Modulation of gene expression in subjects at risk for colorectal cancer by the chemopreventive dithiolethione oltipraz.

Prolonged exposure to mutagenic substances is strongly associated with an individual's risk of developing colorectal cancer. Clinical investigation of oltipraz as a chemopreventive agent is supported by its induction of the expression of detoxication enzymes in various tissues, and its protective activity against the formation of chemically induced colorectal tumors in animals. The goals of the present study were: to determine if oltipraz could induce detoxicating gene expression in human tissues; to identify effective non-toxic doses for more extensive clinical testing; and to establish a relationship between effects in the colon mucosa and those in a more readily available tissue, the peripheral mononuclear cell. 24 evaluable patients at high risk for colorectal cancer were treated in a dose-finding study with oltipraz 125, 250, 500, or 1,000 mg/m2 as a single oral dose. Biochemical analysis of sequential blood samples and colon mucosal biopsies revealed increases in glutathione transferase activity at the lower dose levels. These effects were not observed at the higher doses. More pronounced changes were observed in detoxicating enzyme gene expression in both tissues at all doses. Peripheral mononuclear cell and colon mRNA content for gamma-glutamylcysteine synthetase (gamma-GCS) and DT-diaphorase increased after dosing to reach a peak on day 2-4 after treatment, and declined to baseline in the subsequent 7-10 d. The extent of induction of gene expression in colon mucosa reached a peak of 5.75-fold for gamma-GCS, and a peak of 4.14-fold for DT-diaphorase at 250 mg/m2 ; higher doses were not more effective. Levels of gamma-GCS and DT-diaphorase correlated closely (P < or = 0.001) between peripheral mononuclear cells and colon mucosa both at baseline and at peak. These findings demonstrate that the administration of minimally toxic agents at low doses may modulate the expression of detoxicating genes in the tissues of individuals at high risk for cancer. Furthermore, peripheral mononuclear cells may be used as a noninvasive surrogate endpoint biomarker for the transcriptional response of normal colon mucosa to drug administration.

Glutathione S-transferase activity and glutathione S-transferase mu expression in subjects with risk for colorectal cancer.

The glutathione S-transferases (alpha, mu, and pi), a family of Phase II detoxication enzymes, play a critical role in protecting the colon mucosa by catalyzing the conjugation of dietary carcinogens with glutathione. We investigated the efficacy of using the glutathione S-transferase (GST) activity of blood lymphocytes and GST-mu expression as biomarkers of risk for colorectal cancer. GST activity was measured in the blood lymphocytes of control individuals (n = 67) and in the blood lymphocytes (n = 60) and colon tissue (n = 34) of individuals at increased risk for colon cancer. Total GST activity was determined spectrophotometrically with the use of 1-chloro-2,4-dinitrobenzene as a substrate. The ability to express the um subclass of GST was determined with the use of an ELISA. Although interindividual variability in the GST activity of blood lymphocytes was greater than 8-fold (range, 16.7-146.8 nmol/min/mg), the GST activity of blood lymphocytes and colon tissue within an individual was constant over time and was unrelated to sex, age, or race. The GST activity of blood lymphocytes from high-risk individuals was significantly lower than that of blood lymphocytes from control individuals (P < or = 0.004). No association was observed between the frequency of GST-mu phenotype and risk for colorectal cancer. Blood lymphocytes from high-risk individuals unable to express GST-mu had lower levels of GST activity than did those from control subjects with the GST-mu null phenotype; however, this difference was significant in male subjects only (P < or = 0.006). Analysis of paired samples of blood lymphocytes and colon tissue indicated a strong correlation between the GST activity of the two tissue types (Spearman's rank correlation, r = 0.87; P < or = 0.0001). The GST activity of blood lymphocytes may be used to identify high-risk individuals with decreased protection from this Phase II detoxication enzyme who may benefit from clinical trials evaluating GST modulators as chemopreventive agents for colorectal cancer. The GST activity of blood lymphocytes may also be used in colorectal cancer chemoprevention trials to monitor the responsiveness of colon tissue to regimens that modify Phase II detoxication enzymes.

Preclinical and clinical evaluation of broccoli supplements as inducers of glutathione S-transferase activity.

