computational modeling of drug disposition in active transport M.pharm 2nd sem P'ceutics

for M.pharm Pharmaceutics 2nd sem unit 02 Active transport- P-gp, BCRp, hPEPt 1, OACT, OCT, Nucleoside transporter.

1. 1 A PRESENTATION ON COMPUTATIONAL MODELING OF DRUG DISPOSITION: ACTIVE TRANSPORTERS SUBMITTED BY GUIDED BY: SAKSHI SONI Dr. DINESH K. MISHRA M.PHARM 2 ND SEM PROFESSOR (PHARMACEUTICS) (PHARMACEUTICS) Department of Pharmacy, Guru Ghasidas Vishwavidyalaya Bilaspur C.G. 495001

2. TABLE OF CONTENTS: Introduction Active Transport P-Glycoprotein (P- gp ) Breast Cancer Resistance Protein (BCRP) Nucleoside Transporter Human peptide Transporter (hPEPT1) Apical Sodium dependent Bile Transporter (ASBT) Organic Cation Transporter (OCT) Organic Anion Transporter Polypeptides (OATP) Blood Brain Barrier (BBB)- Choline Transporter 2

3. INTRODUCTION: Computational Modeling are the computer tools used for solving the problems by step-wise, repeated and iterative methods which could be tedious or unsolvable by manual calculations. OBJECTIVES OF COMPUTATIONAL MODELS: The drug Formulation requires the Optimization of bioprocesses (ADMET). The clinical trail procedures are very expensive and also include the expenditure on the clinical failures. CADD is a useful tool for evaluating ADME-Tox processes. The relationship between the structure and drug utilization pathways (in the body) can be established. The electronic effects of chemical structure are implicated for predicting the ADMET profiles. The site of metabolism and possible metabolites can be predicted. 3

4. OBJECTIVES OF COMPUTATIONAL MODELING : 4

5. DRUG DISPOSITION: Drug disposition means the change in the position/movement of drug molecules inside the body after administration into the system irrespective with the route of administration. Process: After entering the body 5

6. Process involved in drug disposition: 6

7. Computational methods for drug distribution 7

8. ACTIVE TRANSPORT (UP-HILL TRANSPORT): Transportation of drug molecules against the concentration gradient and natural thermodynamic fluidity. An energy regulated step, so some suitable inorganic ions, enzymes, proteins acts as support system. Adenosine triphosphate (ATP) dependent binding cassette and solute carrier system were the main types of active transporter system. It is used for enhanced permeation of membrane whereas other system was depend upon energy dependent sodium potassium ion gated proton pump system. P-glycoprotein, BCRp (breast cancer resistance protein), nucleoside transporters, hPEPt1 (human peptide transporter-1), ASBt (apical sodium-dependent bile acid transporter), OCt (organic cation transporter), OATP (organic-anion-transporting polypeptides), BBb -Choline (blood brain barrier choline system) were some important carrier systems related to biomolecules . 8

9. 9

10. TRANSPORTER SYSTEM FOR DISTRIBUTION : Transporters are available in the luminal and basolateral membranes of the enterocytes, hepatocytes, renal tubular epithelium cells, blood brain barrier (BBB), blood placenta barrier (BPB). These transporters either inhibit or induce the metabolism action of CYP450 enzyme. A few transporters are reported in the following sections: P- gp , BCRp , OAT, OATP, BCT, MCT etc.   10

11. 1. P-glycoprotein (P- gp ) (Efflux): It mediates the efflux of endogenous compounds and drugs out of the cells through ATP-dependent mechanism (expel of drugs from the cells) . It is expressed in the Blood brain barrier (BBB) Luminal membrane of the small intestine Apical membrane of excretory cells, hepatocytes and renal proximal tubules. G astrointestinal tract, blood, brain, testes and placenta. P- gp created a barrier in this format. E.g Bioavailability of drugs was also affected by P- gp (inducer or inhibitor) as rifampicin (P- gp inducer) minimized bioavailability whereas verapamil (P- gp inhibitor) increase bioavailability of related drugs. 11

12. The expression of P- gp increases from Proximal to distal regions of the small intestine. Substrates: These do not contribute to the distribution of drugs. E.g. Anthracyclines, alkaloids, peptides, local anesthetics, immunosuppressants, HIV protease inhibitors. Inhibitors: These inhibit the transporter system such that drug distribution can be enhanced. E.g. Calcium channel blockers, Immunosuppressants, and grape fruit juice. Several P- gp models were developed and found adequate for the screening the molecular databases: a. Robust SAR methods b. Pharmacophore model 12

