Lowering the dose of hydroxyurea minimizes toxicity and maximizes anti-HIV potency

Hydroxyurea for the Treatment of Psoriasis with an Emphasis on HIV-Infected Psoriasis Patients: A Review

Hydroxyurea is a drug that has been long forgotten for the treatment of psoriasis. In addition to its anti-psoriatic effects, it has also been shown to have antiviral effects. This dual effect makes it a drug that dermatologists may want to consider when treating psoriasis in HIV-infected patients. Currently, no studies are available that discuss the safety and efficacy of hydroxyurea in the treatment of psoriasis in this immunocompromised group; however, numerous reports discuss the safety and efficacy of hydroxyurea in psoriasis and HIV separately. This review suggests that hydroxyurea is generally safe and effective. The main risk involves the hematologic adverse events (anemia, leukopenia, thrombocytopenia, and macrocytosis), which appear to be dose dependent. Because of the common hematologic adverse events, hydroxyurea may be considered a viable therapeutic option for patients with generalized psoriasis that is inadequately responsive to other safer options, whether or not the patient is HIV positive.

The role of proliferation in the regulation of interferon gamma (IFNγ) expression in foals

Interferon-gamma (IFNγ) plays an important role against viral and intracellular bacterial infections and its production is deficient in foals. Cellular proliferation provides an opportunity for de novo gene expression, though little is known about its role in regulating IFNγ expression in foals. While stimulation of foal peripheral blood mononuclear cells (PBMCs) with concanavalin A (ConA) increased the frequency of IFNγ(+) cells, the overall percentage of IFNγ(+) cells remained below that of adults. By contrast, the proliferative response of foal PBMC was significantly greater than that of the adults. In foals, IFNγ production was predominantly associated with those T cells that underwent proliferation, whereas in adults non-dividing cells also produced IFNγ. While treatment with hydroxyurea inhibited cellular division, it failed to completely block IFNγ production. This residual IFNγ production likely represented memory cells as the proportion of these proliferation-independent IFNγ(+) cells increased with foal age. However, memory cells may not account for all of the IFNγ production as ConA stimulation likely provided additional signals that can control IFNγ expression.

Strategies to improve efficacy and safety of a novel class of antiviral hyper-activation-limiting therapeutic agents: the VS411 model in [corrected] HIV/AIDS

BACKGROUND AND PURPOSE

Antiviral hyper-activation-limiting therapeutic agents (AV-HALTs) are a novel experimental drug class designed to both decrease viral replication and down-regulate excessive immune system activation for the treatment of chronic infections, including human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome. VS411, a first-in-class AV-HALT, is a single-dosage form combining didanosine (ddI, 400 mg), an antiviral (AV), and hydroxyurea (HU, 600 mg), a cytostatic agent, designed to provide a slow release of ddI to reduce its maximal plasma concentration (C(max)) to potentially reduce toxicity while maintaining total daily exposure (AUC) and the AV activity.

EXPERIMENTAL APPROACH

This was a pilot phase I, open-label, randomized, single-dose, four-way crossover trial to investigate the fasted and non-fasted residual variance of AUC, C(max) and the oral bioavailability of ddI and HU, co-formulated as VS411, and administered as two different fixed-dose combination formulations compared to commercially available ddI (Videx EC) and HU (Hydrea) when given simultaneously.

KEY RESULTS

Formulation VS411-2 had a favourable safety profile, displayed a clear trend for lower ddI C(max) (P= 0.0603) compared to Videx EC, and the 90% confidence intervals around the least square means ratio of C(max) did not include 100%. ddI AUC(∞) was not significantly decreased compared to Videx EC. HU pharmacokinetic parameters were essentially identical to Hydrea, although there was a decrease in HU exposure under fed versus fasted conditions.

CONCLUSIONS AND IMPLICATIONS

A phase IIa trial utilizing VS411-2 formulation has been fielded to identify the optimal doses of HU plus ddI as an AV-HALT for the treatment of HIV disease.

Clinical target promiscuity: lessons from ras molecular trials

Mutated ras has been identified in approximately 30% of human tumors, and dysregulation of ras function and signal transduction pathways is a critical step in tumorigenesis. Herein, we review the early data that supports the concept that the intrinsic radiosensitivity of tumor cells can be altered by oncogenic ras expression and that this impacts the PI3K-dependent signaling cascade. This ras-induced radioresistance can be reversed using prenyl transferase inhibitors (PTIs.). We discuss the effects of PTIs as a radiosensitizer in both in vivo and in vitro studies and show that PTIs can lead to increased radiosensitization in vivo through a variety of potential mechanisms that enhance radiation-induced cell kill. We critically evaluate the use of ras biomarkers in predicting the clinical response to PTIs that may explain the mixed results seen thus far in clinical trials using PTIs as a clinical radiosensitizer. We conclude that Ras-mediated radioresistance is the result of multiple intercommunicating pathways functioning against a complex genetic background and a solitary biomarker may not be adequate to predict for PTI-mediated radiosensitization. Nonetheless, our knowledge of the ras-signaling pathway has led to development and testing of specific therapies directed against PI3K-AKT signaling pathways as a future approach towards clinical radiosensitization.

Hydroxyurea induced acute elevations in liver function tests

Hydroxyurea (HU) is a ribonucleotide reductase inhibitor used to treat myeloproliferative diseases including polycythemia vera (PV) and essential thrombocythemia (ET). We describe an 82-year-old male who was started on HU 500 mg three times weekly for the treatment of PV. Eight days after initiation of HU he experienced anorexia, nausea, vomiting, fever, fatigue, dizziness, and shaking chills. Discontinuation of the HU resulted in resolution of his symptoms within 2 days, and HU was re-started. Ten days after re-starting HU, the patient re-presented with nausea and anorexia. Lab tests revealed elevations in liver enzyme function tests, which resolved promptly after cessation of HU. Patients being initiated on HU should be advised that rarely, fevers, chills, nausea, and elevations in liver function tests may occur. J Oncol Pharm Practice (2008) 14: 61—63.

JJ, Bosch RJ, Rosenkranz SL, Cramer YS, Ussery M, Flexner C. Effect of hydroxyurea and dideoxyinosine on intracellular 3'-deoxyadenosine-5'-triphosphate concentrations in HIV-infected patients

Hydroxyurea (HU) significantly enhances the antiretroviral effects of the adenosine analog reverse transcriptase inhibitor dideoxyinosine (ddI). This is believed to be due to a reduction in intracellular de-oxyadenosine triphosphate (dATP) concentrations resulting from HU-mediated inhibition of ribonucleotide reductase (RnR). The effect of combined HU-ddI treatment on intracellular dATP pools in vivo has not been examined. We measured intracellular dATP concentrations in peripheral blood mononuclear cells (PBMCs) from 69 HIV-infected patients receiving 1000 or 1500 mg HU daily for 14 days, 200 mg ddI twice daily for 14 days, or a combination of the two drugs. Median intracellular dATP concentrations decreased from base-line to day 14 by 46% in the ddI + 1000 mg HU arm and by 62% in the ddI + 1500 mg HU arm. When compared to the HU monotherapy arms, these changes proved statistically significant (p = 0.018; stratified Wilcoxon rank-sum test). These findings support reduced intracellular dATP as the mechanism of ddI-HU synergistic activity, and indicate that changes in intracellular nucleotides contribute to HU activity and toxicity in patients. Since a significant reduction in dATP was measurable only when ddI was combined with HU, the antiretroviral activity of ddI may be more complex than previously assumed.