Dietary polyphenolic phytochemicals-promising ... - Wiley Online Library

Int. J. Cancer: 120, 451–458 (2006) ' 2006 Wiley-Liss, Inc.

MINI REVIEW Dietary polyphenolic phytochemicals—Promising cancer chemopreventive agents in humans? A review of their clinical properties Sarah C. Thomasset1,2, David P. Berry2, Giuseppe Garcea2, Timothy Marczylo1, William P. Steward1 and Andreas J. Gescher1* 1 Cancer Biomarkers and Prevention Group, Department of Cancer Studies, University of Leicester, Leicester Royal Infirmary, Leicester, United Kingdom 2 Department of Hepatobiliary and Pancreatic Surgery, Leicester General Hospital, Leicester, United Kingdom

Epidemiological and preclinical evidence suggests that polyphenolic phytochemicals exemplified by epigallocatechin gallate from tea, curcumin from curry and soya isoflavones possess cancer chemopreventive properties. Whilst such naturally occurring polyphenols have been the subject of numerous mechanistic studies in cells, information on their clinical properties, which might help assess their promise as human cancer chemopreventive agents, is scarce. Therefore, we present a review of pilot studies and trials with a cancer chemoprevention-related rationale, in which either healthy individuals or patients with premalignant conditions or cancer received polyphenolic phytochemicals. The review identifies trial design elements specifically applicable to polyphenolic phytochemicals. The available evidence for tea polyphenols tentatively supports their advancement into phase III clinical intervention trials aimed at the prevention of progression of prostate intraepithelial neoplasia, leukoplakia or premalignant cervical disease. In the case of curcumin and soya isoflavones more studies in premalignacies seem appropriate to optimise the nature and design of suitable phase III trials. The abundance of flavonoids and related polyphenols in the plant kingdom makes it possible that several hitherto uncharacterised agents with chemopreventive efficacy are still to be identified, which may constitute attractive alternatives to currently used chemopreventive drugs. ' 2006 Wiley-Liss, Inc. Key words: cancer chemoprevention; flavonoids; tea polyphenols

clinical

trial;

curcumin;

In recent years there has been increasing interest in the potential cancer chemopreventive properties of diet-derived agents. This interest has been elicited by epidemiological research linking variations in geographical distribution of cancer incidence to intake of specific diets, and it has been supported by convincing evidence of chemopreventive efficacy of specific diet constituents in rodent models of carcinogenesis. The ultimate proof of efficacy of a putative cancer chemopreventive agent is provided by long-term phase III clinical intervention studies involving large numbers of individuals. Such studies are complex and expensive to conduct. Only relatively few dietary constituents have undergone, or are currently undergoing, phase III cancer chemoprevention studies. Prominent among them are folate,1 b-carotene plus vitamins A and E,2,3 calcium plus vitamin D4 and selenium plus vitamin E.5 Polyphenolic pytochemicals such as epigallocatechin gallate (EGCG) from tea, the flavonoids quercetin and genistein from onions and soya, respectively, curcumin in curry spice and resveratrol from red grapes (for structures see Fig. 1) constitute a class of diet constituents with notable efficacy in preclinical models of carcinogenesis, including those of the colorectum, breast and prostate.6 To our knowledge, none of these species have to date been the subject of phase III clinical trials. A prominent feature rendering polyphenolic phytochemicals worthy of study is the fact that they have been the subject of intense mechanistic studies in cells in vitro. There is now an extensive literature relating to their anticarcinogenic mechanisms, which rationalises how they may prevent or delay malignancy (for review see Ref. 7). Many issues impacting on the feasibility of advancing a putative chemopreventive agent to phase III clinical evaluation, such as its pharmacokinetic, pharmacodynamic, Publication of the International Union Against Cancer

mechanistic and safety properties, are suitably explored in small and relatively short-term studies in either healthy volunteers, individuals with premalignancies or cancer patients. Such early clinical studies are indispensable for the optimisation of the design of large definitive phase III trials.8 For b-carotene, clinical information gained in such early pilot studies on optimal dosing regimen, pharmacodynamic sequelae and profile of suitable recipient cohort may have obviated its fateful phase III evaluation, establishing its lack of inhibitory effect on lung cancer incidence.9 This article reviews the current literature on early clinical studies of polyphenolic phytochemicals with 2 aims: first, to delineate features of an ÔoptimalÕ early clinical trial design, which could aid the swift development of novel members of this class of agent, and second, to allow a judgement to be made as to whether the clinical information currently available for any polyphenolic phytochemical is sufficient to support its phase III clinical evaluation.