13. c. SOM model d. Homology model for P- gp APPLICATIONS: S olve the efflux related bioavailability problems. P- gp novel inhibitors are co-administered which would optimize the PK profile. It reduces the absorption of anti-cancer drugs, through drug itself is having anti-cancer activity. This is also responsible for multidrug resistance to cancer chemotherapy. Same is the case with HIV protease inhibitors. The intestine P- gp may contribute to the systemic clearance of intravenously administered drugs by active secretion into the intestine lumen. P- gp enhances the excretion (renal and hepatic) and reduces the absorption (de-toxification) 13

14. The in-silico modeling of P- gp are given in the computational methods: Monocarboxylate transporter (MCT): The bidirectional movement of monocarboxylic acids across the plasma membrane is catalysed by a family of protein-lined monocarboxylate transporters (MCTs). 4 MCTs (MCTs 1-4) are well characterised. Blood brain barrier (BCT): these are meant for transporting the nutrients and choline (a cation) across the BBB. Choline like compound (chemical structural similarity) can easily penetrate through BBB. Binding studies are developed from theoretical and empirical methodologies. 2. BCRp (Breast cancer resistance protein): It is composed of 655 amino acids and widely distributed in- 14

15. stem cells, cancerous cells, liver, intestine placenta. BCRp was worked as high gradient transporting system with greater specification for molecules with- negative or positive charge, organic anion and conjugated sulfates. E.g. Fumitremorgin-C was the chemical substance which can reversed the drug resistance due to BRCp activity. Application: This system effectively worked for fetus protection, biliary elimination, and 15

16. 16 decrease in reabsorption through kidney as well as protection of stem cells In this fashion, anticancer drugs, toxins, endogenous substances were behave as substrate whereas multidrug resistant modulators were the inhibitors of this transporting system. In this text, Fumitremorgin-C was the chemical substance which can reversed the drug resistance due to BRCp activity. Models for BCRp : BCRP pharmacophore model: for nelfanivir , and nicardipine. The model is used in the search against clinical drugs (500 drugs). The search identified 37 hits, which included digoxin, indinavir, ritonavir, nicardipine, ( BCRP inhibitors). BCRp 3D-QSAR model: This model was generated by analyzing the activity of 25 flavonoid analogues.

17. 3. Nucleoside transporters: R esponsible for the transportation of nucleosides ( deoxyribo / ribo nucleic acid synthesis starting material) Also regulate the energy dependent neuronal modulation especially transportation of blood to retina. This system was classified into sodium ion dependent and independent transporting systems. These drugs were mainly prodrug in nature, so travelling from administration to destination, these transporter systems showed a positive impact. Nucleoside transporter system was further divided into concentrative: Concentrative nucleoside transporters (CNT-1, CNT-2, CNT-3): high affinity and selectivity CNTs are located on epithelia of intestine, liver, kidney, and brain. Equilibrative nucleoside transporters (ENT-1, ENT-2): broad affinity, low selective ENTs are ubiquitously located. 17

18. Applications: Anti-cancer drugs – cladribine, and anti-viral drug- zalcitabine are nucleoside analogues and hence can be transported. 4. hPEPt1 (human peptide transporter-1): It belongs to peptide transporter, I t is a proton coupled, low affinity, active oligopeptide transport system. It was mainly used for transport of oligopeptide with the exchange of sodium and hydrogen ions, associated with transportation of antibiotics, antiviral and antihypertensive agents as well as movement of nitrogen throughout the body. This system mainly located in- apical membrane of small intestine. In this context oral hypoglycemic agents (sulfonylureas, biguanides and others) inhibited the transporting system. This pharmacophore model is applied to screen the CMC database with over 8000 drugs-like molecules 18

19. 19 A pharmacophore model is developed based on the high affinity substrates ( Gly-sar , bestatin and enalapril). Application : T his transporter facilitates the oral availability peptidomimetics, e.g. beta- lactum antibiotics and valcyclovir . The weak peptide bond feature of the beta- lactum antibiotics ionizes at the intestinal pH. This limits their intestinal absorption. These beta- lactum antibiotics have PEPT carrier mediated transport characteristics and their absorption is facilitated by PETP1 (Proton dependent oligopeptide transporters). The fragments of the milk proteins ( free amino acids and small peptides) in the stomach and duodenum compete for the PETP-1 substrates. The rate of oseltamivir absorption decreases with milk.

