Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ligandin is an abundant soluble protein of relatively short half life which is induced by many drugs and chemicals and stabilized in the absence of thyroid hormone. The protein is strategically concentrated in cells associated with transport and detoxification of a large variety of potential endogenous ligands such as bilirubin and perhaps heme, and exogenous, such as a multitude of drugs and chemicals. The protein is a dimer in rat liver. Whether it is a primary gene product or whether at least two genes are involved is not known. The protein has broad, low affinity catalytic activity for ligands having electrophilic groups and hydrophobic domains. It either catalyzes formation of GSH conjugates (e.g. bromosulphophthalein), noncovalently binds prior to biotransformation or excretion in bile (e.g. bilirubin), or covalently binds (e.g. activated carcinogens) potential ligands. Recent studies expand the scope of ligandinology to include its possible role in chemical carcinogenesis, diagnosis of inflammatory and neoplastic disease of the liver and kidney, and participation in intracellular transport. Although some of the roles that have been outlined are speculative, any single function is important. These are primitive enzymes and nonspecific binding proteins but "it is precisely their simplistic design that allows such protein serviceability".
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PMID:Ligandin: review and update of a multifunctional protein. 39 5

N-methyl-N-nitrosourea (MNU), N-(2-chloroethyl)-N'-(trans-4-methylcyclohexyl)-N-nitrosourea (methylCCNU), and N,N'-bis(2-chloroethyl)-N-nitrosourea (BCNU) were examined for their effect on glutathione (GSH) levels of various tissues of normal and L1210-leukemic mice. BCNU produced significant decreases in the GSH levels of livers of both groups, but caused no change in the GSH content of the L1210 tumor or in the lungs. The GSH content of the kidneys of L1210 tumor-bearing mice, however, was significantly decreased by BCNU at early time points. A small increase in the liver content of oxidized glutathione could not account for the decrease content of GSH. Methyl CCNU and MNU were without effect on any of the tissues examined. These data are consistent with our previous observation that BCNU is a substrate for GSH S-transferase, and suggest that a GSH-dependent process is an important pathway for the metabolism of BCNU.
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PMID:Reduction of glutathione levels in livers of mice treated with N,N'-bis (2-chloroethyl)-N-nitrosourea. 45 78

54 Tumors of Mastomys natalensis (GRA Giessen), described in the literature as "Keratoacanthomas" were investigated by light and electron microscopy. They are induced by a virus of the Papova group. Their histogenesis and their course are very different from human keratoacanthoma. The results reveal problems related to experimental animal tumour models and the similarities of different malignancies in the nomenclatures of several disciplines.
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PMID:["Keratoacanthomas" in mastomys natalensis (author's transl)]. 121 73

This prospective study was undertaken to substantiate observations that glutathione (GSH) inhibits or reverses tumor growth in humans with hepatocellular carcinoma (HCC), a neoplasm with an extremely poor prognosis. Eight patients with biopsy-proven HCC not amenable to surgery were given 5 g of GSH daily from the time of diagnosis. Two patients withdrew shortly after receiving GSH due to intolerable side-effects. Of the six eligible patients, two had mildly advanced tumors and four moderately advanced tumors. At 1-2-month intervals the liver was CT and ultra-sound scanned to assess the growth status of the tumor (progression, stagnation or regression). All the patients, except a male with a fibrolamellar type of HCC, died within 1 year after diagnosis. Two women with moderately advanced tumors survived almost 1 year, tumor growth stopped or regressed and in one of the women an initially abnormal alfa-1-fetoprotein (AFP) returned to normal after GSH treatment. AFP remained normal throughout the treatment period in the other women. These observations indicate that GSH may have a sex-dependent effect on HCC. However, further studies involving more patients are required to pursue this hypothesis.
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PMID:Glutathione treatment of hepatocellular carcinoma. 128 Mar 15

