In silico Identification of Potential Xanthine Oxidase Inhibitors for the Treatment of Gout and Cardiovascular Disease

 

C.Buvana¹, A. Sumathy¹, M. Sukumar²

¹Dept. of Pharmaceutical Chemistry, Grace College of Pharmacy, Palakkad-678004

²Dept. of Pharmaceutical Analysis, College of Pharmacy, Sri Ramakrishna Institute of Paramedical Sciences, Coimbatore.

*Corresponding Author E-mail: Boviblue@gmail.com

Binding interactions of drugs using docking studies is an important component of computer aided drug design. Structure-based lead optimization approaches are a major role in the drug-discovery process. XO(xanthine oxidase) is the key enzyme that catalyzes the oxidation of hypoxanthine to xanthine and then to uric acid. Hyperuricemia is an underlying cause of gout and cardiovascular diseases. Allopurinol, a widely used XO inhibitor and commonly used drug to treat gout. However, a significant portion of the population suffers from adverse effects of allopurinol like gastrointestinal upset and skin rashes. Therefore use of allopurinol-like drugs with minimum side effects is the ideal drug of choice against gout.

 

A series of indole linked with thiazolidinone were computationally designed and energy minimized. The molecular properties were calculated from suitable computational tools. These ligands were investigated for drug like properties by calculating Lipinski’s rule of five using molinspiration. All of the derivatives showed a zero violations of the rule of 5 which indicates good bioavailability. The positive bioactivity score of the derivative were also in agreement with their probability of drug likeness. These compounds were docked into the active site of XO (PDB code-1HZP) using Argus lab docking software which showed good binding energy for the enzyme, when compared with the binding energies of standard drug allopurinol (-6.91kcal/mol.) Among all the designed ligands, the ligand TZ2 and TZ4 showed more binding energy values (-10.074 and = -9.158Kcal/mol). These results highlight the identification of a new class of XO inhibitors that have potential to be more efficacious, than allopurinol, to treat gout and against cardiovascular diseases.  In future we planned to synthesise these ligand and to screen for their xanthine oxidase inhibitory activity

 

 

 

INTRODUCTION^1-6

Xanthine oxidase, localized in vascular endothelium, is an important enzyme in health and disease Hyperuricemia is the underlying cause of gout and other ailments. Xanthine oxidase is the key enzyme which is involved in the oxidation of hypoxanthine to xanthine and then to uric acid. Allopurinol, a widely used xanthine oxidase inhibitor is the most commonly used drug for the treatment of gout.

 

Significant portion of the population suffers from adverse effects of allopurinol that includes gastrointestinal upset, skin rashes and hypersensitivity reactions.

 

Moreover, an elevated level of uric acid is considered as an independent risk factor for cardiovascular diseases. Therefore use of allopurinol-like drugs with minimum side effects is the ideal drug of choice against gout.

 

In this review, synthesis and design of a series of thiazolidinone-4-ones analogues) as effective xanthine oxidase inhibitors has been reported. we have designed some new heterocyclic analogues of thiazolidinone-4-ones derivatives, Moreover the designed compounds were evaluated for xanthine oxidase inhibition binding ability to

identify the new lead compounds by molecular docking. The most potent compounds selected as lead on which carried out structural modification inorder to obtain new ligands with excellent binding ability.

 

MATERIALS AND METHODS:

STEP- I: Calculation of Molecular Physicochemical Properties:^7-8

The physiochemical properties involve determination of drug-like property of the designed compounds. It is based on Lipinski’s rule of five and can be determined by using molinspiration cheminformatics software. All the designed  compounds showed zero violation of  Lipinski^’s rule of five, which indicates good bioactivity and bioavailability.

 

The Rule:

Lipinski's Rule of Five states that in general, an orally active drug has not more than one violation of the following criteria.

·         Not more than 5 hydrogen bond donors (nitrogen or oxygen atoms with one or more hydrogen atoms).

·         Not more than 10 hydrogen bond acceptors (nitrogen or oxygen atoms)

·         A molecular weight under 500 g/ mol.

·         A partition coefficient log P less than 5.

·         Not more than 15 rotatable bonds.

 

STEP-II:

Molecular Docking: ^(9-10)

Preparation of protein molecule:

The experimental structure of xanthine oxidase (XO) (PDB ID: 1FIQ) as shown in Figure 1 was retrieved from the RCSB protein data bank as a PDB file. The protein molecules were prepared mainly by using the software Swiss PDB viewer. Active site residues within a range of 4.0 A0 were selected and saved in PDB format.