Biomarkers of chemopreventive efficacy While reduction in cancer incidence and mortality is the ultimate efficacy criterion for a chemopreventive agent, the use of surrogate biomarkers of chemopreventive activity, minimising trial size, length and cost, is an appealing alternative goal in clinical chemoprevention drug development. Among the range of surrogate efficacy biomarkers that have been evaluated in clinical interventions using polyphenolic phytochemicals are levels or activities of pivotal components of specific oncogenic pathways [e.g. cyclooxygenase-2 (COX-2) or prostaglandin E2, a product of COX-mediated catalysis], levels of circulating disease-related proteins (e.g. prostate specific antigen PSA) and histological, cytological and genomic alterations indicative of apoptosis, proliferation, differentiation and transformation.10 Histological modulation of precursors of cancer by putative chemopreventive agents is considered a promising surrogate efficacy marker.11,12 Such premalignancies are intraepithelial neoplasia of the prostate (PIN) or cervix (CIN), colorectal adenomas, oral leukoplakia and actinic keratoses. The effects of polyphenolic phytochemicals on these have been evaluated as potential efficacy markers. DNA damage, such as that caused by endogenous and exogenous oxidants, has also served as a biomarker of chemopreventive efficacy.13 Tables I–III, which summarise clinical cancer chemoprevention-focussed studies of polyphenolic phytochemicals, list some of the biomarkers that have been used to assess efficacy. In trials of polyphenolic phytochemicals aimed at prostate cancer prevention, the disease biomarker PSA has been utilised as a marker of efficacy, although Grant sponsors: UK Medical Research Council and Cancer Research UK; AICR; Hope Foundation. *Correspondence to: Cancer Biomarkers and Prevention Group, Department of Cancer Studies, University of Leicester, Leicester Royal Infirmary, Leicester LE2 7XL, UK. E-mail: [email protected] Received 4 September 2006; Accepted 25 September 2006 DOI 10.1002/ijc.22419 Published online 27 November 2006 in Wiley InterScience (www.interscience. wiley.com).

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FIGURE 1 – Chemical structures of some of the polyphenolic phytochemicals discussed in this review.

PSA levels are now known not to be directly related to neoplastic progression.66 Interpretation of the results of clinical trials depends crucially on the accuracy of biomarkers to reflect chemopreventive efficacy. The validation of surrogate efficacy biomarkers is difficult and lengthy, and the relative lack of information on such markers has undoubtedly slowed the advancement of dietary compounds, including polyphenols from preclinical studies into clinical trials. Dose and duration of intervention Participants in early clinical trials of polyphenolic phytochemicals have received a large variety of doses. As the polyphenol content of some dietary extracts consumed by trial participants has not been analysed, comparison between trials is sometimes difficult. In the case of green tea the minimum daily dose of catechins administered orally has been 18.6 mg.20 In this study, tea extract was incorporated into meat patties and administered to healthy individuals to assess effects on oxidation status and urinary markers of DNA damage. The maximum daily dose of green tea polyphenols administered has been 3.7 g in capsule form, in a dose escalation study in patients with malignant disease designed to evaluate tolerability, safety and pharmacology.49 Daily doses of curcumin have ranged from 180 mg to 8 g. The low dose was used in trials in which molecular biomarkers were evaluated in patients with colorectal cancer,51,52 the high dose was employed in patients with premalignant disease in which histological changes were measured.44 Daily doses of soy isoflavones have also varied considerably between trials. The minimum daily dose of 40 mg was administered to healthy women to assess effects on levels of sex hormones and their metabolites related to the risk of breast cancer.32 Levels of PSA were evaluated in patients with prostate cancer, who received as much as 900 mg soy isoflavones per day.59 The doses of polyphenolic phytochemicals in trials, in which tangible pharmacological effects have been observed, were generally much higher than those consumed with the diet, especially in Western countries.67 To illustrate this point, a daily intake of 39