The oncosuppressive effect of melatonin on 9,10-dimethyl-1,2-benzanthracene (DMBA) induced rat mammary tumorigenesis led us to assess its possible modulatory influence on representative hepatic and mammary drug metabolizing enzymes in DMBA treated female Holtzman rats, reared in short and long photoperiods. Melatonin treated rats in either photoperiod showed a significant induction in hepatic and mammary levels of glutathione (GSH) and cytosolic activities of glutathione S-transferase (GST) when compared with the corresponding controls, along with a significant drop in hepatic microsomal contents of cytochromes b5 and P450. This induction of GSH and GST, and depletion of cytochromes b5 and P450 by melatonin may possibly be related to its anticarcinogenic potential in this tumor model.
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PMID:A possible modulatory influence of melatonin on representative phase I and II drug metabolizing enzymes in 9,10-dimethyl-1,2-benzanthracene induced rat mammary tumorigenesis. 128 33

Tumour levels of O6-alkylguanine-DNA-alkyltransferase (O6 AT) and glutathione content (GSH) were correlated with 1, 3-Bis (2-chloroethyl)-1-nitrosourea (BCNU) sensitivity in two human ovarian cancer xenografts (HOC8 and HOC18) and in two human glioblastoma xenografts (HG12 and HG15). HOC8 and HOC18, which were not responsive to BCNU treatment, showed O6 AT levels 14 and 23-fold higher than HG12 that was moderately sensitive to the same BCNU treatment. HG15, which was more sensitive to BCNU than HG12, showed significantly lower O6 AT levels. GSH levels were similar in all tumor xenografts. These data further stress the importance of O6 AT level as a relevant parameter for nitrosourea response in human tumours.
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PMID:Tumour levels of O6-alkylguanine-DNA-alkyltransferase and sensitivity to BCNU of human xenografts. 129 58

Platinum-based chemotherapy has led to an improvement in complete response rates and duration of median remission, but has only given a modest improvement in overall survival in patients with advanced ovarian cancer. Chemotherapy will in the future focus upon: (1) improving the complete remission rate with new induction regimens; (2) identifying strategies capable of converting partial remission into complete remission; (3) preventing or delaying recurrences in patients who do achieve a complete remission; (4) identifying mechanisms of antineoplastic drug resistance and pharmacologic techniques capable of reversing drug resistance. Among the treatment approaches being utilized are high-dose chemotherapy with autologous bone marrow transplantation, development of new chemotherapeutic regimens which include Taxol and hexamethylmelamine, and intraperitoneal chemotherapy. In addition, our understanding of the mechanisms of antineoplastic drug resistance has led to the development of novel therapeutic approaches. It has been demonstrated that resistance to platinum and alkylating agents is associated with both increased concentrations of cellular glutathione (GSH) as well as an increased capacity of tumor cells to repair damage to DNA. Inhibition of GSH biosynthesis with buthionine sulfoximine (BSO), a synthetic inhibitor of the enzyme gamma glutamyl cysteine synthetase, has led to the potentiation of alkylating agent activity in vitro and in vivo. A phase I trial of BSO plus melphalan is currently in progress and a trial of BSO plus carboplatin is planned. Inhibition of the DNA repair process with aphidicolin potentiates the cytotoxicity of cisplatin in drug-resistant tumor cells. Clinical trials of aphidicolin plus cisplatin await the completion of ongoing phase I trials of aphidicolin.
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PMID:Role of chemotherapy in the future treatment of ovarian cancer. 135 5

