AChE bivalent inhibitors

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-	==PART I==	+	==PART I. Tacrine- and hupyridone-containing compounds==
	'''This page is a continuation of the page "[[AChE inhibitors and substrates]]".'''		'''This page is a continuation of the page "[[AChE inhibitors and substrates]]".'''
-	==Selected 3D Structures of AChE ==	+
-	* [[2ace]] This is the original solved structure for '''Torpedo Californica'''	+
	* [[1zgb]] Complex with (''R'')-tacrine-(10)-hupyridone (cmp '''R-3''')		* [[1zgb]] Complex with (''R'')-tacrine-(10)-hupyridone (cmp '''R-3''')
	* [[1zgc]] Complex with (''S'')-tacrine-(10)-hupyridone (cmp '''S-3''')		* [[1zgc]] Complex with (''S'')-tacrine-(10)-hupyridone (cmp '''S-3''')

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Revision as of 13:12, 1 March 2009

PART I. Tacrine- and hupyridone-containing compounds

This page is a continuation of the page "AChE inhibitors and substrates".

• 1zgb Complex with (R)-tacrine-(10)-hupyridone (cmp R-3)
• 1zgc Complex with (S)-tacrine-(10)-hupyridone (cmp S-3)
• 1acj Complex with tacrine alone
• 1h22 Complex with (S,S)-(-)-Bis(12)-hupyridone (cmp (S,S)-(-)-4b)
• 1h23 Complex with (S,S)-(-)-Bis(10)-hupyridone (cmp (S,S)-(-)-4a)
• 2cmf Complex with Bis(5)-tacrine derivative (cmp 2d)
• 2ckm Complex with Bis(7)-tacrine derivative (cmp 2f)
• 1ut6 Complex with N-9-(1',2',3',4'-TETRAHYDROACRIDINYL)-1,8-DIAMINOOCTANE (cmp 6)
• 1odc Complex with cmp 7

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The of TcAChE consists of two binding subsites. First of them is the "catalytic anionic site" (CAS), which involves mentioned above catalytic triad (colored orange) and the conserved residues and also participating in ligands recognition. Another conserved residue (colored cyan) is situated at the second binding subsite, termed the "peripheral anionic site" (PAS), ~14 Å from CAS. Therefore, the ligands that will be able to interact with both these subsites, will be more potent AChE inhibitors in comparison to compounds interacting only with CAS. One of the ways to produce such ligands is to introduce two active substances into one compound. If it is spatially necessary these subunits could be divided by alkyl linker with suitable length. According to the strategy of the use of a bivalent ligand, the (RS)-(±)-tacrine-(10)-hupyridone ((R)-3 or (S)-3) was designed and synthesized. It consists of mentioned in the page 'AChE inhibitors and substrates' (colored magenta), 10-carbon (yellow), and (red). The tacrine moiety of this inhibitor binds at the CAS, the linker spans the gorge, and the hupyridone moiety binds at the PAS.

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The comparison of the (R)-3/TcAChE and tacrine/TcAChE complexes at the . A of the trigonal (R)-3/TcAChE structure (1zgb; (R)-3 colored cyan; TcAChE residues interacting with (R)-3 are colored sea-green) with the crystal structure of tacrine/TcAChE (1acj, (tacrine colored magenta; residues interacting with tacrine are colored pink) reveals a similar binding mode for the tacrine moiety. In both structures the tacrine ring is situated at the CAS, between the aromatic residues Trp84 and Phe330. Steric clash with the 10-carbon linker could explain the tilt observed for the Phe330 (yellow and transparent in the tacrine/TcAChE). Water molecules are shown as red spheres. The tacrine unit of (R)-3 N forms with His440 O (3.0 Å) similar to that of tacrine alone. Similarly to the tacrine/TcAChE structure the system of three water molecules at the CAS ((R)-3/TcAChE) binds the tacrine-linker N via hydrogen bonds to Ser81 O, Ser122 Oγ, and Asn85 Oδ1 (2.6-3.5 Å) .

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The comparison of the (R)-3/TcAChE (1zgb) and bis-hupyridone/TcAChE complexes (1h22 and 1h23) at the . of the (R)-tacrine-(10)-hupyridone ((R)-3, cyan) and (S,S)-(-)-Bis(12)-hupyridone ((S,S)-(-)-4b, orange, i.e. 12-carbon-tether-linked hupyridone dimer) and (S,S)-(-)-Bis(10)-hupyridone ((S,S)-(-)-4a, plum) complexes demonstrates the binding mode of the hupyridone moiety. TcAChE residues of symmetry-related molecule are shown in magenta. X-ray structures of TcAChE complexed with these 10- and 12-carbon-tether-linked 2 (S,S)-(-)-4a and (S,S)-(-)-4b show one subunit bound at the , the linker spanning the gorge, and the other subunit bound at the . There are two connecting the hupyridone O to Lys11 Nζ and hupyridone N to Gln185 Oε1 of a symmetry-related molecule at (R)-3/TcAChE complex. Water molecules are shown as red spheres. Another hydrogen bond connects the hupyridone O to a water molecule, which is bound to Ser286 N. Similarly, the hupyridone-PAS unit of both (-)-4a and (-)-4b forms direct and an indirect hydrogen bonds with the protein backbone in the PAS region.

