huang Y . , 2004). ATP- dependent drug transporters control the action of drug uptake.

Chemoresistance is associated with some transporter proteins like, P-glycoprotein (Endicott JA and Ling V . , 1998), multi- drug resistance protein (MRP 1) ( Deeley SP and Cole SP . , 1997), lung resistance- related protein (LRP) (Izquierdo MA . , 1995) and breast cancer resistance protein ( BRCP) (Lee JS . , 1991). Some reports indicate the important role played by Glutathione/ Glutathione S- transferase system in chemoresistance (Batist G . , 1989). As the expression of Glutathione/ Glutathione S- transferase increases, the chemoresistance also increases (Chao CC . , 1992 ).

The primay catabolization of 5- FU occurs in liver by Dihydropyrimidine dehydrogenase (DPD). This makes colorectal cancer resistant to the drug (Diasio BB and Harris BE . , 1989).

During the course of chemotherapy, some molecular targets like Topoisomerase II, gets modified or decreases to a level where it stops to get significant cellular responses. This can lead to chemoresistance ( Webb CD . , 1991, Cloe SP . , 1991).

Some chemotherapeutic drugs cause direct or indirect alteration to DNA. Base Exicision Repair cause resistance to lesions formed during chemotherapy (Liu L . , 1991 ). Exicision repair cross- complementing 1 protein, involved in the Nucleotide Excision Repair , when up- regulated can cause chemoresistance (Youn CK . , 2004).

Over expression of some growth factors like, EGFR, can also cause chemoresistance (Chen X et al . , 2000). Activation of a growth factor causes the expression of molecules downstream to it, like AKT or MAPK pathway. This can lead to chemoresistance (Magne N . , 2002).

Cancer cells gets resistance to apoptosis by down- regulation of pro- apoptotic molecules and up- regulation of anti- apoptotic molecules and activates survival signals ( Hanahan D and Weinberg RA . , 2000). Many studies also have shown that STAT 3 can lead to chemoresistance ( Bharti AC . ,2004, Real PJ . , 2002).

Metastasis in mouse embryo fibroblast and human lung cancer cells can be increased by enhancing the expression of HER- 2/neu ( Yu et al ., 1992; Yu and Hung . , 1991). In non- small- cell- lung cancer cell line , over expression of HER- 2/neu cause chemoresistance (Tsai et al . , 1994, 1995). MDA-MB-453, MDA-MB-361, BT-474, BT-483, and SK-Br-3 are some breast cancer cell line that over expresses HER- 2/ neu. These cell lines are also resistant to two chemotherapeutic drugs, paclitaxel and docetaxel (Yu et al., 1996). Adenovirus Type 5 E1A, has been found to chemo sensitize the expression of HER-2/ neu expression in the breast cancer cell line (Naoto T et al., 1997). HER- 2/ neu over expression are a poor prognostic factor in breast cancer patient (Gusterson et al., 1992; McCann et al., 1991). Both clinical trials and laboratory research have strongly suggested that HER-2/neu over expression may be a chemotherapeutic resistance marker in breast cancers (Gusterson et al . , 1992; McCann et al . , 1991).

Another molecule COX-2, which is involved in inflammation is found to have role in tumour growth, metastasis, chemoresistance (Koki AT, Leahy KM and Masferrer JL . , 1999; Milas L . , 2001). Its presence has been noted in many tumours with aggressive nature. It had shown worse outcomes for the people with breast cancer, colon cancer. Recent studies are being carried out making COX- 2 as target for anti cancer therapy (Milas L et al . , 2003; Nakata E et al . , 2004). Inhibitors of COX-2 have been used to try sensitizing the cancer cells for chemotherapy and radiation therapy.

Due to these many side effects and chemoresistance for the available treatments and therapies, and also increasing number of failure cases for these treatments, there arise a need for searching new methods to treat cancer that can reduce the side effects and chemoresistance. One such method is chemo sensitization, a more promising way to treat cancer and new hope for the cancer patients.

