Antiviral drugs

lipoprotein envelope nucleic acid protein capsule

Simplified viral structure

Viral replication cycle

1. Adhesion

2. Penetration

3. Uncoating

4. Early proteosynthesis 5. NAc synthesis

6. Late proteosynthesis

7. New viruses assembling

8. Viral shedding

1. Viral adhesion: g-globulins, fusion inhibitors

2. Penetration: g-globulins, fusion inhibitors

3. Uncoating: cyclic amines

4. Early proteosynthesis: no drug yet

5. Nucleic acid synthesis: NRTI, NNRTI, integrase inhibitors

6. Late proteosynthesis: Protease inhibitors (PI)

7. Viral assembling: neuraminidase inhibitors

8. Viral shedding: neuraminidase inhibitors

Targets of antiviral drugs

M-channel protein inhibitors

Cyclic amines Amantadin, rimantadin, tromantadin

Nucleic acid synthesis inhibitors

DNA synthesis Ribavirin

DNA polymerase and DNA synthesis

Cyclic nucleosides

Purin analogues Deoxypropyladenin, arabinofuranosyl-adenin, vidarabin,

Pyrimidin analogues

Brivudin, trifluridin, idoxuridin

Acyclic nucleosides

Purin analogues Aciklovir, valacyklovir, penciklovir, famciklovir, gancyklovir, valgancyklovir

DNA polymerase and reverse

Phosfonic acid derivatives

Foscarnet, fosfonet

transcriptase Cyclic nucleosides

Purin analogues

Didanosin, abacavir

Pyrimidin analogues

Zidovudin, zalcitabin, stavudin, lamivudin, sorivudin, alovudin, fluorothiacytidin, emtricitabin

Acyclic nucleotides

Purin analogues

Tenofovir, adefovir, adefovir dipivoxil

Pyrimidin analogues

cidofovir

Non nenucleoside analogues

Nevirapin, delaviridin, efavirenz, lovirid, capravirin, emivirin

Proteosynthesis inhibitors (POL-protein)

Thiosemicarbasones

Methisazon,

Ansamycins Rifampicin

Asp-protese (proteinase) inhibitors Peptides Saquinavir, ritonavir, nelfinavir, amprenavir, indinavir, lopinavir

Non pepeptides

Tipranavir

Neuraminidase inhibitors

Zanamivir, oseltamivir

Classification of antiviral agents

Antiviral drugs against herpetic

viruses

Acyclovir (UASN) Aciclovir (INN)

• DNA synthesis inhibitor

– Viral TK phosphorylation needed (200 x higher affinity against viral in comparison to mammal TK)

– Cellular enzymes convert acyclo-GMP to acyclo-GTP

– This process is 40 - 100 x more potent in infected cells than in intact cells

Mode of action of acyclovir

Inhibition of viral DNA synthesis

x

x

Deoxyribonucleosides

Acyclovir Viral thymidine kinase

Acyclovir monophosphate

Acyclovir diphosphate

Acyclovir triphosphate

Viral kinases or

cellular enzymes

Cellular enzymes

DNA/Acyclovir monophosphate

DNA polymerase Deoxyribonucleoside

trifosphate Viral DNA polymerase

Mode of action of acyclovir

Inhibition of viral DNA synthesis

Acyclovir - pharmacokinetics (1)

tmax (oral) 1,5 - 2,5 h

Oral bioavailability 15 - 20 %

Distribution

Kidney 1000% plasma conc.

Liver, heart, lungs 130%

CSF 50%

Maternal milk 325% mater. plasma conc.

t 0,5

Adults 2 - 3 h (i.v.)

Newborn 2,5 - 5,0 h

Maternal milk 2,8 h (p.o.)

