Lipoxygenases (LOXs) are a group of enzymes involved in the oxygenation of polyunsaturated fatty acids. Among these 5-lipoxygenase (5-LOX) is the key enzyme leading to the formation of pharmacologically important leukotrienes and lipoxins, the mediators of inflammatory and allergic disorders. In view of close functional similarity to mammalian lipoxygenase, potato 5-LOX is used extensively. In this study, the homology modeling technique has been used to construct the structure of potato 5-LOX. The amino acid sequence identity between the target protein and sequence of template protein 1NO3 (soybean LOX-3) searched from NCBI protein BLAST was 63%. Based on the template structure, the protein model was constructed by using the Homology program in InsightII. The protein model was briefly refined by energy minimization steps and validated using Profile-3D, ERRAT and PROCHECK. The results showed that 99.3% of the amino acids were in allowed regions of Ramachandran plot, suggesting that the model is accurate and its stereochemical quality good. Like all LOXs, 5-LOX also has a two-domain structure, the small N-terminal beta-barrel domain and a larger catalytic domain containing a single atom of non-heme iron coordinating with His525, His530, His716 and Ile864. Asn720 is present in the fifth coordination position of iron. The sixth coordination position faces the open cavity occupied here by the ligands which are docked. Our model of the enzyme is further validated by examining the interactions of earlier reported inhibitors and by energy minimization studies which were carried out using molecular mechanics calculations. Four ligands, nordihydroguaiaretic acid (NDGA) having IC(50) of 1.5 microM and analogs of benzyl propargyl ethers having IC(50) values of 760 microM, 45 microM, and no inhibition respectively were selected for our docking and energy minimization studies. Our results correlated well with the experimental data reported earlier, which proved the quality of the model. This model generated can be further used for the design and development of more potent 5-LOX inhibitors.

Cyclooxygenases (COXs), the enzymes involved in the formation of prostaglandins from polyunsaturated fatty acids such as arachidonic acid, exist in two forms--the constitutive COX-1 that is cytoprotective and responsible for the production of prostaglandins and COX-2 which is induced by cytokines, mitogens and endotoxins in inflammatory cells and responsible for the increased levels of prostaglandins during inflammation. As a result COX-2 has become the natural target for the development of anti-inflammatory and anti-cancer drugs. While the conventional NSAIDs with gastric side effects inhibit both COX-1 and COX-2, the newly developed drugs for inflammation with no gastric side effects selectively block the COX-2 enzyme. NSAIDs, nonselective non-aspirin NSAIDs and COX-2 selective inhibitors, are being widely used for various arthritis and pain syndromes. Selective inhibitors of COX-2, however, convey a small but definite risk of myocardial infarction and stroke; the extent of which varies depending on the COX-2 specificity. In view of the gastric side effects of conventional NSAIDs and the recent market withdrawal of rofecoxib and valdecoxib due to their adverse cardiovascular side effects there is need to develop alternative anti-inflammatory agents with reduced gastric and cardiovascular problems. The present study reviews various Computer Aided Drug Design (CADD) approaches to develop Cyclooxygenase based anti-inflammatory and anti-cancer drugs.

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