mg isoflavones has been reported in China,68 whereas on average less than 5 mg isoflavones per day are consumed in the US.57 A daily intake of 76 mg catechins has been reported in a cohort of Australian women,69 a level significantly below the dose administered in most cancer chemoprevention trials. This juxtaposition illustrates the considerable discrepancy between ÔpharmacologicalÕ and Ôdietary-relatedÕ dose of phytochemicals, which is often 10- to 100-fold. The discrepancy severely confounds the extrapolation of the potential value of dietary intake of a specific molecule from results of studies, in which pharmacologically efficacious doses have been evaluated. Length of intervention in pilot studies of polyphenolic phytochemicals has also varied considerably, from trials, in which participants received only 1 dose, to those, in which daily dosing continued for up to a year or longer. Obviously the objectives of a pilot study determine trial duration. Pilot studies with pharmacokinetic or pharmacodynamic (mechanistic) aims may be conducted with only a short duration, whilst trials directed at the exploration of safety or quasi-efficacy endpoints can require months or years. Preclinical evidence suggests that inhibition of proteolytic enzymes and altered intracellular signalling cascades contribute towards the chemopreventive effect of tea polyphenols.7,70 Whilst it is conceivable that such mechanism-based pharmacodynamic changes can be detected in suitable tissues within days or weeks of initiation of intervention, they are likely to have to be engaged for prolonged periods of time to impact on carcinogenesis. Safety of polyphenols Consistent with the expectation, that dietary constituents are harmless and well tolerated, unexpected cases of severe toxicity associated with consumption of polyphenolic phytochemicals have been rare. Adverse effects were encountered with polyphenolic phytochemicals, include nausea, abdominal pain, diarrhoea, fatigue and insomnia. Most noteworthy are 2 reports of grade 4 toxicity reactions associated with consumption of green tea polyphenols and quercetin. Following daily consumption of 6 g of

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CLINICAL TRIALS OF POLYPHENOLIC PHYTOCHEMICALS TABLE I – CLINICAL STUDIES OF POLYPHENOLIC PHYTOCHEMICLAS IN HEALTHY INDIVIDUALS Type of polyphenol

Biomarkers

Green tea14 Green tea15 Green tea16 Green tea, black tea17

DNA damage DNA damage DNA damage DNA damage

Green tea18

DNA damage, DNA content, apoptosis DNA damage, free radicals DNA damage, oxidation status DNA damage, oxidation status Oxidation status Oxidation status

Green tea

19

Numbers recruited

52 10 6 143 6

Maximal length of treatment

6 months 1 dose 1 dose 4 months 1 month 1 week

16

3 weeks

20

2 doses

2

6 12

1 dose 1 dose

Green tea24 Oxidation status Green tea, Oxidation status black tea25

10 30

3 doses2 3 doses2

Green tea, black tea26 Black tea27 Green tea28 Green tea29 Soy30 Soy31 Soy32

24

2 doses

Green tea

21 22

Green tea Green tea23

Soy33 34

Soy Soy35 Red clover36 Quercetin37

3 cups,1 beverage 3 cups,1 beverage 4 mg/2.5 cm2, topical 583 mg green tea polyphenols/ 447 mg black tea polyphenols, beverage 798 mg catechins, beverage 1

67

Green tea20

Maximum daily dose of polyphenol and method of administration

3 cups, beverage 18.6 mg catechins, prepared diet 1 g Polyphenon E/580 mg EGCG, oral capsules 1 mg EGCG/ cm2, topical 1 cup,1 beverage

Oxidation status COX-2 PGE2, apoptosis Mammographic density Mammographic density Sex hormones and metabolites Sex hormones

9 9 15 220 34 26

2 doses 1 dose 1 dose 24 months 12 months 2 months

1 cup,1 beverage 697 mg green tea flavanols/547 mg black tea flavanols, beverage 462 mg green tea flavanols, oral capsule 640 mg green tea catechins/140 mg black tea catechins, beverage 6 cups,1 beverage 1 mg extract/ cm2,1 topical 180 mg polyphenols, beverage 50 mg isoflavones, prepared diet 100 mg isoflavones, oral tablets 40 mg isoflavones, prepared diet

