What is the mechanism of action of Ritonavir?

Wnt proteins that signal via the canonical Wnt/β-catenin pathway directly regulate osteoblast differentiation. In contrast, most studies of Wnt-related effects on osteoclasts involve indirect changes. While investigating bone mineral density loss in the setting of human immunodeficiency virus (HIV) infection and its treatment with the protease inhibitor ritonavir (RTV), we observed that RTV decreased nuclear localization of β-catenin, critical to canonical Wnt signaling, in primary human and murine osteoclast precursors. This occurred in parallel with upregulation of Wnt5a and Wnt5b transcripts. These Wnts typically stimulate noncanonical Wnt signaling, and this can antagonize the canonical Wnt pathway in many cell types, dependent upon Wnt receptor usage. We now document RTV-mediated upregulation of Wnt5a/b protein in osteoclast precursors. Recombinant Wnt5b and retrovirus-mediated expression of Wnt5a enhanced osteoclast differentiation from human and murine monocytic precursors, processes facilitated by RTV. In contrast, canonical Wnt signaling mediated by Wnt3a suppressed osteoclastogenesis. Both RTV and Wnt5b inhibited canonical, β-catenin/T cell factor-based Wnt reporter activation in osteoclast precursors. RTV- and Wnt5-induced osteoclast differentiation were dependent upon the receptor-like tyrosine kinase Ryk, suggesting that Ryk may act as a Wnt5a/b receptor in this context. This is the first demonstration of a direct role for Wnt signaling pathways and Ryk in regulation of osteoclast differentiation, and its modulation by a clinically important drug, ritonavir. These studies also reveal a potential role for noncanonical Wnt5a/b signaling in acceleration of bone mineral density loss in HIV-infected individuals, and illuminate a potential means of influencing such processes in disease states that involve enhanced osteoclast activity.

Ritonavir is commonly used as a pharmacokinetic booster for antiretroviral regimens in the management of human immunodeficiency virus infections. Limitations to ritonavir boosting include increased pill burden, adverse effects, and a wide range of clinically significant drug-drug interactions. Cobicistat is a new pharmacokinetic booster that is a selective inhibitor of cytochrome P450 3A, the main metabolizing pathway of several antiretrovirals. Cobicistat has been studied as a booster for elvitegravir, a second-generation integrase inhibitor, and protease inhibitors. Based on successful clinical trials, a new single-tablet regimen of elvitegravir, cobicistat, emtricitabine, and tenofovir has been approved for the management of treatment-naïve patients. Additional studies are underway investigating the safety and efficacy of cobicistat-boosted protease inhibitor regimens for both treatment-naïve and treatment-experienced patients. Cobicistat is well tolerated and may become a preferred booster for antiretroviral regimens, as it can be coformulated with several agents to create simpler regimens.

Ritonavir-boosted lopinavir (LPV/r) is a boosted protease inhibitor (PI) combination used as an alternative agent in the management of the human immunodeficiency virus (HIV). HIV treatment consists of combinations of classes of medications with complementing mechanisms of action. Protease inhibitor-based therapy is one of the mainstays of therapy. Ritonavir-boosted lopinavir can be dosed once- or twice-daily based on previous antiretroviral therapy, patient characteristics, and concomitant medications. It is currently available as an oral solution or tablet formulation and can be given without regard to food if given as a tablet. Lopinavir is extensively metabolized via the cytochrome (CYP) P450 3A4 and 3A5 hepatic isoenzymes and ritonavir is a potent inhibitor of CYP34A. Co-administration of low-dose ritonavir leads to increased plasma concentrations of lopinavir. There is potential for numerous drug-drug interactions when additional medications are administered. Clinical trials have been reported previously demonstrating the safety and efficacy of LPV/r in children, adolescents and adults and it is readily used throughout these populations. Current clinical trials are focused on examining the efficacy and toxicity of boosted-PI monotherapy as a treatment option in previously suppressed adults.

