Chemoprevention of breast cancer

In vitro comparative models for canine and human breast cancers

During the past four decades, an increased number of similarities between canine mammary tumors and human breast cancer have been reported: molecular, histological, morphological, clinical and epidemiological, which lead to comparative oncological studies. One of the most important goals in human and veterinary oncology is to discover potential molecular biomarkers that could detect breast cancer in an early stage and to develop new effective therapies. Recently, cancer cell lines have successfully been used as an in vitro model to study the biology of cancer, to investigate molecular pathways and to test the efficiency of anticancer drugs. Moreover, establishment of an experimental animal model for the study of human breast cancer will improve testing potential anti-cancer therapies and the discovery of effective therapeutic schemes suitable for human clinical trials.

In this review, we collected data from previous studies that strengthen the value of canine mammary cancer cell lines as an in vitro model for the study of human breast cancer.

Defective DNA repair systems and the development of breast and prostate cancer (review)

Genetic defects in DNA repair and DNA damage response genes often lead to an increase in cancer incidence. The role of defects is also associated with the modulation of hormone signaling pathways. A number of studies have suggested a role for estrogen in the regulation of DNA repair activity. Furthermore, mutations or epigenetic silencing in DNA repair genes have been associated with the sensitivity of cancers to hormonal therapy. The molecular basis for the progression of cancers from hormone-dependent to hormone-independent remains a critical issue in the management of these types of cancer. In the present review, we aimed to summarize the function of DNA repair molecules from the viewpoint of carcinogenesis and hormone-related cell modulation, providing a comprehensive view of the molecular mechanisms by which hormones may exert their effects on the regulation of tumor progression.

Artemisinin selectively decreases functional levels of estrogen receptor-alpha and ablates estrogen-induced proliferation in human breast cancer cells

MCF7 cells are an estrogen-responsive human breast cancer cell line that expresses both estrogen receptor (ER) alpha and ERbeta. Treatment of MCF7 cells with artemisinin, an antimalarial phytochemical from the sweet wormwood plant, effectively blocked estrogen-stimulated cell cycle progression induced by either 17beta-estradiol (E(2)), an agonist for both ERs, or by propyl pyrazole triol (PPT), a selective ERalpha agonist. Artemisinin strongly downregulated ERalpha protein and transcripts without altering expression or activity of ERbeta. Transfection of MCF7 cells with ERalpha promoter-linked luciferase reporter plasmids revealed that the artemisinin downregulation of ERalpha promoter activity accounted for the loss of ERalpha expression. Artemisinin treatment ablated the estrogenic induction of endogenous progesterone receptor (PR) transcripts by either E(2) or PPT and inhibited the estrogenic stimulation of a luciferase reporter plasmid driven by consensus estrogen response elements (EREs). Chromatin immunoprecipitation assays revealed that artemisinin significantly downregulated the level of endogeneous ERalpha bound to the PR promoter, whereas the level of bound endogeneous ERbeta was not altered. Treatment of MCF7 cells with artemisinin and the pure antiestrogen fulvestrant resulted in a cooperative reduction of ERalpha protein levels and enhanced G(1) cell cycle arrest compared with the effects of either compound alone. Our results show that artemisinin switches proliferative human breast cancer cells from expressing a high ERalpha:ERbeta ratio to a condition in which ERbeta predominates, which parallels the physiological state linked to antiproliferative events in normal mammary epithelium.

Single-Dose and Multiple-Dose Administration of Indole-3-Carbinol to Women: Pharmacokinetics Based on 3,3′-Diindolylmethane

We have completed a phase I trial in women of the proposed chemopreventive natural product indole-3-carbinol (I3C). Women received oral doses of 400, 600, 800, 1,000, and 1,200 mg I3C. Serial plasma samples were analyzed by high-performance liquid chromatography-mass spectrometry for I3C and several of its condensation products. I3C itself was not detectable in plasma. The only detectable I3C-derived product was 3,3'-diindolylmethane (DIM). Mean Cmax for DIM increased from 61 ng/mL at the 400-mg I3C dose to 607 ng/mL following a 1,000-mg dose. No further increase was observed following a 1,200-mg dose. A similar result was obtained for the area under the curve, which increased from 329 h ng/mL at the 400-mg dose to 3,376 h ng/mL after a 1,000-mg dose of I3C. Significant interindividual quantitative variation was seen in plasma DIM values within each dosing group, but the overall profiles were qualitatively similar, with no quantifiable DIM before dosing, tmax at approximately 2 h, and DIM levels near or below 15 ng/mL (the limit of quantitation), by 24 h. Different results were obtained for 14 subjects who received a 400-mg dose of I3C after 8 weeks of twice-daily I3C dosing. Although the predose sampling occurred at least 12 h after the last known ingestion of I3C, 6 of 14 subjects exhibited Cmax for DIM in their predose plasma. Despite this high initial value, plasma DIM for all subjects decreased to near or below the limit of quantitation within the 12-h sampling period. Possible reasons for this disparity between apparent t1/2 of DIM and the high predose values are discussed.

