Nuclear receptors for developing new drug therapy By Dr. Armaan Singh

Nuclear receptors for developing new drug therapy By Dr. Armaan Singh

1. By
Dr. Armaan Singh
NUCLEAR RECEPTORS FOR DEVELOPING NEW DRUG THERAPY

2. RECEPTOR :( Latin: means a receiver)
DEFINITION:
 A macromolecular component
of the organism that binds the drug
and initiates its effect.
 To elicit the pharmacological
action , the functional group of the
drug have to interact with the
complementary chemical groupings
of the biologically important integral part of the organism is
called receptor.

3. Functions of Receptors:
Receptors regulates the:-
1.Enzyme activity
2. Permeability/Transport
3. Structural features
4. Template function
5. Homoeostasis
6. Cellular regulatory signals
etc

4. Historical background of receptor:
The concept of receptor is
first established in 1878 by
John N. Langley demonstrating
the interaction of atropine and
pilocarpine with cellular component
to elicit the action.
Paul Ehrlich coined the
cellular component as receptive
substance or receptor in 1907.
John Newport Langley(1856-1926)
An English Physiologist
Paul Ehrlich (1854-1915)
A German Microbiologist

5. Types of RECEPTORS:
1. Cell surface receptors
I. Ligand gated ion Channels)
eg: Nicotinic Cholinergic, GABAa
II. G-protein coupled receptors.
eg: Muscarinic, β-adrenergic, DopamineD2
2. Enzyme linked receptors.
eg: Tyrosine Protein kinase receptor
3. Nuclear receptors.
eg:GR receptor, AR receptor, PPAR

6. How does Cell surface Receptor elicits
its action:
Cell Membrane
Unbound Endogenous Activator
(Agonist) of Receptor
Inactive Cell Surface Receptor
Extracellular
Compartment
Intracellular
Compartment
N.B : Receptors are Present in equilibrium state of active and inactive
conformation.
Agonists binds with the active conformations.

7. Extracellular
Compartment
Intracellular
Compartment
Cell Membrane
Bound Endogenous Activator (Agonist) of Receptor
Active Cell Surface Receptor
Cellular Response

8. Cell Membrane
Displaced Endogenous Activator (Agonist) of Receptor
Inactive Cell Surface Receptor
Extracellular
Compartment
Intracellular
Compartment
Bound Antagonist of Receptor (Drug)
N.B: Antagonist binds to the inactive conformations of the receptor.

9. How does Enzyme Receptor
elicit its action:
Active Enzyme
Substrate Product
Cellular Function
Inactive Enzyme
Substrate
Bound Enzyme
Inhibitor (Drug)

10. NUCLEAR RECEPTOR :
Hormone receptors that bind ligand and act in the cell nucleus rather
than at the cell surface and regulate gene expression.
 Nuclear receptor is also called as true receptors which involved in
increase or decrease in the production of certain RNAs and mRNA along
with corresponding enzyme and protein.
 Recent data demonstrates that these are the prototypes of a
large family of receptors for small lipophilic signaling molecules
including steroid hormone, fat soluble vitamins fatty acid
metabolites and cholesterol metabolites.

11. How does Nuclear Receptor
elicit its action:
Intracellular
Compartment
Nucleus
DNA
Modulation of
Transcription
Active Nuclear Receptor
Bound Endogenous Activator
(Agonist) of Nuclear Receptor

13. Displaced Endogenous Activator
(Agonist) of Nuclear Receptor
Intracellular
Compartment
Nucleus
DNA
Bound Antagonist
of Receptor (Drug)
Inactive Nuclear Receptor
In Cytosolic Compartment
Inactive Nuclear Receptor
In Nuclear Compartment

14. Classification of nuclear receptors:

The following is a list of the 48 known human nuclear receptors
categorized into the following families:
Subfamily 1: Thyroid Hormone Receptor-like
Group A: Thyroid hormone receptor (Thyroid hormone)
1: Thyroid hormone receptor-α (TRα; NR1A1, THRA)
2: Thyroid hormone receptor-β (TRβ; NR1A2, THRB)
Group B: Retinoic acid receptor (Vitamin A and related compounds)
1: Retinoic acid receptor-α (RARα; NR1B1, RARA)
2: Retinoic acid receptor-β (RARβ; NR1B2, RARB)
3: Retinoic acid receptor-γ (RARγ; NR1B3, RARG)
Group C: Peroxisome proliferator-activated receptor(fatty acids,
prostaglandins)
1: Peroxisome proliferator-activated receptor-α (PPARα; NR1C1, PPARA)
2: Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ; NR1C2,
PPARD)
3: Peroxisome proliferator-activated receptor-γ (PPARγ; NR1C3, PPARG)

