RESUMEN
Hydroxymethylglutaryl-CoA reductase inhibitors (statins) are widely used to inhibit biosynthesis of cholesterol in individuals with elevated serum levels of this risk factor for cardiovascular disease. We find that statins are toxic to human lymphocytes in cell culture at concentrations less than 0.1 microg/ml. Addition of their own plasma reverses this toxicity in some, but not all, individuals. Addition of coenzyme Q10 (CoQ10) with plasma is more effective than plasma alone in reversing toxicity in some individuals. Apparently, two factors are required to reverse the cellular toxicity of statins: CoQ10 and a plasma factor found in a subset of individuals. These observations may provide the basis for a method to assess individual susceptibility to statin toxicity and to predict which individuals may benefit from supplements of CoQ10.
Asunto(s)
Citoprotección/efectos de los fármacos , Inhibidores de Hidroximetilglutaril-CoA Reductasas/efectos adversos , Linfocitos/efectos de los fármacos , Ubiquinona/análogos & derivados , Antioxidantes/farmacología , División Celular/efectos de los fármacos , Células Cultivadas , Coenzimas , Relación Dosis-Respuesta a Droga , Humanos , Linfocitos/citología , Plasma , Ubiquinona/farmacologíaRESUMEN
Aberrant promoter hypermethylation and associated gene silencing are epigenetic hallmarks of tumorigenesis. It has been suggested that aberrant DNA methylation can affect the sensitivity of cancers to antineoplastic agents by altering expression of genes critical to drug response. To study this issue, we used bisulfite PCR to assess DNA methylation of 32 promoter-associated CpG islands in human cancer cell lines from the National Cancer Institute (NCI) drug-screening panel (NCI-60 panel). The frequency of aberrant hypermethylation of these islands ranged from 2% to 81% in NCI-60 cancer cells, and provided a database that can be analyzed for the sensitivity to approximately 30,000 drugs tested in this panel. By correlating drug activity with DNA methylation, we identified a list of methylation markers that predict sensitivity to chemotherapeutic drugs. Among them, hypermethylation of the p53 homologue p73 and associated gene silencing was strongly correlated with sensitivity to alkylating agents. We used small interfering RNA to down-regulate p73 expression in multiple cell lines, including the resistant cell lines TK10 (renal cancer) and SKMEL28 (melanoma). Down-regulating p73 substantially increased sensitivity to commonly used alkylating agents, including cisplatin, indicating that epigenetic silencing of p73 directly modulates drug sensitivity. Our results confirm that epigenetic profiles are useful in identifying molecular mediators for cancer drug sensitivity (pharmaco-epigenomics).
Asunto(s)
Islas de CpG , Metilación de ADN , Proteínas de Unión al ADN/metabolismo , Resistencia a Antineoplásicos , Regulación Neoplásica de la Expresión Génica , Neoplasias Renales/genética , Melanoma/genética , Proteínas Nucleares/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Antineoplásicos/farmacología , Apoptosis/efectos de los fármacos , Western Blotting , Línea Celular Tumoral , Cisplatino/farmacología , Proteínas de Unión al ADN/antagonistas & inhibidores , Proteínas de Unión al ADN/genética , Ensayos de Selección de Medicamentos Antitumorales , Tolerancia a Medicamentos , Epigénesis Genética , Perfilación de la Expresión Génica , Humanos , Neoplasias Renales/tratamiento farmacológico , Neoplasias Renales/metabolismo , Melanoma/tratamiento farmacológico , Melanoma/metabolismo , Proteínas Nucleares/antagonistas & inhibidores , Proteínas Nucleares/genética , Reacción en Cadena de la Polimerasa , Regiones Promotoras Genéticas , ARN Mensajero/metabolismo , Proteína Tumoral p73 , Proteínas Supresoras de Tumor/antagonistas & inhibidores , Proteínas Supresoras de Tumor/genéticaRESUMEN
BACKGROUND: Sporadic colorectal cancers often arise from a region of cells characterized by a "field defect" that has not been well defined molecularly. DNA methylation has been proposed as a candidate mediator of this field defect. The DNA repair gene O6-methylguanine-DNA methyltransferase (MGMT) is frequently methylated in colorectal cancer. We hypothesized that MGMT methylation could be one of the mediators of field cancerization in the colon mucosa. METHODS: We studied MGMT promoter methylation by three different bisulfite-based techniques in tumor, adjacent mucosa, and non-adjacent mucosa from 95 colorectal cancer patients and in colon mucosa from 33 subjects with no evidence of cancer. Statistical tests were two-sided. RESULTS: MGMT promoter methylation was present in 46% of the tumors. Patients whose cancer had MGMT promoter methylation also had substantial MGMT promoter methylation in apparently normal adjacent mucosa. This methylation was seen with a quantitative assay in 50% (22/44; 95% confidence interval [CI] = 34% to 65%) of normal samples with MGMT promoter methylation in the adjacent tumors, 6% (3/51; 95% CI = 1% to 16%) of samples without MGMT methylation in adjacent tumors, and 12% (4/33; 95% CI = 3% to 28%) of control samples (P < .001 for comparison between each of the latter two groups and the first group). MGMT methylation was detected with a more sensitive assay in 94%, 34%, and 27% of these samples, respectively (P < .001). In grossly normal colonic mucosa of colon cancer patients, methylation was detected 10 cm away from the tumor in 10 of 13 cases. Tumors with MGMT promoter methylation had a higher rate of G-to-A mutation in the KRAS oncogene than tumors without MGMT promoter methylation (10/42 versus 3/46, P = .03). Using a sensitive mutant allele-specific amplification assay for KRAS mutations, we also found KRAS mutations in 12% (3/25; 95% CI = 2.5% to 31%) of colorectal mucosas with detectable MGMT methylation and 3% (2/64; 95% CI = 0.4% to 11%) of colorectal mucosas without MGMT methylation (P = .13). CONCLUSION: Some colorectal cancers arise from a field defect defined by epigenetic inactivation of MGMT. Detection of this abnormality may ultimately be useful in risk assessment for colorectal cancer.