Chemo sensitization

Chemo sensitization is the mechanism of sensitizing the tumour cells for the cancer treatment. It is the synergistic effect of two drugs, being greater than the sum of the effects of each used alone. Those compounds that sensitizes the cells for the cancer treatment is called chemo sensitizers. These can be mainly plant compounds. These compounds are pharmacologically safe. They reduce the dose of chemotherapeutic drugs used. They also thereby reduce the side effects and chemoresistance. The very important plus point of using chemo sensitizers is that, they will not act on normal cells. There are many plant compounds that have been identified as chemo sensitizers. They include curcumin, resveratrol, genistein, allincin etc. Some of these compounds are also considered as chemo preventives that have the ability to prevent the cancer. These chemo sensitizers alter the functions of transcription factors, apoptotic molecules and many other signalling pathways. They alter the signalling pathway through which the cancer cells undergo proliferation, survival signals like MAPK, NF-κB etc. They also alter the cell cycle by acting upon cyclins and cyclin dependent kinases. Thus they alter the cell cycle and at times cause the cell cycle arrest also. They can suppress cancer cell proliferation, inhibit angiogenesis and induce apoptosis, in addition to their traditional medicinal values. Since they are pharmacologically safe, they can be used with the chemotherapeutic drugs to reduce its dosage and side effects. . These compounds can be used with chemotherapeutic drug to enhance the activity of drug at its lower concentration.

Some chemical inhibitors of some proteins are also used as chemo sensitizers and their chemo sensitizing properties has been proved by various researchers ( MacKeigan et al . , 2000 ; McDaid et al . , 2005 ; Nugyen et al . , 2004). But phytochemicals, since they are obtained from natural sources, they are more preferred over chemical inhibitors.

Chemo sensitizers

Any compounds that inhibit the function of the cellular glycoproteins of the tumour cells and make them sensitive to the chemotherapeutic agents are called chemo sensitizers. Chemo sensitizers can be natural compounds or chemical inhibitors. Cells mainly develop chemoresistance by up-regulating the survival signals. Any compound that can down regulate these survival signals can act as chemo sensitizer. Mostly, chemo sensitizers are phytochemicals. These phytochemicals, mainly belongs to phenol groups. Some examples of chemo sensitizers are curcumin, resveratrol, genistein, emodin, quercetin, gingerol, capsaicin, epigallocatechin- 3- gallate etc. They inhibit anti apoptotic molecules and pro survival signal molecules. They enhances the apoptosis ( Vinod BS et al . , 2013). Even though, these compounds possess anti cancer capabilities, due to their low bioavailability, their chemotherapeutic potentials cannot be used properly. But still these compounds can act as chemo sensitizers and chemo preventives.

Genistein is an isoflavone obtained from Soya bean. Its ability to stop the growth of cancer cells without effecting normal cells, both in vivo and in vitro has been reported (EI- Rayes et al . , 2011). It has also increased the efficacy of  gemcitabine by down regulating the transcription factor NF-κB and AKT in osteosarcoma ( Liang C et al . , 2012) and in pancreatic cancer cells ( Banerjee S et al . , 2005). When genistein is used in combination with 5- FU to treat colon cancer cells, it down regulated COX- 2 ( Hwang JT et al . , 2005). The synergistic effect of genistein and Docetaxel in treating bone metastasis is studied and is reported to alter the NF-κB pathway ( Li Y et al . , 2006).

Epigallocatechin gallate, obtained from green tea, has very powerful anti oxidant activity. It is a good chemo preventive agent. The TRAIL resistance reported in many cancers has been overcome by chemo sensitizing ability of epigallocatechin gallate. This compound is also capable of enhancing 4- hydroxy Tamoxifen in treating breast cancer ( Chisholm K et al . , 2004). It can enhance the paclitaxel chemotherapy by down regulating Bcl2 ( Ping SY et al . , 2010). Even though EGCG enhances the cyto toxicity of cisplatin in glioma cells (Shervington A et al . , 2009), it protects oral cancer cells against cisplatin-induced cyto toxicity ( Yamamoto et al . , 2004). Epigallocatechin gallate will decrease the toxic effect of IFN-α therapy by down regulating the NF-κB that is constitutively expressed ( Nihal M et al . , 2009). Epigallocatechin gallate when used in combination with COX- 2 inhibitor, increases its efficiency and reduces the dose of inhibitor to be used and provides better outcome with lesser toxicity (Suganuma M et al . , 2006).

