Treatment of AIDS

Replication of the human immunodeficiency virus (mV), the causative agent of AIDS, is susceptible to targeted interventions, because several virus-specific metabolic steps occur in infected cells (A). Viral RNA must first be transcribed into DNA, a step catalyzed by viral reverse transcriptase. Double-stranded DNA is incorporated into the host genome with the help of viral inte-grase. Under control by viral DNA, viral replication can then be initiated, with synthesis of viral RNA and proteins (including enzymes such as reverse transcriptase and integrase, and structural proteins such as the matrix protein lining the inside of the viral envelope). 

These proteins are assembled not individually but in the form of polyproteins. 

These precursor proteins carry an N-ter-minal fatty acid (myristoyl) residue that promotes their attachment to the interior face of the plasmalemma. As the virus particle buds off the host cell, it carries with it the affected membrane area as its envelope. During this process, a protease contained within the polyprotein cleaves the latter into individual, functionally active proteins. 

These substances are analogues of thymine (azidothymidine, stavudine), adenine (didanosine), cytosine (lami-vudine, zaldtabine), and guanine (car-bovir, a metabolite of abacavir). They have in common an abnormal sugar moiety. Like the natural nucleosides, they undergo triphosphorylation, giving rise to nucleotides that both inhibit reverse transcriptase and cause strand breakage following incorporation into viral DNA. 

The non-nucleoside inhibitors of reverse transcriptase (nevirapine, dela-virdine, efavirenz) are not phosphory-lated. They bind to the enzyme with high selectivity and thus prevent it from adopting the active conformatioa Inhibition is noncompetitive. 

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Table 15 gives a sampling of other pharmaceuticals derived from hydraziae. Cefazolin, a thiadiazole tetrazole derivative, is one of the most widely used antibacterial dmgs in U.S. hospitals (see Antibiotics, P-LACTAMs). Procarbazine, an antineoplastic, is a monomethyUiydrazine derivative (220). Fluconazole has shown some promise in the treatment of AIDS-related fungal infections. Carbidopa is employed in the treatment of Parkinson s disease. FurazoHdone is a veterinarian antibacterial. 

Blundell, T, et al., 1990. The 3-D. structure of HIV-1 proteina.se and the design of andviral agents for the treatment of AIDS. Trends in Biochemical Sciences 15 425-430. 

New active substances for treatment of AIDS, cancer, diabetes, neurodegenerative disorders, (and from 2008) autoimmune or other immunological disorders and viral diseases. 

For the treatment of AIDS, TDF is now available in three commercial preparations, as such (Viread ), in combmation with emtricitabine (Truvada ) and m combination with emtricitabme and efavirenz (Atripla ). The latter represents a three-drugs-in-once combination piU, which has become available for the treatment of AIDS since July 2006. The different milestones mat marked the development and ultimate commercialization of Atripla (m 2006) smce the original identification of adefovir as an antiretroviral agent (m 1986) have been previously reviewed (De Clercq 2006, 2007a-c). 

At present there are seven NRTIs, which have been formally approved for the treatment of AIDS 3 -azido-2, 3 -dideoxythymidine (AZT, zidovudine), 2, 3 -dideoxyinosine (ddl, didanosine), 2, 3 -dideoxycytidine (ddC, zalcitabine), 2, 3 -didehydro-2, 3 -dideoxythymidine (d4T, stavudine), (—)-L-3 -thia-2, 3 -dideoxycytidine (3TC, lamivudine), cyclopentenyl V -cyclopropylaminopurine (abacavir, ABC), and (—)-L-5-fluoro-3 -thia-2, 3 -dideoxycytidine ((—)FTC, emtricitabine) (De Clercq 2004a) (Fig. 3). 

Shulman NS, Bosch RJ, MeUors JW, Albrecht MA, Katzenstein DA (2004) Genetic correlates of efavirenz hypersusceptibility. AIDS 13 1781-1785 Staszewski S, Morales-Ramirez J, Tashima KT, Rachlis A, Skiest D, Stanford J, Stryker R, Johnson P, Labriola DE, Earina D et al (1999) Efavirenz plus zidovudine and lamivudine, efavirenz plus indinavir, and indinavir plus zidovudine and lamivudine in the treatment of HIV-1 infection in adults. Study 006 Team. N Engl J Med 341 1865-1873 SteUbrink HJ (2007) Antiviral drugs in the treatment of AIDS what is in the pipeline Eur J Med Res 12 483 95... 