20. 4. ASBt (apical sodium-dependent bile acid transporter): This carrier system observed with presence of 348 amino acids with 38 kilo dalton of molecular weight. The system comprised two glycosylation sites at N10 and N328 OCt (organic cation transporter). ASBt was responsible for transportation and reabsorption of bile acids from gut lumen as well as active against liver disease, hyperglycemia and hyperlipoproteinemia. The ASBt is expressed on the apical membrane of intestinal epithelia and cholangiocytes . ASBt assist in the absorption of bile acids and a pivotal role in cholesterol metabolism. 20

21. 21 The pharmacophore model is developed based on the training set of 17 chemically active diverse inhibitors of ASBt . OAtp (organic-anion-transporting polypeptides): T hese are responsible for actively transporting the anions present in the plasma and thus promoting drug excretion. These transporters also transport organic cation drugs. These transporters mediate sodium dependent transport of a diverse range of amphiphilic organic compounds with relatively high molecular weight. It include- bile acids, steroid conjugates, thyroid hormones, anionic peptides and numerous drugs. This family mainly located in liver, intestine, kidney, brain and placenta.

22. Organic cation transporters (OCT) (influx): This includes drugs and metabolites, carrying a net positive charge at physiological pH. It facilitates the uptake of many cationic drugs across the barrier membranes from kidney, liver and intestine epithelium. It transport relatively hydrophilic and low molecular mass organic cations. 22

23. CONCLUSION: This chapter mainly focused on the journey of a drug molecule inside the body. In this intriguing viewing process, various pathophysiological aspects help us to know or visualize the path of a drug molecule in achieving the ultimate goal. When a drug molecule enters our system, our physiological system treat the substance as foreign material, so it always try to expel out the substance and in this expelling process both molecule and body system comes under an iterative process and finally some positive or negative effect is observed by the system. In this fate determining process, physicochemical nature of the chemical substance and physiological environment (composition) of system makes this movement more interesting. In this context, pharmacokinetic features along with toxicity profile of the drug substance regulate the ultimate fate of the molecule. Nowadays various computational processes are considered such as in silico assessment of drug molecule after absorption through biological membrane, distribute throughout the system based on the percent ionization or partition coefficient factors followed by biologically transformed into another entity in presence of microsomal enzymes and finally excrete out from system using various cellular transport systems. 23

24. So we focused on detailed computational studies related to Computer aided drug development on Active transporters on drug disposition Transportation of drug molecules against the concentration gradient and natural thermodynamic fluidity. This is an energy regulated step, so some suitable inorganic ions, enzymes, proteins acts as support system. Adenosine triphosphate (ATP) dependent binding cassette and solute carrier system were the main types of active transporter system. The energy dependent system was used energy for enhanced permeation of membrane whereas other system was depend upon energy dependent sodium potassium ion gated proton pump system. P-glycoprotein, BCRp (breast cancer resistance protein), nucleoside transporters, hPEPt1 (human peptide transporter-1), ASBt (apical sodium-dependent bile acid transporter), OCt (organic cation transporter), OATP (organic-anion-transporting polypeptides), BBb -Choline (blood brain barrier choline system) were some important carrier systems related to biomolecules . 24

25. REFERENCES: Saha, S. U. P. R. I. Y. O., & Pal, D. I. L. I. P. K. U. M. A. R. (2021). Computational approaches related to drug disposition.  Int J Pharm Pharm Sci ,  13 (7), 19-27. Subrahmanyam CVS, Kumar Ananda Durai T., Swathi N, Thimmasetty J. a textbook of principles and practice of computer aided drug development published by M.K. jain for Vallabh prakashan , New delhi 1 st edition 2020,178-198. Saha S, Banerjee A, Rudra A. 2D QSAR approach to develop newer generation molecules active aganist ERBB2 receptor kinase as potential anticancer agent. Int J Pharm Chem 2015;5:134-48. Saha S, Constance V, Luv Kush, Percha V. Exploring descriptor combination by chemometric approach to develop newer molecules active through corticosteroid binding globulin receptor. J Appl Pharm 2015;7:223-36. 25

26. THANK YOU ALL FOR PAYING YOUR ATTENTION. 26