Transcript pigmentation disorder

Faculty of Pharmacy, Lille II
Pauline Fontaine
Friday 12th, February 2010
Clotilde Bourdon
Antoine Henninot
The skin: an heterogeneous system
5 main functions:
•Barrier : Langerhans cells + Sebaceous glands + Melanocytes + Hair
follicles
•Sens of touch, sensation : Nerve endings Merkel cells
•Regulates body temperature
•Excretes waste product and excess salt
•Syntheses vit D
Skin appendages: hair, nails, sweat glands, sebaceous glands
CAUTION WITH THE TARGETS
TOUGH TO PENETRATE
Epidermis
 Skin's outer structure
 Stratified
 Stratum corneum = outermost layer, dead cells: not
permeable
 Keratinocytes (++), melanocytes, Langerhans cells,
Merkel cells
 Melanocytes (5% of the cells)
 Avascular
Dermis
 Melanocytes underneath the basal layer i.e. within the
dermis
 Contains:
- blood vessels
- lymph vessels
- hair follicles
- glands (produce sweat and sebum)
=> Rich capillary bed for systemic
drug absorption
3 major routes to entry into the skin
 Sebum and surface material (1)
 Skin appendages (3)
 Epidermal route (2) -> Inter- or trans-cellular route
Lipophilic
substances
Hydrophilic
+ Lipophilic
substances
Figure 1. Simplified representation of skin showing routes of penetration: (1) through the sweat ducts; (2)
directly across the stratum corneum; (3) via the hair follicles.Reproduced with permission from Ref 10.
Origin of cutaneous pigmentation
 Skin color determined by its content in pigments
 Melanins +++++,
 Oxygenated and reduced hemoglobin
 and Carotene
 Other factors
 epidermal thickness
 vascular supply
Synthesis of Melanins
 In the melanocytes, within melanosomes
 Through fixation of α-MSH on MC1R

with UVB rays
 Melanins absorb UV rays => protection
α-Melanocyte-Stimulating Hormone
Hypophysis
Synthesis/Secretion
POMC
Hydrolysis
ACTH
α-MSH
 Peptide
 endogenous agonist for all Melanocortin Receptors
 regulator of skin and hair pigmentation
 Short t1/2 in circulation
POMC
ACTH
Melanocyte
↗AMPc
α-MSH
Eumelanin
+
+
-
MC1R
ASIP
↘AMPc
Phemelanin
Tyrosinase
Tyrosine
Dopaquinone
DOPA
Glutathion
ou Cystein
Leucodopaquinone
TRP1
Cysteinyl
dopa
dopachrome
DHICA
DHI
Indole-5,6quinone
DHICA-melanin
Eumelanin
TRP2
1,4-benzothiazinyl
Alanine
Phaeomelanin
Melanosome migration within
melanocytes
=> Maturation
(polymerisation)
Migration of the melanosomes to the
keratinocytes
Melanins matured:
Melanosomes -> keratinocytes
Melanosomes accumulate above
nucleus of keratinocytes
Keratinocytes -> superficial layers of
the epidermis
Membrane of the melanosomes
digested by enzymes
Melanocytes
Black skin
White skin
Similar number of melanocytes BUT melanin synthesis and melanocytes’
migration to the keratinocytes more significant for black skin
Faculty of Pharmacy, Lille II
Pauline Fontaine
Friday 12th, February 2010
Clotilde Bourdon
Antoine Henninot
Overview of the diseases
Melasma
Lentigo
Hyperpigmentation
Iatrogenic
hyperpigmentation
Pregnancy mask
Post-acneic or
cicatricial
hyperpigmentation
Hypopigmentation
Vitiligo
Vitiligo
Hyperpigmentation disorders
 Unknown etiologic origin
 High prevalence
 Lentigo: 90% of the population over 70
 Melasma (chloasma): 8.8% of the latino american women
 Alter people’s quality of life
hyperactivation
of the
melanocytes
melanin
 Melasma: reemergence of the lesions as soon as the
first exposition to the sunlight
Melasma
Lentigo
Current treatments
 Old bleaching agents



Hydroquinone (tyrosinase inhibitor)
Azelaic acid
Corticoïd
 Associated with « peeling » / dermabrasion products


Vitamin A
Glycolic acid
 Best treatment: Kligman trio



Corticoïd (dexamethasone)
Hydroquinone
Retinoic acid
Current treatments (continued)
 Satisfying BUT: - unconstant treatment
- local treatment very long
- numerous Adverse Events : irritation
(hydroquinone (5%), retinoic acid)
• Depigmenting duo: hydroquinone corticoid
(hydrocortisone) less irritant BUT less effective
• => B/R ratio NOT acceptable for skin disorders
•
1st TREATMENT= SOLAR PROTECTION!!!