Mechanisms of tumor resistance to 4-hydroperoxycyclophosphamide (4-HC) were studied by using a panel of human medulloblastoma cell lines either passaged in the laboratory for resistance to 4-HC or established from tumors showing clinical resistance to cyclophosphamide. Multiple distinct mechanisms of resistance were demonstrated. Daoy (4-HCR), a line that was 6-fold more resistant than Daoy, contained elevated levels of aldehyde dehydrogenase (ALDH). Most of the difference in sensitivity between the Daoy (4-HCR) and Daoy cell lines was abolished when 4-HC was replaced with phenylketocyclophosphamide, a 4-HC analogue that cannot be detoxified by ALDH. Thus, elevated levels of ALDH appear to play a role in the resistance of Daoy (4-HCR). Several of the cell lines [D283 Med (4-HCR), D341 Med (4-HCR), Daoy (4-HCR), D458 Med] contained elevated levels of glutathione (GSH). No changes in glutathione-S-transferase activity or isozyme pattern were observed, but in two of these three lines, the elevation in GSH was accompanied by elevated levels of gamma-glutamyl transpeptidase. To confirm the role of elevated GSH content in 4-HC resistance, the sensitivity of the cell lines to 4-HC was repeated after depletion of GSH by treatment with L-buthionine-S,R-sulfoximine. In medulloblastoma cell lines without other mechanisms of resistance, a linear relationship was seen between GSH content and resistance to 4-HC. Moreover, cells with GSH content greater than 5 nmol/mg protein and no other overriding mechanism of resistance could be sensitized to 4-HC treatment with L-buthionine-S,R-sulfoximine. Finally, D283 Med (4-HCR) cells had mild elevations in both ALDH and GSH content, but were resistant to phenylketocyclophosphamide and were not significantly sensitized by L-buthionine-S,R-sulfoximine. This cell line appears to demonstrate a third mechanism of resistance to 4-HC. These results suggest that 4-HC resistance in medulloblastoma can be multifactorial.
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PMID:Cyclophosphamide resistance in medulloblastoma. 135 17

Tumors that formerly were uniformly fatal can now be cured by cancer chemotherapy. However, successful anticancer therapy is faced by many obstacles, such as excessive normal tissue toxicity and drug resistance. Tumor drug resistance may be either intrinsic or acquired. The multidrug resistance (MDR) is a unique phenomenon and is characterized by tumor resistance to various structurally unrelated drugs. Known mechanisms for MDR include overexpression of a membrane P-glycoprotein 170 and elevated cellular levels of reducing agents, such as glutathione (GSH). Currently available strategies for overcoming drug resistance include competitive inhibitors of the P-glycoprotein 170, inhibitors of GSH synthesis, and adjuvant therapy with hyperthermia. Development of drug resistance is analogous to a physiological detoxification mechanism and may continue to limit the effectiveness of cancer chemotherapy in the near future.
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PMID:Tumor cell drug resistance and its reversal. 136 8

Clinical success in the treatment of tumors with chemotherapy has significantly improved over the past several years. However, treatment failures due to drug resistance of cancer cells has remained a major problem. The classical form of multiple drug resistance is perhaps also the most common type of drug resistance, and represents the overexpression of a transmembrane glycoprotein pump (P-170) that mediates the efflux of a spectrum of structurally and functionally unrelated drugs. Here, we discuss recent evidence that support the concept that the total phenomenon of multiple drug resistance (MDR) involves several other mechanisms in addition to that underlying "classical" MDR. These include the action of other energy-dependent membrane efflux pumps, elevated levels of GSH for drug conjugation and detoxification to facilitate export, enhanced DNA repair facility, gene amplification and oncogene activation. The combination of mechanisms used by any particular cell line is variable and suggests that many of these mechanisms are independent. Successful reversal of drug resistance appears to require the identification of relevant operative resistance mechanisms. An example is the competitive inhibition of P-170 with verapamil, quinine and tamoxifen. A broadly successful strategy for killing drug-resistant cancer cells, however, could be based on either selective energy depletion of cancer cells or the permeabilization of tumor cells with an effective bypass of efflux pumps, since many mechanisms of drug resistance entail the energy-dependent export of toxins. The latter approach may be achieved via membrane lipid modifications or the introduction of membrane pores by biological or physical (electroporation) means.
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PMID:Multidrug resistance: prospects for clinical management. 137 33


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