Phytochemicals in Cancer Chemoprevention

1. Phytochemicals in Cancer Chemoprevention MJ Wargovich wargovic@musc.edu

2. What Is Chemoprevention? • The science of trying to apply natural and synthetic compounds to interfere with the earliest stages of carcinogenesis, before invasive cancer appears

5. The Ideal Chemopreventive Agent • Is effective • Easily administered • Preferably once/twice day • Little or ideally no toxicity • Affordable

6. Mechanisms of Chemoprevention • Antioxidants: defense against radicals • Phase 1 enzyme inducers • Phase 2 enzyme inducers • Anti-proliferative agents • Anti-hormonal compounds • Disruption of mutational gain or loss of function • Epigenetic effects

7. Antioxidants • Oxygen is actually a very toxic substance • Antioxidants are the first line defense mechanism against oxidative damage in plants • Fruits and vegetables are loaded with antioxidant chemicals

8. Total Daily Intake of Antioxidants

9. Antioxidant Potential of Fruits and Vegetables

11. Anthocyanin - berries Flavanone - citrus Flavanol - red wine teas chocolate fruit Flavonol - fruit vegetables Hydroxycinnamates - most fruit & some vegetables Flavonoids: naturally occurring low molecular wt phenols consisting of 2 benzene rings linked via a heterocyclic pyrone or pyran ring

12. STRUCTURAL REQUIREMENTS FOR H-DONATING ANTIOXIDANT ACTIVITY:ortho-dihydroxy substitution in B-ring2,3-unsaturation in C-ring4-carbonyl group O H O H B Bors et al. 1990; Rice-Evans et al. 1996; QUERCETIN H O O A C O H O H O

13. Flavanone Flavonol Flavanol e.g. e.g. hesperetin quercetin e.g. epicatechin onion, cranberry, red apple Citrus fruit, orange red wine, green tea, many fruit and vegetables as procyanidins in apple, chocolate OH OH HO O OH OH Hydroxycinnamate e.g. caffeic acid most fruit especially tomato, apple some vegetables e.g. egg plant grains COOH OH OH OH OH HO O OH OH O Anthocyanidin e.g. cyanidin major constituents of dark red fruit berries e.g. raspberries OH OH OH OH + HO HO O O OH OH OH

14. Green Tea • Epidemiologic studies support a protective effect for green tea but not black tea in prevention of certain cancers • Animal studies are highly supportive of a preventive effect of green tea, GTP, and purified polyphenols, especially EGCG against certain cancers Camellia sinensis

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16. Evidence for Tea Drinking and Prevention of Human Cancer • Ecological Studies • Cohort Studies • Case-Control Studies

18. Bioflavonoids • Naturally occurring chemicals present in many fruits and vegetables • Major flavonoids in onion are quercetin and its glycoside, rutin • Can reach appreciable levels in onions but tea also is a major source

19. Bioflavonoids and Reduced Risk for Heart Disease • Quercetin inhibits oxidation of LDL cholesterol • Inhibits development of fatty streaks in animals

20. Agents That Influence Drug Metabolism

21. Surh et al Nat Reviews 3:2003

22. Garlic • Consumption in China and Italy linked to lower gastric cancer risk • Sulfur compounds inhibit cancers of colon, breast, esophagus, lung, skin • Primarily acts through modulation of Phase 1 ( activation) and Phase 2 (detoxification) enzymes Allium sativum

23. Organosulfur Compounds in Garlic • Member of the plant genus Allium • Over 20 different compounds in garlic are being tested for cancer inhibition. • Diallyl sulfide was the first organosulfur compound known to inhibit experimentally-induced cancer. • Proposed mechanisms of chemoprotection lie in modification of carcinogen metabolism and/or detoxification. Alliin Allinase Allicin Lipophilic compounds diallyl sulfide diallyl disulfide methyl propyl sulfide dipropyl disulfide dimethyl trisulfide methyl propyl trisulfide methyl propyl thiosulfinate Water soluble compounds L-cysteine S-allyl-l-cysteine S-methyl-l-cysteine L-methionine

24. Cyp2e1 • One subset of many cytochromes P450 • Main task is to activate compounds; eliminate them from the body • This enzymes metabolizes many small molecular weight compounds • Ethanol, nitrosamines, hydrazines

25. CYP2E1 and Colon Cancer Dimethylhydrazine (DMH) Model CH3-NH-NH-CH3 1,2-Dimethylhydrazine LIVER COLON CH3-N=N-CH3 azomethane CYP2E1 Spontaneous breakdown H3C + N2 CH3-N N CH3-N=N-CH3 methyldiazonium O azoxymethane CYP2E1 CH3-N=N-CH2OH methylazoxymethanol

26. Typical Chemoprevention Assays in Rodents

28. Chemopreventive activity of oil-soluble OSCs in ACF assay(M. Wargovich, 1997)

29. Garlic Compounds and Phase II Enzymes

32. Antiproliferative or Growth Suppressing Agents:Modulation of Cell Signaling

33. COX Inhibitors Reduce Colorectal Carcinogenesis – Observational Data

34. How Do NSAIDs Work? • Aspirin transfers acetyl group to serine on the cyclooxygenase enzyme, blocking its affinity for arachidonic acid • All other NSAIDs are competitive inhibitors of the COX enzymes

35. BIOLOGICAL ROLE OF PROSTANOIDS

36. Inflammation and Cancer • Chronic, clinically invisible, unresolved inflammation may create a very high risk for common cancers • Tumors corrupt the inflammatory pathway to survive

37. A model of chronic inflammationsetting a threshold for cancer Chronic Inflammation Esophagitis Gastritis Colitis Pancreatitis Hepatitis Initiation Tumor Mutation ROS/RNS Growth advantage ROS/RNS Replacement hyperproliferation Cell damage Promotion  apoptosis  angiogenesis

38. Loss of 18q APC mutation K-ras mutation p53 mutation COX-2 Overexpression Multistage Colon Carcinogenesis

39. NSAIDs Inhibit ACFs in the Colon

41. NSAIDS, COX Specificity and Chemoprevention COX 1COX 2 100% Indomethacin 0% Sulindac Piroxicam Diclofenac Naproxen Meclofenamate Etodolac Nimsulide Celecoxib 0% 100%

42. Ibuprofen Diclofenac Naproxen Ketoprofen Indomethacin Piroxicam - + +/- + +/- + + ++ +++ +++ +++ +++ Toxicity of NSAIDs Compound Toxicity* Inhibit ACF? * Clinical manifestations: Colitis, perforation, fistulae, GI bleeding Peptic and small bowel ulcers, strictures

43. 35 35 Late treatment (days 55-80) Early treatment (days 30-80) 30 30 25 25 20 20 * Multiplicity (tumors/animal) 15 15 * * * 10 10 5 5 0 0 Vehicle 1500 50 Vehicle 150 500 1500 50 500 Piroxicam Celecoxib Celecoxib Piroxicam (mg/kg diet) (mg/kg diet) Celecoxib Inhibits Tumor Multiplicity in the MIN Mouse Model * P < 0.05; n=12/group Jacoby et al: Cancer Res 60:5040-4, 2000

44. Effect of COX-2 Selective Inhibition on Colorectal Adenomas in Patients with FAP Steinbach et al, NEJM, 2000

48. Plant-based NSAIDS...

50. Herbal NSAIDS • Overuse could potentially result in bleeding, prolonged platelet aggregation, and ulceration • Combined use might reduce the need for high strength NSAIDs • Could help in long term chemoprevention trials for colon and breast cancer