Quercetin is a flavanoid that is seen in many fruits and vegetables. It has anti cancer properties. It has the ability to down regulate HER-2/neu ( Jeong JH et al . , 2008). Quercetin will down regulates the AKT ( Siegelin MD et al . , 2009) and surviving ( Kim YH et al . , 2008). Quercetin is also reported as a potent and non toxic agent that can reverse the multi drug resistance in many tumour models (Chen C, Zhou J, and Ji C . , 2010).

Resveratrol is a polyphenol mainly present in red wine and grapes. Resveratrol alters the main molecular players in chemoresistance and makes the cells sensitive to therapy. It can cause apoptosis by depleting the surviving ( Fulda S and Debatin KM . , 2005). Studies have also suggested that the resveratrol has the capability to up- regulate the pro apoptotic molecules and to down regulate the anti apoptotic molecules. This gives the compound a chemo sensitive effect ( Shankar S et al . ,2007). Resveratrol along with doxorubicin can down regulate the surviving molecule ( Fulda S and Debatin KM . , 2004). In breast cancer and bladder cancer, it has the ability to scavenge the reactive oxygen species ( Fukui M, Yamabe N, and Zhu BT . , 2010)

These are some of the common chemo sensitizers studied. The major drawback of using these phytochemicals is its poor bioavailability. This is because their biological activity gets reduced or its reduced after its metabolism. And also its low serum level, rapid metabolism, limited tissue distribution and short half life also contributes for its low bioavailability. New studies are going on to increase their bioavailability by modifying them.

Curcumin

The most common chemo sensitizer studied is always curcumin. . It is safe, affordable and efficacious. There are many studies being conducted on curcumin based on its various medicinal properties. It has been used from ancient time to treat many diseases.

Curcumin is a polyphenol obtained from the rhizome of Curcuma longa, belonging to the family, Zingiberaceae. Turmeric consists of turmeric, essential oils and curcuminoids including curcumin. The major curcuminoids are curcumin, demethoxycurcumin, bisdemethoxycurcumin and also cyclocurcumin (Kiuchi F et al . , 1993).

Curcumin is a yellow coloured polyphenol. The structure of curcumin was first described by Lampe and Milobedska in 1910. This curcumin. diferuloylmethane was first crystallized in 1870. The molecular formula of curcumin is C12H20O6 and its molecular weight is 368.39. Its melting point is 183° C. Its insoluble in water but soluble in ethanol, ketone, acetic acid and dimethylsulfoxide (Aggarwal et al . , 2003). Curcumin is unstable in basic pH but , in acidic pH it degrades very slowly.

Studies have shown that curcumin can inhibit tumour initiation ( Huang MT et al . , 1992) and its promotion ( Conney AH et al . , 1991). There are many molecular targets for curcumin which includes, growth factors , transcription factors, enzymes, cytokines and genes regulating cell growth and cell death (Aggarwal et al . , 2007). Studies have shown that it affects many structurally unrelated membrane proteins through several signalling pathways ( Bilmen JG et al . , 2001). Some recent studies have shown that curcumin gets deep inserted into cell membrane by transbilayer orientation. It causes negative curvature in the bilayer as it anchors by hydrogen bonding to phosphate group of lipids (Barry J et al . ,2009).

Curcumin has chemo preventive action also. This may be due to its ability to induce apoptosis and alter several signalling pathways. Curcumin can also inhibit angiogenesis, invasion and metastasis of cancer. Besides these properties, it also has properties of lowering blood cholesterol, stimulating muscles, healing wounds, inhibition of myocardial infraction and prevents viral infection. Systematic preclinical studies by administering curcumin to rats, dogs, monkeys, conducted by National Cancer Institute, US, couldn’t report any unfavourable results , even when administered up to 3 months ( Sharma et al . ,2005).

