Systematic review of combination antiretroviral therapy with didanosine plus hydroxyurea: a partial solution to Africa's HIV/AIDS problem?

Looking back at paediatric HIV treatment in South Africa. My, how we have grown!

Antiretroviral treatment has undergone major changes in the last 20 years, from monotherapy, to dual therapy and finally to triple therapy. Lately, more focus has been placed on better, more well-tolerated combinations and formulations. As in most other disciplines in medicine, the development of paediatric HIV dosages and formulations always tends to lag behind adult research. Twenty years ago, it could take several years before data were available to enable the use of life-saving antiretrovirals in children. Paediatricians, being ever resourceful, were not prepared to let their paediatric patients suffer despite the lack of data or formulations and so made a plan. This article describes some of the trials and tribulations that we went through trying to make sure that our paediatric HIV patients not only survived but thrived. Clinicians treating paediatric patients today have it so much easier because of what our colleagues and their patients went through in those early days.

Psoriasis in patients with HIV infection: from the medical board of the National Psoriasis Foundation

BACKGROUND

Patients with psoriasis and HIV infection often present with more severe and treatment-refractory cutaneous disease. In addition, many of these patients have significant psoriatic arthritis. Many effective drugs for psoriasis and psoriatic arthritis are immunosuppressive. Therefore, therapy for the HIV-infected patient is more challenging, requiring both careful consideration of the potential risks and benefits of treatment and more fastidious monitoring for potential adverse events.

OBJECTIVE

A task force of the National Psoriasis Foundation Medical Board was convened to evaluate treatment options. Our aim was to arrive at a consensus on therapy for psoriasis in patients with HIV.

METHODS

A MEDLINE search of the terms "psoriasis," "psoriatic arthritis," "human immunodeficiency virus (HIV)," and "HIV skin diseases" was performed and literature relevant to HIV-associated psoriasis and the treatment of HIV-associated psoriasis were reviewed.

RESULTS

Based on a review of the literature, 29 reports were included as evidence in this review. Topical therapy is the first-line recommended treatment for mild to moderate disease. For moderate to severe disease, phototherapy and antiretrovirals are the recommended first-line therapeutic agents. Oral retinoids may be used as second-line treatment. For more refractory, severe disease, cautious use of cyclosporine, methotrexate, hydroxyurea, and tumor necrosis factor-alpha inhibitors may also be considered.

LIMITATIONS

There are no randomized, placebo-controlled trials evaluating the therapeutic efficacy or safety of treatments for patients with HIV-associated psoriasis; consequently, the evidence supporting this review consists mainly of case reports or case series.

CONCLUSIONS

HIV-associated psoriasis is often refractory to traditional treatments. Treatment is challenging and requires careful consideration and should be tailored to patients based on disease severity and the input from an infectious disease specialist. Close monitoring for potential adverse events is necessary.

Time-dependent changes in HIV nucleoside analogue phosphorylation and the effect of hydroxyurea

BACKGROUND

Nucleoside analogues are activated to their triphosphates, which compete with endogenous deoxynucleoside triphosphate (dNTP) pools to inhibit HIV reverse transcriptase. Hydroxyurea has been administered with nucleoside analogues to modulate intracellular dNTP pools and thus the ratio of drug triphosphate:endogenous triphosphate.

OBJECTIVES

To examine changes in drug activation over time and investigate the effects of hydroxyurea on intracellular phosphorylation of antiretroviral nucleoside analogues.

PATIENTS

A total of 229 HIV-infected individuals receiving abacavir, lamivudine and zidovudine were randomly assigned to receive or not nevirapine and hydroxyurea. Twenty-four patients were recruited to an observational substudy measuring intracellular drug triphosphate and dNTP concentrations at 0, 2, 6, 12, 24 and 48 weeks.

METHODS

Drugs were extracted from isolated peripheral blood mononuclear cells before analysis of endogenous dNTP and drug triphosphates by primer extension assays.

RESULTS

Twenty-two out of 24 patients were followed to completion of the substudy. Hydroxyurea had no demonstrable effect on endogenous dNTP or drug triphosphate levels at any timepoint. However, the ratio of zidovudine triphosphate to endogenous deoxythymidine triphosphate was significantly increased with hydroxyurea. A significant decrease in lamivudine triphosphate (3TCTP) and the 3TCTP:endogenous deoxycytidine triphosphate ratio was seen over 48 weeks. In five patients who failed therapy in the first 24 weeks, significantly reduced 3TCTP was seen.