15. Group D: Rev-ErbA (heme)
1: Rev-ErbAα (Rev-ErbAα; NR1D1)
2: Rev-ErbAβ (Rev-ErbAβ; NR1D2)
Group F: RAR-related orphan receptor(cholesterol, ATRA)
1: RAR-related orphan receptor-α (RORα; NR1F1, RORA)
2: RAR-related orphan receptor-β (RORβ; NR1F2, RORB)
3: RAR-related orphan receptor-γ (RORγ; NR1F3, RORC)
Group H: Liver X receptor-like (oxysterol)
3: Liver X receptor-α (LXRα; NR1H3)
2: Liver X receptor-β (LXRβ; NR1H2)
4: Farnesoid X receptor (FXR; NR1H4)
Group I: Vitamin D receptor-like
1: Vitamin D receptor (VDR; NR1I1, VDR) (vitamin D)
2: Pregnane X receptor (PXR; NR1I2) (xenobiotics)
3: Constitutive androstane receptor (CAR; NR1I3) (androstane)

16. Subfamily 2: Retinoid X Receptor-like
Group A: Hepatocyte nuclear factor-4(HNF4) (fatty acids)
1: Hepatocyte nuclear factor-4-α (HNF4α; NR2A1, HNF4A)
2: Hepatocyte nuclear factor-4-γ (HNF4γ; NR2A2, HNF4G)
Group B: Retinoid X receptor(RXRα) (retinoids)
1: Retinoid X receptor-α (RXRα; NR2B1, RXRA)
2: Retinoid X receptor-β (RXRβ; NR2B2, RXRB)
3: Retinoid X receptor-γ (RXRγ; NR2B3, RXRG)
Group C: Testicular receptor
1: Testicular receptor 2 (TR2; NR2C1)
2: Testicular receptor 4 (TR4; NR2C2)
Group E: TLX/PNR
1: Human homologue of the Drosophila tailless gene (TLX; NR2E1)
3: Photoreceptor cell-specific nuclear receptor (PNR; NR2E3)
Group F: COUP/EAR
1: Chicken ovalbumin upstream promoter-transcription factor I (COUP-TFI; NR2F1)
2: Chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII; NR2F2)
6: V-erbA-related gene|V-erbA-related (EAR-2; NR2F6)

17. Subfamily 3: Estrogen Receptor-like:
Group A: Estrogen receptor (Sex hormones: Estrogen)
1: Estrogen receptor-α (ERα; NR3A1, ESR1)
2: Estrogen receptor-β (ERβ; NR3A2, ESR2)
Group B: Estrogen related receptor
1: Estrogen-related receptor-α (ERRα; NR3B1, ESRRA)
2: Estrogen-related receptor-β (ERRβ; NR3B2, ESRRB)
3: Estrogen-related receptor-γ (ERRγ; NR3B3, ESRRG)
Group C: 3-Ketosteroid receptors
1: Glucocorticoid receptor (GR; NR3C1) (Cortisol)
2: Mineralocorticoid receptor (MR; NR3C2) (Aldosterone)
3: Progesterone receptor (PR; NR3C3, PGR) (Sex hormones:
Progesterone)
4: Androgen receptor (AR; NR3C4, AR) (Sex hormones: Testosterone)

18. Subfamily 4: Nerve Growth Factor IB-like
Group A: NGFIB/NURR1/NOR1
1: Nerve Growth factor IB (NGFIB; NR4A1)
2: Nuclear receptor related 1 (NURR1; NR4A2)
3: Neuron-derived orphan receptor 1 (NOR1; NR4A3)
Subfamily 5: Steroidogenic Factor-like
Group A: SF1/LRH1
1: Steroidogenic factor 1 (SF1; NR5A1) (phospholipids)
2: Liver receptor homolog-1 (LRH-1; NR5A2)
Subfamily 6: Germ Cell Nuclear Factor-like
Group A: GCNF
1: Germ cell nuclear factor (GCNF; NR6A1)
Subfamily 0: Miscellaneous
Group B: DAX/SHP
1: Dosage-sensitive sex reversal, adrenal hypoplasia critical region, on
chromosome X, gene 1 (DAX1, NR0B1)
2: Small heterodimer partner (SHP; NR0B2)
Group C: Nuclear receptors with two DNA binding domains (2DBD-NR) (A novel
subfamily)

19. Why Nuclear Receptor is
preferred:
Nuclear receptors
have the ability to
directly bind to DNA and
regulate the expression
of adjacent genes.
Consequently nuclear
receptors play key roles
in both embryonic
development and adult
homeostasis.

