Benzylmorpholine analogs as selective inhibitors of lung cytochrome P450 2A13 for the chemoprevention of lung cancer in tobacco users.

PURPOSE: 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), one of the most prevalent and procarcinogenic compounds in tobacco, is bioactivated by respiratory cytochrome P450 (CYP) 2A13, forming DNA adducts and initiating lung cancer. CYP2A13 inhibition offers a novel strategy for chemoprevention of tobacco-associated lung cancer. METHODS: Twenty-four analogs of a 4-benzylmorpholine scaffold identified by high throughput screening were evaluated for binding and inhibition of both functional human CYP2A enzymes, CYP2A13 and the 94%-identical hepatic CYP2A6, whose inhibition is undesirable. Thus, selectivity is a major challenge in compound design. RESULTS: A key feature resulting in CYP2A13-selective binding and inhibition was substitution at the benzyl ortho position, with three analogs being >25-fold selective for CYP2A13 over CYP2A6. CONCLUSIONS: Two such analogs were negative for genetic and hERG toxicities and metabolically stable in human lung microsomes, but displayed rapid metabolism in human liver and in mouse and rat lung and liver microsomes, likely due to CYP2B-mediated degradation. A specialized knockout mouse mimicking the human lung demonstrates compound persistence in lung and provides an appropriate test model. Compound delivered by inhalation may be effective in the lung but rapidly cleared otherwise, limiting systemic exposure.

Spectral modification and catalytic inhibition of human cytochromes P450 1A1, 1A2, 1B1, 2A6, and 2A13 by four chemopreventive organoselenium compounds.

Several organoselenium compounds including benzyl selenocyanate (BSC), 1,2-phenylenebis(methylene)selenocyanate (o-XSC), 1,3-phenylenebis(methylene)selenocyanate (m-XSC), and 1,4-phenylenebis(methylene)selenocyanate (p-XSC) have been shown to prevent cancers caused by polycyclic aromatic hydrocarbons (PAHs) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in experimental animals; these chemical carcinogens are activated by human P450 1 and 2A family enzymes, respectively, to carcinogenic metabolites. In this study, we examined whether these selenium compounds interact with and inhibit human P450 1 and 2A enzymes in vitro. Four organoselenium compounds induced reverse Type I binding spectra with P450 1A1, 1A2, and 1B1 and Type I binding spectra with P450 2A6 and 2A13. The spectral dissociation constants (K(s)) for the interaction of P450 1B1 with these chemicals were 3.6-5.7 µM; the values were lower than those with seen with P450 1A1 (19-30 µM) or 1A2 (6.3-13 µM). The K(s) values for Type I binding of P450 2A13 with m-XSC and BSC were both 0.20 µM; the values were very low compared to those for the interaction of P450 2A6 with m-XSC (5.7 µM) and BSC (2.0 µM). Four selenium compounds directly inhibited 7-ethoxyresorufin O-deethylation activities catalyzed by P450 1A1, 1A2, and 1B1 with IC(50) values <1.0 µM, except for the inhibition of P450 1A2 by BSC (1.3 µM). Coumarin 7-hydroxylation activities of P450 2A13 were more inhibited by four selenium compounds than those of P450 2A6, with IC(50) values of 0.22-1.4 µM for P450 2A13 and 2.4-6.2 µM for P450 2A6. Molecular docking studies of the interaction of four organoselenium compounds with human P450 enzymes suggest that these chemicals can be docked into the active sites of these human P450 enzymes and that the sites of the selenocyanate functional groups of these chemicals differ between the P450 1 and 2A family enzymes.

[Methyldopa-induced acute reactive hepatitis in pregnancy, drug-metabolizing capacity of the liver]. / Methyldopa által indukált akut reaktív hepatitis terhességben, a máj gyógyszer-metabolizáló képességének alakulása.