Meeting with Dr.Riboulet, Dermatologist
Main ideas :
 Keratolytic peeling : caution with the concentration, otherwise ->
inflammation, post –inflammatory hyperpigmentation
 Total depigmentation with MBEH (Mono Benzyl Ether
Hydroquinone) prohibited in France to treat Melasma -> too
hazardous
 Whitening agent : undesired hypopigmentation risk
Hypopigmentation disorders
 Vitiligo
 High prevalence: 0.5 - 2% of the population
 Unknown etiology
 3 major hypotheses, not exclusive of each other:
 immunologic factors
 oxidative stress
 sympathetic neurogenic disturbance
VITILIGO
Current treatments
 Puvatherapy (psoralen + UVA) no longer used
(known carcinogenic risk)
 UVB narrow band
 For 10 years: unknown risk cancer
 Topical treatments
 Tacrolimus (off label)
 Corticoïd
 Surgery: too invasive technique
 If spot entirely healed, no relapsing
Meeting with Dr.Riboulet, Dermatologist
 « patients with vitiligo have a bad observance with their
treatments because they are restrictive and difficult.
There is then definitely a market for new efficacious
treatments »
 « So old treatments! »
 « Camouflage »
Meeting with Dr.Riboulet, Dermatologist
Conclusion :
 patients disappointed with their treatments
 the market exists, patients are waiting for
efficacious treatments
=> new potential targets exploration
Real diseases or just
quality of life?
 Skin =body's envelope, reactions and emotions
expressed via the skin
 Means of exercising power over others, captivating,
influencing impressions and judgement, conquering
 Significant psychological impact
 Dermatology Life Quality Index (DLQI)
Reasoning
 list of potential targets for each indication (hypo- +
hyper- pigmentation)
 For each target
 Location
 Advantages / Inconvenients
 Drugs on the market
 Target’s mechanism of action
Is the target interesting???
If YES => development
Hypopigmentation
TARGET
LOCATION (skin or
ubiquitous)
Advantages
Drawbacks
Marketed
medicines
Mechanism of action
POMC
Ubiquitous, synthesis in the
hypophysis, the hypothalamus
and the melanocytes.
Action through Alpha-MSH
Production of alpha, betha
gamma MSH, and some other
different lipocortineq
=> Different levels of action, no
specificity.
ACTH
Storage in the hypophysis
Action through Alpha-MSH
•Not specific
•Production of
mineralocorticoids,
glucocorticoids, androgens by
the surrenal glands
Stimu-ACTH
(diagnosis
product)
Binding to transmembrane
MC2R of the surrenal glands’
cells
Preo cAMP=> kinase
activation
Enzymatic activation and
hormones production
Alpha-MSH
•Action in learning and
memory, blood pressure,
pigmentation, immune
modulation,weight
homeostasis, and others
•Skin pigmentation with exposition
to UV-B or sunlight
•Potent anti-inflammatory effects
•Repair of DNA photoproducts
caused by UV
• Reduce oxidative stress
•Up-regulation of genes and their
encoded proteins: Mitf
• ErbB3 decreased by αMSH
Peptide => parenteral
administration (SC )
Topical administration:
biodisponibility 0.05%
Withdrawn of the
market:
•Afamelanotide
•Menalotan
•Natural ligand of MC1R,
provoks increase in the
intramelanocyte cAMP
concentration
and stimulates
eumelanogenesis
• UV induced oxidative DNA
damage by
inhibiting the generation of
hydrogen peroxide, and
enhances the repair of DNA
photoproducts
• Stimulates the differentiation
of melanocytes
MC1R
Skin cells (melanocytes,
keratinocytes,sebocytes and
others), liver, testis, fat tissue,
ovary (corpus luteum), intestin,
red muscle, splin, kidney, heart,
eyes, brain, immune cells
(macrophages,
fibroblasts, monocytes, mast
cells, and neutrophils
dendritic cells), the pituitary,
placenta, endothelial cells,
glioma cells, astrocytes, brain
(low levels)
• High constitutive activity
• Involvement in endogenous
control of some inflammatory
processes
•Mc1r is activated by all
melanocortin mimetics
•Several MCRs exist.
