Medchem 310 Quiz 6

What happens when HIV integrates into your cells?

Proviral dsDNA relocates to the host cell nucleus

Viral integrase integrates viral DNA into the host nucleus at random location so that the cell is now a permanent carrier of the provirus

After integration, the virus is either in a latent state or is activated

What is 3’ processing when it comes to HIV?

Integrase locates CAGT on both 3’ ends of the viral DNA and trims it. The trimmed ends of the viral DNA are now integrated into the host cell’s DNA (strand transfer) and the host cell repairs its DNA with the viral genome in it.

No ATP is needed

What are the 3 inactive proproteins host cells produce after HIV is integrated?

env: cellular proteases cleaves this into gp120 and gp41, which migrate to the plasma membrane in cholesterol-rich regions

gag: structural proteins

pol: reverse transcriptase, protease, integrase

What happens in the activation stage of HIV?

the host cell machinery produces viral RNA and 3 large inactive proproteins

Structural proteins cleaved apart and assemble around genomic RNA to form nucleocapsid

Nucleocapsid core and reverse transcriptase directed envelope proteins on cell surface to bud new viral particles

Viral protease completes the cutting of the pro-proteins into viral structural proteins and enzymes

What is the 1st step in the HIV life cycle?

Virus gp160 (composed of gp41 and gp120) contacts host cell’s CD4 and chemokine receptors

What is the 2nd step in the HIV life cycle?

Fusion of host and HIV membrane releases viral ssRNA in the cell

What is the 3rd step in the HIV life cycle?

Viral reverse transcriptase converts RNA to DNA

What is the 4th step in the HIV life cycle?

Viral integration and replication

• viral integrase inserts a DNA copy of HIV genome into host cell genome

• host transcription machinery makes RNA

What is the 5th step in the HIV life cycle?

Viral particle formation

• mRNA exported from the nucleus and translated

• pro-protein gal-pol is processed

• genomic viral RNA is packaged with proteins

What is the 6th step in the HIV life cycle?

Plasma membrane

• viral core buds from plasma membrane to form immature coated viral particle

• viral protease continues to cleave to mature virus

Summary of HIV life cycle

1. Attachment

2. Fusion

3. RNA → DNA using reverse transcriptase

4. Viral integration and replication

5. Viral particle formation

6. Plasma membrane + budding

Why is it impossible for HIV to be cleared from the host’s body?

• Integrates into the host cell and makes it apart of the host’s genome

• HIV latency - when HIV is latent, drugs can’t kill it

Why is HIV so persistent?

• Mutational rate → immunological escape

• Infectional and killing of cells involved in the anti-HIV response

• Long stage of latent infection in resting t-cells when virus is not susceptible to immune response of drugs that target replication

Pandemic

contagious, infectious, or viral illness that spreads beyond one specific geographic region to include millions of people in many areas and countries across the globe

Epidemic

contagious, infectious, or viral illness that attacks many people at about the same time and may spread through one or several communities (more local than pandemic)

Prevalence

Number of people living with a disease in a given year (with or without diagnosis)

• HIV prevalence: 1.1 million in US at the end of 2015

AIDs cases

estimated number of persons living with diagnosed AIDs

• half a million in US at end of 2007

How is HIV transmitted?

contact with:

• blood

• semen, pre-seminal fluid

• rectal fluids

• vaginal fluids

• breast milk

In the US, HIV spread mainly by sex or sharing injection equipment

How does our body recognize a virus?

Antigens → Antigen Presenting Cells (APC) → MCH2 presents processed antigens to surface → CD4+ on T helper cell binds to presented antigen

• T helper cell activates Killer T cells

• → T helper cell → macrophages

• → T helper cell → B cells → antibodies

What are the 3 stages of HIV infection?

1. Acute primary infection: fever and acute mononucleosis-like disease occurs 3-6 weeks after infection as virus infects CD4+ immune cells

2. Latency: initial immune response reduces plasma viral load. With treatment, slow but continued viral replication and loss of CD4+ T Cells , but otherwise asymptomatic

3. AIDs: # of CD4+ T cells become critically suppressed, patient becomes susceptible to opportunistic infections

TCell counts and their meanings

• >500 T cells/mL = immune system is normal

• 200-500 T cells/mL = immune system is weakened

• <200 T cells/mL = immune system is very weak. High risk for opportunistic infection

Opportunistic infections targets

Lungs

Intestinal Tract

Brain

Eyes

Organs

Debilitating weight loss

Diarrhea

Neurologic conditions

Cancers

How long can people survive without treatment?