Alpha-methyldopa is a regularly used antihypertensive drug during pregnancy. Methyldopa, which decreases the sympathoadrenal system, is the first drug of choice since decades. The reactive hepatitis is not frequent, but known serious side effect of alpha-methyldopa. In non-pregnant women the estimated rate of manifest hepatotoxicity is 2.5-10%. In our case, gestation hypertension developed at the 21st gestation week of a 35 year-old pregnant woman. Oral methyldopa, a central alpha adrenergic blocker therapy was introduced. On the 23rd gestation week acute hepatitis developed. During differential diagnosis of hepatitis, the etiology of methyldopa was taken into account. Viral and autoimmune origin was rolled out. No fetal aberration was found during ultrasound examination. The function of drug metabolizing function from blood was measured by CYP phenotyping (CYP gene expression analysis). CYP3A4 enzyme plays a primary role in the metabolism of nifedipine. Antihypertensive therapy was changed from methyldopa to nifedipine. Nifedipine dosage was based on the value of CYP3A4 gene expression. With the reduced nifedipine therapy (30 mg daily), blood pressure was successfully under control. The diagnosis of alpha-methyldopa induced hepatitis was based on anamnesis, clinical picture and the results of chemical and radiological examination and confirmed by the level of drug-metabolizing capacity. The gestation hepatotoxicity of alpha-methyldopa was reported first in 1969 by Elkington Smith, who suggested the monitoring of serum aminotransferase during alpha-methyldopa therapy in pregnancy in their case report. Our case report confirms that monitoring of serum aminotransferase level is still valuable when treating a pregnant woman with alpha-methyldopa.

[Possibility of correction of the lipid disorders in patients with cholelithiasis and gallbladder cholesterosis].

OBJECTIVE: To evaluate the possibility of incorporating organic drugs Hepatosan and Entherosan in the complex therapy of patients with gallstone disease and gall bladder cholesterosis (reticulated polypus form) on the basis of literature data and own research. RESULTS: It has been found that the physiological effect of drugs Entherosan and Hepatosan is directed on the improvement cavity and wall digestion processes, that leads to the reduction (disappearance) of dyspeptic symptoms (eliminating discomfort in the epigastrium, bloating, diarrhea) in most of the patients. The main features of Entherosan are: normalization of gastro-intestinal tract motor activity, intestinal microflora, enteroprotective effect of the drug and its influence on intestinal and cellular pools of cholesterol that leads to the activation of cavitary and parietal digestion. The essential point of Hepatosan is to stimulate 7alpha-hydroxylase, resulting in strengthening of cholesterol oxidation and to an increase the pool of LCD in enterohepatic circulation. This factor, coupled with hepatoprotective action of the drug, ensures the deletion of biliary insufficiency. CONCLUSION: The incorporation of drugs Entherosan and Hepatosan in the complex conservative therapy of cholelithiasis and reticulated polypus forms of gall bladder cholesterosis is pathogenetically substantiated.

Altered cytochrome p450 metabolism of calcineurin inhibitors: case report and review of the literature.

A 19-year-old woman was admitted to receive a kidney transplant from a nonliving donor. At the time of transplantation, she was taking oral phenytoin 300 mg every morning, 100 mg at noon, and 300 mg every evening (total of 700 mg/day) to treat seizures secondary to hemodialysis. Immediately after the transplantation, phenytoin treatment was resumed, and immunosuppressive therapy consisting of antithymocyte globulin, cyclosporine, mycophenolate mofetil, and corticosteroids was started. Her cyclosporine blood levels varied over the first 10 days after transplantation. Cyclosporine was discontinued, and tacrolimus was begun after acute rejection was discovered. The rejection was treated with antithymocyte globulin, plasmapheresis, and intravenous immunoglobulin, and subsequently resolved; however, the patient's blood concentrations of tacrolimus varied widely. Phenytoin is an antiepileptic drug that induces hepatic enzymes, affecting the cytochrome P450 3A family. These enzymes metabolize approximately 50% of all prescribed drugs, including cyclosporine and tacrolimus. According to the Naranjo adverse drug reaction probability scale, this patient's adverse drug reaction probably occurred from altered metabolism of cyclosporine and tacrolimus due to phenytoin therapy. Clinicians must identify drug interactions between metabolic enzyme inducers or inhibitors and drug substrates with narrow therapeutic ranges, closely monitor drug concentrations, and observe patients for clinical signs and symptoms of therapeutic failure or toxicity. In daily practice, clinicians should explore the metabolic characteristics of drugs and their biotransformation pathways to identify patients who require alternative therapy.

[Clopidogrel and proton pump inhibitors: insufficient evidence of interaction]. / Clopidogrel en protonpompremmers: onvoldoende bewijs van interactie.