35

2 months

90 mg isoflavones, beverage

PSA PDGF Mammographic density, sex hormones DNA damage

128 23 205

12 months 9 days 12 months

83 mg isoflavones, beverage Soy,1 prepared diet 42.5 mg isoflavones, oral tablet

2 weeks

91.1 mg quercetin, prepared diet

Oxidation status

42

Chemopreventive outcome

fl DNA damage (leukocytes) fl DNA damage (leukocytes) fl DNA damage (skin) fl DNA damage with green tea (urine) fl DNA damage, › diploid DNA, › apoptosis (oral cytology) fl DNA damage (leukocytes, urine), fl free radical generation (urine) M DNA damage (urine), › antioxidant activity (plasma) M DNA damage (leukocytes), fl antioxidant activity (plasma) › antioxidant activity (skin) › antioxidant activity (plasma and urine) › antioxidant activity (plasma) › antioxidant activity with green tea capsules (plasma) › antioxidant activity (plasma) › antioxidant activity (plasma) fl COX-2 (skin) fl PGE2, M apoptosis (rectum) M mammographic density M mammographic density M sex hormones and metabolites (serum and urine) fl estrone, M estradiol, testosterone, SHBG (serum) M PSA (serum) › PDGF (serum) M mammographic density, sex hormones (serum) M DNA damage (leukocytes)

EGCG, epigallocatechin-3-gallate; COX-2, cyclooxygenase-2; PGE2, prostaglandin E2; SHBG, sex hormone-binding globulin; PSA, prostate specific antigen; PDGF, platelet derived growth factor. › increase, fl decrease, M unchanged. 1 Dose of polyphenol unknown.–2Weekly dosing.

green tea extract, a patient with advanced prostate cancer exhibited grade 4 toxicity, manifested as confusion requiring a 5-day hospital stay. The extract was not analysed to discover amounts of polyphenols ingested.46 During a dose escalation study evaluating intravenous quercetin in advanced malignancy, an episode of grade 4 nephrotoxicity occurred at a weekly dose of 1,400 mg/m2. In this trial a second episode of grade 4 nephrotoxicity occurred during 3-weekly dosing at 1,700 mg/m2. The same patient also experienced grade 4 emesis.65 Doses of quercetin associated with toxicity were significantly higher than the average dietary intake, estimated to be 16 mg/day.71 Quercetin seems to be less well absorbed than other polyphenolic phytochemicals,72 and it is conceivable that the rather high circulating levels inevitably achieved after intravenous administration may have elicited toxicity.

Trials of polyphenols in healthy individuals Studies on healthy individuals have helped explore the human pharmacokinetics of polyphenolic phytochemicals and provided useful information on potential surrogate biomarkers of chemopreventive efficacy (Table I). Oral consumption of tea polyphenols has been associated with an increase in plasma and urine antioxidant activity. In one study plasma antioxidant activity, as determined by the Ôtrolox equivalent capacity assayÕ, was raised by 12.7% individuals 2 hr after they had consumed 7.5 g green tea extract.24 Consumption of 6 cups of black tea was associated with a 76% increase in plasma antioxidant capacity as determined by

the Ôferric reducing antioxidant power assayÕ at 7 hr.27 Some papers suggest that consumption of green tea also protected against smoking- and radiation-induced DNA damage in healthy individuals. Reduced levels of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage, were detected in oral cells,18 urine17 and leukocytes19 of smokers following green tea consumption. Ingestion of green tea protected against UV-induced DNA damage in leukocytes.15 This finding in concert with observations, according to which topical application of green tea furnished reduced levels of radiation-induced dermal DNA damage16 and COX-2 expression,28 hint at a potential role of tea polyphenols in the chemoprevention of skin cancer. In one study the effect of green tea on putative biomarkers of colorectal cancer was evaluated in healthy volunteers. Serial rectal biopsies following a single oral dose of up to 180 mg green tea polyphenols revealed efficacy in terms of decreased levels of prostaglandin E2 at 4–8 hr post dosing.29 More extended and definitive trials, perhaps in patients with polyps, are necessary to allow assessment of the potential of green tea to prevent colorectal cancer. Some trials involving healthy individuals have evaluated the role of soy polyphenols, particularly in the prevention of breast cancer. Given their structural similarity to mammalian estrogens, soy isoflavones are thought to affect hormone-dependant cancers.73 In two randomised controlled trials involving healthy premenopausal women, the effect of soy isoflavones on mammographic density, a known risk factor for malignancy, has been assessed.74 No statistically significant difference was observed following the ingestion of 100 mg isoflavones daily for 1 year or 50 mg isoflavones daily for 2 years.30,31 Levels of sex hormones associated with