Previous studies suggest that cruciferous vegetables may provide protection against carcinogen exposure by inducing detoxification enzymes. ICR(Ha) mice were gavaged with broccoli tablets (1 g/kg), and colon tissues were collected after treatment. Glutathione S-transferase (GST) activity was assayed and peaked on days 1 and 2 after treatment, respectively (P = 0.03). Elevations in GST activity were attributed to the increased expression of mu and pi. These data supported a clinical assessment of broccoli supplements. Twenty-nine subjects at increased risk for colorectal cancer were randomized to group 1 (no cruciferous vegetables) or group 2 (broccoli supplements, 3 g/day) for 14 days. Blood samples and colon biopsies were obtained pre- and postintervention. No significant difference was observed between the GST activities of the control and broccoli supplementation groups posttreatment. Mean lymphocyte GST activity was 107% of baseline in the broccoli supplementation group (range, 79-158%) and 102% of baseline in the control group (range, 75-158 percent;). Correlation of the GST activities of blood lymphocytes and colon mucosa taken simultaneously suggested that the GST activity of blood lymphocytes may be used as a biomarker of the responsiveness of colon tissue to chemopreventive regimens. Future clinical studies evaluating cruciferous vegetables should consider using concentrated dietary supplements in subjects with a previous history of colorectal cancer.

Phase I pharmacokinetic trial of perillyl alcohol (NSC 641066) in patients with refractory solid malignancies.

Perillyl alcohol (POH) is a monoterpene with anticarcinogenic and antitumor activity in murine tumor models. Putative mechanisms of action include activation of the transforming growth factor beta pathway and/or inhibition of p21ras signaling, leading to differentiation or apoptosis. In this Phase I trial, 17 patients took POH p.o. three times daily for 14 days of each 28-day cycle. The starting dose of POH was 1600 mg/m2/dose, with escalations to 2100 and 2800 mg/m2/dose in subsequent cohorts. Chronic nausea and fatigue were dose-limiting toxic effects at 2800 mg/m2. Grade 1-2 hypokalemia was common at 2100 and 2800 mg/m2. Although POH could not be detected in plasma, two of its metabolites, dihydroperillic acid (DHPA) and perillic acid (PA), were measured in plasma and urine on days 1 and 15 after the first and last doses of POH, respectively. Both area under the concentration versus time curve and peak plasma concentration (Cmax) values increased with dose and exhibited high intersubject variability. Day 15 DHPA Cmax values ranged from a mean +/- SD of 22.6+/-12 microM at 1600 mg/m2/dose to 42.4+/-15.24 microM at 2800 mg/m2/dose. Corresponding mean +/- SD Cmax values for PA were 433.2+/-245.8 and 774.1+/-439.6 microM. One patient treated at the 2800 mg/m2/dose had markedly prolonged plasma levels of both PA and DHPA and developed grade 3 mucositis. POH treatment did not consistently alter the expression of p21ras, rap1, or rhoA in peripheral blood mononuclear cells obtained from patients treated at the highest dose level. The metabolites PA and DHPA did not change expression or isoprenylation of p21ras in MCF-7 breast or DU145 prostate carcinoma cells at concentrations that exceeded those achieved in patient plasma after POH treatment. We conclude that POH at 1600-2100 mg/m2 p.o. three times daily is well tolerated on a 14-day on/14-day off dosing schedule. Inhibition of p21ras function in humans is not likely to occur after POH administration at safe doses of the present oral formulation.

Glutathione S-transferases--biomarkers of cancer risk and chemopreventive response.

The critical role of the glutathione S-transferase (GST) multigene family in cellular protection in combination with the large interindividual variability in the expression of these enzymes has prompted an investigation of their importance in cancer prevention and susceptibility. Previous preclinical and clinical studies from this laboratory have established an association between decreased GST activity and increased risk for colorectal cancer. Based upon the increased incidence of colon malignancies among patients with ulcerative colitis, GST activity has been examined in a mouse model of induced colitis. Significant decreases (50% of controls) in the GST activity of colon tissue were observed during the establishment and progression of colitis. These data suggested that depletion of cellular protection may be an important event in the carcinogenic progression of ulcerative colitis. The ability of the dithiolthione oltipraz to induce GST expression within the murine colon has been demonstrated. Use of chemopreventive regimens to induce phase 2 detoxication enzyme expression represents a promising strategy for the prevention of cancer. Clinical studies revealed that the GST activity of blood lymphocytes from individuals with either a personal or family history of colorectal cancer or a personal history of colon polyps was decreased significantly when compared to that of healthy controls. Phase 1 clinical evaluation of oltipraz has demonstrated its ability to induce GST activity as well as the level of transcripts encoding gamma-glutamylcysteine synthetase (gamma-GCS) and DT-diaphorase in the colon mucosa of individuals at increased risk for colorectal cancer. The observed correlation between the posttreatment response in blood lymphocytes and colon mucosa suggested that blood lymphocytes may be used in future trials as a surrogate biomarker of the responsiveness of colon tissue to chemopreventive regimens.