Curcumin has anti proliferative activity. It inhibits the proliferation of tumour in leukemia (Kuo et al . , 1996), colon cancer ( Chen et al . , 1999) and in breast cancer cells ( Mehta et al . , 1997). In various cell lines, curcumin induces both receptor and mitochondrial mediated apoptosis ( Karmakar et al . ,2006). Curcumin has effect on cell cycle, but its not stable. The effect depends on the type of cell line. Curcumin blocks the cell cycle at S phase and thus inhibits the proliferation of human umbilical vein endothelial cells ( Singh et al . , 1996). Curcumin can cause cell cycle arrest at S phase or G2/M phase in colon cancer cells ( Chen et al . , 1999). It also inhibits the action of NF-κB ( Zheng et al . , 2004).

Curcumin has anti tumourigenic effect. Curcumin has been reported to have chemo preventive and chemotherapeutic effects. Curcumin has found to stop tumour initiation, promotion, invasion, angiogenesis and metastasis. Curcumin induces the expression of Cyclin- dependent kinase (CDK) inhibitors. It can also inhibit Cyclin E and Cyclin D2 and hyperphosphorylation of retinoblastoma (Choudhuri T et al . , 2005).

Curcumin has anti angiogenic activity which has been proved both in vivo and in vitro ( Arbiser et al . , 1998). It prevents the migration of endothelial cells and growth of tumour cells ( Gao et al . , 2003). Curcumin can be used to treat multiple myeloma by blocking the interaction between the myeloma cells and endothelial cells ( Wang et al . , 2006). Reports have also indicated that the curcumin interrupts the expression of the cell surface adhesion molecules on endothelial cells. This prevents the adhesion of tumour cells to endothelial cells, which in turn, prevents metastasis of tumour ( Kumar et al . , 1998).

Antioxidant and anti inflammatory activity of curcumin has also been reported in many studies. The free radicals especially, Reactive Oxygen Species, play a very crucial role in the carcinogenesis. Thus this reactive oxygen species has to be removed for curing cancer. Curcumin has the ability to scavenge free radicals (Tonneson et al . , 1992) and acts as an anti oxidant agent. It also alters the glutathione levels. Its anti inflammatory action arises from its ability to inhibit IL-8 release in lung cancer ( Biswas et al . , 2005). Curcumin scavenges superoxide anions ( Donatus et al . , 1990). It can also control the release of inflammatory mediators and hydrolytic enzymes secreted by macrophages. It also interferes with the neutrophile responses happening during various stimuli ( Srivastava et al . , 1989). Curcumin can also induce the inhibition of COX-2, iNOS and production of cytokines ( Kim et al . , 2003).

Reports have shown that curcumin has sensitized prostate cancer cells to the cyto toxic effects of 5- FU by down regulating constitutively expressed NF-κB and a p53 independent cell cycle arrest ( Hour TC et al . , 2002). Curcumin can also down regulate COX-2 and it alters EGFR , insulin- like growth factor 1 receptor thus enhancing the cyto toxic effect of 5- FU in colon cancer ( Patel BB et al . , 2008). Curcumin can also enhance the efficacy of mitotic inhibitors like docetaxel ( Wang Q and Wieder R et al . , 2004) , paclitaxel ( Banerjee M et al . , 2010) etc. Curcumin can down regulate the NF- κB targets like Bcl-2, Bcl- xL, cyclin D1 and IL- 6. This causes the cell cycle arrest at G1/S phase and suppresses the cell proliferation (Bharti AC et al . ,2003). Some studies have reported that the curcumin can act as stimulator of intracellular Ca2+ uptake into mitochondria through uniport pathway and might involve execution of programmed cell death (Bae JH et al . , 2003). Curcumin can also cause damage to DNA, stress to endoplasmic reticulum and mitochondrial dependent apoptosis through the activation of caspase- 3 (Lin SS et al . , 2008). Curcumin leads to the release of cytochrome C from the mitochondria. This leads to the activation of caspase 3 and PARP cleavage which marks the caspase dependent apoptosis (Thayyullathil F et al . , 2008).