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THOMASSET ET AL. TABLE II – CLINICAL STUDIES OF POLYPHENOLIC PHYTOCHEMICALS IN PATIENTS WITH PREMALIGNANT DISEASE Type of polyphenol and cancer

Green tea, prostate cancer38 Green tea, oral cancer39

Participants

Prostate intra-epithelial neoplasia Oral leukoplakia

Soy, colorectal cancer45

Maximal length of treatment (months)



fl progression to prostate cancer (histology), M PSA (serum) › rate of partial regression (clinically), fl DNA damage, fl proliferation (oral mucosa) fl DNA damage (urine)

60

12

600 mg catechins, oral capsules

64

6

1.2 g polyphenols, oral capsules and tea in glycerine, topical

124

3

1g polyphenols, oral capsules

88

3

51

3

Oral leukoplakia

82

12

200 mg Polyphenon E or EGCG, fl HPV DNA (cervical lesion), oral capsules or Polyphenon E, improvement in topical histology/cytology 0.5 ml EGCG 5.5–8.5%, topical M proliferation, cellular morphology, cell cycle regulation (skin lesion) 1 3 cups black tea, beverage fl DNA damage (oral mucosa)

Recently resected bladder cancer, oral leukoplakia, intestinal metaplasia of the stomach, cervical intra-epithelial neoplasia, Bowen’s disease Colorectal polyps

25

3

8 g curcumin, oral capsules

Histological improvement in 7 patients, 2 developed malignancy

150

12

83 mg isoflavones, beverage

› cell proliferation (sigmoid colon and caecum)

Green tea, High risk for hepatocellular hepatocellular 40 carcinoma carcinoma Chronic cervicitis, Green tea, cervical intra-epithelial cervical cancer41 neoplasia Green tea, skin Actinic keratoses 42 cancer Black tea, oral cancer43 Curcumin, high-risk or premalignant lesions44

Numbers recruited

PSA, prostate specific antigen; EGCG, epigallocatechin-3-gallate; HPV, human papilloma virus. › increase, fl decrease, M unchanged. Dose of polyphenol unknown.

1

increased risk of breast cancer were also unaffected by soy consumption.32 These results seem inconsistent with evidence from epidemiological and preclinical studies.75,76 It is conceivable that soy consumption throughout life has a greater influence on mammographic density than short-term exposure during middle age, or that effects may be more pronounced in women at a greater risk of developing malignancy.73 Trials of polyphenols in patients with premalignancies The ability of an agent to interfere with progression to malignancy can be tested in trials in patients with premalignant disease. Table II summarises studies of polyphenolic phytochemicals in such individuals. Assessment of cancer as an end point is advantageous as it eliminates the need to rely on surrogate biomarkers of chemopreventive efficacy. However, progression of premalignancy to frank malignancy can take years. Unfortunately, relatively few cancers are associated with a definite premalignant stage and therefore amenable to this form of trial design. Furthermore, in cases in which premalignant conditions are diagnosed and curative treatment exists, clinical interventions involving unknown agents are ethically unacceptable. PIN lends itself particularly well to this type of trial, as there is currently no specific treatment advocated at diagnosis, and serial biopsies are recommended to detect progression to prostate cancer at an early stage. A good example is a recent double-blind trial, in which individuals with high-grade PIN received either 600 mg of green tea catechins daily or placebo.38 After 1 year of treatment repeat prostate biopsies revealed a 10-fold reduction in progression to prostate cancer in those participants who received green tea. There were no significant changes in PSA. A limitation of this trial is that the major endpoint, histological progression to cancer, may not be robust. A study in which 7 pathologists reviewed a range of prostate biopsies of benign tissue, varying degrees of PIN and cancer highlights interobserver variability associated with assessment of these differences.77 Similar difficulties arise in other studies in which chemopreventive efficacy has been gauged by assessment of accompanying histological changes. Histological changes in a variety of premalignant lesions have been assessed in 25 patients following consumption of up to 8 g of curcumin daily for 3 months.