CONCLUSION

Hydroxyurea does not affect measurable pools of endogenous nucleosides in vivo. Decreased lamivudine phosphorylation over time may provide a novel pharmacological explanation for the mechanism of resistance to this drug.

Short-term treatment with novel ribonucleotide reductase inhibitors Trimidox and Didox reverses late-stage murine retrovirus-induced lymphoproliferative disease with less bone marrow toxicity than hydroxyurea

We evaluated the ability of a short course of treatment with the ribonucleotide reductase (RR) inhibitor hydroxyurea (HU) and two novel RR inhibitors Trimidox (TX) and Didox (DX) to influence late-stage murine retrovirus-induced lymphoproliferative disease. LPBM5 murine leukaemia virus retrovirus-infected mice were treated daily with HU, TX or DX for 4 weeks, beginning 9 weeks post-infection, after development of immunodeficiency and lymphoproliferative disease. Drug effects on disease progression were determined by evaluating spleen weight and histology. Effects on haematopoiesis were determined by measuring peripheral blood indices (white blood cells and haematocrit) and assay of femur cellularity and femoral and splenic content of colony-forming units granulocyte-macrophage (CFU-GM) and burst-forming units-erythroid (BFU-E). HU, TX and DX partially reversed late-stage retrovirus-induced disease, resulting in spleen weights significantly below pre-treatment values. Spleen histology was also improved by RR inhibitor treatment (DX>TX>HU). However, as expected, HU was significantly myelosuppressive, inducing a reduction in peripheral indices associated with depletion of femoral CFU-GM and BFU-E. In contrast, although TX and DX were moderately myelosuppressive, both drugs were significantly better tolerated than HU. In summary, short-term treatment in late-stage murine retroviral disease with HU, TX or DX induced dramatic reversal of disease pathophysiology. However, the novel RR inhibitors TX and DX had more effective activity and significantly less bone marrow toxicity than HU.

Ribonucleotide reductase and thymidine phosphorylation: two potential targets of azodicarbonamide

Azodicarbonamide tested as an anti-HIV agent was reported to expulse zinc from viral zinc-cysteine factors and to inhibit calcium mobilization machinery. It has structural analogy with hydroxyurea that inhibits ribonucleotide reductase and could also act on this target. Azodicarbonamide was therefore tested for its capacity to modulate deoxyribonucleotides triphosphate pools alone or in combination with other agents in the lymphoblastic SUP-T1 cell line susceptible to HIV infection. The deoxyribonucleotides triphosphate were evaluated by an enzymatic assay using sequenase. Two hours exposure of SUP-T1 cells to 100 microM azodicarbonamide induced a 50% reduction of each deoxyribonucleotide triphosphate. Among other inhibitors of nucleotide metabolism (hydroxyurea, methotrexate and thymidine), hydroxyurea only reproduces the effect of azodicarbonamide. This suggests, but does not demonstrate directly, that azodicarbonamide inhibits ribonucleotide reductase activity. The combination of azodicarbonamide with each of these inhibitors affected particularly the dCTP pool. During this study it was also suggested that azodicarbonamide could interfere with thymidine phosphorylation. Thymidine phosphorylating activity was measured with 3H-thymidine as substrate. In acellular preparations, azodicarbonamide also non-competitively inhibits thymidine phosphorylating activity. This effect was not reproduced by hydroxyurea. Thus, in vitro azodicarbonamide decreases the intracellular pool of deoxyribonucleotide and thymidine phosphorylation.

Intracellular pharmacology of nucleoside analogues and protease inhibitors: role of transporter molecules

Antiretroviral agents target HIV replication within infected cells. It is therefore important to focus on the pharmacology of these drugs at their site of action rather than just in plasma. Activation of nucleoside analogues to a triphosphate is essential for antiretroviral activity. Following activation, by intracellular kinases, drug triphosphates compete with endogenous triphosphates for HIV reverse transcriptase. Methodologies to measure triphosphates in peripheral blood mononuclear cells from HIV patients have been described. This has allowed investigation of once-daily dosing regimens, drug interactions, modulation of intracellular activation and the bypassing of initial phosphorylation steps. Drug accumulation within a cell is a balance between influx and efflux. There is a growing body of evidence indicating that transport proteins are vitally important in regulating intracellular concentrations of antiretroviral drugs. Allelic variants, inhibition (or induction) are all potentially critical determinants of active drug present in the cell. It is hoped that understanding the intracellular pharmacology will improve long-term therapy and reduce the likelihood of cellular resistance in therapeutic failure.