Chemoprevention of cancer.

Chemoprevention is a strategy used to block the development of cancers in human beings. This emerging field has broad potential for influencing cancer incidence rates in defined high-risk groups and the general population. In this review, we define some of the mechanisms of carcinogenesis, describe some of the genetic markers of carcinogenesis, and list possible biomarkers that may serve as surrogate end points in chemoprevention studies. A major component of this review is a description of the agents that are currently under investigation in animal systems or in human trials. They are grouped according to the agents that block or suppress mutation, such as oltipraz, selenium, vitamin C and the flavones, or according to agents that block promotion and proliferation, such as difluoromethylornithine, tamoxifen, nonsteroidal antiinflammatory drugs, and the vitamin A derivatives. We describe the issues that are considered in the design of chemoprevention trials and in the phase I, II, and III components of these trials. The following national trials are discussed: the Breast Cancer Prevention Trial, which uses tamoxifen; the Prostate Cancer Prevention Trial, which uses finasteride; and a Lung Cancer Prevention Trial, which uses 13-cis-retinoic acid. The review ends with some insights about future studies in chemoprevention.

Trimodality therapy for advanced gallbladder cancer.

We conducted a retrospective review of all patients who underwent surgical extirpation for stage III, stage IV, or recurrent carcinoma of the gallbladder. Between 1991 and 1999 ten patients underwent surgical resection for advanced gallbladder cancer. All patients received adjuvant therapy either pre- or postoperatively. Radiotherapy was used in all patients and chemotherapy in 90 per cent of patients. Two patients subsequently underwent resection for locally recurrent disease. An additional patient with stage II disease initially was also treated surgically for a local recurrence. Surgical management involved cholecystectomy and resection of various amounts of liver surrounding the gallbladder bed and regional lymphadenectomy. Contiguously involved structures were resected en bloc. Resection of recurrent disease included excision of all gross tumor. The median overall survival excluding the one 30-day mortality was 53.6 months (range 8-73 months). Four patients have survived 4 or more years, and currently four patients are alive and disease free at 73, 49, 33, and 8 months. Median disease-free interval after each resection of recurrent disease was 13.8 months (range 4-28 months). We conclude that trimodality therapy in selected patients with stage III, IV, or recurrent carcinoma of the gallbladder is possible and may result in prolonged survival.

Chronic dosing of oltipraz in people at increased risk for colorectal cancer.

The dithiolethione oltipraz is being developed as a chemopreventive agent for many malignancies, including colorectal cancer, on the basis of its in vivo protective activity against chemically induced tumors in a variety of animal models. This protection has been associated with an enhanced capacity to detoxify reactive carcinogens and, more recently, with increased DNA repair. In a previous single-dose study, elevated detoxification gene expression was observed in the days after oltipraz dosing. Now, in this clinical study, we evaluated the effects of oltipraz when given over a 3-month period. Fourteen individuals with increased risk for colorectal cancer were randomly assigned to one of two oral doses (125 or 250 mg/m2) of oltipraz twice weekly for 12 weeks. Two of seven subjects at the 250 mg/m2 dosage required dose reductions, owing to significant fatigue. The 125 mg/m2 dose level was well tolerated by all patients. Blood or colon tissue (or both) for evaluation of glutathione, glutathione S-transferase, DT-diaphorase activity, and DT-diaphorase mRNA expression were obtained prior to treatment and at weeks 6, 12, and 16. No significant modulation of phase II detoxification enzymes was seen at either dose studied during this period. Phase II trials evaluating a tolerable regimen of oltipraz (as demonstrated in this study) and other possible mechanisms that may be responsible for the protective activity of oltipraz should be pursued.