Results from this nonblinded study revealed histological improvement in 7 patients with 2 progressing to frank malignancy. A clear definition of what constituted Ôhistological improvementÕ was unfortunately not provided.68 In another study, women with chronic cervicitis or cervical intraepithelial neoplasia received green tea catechins for up to 12 weeks. A positive response in terms of histology was defined as patients showing no lesion at repeat biopsy.41 Approximately 60% of low grade cervical lesions undergo spontaneous regression78 causing difficulty in ascribing histological changes to intervention. A further difficulty arises in ensuring that the same area of tissue is biopsied when no macroscopic areas of abnormality are present. Optical mapping to precisely define lesion location has been proposed to overcome this difficulty.12

Trials of polyphenols in cancer patients Trials in which patients with cancer receive putative cancer chemopreventive agents are interpreted differently from those involving healthy individuals or patients with premalignant disease. Many studies of this type have a mixed chemoprevention- and chemotherapy-related rationale. An advantage of intervention studies in patients with cancer is that, where disease is operable, resected tissue can be analysed to gather pharmacokinetic and pharmacodynamic information in the target organ. Table III lists such trials in cancer patients conducted with polyphenolic phytochemicals. In 4 trials, patients with advanced cancer received green tea polyphenols without any detectable alterations in biomarkers or chemotherapeutic effects.46–49 In 2 of these trials the primary aims were detection of adverse effects and assessment of maximum tolerated dose, whilst evaluation of chemotherapeutic effects using clinical and radiological criteria was a secondary objective.48,49 In a chemotherapy study, in which patients with advanced lung cancer received green tea extract, disappearance of all clinical evidence of active tumour for a minimum of 4 weeks was defined as a complete response.48 A partial response was defined as a 50% or greater decrease in tumour diameter for 4 weeks. None of the 17 participants met these criteria. This result is perhaps not surpris-

455

CLINICAL TRIALS OF POLYPHENOLIC PHYTOCHEMICALS TABLE III – CLINICAL STUDIES OF POLYPHENOLIC PHYTOCHEMICALS IN PATIENTS WITH CANCER Type of polyphenol and cancer

Participants

Maximal length of treatment

Numbers recruited


Green tea, prostate cancer46 Green tea, prostate cancer47 Green tea, lung cancer48

Advanced prostate cancer

54

5 months

6 cups,1 beverage

Hormone refractory prostate cancer Advanced lung cancer

19

5 months

17

16 weeks

375 mg polyphenols, oral capsules 2.7 g/m2 polyphenols, oral capsules

Green tea, solid tumours49

Non-small cell lung cancer, head and neck cancer, mesothelioma, thymoma Advanced colorectal cancer

49

6 months

3.7 g catechins, oral capsules

15

4 months

3.6 g curcumin, oral capsules

Curcumin, colorectal cancer51

Advanced colorectal cancer

15

4 months

180 mg curcumin, oral capsules

Curcumin, colorectal cancer52 Curcumin, colorectal cancer53 Curcumin, colorectal liver metastases54 Soy, prostate cancer55

Advanced colorectal cancer

15

29 days

Operable colorectal cancer

12

7 days

Operable colorectal liver metastases Prostate cancer Gleason grade 6 Advanced prostate cancer

12

7 days

76

12 weeks

20

84 days

180 mg curcumin, oral capsules 3.6 g curcumin, oral capsules 3.6 g curcumin, oral capsules 60 mg isoflavones, beverage 898 mg isoflavones, oral capsules

Soy, prostate cancer57

Advanced prostate cancer

20

12 weeks


History of prostate cancer, elevated PSA levels

19

45 months


History of prostate cancer, elevated PSA levels Prostate cancer prior to radial prostatectomy Advanced prostate cancer, advanced colorectal cancer Operable breast cancer