Reverse transcriptase inhibitors prevent DNA from being produced in newly infected cells. They do not, however, prevent the reactivation of HIV from previously infected cells, the reason being that the enzyme is not involved in this process. Thus, agents that act at a later point in the replication cycle, possibly preventing reactivation, would be a major advance in the treatment of AIDs sufferers. The HIV protease inhibitors, which are currently receiving considerable attention, are believed to act in the manner depicted in Fig. 5.24. 

The nonnucleoside reverse transcriptase inhibitors (NNRTIs), used in the treatment of AIDS, provide interesting examples of clinically relevant noncompetitive inhibitors. The causative agent of AIDS, HIV, belongs to a virus family that relies on an RNA-based genetic system. Replication of the vims requires reverse transcription of the viral genomic RNA into DNA, which is then incorporated into the genome of the infected host cell. Reverse transcription is catalyzed by a virally encoded nucleic acid polymerase, known as reverse transcriptase (RT). This enzyme is critical for viral replication inhibition of HIV RT is therefore an effective mechanism for abrogating infection in patients. 

Severe, and in particular chronic, infection can also sometimes induce anaemia, which is often made worse by drugs used to combat the infection. For example, anaemia is evident in 8 per cent of patients with asymptomatic HIV infection. This incidence increases to 20 per cent for those with AIDS-related complex, and is greater than 60 per cent for patients who have developed Kaposi s sarcoma. Up to a third of AIDS patients treated with zidovudine also develop anaemia. Again, several trials have confirmed that EPO treatment of AIDS sufferers (be they receiving zidovudine or not) can increase haematocrit values and decrease transfusion requirements. 

Serostim Serono Laboratories Treatment of AIDS-associated catabolism/wasting... 

Treatment of AIDS-related lymphoma is difficult because underlying immunodeficiency increases the risk of treatment-related myelosuppression. 

Carbocyclic analogues of nucleosides have attracted much attention as potential antiviral and antitumor therapeutic agents. Carbovir 72 is one of the most famous derivatives of this series, but its closely related analogue 1592U89 73 also holds remarkable promise for the treatment of AIDS and is currently in phase II clinical trials. 

The major problems for AIDS patients generally are the opportunistic infections that result from the lack of immunological protection. Thus, development of better therapies for these infections will play an important role in improved treatment of AIDS patients. 

Peptidases encoded by many viruses play essential roles at various stages of viral replication, including the coordinated assembly and maturation of virons [7a]. Viral peptidases have become important drug targets in the treatment of viral infections. Of note are inhibitors of proteases of the human immunodeficiency virus (HIV), particularly HIV-1 protease (HIV-1 retropepsin, EC 3.4.23.16) and HIV-2 protease [47-50], Drugs in this class, which include indinavir, ritonavir, and saquinavir, are useful in the treatment of AIDS, especially when administered as a cocktail together with one of the drugs that act on the viral retrotranscriptase (e.g., didanosine, stavudine, and zidovudine (AZT)). 

Cannabinoids produced positive results for treatment of AIDS-related anorexia. Positive results of open trials were later confirmed with methodologically controlled studies. Dronabinol (2.5 mg PO twice daily) produced consistent and substantial improvement in appetite in patients with AIDS (Beal et al. 1995, 1997). Patients also reported improved... 

Taylor, S.J.C., Sutherland, A.G., Lee, C., Wisdom, R., Thomas, S., Roberts, S.M. and Evans, C., Chemoenzymatic synthesis of (—)-carhovir utilizing a whole cell catalysed resolution of 2-azabicyclo[2.2.1 ]hept-5-en-3-one. J. Chem. Soc. Chem. Commun., 1990, 1120-1121 Evans, C.T., Roberts, S.M., Shoheru, K.A. and Sutherland, A.G., Potential use of carbocyclic nucleosides for the treatment of AIDS chemo-enzymatic syntheses of the enantiomers of carbovir. J. Chem. Soc. Perkin Trans. 1,1992, 589-592. 

Northfelt DW, Dezube BJ, Thommes JA, et al. Pegylated-liposomal doxorubicin versus doxorubicin, bleomycin, and vincristine in the treatment of AIDS-related Kaposi s sarcoma results of a randomized phase III clinical trial. J Clin Oncol 1998 16 2445. 

There are three liposomal forms of doxorubicin or daunorubicin on the market (Table 8.6). Doxil and DaunoXome have been approved for the treatment of AIDS-related Kaposi s sarcoma and are being evaluated in clinical trials for the treatment of a variety of cancers [148-151]. Evacet (liposomal doxorubicin) has recently been tested in large phase II and III clinical trials for the treatment of metastatic breast cancer and is awaiting approval by the FDA [151], Data obtained from trials thus far suggest that all three liposomal drugs offer significant therapeutic benefit compared with the free drug [113]. 

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