This study represents a novel approach to conducting a phase I trial evaluating long-term safety and determining the optimal dose of a potential chemopreventive agent, Polyphenon E. We encountered 5 DLTs during the trial: 2 occurring within the first month on study drug and the others up to nearly 5 months on study drug. Other toxicities were generally mild and did not differ significantly compared to placebo. Although there were transient increases in liver function tests and pancreatic enzymes, there was no evidence of clinically significant liver or pancreatic disease.
The TITE-CRM is a novel statistical methodology that considers long-term (e.g., 6-month) toxicity in dose escalation, while allowing staggered participant entry. Therefore, the trial was conducted in a continuous fashion without accrual suspension. The TITE-CRM on average allocates more participants at the correct MTD, thus enhancing comparison between the placebo and the MTD on other secondary endpoints. However, in our study more women were assigned to the 400mg dose (n = 16) rather than 600mg dose (n = 11). The main advantage of the TITE-CRM is that it allows for the evaluation of long-term toxicities, unlike a conventional dose escalation method with one month of observation which may underestimate late toxicities. Thus, by allowing additional participants to be enrolled at lower dose levels, the TITE-CRM will account for late toxicities that occur after months of treatment, as well as acute toxicity that may appear in the first month. With this trial, we were able to demonstrate that an adaptive method of dose escalation that has been used extensively in cancer treatment trials may also be useful in an early phase chemoprevention trial. An alternative to defining the optimal dose by the MTD (dose with a 25% DLT rate) is to determine the minimal effective dose. One could argue that since there was no difference in urinary tea catechin levels and biomarker effects at the three dose levels of Poly E, the dose of 400mg bid (total of 800mg EGCG daily) may be preferable with a DLT rate of 6%.
This study highlights the importance of assessing long-term toxicity for any chemopreventive agent being developed for chronic use in healthy individuals. The toxicities that we observed with Poly E were consistent with the published literature. For example, we had a case of grade 3 rectal bleeding and liver function abnormalities. A 9-month study in Beagle dogs demonstrated significant GI toxicity and mortality when Poly E was administered in the fasting compared to the fed state (21
). Therefore, Poly E was administered within one hour after a substantial meal in this trial to minimize GI toxicities. A recent review reported 34 cases of hepatitis following consumption of green tea supplements used as weight loss products (22
). In a phase I dose escalation trial of Poly E 400mg to 2000mg twice daily in patients with chronic lymphocytic leukemia, 33% developed grade I transaminitis (23
). Although the pervading public perception is that dietary supplements are generally safe, these toxicities need to be taken into account when weighing the risk:benefit ratio of any chemopreventive agent.
Since individual dietary components have not been successful in preventing cancer (24
), perhaps using a polyphenolic mixture may be more effective. In a mouse model of lung carcinogenesis, the mixture of catechins with Poly E had more anti-tumor activity than EGCG alone (29
). Bioavailability is another common issue with dietary supplements and often the doses used in preclinical studies are not always achievable in humans. Previous studies have found low bioavailability of tea catechins (15
). However, when large pharmacological doses of polyphenols are orally administered, peak plasma EGCG concentrations of 5-7 μM are observed in humans, compared to 0.5 μM with green tea consumption (11
). We tested pharmacologic doses of Poly E (400-800mg twice daily or a total of 800-1600mg of EGCG daily) with the EGCG content equivalent to 8-24 cups of brewed green tea daily. We demonstrated high levels of urinary EGC and related metabolites (>150 μmol/g Cr) at these doses, compared to individuals who drink upwards of 4-5 cups of green tea daily with urinary metabolites in the 50-100 μmol/g Cr range (18
For the secondary exploratory analyses, we focused on systemic biomarkers which have been correlated with breast cancer risk, such as circulating sex steroid hormones (31
) and IGF axis markers (32
). Observational studies have correlated these biomarkers of breast cancer risk with green tea intake. In a cross-sectional study from Japan, higher serum IGF-1 levels, which have been hypothesized to promote rather than prevent cancer growth, were positively associated with green tea consumption (33
). Green tea intake has also been correlated with lower circulating estrogen levels in premenopausal and postmenopausal women (34
). Proposed mechanisms include tea polyphenols preventing binding of estrogen to its receptor in breast cancer cells (36
) and inhibition of aromatase activity (37
). In our trial, the Poly E intervention resulted in favorable but not statistically significant changes in serum estradiol and IGF-1/IGFBP-3 ratio. Since we did not adjust for multiple comparisons, we should interpret these trends in biomarker changes with caution given the small sample size. Our results are consistent with a recently published trial of 103 postmenopausal women randomized to a 2-month intervention of placebo vs. Poly E 400mg or 800mg daily (39
). Administration of Poly E did not produce consistent patterns of changes in estradiol, testosterone, SHBG, IGF-1, and IGFBP-3. Other explanations for the negative biomarker results include the relatively short-term drug intervention or Poly E mediating its effects via alternative pathways.
