"AIDS: Disease and TherapeuticsWhat is HIV?• Human:Infecting human beings• Immunodeficiency:Decrease or weakness in the body’s ability to fight off infections and illnesses• Virus:A pathogen having the ability to replicate only inside a living cell LIFE cycle of HIVDuring early course: HIV Infects macrophages: on skin and mucous membranesLater infects T cells• Receptor for HIV: CD4 (abundant on T cells. Low conc on macrophages)Co-receptor on Macrophages: CCR5Co-receptor on T cells: CXCR4The rapid spread of HIV has been attributed to its switch from CCR5 to CXCR4• Binding to CD4 receptor with gp120 leads to conformational change in gp120.This leads to binding to co-receptor. This binding leads to change in gp41 that allows folding of gp41 on itselfto cause fusion between viral and cell membrane. The folded gp41 is called as hairpin structure.• HIV particle enters the cytoplasm and uncoats. • In the cytoplasm, the viral RNA is converted to DNA by reverse transcriptase.lys• RT binds to tRNA present in the viral genome.• RT converts RNA to RNA-DNA hybrid and then to DNA-DNA. The virus replicates and progeny virions are released by budding.The primary pathogenic mechanism in HIV is the damage caused to the CD4+ T lymphocytes. The T4cellsdecrease in number and the T4:T8 (helper: suppressor) cell ratio is reversed.What is AIDS?• Acquired: To come into possession of something new • Immune Deficiency:Decrease or weakness in the body’s ability to fight off infections and illnesses• Syndrome:A group of signs and symptoms that occur together and characterize a particularabnormalityNote:• HIV is the virus that causes AIDS• Not everyone who is infected with HIV has AIDS• Everyone with AIDS is infected with HIV• AIDS is result of the progression of HIV Infection• Anyone infected with HIV, although healthy, can still transmit the virus to another personAIDS is the last stage in the wide spectrum of clinical features in HIV infection. • HIV multiplies inside the CD4+ cells, destroying them • As CD4+ cell count decreases and viral load increases, the immune defences are weakened• HIV-infected people become vulnerable to opportunistic infections• HIV is a chronic viral infection with no known cure• Without treatment, HIV progresses to symptomatic disease and AIDS Progression of HIV Infection• HIGH viral load (number of copies of HIV in the blood)• LOW CD4 count (type of white blood cell)• Increasing clinical symptoms (such as opportunistic infections) Stage 1: Acute HIV InfectionWithin 3-6 weeks of HIV infection, 50% people experience: ? Low grade fever? Malaise? Headache? Lymphadenopathy? Rash? Sore throat (pharyngitis)? Ulceration in mouth or genitals? DiarrheaTests for HIV antibodies are negative initially but become positive during the course of illness. Hence, thisstage is known as “seroconversion illness”. Pathogenesis of seroconversion illness is due to: Immunecomplexes and viral multiplicationSeroconversionThis is the process of rapid HIV replication and the build-up of HIV-anti-bodies. During seroconversion yourbody is producing antibodies, and HIV is continually replicating and spreading through bodily fluids. Window PeriodThe "window period" is the time it takes for a person whohas been infected with HIV to produce antibodies to thevirus. When we become infected with any virus (cold virus,flu virus, HIV etc.), our immune system produces antibodiesto destroy that particular virus. However, unlike cold and fluviruses, the antibodies produced to fight HIV are not capableof destroying it.The window period is the time between initial infection and the time that your body produces anti-bodies to thevirus. The HIV test doesn't actually test for HIV, but these anti-bodies. Antibodies to the HIV virus will appearwithin 3 months of infection. During the window period and process of seroconversion someone can beunaware that they have HIV in their system.Stage 2: Asymptomatic or latent infectionAll HIV infected people who experience seroconversion illness or not, show a phase of symptomless infection(latency). This may last for several years.HIV positive antibodies are shown during this phase.Asymptomatic infection is the period after testing positive forHIV, when the person remains healthy without any symptoms ofHIV disease. This may last for many years. Although patientremains well, the HIV virus continues to spread. The length of this phase is highly variable and depends upon ? the replication of HIV in the individual? Genetic differences in immune system i.e. the way theimmune system handles the virusAsymptomatic infection can last 10 years or more in somepeople. It is characterized by the lack of symptoms associatedwith HIV.This period of latency doesn’t mean microbiological latency asthe viral multiplication goes on throughout. The host mounts HIand CMI against the virus, which limits the viral load, but notclears it completely. Stage 3: Persistent generalized lymphadenopathy (PGL)? Enlarged lymph nodes atleast 1cm in diameter in two or more extra inguinal sites that persists for at least3 months? This should occur in absence of any current illness or medication that can cause lymphadenopathyStage 4: