The human 26S proteasome is a target of antiretroviral agents

HIV protease inhibitors as new treatment options for Kaposi's sarcoma

A reduced incidence and regression of Kaposi's sarcoma (KS) and other tumours has been reported in Acquired Immune Deficiency Syndrome (AIDS) patients treated with antiretroviral combination therapies containing Human Immunodeficiency Virus (HIV) protease inhibitors (PIs) such as indinavir or saquinavir. Indeed, evidence indicates that although PIs were designed to selectively inhibit the HIV protease activity, they can interfere with several cellular pathways and can inhibit tumour growth. In particular, our recent results indicate that doses of indinavir or saquinavir similar to those employed to treat AIDS patients can induce regression of experimental KS by directly blocking two fundamental steps of KS initiation and progression: new blood vessel formation (angiogenesis) and KS tumour cell invasion. This is because indinavir or saquinavir inhibit the activation of matrix metalloproteinase-2 (MMP-2), a basement membrane-degrading enzyme, which is required for the progression of most tumours. Based on these results, a multicentre clinical trial is now starting in Italy, which will assess PI effects on the progression of KS in HIV-uninfected individuals (classical KS).

Overcoming obstacles to the success of protease inhibitors in highly active antiretroviral therapy regimens

Success with current protease inhibitors (PIs) is limited by substantial variability in pharmacokinetics, onset of adverse metabolic effects that include sustained lipid elevations and insulin resistance, and increased risk of lipodystrophy. Additionally, poor adherence to the often complex regimens can lead to emergence of PI-resistant human immunodeficiency virus (HIV) variants and treatment failure. Boosting blood levels of current PIs through coadministration of ritonavir can improve the pharmacokinetic characteristics of these agents, increasing the chances of success, but often at the price of additional adverse effects. New PIs in development have the potential to overcome at least some of these obstacles. Tipranavir, mozenavir, and atazanavir have favorable and unique resistance profiles, making them potentially effective in new treatment strategies in both PI-naïve and PI-experienced patients. Atazanavir does not cause the lipid elevations seen with current PIs, and it may improve adherence through once-daily dosing.

The role of the ubiquitination-proteasome pathway in breast cancer: applying drugs that affect the ubiquitin-proteasome pathway to the therapy of breast cancer

The ubiquitin-proteasome pathway is responsible for most eukaryotic intracellular protein degradation. This pathway has been validated as a target for antineoplastic therapy using both in vitro and preclinical models of human malignancies, and is influenced as part of the mechanism of action of certain chemotherapeutic agents. Drugs whose primary action involves modulation of ubiquitin-proteasome activity, most notably the proteasome inhibitor PS-341, are currently being evaluated in clinical trials, and have already been found to have significant antitumor efficacy. On the basis of the known mechanisms by which these agents work, and the available clinical data, they would seem to be well suited for the treatment of breast neoplasms. Such drugs, alone and especially in combination with current chemotherapeutics, may well represent important advances in the therapy of patients with breast cancer.

Proteasome Inhibitors: A Novel Tool to Suppress Human Cytomegalovirus Replication and Virus-Induced Immune Modulation

Recently, we like others, demonstrated that systemic inflammation is the most important mechanism involved in (re)activation of human cytomegalovirus (HCMV) in both immunocompromised and immunocompetent patients. By in vitro studies the eukaryotic transcription factor NF-κB could be identified as the key mediator of TNF-α- and IE1-dependent stimulation of the HCMV IE1/2 enhancer/promoter activity, which is crucial for initiation of viral gene expression during reactivation from latency as well as productive infection. The enzymatic proteasome complex plays a central role in regulating intracellular processes, including the activation of NF-κB. As present antiviral strategies target mainly late events in HCMV replication (DNA replication, virus assembly) that do not completely prevent virus mediated immunopathogenesis, we wondered whether proteasome inhibitors might be a novel tool for targeting the interaction between inflammation and HCMV (re)activation. Here, proteasome inhibitors like MG132, PSI, II and III (MG262) have been shown to block both TNF-α-associated up-regulation of the HCMV IE1/2 enhancer/promoter in monocytic cells in an in vitro transient transfection system and HCMV replication in permissive human embryonal lung fibroblasts. Importantly, ganciclovir-resistant HCMV strains are sensitive to proteasome inhibitors. The effect of proteasome inhibitors on HCMV replication was found to be specific as replication of other herpes viruses, like HSV-1 and HSV-2, under identical experimental conditions was not influenced. Inhibition of HCMV replication correlated with a delayed and significantly reduced expression of IE proteins, particularly of the IE2 protein, suggesting that MG132 blocks HCMV replication at an immediate early stage of infection. Early and late protein synthesis as shown exemplary for the pp52 (DNA-binding protein) and p68 (structural protein) protein production and viral DNA synthesis were also inhibited. Suppression of HCMV replication could be correlated with an increased cytosolic accumulation of IκB as well as a reduced NF-κB binding activity in nuclear extracts of MG132-treated cells, which mainly regards NF-κB p50. MG132 also reduced the immune modulatory activity of the virus by abrogating virus-induced up-regulation of cellular ICAM-1. These data suggest that short-term therapy with proteasome inhibitors might be an alternative strategy to prevent (re)activation, replication and immune modulatory activity of HCMV in patients with systemic inflammation.