Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We report the identification and characterization of a novel potent inhibitor of DNA topoisomerase I: lamellarin D (LAM-D), initially isolated from a marine mollusk, Lamellaria sp., and subsequently identified from various ascidians. This alkaloid, which displays potent cytotoxic activities against multidrug-resistant tumor cell lines and is highly cytotoxic to prostate cancer cells, bears a 6H-[1]benzopyrano[4',3':4,5]pyrrolo[2,1-a]isoquinolin-one pentacyclic planar chromophore, whereas its synthetic 5,6-dehydro analogue, LAM-501, has a significantly tilted structure. DNA binding measurements by absorbance, fluorescence, and electric linear dichroism spectroscopy show that LAM-D is a weak DNA binder that intercalates between bp of the double helix. In contrast, the nonplanar analogue LAM-501 did not bind to DNA and failed to inhibit topoisomerase I. DNA intercalation may be required for the stabilization of topoisomerase I-DNA complexes by LAM-D. In the DNA relaxation assay, LAM-D strongly promoted the conversion of supercoiled DNA into nicked DNA in the presence of topoisomerase I. The marine product was approximately 5 times less efficient than camptothecin (CPT) at stabilizing topoisomerase I-DNA complexes, but interestingly, the two drugs exhibited slightly distinct sequence specificity profiles. Topoisomerase I-mediated DNA cleavage in the presence of LAM-D occurred at some sites common to CPT, but a few specific sites identified with CPT but not with LAM-D or conversely unique sites cleaved by LAM-D but not by CPT were detected. The distinct specificity profiles suggest that LAM-D and CPT interact differently with the topoisomerase I-DNA interface. A molecular modeling analysis provided structural information on the orientation of LAM-D within the topoisomerase I-DNA covalent complex. The marine alkaloid did not induce DNA cleavage by topoisomerase II. Immunoblotting experiments revealed that endogenous topoisomerase I was efficiently trapped on DNA by LAM-D in P388 and CEM leukemia cells. P388/CPT5 and CEM/C2 cell lines, both resistant to CPT and expressing a mutated top1 gene, were cross-resistant to LAM-D. Collectively, the results identify LAM-D as a novel lead candidate for the development of topoisomerase I-targeted antitumor agents.
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PMID:Lamellarin D: a novel potent inhibitor of topoisomerase I. 1461 38

Lamellarin D (LAM-D) is a marine alkaloid endowed with potent cytotoxic activities against various tumor cells, in particular human prostate cancer cells and leukemia cells. Its cytotoxic action is dependent, at least in part, to its capacity to inhibit topoisomerase I. P388CPT5 murine leukemia cells resistant to the reference topoisomerase I poison camptothecin (CPT) are cross-resistant to LAM-D but the relative resistance index (RRI) is significantly reduced with LAM-D (RRI=21) compared to CPT (RRI=103). To comprehend further the mechanism of action of this novel marine antitumor agent, we have investigated the influence of the P glycoprotein (Pgp) on the cytotoxicity of LAM-D and the proapoptotic effects induced by the alkaloid. P388CPT5 cells, expressing a mutated top1 gene, display a functional Pgp, as judged from cytometry experiments performed with cells treated with rhodamine 123 or calcein-ester whereas no Pgp activity was detected with the parental P388 cells. P388CPT5 cells are also cross-resistant to the topoisomerase II poisons doxorubicin and etoposide but the resistance is abolished in the presence of verapamil or quinine (at non toxic concentrations) which reverse the multidrug resistance (MDR) phenotype. In contrast, the RRI measured with LAM-D and CPT remain unchanged in the presence of the two MDR reversal agents. The effects of LAM-D on the cell cycle progression were different in the parental P388 cells compared with the CPT-resistant which were blocked in the S and subsequently G2-M phases of the cell cycle. Cytometry experiments with the JC-1 fluorescent marker revealed that LAM-D and CPT promoted apoptosis in parental P388 cells via an activation of the mitochondrial pathway. In contrast, a massive depolarisation of the mitochondrial membrane potential and a nuclear fragmentation were detected only with LAM-D on P388CPT5 cells. This in vitro work identifies LAM-D as a potent pro-apoptotic agent and its cytotoxic action is fully maintained in multidrug-resistant cells compared to the sensitive parental cell line.
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PMID:Lamellarin D: a novel pro-apoptotic agent from marine origin insensitive to P-glycoprotein-mediated drug efflux. 1580 2