CSF 28,0 h (i.v. inf. + probenecid)

Renal elimination 45 - 79% (i.v. dose)

Acyclovir - pharmacokinetics (2)

Valaciclovir and other esters

Valaciclovir – mode of action

• ACV selective activation of viral thymidin

kinase (TK)

• Cellular TK does not activate ACV (ACV

itself does not have cytotoxic effects)

• ACV triphosphate is 100 x more potent

then penciclovir triphosphate

• ACV is obligate chain terminator on the

level of guanosine

Valaciclovir - metabolism

Valaciclovir p.o.

45% into GIT as ACV 55% absorption

Valaciclovir hydrolase

Valin 1% nonmetabolised VCV

55% ACV bioavailability

Comparative kinetics

Parameter pen/fam aciclo/vala

tmax (h) 1,0 1,5

t0,5 (h) 2,2 3,1

F (%) 0/77 15/55

Single dose kinetics

• Fast conversion of VCV into ACV = first

pass effect

• Absorption not influenced by food

• t0,5 – 2,6 - 3,0 h

Repeated dose kinetics

Generic Brand

Aciklovir

Valaciklovir

Famciklovir

Ganciklovir

Cidofovir

Valganciklovir

Methisoptinol

Zovirax, Herpesin, Virolex, Aciclovir

Valtrex

Famvir

Cymevene

Vistide

Valcyte

Isoprinosine

Antivirals against herpetic viruses incl. CMV

Generic

Aciklovir

Penciklovir

Tromantadin

Podofylotoxin

Imikvimod

Zovirax, Herpesin, Virolex, Aciclovir

Vectavir

Viru-Merz

Wartec (condylomata/bradavice)

Aldara

Local antivirals against herpetic viruses

and warts (verrucae)

Generic Brand

Postherpetic neuralgia

Valaciclovir

• Prodrug of acyclovir

• Higher bioavailability = higher efficacy

• Effective also against less sensitive viruses

• Dosage (3 x 1 000 mg/d)

• Safety – more than 35 000 000 treatment

cures with active compound – acyclovir

Valaciclovir - summary

• Ester

• Fast conversion to acyclovir (99%)

• 3 – 5times higher bioavailability vs. ACV

• No change in bioavailability (food, age, co

morbidity)

• Active only after conversion of VCV to ACV

• Conversion (hydrolysis) - ACV + valin

(essential amino acid)

Acts independently on viral thymidinkinase

– direct metabolism by cellular enzymes

Direct conversion into diphospho

derivatives

Interaction with viral DNA

Main indication:

Cidofovir: CMV, HSV, papiloma viruses

Adefovir: HBV see hepatitis

Acyclic nucleoside phosphonates

cidofovir and adefovir

Antiviral drugs against HIV viruses

HIV virus

Lipid bilayer

Zidovudine (azidothymidine, AZT)

Zidovudine – highly effective antiretroviral

compound.

Nonselective phosphorylation into MP- DP-

TP by cellular TK and nonspecific kinases

Zidovudine TP - inhibits substrate of viral

reverse transcriptase with100 x higher affinity

to HIV RT than cellular DNA and polymerase.

AZT – pharmacokinetics and dosage

Kinetics Oral bioavailability 60 - 80%

t0,5 1,1 - 1,5 h

Elimination route GF a Ts

Metabolism 5´glucuronide

5´glucuronid in urine adults 60-80%, children 45%

Protein bound 35 - 40%

CSF/Plasma ratio 0,5 - 0,8 (in interval 1 - 4h)

Dosage Adults 500 mg/day (in 2 doses)

Children 720 mg/m2/day (in 4 doses)

AZT – adverse events (AEs)

Hematotoxicity (long term use of high dosages

- follow blood count)

Lactate acidosis connected with hepatomegaly

and steatosis (LFT check – AST, ALT needed)

Mutagenity (significant chromosomal

aberrations not proved)

Cancerogenity (in high doses in animals)

Gravidity (only when clearly indicated)

Lamivudine (3-thiacytidine)

• Lower toxicity in vitro than zalcitabine a didanosine

• Oral bioavailability – 80%

• No myelotoxicity

• No mitochondrial toxicity in concentration inhibiting

viral replication

•Effective in HIV and HBV

• Combination with other antiretroviral drugs and

interferon possible

Abacavir (ABC)

Higher generation RTI,

More potent than current antiretroviral

drugs (tricyclic guanosine derivative).