The molecule has to be selective
for MC1R in order to avoid AE
•Perhaps Increased risk of skin
cancers (regulation of
melanocytes proliferation)
•Several agonists
have been
synthetised by
different
laboratories.
•MC1R activation via its ligands
leads to the kinase A activation,
increase in the intramelanocyte
cAMP concentration
and stimulates
eumelanogenesis
•stimulates the differentiation
of melanocytes
Production des differentes
hormones selon la cellule ou
l’on se trouve
Hypophyse
Melanotrope de l’hypophyse
melanocytes
Hypopigmentation
α-MSH Synthesis
 POMC
 Central action
 Involved too early in the α-MSH pathway and involved
in too many signalling pathways
 ACTH
 Central + Peripheral actions
 Involved in too many signalling pathways
 Production of mineralocorticoids, glucocorticoids,
androgens by the surrenal glands
Hypopigmentation
Action on MC1R
 α-MSH
 Action on the different MCRs (MC1R)
 Activation of melanogenesis
 Anti inflammatory effect
 MC1R
 Present on inflammatory cells and melanocytes
 Role within melanocytes: melanogenesis alone
POMC
ACTH
Melanocyte
↗AMPc
α-MSH
Eumelanin
+
+
-
MC1R
ASIP
↘AMPc
Phemelanin
MC1R belongs to the MCRs family
 5 G-protein-coupled transmembrane receptors (MC1R-5R),
 Positively coupled to adenylyl cyclase
Pigmentation
MC1R
Adrenal
function
MC2R
Sexual
function
MC4R
Energy
homeostasis
MC3,4R
MCR
Immunity
MC1R
Sebaceous
gland lipid
production
MC3,4R
Weight
control
MC3,4R
Melanocortin Receptor 1: MC1R
Melanocytes
Endothelial /
Immune cells
Testis- Ovaris
Distribution
Sebocytes
Hypophysis
α-MSH binds preferentially to MC1bR
Binding Assay IC50a (nM)
MC-1bR
MC-3R
MC-4R
MC-5R
3.9 ±0.9
19 ± 2
19 ± 2
120 ± 19
Ideas to develop for Vitiligo
 MC1R : preferential target
+
Cutaneous
pigmentation
Antiinflammatory
effect
No
carcinogenic
effect
MC1R agonist
-
Screening
difficulty
Type b receptors very difficult to screen EXCEPT for MC1bR!!!
MC1R: Peptide Rc with an external loop (≠ Opiate Rcs)
Action on MC1R
 Agonist MC1R discovered by BMS
 Peptidic agonist: Melanotan I
Ac-Ser-Tyr-Ser-NorLeu-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2
Some other peptidic agonists
1) Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg-Ava-Lys-Pro-Val-NH2
Ava9-10-NDP-αMSH

2 ) Ac-Ser-Tyr-Ser-Nle-Glu-His-D-Phe-Arg–Gly-Lys-Pro-Val-NH2
desTrp9-NDP- α MSH
MC1bR Agonists: Analogs of NDP- αMSH
Binding Assay IC50a (nM)
Assay EC50b
hMC-1bR
hMC3R
hMC4R
1
5.1 ± 0.5
>5000
>5000
3500±
190
2.9 ± 0.21
2
16 ± 1
>2500
>2500
>2500
9.6 ± 0.71
hMC5R
hMC-1bR
hMC3R
11% at
2 µM
2% at
2 µM
hMC4R
hMC5R
0% at
2 µM
>1500
1% at
2 µM
9% at 1
Clinical trials of Melanotan I
 Subcutaneous administration
 2 significant findings: Melanotan I tolerable and effective at :
 melanin density in the skin (significant)
 UV-induced sunburn cells (significant) in subjects most at risk
for UV induced skin damage
 1% increase in melanin density => skin cancers roughly
decreases by a factor of 2
MTI beneficial as a protection against UV-induced
skin damage in populations most at risk for sunlightinduced skin damage and carcinogenesis
Phase III, 1991
Melanotan I
 Melanotropins : the minimal message sequence (bioassays in frog and
lizard skin)
α-MSH :
Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2
minimal sequence required for agonistic activity, minimal chain length for observable biological
activity
Important potentiating AA, contibute significantly to the biopotency of alpha MSH
A super potent melanotropin????? How???
