RATIONAL DRUG DESIGN:
GRID- AND LUDI-BASED STRUCTURAL MODIFICATIONS OF A HUMAN SYNOVIAL FLUID
PHOSPHOLIPASE A2 INHIBITOR LEADING TO ENHANCED ACTIVITY

M.T. Pisabarro,*a A. Palomer,** A.R. Ortiz,* R.C. Wade,* F. Gago,a D. Mauleon,** and G. Carganico**

*European Molecular Biology Laboratory, Heidelberg'FRG
**R D Departament, Laboratories Menarini S.A.Badalona, Spain
a Departamento di Fisiologia y Farmacologia, Universidad de Alcala de Henares, Madrid, Spain


GRID is a computational procedure for detecting energetically favorable binding sites on molecules of known structure.' LUDI is a recently introduced automatic method for de novo ligand design. A combination of both methodologies has been used here to suggest modifications that could be introduced into the structure of a known phospholipase A2 (PLA2) inhibitor in order to enhance its binding affinity for this enzyme.

PLA2 is a lipolytic enzyme that splits the 2-acyl bond in 1,2-diacylphosphatides. Release of fatty acids provides the substrate required for the synthesis of eicosanoids, involved in pathological processes such as inflammation. Thus, modulation of PLA2 activity is a pharmacological goal of great interest. The three-dimensional structure of the human synovial fluid PLA2 (HSF-PLA2) is known both in its native form and in a complex with the transition state analogue L-1-O-octyl-2-heptylphosphonyl-sn-glycero-3-phosphoethanolomine.
Novel putative ligand-binding sites on HSF-PLA2 were identified by use of water and aromatic atom probes, as implemented in the GRID suite of programs. Strong hydrophobic and aromatic interactions were observed within a cage region on the surface of the enzyme delimited by residues VAL46, THR130, PRO131, GLY33, and the disulfide bridge linking CYS50 and CYS133. LUDI was also used to explore the same enzyme substructure. An interesting suggestion from this program was that this hydrophobic region could be filled with an aromatic ring template.


In the known enzyme-inhibitor complex, the amino group of the inhibitor is located close to the above mentioned region. Therefore, the rationale for structural modification of this inhibitor was that exploitation of this additional interaction site could lead to enhanced affinity for the enzyme. 2-Decylsulfonylamino-1-octyl-phosphoglycol (LM- 1230) and its O-benzyl ether derivate (LM-1228) were synthesised and tested. Their inhibition of HSF-PLA2 activity yielded Xi(50) values of 0.026 and 0.0036, respectively. Therefore, these bencylated derivates are indeed endowed with the predicted enhancement in affinity, and present a good inhibitory activity.


J. Mol. Graph. (1994) 12, 72.


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