Antiviral Agents I. Tutorial 6

Transcription

1 Antiviral Agents I Tutorial 6 Viruses, the smallest of pathogens, are unable to conduct metabolic processes on their own, they use the metabolic system of the infected cell to replicate ( intracellular parasites )

2 1) a) Draw a schematic structure of a virus naming all components.

3 Antiviral Agents I RNA virus DNA virus

4 Anti-Influenza Agents Uncoating Inhibitors Amantadine Rimantadine Neuraminidase Inhibitors Zanamivir Oseltamivir 4

5 1) b) Explain the replication cycle of DNA viruses and indicate the steps which are targets for antiviral drugs. DNA viruses Inhibition of viral DNA polymerase Acyclovir, Vidarabine, Foscarnet, Ganciclovir

6 b) explain the replication cycle of RNA (influenza) viruses and indicate the steps which are targets for antiviral drugs. RNA viruses Zanamavir Oseltamivir Amantidine Rimantidine

7 Influenza virus Neuraminidase (NA) = N spikes Haemagglutinin (HA) = H spikes glycoconjugates with a terminal sialic acid moiety host epithelial cells 7

8 Host cell surface Before leaving the host cell the newly formed virus is bound to its surface by the own surface glycoprotein hemagglutinin through the terminal sialic acid residue. Host cell surface Neuraminidase is a viral enzyme catalyzing the cleavage of a glycosidic bond between hemagglutanin and sialic acid virus release

9 2) Draw the structures of amantadine and rimantadine, give the indication of both drugs and explain their mechanism of action. Amantadine Rimantadine Amantadine: Prevention and treatment of influenza A virus (no effect on influenza B) Used against Parkinson s disease. Rimantadine: Same indication but is more effective against influenza A Mechanism of action: Both inhibit virus uncoating via blocking M2-protein that allows H + influx into the virus promoting the uncoating and release of virus RNA into the host nucleus where it replicated or transferred to mrna.

10 3) Give the names of the following neuraminidase inhibitors and explain their mechanism of action by comparing their structures with that of sialic acid. Sialic acid Zanamivir Oseltamivir Point of comparison Zanamivir Oseltamivir Structural differences 4 differences (encircled) Extra binding interactions Salt bridge (ionic and H-bond) Salt bridge and hydrophobic Oral bioavailability Orally inactive (hydrophilic guanido gp., glyceryl chain, COOH gp.) Orally active (lipophilic ester prodrug, pentoxy) Active/Prodrug Active Prodrug (free COOH essential) Dosage Forms Inhalation locally (dry powder), IV administration Oral tablet (lipophilic ester prodrug, pentoxy) Metabolism 90% excreted unchanged Ester hydrolysis (major) ω-oxidation (minor)

11 Mechanism of action: The virus is bound to the host cell surface by its haemagglutinin using terminal sialic acid residue. Neuraminidase is a viral enzyme that catalyzes the cleavage of a glycosidic bond between hemagglutinin and sialic acid thus facilitates virus release. Zanamivir and Oseltamivir are sialic acid analogs which block neuraminidase and therefore prevent virus escape the host cell and infect other cells

12 Antiherpesvirus Agents Acyclovir Valacyclovir Famciclovir Penciclovir Ganciclovir Cidofovir Idoxuridine Trifluorothymidine 12

13 4) Give the names of the most important herpes virus infections and the types of the viruses causing them. Herpes simplex virus (HSV) HSV-virus type 1 (HSV-1) infections: mouth, face, skin, brain HSV-virus type 2 (HSV-2) infections: genitals, rectum, skin, hands, meninges HSV-infection can be a primary or a nonprimary one (activation of a latent infection) Varicella-zoster virus (VZV, chickenpox virus, human herpes virus type 3, HHV-3) Causes chickenpox in children and shingles and postherpetic neuralgia in adults Cytomegalovirus (CMV, human herpesvirus5, HHV-5) Can be life-threatening for immuno-compromised patients (e.g. HIV, organ transplant recipients, neonates) -the most important viral cause of birth defects

14 5)a) Explain the difference between a nucleotide and a nucleoside. Nucleoside: Base + Sugar Nucleotide: Base + Sugar + Phosphate

15 Names of nitrogenous bases and their nucleosides Base Nucleoside (Base + Ribose OR Deoxyribose) Ribonucleoside Deoxyribonucleoside Uracil Uridine Deoxyuridine Thymine Thymidine Deoxythymidine Cytosine Cytidine Deoxycytidine Adenine Adenosine Deoxyadenosine Guanine Guanosine Deoxyguanosine Nucleotide name must indicate the number of phosphates present in the nucleotide

16 5)b) Give the names and abbreviations of the following nucleotides. Uridine monophosphate UMP Deoxy Uridine monophosphate dump Deoxy Thymidine monophosphate dtmp Adenosine triphosphate ATP Cytidine monophosphate CMP Guanosine diphosphate GDP

17 6)a) Consider the structure of acyclovir and explain its design, mechanism of action, and selectivity for infected cells. base sugar Modify the sugar 2'-deoxy guanosine Normal nucleoside Acyclovir False nucleoside Inhibitor

18 It is preferentially uptaken by the virus infected cells where it is rapidly phosphorylated by viral thymidine kinase then further to triphosphate by host cellular kinases. Nucleotide It inhibits viral DNA synthesis Acyclovir triphosphate inhibits viral DNA polymerase and its incorporation into viral DNA terminates its elongation due to lack of 3 OH group

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20 6)b) Draw the structure of valacyclovir and compare its oral bioavailability and indications to those of acyclovir Acyclovir Valacyclovir poor oral bioavailability Oral bioavailability Indications Valacyclovir increased oral bioavailability (50%) approved for the treatment of herpes zoster (shingles) in immunocomprimised patients Acyclovir poor oral bioavailability (15-30%) most active against HSV-1, also active against HSV-2, and VZV

21 6)c) Draw the structure of ganciclovir and give its advantage and disadvantage when compared to acyclovir. What is the main therapeutic indication of ganciclovir? Acyclovir Ganciclovir used only for the treatment CMV retinitis in immuno-compromised patients and to prevent life-threatening CMV infections in transplant patients.

22 Acyclovir DNA chain termination Ganciclovir Same mechanism of action as acyclovir except DNA chain termination (the second OH-group allows the DNA elongation) Lower toxicity High toxicity probably caused by the inhibition of the host cells DNA polymerase (myelosupression, neutropenia, anemia..), mutageneic, cancerogenic, and teratogenic in animals Oral bioavailability (15-30%) Oral bioavailability (5-10%)

23 Study Guide (tut 6) The virus life cycle is to understand how the infection takes place and to know the possible targets for treatment but not to memorize Structures to be memorized amantadine, rimantadine, valacyclovir and ganciclovir For the other structures you will be given the drug structure and answer the required questions about the drug.