AIDS related complex (ARC)Patients suffer from immunodeficiency. Minor opportunistic infections occur. Typical symptoms are:? Fatigue? Unexplained fever? Persistent diarrhea? Marked weight loss (>10% of body weight)? Night sweatsCommon opportunistic infections are:? Oral candidiasis? Herpes zoster? Salmonellosis? Tuberculosis? Splenomegaly? LymphadenopathyOver time the immune system becomes severely damaged by HIV. This is thought to happen for three mainreasons:? The lymph nodes and tissues become damaged or "burnt out" because of the years of activity;? HIV mutates and becomes more pathogenic? The body fails to keep up with replacing the T helper cells that are lost.As the immune system fails, so symptoms develop. Initially many of the symptoms are mild, but as the immunesystem deteriorates the symptoms worsen.Patients are severely ill and progress to full blown AIDS in few monthsStage 5: AIDSEnd stage disease representing the irreversible breakdown of immune defense mechanism, leaving the patientprey to opportunistic infections and malignancies. Advanced HIV disease or AIDS is a technical classificationfor a person who has a low CD4 count, and/or, an opportunistic infection. An opportunistic infection is aninfection or a cancer that would normally be eradicated by a healthy immune system. AIDS is characterized by a compromised immune system and involves severe symptoms such as wasting,pneumonia, and other life threatening conditions. Sometimes people say that someone "died of AIDS"; this isnot entirely accurate, since it is the opportunistic infections that cause death. AIDS is the condition that lets theopportunistic infection take hold.Characteristic Features of AIDS? Lymphopenia? Selective Tcell deficiency- Reduction in number of T4 (CD4) cells, inversion of T4:T8 ratio? Decreased DTH on skin testing? Polyclonal activation of Bcells and increased spontaneous secretion of immunoglobulinOther features? Decreased invitro lymphocyte proliferative response to mitogens and antigens? Decreased cytotoxic response by Tcells and NK cells? Decreased antibody response to new antigens? Altered monocytes/macrophage function? Elevated levels of immune complexes in serumMost patients commonly complain of:? Dry cough? Fever? Tuberculosis by M.tuberculosis (many MDR strains)? Pneumonia either viral (CMV) or fungal (Cryptococcus, histoplasma)System Examples of Infection/CancerRespiratory system Pneumocystis Carinii Pneumonia TuberculosisKaposi’s SarcomaGastro-intestinal system ThrushHerpetic stomatitisHairy leukoplakiaCryptosporidiosisCandida Cytomegolavirus (CMV) IsosporiasisChronic colitis Kaposi’s SarcomaCentral/peripheral Nervous Cytomegolavirus system Toxoplasmosis Cryptococcosis Papoviruses CandidaMycobacteriaAspergillusNon Hodgkin’s lymphomaHodgkins lymphomaHerpes simplexSkin Herpes simplex Kaposi’s sarcomaXerodermaSeborheic dermatitisImpetigoHIV may cause direct cytopathogenic damage in the CNS. It can cross the blood brain barrier and causeencephalopathy leading to loss of higher functions, progressing to dementia.Some other immune cells also possess the CD4 antigen on the surface and so are susceptible to infection. Thusabout 5-10% of Bcells and 10-20% monocytes and macrophages, including specialized macrophages such asalveolar macrophages in lungs and Langerhans cells in the dermis are susceptible. Glial cells and microglia inthe CNS are also susceptible. Thus dementia is caused due to direct effect of HIV on the CNS.THERAPEUTICSStep 1: BindingHIV has proteins on its envelope that are strongly attracted to the CD4+surface receptor on the outside of the T4-cell. When HIV binds to a CD4+surface receptor, it activates other proteins on the cell's surface, allowing theHIV envelope to fuse to the outside of the cell.Entry can be blocked by entry inhibitors.What are Attachment and Entry Inhibitors?Entry inhibitors work by preventing HIV from entering healthy CD4 cells (T-cells) in the body. Other drugs areeffective AFTER the virus had entered the cell, but Entry Inhibitors acts before the virus infects and enters acell. Entry inhibitors work by attaching themselves to proteins on the surface of CD4 cells or proteins on the surfaceof HIV. In order for HIV to bind to CD4 cells, the proteins on HIV's outer coat must bind to the proteins on thesurface of CD4 cells. Entry inhibitors prevent this from happening.Some entry inhibitors target the gp120 or gp41 proteins on HIV's surface. Some entry inhibitors target the CD4 protein or the CCR5 or CXCR4 receptors on a CD4 cell's surface. If entry inhibitors are successful in blocking these proteins, HIV is unable to bind to the surface of CD4 cellsand gain entry into the cells.Viral entry currently represents one of the most attractive targets in the search for new drugs to treat HIVinfection. Thanks to the advances in the knowledge of the molecular basis of the mechanisms involved in theentry process, it has been possible to split it into several steps and design molecules to block each one of them.The main steps in the viral entry process are(i) attachment of the viral gp120 to the CD4 T cell receptor(ii)binding of the gp120 to CCR5 or CXCR4 co-receptors(iii) fusion