A phase I study of indole-3-carbinol in women: tolerability and effects

We completed a phase I trial of indole-3-carbinol (I3C) in 17 women (1 postmenopausal and 16 premenopausal) from a high-risk breast cancer cohort. After a 4-week placebo run-in period, subjects ingested 400 mg I3C daily for 4 weeks followed by a 4-week period of 800 mg I3C daily. These chronic doses were tolerated well by all subjects. Hormonal variables were measured near the end of the placebo and dosing periods, including determination of the urinary 2-hydroxyestrone/16alpha-hydroxyestrone ratio. Measurements were made during the follicular phase for premenopausal women. Serum estradiol, progesterone, luteinizing hormone, follicle-stimulating hormone, and sex hormone binding globulin showed no significant changes in response to I3C. Caffeine was used to probe for cytochrome P450 1A2 (CYP1A2), N-acetyltransferase-2 (NAT-2), and xanthine oxidase. Comparing the results from the placebo and the 800 mg daily dose period, CYP1A2 was elevated by I3C in 94% of the subjects, with a mean increase of 4.1-fold. In subjects with high NAT-2 activities, these were decreased to 11% by I3C administration but not altered if NAT-2 activity was initially low. Xanthine oxidase was not affected. Lymphocyte glutathione S-transferase activity was increased by 69% in response to I3C. The apparent induction of CYP1A2 was mirrored by a 66% increase in the urinary 2-hydroxyestrone/16alpha-hydroxyestrone ratio in response to I3C. The maximal increase was observed with the 400 mg daily dose of I3C, with no further increase found at 800 mg daily. If the ratio of hydroxylated estrone metabolites is a biomarker for chemoprevention, as suggested, then 400 mg I3C daily will elicit a maximal protective effect.

Can animal models help us select specific compounds for cancer prevention trials?

Animal models provide unparalleled mechanistic insights into cancer development and potential opportunity for cancer prevention. Nevertheless, species differ markedly with regard to dietary exposures, cancer development, drug effects, and toxicity thresholds; therefore, testing in a single animal system may not predict human responses. Although replication of human cancer in animal models remains inexact, more than two decades of research have clearly yielded significant gains, as is evident in agents tested--and in certain cases, approved--for the prevention of epithelial cancers. Research efficiencies achievable through preliminary testing in genetically engineered and carcinogen-induced animal models enable us to probe genetic and signaling pathways that drive normal and neoplastic processes, and thereby figure prominently in decision trees for agent development.

Clinical trials in cancer prevention: current results and perspectives for the future

Cancer prevention remains the ideal strategy for reducing the burden of cancer on society. Progress in cancer prevention has been accelerated as prevention clinical trials are completed and reported. A promising strategy is the identification of cancer risk factors through epidemiologic and experimental research with lifestyle and medical approaches that allow translation of clinical trial results to clinical practice. A major focus of cancer prevention clinical trials has been on modulation of hormones and nutritional modifications using natural or synthetic bioactive food components for breast and prostate cancer. Breast cancer prevention clinical trials have investigated the role of estrogen antagonists with agents such as tamoxifen, raloxifene, and newer agents such as aromatase inhibitors and bioactive food components. Among the promising bioactive food components being investigated at the National Cancer Institute in prevention clinical trials to reduce breast cancer risk are indole-3-carbinol, sulforaphanes, phytoestrogen isoflavones, perillyl alcohol, and green tea polyphenols. Prostate cancer prevention trials have focused on hormone modulation with the 5-alpha-reductase inhibitor finasteride and bioactive food components such as selenium and vitamin E. Soy isoflavones, green tea polyphenols, and doxercalciferol also are being investigated for prostate cancer prevention. Future prevention clinical trials will rely on multidisciplinary medical approaches that bring together expertise in many fields to address disease across the cancer spectrum. Nutritional science can play an important role in this effort through the use of new and emerging technologies to better understand the influence of bioactive food components on the genes, proteins, and cellular processes that are associated with cancer risk.