62

6 months

32

31 days

13

2 doses2

17

2 weeks

Curcumin, colorectal cancer50

Soy, prostate cancer

Soy, prostate cancer

56

60

Soy, solid tumours61 Soy, breast cancer62 Soy, breast cancer

63

Post treatment for breast cancer

7

5 days

600 mg isoflavones, oral capsules 121 mg isoflavones, beverage 900 mg isoflavones, oral capsules 117 mg isoflavones, manufactured bread 8mg/kg isoflavones, oral capsules 200 mg isoflavones, oral tablet 138 mg isoflavones, oral capsules

Red clover, prostate cancer64

Prostate cancer prior to radical prostatectomy

38

54 days

160 mg isoflavones, oral capsules

Quercetin, solid tumours65

Advanced gastrointestinal cancers, ovarian cancer, melanoma, nonsmall cell lung cancer, renal carcinoma

51

Unknown3

2000 mg/m2 quercetin, intravenous infusion


fl 50% of baseline PSA value in 1 participant Disease progression in all participants (PSA/ imaging) Disease progression in all participants (clinically/ imaging) Disease progression in all participants (imaging) fl inducible PGE2, M GST and M1G (leukocytes) 1 participant exhibited stable disease for 4 months (imaging) fl GST activity, M M1G (leukocytes) 2 participants exhibited stable disease for 4 months (imaging) fl inducible PGE2 (leukocytes) fl M1G, M COX-2 (malignant colorectal tissue) › M1G (normal and malignant liver tissue) M PSA, testosterone, estradiol, SHBG (serum) fl dehydroepiandosterone (serum), M PSA, testosterone, LH M DNA damage (leukocytes) › PSA doubling time and time to progression (PSA/ imaging) fl 50% of baseline PSA value in 1 participant fl total PSA, › free/total PSA ratio › tyrosine phosphorylation (leukocytes) M apoptosis/mitosis ratio › superoxide dismutase activity (erythrocytes), M 8-OHdG (urine), ceruloplasmin (plasma) › apoptosis (prostatectomy specimens), M PSA, testosterone (serum), Gleason score (prostatectomy specimens) fl tyrosine kinase activity (leukocytes), M tumour (imaging)

PSA, prostate specific antigen; PGE2, prostaglandin E2; GST, glutathione S-transferase; M1G, malondialdehyde-DNA; COX-2, cycloxygenase-2; SHBG, sex hormone-binding globulin; LH, lutenising hormone; 8-OHdG, 8-hydroxyguanosine. › increase, fl decrease, M unchanged. 1 Exact dose of polyphenol unknown.–2Weekly dosing.–3Weekly or 3-weekly dosing.

ing, as it seems a priori unlikely that a relatively short course of a diet-derived chemopreventive agent can cause overt chemotherapeutic responses in advanced cancer. Assessment of molecular biomarkers seems more appropriate. This approach has been adopted in studies of curcumin. Patients with advanced colorectal cancer who consumed up to 3.6 g curcumin daily for up to 4 months showed a consistent reduction in inducible PGE2 levels, as an indicator of COX-2 activity, in peripheral blood samples.50,52 A significant reduction in the level of deoxyguanosine adduct

(M1G), a marker of oxidative DNA damage, occurred in malignant colorectal tissue following ingestion of 3.6 g curcumin for 7 days.53 In the case of soya isoflavones, many trials involved individuals with prostate cancer and they utilised levels of PSA as a marker of chemopreventive efficacy. When a 50% decline in serum PSA was gauged as end point, a statistically significant effect was not observed.59,58 However, smaller declines in PSA and increases in PSA doubling times have been observed in trials of soya isoflavones.58–60 The link between PSA and neoplastic progression is unclear, and the

456

THOMASSET ET AL.