No activity against hepatitis B and C viruses

Synergy with zidovudine and nevirapine

• ABC is prodrug

• Phosphorylation is needed to generate effect

• Resulting antiretroviral substance - carbovir TP (carbocyclic GTP) action:

–dGTP competitive inhibition (deoxyguanosine-TP)

–DNA chain termination by means of incorporation of false nucleoside analogue

Abacavir (ABC) – mode of action

Intracellular activation

2´deoxyguanosine and abacavir

dG

dGMP

dGDP

dGTP

ABC

ABC-MP

CGMP

CGDP

CGTP

Proviral DNA

RT RT

Abacavir (ABC) – mode of action

• Good absorption and bioavailability

(F=83%)

• Good CNS penetration (30 - 44%)

• Low plasma protein binding (49%)

• Metabolism – 1st step: ADH, 2nd step:

glucuronidation

• No P-450 interactions

Abacavir (ABC) – pharmacokinetics

• Contraindications

–moderate – severe liver dysfunction

–terminal stage of renal failure

• Cave: in 3% patients hypersensitivity

(very serious!!!)

–Be alert in first 2 month of treatment!

Abacavir (ABC) – KI

Plasma/CSF = 0,35

Cmax = 3,0 g/l

Tmax = 1,5 h

D = 300 mg

abacavir

F = 83 %

Vd = 0,8 l/kg

t1/2 = 1,5 h

Plasma/CSF = 0,06

Cmax = 1,5 g/l

Tmax = 0,75 h

D = 150 mg

lamivudin

F = 85 %

Vd = 1,3 l/kg

t1/2 = 6,0 h

Plasma/CSF = 0,60

Cmax = 1,8 g/l

Tmax = 0,5 h

D = 300 mg

zidovudin

F = 70 %

Vd = 1,6 l/kg

t1/2 = 1,1 h

Srovnání farmakokinetiky

Trizivir – combo: abacavir + lamivudine + zidovudine

Activation of abacavir, lamivudine and

zidovudine (3 different modes of action)

ABC

ABC MP

Carboxyl GMP

Carboxyl GDP

Carboxyl GTP

3TC (also ddC)

3TC MP

3TC DP

3TC TP

AZT (also d4T)

AZT MP

AZT DP

AZT TP

adenosin

phosphotrans-

ferase

cytosolic

enzymes

deoxycitidin

kinase

deoxycitidin

MP kinase

Purin

nucleoside

DP kinase

thymidin

kinase

thymidilat

kinase

pyrimidin

nucleoside

DP kinase

Protease inhibitors (PI) – mode of action

HIV-1, (2) protease inhibition

Inhibition prevents gag-pol polyprotein

cleft

structural genes: gag, pol, env - encoding

structural proteins

Resulting virus is immature and non-

infectious

INN amprenavir nelfinavir indinavir ritonavir saquinavir

Brand Agenerase Viracept Crixivan Norvir Invirase

Efficacy +++ +++ +++ +++ +

Dosage 2xd 3xd 3xd 2xd 3xd

Tbl./d - Nos 12-16 9 6 12 12

Tolerance +++ +++ ++ + +++

IT.-p-450* ++ ++ ++ +++ +

IT.-food - ++ +++ ++ -

CNS penetr. + - - - -

x-resist. + + +++ +++ +

Protease inhibitors - comparison

•Enzyme inhibitors – AE : Lipid spectrum abnormities up to influence on adipogenesis

•New PI: Atanzavir, Fosamprenavir, Tipranavir

NNRTI – efavirenz

NNRTI (noncompetitive)

Does not inhibit DNA polymerase

Protein bound - 99,5 - 99,8%

Metabolism - CYP 3A4 a CYP 2B6

Enzyme inducer – after repeated dose

shorter elimination half live

Frequent interactions similar as in PIs

Nevirapine: bioavailability 90%, t 0,5 27 h,

metabolism – P-450, enzyme inducer -

decreasing concentrations of PIs and

contraceptives …

Delaviridine: bioavailability 85%, t 0,5 5,8 h,

metabolism – P-450, enzyme inhibitor -

increasing concentration of antiepileptics,

astemizole, cizapride … (Contraindication!!!)

