Structural insights into CPT-11 activation by mammalian carboxylesterases.
Mammalian carboxylesterases cleave the anticancer prodrug CPT-11 (Irinotecan) into SN-38, a potent topoisomerase I poison, and 4-piperidino-piperidine (4PP). We present the 2.5 A crystal structure of rabbit liver carboxylesterase (rCE), the most efficient enzyme known to activate CPT-11 in this manner, in complex with the leaving group 4PP. 4PP is observed bound adjacent to a high-mannose Asn-linked glycosylation site on the surface of rCE. This product-binding site is separated from the catalytic gorge by a thin wall of amino acid side chains, suggesting that 4PP may be released through this secondary product exit pore. The crystallographic observation of a leaving group bound on the surface of rCE supports the 'back door' product exit site proposed for the acetylcholinesterases. These results may facilitate the design of improved anticancer drugs or enzymes for use in viral-directed cancer cotherapies.
Bencharit
Sompop
S
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
Morton
Christopher L
CL
Howard-Williams
Escher L
EL
Danks
Mary K
MK
Potter
Philip M
PM
Redinbo
Matthew R
MR
D000595:Amino Acid Sequence; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000737:chemistry / Q000378:metabolism*; D001216:Asparagine / Q000378:metabolism; D001665:Binding Sites; D002166:Camptothecin / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D006031:Glycosylation; D000077146:Irinotecan; D008099:Liver / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018583:Pliability; D011355:Prodrugs / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits; D013329:Structure-Activity Relationship
D000972:Antineoplastic Agents, Phytogenic; D011355:Prodrugs; D001216:Asparagine; D000077146:Irinotecan; D002265:Carboxylic Ester Hydrolases; D002166:Camptothecin