Future of Cancer Therapy-COX-2 Inhibitors: A Review

 

Bhasker. S1*, Sandeep. G2 and Ranganath YS3

1Department of Pharmacology, University College of Pharmaceutical Sciences, Kakatiya University, Warangal-506002, Andhra Pradesh.

2Department of Pharmaceutics, J.K.K.M.M.R.F. College of Pharmacy, Komarapalayam, Pin; 638183, Namakkal, Tamilnadu

3Department of Pharma. Chemistry, G. Pulla Reddy College of P harmacy, Mehdipatnam, Hyderabad-500082

*Corresponding Author E-mail:  bhaskersriramoju@gmail.com

 

ABSTRACT

Cycloxygenases (COX) are the principle enzymes involved in the metabolism of arachidonic acid generating prostaglandins which are the genuine mediators of inflammation and pain. COX are classified into Type-1 and Type-2 which are constitutive and inducible respectively. Recent research has brought into light the possible role of these PGs in the COX-2 cascade of tumor proliferation, angiogenesis and metastasis with significant overexpression. Thus COX-2 can serve as a useful biomarker in the early diagnosis and can be selectively targeted in the tumour cells with greater proven safety. The review deals with the potential role of COX-2 inhibitors in canceling the PG mediated Signaling, the role of COX-2 in different types of cancers. (Lung, Head and Neck, Bladder, Cervical Cancer and Other Oncology applications), the beneficial outcomes of combination therapy of COX-2 inhibitors along with either chemotherapy or radiotherapy. In conclusion a note on future research options for treating neuroblastomas with COX-2 inhibitors was elucidated.

 

KEYWORDS: Cycloxygenases, Prostaglandins, cancer, angiogenesis and over expression.

 


INTRODUCTION:

Cyclooxygenase (COX) the enzyme responsible for the formation of important biological mediators called prostanoids which are prostaglandins, prostacyclin and thromboxane. Pharmacological inhibition of COX can provide relief from the symptoms of inflammation and pain.

 The mechanism by which series-2 Prostanoids formed are by the conversion of arachidonic acid to prostaglandin (PGH2) mediated by COX. It has two active sites: a heme, with peroxidase activity responsible for the reduction of PGG2 to PGH2 and a cyclooxygenase site, where arachidonic acid is converted into the hydroperoxy endoperoxide prostaglandin G2 (PGG2). There are three different isoenzymes of COX which are—COX-1, COX-2 and COX-3 and COX-3 is a splice variant of COX-1 retaining one intron and has a frame shift mutation.1

 

When compared, COX-1 and COX-2 have the similar molecular weight of approximately 70 and 72 kDa respectively. They have a 65% of amino acid sequence homology and near-identical catalytic sites. The selective inhibition of COX is possible due to the substitution of isoleucine at position 523 in COX-1 with valine in COX-2 which is therapeutically significant.

 

COX-1 and COX- 2 expression is varied in different tissues though both these enzymes act basically in a similar way, their selective inhibition will make a difference in terms of side-effects. COX-1 is the constitutive enzyme being expressed in most mammalian cells. On the other hand COX-2 is inducible and undetectable in most normal tissues. Recent investigations have revealed that it has been upregulated in various carcinomas and found to have a pivotal role in tumorigenesis.

 

There is now substantial evidence for a role for cyclooxygenase-2 (COX-2)-mediated prostaglandin (PG) signaling during carcinogenesis in a number of tissues and selective COX-2 inhibitors (coxibs) were considered attractive candidate chemoprevention agents2.

 

Pathological role of COX-2

Its role in tumorigenesis and the malignant phenotype of tumor cells are elucidated by3

(1) Inhibition of apoptosis

(2) Stimulation of angiogenesis

(3) Increased invasiveness

(4) Modulation of inflammation/immuno-suppression and

(5) Conversion of procarcinogens to carcinogens.

 

Induction of COX-2 expression is associated with simultaneous increase in prostaglandins. This leads to the modulation of pro- and anti-apoptotic factors (e.g., bcl-2, MAKs/ras, caspase-3, Par-4) and a clear positive correlation has been established between COX expression and tumor induction. The expression of growth factors like e.g: Vascular endothelial growth factor (VEGF), Platelet derived growth factor (PDGF) and matrix metalloproteinases (MMPs) are also found to increase with   COX-2 overexpression. This plays an important role in angiogenesis and invasiveness. Hence COX-2 and its gene product are found to be attractive targets for therapeutic and chemoprotective strategies.

 

COX-2 as a biomarker

Kanaoka S et al., reported that COX-2 can serve as a potential biomarker in evaluating the tumor prognosis. COX -2 has a clear cut role in cellular proliferation, stimulation of angiogenesis, blockade of apoptosis, tumor invasiveness, modulation of immune system, and increased mutagenesis. Thus COX-2 serves as the potential tool for evaluating the neoplasms4.