Curcumin and normal cells

Curcumin is a pharmacologically safe compound. It does not affect the normal cells. It affects are mainly reported in the tumour cells. The exact reason for this is not known. But many reasons are suggested. The cellular uptake of curcumin is more in tumour cells than in normal cells (Kunwar A et al . , 2008). Nucleus and cell membrane are the main locations where the curcumin gets distributed to the maximum. The tumour cells have less amount of glutathione in them when compared with the normal cells. This makes tumour cells more sensitive to cancer therapy (Syng-Ai C, Kumari AL and Khar A. , 2004). Tumour cells have constitutively expressed NF-κB in them, that helps them to survive (Shishodia S, Amin HM, Lai R and Aggarwal BB . , 2005). Curcumin can control tumour growth by suppressing NF-κB.

Curcumin have effect on wide variety of tumour cells. It also has action on various molecules. It sensitizes the tumour cells through a wide range of mechanism. Since curcumin does not affect the normal cells , it has become a striking molecule for many researchers and research. Many more studies have to be done to elucidate more benefits from curcumin.

Chemotherapeutic Drugs

Chemotherapeutic drug is a cyto toxic drug that has the ability to kill cells. An ideal chemotherapeutic drug should kill only cancer cells and should not cause any damage to normal cells. This has to be attained by causing apoptosis to the cancer cells, without harming our normal cells. But unfortunately, none of the available chemotherapeutic drug could attain this. Even though, based on the mechanism, there are many different types of chemotherapeutic drugs like alkylating agents, anti-tumour antibiotics, anti-metabolites, mitotic inhibitors, hormones etc, they all induce cell death either by apoptosis or by necrosis or by autophagy causing genotoxic stress to the cells (Gerl R and Vaux DL . , 2005). Most of the drugs available today are targeting the cell division. Since they target cell division normal cells are also not spared. This leads to different side effects.

Major cell death in the hematopoietic cells, intestinal epithelial cells, hair matrix keratinocytes cause reduced immunity, digestive problems, hair loss ( Chidambaram M, Manavalan R, and Kathiresan K . , 2011). These side effects may be either short term or long term. Short term can be hair loss, nausea, stomatitis etc which will be cured after few months of treatment. Long term can be weight loss, infertility, secondary leukemia etc. But the main difficulty rather than the side effects for these drugs are, the chemoresistance developed by the cancer cells. Due to the chemoresistance, the cancer cells are not affected but the normal cells are affected badly and this increases the severity in the condition of the patient. This poses a major hurdle in the development of an ideal chemotherapeutic drug to treat cancer.

5- Fluorouracil

Its a chemotherapeutic drug, also called 5- FU or Adrucil. It is an anti metabolite used to treat various cancers ( Longely DB, Harkin DP, Johnston PG . , 2003). It prevents the growth of cancer cells and targets the thymidylate synthase, an important enzyme in de novo synthesis of DNA, and leads the cell to apoptosis ( Chu E et al . , 2003). It incorporates fluorinated nucleotides and causes breakage of DNA and RNA strands ( Ghoshal K and Jacob ST . , 1997 ; Major PP et al . , 1982).

In vitro and in vivo studies have reported a sturdy link between up- regulated thymidylate synthase expression and development of chemoresistance to 5- FU ( Chu E et al . , 1993). Many studies have reported a positive result for 5- FU chemotherapy in patients with low levels of thymidylate synthase ( Lenz HJ et al . , 1989). Even though, thymidylate synthase is proved to be a target of fluoropyrimidine, it is reported to be an oncogene too ( Rahman L et al . , 2004). Several survival signals are up-regulated by 5- FU which includes NF-κB and AKT. NF-κB is already reported as an important molecule involved in chemoresistance ( Wang S et al . , 2005). Studies have proved that, when NF-κB nuclear translocation and activation is prevented, the efficiency of the drug, 5- FU being increased ( Wang W et al . , 2003). Down regulation of NF-κB is required to deal with drug resistance ( Nakanishi C and Toi M . , 2005). One other molecule that plays an important role in cell survival and proliferation is AKT ( Jin W et al . , 2003). There are evidences to support the fact that AKT being activated in breast cancer patients and leading to tumour relapses and metastasis ( Perez- Tenorio G and Stal O . , 2002). Some other molecules that plays an important role in chemoresistance due to their constitutive and drug induced activation are ERK ½ (p42/p44), p38 and JNK- all three belonging to MAPKs ( mitogen- activated protein kinases) ( Chang L and Karin M . , 2001).