NNRTI – delaviridine and nevirapine

Differencies in mode of action

between NRTI and NNRTI

NNRTI NRTI

Intracellular activation

not needed

Phosphorylation to

nucleoside 3-P

Allosteric inhibition

noncompetitive

Competitive substrate inhibitor

on catalytic subunit

Enzyme conformation

changes - inactivation

Nucleotide sequence

synthesis termination

HIV-1 reverse transcriptase inhibition

Generic Brand

Zidovudine

Stavudine

Didanosine

Lamivudine

Abacavir

Tenofovir disoproxil

Emtricitabine

Retrovir

Zerit

Videx

Epivir/Zeffix

Ziagen

Viread

Emtriva

Antivirals against HIV viruses (RTIs)

Generic Brand

Saquinavir

Ritonavir

Indinavir

Nelfinavir

Amprenavir

Lopinavir

Fosamprenavir

Invirase, Fortavase

Norvir

Crixivan

Viracept

Agenerase

Kaletra

Antivirals against HIV viruses (PIs)

Generic Brand

Efavirenz

Nevirapine

Stocrin, Sustiva

Viramune

Antivirals against HIV viruses (NNRTIs)

Antiviral drugs against Hepatitis B and C

viruses

Generic Brand

Lamivudine

Adefovir dipivoxil

Ribavirin

Zeffix/Epivir - Hep. B

Hepsera - Hep. B

Rebetol, Copegus - Hep. C in combination

with IFN

Antivirals against Hepatitis B and C viruses

Interferons – immunomodulating cytokines

• Interferon alpha (IFN alpha) – leucocyte

• Interferon beta (IFN beta) – fibroblast

• Interferon gama (IFN gamma) – T-lymphocyte

• Mode of action

– Antiproliferative – slow down transition from G1 to S phase

– Immunomodulating effects – increased expression of cytotoxic lymphocytes,

macrophages and NK-cells,

– Increase of expression of main histocompatible complex needed for induction

of cytotoxic reaction

– Viral inhibition replication inductors

– Antitumor activity – oncogen expression decrease c-myc, v-myc…

1. IFN binding on membrane receptor

2. Internalization of the complex

3. Initiation of intracellular steps

• Adverse events

– Anti-platelet effects and suppression of

granulopoesis (Decrease in platelet count -

limiting factor for application)

– Flu-like syndrome (2 – 4 h after application, lasts

4 – 8 h)

– Less frequent AEs

• Hypotension, BP fluctuation, arrhythmias

• Interferon pneumonia

• Autoimmune symptoms

• Proteinuria

Interferons – immunomodulating cytokines

• Aim – immediate short term protection

(acquired)

– Antisera (heterologous) – immunoglobulins from

purified immunized animal sera

– Homologous immunoglobulins – produced by B

lymphocytes as humoral response to

heterologous antigen

• Normal human Ig

• Specific Ig

Passive immunization –

immunoglobulins

Immunoglobulin structure

Fab

Fc

F(ab)2 VH

VL

CL

CH1

–S–S– –S–S–

CH2

CH3 Papain Pepsin

V = variable

domain (antigenic

variability)

C = constant

domain (link with

complement, link with

Fc receptor of

immunocompetent

cells …)

1-3 – hyper-

variable part

(antigenic specificity)

VL-VH = Fv (link to

antigen)

m, d, a, g, e = isotype of

heavy chains (IgM,

IgD, IgA, IgG, IgE)

1

2

3

• Aim – long term prevention (post vaccination

immunity)

– Vaccines

• Alive

– Heterologous – smallpox (variola) - (eradicated)

