The role of the PGE2-aromatase pathway in obesity-associated breast inflammation

COX2 induction: a mechanism of endocrine breast cancer resistance?

PURPOSE

Urine prostaglandin E2 (PGE2) levels have shown to be a risk factor of breast cancer, and the use of nonsteroidal anti-inflammatory drugs (NSAIDs) is known to be beneficial in preventing breast cancer risk and/or recurrence with or without aromatase inhibitors. We hypothesized that the use of an aromatase inhibitor triggers the activation of the inflammatory pathway via release of PGE2.

METHODS

A single oral 25 mg dose of an aromatase inhibitor (exemestane) was given to 14 healthy postmenopausal female volunteers. Blood and urine samples were collected between 0 and 72 h post-dosing for pharmacokinetic and pharmacodynamic analysis.

RESULTS

Our findings showed that urine PGE2 levels were markedly increased 72 h after exemestane administration (average pre-dosing PGE2 levels, 4061.1 pg/mL vs. post-dosing average PGE2 levels, 10732.5 pg/mL, P = 0.001, Wilcoxon Rank Test). Out of 14 subjects enrolled in the study, one subject showed no change in PGE2; another showed a 23-fold decreased in PGE2; and the remaining 12 showed an average of 8.4-fold increase in PGE2 levels (range 1.3-30.5, standard deviation 9.2) after exemestane administration. We found no statistically significant correlations between fold increase in urine PGE2 levels and the pharmacokinetics of either exemestane or 17-hydroexemestane (major in vivo metabolite of exemestane).

CONCLUSION

Our results indicate that one of the pharmacological effects to aromatase inhibitors (e.g., exemestane) involves the activation of the inflammatory pathway via release of PGE2. Further in vitro mechanistic and in vivo translational studies designed to elucidate the role of this newly discovered effect are now warranted.

Urinary prostaglandin E2 metabolite and breast cancer risk

BACKGROUND

Levels of the cyclooxygenase 2 (COX2) enzyme are elevated in breast cancer tissue, and most COX2 effects are believed to be mediated through overproduction of prostaglandin E2 (PGE2). We evaluated associations between the primary urinary metabolite of PGE2 (PGE-M) and breast cancer risk.

METHODS

A nested case-control study of 504 cases and 1,082 controls was conducted using data from the Shanghai Women's Health Study, a large population-based prospective cohort study of 74,941 Chinese women. Urinary PGE-M was measured using a liquid chromatography/tandem mass spectrometric method. Logistic regression estimated odds ratios (OR) and 95% confidence intervals (95% CI) with adjustment for potential confounders.

RESULTS

Overall, no association between urinary PGE-M and breast cancer was detected. However, a suggestive positive association was found among postmenopausal women. In particular, a clear dose-response relationship between urinary PGE-M and breast cancer was observed among postmenopausal women with a body mass index (BMI) < 25 kg/m(2) (Plinear trend = 0.005). Among these women, risk of breast cancer increased from 1.00 (reference) to 1.06 (95% CI, 0.56-1.99), 1.50 (95% CI, 0.79-2.83), and 2.32 (95% CI, 1.24-4.41) for the lowest to highest quartiles of PGE-M, and such associations were stronger among those who were diagnosed with cancer within the first four years of sample collection. No apparent association was observed among overweight postmenopausal women (BMI ≥ 25 kg/m(2)).

CONCLUSION

High urinary PGE-M level was associated with elevated risk of breast cancer among normal weight, postmenopausal women.

IMPACT

Urinary PGE-M level may be useful for breast cancer risk assessment among normal weight, postmenopausal women. Cancer Epidemiol Biomarkers Prev; 23(12); 2866-73. ©2014 AACR.