20. Differences of between Nuclear
Receptors and other types of receptors:
Other Types of Receptors Nuclear Receptors
1.They present in different sites of
tissues and cells and bind and elicit
without involvement of nucleus.
2. Elicit pharmacological response due
to release/inhibition of endogenous
mediators. ( transmitter, hormones,
autacoids).
3.Drugs acts by modulating the
receptor to produce/inhibit the release
of mediators.
4. They shows changes in
physiological parameters,
1.They present with association of
nucleus and elicit the response with
involvement of nucleus.
2. Elicit the response on the basis of
transcription of gene, regulates protein
synthesis.
3. Drugs acts which cause the
transcription of gene from its genetics
based.
4. They shows changes on structural
basis of target cells.

21. Functions of Nuclear receptor:
To propagate the regulatory signals from outside to within effectors
cell.
To amplify the signal.
To integrate various extracellular and intracellular regulatory signals.
To adapt changes and maintain homeostasis.
To facilitates gene expression so that specific mRNA is synthesized ,
which moves to ribosome and directs synthesis of specific proteins
which regulates the activity of target cells.

22. Nuclear Receptors in Therapy:
 Nuclear Receptors are one of the major target area of modern
therapy and of research.
 A large number of receptors are identified and so screening of
their Ligands are going in clinical trials as well as few of them
becoming patent.

23. PPAR (Peroxisome proliferators activated
receptor)
Types of PPAR Receptors:
PPARα expressed in Liver, Kidney, Heart, Muscle, Adipose Tissue
and others.
PPAR β expressed mainly in brain, adipose tissue and skin.
PPAR γ almost all the tissue.
PPARs heterodimerize
with Liver X Receptors ( LXR),
or Retinoid X Receptors( RXR),
or Vitamin D receptors.

24. Functions:
 Control of Cellular differentiation and Development.
 Control of Metabolism ( Carbohydrate, Lipid, protein).
Genetics:
PPARα - chromosome22q12-13.1 (OMIM 170998) PPARβ/δ
- chromosome 6p21.2-21.1 (OMIM 600409)
PPARγ- chromosome 3p25 (OMIM 601487).
Disease involved : Diabetes Type 2, Atherosclerosis, Obesity
and Hyperlipidemia.

25. PPAR Agonists for treatment:
PPARα : Fibrates ( Clofibrate, Gemfibrozil,
Fenofibrate).
PPARγ : Thiazolidinediones ( Roziglitazone,
Pioglitazone, Perflurooctanoic acid).
Pharmacology:
Agonist Receptor Enhance
Transcription of responsive
genes
Glucose entry to muscle
and suppressed Reverse insulin resistance
Gluconeogenesis.

26. Gene transcription cartoon showing interactions of ligand/PPAR/RXR heterodimer with
cofactors and basal transcription machinery(RNA Polymerase II).

27. GR ( Glucocorticoid Receptors):
Physiological function:
 GR express and regulates the genes controlling for
development , metabolism and immmune response.
GR and LRH-1(Liver Receptor Homolog-1) upregulates the
expression anti-inflamatory proteins in nucleas.
Disease involved: Inflammatory bowel syndrome, Auto
Immune disorder, rheumatoid arthritis, gout etc.

28. Agonists : Cortisol, Prednisolone,
Dexamethasone.
Genetics: NR3C1, NR5A2 , NR3C2 Gene
Pharmacology: ( Anti- inflammatory activity)
Agonist Receptor Enhance
Transcription of
responsive genes
.Inhibition of PhospolipaseA2Production of lipocortin TNF, PAF
and related proteins.

29. Immunosuppressive activity of GR
Agonist Receptor Transcription of
Responsive Genes
Decrease proliferation of Inhibition of IL
synthesis.
B-Lymphocytes.
Inhibition of T-
lymphocyte
production Decrease antibody
production

30. Xeroreceptors targets for Liver
Disease
Xeroreceptors:
CAR ( Constitutive Androstane Receptor)
PXR (Pregnane X Receptors).
Physiological function:
Activation and consequences on Lipid metabolism
Glucose Homeostasis
Inflammatory Responses
Genetics: Targeted Genes
CYP3A4, CYP2B6, CYP2C9
MDR1, GT1A1, MRP2, UGT1A1