People die within 3 years of getting AIDs

CNS effects of HIV

HIV enters the CNS early by infecting macrophages and monocytes that cross the BBB, carrying the virus with them

• causes cognitive dysfunction: impaired concentration to dementia

• vacuolar myelopathy: “holes” due to degeneration of spinal cord, spastic partial paralysis, leg weakness

• HIV peripheral neuropathy: sensory neuropathy, myalgia, fatigue

Bacterial (AIDs Opportunistic Infections)

Mycobacterium tuberculosis: major cause of HIV-related morbidity and mortality

Salmonella septicemia

Protozoal (AIDs Opportunistic Infections)

Cryptosporidiosis - GI infection

Toxoplasmosis - of brain

Fungal (AIDs Opportunistic Infections)

Candidiasis lung, trachea, bronchim oral

Cryptococcal meningitis

Pneumocystis pneumonia

Viral (AIDs Opportunistic Infections)

Herpes virus

Hepatitis B and C virus

Cancer (HIV pathogenesis)

HIV-associated malignancies almost always caused by opportunistic infections by other viruses

• Kaposi sarcoma (KSV or KSHV)

• Hodgkin and non-Hodgkin lymphoma, nasopharyngeal carcinoma (EBV)

• Brain lymphoma

• Invasive cancer of the uterine cervix

Wasting syndrome (HIV pathogenesis)

weight loss and anorexia

• loss of >10% of both fat and lean tissue

• diarrhea or chronic weakness and fever

• contributing factors: infections and neoplasms, malabsorption, cytokine production

How do we treat HIV?

antiretroviral therapy (ART)

• cannot cure HIV but can help people live longer, healthier lives

• reduces risk of transmission

• main goal is to reduce a person’s viral load to an undetectable level

Principles of HIV chemotherapy

Suppress viral replication as much as possible

Current standard of care for HIV chemotherapy

Highly active antiretroviral therapy (HAART): combo of 3+ drugs simultaneously to help prevent resistance

Regardless of CD4+ T cell count

No break or termination

Should result in undetectable viral load (<50 plasma HIV RNA/mL) within 24 weeks

Classes of drugs used to treat HIV

Entry inhibitors

Reverse Transcriptase inhibitors

Integrase inhibitors

Protease inhibitors

Enfuvirtide (T-20, Fuzeon)

General structure:

• 36-amino acid peptide (based on HIV-1’s gp41 subunit)

Mech of action + Limitations:

• binds gp41(viral) and prevents envelope/membrane fusion by preventing gp41 folding (blocks trimer from happening)

• Not effective against HIV-2

• very potent

Type of inhibitor: fusion inhibitors

ADME

• Twice daily - subcutaneous injection

• Proteolytic metabolism

• Salvage therapy for advanced (MDR) disease state

Resistance Issues

• mutation of gp41 so enfuvirtide can’t bind

Maraviroc (Selzentry) - General structure, mech, type of inhibitor, adme, resistance?

General structure:

• small molecule

Mech of action + Limitations:

• binds to CCR5 (human) and prevents interaction with HIV gp120

• can’t use against CXCR4-tropic or dual-tropic HIV

Type of inhibitor: noncompetitive inhibitor (allosteric)

ADME

• Orally administered

• Metabolized by phase 1 cytochrome P450 CYP3A4

• Substrate for the efflux transporter P-glycoprotein (Pgp)

• Pharmacokinetics affected by coadministration with inhibitors and inducers of the above enzyme/transporters

Resistance Issues

• Mutation of gp120 to allow binding to CCR5 even in presence of inhibitor

• Switch to CXCR4-tropism

Ibalizumab (Trogarzo)- General structure, mech, type of inhibitor, adme, resistance?

General structure:

• recombinant human monoclonal antibody

Mech of action + Limitations:

• blocks HIV binding to both coreceptors

• does not block parts of CD4+ needed for normal immune function

• HIV can still bind to CD4+

Type of inhibitor: fusion inhibitor

ADME

• IV/infusion by healthcare provider

• recurrent dosing

• metabolized by CD4 receptor internalization + lysozome

Resistance Issues

• used for MDR HIV