ABSTRACTThis study evaluated whether highly active antiretroviral therapy for human immunodeficiency virus (HIV) including ritonavir is independently associated with increased critical respiratory events after general anesthesia with opioid analgesia. The impact of ritonavir on hepatic microsomal enzymes was considered due to the effect of these enzymes on opioid metabolism. Medical records of over 1900 patients were reviewed, and those of 941 patients met inclusion criteria and were analyzed. Chronic treatment with ritonavir was not associated with critical respiratory events in HIV-positive patients.

Background. The protease inhibitor ritonavir is part of highly active anti-retroviral therapy (HAART) used successfully in the treatment of human immunodeficiency virus (HIV) infection. There is evidence that ritonavir alters intestinal permeability and induce damage to the small intestine. Because HIV infected patients taking HAART are at high risk of developing cardiovascular complications, there might be a need to use low dose of aspirin (ASA) to prevent inschemic event. Similarly, long term survival exposes HIV infects persons to detrimental interaction of ritonavir with NSAIDs, since both agents might cause intestinal injury. Aims. To test whether ritonavir worsens intestinal injury caused by NSAIDs and ASA. Methods. C57BL6 mice were treated for 25 days with ritonavir (50 mg/Kg/day per os) and than for others 5 days with the combination of ritonavir plus ASA (50 mg/Kg/day per os) or naproxen (100 mg/Kg/day per os). In a second set of experiments C57BL6 mice were treated for 25 days with ritonavir (50 mg/Kg/day per os) alone or in combination with the PGE2 analog misoprostol (100 μg/Kg per os). Results. Ritonavir administration per se caused intestinal damage and its co-administration in combination with naproxen or ASA exacerbated the severity of intestinal damage and intestinal inflammation as assessed by measuring haematocrit, MPO activity, relative mRNA expression of iNOS, MCP-1 and VLA-1 (Figure). All treatments caused reduced mucosal PGE2 . Co-administration of misoprostol, a PGE2 analogue, protected against intestinal damage induced by naproxen and ritonavir. Conclusions. The protease inhibitor ritonavir causes intestinal damage and its association with NSAIDs or ASA worsens damage caused by the COX-inhibitors. Misoprostol protects from damage caused by ritonavir. Further studies are need to clarify whether this observation has a clinical readout.

Antiretroviral protease inhibitors are a class of important drugs that are used for the treatment of human immunodeficiency virus infections. Among those compounds, ritonavir is applied frequently in combination with other antiretroviral protease inhibitors, as it has been reported to boost their therapeutic efficiency. To test whether ritonavir affects the viability and the glutathione (GSH) metabolism of brain cells, we have exposed primary astrocyte cultures to this protease inhibitor. Application of ritonavir in low micromolar concentrations did not compromise cell viability, but caused a time- and concentration-dependent loss of GSH from the cells which was accompanied by a matching increase in the extracellular GSH content. Half-maximal effects were observed for ritonavir in a concentration of 3 μM. The ritonavir-induced stimulated GSH export from astrocytes was completely prevented by MK571, an inhibitor of the multidrug resistance protein 1. In addition, continuous presence of ritonavir was essential to maintain the stimulated GSH export, since removal of ritonavir terminated the stimulated GSH export. Ritonavir was more potent to stimulate GSH export from astrocytes than the antiretroviral protease inhibitors indinavir and nelfinavir, but combinations of ritonavir with indinavir or nelfinavir did not further stimulate astrocytic GSH export compared to a treatment with ritonavir alone. The strong effects of ritonavir and other antiretroviral protease inhibitors on the GSH metabolism of astrocytes suggest that a chronic treatment of patients with such compounds may affect their brain GSH metabolism.