Combinatorial chemoprevention of intestinal neoplasia

A combination of two drugs afforded remarkable protection from intestinal neoplasia in APC(Min/+) mice, a murine model of human familial adenomatous polyposis (FAP). One of the drugs was sulindac, a prototypical non-steroidal anti-inflammatory drug with established chemopreventative activity. The second drug was EKI-569, a newly developed, irreversible inhibitor of the epidermal growth factor receptor kinase. Although 100% of the untreated APC(Min/+) mice developed approximately 20 polyps, nearly half the mice treated with these two agents developed no polyps at all. These results suggest a powerful strategy for the chemoprevention of human colonic neoplasia.

Surgery, radiotherapy, and chemotherapy in carcinoma of the esophagus

Esophageal carcinoma remains a highly lethal disease that has shown a recent profound increase in prevalence and an equally dramatic epidemiologic shift. There is a well recognized causal association between gastroesophageal reflux disease and adenocarcinoma of the esophagus, and the molecular events underlying this progression from mucosal injury, to metaplasia, to dysplasia, to carcinoma are now becoming clear. Current diagnostic modalities and preoperative staging systems all have significant limitations. Fortunately, chemoprevention strategies and the identification of clinically useful molecular biomarkers that may be used to stage disease and select appropriate therapy are on the horizon. The extent of surgical resection for esophageal carcinoma remains an area of great controversy. Disease that is confined to the mucosa is being diagnosed more commonly, and endoscopic ablative techniques have been proposed. To date, however, preoperative discrimination of tumor depth and presence of regional nodal metastases remains inadequate in these very early lesions, and caution is urged before adopting therapies that may compromise cure. For disease penetrating the mucosa, the extent of surgical therapy must be tailored by the objectives of treatment (cure vs palliation) and preoperative stage. Surgical resection is the current standard of care, with combined-modality therapy reserved for prohibitive surgical candidates. No clear survival benefit has been documented for neoadjuvant radiotherapy or chemotherapy alone. The results of preoperative combined-modality therapy, including three prospective, randomized trials, are encouraging but to date have not shown a definite benefit.

Incidence of BRCA1/2 germ line alterations in a high risk cohort participating in a phase II chemoprevention trial

It is unknown what proportion of women at high risk for breast cancer, entering phase II chemoprevention trials, have BRCA1/2 alterations, and whether their initial biomarker patterns or response to preventive interventions will differ between carriers and non-carriers. As part of a 6-month phase II chemoprevention trial of diflouromethlyornithine (DFMO), high-risk subjects (family history, prior precancerous breast disease or prior breast cancer), who had random peri-areolar fine needle evidence of epithelial hyperplasia with or without atypia, were offered genetic counselling and testing at the completion of their study participation. 97% of the 119 women eligible for testing underwent BRCA1/2 gene sequencing, 3 declined. 26 (22%) of the 116 women had an alteration in BRCA1/2. Known deleterious mutations were present in 3 (3%), uncertain significance mutations in 19 (16%), and probable polymorphisms in 6 (5%). There does not appear to be a difference in initial biomarker distribution between participants with and without germ line alterations.

Evaluation and treatment of BRCA-positive patients

The recent discovery of the breast cancer-associated genes BRCA1 and BRCA2 has now made it possible to identify individuals who are at a very high risk for the future development of breast cancer. To some extent, however, society has fallen victim to its molecular genetic technology. The significance of these discoveries to the detection, treatment, and prevention of breast cancer cannot be overstated. Nevertheless, the appropriate administration and interpretation of BRCA genetic testing and the treatment of BRCA-positive patients remain controversial issues. Complexities of BRCA testing require that such genetic screening be restricted to selected high-risk patients and that test results be interpreted by a knowledgeable molecular geneticist. Although no medical prophylaxis has been demonstrated to be of benefit in BRCA-positive patients, recent evidence suggests that a prophylactic mastectomy, with or without reconstruction, is a reasonable treatment option that substantially reduces cancer risk.