 

Farooqui M et al., reported that chronic treatment with celecoxib (by gavage) and/or morphine (subcutaneously), or phosphate buffer saline(PBS) on tumour prostaglandin E(2) (PGE(2)), COX-2, angiogenesis, tumour growth, metastasis, pain behaviour in a highly invasive SCK breast cancer model in A/J mice and determined their survival.

 

Two weeks of chronic administration of clinically relevant doses of morphine treatment is accompanied by increased tumour weight (approximately 35%) and increased metastasis and reduced survival in mice. When Co-administered with celecoxib, morphine-induced effects were found to be reduced5.

 

Immunohistochemistry of Cox-2 Protein

Becker, Maria R, et al., analyzed the expression of COX-2 protein by immunohistochemistry in 101 primary malignant melanomas and 28 metastases and correlated the data with Breslow tumor thickness, Clark levels, different melanoma subtypes, metastases, and overall survival. They found a strong COX-2 expression in 95% of all primary melanomas, primarily restricted to melanoma cells as shown by various immunohistochemical methods and levels of COX-2 expression in primary melanoma and corresponding metastases remained stable. A significant correlation between immuno histochemical staining intensity and tumor thickness was demonstrated. These findings emphasize that the COX-2 protein might be a novel prognostic marker owing to its strong expression in melanoma cells it might also be a reasonable therapeutic target 6.

 

Cyclooxygenase-2 (COX-2) is an enzyme induced by inflammatory and mitogenic stimuli and results in enhanced synthesis of PGs in inflamed and neoplastic tissues. It is associated with cell proliferation and growth, in various cancerous conditions. Results of the study show that COX-2 is a regulatory factor for a number of pathways that can result in cancer. COX-2 makes cells resistant to apoptosis and promotes angiogenesis, metastasis and cancer cell cycle by controlling number of targets. They found that, COX-2 selective inhibitors (like celecoxib and NS-398) can suppress the cancer both by COX-2 dependent and COX-2 independent pathways. COX-2 inhibitors can also produce synergic effects when used with other anti-cancer therapies. Thus, it is concluded that COX-2 selective inhibitors may be promising agents for prevention and treatment of cancer7.

 

Clinically tamoxifen is used for breast cancer Prevention, squamous cell skin cancer with actinic keratosis by diclofenac gel and in familial polyposis with anti-inflammatory drug (COX-2) celecoxib. The latter effect has dragged the attention of cancer investigators enormously due to its mechanism and chances of its further use in different neoplasms. Other agents of this anti-inflammatory class like   aspirin and sulindac also have a proven chemoprevention of cancer by cycloxygenase inhibition8.

 

COX-2 - Anti-Cancer Research 12

Research on the use of COX-2 inhibitors enlightened their usefulness for wide range of cancers which includes:

·        Basal cell (skin) carcinomas

·        Pre-cancerous adenomatous polyps of the colon

·        Non-small-cell lung cancer

·        Barrett's esophagus

·        Bladder Cancer

·        Oral pre-malignant lesions,

Other investigation has proved that dietary constituents such as resveratrol, and omega-3 fatty acids can prevent cancer by inhibiting COX-2.

 

COX-2 and Breast cancer

The risk of breast cancer may be reduced by 71 percent with the frequent use of pain relievers. The results are often similar in the prevention of prostate, colon and lung cancers.

 

Harris et al., carried out a study among 323 women with breast cancer. They were prescribed with celecoxib (Celebrex), rofecoxib (Vioxx), regular aspirin, low-dose aspirin, ibuprofen and acetaminophen. The results were compared with a control group of 649 cancer-free women who were of the same age, race and county. The results are tabulated in Table.1.

 



Table.1 showing Drug induced inhibition of Breast cancer

Prescribed drug

% Inhibition of Breast cancer

celecoxib or rofecoxib

71

Ibuprofen

64

Aspirin

51

Acetaminophen

Negligible effect

 

 

Many key steps in cancer development like proliferation, angiogenesis and metastasis are mediated by COX-2 signaling pathway. Thus a regular intake of optimum dose of COX-2 inhibitors can prevent the COX-2 cascade and ameliorate the secondary events of cancer genesis.

 

Barnes NL et al., developed tumours in a nude mouse xenograft model by injecting Oestrogen receptor (ER)-positive MCF7/HER2-18 and ER-negative MDAMB231 breast cancer cell lines. The effects of COX-2 were determined by feeding the mice with chow containing Celecoxib (a COX-2 inhibitor) or control and the tumour growth apoptosis and lymphangiogenesis were assessed by immunohistochemistry. The results were compared with the control group.

