2. Introduction Types of transport Role of transporters
Regulation of transporters on genetic level ABC Superfamily P
glycoprotein SLC transporters OAT/OCT Hepatic transporters Renal
transporters
3. A pt comes to you with chief complaints of diarrhoea. He is
a known case of arrhythmias on quinidine. You advice him to take
loperamide. After taking the drug , he goes into respiratory
depression. What do you think happened?
4. transport Carrier mediated Active primary secondary
Facilitated Non carrier mediated Passive
5. Transport Ion Channels Transporters Aquaporins
6. Aquaporins bi-directional membrane channels -transport water
not ion channels- H2O is transported as an uncharged molecule
driving force-osmotic gradient 13 AQP genes in the human
genome
7. Transporters It forms an intermediate state with the
substrate Turnover is 101 to 103 s saturable Channels They occur in
an open and closed state Turnover is 106 to 108 s1 Non
saturable
8. Transporters membrane proteins control influx of essential
nutrients and ions efflux of cellular waste, environmental toxins,
drugs, and other xenobiotics coded by 7% of the total number of
genes
9. Physiological Role of Transporters Regulates the
distribution and bioavailability of drugs Removal of toxic
metabolites and xenobiotics from cells into urine,bile and
intestinal lumen Transport of compounds out of the brain across the
blood brain barrier
10. Types of membrane transporters 2000 genes in humans code
for transporters or transporter related proteins 2 major
superamilies- ABC and SLC Most ABC proteins are primary active
transporters SLC superfamily includes facilitated transporters and
ion coupled secondary active transporters
11. ABC 49 genes- classified into 7 families unidirectional
Widely recognised are P- glycoprotein and CFTR SLC 48 families with
315 transporters bidirectional SERT encoded- SLC6A4 DAT encoded-
SLC6A3
12. Vectorial transport
13. What does the term vectorial imply?? Transport of an ion or
molecule across an epithelium in a certain direction (e.g.
absorption of glucose by the gut). Vectorial transport implies a
nonuniform distribution of transport proteins on the plasma
membranes of two faces of the epithelium.
14. Regulation of transporter expression
15. Following receptors form heterodimers with 9 cis- retinoic
acid receptors Pregnane X receptor (PXR) Peroxisome proliferator
activated receptor (PPAR) Retinoic Acid Receptor (RAR) Farnesoind X
Receptor (FXR)
16. Pregnane X Receptor Activated by 1.Phenobarbitone
2.Rifampicin 3.Carbemezapine 4.Phenytoin
17. ATP Binding Cassette Transporter protein superfamily
Transmembrane proteins utilize the energy of ATP hydrolysis 48 ABC
genes in humans Can be divided into 7 groups
19. Structure The common structure of all ABC consists of 2
Distinct domains Transmembrane domain (TMD) Nucleotide binding
Domain (NBD)
20. In most Exporters- the N terminal TMD and C terminal NBD
are fused to form a single polypeptide chain arranged as
TMD-NBD-TMD-NBD Importers- have an inverted organisation- NBD-TMD-
NBD-TMD where the ABC domain is N- terminal whereas the TMD is C
terminal
21. ABC EXPORTER
22. GENE NAME FAMILY NAME NO. OF FAMILIES DIS. ASOCIATED ABCA
ABC A 12 Tangiers dis Stargadts dis ABCB ABC B 11 PFIHC ABCC ABC C
13 Cystic fibrosis Dubin Johnson syn ABCD ABC D 4
Adreno-leukodystrophy ABCE ABC E 1 ABCF ABC F 3 ABCG ABC G 5
Sitosterolemia
23. Dubin Johnson syndrome
24. Dubin Johnson syndrome
25. SLC Transporters Includes 48 families and represents 315
genes in human genome Contain hydrophobic transmembrane alpha
helices Includes facilitative transporters and secondary active
transporters
26. Nomenclature SLCnXm : SLC : root name n: family X:
subfamily m: isoform
27. Intestinal Transporters
28. Various transporters are expressed on the brush border of
the intestine Influx transporters expressed In the gut, improve
absorption eg. PEPT-1, OATB1 PEPT1- mediates transport of drugs-
B-Lactams, ACEI, Valacyclovir Efflux transporters limit the