 

Preparation of ligand:

The ligand compounds thiazolidinone derivatives were drawn using ACD/ Chemsketch (12.0) (Alex, 2009) and saved in mol 2 format. The saved ligand compounds were later imported and minimized in Argus Lab after adding hydrogen bonds. The molecules thus obtained were saved in PDB format.

 

 

 

 

Physical properties and biological activities:

Table 1-  Lipinski rule of thiazolidinone derivatives and allopurinol drug.

Compound Code	Log P	MW	"H" Donor	"H" Acceptor	Violation	GPCR Ligands
TZ1	1.939	353.40	5	2	0	0.20
TZ2	3.096	371.84	2	5	0	0.17
TZ3	2.521	380.47	4	3	0	0.17
TZ4	2.475	367.43	2	6	0	0.15
TZ5	1.758	383.42	3	7	0	0.15
Allopurinol	0.534	152.00	2	5	0	-0.18

 

 

Table 2 ARGUS LAB  scores and interactions of Allopurinol  drug and thiazolidinone  derivatives.

S.No	Compound	Argus- Lab ( Kcal/mol)
1	TZ1	-9.126
2	TZ2	-10.074
3	TZ3	-8.519
4	TZ4	-9.158
5	TZ5	-8.433
6	Alloporinol	-6.91

 

Fig. 1 Crystal structure of bovine milk XO (1FIQ) from Protein Data Bank (entry code: 1FIQ)

 

Fig. 2 Amino acid residues that contribute in the catalytic reaction in the active site

 

Structure of Designed Ligands:

S.No.                          R.

TZ1                       4-OH TZ2                       4-Cl TZ3                       4-N(CH3)3 TZ4.                      4-OCH3 TZ5                       4OH, 3-OCH­3

 

Docking of thiazolidinone derivatives to xanthine oxidase:

Docking of thiazolidinone derivatives (TZ1-TZ5) with xanthine oxidase was performed using ARGUS LAB4.0. The algorithm exhaustively searches the entire rotational and translational space of the ligand with respect to the receptors. The various solutions evaluated by a score, which is equivalent to the absolute value of the total energy of the ligand in the protein environment. The best docking solutions ARGUS LAB score for each compound was considered. It was noted that ARGUS LAB scores of comp TZ1 and TZ4 was -10.074 and -9.158 respectively, which is greater than allopurinol drug score value -6.91. as shown in Table 2, Figures 3,4 and 5.

 

The drug like activity of the ligand molecules are characterized using ADME properties. Allopurinol and thiazolidinone derivatives satisfy Lipinski rule of 5 and ADME properties results are shown in Table 1.

 

Fig: 3 Molecular docking  in Argus Software(TZ2)

 

Fig :4  Molecular docking  in Argus Software(TZ4)

 

Fig. 5Molecular docking  in Argus Software(allopurinol)

 

RESULT AND DISCUSSION:

Drug likeness:

All the designed compounds (TZ1-TZ5) showed zero violation of Lipinski’s rule of five, which indicates good bioactivity and bioavailability.(Table-1)

 

Docking:

Docking of designed ligands (TZ1-TZ5 with xanthine oxidase  was performed using ARGUS LAB4.0 Based on the literature, it has been found that indole linked thiazolidinone derivatives  can be used to target xanthine

oxidase. The energy values were calculated using Argus lab.  

 

Among all the designed ligands, the ligand TZ2 and TZ4 showed more binding energy values (-10.074 and = -9.158Kcal/mol), which is greater than allopurinol drug score value -6.91kcal/mol.) as shown in Table 2.

 

CONCLUSION:

Xanthine oxidase  is a key condensing enzyme responsible for initiation of catabolism of purine pathway, and has emerged as an attractive new target for treatment of gout in recent years.

 

It was observed that xanthine oxidase when docked with the compounds, give good scores,  also showed good result for ligand TZ2  and TZ4 . The predicted potency of the five compounds with unknown potency showed  that two ligands had very low activity value which ensures the potentiality of the compounds used as treatment of gout. In future research work we planned to synthesis these thiazolidinone derivatives and screen for their xanthine oxidase inhibitor activity.

 

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Received on 07.09.2013          Modified on 24.09.2013

Accepted on 28.09.2013          © AJRC All right reserved