 

The median tumour growth in MCF7/HER2-18 and MDAMB231 was inhibited by (58.7%, P=0.029) and (46.3%, P=0.0002) respectively by Celecoxib and cell lines compared to control.

 

Celecoxib increased apoptosis in MCF7/HER2-18 tumours (TUNEL 0.52% control vs. 0.73% treated, P=0.0004) via inactivation of AKT (family of protein kinaseB).

Breast cancer is associated with high levels of activated AKT and lymphangiogenesis Thus Cyclooxygenase-2 inhibition reduces tumour growth, and its recurrence, by decreasing lymphangiogenesis and inactivating AKT9.

 

COX-2 inhibitors affect the growth of both COX-2 positive as well as COX-2 negative tumor cell lines, indicating the potential of these compounds targeting proteins that plays a key role in the proliferation of tumor cells10.

 

Lung-Cancer Study 11

According to a published issue of the Journal of Clinical Oncology, patients with Non small cell lung carcinoma  when treated with a COX-2 inhibitor, in conjunction with paclitaxel and carboplatin, resulted in reduced levels of intra tumoral prostaglandin E2 (PGE2),  which is associated with tumor growth, The study also demonstrated that the treatment was feasible and safe.

 

Dr. Dannenberg and colleagues findings, a lung carcinoma clone was injected into the paws of mice and tested against selective and nonselective COX-2 inhibitors, including SC236, celecoxib, and indomethacin. When the results were analyzed it was found that COX-2 inhibitor (selective or nonselective) were beneficial in combination with chemotherapy by decreasing COX-2-derived prostaglandin levels.

 

COX-2 in Prostate cancer12

Xin-Hua Liu et al., elucidated the effects of COX-2 on p53 in response to hypoxia, by transfecting the COX-2 gene into the p53-positive, COX-2-negative MDA-PCa-2b human prostate cancer cell line. Hypoxia and other stressors which are regulated by the Mdm2 protein were found to have a role in human cancers. It also induces (COX)-2.This elevates prostaglandins and results in tumor cell proliferation, resistance to apoptosis, and angiogenesis. Thus COX-2 inhibitors which have a reciprocal relationship with p53 are found to be beneficial in human Prostate cancer.

 

COX-2 in Head and Neck Cancer13

Dannenberg and colleagues measured COX-2 messenger RNA (mRNA) in 24 patients with head and neck cancer using quantitative reverse transcriptase polymerase chain reaction (RT-PCR). And compared with COX-2 mRNA levels in 17 control patients. The results shown COX-2 mRNA levels were found to increase by 150-fold among the squamous cell carcinoma patients compared to 50-fold higher level of expression than normal oral mucosa.

Bladder Carcinoma and COX Overexpression14, 15

The Cornell research team reported that the COX-2 inhibitor, nimesulide reduced the nitrosamine-induced bladder cancer in a dose-dependent fashion in laboratory animals similar results were obtained with celecoxib.

 

COX-2 and Cervical Cancer 13

Overexpression of COX-2 was also found in cervical intraepithelial neoplasia (CIN), a premalignant lesion.

 

 COX-2 and colon carcinoma

Tsujii M et al., explored the role of COX in endothelial cell migration and angiogenesis, using in vitro model systems of colon carcinoma cells. Overexpression of COX-2- cells produce prostaglandins, proangiogenic factors, which stimulate both endothelial migration while this activity is fewer in control cells.

 

COX regulates colon carcinoma-induced angiogenesis by following mechanisms:

Ø  COX-2  modulated production of angiogenic factors by colon cancer cells

Ø  COX-1 regulates angiogenesis in endothelial cells16.

Other Applications

Overexpression of COX-2 is observed in majority of hepatocellular carcinoma and also in the patients with chronic hepatitis inhibition of COX-2 may prevent the progression of chronic hepatitis to hepatic cancer. Tumor growth in colorectal cancer was found to be inhibited by Selective and the nonselective COX inhibitors Another potential benefit of COX-2 inhibition is that they increase the antitumor activity of radiotherapy and chemotherapy 17, 18.Because of the overexpression of COX-2 in various types of cancer catalyzing the formation of bioactive lipid molecules, such as prostaglandins which inhibit apoptosis and increase proliferation, motility, and metastatic potential. This significance of COX in the pathology of cancer


dragged the attention and made their way in to the clinical trials19.

 

Future perspective

COX-2 Inhibitors in treatment for neuroblastomas

John I. Johnsen et al. have reported that abnormal expression of COX-2 are implied in the tumors of the sympathetic nervous system i.e., neuroblastomas with relative adverse effect on p53, the tumor suppressor gene which plays a role in apoptosis. Two of the prostaglandins, the metabolites of COX-2 when present in high quantities prevent the entry of p53 in the cytosol into the nucleus by binding to it and inhibiting the apoptosis. The overexpression of COX-2is selectively inhibited by COX-2 Inhibitors, allowing the normal functioning of p53.This will keep the tumor growth in check hastening the cell death20.