In vivo, fluorouracil is converted to the active metabolite 5-fluoroxyuridine monophosphate (F-UMP), replacing uracil, F-UMP incorporates into RNA and inhibits RNA processing, thereby inhibiting cell growth. Another active metabolite, 5-5-fluoro-2'-deoxyuridine-5'-O-monophosphate (F-dUMP), inhibits thymidylate synthase, resulting in the depletion of thymidine triphosphate (TTP), one of the four nucleotide triphosphates used in the in vivo. Due to this, cells undergo thymidine less cell death.

It has antineoplastic activity. Along with the side effects, prolonged use of the drug had made the cells resistant to the drug. The drug poses many side effects which includes, leukopenia, diarrhea, anorexia and vomiting ( Cho IJ et al . , 2009). To reduce the side effects, the dosage of the drug has to be reduced and combined with some phytochemicals to give more effect against cancer. This combination may show different effects like synergistic, additive etc. These effects are studied by the researchers while chemo sensitizing the cells.

ERK ½ ( Extracellular signal regulated kinases ½)

ERK ½ a member of Mitogen- Activated Protein Kinase (MAPK). ERK 1 and ERK 2, in humans are 84% similar in sequence and share many functions. Hence they are usually called as ERK ½. ERK 1 in humans has 379 amino acid residues while ERK 2 in humans has 360 amino acid residues. ERK ½ family has 31 amino acid residue insertion in the kinase domain that provides its specific function. Most of the stimuli that activates ERK ½ causes the parallel activation of ERK 1 and ERK 2 molecule (Lefloch R, Pouyssegur J and Lenormand P . , 2009). ERK ½ is a ubiquitously expressed hydrophobic non receptor protein that participate in Ras- Raf- MEK- ERK ½ signal transduction pathway (Wortzel I and Seger . , 2011).

ERK ½ is activated by growth factor and has an important role in the cellular proliferation and cell differentiation. Its major functions include regulation of mitosis, meiosis, cell proliferation, differentiation and migration. It can also regulate transcriptional repression and chromatin modelling ( Plotnikov et al . , 2011). ERK ½ can phosphorylate the transcriptional factors and their regulators ( Yoon S and Seger R . , 2006). ERK ½ has nuclear substrates like TCF ( ternary complex factor), which belongs to the family of transcription factors. ERK ½ can induce early immediate gene such as c- Fos and c-Jun ( Kamakura S, Moriguchi T and Nishida E . , 1999). These immediate genes can induce late response genes which are required for the cell division, cell survival and cell motility (Dhillon AS et al . , 2007). Thus ERK ½ is an essential contributor to cellular proliferation ( Lewis et al . , 1998). There are more than 50 cytoplasmic substrates identified for ERK ½ . This can include phosphoprotein phosphatases, RSK family protein kinases, cAMP phosphodiesterase (PDE4), cytosolic phospholipase A2, cytoskeletal proteins, apoptotic proteins, and regulatory and signaling molecules ( Yoon S and Seger R . , 2006). ERK ½ can also control the cyclin D1 expression that in turn controls G1/S transition ( Mulloy et al . , 2003). ERK ½ is required for the mesoderm formation. Unphosphorylated proteins move faster than phosphorylated proteins in polyacrylamide gel electrophoresis. Based on this, it was found that serum stimulation can cause increased expression of ERK ½ and its activation, both in cytoplasm and in nuclear fractions ( Chen RH et al . , 1992).