absorption of drugs eg. P gp, BCRP, MRP2
29. BCRP member of the ABC Transporter family Plays role in
secretion of topotecan When topotecan, substrate for BCRP and
GF120918( ELACRIDAR), an inhibitor of both BCRP and P gp were
administered orally, bioavailability of topotecan was increases in
P- gp deficient mice
30. BCRP Is expressed also in the bile canalicular membrane and
placenta In pregnant GF120918 Treated P gp deficient mice,fetal
penetration of topotecan was 2 fold higher
31. Oral drug inhibitor transporter Digoxin quinidine P gp
Paclitaxel Cyclosporin P gp methotrexate Omeprazole BCRP irinotecan
gefitinib BCRP
32. Hepatic transporters
33. Statins are substrate for uptake transporters Uptake
transporter- OATP1B1 Efflux transporter- MRP2
34. Temocapril Temocaprilat- excreted in both bile and urine
Plasma concentration of temocaprilat remains unchanged even in
patients of renal failure Temacoprilat is a bisubstrate of OATP and
MRP2, whereas other ACEI are not good substrates of MRP2
35. IRINOTECAN CPT-11 SN-38 Glucuronide conjugation Excreted in
bile by MRP-2 DIARRHOEA PROBENECID
36. Renal Transporters Renal transporters play an important
role in drug elimination ,toxicity and response Transporters may
have dual specificity for organic anions and cations
41. Role in CNS Involved in neuronal reuptake- SLC1 and SLC6
SLC6 responsible for reuptake of 1. norepinephrine 2. dopamine 3.
serotonin 4. GABA
42. SLC6A1 /GAT1- Target for the drug tigabine SLC6A2/NET -
Target for despramine SLC6A3/DAT- cocaine and its analogs
SLC6A4/SERT- Target for fluoxetine and paroxetine
43. Role of transporters in drug resistance
44. In 1976, Ling reported the overexpression of a membrane
protein in colchicine resistance Chinese hamster ovary cells,
acquired resistance to various other drugs!!
45. Q.1. What is the genetic basis??? Q.2. How frequency will
it occur?????
46. Hypothesis If a drug resistance occurs at rate of 10-7
Resistance to 2 unrelated drugs 10 -14 Shouldnt that be very
rare????
47. P glycoprotein
48. 170 kDa transmembrane glycoprotein ATP-dependent drug
efflux pump responsible for decreased drug accumulation mediates
the development of resistance to anticancer drugs also functions as
a transporter in the BBB
49. P gp in humans MDR1 Responsible for efflux of drugs MDR2
Transport of phosphatidylcholine to bile
57. Relation between Pgp and cyp3A4 Both are regulated by PXR P
gp keeps intracellular concentration within the range of CYP3A4
Metabolism results In better substrates of P gp cyp3A4 P gp
58. PXR P gpCYP3A4
59. Transporters and drug resistance Play a critical role in
developing resistance to Anti cancer Anti microbials Anti
epileptics
60. Why resistance is so important to study? result in
treatment failure increased costs, prolonged duration of hospital
stay higher morbidity and mortality rates
61. How to over come this resistance?
62. Approaches to overcome MDR 1. REVERSAL AGENTS known as
chemosensitisers inhibit P gp increase intracellular concentration
of the drug
63. First generation agents Have their own pharmacological
action Were used in high doses Not selective to P gp Therefore,
high toxicity 1. Cyclosprine hepatic, renal, myeloid ,
neurotoxicity 2. Verapamil- cardiotoxicity
64. Second Generation Agents Selective and less toxic
Substrates of P gp and CYP3A4 Lead to unpredictable absorption and
metabolism 1. Valspodar ( R enantiomer of verapamil) 2.
Biricodar
65. Third generation agents Agents were not substrates of
CYP3A4 Selectively and potentially inhibit Pgp 1. Tariquidar XR9576
2. Zosuquidar LY335979 3. Laniquidar R101933
66. Newer ways to overcome MDR Monoclonal Ab- MRK 16- reversed
MDR in transgenic mice Epothilones- not recognised by P gp Increase
rate of influx of anticancer drug by increasing lipophilicity of
the compound
67. So why do we need these transporters??? To regulate
bioavailability To act as drug targets To eliminate toxins To
overcome resistance
68. Involvement of a transporters is more of a rule than an
exception!!!!