Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Many clinically important drug interactions occur due to inhibition of human liver cytochrome P450 3A (CYP3A) metabolism. The drug efflux pump P-glycoprotein (Pgp) can be an additional locus contributing to these drug interactions because there is overlap in drugs that are substrates for both proteins. We screened a number of CYP3A inhibitors (macrolide antibiotics, azole antifungals, and ergotpeptides) for their ability to interact with Pgp, compared with prototypical Pgp inhibitors. We used cell lines expressing human, mouse, and rat mdr1 genes. Pgp antagonism was defined by interactions of the drugs with four cell lines (LLC-PK1, L-MDR1, L-mdr1a, and L-mdr1b) using a microfluorometric calcein-AM assay and characterized for their inhibitor constant (K(i)) toward calcein-AM. The compounds were further defined for their ability to inhibit MDR1 by their effect on vinblastine accumulation into L-MDR1 cells. Representative compounds from each class of drugs were further tested as Pgp substrates, defined by the ability of human Pgp or mouse mdr1a/Pgp to transport them across a polarized kidney epithelial cell in vitro. These same compounds were administered radiolabeled in vivo to mdr1a (+/+) and (-/-) mice and the distribution of radioactivity compared. The results are summarized as follows: 1) Some drug interactions with Pgp were substrate- and/or assay-dependent. 2) Ergot alkaloids were identified as a class of MDR1/Pgp chemosensitizers. 3) The Ergot alkaloids revealed species differences in the structure-activity relationships for inhibition of Pgp. Simultaneous inhibition of Pgp by many CYP3A inhibitors contributes to human variation in the extent of drug-drug interactions.
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PMID:Interaction of cytochrome P450 3A inhibitors with P-glycoprotein. 1223 67

Ergot alkaloids are psychoactive and vasoconstricting agents of the fungus Claviceps purpurea causing poisoning such as ergotism in medieval times (St. Anthony's Fire). This class of substances also inhibits tumor growth in vitro and in vivo, though the underlying mechanisms are unclear as yet. We investigated six ergot alkaloids (agroclavine, ergosterol, ergocornin E, ergotamine, dihydroergocristine, and 1-propylagroclavine tartrate) for their cytotoxicity towards tumor cell lines of the National Cancer Institute, USA. 1-Propylagroclavine tartrate (1-PAT) revealed the strongest cytotoxicity. Out of 76 clinically established anticancer drugs, cross-resistance was found between the ergot alkaloids and 6/7 anti-hormonal drugs (=85.7 %) and 5/15 DNA-alkylating drugs (=33.3 %). The IC50 values for the six alkaloids were not correlated to well-known determinants of drug resistance, such as proliferative activity (as measured by cell doubling times, PCNA expression, and cell cycle distribution), the multidrug resistance-mediating P-glycoprotein/MDR1 and expression or mutations of oncogenes and tumor suppressor genes (EGFR, RAS, TP53). While resistance of control drugs (daunorubicin, cisplatin, erlotinib) correlated with these classical resistance mechanisms, ergot alkaloids did not. Furthermore, COMPARE and hierarchical cluster analyses were performed of mRNA microarray data to identify genes correlating with sensitivity or resistance to 1-PAT. Twenty-three genes were found with different biological functions (signal transducers, RNA metabolism, ribosome constituents, cell cycle and apoptosis regulators etc.). The expression of only 3/66 neuroreceptor genes correlated with the IC50 values for 1-PAT, suggesting that the psychoactive effects of ergot alkaloids may not play a major role for the cytotoxic activity against cancer cells. In conclusion, the cytotoxicity of ergot alkaloids is not involved in classical mechanisms of drug resistance opening the possibility to bypass resistance and to treat otherwise drug-resistant and refractory tumors. The modes of action are multifactorial, which is a typical feature of many natural compounds.
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PMID:Identification of cellular and molecular factors determining the response of cancer cells to six ergot alkaloids. 2534 40