As both proton pump inhibitors (PPIs) and clopidogrel are metabolized by CYP2C19, an enzyme of the cytochrome P450 system, this could lead to drug competition. Recent studies have raised concerns that interaction of PPIs and clopidogrel could reduce the efficacy of clopidogrel and thus increase events such as myocardial infarction. This has resulted in opposing opinions and controversial recommendations. Optimal protection of patients at high risk for cardiovascular events is warranted. On the other hand, optimal gastroprotection for patients at risk for gastrointestinal bleeding is of clinical relevance. Despite the large number of studies, current evidence does not support the existence of an interaction between PPIs and clopidogrel. In agreement with international guidelines the approach of providing this combination therapy to those patients with an accepted indication for gastroprotection and secondary cardiovascular prevention is justified.

Effects of benzyl and phenethyl isothiocyanate on P450s 2A6 and 2A13: potential for chemoprevention in smokers.

Isothiocyanates have been shown to be potent inhibitors of carcinogenesis in animals exposed to a number of chemical carcinogens including the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In this study the effects of benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC), two naturally occuring isothiocyanates, on P450 2A6 and 2A13 were investigated. P450s 2A6 and 2A13 are thought to be the primary human P450 enzymes responsible for the in vivo metabolism of nicotine and NNK, respectively. In vitro, BITC and PEITC efficiently inhibited P450 2A6- and 2A13-mediated coumarin 7-hydroxylation. The inhibition of P450 2A6 and 2A13 by BITC was non-competitive with KI's of 4.1 and 1.3 microM, respectively. PEITC was a more potent inhibitor of both enzymes than BITC, with a KI of 0.37 microM for P450 2A6 and 0.03 microM for P450 2A13. P450 2A6-mediated metabolism of nicotine and P450 2A13-mediated alpha-hydroxylation of NNK were also inhibited significantly by these two isothiocyanates. Both BITC and PEITC were able to inactivate P450 2A6 and 2A13 in an NADPH-dependent manner potentially through the formation of adducts to the apoprotein. The potent inhibition of P450 2A6- and 2A13-mediated metabolisms together with the ability of BITC and PEITC to inactivate the enzymes suggests the possibility that these isothiocyanates could be developed as chemopreventive agents to protect smokers who are unwilling or unable to quit smoking against lung cancer.

In vitro evaluation of cytochrome P450-mediated drug interactions between cytarabine, idarubicin, itraconazole and caspofungin.

PURPOSE: Antifungal prophylaxis is an important component of induction therapy for patients with acute myeloid leukemia (AML). Azole antifungal agents are increasingly used in this context. In vitro assays were performed to assess whether cytochrome P450 (CYP450) enzymes were affected by combinations of cytarabine or idarubicin with itraconazole or caspofungin. METHODS: The high throughput microtiter assay was used to determine whether cytarabine, idarubicin and itraconazole or caspofungin were CYP450 isoenzyme substrates, inhibitors of CYP450 isoenzymes, and to determine potential CYP450 metabolism interactions between these agents. RESULTS: Idarubicin is a substrate for CYP450 2D6 and 2C9. Cytarabine is a substrate of CYP450 3A4. Idarubicin inhibits CYP450 2D6, and cytarabine, itraconazole, and caspofungin inhibit CYP450 3A4. Cytarabine metabolism was significantly decreased when combined with caspofungin or itraconazole. CONCLUSIONS: The inhibition of cytarabine metabolism may have important clinical implications. These in vitro findings warrant investigation with in vivo pharmacokinetic studies.

Pharmacological modification of epidermal detoxification systems.

The skin is a major interface between the body and the environment and possesses membrane-bound cytochrome P-450-dependent enzyme activity that is capable of both detoxifying endogenous and exogenous substrates and enhancing the toxic effects of selected substances. The use of chemical inhibitors of enzyme activation by P-450-dependent enzymes represents one possible approach to controlling toxic responses in target tissue such as the skin. Our data indicate that certain polyphenols and imidazoles are potent inhibitors of epidermal carcinogen metabolism, and of the DNA binding and the carcinogenicity of PAHs such as BP. The use of such agents may offer a novel approach to the prevention of environmentally induced cancer.