Strategie per lo sviluppo di antivirali
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Attacco del virus al recettore
Ingresso
Spoliazione
Trascrizione e traduzione
Modifiche post-traduzionali
Replicazione del genoma virale
Assemblaggio/maturazione
Liberazione
Binding
Reverse transcription
Fusion
Integration
Transcription
Endocytosi
s
Nuclear localization
Uncoating
Splicing
Lysosome
RNA export
Maturation
Genomic RNA
Modification
mRNA
Translation
Assembly
Budding
Indice terapeutico:
Minima dose tossica per le cellule
Minima dose inibente il virus
= 100-1000
Chemotherapy
1962 Idoxuridine
• Pyrimidine analog
• Toxic
• Topical - Epithelial herpetic keratitis
1983 Acyclovir
• Purine analog
• Sugar modification
• Chain terminator
• Anti-herpes
• Selective to virus-infected
cells
1990’s Protease inhibitors
Inibitori dell’ingresso del virus
Chemotherapy
Amantadine: 1966
Rimantadine: 1993
Only effective against ‘flu A (200mg/day)
• Marginally effective therapeutically
• Prophylaxis: Reduce flu by 90%
Since disease usually mild and avoidable not used much
here
Good alternative to vaccine for:
Lysosomotropic
drugs?
• Elderly
• Immunocompromized
• Allergic
• Where causative strain not the
vaccine strain
Affects M2 Golgi ion
channel involved in
activation of virus before
release from cell
Inibitori della spoliazione
Chemotherapy
Membrane Fusion
• Endosome low pH often necessary for membrane fusion
• Lysosomotropic agents
Uncoating of core of membrane and non-membrane
viruses
• Uncoating of picornavirus e.g.
polio, echo, rhino
• Stabilize coated virus?
Chemotherapy
3-methyl
isoxazole
group
N
O
CH3
O
WIN 71711
(Disoxaril)
O N
• Stabilizes picornaviruses coated virus remains in
cytoplasm
• 3-methylisoxazole group inserts
in capsid VP1 and covers ion
channel Similar mechanism:
Pleconaril
Inibitori delle polimerasi v
Chemotherapy
Adenine arabinoside (Ara-A)
Problems : Severe side effects
• Resistant mutants (altered polymerase)
Competitive
• Chromosome breaks (mutagenic)
inhibitor of
virus DNA
• Tumorigenic in rats
polymerase
• Teratogenic in rabbits
which is
much more
• Insoluble
sensitive
Use: topical applications in ocular herpes simplex
than host
polymerase
Inibitori delle polimerasi v
Chemotherapy
Guanine analogs
Acyclovir =
acycloguanosine =
Zovirax
Ganciclovir = Cytovene
• Activated by viral TK
Acyclovir
Ganciclovir
Excellent anti-herpes drug
• Activated ACV is
better (10x) inhibitor
of viral DNA
polymerase than
inhibitor of cell DNA
polymerase
Inibitori delle polimerasi v
Inibitori delle polimerasi v
Inibitori delle polimerasi v
Inibitori delle proteasi
Chemotherapy
T-20
Peptides derived from gp41 can inhibit
infection
Probably block interaction of gp41 with
cell membrane proteins during fusion
T-20: In clinical trials, a nearly two log
reduction in plasma HIV levels achieved
Inibitori delle polimerasi v
Chemotherapy
Ribozymes
RNA molecules that have catalytic properties among which
are the specific cleavage of nucleic acids
Heptazyme
Ribozyme that cleaves
hepatitis C RNA at highly conserved regions
Recognizes and cuts all known types of the hepatitis C virus,
thereby stopping viral replication
Poor in clinic
Resistenza
• Ridotta sensibilità ad un farmaco dimostrata
in un sistema di coltura in laboratorio,
espressa come alterata IC50 o IC90
• Mutazioni specifiche nel genoma virale
modificazioni nella proteina bersaglio
del farmaco
Resistenza
• Errori delle polimerasi virali (++ RT)
• Elevata attività replicativa
• Pressione selettiva del farmaco
Talvolta:
• Variante resistente
minore attività
replicativa
mutazioni accessorie
compensative
HSV-Aciclovir
• Varianti TK –
• Varianti TK’
• DNA pol*
• Più frequenti;
attenuate
• Alterata specificità
TK; rare
• Bassa affinità per
l’analogo
nucleosidico; molto
rare
Terapia HBV
• Interferon
Immunomodulatore
2’-5’ oligoadenilato
sintetasi: m RNA
Azione lamivudina
Lamivudina
lamivudina trifosfato
enzimi cellulari
DNA pol virale
chain terminator
Metodi
• Classico (test fenotipici): coltura del ceppo
e saggio di riduzione delle placche in
presenza del farmaco
• Metodi molecolari (test genotipici):
restriction fragment lenght polymorphism
(RFLP); point mutation assay;
sequenziamento;... gene chip technology
Incidenza del fenomeno
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•
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Virus erpetici
rara nei pazienti immunocompetenti;
5-10%nei pazienti con AIDS e nei
trapiantati
Resistenze multiple?
Ceppi trasmissibili?
Incidenza del fenomeno
• HBV-lamivudina 10-20 % pazienti con
epatite cronica in trattamento per un anno
• Virus influenzali-amantidina –frequente
• Virus influenzali- zanamivir -rara