– Attenuated

» Viruses (polio, measles, mumps, rubella, yellow fever)

» Bacteria (BCG)

• Inactivated

– Viruses (flu)

– Bacteria (whooping cough, cholera)

– Inactivated anatoxins (toxoids) - (diphtheria, tetanus)

Active immunisation – vaccination

Anti flu antivirals

Mixovirus influenzae

M2

Flu – etiology

• Flu viruses - 3 types

– Orthomyxoviridae: Myxovirus influenzae A, B, C

• Different structure

– A – cause of large epidemics and/or pandemic

– in humans and other mammals and birds

– B and C – typically in humans only

Flu virus

Neuraminidase

Matrix protein

Lipid bilayer

Ribonucleoprotein

RNA

Polymerase

Haemagglutinin

M2 channel protein not depicted

Haemagglutinin (HA)

Principal antigenic determinant of A and B flu virus

Responsible for adhesion to receptor and endocytosis, contains sialic acid

Continuous development of new variants (shift) essential for survival

Neuraminidase (NA)

One of essential glycoproteins (antigenic

determinants) of A and B flu virus

NA inhibition prevent viral shedding

Viral ion channels

M2 channels in flu A virus only

Responsible for uncoating after virus

entry in to the cell

attachment

entry

cytoplasm

endosomal

vesicle

releasefrom vesicle

Ô

RNA

replication in nucleus

new RNA genomes

proteinsynthesis

release of progeny virions

respiratory

cell surfaceassembly of new viruspartic les

Replication cycle of flu virus

Antigenic shift

• Antigenic shift – new virus in 10 – 30y

interval (e.g. H5N1)

• Combination of human and animal flu antigens

probably in pigs in SE Asia

• Source water birds and poultry

• Type A flu - No antibodies against new

antigenic variant!!!

Antigenic drift

• Antigenic drift – small antigenic changes

(point mutations)

• Typical for flu B virus

• Flu C virus responsible only for sporadic

disease

Shift and drift

mechanism

Flu virus in RTI

1 Adhesion

2 Replication

3 Shedding

1

3

2

Respiratory tract is the main target of flu viruses

Flu management

Vaccination

Prevention Antiviral drugs

Treatment Causative

Antiviral drugs

Symptomatic

Symptomatic treatment

Flu treatment

Causative – antiviral drugs

Cyclic amines - M2 channel protein inhibitors,

flu A only. Issue - resistance

Amantadin

Rimantadin

Neuraminidase inhibitors – flu A and B.

Oseltamivir

Zanamivir

NA inhibitors

Prophylactic and therapeutic use in A and

B flu

Mode of action – selective NA inhibitor.

Prevention of viral shedding.

Zanamivir inhalation device

Rotadisk

Inhalation Powder Cover

Mouthpiece Piercing Needle

Zanamivir – lung deposition

Zanamivir – adverse events

0

0,5

1

1,5

2

2,5

3

3,5

4

% patients

na

sal sym

pto

ms

dia

rrho

ea

na

use

a

he

ad

ach

e

bro

nch

itis

cou

gh

sinu

sitis

sore

thro

ut

vom

itus

vertig

o

OR

L in

fectio

n

OR

L b

lee

din

g

placebo zanamivir

Oseltamivir

• Oral form - prodrug

• Bioavailability 80 %

• Metabolism - liver esterases to carboxylate =

active substance – NA inhibitor

• Renal elimination

Generic Brand

Rimantadin

Oseltamivir

Zanamivir

Maridin

Tamiflu

Relenza

Anti flu antivirals

New trends

• Herpetic protease inhibitors

• HIV fusion inhibitors (CD4 molecule on

lymphocyte) (chemokin co-receptor

antagonists - 5, CCR5)

– Prevention of HIV adhesion and fusion with cell

membrane close to gp 41 and gp 120.

– No cross resistance with RTI and PI.

• HIV integrase inhibitors

– Prevention of integration of bihelical HIV DNA into

host genome

New trends