The most well-documented modifiable biomarkers of breast cancer risk include mammographic density (40
), Ki-67 (41
) and ER (42
) expression in benign breast tissue. One study demonstrated that daily green tea drinkers had significantly lower percent mammographic density (19.5%) than non-tea drinkers (21.7%, P=0.002) (43
). We did not observe a significant change in breast density or the Ki-67 proliferation index after 6 months of Poly E. Of note, the yield of epithelial cells from the random core biopsies and low baseline levels of Ki-67 staining in benign breast tissue may have limited our ability to detect change over time with this drug intervention. In addition, the 1-month washout period for tea consumption may have been insufficient to change baseline breast density measurements among regular green tea drinkers. ER expression in benign breast epithelium increases with age, postmenopausal status, and increasing morphologic abnormality, supporting a positive correlation with breast cancer risk (42
). We observed a nonsignificant decrease in mean ER-α expression in the Poly E and placebo groups. We did not measure catechin levels at the tissue level and a potential reason for these negative results may be due to low achievable tissue concentrations of these polyphenols. A recent trial of Poly E 800mg daily for 3-6 weeks in prostate cancer patients demonstrated low bioaccumulation of green tea polyphenols in prostate tissue (46
). Therefore, bioavailability at the tissue level may have influenced the effects of Poly E on breast tissue-based biomarkers.
Bioavailability of green tea is also influenced by host-related factors, such as genetic polymorphisms which modulate the metabolism of tea polyphenols. A single G to A transition at codon 158 of COMT
results in an amino acid change causing a 3- to 4-fold decrease in enzymatic activity (47
). Data from the Shanghai Cohort Study showed that individuals who were homozygous for the low-activity associated COMT
) had significantly lower urinary levels of tea polyphenol metabolites relative to those who had at least one high-activity allele (18
). We did not observe a significant association between COMT
genotype and urinary tea polyphenols among Poly E-treated women. However, our sample size was likely too small to show an association given the 18% incidence of the low-activity (AA
We demonstrated the feasibility of enrolling breast cancer survivors in an early phase chemoprevention trial with frequent study visits and involving invasive procedures (e.g.,
core breast biopsy). Secondary prevention trials in breast cancer survivors evaluating the contralateral breast for surrogate endpoint biomarkers is a useful clinical model for testing novel chemopreventive agents (48
). These women have a risk of developing contralateral breast primaries of 0.5-1% per year (49
). One study demonstrated a high concordance of 70% among women diagnosed with an ER-negative primary breast cancer having an ER-negative contralateral breast cancer (50
). Therefore, this serves as a relevant clinical model for testing chemopreventive agents targeting ER-negative breast cancer.
Strengths of this study include the novel adaptive study design for assessing long-term toxicity of a potential chemopreventive agent. The placebo group provided the background rate of lower grade toxicities, as well as important reference levels for all biomarkers. We had relatively good participant retention with 85% completing the 6-month evaluations. The main weakness is the relatively small sample size for assessing secondary biomarker endpoints. Future studies using this clinical model will need to account for rates of missing data due to inadequate samples for biomarker analysis, particularly for the tissue biomarkers. Our goal was to obtain preliminary data on the biological effects of Poly E, which may elucidate potential mechanisms of action that would inform future clinical efficacy trials. Ongoing trials of green tea in breast cancer include a study in 50 women with newly diagnosed ductal carcinoma in situ
given Poly E 600mg daily for 4-6 weeks prior to surgical resection (http://clinicaltrials.gov
, NCT01060345) and a placebo-controlled trial of a 1-year intervention of a green tea extract (800mg EGCG daily) in postmenopausal women with high mammographic density (NCT00917735). These trials include biomarker endpoints, such as Ki-67 and mammographic density.
In conclusion, using a novel clinical trial design for phase I testing which evaluates long-term toxicity, we determined the MTD for Polyphenon E to be 600mg bid (total of 1200mg EGCG daily), which will serve as the upper safety limit in future long-term intervention trials. We also demonstrated the bioavailability of Poly E at pharmacologic levels and the feasibility of conducting an early phase chemoprevention trial in a highly-motivated group of women with hormone receptor-negative breast cancer. However, in order to conduct more efficient chemoprevention studies, we need to validate surrogate endpoint biomarkers for short-term breast cancer risk assessment. In general, the public perception is that dietary supplements are safe and therefore may gain wider acceptance in the prevention setting compared to pharmacologic drugs. These agents need to be rigorously tested and future studies should evaluate the clinical efficacy of Poly E on biomarkers of breast cancer risk.