31. Disease Involved:
Non-alchoholic fatty liver, Hepatic Steatosis,
Obesity, Inflammation
Agonists : Rifampin, Nifidipine, Hyperferlin, RU486, HNF4

32. Nuclear Receptor Targets of
Cancer Therapy:
Nuclear Receptors targeted
mainly for Cancer therapy are.
1.Estrogen Receptor ( ER)
2. Vitamin D Receptor (VDR)
3.PPAR γ
4. Androgen Receptor (AR)
5. Progesterone Receptor (PR)

33. Estrogen Receptor and Cancer
 Estrogens are key
regulator of growth,
differentiation, and function in
large number of tissue.
 Biological effects of
estrogens are mediated by
ERα and ERß
Structure of estrogen

34. Esrogen Receptors Types:
1: Estrogen receptor-α (ERα; NR3A1, ESR1)
2: Estrogen receptor-β (ERβ; NR3A2, ESR2)
ERα is predominant and expressed in breast,
uterus, cervix and Vagina.
ERß is predominantly localized in ovary,
prostate, testis, spleen, Lung, hypothalamus
and thymus.

35. SERM and Breast Cancer
therapy:
Pharmacology:
Breast cancer dependent upon the presence of estrogen for
growth.
The objective of treatment is SERMs ( Selective estrogen
receptor modulators) to inhibit tumor growth by interrupting
the estrogen signaling process.
SERMs shows estrogenic effect in some tissue and anti
estrogenic in others.

36. Tamoxifen ( Nolvadex®, Astra Zeneca ):-
It has antagonistic effect in mammary tissue, while agonist effect in
bone, uterine and cardiovascular tissue.
An ideal agents foe breast
cancer which retain the
beneficial effects of estrogen
in bone, brain and
cardiovascular tissue.
It inhibit the mutagenic effect of estrogen in breast.

37. Role of VDR in Breast Cancer:
VDR binds with 1a, 25-dihydroxy cholecalciferol D3 and
regulates the transcription of Vit-D responsive gene.
This regulates the calcium endocrinology and involved in
homeostasis such as skin, muscle, pancreas and
reproductive organs.
Activated VDR induces genes that suppress proliferation and
stimulate differentiation of cells in the normal mammary
gland.
Vitamin D receptor (VDR) and
Postmenopauseal breast cancer:

38. VDR in Breast cancer therapy in post
menopausesal women:
Pathogenesis:
Aging reduces the production of Vitamin D by
epidermis.
Estrogen deficiency decreases both metabolic
activation of Vitamin D and expression of the
VDR.
VDR agonists:
Nearly 400 structural analogs of Vit.D have
been synthesized but few have advanced in
clinical trials due to preliminary toxicity testing.

39. VDR and Colorectal Cancer:
N.B:
Cancer of the large intestine (colon) and rectum, collectively termed
colorectal cancer.
 It is the third most common form of cancer, behind lung and breast
cancer.
Vitamin D receptors is also considered as target of colon cancer along
with Glucocorticoid receptor.

40. Pathogenesis:
Diet with high fat
Bile acid ( Lithocholic acid) poorly reabsorbed
A toxic metabolite in enterohepatic
circulation
High conc. In colon
Induce DNA strand breakage, inhibit DNA repair
enzyme
Colon Cancer

41. Pharmacology of VDR in colon cancer
Vit-D
VDR
LCA Catabolism of CYP3A, a target
gene
Increased detoxification of LCA
and elimination
Protection against colon cancer.

43. Examples: Ligands and target Genes of
some nuclear receptors:
Receptor typeLigands / Drug Disease target
PPARα
PPARγ
PPARγ
GR
LXR
ER ( SERM)
ER β
Fibrates :
Clofibrate
Gemfibrozil
Fenofibrate
Thiazolidinediones
Roziglitazone
Pioglitazone
Perflurooctanoic acid
RS544
Dexamethasone
Prednisolone
TO901317
Tamoxifen
Raloxifen
Mifepristone( Antagonist)
Diabetes Type2, Hyperlipidemia.
Diabetes Type2, Hyperlipidemia
Atherosclerosis
Anaplastic cancer
Different inflammatory syndromes.
Alzheimer Disease
Breast cancer, Osteoporosis
Unwanted abortion

44. Conclusion:
Functioning as transcription factors and controlling
cellular process at the level of gene expression.
Modulation of NR activity produces selective
alterations in downstream gene expression.
Nuclear Receptors are an attractive and relatively
unexploited target for drug development.

45. References:
Books:
Essential of Medical Pharmacology, 6
th
Edition
by K. D. Tripathi, Page no. 40-53