 Protect α-MSH from inactivation by oxidative mechanisms :
Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2
Norleucine : resulting analogue active or more active in most bioassays
D-enantiomer instead of L-Phe : analoque proved to be 10-1000 times more active in one or more
bio essays
Melanotan II
 Lactam bridge between amino acids 5 and 10
Ac -Nle- Asp-His-D-Phe-Arg-Trp-Lys-NH2
 Subcutaneous administration
 Much more active than Melanotan I in stimulating
melanogenesis
 Very long t1/2
Melanotan I and II
 Advantages of those peptides :
More
active
Resitant to
enzimatic
inactivation
 Capacity of increasing melanin production =>
Potent
stimulators of
melanogenesis
of skin
cancer incidence
Photoprotective strategy: «tanning without the sun»
Melanotan I and II side effects:
Racoon effect
«I got some completely new spots. Got a few facial freckles and some black
spots elsewhere. So I suppose neither I or II are completely free of
hyperpigmentation side effects »
Epitan trial in 2003 for the melanotan implant
Side effects (continued)
 Spots and hyperpigmentation
 Nausea
=>
 Flushing
TOPICAL
ADMINISTRATION
 Action on sexual arousal
 Despite all those AE, Melanotan (normally used
for Congenital Protoporphyria) is misued to get
a tan
Inconvenients of peptides
 Peptides-> unstable orally
 Subcutaneous administration too complicated if
repeated
 Topical administration
=> skin permeation poor
Epidermal delivery:
stratum corneum = skin’s barrier to peptide penetration
How to increase skin permeability ?
Formulation
Liposome
Avoid
polypeptide : try
to find a small
molecule
????
-
Graft palmitic
acid : lipidic tail
=>increase
penetration
Cutaneous
penetration
methods
Peeling first :
decrease cornea
thickness
Skin
electroporation
(electropermeabiliz
ation /Iontophoretic
route)
Microneedles
ac glycolique,vit A
-
complicated if
daily application
Microneedles (1)
2 categories
 Solid microneedles
- pierce the skin then penetration
of the drug from an extendedrelease patch
- drug coated on microneedles ->
rapid release
- drug encapsulated within
microneedles -> controlled release
 Hollow microneedles
delivery by infusion
Microneedles (2)
 A variety of needle sizes, shapes and materials
 Made out of silicon, metals and polymers
• risk of breakage
•expensive
more robust
•sufficient strength
to insert into skin
•safe alternative
•water-soluble <->
dissolve in the skin
over a timescale of
minutes
Low-cost manufacturing methods
Microneedles: mechanism
Microneedle array applied to the
skin surface
Microneedles penetrate the
epidermis to bypass the stratum
corneum
Microneedles deliver drug
directly to the viable epidermis
Microneedles (3)
 Advantages:
- Minimally invasive technique
- Painlessness (epidermis: absence of nociceptors)
- Well tolerated
- Minimal irritation, short lasting
- Insertion by hand + not damaged during skin
insertion
 Roles
-
skin permeability =>
delivery
M.A.P: topical molecule
Safety profile
Sun protector
Short t1/2,
controlled released
Acceptable cost
Compatibility
with textile
Administration
rhythm: max once
daily
Satisfactory
organoleptic
characteristics
(odor, taste, color,
water resistant…)
for acceptability
NO systemic
absorption, cannot
go over the dermis
Proposed drug
 Based on α-MSH and melanotan structure
 Short t1/2 :
• NorLeu
• Melanotan II




Melanotan I
Method increasing skin permeability : Microneedles
Controled liberation : encapsulated microneedles
made of polymers
bandage of microneedles
Sun protector : add chemical filter (benzylidene)
SWOT
Strenghts
-First-in-class in this
indication
- Action on several
different etiologies of
Vitiligo
-“tanning without the
sun” => photoprotective
strategy against skin
cancer
-A lot of work done on
MC1R but no marketed
product
- Numerous adverse
effects
Opportunities
Threats
- No effective treatment
already on the market
Weaknesses
-Currently significant
research on
pigmentation disorders
Hyperpigmentation
TARGET
LOCATION (skin or
ubiquitous)
Advantages
Drawbacks
Agouti signaling
protein
(ASIP)
•A secreted factor
•Skin, heart, reproductive
tract, fat tissue, liver, and kidney
•Down-regulation of
genes and their encoded
proteins involved in
biosynthesis (e.g.,
pigmentation,
translation, transporters,
alcohol metabolism, DNA
replication, GSH
anabolism, and
mitochondrial redox
abilities of melanocytes):
Mitf, Tyr, Tyrp1, Dct, Si ,
Mart-1, Gpr143, Rab27a,
Met and
Cdk2
•Inhibition of other
pigment genes: Rab38, P
and Gpnmb
•Modulated expresion of genes
involved in other cellular pathways:
gluthathione synthesis and redox
metabolism (up-regulation of genes
involved in nervous sytem, skeletal,
bone, cartilage, kidney, muscle
development; vasculogenesis;
differentiation; cell adhesion;
motility; and extracellular matrix-Rc
interactions)
•Tcf4, Lef1, Tcfap2a/Ap2a are upregulated
• ErbB3
•AGRP (agouti related protein)
•Responsible for lighter
phenotypes in humans => ↗ risk
of skin cancer
• Down- regulation of genes
encoding proteins involved in repair
of DNA damage.