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The of (R)-3 (cyan) and (S)-3 (1zgc) bound to the TcAChE active site in the orthorhombic forms is shown. The residues important for inhibitor binding are in green. In contrast to the trigonal form (1zgb), the residues Gln*185 and Lys*11 (yellow) of an other symmetry-related monomer do not form hydrogen bonds with the ligands. of (S,S)-(-)-4a (1h22) and (S)-3, orthorhombic TcAChE (1zgc) demonstrates the similar mode of binding of the hupyridone unit at the PAS. The residues Trp279 (top) and Trp84 (bottom) represent the PAS and the CAS, respectively.

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2d and 2f are bis(n)-tacrine derivatives with n=5 and 7 (number of carbons in the linkers), respectively. These compounds are more potent and selective AChE inhibitors than tacrine alone. The binding of the first ring of at the TcAChE CAS is similar to that of tacrine itself (1acj). The second ring of the 2d interacts with PAS near the Trp279. The interaction of 2d at CAS caused increase of the between Ser200 Oγ and H440 Nε2 atoms, and, therefore, disruption of the catalytic triad (Ser200, H220, E327) compared with native structure (2ace). This binding also caused in the Val281-Ser291 loop resulting in significant change in the surface of the active-site gorge in compararison to native structure (2ace). The first ring of the compound 2f (heptylene-linked bis-tacrine, 2ckm) also adopts similar as tacrine alone and first ring of the 2d at the CAS. The second tacrine ring of the 2f also interacts with PAS near the Trp279, as well as 2d. The of the 2f did not cause significant structural changes in the TcAChE complexed with it in comarison to native structure (2ace). Of course, of the 2d and 2f revealed significantly different contacts between second rings of these compounds with TcAChE. There are two additional tacrine-containing AChE inhibitors: compounds (1ut6) and (1odc). The tacrine moieties of these compounds also adopt similar conformations and interactions with CAS as tacrine alone, 2f and 2d. Both these inhibitors 6 and 7 spanning up to PAS, but since compound 7 misses the second ring, Trp279 adopts different conformation in complex with it. Except Trp279, all other TcAChE active-site residues have relatively similar conformations in all these complexes (with tacrine alone, cmp 6 (colored white), and cmp 7.

For information about additional AChE inhibitors see page AChE bivalent inhibitors (Part II).

References

• Sussman JL, Harel M, Frolow F, Oefner C, Goldman A, Toker L, Silman I. Atomic structure of acetylcholinesterase from Torpedo californica: a prototypic acetylcholine-binding protein. Science. 1991 Aug 23;253(5022):872-9. PMID:1678899
• Greenblatt HM, Guillou C, Guenard D, Argaman A, Botti S, Badet B, Thal C, Silman I, Sussman JL. The complex of a bivalent derivative of galanthamine with torpedo acetylcholinesterase displays drastic deformation of the active-site gorge: implications for structure-based drug design. J Am Chem Soc. 2004 Dec 1;126(47):15405-11. PMID:15563167 doi:http://dx.doi.org/10.1021/ja0466154
• Harel M, Hyatt JL, Brumshtein B, Morton CL, Yoon KJ, Wadkins RM, Silman I, Sussman JL, Potter PM. The crystal structure of the complex of the anticancer prodrug 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxycamptothecin (CPT-11) with Torpedo californica acetylcholinesterase provides a molecular explanation for its cholinergic action. Mol Pharmacol. 2005 Jun;67(6):1874-81. Epub 2005 Mar 16. PMID:15772291 doi:http://dx.doi.org/10.1124/mol.104.009944
• Rydberg EH, Brumshtein B, Greenblatt HM, Wong DM, Shaya D, Williams LD, Carlier PR, Pang YP, Silman I, Sussman JL. Complexes of alkylene-linked tacrine dimers with Torpedo californica acetylcholinesterase: Binding of Bis5-tacrine produces a dramatic rearrangement in the active-site gorge. J Med Chem. 2006 Sep 7;49(18):5491-500. PMID:16942022 doi:http://dx.doi.org/10.1021/jm060164b