Pathway

A Extracellular stimuli or environmental stresses activates MAPK pathway which consists of a sequence of kinase molecules, Raf MAP kinase kinase kinase (MAPKKK) MAP kinase kinase (MAPKK), MAP kinase (MAPK). ERK ½ can also be stimulated by cytokines, osmotic stress, activated seven transmembrane G- protein coupled receptor (Raman M, Chen W and Cobb MH . , 2007). After the stimulation by growth factors, Ras is activated by associated SOS( Son of Sevenless). Ras- GTP then cause the activation of Raf, a MAPKKK ( Wellbrock et al . , 2004). This Raf then phosphorylates MEK ½ which is a dual specificity protein . MEK ½ then phosphorylates Threonine and Tyrosine of the sequence Thr- Glu- Tyr (TEY sequence) of ERK ½ . the ERk ½ which is not activated will b e present in the cytoplasm. This activates ERK ½ . This activated ERK ½ will get translocated to the nucleus. This translocation can occur through three mechanisms : passive diffusion of the monomer, active transport of a dimer and direct interaction with the nuclear pore complex ( Adachi et al . , 1999) This activated ERK ½ has many substrates which includes, transcriptional factors like, Elk 1, AP- 1, NF- κB, c- Myc and Bcl-2 and causes cell proliferation. According to the strength and duration of the stimulation, activation of ERK ½ leads to either cellular proliferation or cellular differentiation( Marshall 1995).

Ras is a molecule that frequently gets mutated in tumour cell and cause activation of ERK ½ molecule promoting the cancer growth ( Qi and Elion . , 2005). 30% of all human cancers have Ras gene activated in it (Bos JL . , 1989). 7% of all human cancer (Davies H et al . , 2002 ; Garnett MJ and Marais R . , 2004). Even when there is no presence of any oncogenic mutations, the Ras-Raf- MEK- ERK ½ pathway is up- regulated in many cancers. Reports , both in vivo and in vitro show that some oncogenes can constitutively express ERK ½. This causes the transformation of cells to malignant tumour (Webb et al . , 1998).

Some recent studies has reported down regulation of ERK ½ is required in controlling cancer. Many inhibitors have been developed to inhibit ERK ½ . But none is able to get FDA approval ( Vakiani E and Solit DB . , 2001). A FDA approved drug, Sorafinib, is used to treat the renal carcinoma. It is developed to inhibit the Raf. But its therapeutic efficiency is by VEGF ( vascular endothelial growth factor) and thereby preventing angiogenesis ( Vakiani E and Solit DB . , 2001). Thus most of inhibitors of the ERK ½ are clinically unsuccessful.

Apoptosis

Apoptosis is a complex process of programmed cell death. This can occur through two pathways : the extrinsic pathway and the intrinsic pathway. The extrinsic pathway has the cell surface receptors, their inhibitory compartments and their associated cytoplasmic proteins included in it. The intrinsic pathway requires the mitochondrial involvement and the formation of the apoptosome.

In the intrinsic pathway, signals for the cell death cause the release of the cytochrome C from the mitochondria. This then binds to the apoptotic protease activating factor ( Apaf-1). This leads to oligomerisation and recruitment of procaspase- 9. Apoptosome formation causes the activation of caspase- 9. This triggers caspase- 3 and the apoptosis.

Caspase acts as the central initiators and executioners of apoptosis. The term caspase is derived from cytokine-dependent aspartate-cysteine proteases. In the cell, caspases are synthesized as inactive zymogens, the so called procaspases, which at their N terminus carry a prodomain followed by a large and a small subunit which sometimes are separated by a linker peptide. Upon maturation, the procaspases are proteolytically processed between the large and small subunit, resulting in a small and a large subunit. The prodomain is also frequently but not necessarily removed during the activation process. A heterotetramer consisting of each two small and two large subunits then forms an active caspase. The proapoptotic caspases can be divided into the group of initiator caspases including procaspases-2, -8, -9 and –10, and into the group of executioner caspases including procaspases-3, -6, and –7. Whereas the executioner caspases possess only short prodomains, the initiator caspases possess long prodomains, containing death effector domains (DED) in the case of procaspases-8 and –10 or caspase recruitment domains (CARD) as in the case of procaspase-9 and procaspase-2 Via their prodomains, the initiator caspases are recruited to and activated at death inducing signalling complexes either in response to the ligation of cell surface death receptors (extrinsic apoptosis pathways) or in response to signals originating from inside the cell (intrinsic apoptosis pathways).