=> genes increased by ASIP
implicated in
various cancers
TRP1 (implicated in
the
eumelanogenesis)
Dopachrome
tautomerase (DCT
ou TRP2)
enzymes
that influence the
metabolism of these
sulfhydryls
Removal of the enzyme
leads to
hypopigmentation.
• Melanocyte specificity
Marketed
medicines
Mechanism of action
•Acts as a competitive
antagonist of α-MSH:
when binding to MC1R, it
prevents α-MSH from
increasing
intramelanocyte cAMP
levels and then stimulates
pheomelanogenesis
•ASIP also suppresses
the basal, ligandindependent activity of
hMC1R
•Inhibition of melanocyte
differentiation (↘ in
expression of numerous
melanogenic proteins)
TRP-1: catalyses
oxydation: DHICA ->
acide indole 5,6-quinone2-carboxylique
TRP-2: activity of
dopachrome tautomérase,
catalyses transformation:
dopachrome -> acide 5,6dihydroxyindole-2carboxylique (DHICA) (not
DHI)
Glutamine or cystéine
bind to DOPAquinone =>
availability of
sulfhydryls=primary
Hyperpigmentation
TARGET
LOCATION (skin or
ubiquitous)
Advantages
Drawbacks
Marketed medicines
Mechanism of action
Tyrosinase (most
essential enzyme in
the melanin
biosynthetic
pathway)
• Ubiquitous amino acid
tyrosine= substrate
• melanocye specificity
•Inhibitor leading to
hypopigmentation
•Reversible effect
•DOPA: proceed
spontaneously
at physiological pH
=> AE
• activated by ferrous
ions to hydroxylate
tyrosine
•Metabolism of melanin:
catalyses 3 different chemical
reactions
• Lack of direct correlation
between tyrosinase synthesis
and expression and pigment
production.
•↘ transcription: Vitamin
A and derivates,
glucosamine
•Inhibition:
Hydroquinone, Azelaic
acid, Kojic acid
•↗degradation: Elagic
acid
• indirect inhibition: Nacetyl glucosamine (a
sugar itself)
Catalyses the 3 following
transformations:
- tyrosine -> 3,4dihydroxyphénylalanine
(DOPA)
- DOPA -> dopaquinone
- DHI -> indole-quinone
•melanosomal
association
melanosome
Motility
By binding to diverse
effector molecules,
Rabs regulate
vesicule budding,
vesicule delivery,
vesicule tethering,
and vesicule
membrane fusion
with the membrane
of the target
compartment
Down-regulated by ASIP
Exocytic transport of
lysosome-related organelles
such as lytic granules in
cytotoxic T lymphocytes
Blockage of Rab 27a leads
to IMMUNODEFICIENCY
Rab 27 subfamily
(Rab27a and b)
Multiple molecules have a Nterminal homologous Rabbinding region and then
function as Rab 27 effectors
(exophilin, Slp/Slac2)
Rab 27a/b effectors: role in a
broad range of regulated
exocytic pathways
Granuphilin, another Rab27a
effector: regulates the
exocytosis of of classical
secretory granules
Gene encoding proteins involved
in melanosome transport
Hyperpigmentation
TARGET
LOCATION (skin or
ubiquitous)
Advantages
Drawbacks
Melanosomes’
transfer
NCK5 (a member of
the potassiumdependent sodium
calcium
exchanger family)
Mechanism of action
Inhibition: Linoleic acid
Niacinamide (=vitamin B3)
Epidermal turnover
Slc24a5 (solute
carrier family gene)
Marketed medicines
Chromosome 15
intracellular compartments
in skin and the pigmented
epithelium of the eye
(+++)
also a broad tissue
distribution
↗ cutaneous
permeability
↘ melanin
concentration
=> ↘ pigmentation
Risk of inflammatory
lesions following by a
hyperpigmentation if
too powerful
•up-regulated by
MSH
•SLC24A5
expression is
required for melanin
synthesis
•SLC24A5
knockdown with two
different siRNA
duplexes in greater
than
a 20% reduction in
the total normalized
melanin content of
these cells with no
effect on cell viability
decreased by ASP
•NCKX5directly
regulates human
epidermal
melanogenesis