 

CONCLUSIONS:

More anticipation towards the discovery of COX-2 inhibitors and their activity finds more of its applicability in cancer therapy. Various cancers and similar syndromes can be effectively targeted ensuring the safety with COX-2 inhibitors. Cancer therapy is associated with severe pain, the use of these agents can outweigh the additional benefits in relieving the pain together with their anti-cancer activity. Thus minimizing the use of narcotic analgesics and their mediated adverse effects. To conclude research on COX-2 inhibitors in cancer therapy has to be encouraged to overcome the proven hurdles.

 

REFERENCES:

1.       Chandrasekharan et al. COX-3, a cyclooxygenase-1 variant inhibited by acetaminophen and other analgesic/antipyretic drugs: Cloning, structure, and expression. Proceedings of the National Academy of Sciences of the United States of America. 2002; 99(21): 13926-31.

2.       Hull MA. Cyclooxygenase-2: how good is it as a target for cancer chemoprevention? Eur J Cancer. 2005; 41(13):1854-63.

3.       Christoph R et al. Cyclooxygenase-2: a novel target for cancer chemotherapy? Journal of Cancer Research and Clinical Oncology. 2001; 127(7): 411-417.

4.       Kanaoka S et al. Cyclooxygenase-2 and tumor biology. Adv Clin Chem. 2007; 43: 59-78.

5.       Farooqui M et al. COX-2 inhibitor celecoxib prevents chronic morphine-induced promotion of angiogenesis, tumour growth, metastasis and mortality, without compromising analgesia. Br J Cancer. 2007; 97(11): 1523-31.

6.       .Becker et al. COX-2 expression in malignant melanoma: a novel prognostic marker? Melanoma Research. 2009; 19(1): 8-16.

7.       Amir M, Agarwal HK. Role of COX-2 selective inhibitors for prevention and treatment of cancer. Pharmazie. 2005; 60(8): 563-570.

8.       Grau de Castro JJ. COX-2 inhibitors in cancer prevention. Rev Clin Esp. 2005; 205(9): 446-56.

9.       Barnes NL et al. Cyclooxygenase-2 inhibition: effects on tumour growth, cell cycling and lymphangiogenesis in a xenograft model of breast cancer. Br J Cancer. 2007;   96(4): 575-82.

10.     E. P. Reddy. Novel COX-2 Inhibitor for Breast Cancer Therapy. (http://www.stormingmedia.us/25/2530/A253024.html)

11.     First Clinical Study to Suggest Benefit of COX-2 Inhibitor for Cancer Treatment. (http://nyp.org/news/hospital/altorki-celecoxib-chemo.html)

12.     Xin-Hua Liu et al. Cyclooxygenase-2 Suppresses Hypoxia-induced Apoptosis via a Combination of Direct and Indirect Inhibition of p53 Activity in a Human Prostate Cancer Cell Line. J. Biol. Chem. 2005; 280(5): 3817-3823.

13.     .http://www.medscape.com/viewarticle/412929_6

14.     Kitayama W et al. Increased expression of cyclo-oxygenase-2 protein in rat urinary bladder tumors induced by N-butyl-N-(4-hydroxyburyl) nitrosamine. Carcinogenesis. 1999; 20: 2305-2310.

15.     Ziegler J. Early trials probe COX-2 inhibitors' cancer-fighting potential. J Natl Cancer Inst. 1999; 91: 1186-1187.

16.     Tsujii M et al. Cyclooxygenase regulates angiogenesis induced by colon cancer cells. Cell.1998; 93(5): 705-16.

17.     Kishi K et al. Preferential enhancement of tumor radioresponse by a cyclooxygenase-2 inhibitor. Cancer Res. 2000; 60: 1326-1331.

18.     Milas L et al. Enhancement of tumor response to gamma-radiation by an inhibitor of cyclooxygenase-2 enzyme. J Natl Cancer Inst. 1999; 91: 1501-1504.

19.     Jennifer Michalowski. NEWSCOX-2 Inhibitors: Cancer Trials Test New Uses for Pain Drug .  Journal of the National Cancer Institute. 2002; 94(4): 248-249.

20.     John I et al. Cyclooxygenase-2 Is Expressed in Neuroblastoma, and Nonsteroidal Anti-Inflammatory Drugs Induce Apoptosis and Inhibit Tumor Growth In vivo Cancer Research. 2004; 64: 7210-7215.

 


 

 

 

 

Received on 25.02.2009       Modified on 23.04.2009

Accepted on 26.05.2009      © RJPT All right reserved

Research J. Pharm. and Tech.2 (4): Oct.-Dec. 2009; Page617-62039