There are two phases for the apoptosis: commitment to the cell death and execution ohase where morphological changes to the cell structure occur. In the apoptotic cells, inter- nucleosomal cleavage of DNA occurs which can be visualized through DNA ladder procedure on agarose gel electrophoresis. This is an important and essential nuclear alteration that occurs to the cell that is going to undergo apoptosis. This can be considered as the ultra structural changes of the programmed cell death ( Halder S et al . , 2000).

The Bcl-2 family of proteins regulate the mitochondrial changes during both apoptosis and necrosis. The Bcl-2 family of apoptosis- regulating proteins functions to either promote or suppress cell death. Increased expression of the anti apoptotic protein has been reported in many caners ( Krajewski S et al . , 1993). Bcl-2 is an anti apoptotic protein.

The intrinsic pathway includes the down regulation of the anti apoptotic proteins from the Bcl-2 family, an increase in the mitochondrial membrane permeability and an increased release of cytochrome C into the cytoplasm, which activates caspase-9 and caspase-3, leading to apoptosis. The extrinsic pathway is initiated by the activation of death receptors that involves the formation of a death inducing signalling complex (DISC), which contains Fas, a member of the TNF super family. DISC formation results in the activation of caspase- 8, which activates caspase- 3, executing the cell death ( Chinnaiya AM et al . , 1995).

The intrinsic pathway

The intrinsic pathway requires cytochrome C to be released from the mitochondrial inner membrane space to the cytosol. This released cytochrome C will attach with adapter protein, Apaf -1. This activates the caspases which are necessary for the recognition and clearance of the stressed cells. The major function of the Bcl-2 family of protein is to regulate the integrity of the mitochondrial outer membrane ( Kluck RM et al . , 1997). The Bax and Bak proteins, oligomerize into proteolipid pores and permeabilize the outer mitochondrial membrane.

It allows the uptake of cytochrome C and other inter membrane space proteins to the cytosol during apoptosis ( Wei M et al . , 2001). Other apoptotic factors that are released from the mitochondrial intermembrane space into the cytoplasm includes apoptosis inducing factor (AIF), second mitochondria-derived activator of caspase (Smac), direct IAP Binding protein with Low pH (DIABLO) and Omi/high temperature requirement protein A (HtrA2). Cytochrome c released to the cytoplasm will lead to the activation of caspase 3, which in turn leads to the formation of a complex known as apoptosome which is made up of cytochrome c, Apaf-1 and caspase 9. At the same time Smac/DIABLO or Omi/HtrA2 promotes caspase activation by binding to inhibitor of apoptosis proteins. This subsequently leads to interruption in the interaction of inhibitor of apoptosis proteins with caspase- 3 or caspase- 9.

The extrinsic pathway

The extrinsic pathway, requires death ligands binding to a death receptor. Even though many death receptors have been described, the best known death receptors is the type 1 TNF receptor (TNFR1) and a related protein called Fas and their ligands named TNF and Fas ligand respectively. These death receptors have an intracellular death domain that recruits adapter proteins, TRADD ( TNF receptor-associated death domain) and FADD ( Fas-associated death domain), as well as caspase 8. Binding of the death ligand to the death receptor results in the formation of a binding site for an adaptor protein and the whole ligand-receptor-adaptor protein complex is known as the DISC ( death-inducing signalling complex). DISC then begins the activation of pro-caspase 8. The active form , caspase 8 is an initiator caspase, which initiates apoptosis by cleaving other downstream or executioner caspases.

The common pathway

The second phase of the apoptosis is the execution phase where the activation of a series of caspase occurs. The upstream caspase for the intrinsic pathway is caspase 9 while that of the extrinsic pathway is caspase 8. The intrinsic and extrinsic pathways converge to caspase 3. Caspase 3 then cleaves the inhibitor of the caspase-activated deoxyribonucleic, which is responsible for nuclear apoptosis. Along with it, downstream caspase induce cleavage of protein kinases, cytoskeletal proteins, DNA repair proteins and inhibitory subunits of endonucleases family. They also have an effect on the cytoskeleton, cell cycle and signalling pathways, which together contribute to the typical morphological changes in apoptosis.