of the viral and cellular membranesDrugs Target Resistance PathwayCD4-gp120 inhibitors? TNX-355 ? Mab against CD4Changes within gp120 surrounding? BMS-806 ? Binds to gp120, blockingthe Phe-43 cavity the conformational changes after CD4 binding? CADA ? Decrease CD4 expressionon the cell surfaceCCR5 antagonists? SCH-C, Vicriviroc, SCH-D? Binds to transmembraneMaraviroc domains of CCR5 Changes within gp120 (V3, C2, V2,C4) Co-receptor shift to CXCR4TAK-220, TAK-652 use? PRO-140 ?Monoclonal antibodyagainst CCR5CXCR4 antagonistsChanges within gp120 (V3, V1, V2,? AMD070 ? Binds to CXCR4V4) Co-receptor shift to CCR5 useFusion inhibitorsChanges at residues 36–45 in the? Enfuvirtide? Synthetic peptide whichHR1 region of gp41mimics a HR2 fragment andblocks the formation of thesix-helix bundleCD4-gp120 inhibitorsTNX-355 is a non-immunosuppressive Mab against the CD4 receptor. Itcompetes with HIV gp120 for CD4 binding. The antibody binding site in theCD4 receptor is different from the site involved in the interaction with HIVgp120. Thus, TNX-355 might prevent post-viral binding conformational changeswhich are required for the successful entry of HIV into the cell. Preliminarytrials in HIV-infected patients revealed that single doses of TNX-355 reducedplasma HIV-1 RNA load and increased CD4+ Tcells counts. A Phase II trial is in progress. CADA (cyclotriazadisulfonamide) is a specificinhibitor of the CD4–gp120 binding that does notinteract directly with the CD4 receptor or withgp120. CADA antiviral activity is assumed todown-regulate the CD4 receptor expression at thepost-translational level. BMS-806 binds with high affinity to HIV gp120, blocking the conformationalchanges induced in gp120 after CD4 binding.The binding of BMS-806 to HIVgp120 is specific, reversible and co-receptor independent. The drug is inactiveagainst HIV-2 and simian immunodeficiency virus (SIV). The molecule exhibitsno significant cytotoxicity, shows good oral bioavailability and lacks toxicity in animal models.CCR5 antagonistsMaravirok is an orally bioavailable CCR5 antagonist. Initialresults from Phase II trials were very promising. Almost allpatients experienced a remarkable reduction in plasmaviraemia and remained suppressed for at least 10 days post- treatment. The drug is currently in advanced steps of clinicaldevelopment and is expected to be approved in the near future. PRO-140 is a monoclonal antibody directed against the CCR5co-receptor, and in this way it blocks the binding of HIVgp120. In addition to the inhibiting the entrance of HIV-1subtype B Fusion inhibitorsThe final step for virus entry into the target cell results from conformational changesproduced after the binding of gp120 to CD4 and the coreceptors. These conformationalchanges expose another viral protein called gp41. Changes in the transmembraneprotein gp41 triggers release of a peptide that is then inserted into the target cellmembrane to form a pore, allowing entry of the virus. This last step is inhibited bycompounds called fusion inhibitorsEnfuvirtide is a synthetic peptide of 36 amino acids that mimics an HR2 fragment ofgp41. Its binding to the HR1 region blocks the formation of the six-helix bundlestructure, which is critical for the fusion process.The clinical efficacy and safety ofenfuvirtide was demonstrated in the TORO 1 and 2 clinical trials, in which thevirological and immunological benefits of adding enfuvirtide along with an optimizedantiretroviral regimen in multidrug-experienced patients was demonstrated.Step 2: Reverse TranscriptionHIV's genes are carried in two strands of ssRNA, while the genetic material ofhuman cells is found in DNA. In order for the virus to infect the cell, a processcalled "reverse transcription" makes a DNA copy of the virus's RNA.After the binding process, the viral capsid (the inside of the virus which contains theRNA and important enzymes) is released into the host cell. A viral enzyme calledreverse transcriptase makes a DNA copy of the RNA. This new DNA is called"proviral DNA."Reverse transcription can be blocked by: Nucleoside ReverseTranscriptase Inhibitors (NRTIs), and Non-Nucleoside Reverse TranscriptaseInhibitors (NNRTIs).What are Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTIs)?NRTIs were the first antiretroviral drugs used to treat HIV infection; their structures mimic those of naturalnucleosides. After being phosphorylated by intracellular enzymes, they compete with natural nucleosides andare preferentially incorporated by HIV RT into new viral DNA. The incorporation of an NRTI inhibits theelongation of the new DNA chain and thereby halts the replication processEg: Combivir, Retrovir, Epivir, Viread etcTenofovir disoproxil fumarate (Viread) is the first nucleotide analogreverse transcriptase inhibitor to be approved by the Food and DrugAdministration for the treatment of HIV infection. It is a potent agentwith a long intracellular half-life that allows for once-daily dosing. Ithas been well-tolerated in clinical trials to date, without evidence oflong term toxicity, including the mitochondrial toxicity that has beenassociated with some nucleoside analog reverse transcriptaseinhibitors. "