FIGURE 2 – Suitable design elements in the clinical development of polyphenolic phytochemicals. PK, pharmacokinetics; PD, pharmacodynamics; crc, colorectal carcinogenesis.

currently ongoing large NCI prostate, lung, colorectal and ovarian screening trial, in which more than 30,000 men are randomised to receive an annual PSA test and digital rectal examination or usual medical care, is likely to help adjudge the suitability of PSA as a biomarker of disease.79 This insight may also clarify its value as marker of chemopreventive efficacy. Towards an optimal trial design The information shown in Tables I–III in concert with the abundantly existing preclinical information, which has frequently been reviewed,7 provides a basis for the design of trials involving polyphenolic phytochemicals. Figure 2 summarises some of these elements and illustrates a pathway for the progression of such agents from preclinical through clinical studies. In general, polyphenolic phytochemicals tend to undergo avid metabolic conjugation in the liver and gastrointestinal tract, a property which constitutes a pharmaceutical ÔAchilles heelÕ, as it reduces their systemic bioavailability.80 For polyphenols with poor bioavailability, e.g. curcumin, studies aimed at prevention of cancer of the colon, skin or oral cavity, for which systemic availability is unimportant, seem to be especially appropriate, if supported by evidence from rodent models. Experiments in rodent models have shown that levels of unabsorbed curcumin achievable in the gastrointestinal tract are consistent with pharmacological activity, based on the knowledge of its biological properties in cells in vitro. In ApcMin mice intestinal adenoma multiplicity was reduced by up to 40% by the administration of 0.2% curcumin in the diet, and the mucosal level accompanying this activity was near 100 nmol/g tissue.81 Such results hint at the rationale for exploring curcumin in human adenoma recurrence prevention trials. To gain information relevant to prepare polyphenolic

phytochemicals such as curcumin for clinical intervention, pilot studies in colorectal cancer patients who are to undergo colectomy (Ôpresurgery modelÕ) are often indicated. Such studies, exemplified by Garcea et al. for curcumin,53 allow measurement in the target tissue of suitable biomarkers and of levels of agent and metabolites. Results can then be compared with pharmacokinetic and pharmacodynamic observations, which accompanied efficacy in the rodent model. Such comparison permits a rational, albeit tentative, judgment to be made as to the chance of efficacy of the administered dose in humans. If the polyphenol under study possesses adequate systemic availability, clinical pilot studies incorporating the presurgery approach in prostate, breast, lung or other solid tumours may suitably be initiated, guided by the chemopreventive activity spectrum observed in rodent models and mindful of the range of mechanisms which it has been shown to engage in cells in vitro. In the case of green tea, which like curcumin is characterized by low systemic availability, most rodent studies have been in models of skin cancer.6 Topical application of EGCG for 18 weeks reduced the incidence of UV-induced malignant skin tumours by 66%, providing a rationale for human skin cancer chemoprevention trials.82 The bioavailability of genistein is superior to that of curcumin and green tea catchins,6 and chemopreventive activity has been observed in several rodent models of prostate and breast carcinogenesis. Therefore, genistein may be suitably developed involving the presurgery pilot study paradigm in prostate and breast cancer patients. Which polyphenol should be advanced to phase III? Tables I–III illustrate that among polyphenolic phytochemicals, green tea polyphenols have arguably been subjected to the largest

CLINICAL TRIALS OF POLYPHENOLIC PHYTOCHEMICALS

number of early clinical investigations. Results in individuals with premalignant disease who consumed green tea polyphenols (Table II) support their advancement into phase III clinical intervention trials aimed at the prevention of PIN, leukoplakia or premalignant cervical disease. Less convincing evidence exists for curcumin and soy isoflavones in premalignant disease, so that further pilot studies of these agents seem appropriate. Multiple trials of soy isoflavones in men with prostate cancer have assessed PSA as a marker of efficacy and failed to replicate results of epidemiological and preclinical studies. Therefore, evaluation of soy isoflavones in PIN utilising histological changes or progression to cancer as endpoints seems indicated. The search for, and validation of, novel biomarkers remains important. Furthermore, vigorous

457

preclinical attempts to identify novel agents with putative chemopreventive activity and low (or no) toxicity seem highly opportune. The considerable abundance in the plant kingdom of flavonoids and related polyphenols72 provides a promising hunting ground for new candidate agent identification. Among polyphenolic phytochemicals, for which promising results in preclinical models exist, even though they have thus far not been studied in the clinic, are resveratrol extracted from red grapes, xanthomulol from hops and anthocyanidins from soft berries and fruits. Their inclusion in pilot studies conducted on the lines outlined briefly earlier seems timely and appropriate, especially in the light of the recent realisation of a potential role of chemopreventive agents as enhancers of the efficacy of established cancer therapy.83

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