and natural skin
color
•Removal of the
NCKX5 protein
through small
interfering
RNAmediated
knockdown disrupts
melanogenesis
causing a significant
presence in multiple
tissues -> contribute to
other Ca2+ signaling
events in addition to
those involved in skin
pigmentation
Increased: Vitamins C, E, A,
Glycolic acid
melanogenesis (encode
melanosomal proteins)
gene that encodes NCKX5
•intracellular potassiumdependent
exchanger activity
•extrude cytosolic Ca2+ and K+ in
exchange for Na+ ions
Hyperpigmentation
MC1R Antagonism
 ASIP
 Decrease in skin pigmentation
 Involvement in multiple pathways
 Inflammatory risk
 Related to numerous cancers
POMC
ACTH
Melanocyte
↗AMPc
α-MSH
Eumelanin
+
+
-
MC1R
ASIP
↘AMPc
Phemelanin
Hyperpigmentation
Epidermal Turnover
 Increase in the epidermal turn-over
 Found in certain « peeling » products
 Risk of lesions => unpleasant
 Risk of post inflammatory hyperpigmentation
Melanosome transfer
 Rab27 subfamily
- Too many effectors involved in exocytic pathways
such as exocytic transport of lytic granules in
cytotoxic T Lc
=> risk of IMMUNODEFICIENCY
Hyperpigmentation
Melanin Synthesis
 Tyrosinase
 Enzyme involved in the 2 melanins synthesis
Not specific of the eumelanogenesis
 Activity variation not always well porportional with the
pigmentation variation
 TRP1 and TRP2
 Enzymes specific of the melanocytes
 Enzymes involved in the eumelanogenesis
Tyrosinase
Tyrosine
Dopaquinone
DOPA
Glutathion
ou Cystein
Leucodopaquinone
TRP1
Cysteinyl
dopa
dopachrome
DHICA
DHI
Indole-5,6quinone
DHICA-melanin
Eumelanin
TRP2
1,4-benzothiazinyl
Alanine
Phaeomelanin
Ideas to develop for hyperpigmentation
 MC1R = target?
 Proinflammatory effect of a MC1R antagonist
=> MC1R
 Seems safer to act later on the melanin synthesis
 Potential targets: INHIBITION of
 TRP1
 TRP2
Screening of TRP1 TRP2 inhibitors
 Cells with recombinant TRP1, TRP2
 TRP substrates
modification
TRP inhibitors
 Evolution of the skin coloration (easy to mesure)
Other way of TRP inhibition: siRNA
 Small interfering RNA (siRNA), double-stranded
RNA: inhibition of mRNA translation
 about 20-nucleotides
 siRNA for the mRNA of TRP1 and/or TRP2 by
topical administration
 Specific action
 Main issue: siRNA very fragile
=> Might be an asset when topical action
siRNA (continued)
 siRNA structure requirements:
- low G+C content (30-50%)
- lack of internal repeats
- an A/U-rich 5' end
- minimum distance of the siRNA from the start codon
and the stop codon (set at 100 nt by default) +++
 Target site accessibility
siRNA: mechanism
Nucleus
Cytoplasm
Transfection agent
 Entry into the cells -> transfection agent
 Different types of transfection reagents:
 nanoparticule
 polymer
 cationic lipid
M.A.P: inhibition of TRP1 and 2
less exigent talking about absorption
Sun filter
Safety profile
Acceptable cost
Absolute specificity
on TRP1-2
Compatibility with
textile if topical
Administration
rhythm: max once
daily
Satisfactory
organoleptic
characteristics
(odor, taste) for
acceptability
SWOT
Strenghts
- Melanogenesis
specific enzyme
Very specific of
eumelanin
No risk if eventual
systemic
absorption
Opportunities
• No existing
effective
treatment for
hyperpigmentati
on disorders
Weaknesses
• No work on
these targets
Threats
Currently
significant
research on
pigmentation
disorders
Overall conclusion
 High prevalence, existing market
 Altered quality of life
 Of the patients with vitiligo, 32.9% would pay more
than 5000 € in order to achieve complete disease
remission
 Not only a cosmetical disease but also a REAL
disease