The human immunodeficiency virus protease inhibitor ritonavir has recently been shown to have antineoplastic activity, and its use in urological malignancies is under investigation with an eye toward drug repositioning. Ritonavir is thought to exert its antineoplastic activity by inhibiting multiple signaling pathways, including the Akt and nuclear factor-kappaB pathways. It can increase the amount of unfolded proteins in the cell by inhibiting both the proteasome and heat shock protein 90. Combinations of ritonavir with agents that increase the amount of unfolded proteins, such as proteasome inhibitors, histone deacetylase inhibitors, or heat shock protein 90 inhibitors, therefore, induce endoplasmic reticulum stress cooperatively and thereby kill cancer cells effectively. Ritonavir is also a potent cytochrome P450 3A4 and P-glycoprotein inhibitor, increasing the intracellular concentration of combined drugs by inhibiting their degradation and efflux from cancer cells and thereby enhancing their antineoplastic activity. Furthermore, riotnavir’s antineoplastic activity includes modulation of immune system activity. Therapies using ritonavir are thus an attractive new approach to cancer treatment and, due to their novel mechanisms of action, are expected to be effective against malignancies that are refractory to current treatment strategies. Further investigations using ritonavir are expected to find new uses for clinically available drugs in the treatment of urological malignancies as well as many other types of cancer.

Episodes of human immunodeficiency virus low-level viremia (LLV) are common in the clinical setting, but its association with antiretroviral therapy (ART) regimen and adherence remains unclear. Antiretroviral therapy adherence was evaluated in participants of the Research on Access to Care in the Homeless cohort by unannounced pill counts. Factors associated with increased risk of LLV include treatment with a protease inhibitor (PI)-based regimen (ritonavir-boosted PI vs nonnucleoside reverse-transcriptase inhibitor: adjusted hazard ratio [HR], 3.1; P = .01) and lower ART adherence over the past 3 months (HR, 1.1 per 5% decreased adherence, adjusted; P = .050). Patients with LLV may benefit from ART adherence counseling and potentially regimen modification.

Selection of preexisting minority variants of drug-resistant human immunodeficiency virus type 1 (HIV-1) can lead to virological failure in patients who receive antiretroviral therapy (ART) with low genetic resistance barriers. We studied treatment response and dynamics of minority variants during the first weeks of ART containing a ritonavir-boosted protease inhibitor (PI) and 2 nucleoside reverse-transcriptase inhibitors (NRTIs), which is a regimen with a high genetic resistance barrier. Plasma samples obtained prior to initiation of ART from 109 patients with primary HIV infection and samples obtained during viral decay during early ART from 17 of these 109 patients were tested by allele-specific polymerase chain reaction for K103N and M184V variants. K103N and/or M184V mutations were detected in 15 (13.8%) of 109 patients prior to ART as minority variants. No selection of these variants was observed within the first weeks of ART in 7 of 15 patients with preexisting drug resistance mutations, nor was any selection observed in 10 patients without preexisting drug resistance mutations. Most patients received ART immediately after diagnosis of HIV-1 infection, showed a rapid decrease in viral load, and experienced sufficient suppression of viremia for 48 months. Minority variants, in particular viruses harboring the M184V mutation, were efficiently suppressed in patients with acute infection who received a ritonavir-boosted PI and 2 NRTIs (most regimens included lamivudine). Under this high genetic resistance barrier regimen, the M184V was not further selected.

Lopinavir/ritonavir (LPV/r) is now the protease inhibitor regimen of choice in the first-line antiretroviral therapy for children <6 years of age. We included all the human immunodeficiency virus (HIV) type 1-infected highly active antiretroviral therapy (HAART)-naive children who started an LPV/r-based regimen between 2000 and 2009 at the Necker Hospital (Paris, France). Virologic failure (VF) was defined as an HIV-RNA ≥50 copies/mL. Resistance genotypic test was performed in case of VF. A total of 43 children were included at a median age of 4.8 years (1.8-8.0). Median level of HIV RNA and percentage of CD4 cell count was 5.5 log₁₀ copies/mL (4.6-6) and 15% (8-27.5), respectively. HAART included LPV/r and 2 nucleoside reverse-transcriptase inhibitors, mainly lamivudine (3TC), zidovudine, and/or abacavir. The median follow-up period was 36 months (18-72). Less than 50 copies/mL of HIV RNA was observed in 46%, 67%, and 70% of the children at months 6, 9, and 12, respectively. In all, 20 children (46.5%) experienced a VF. The risk factors of primary VF were a young age and a low socioeconomic status. The genotypic resistance test, performed for 18 of 20 children with VF, revealed 1 LPV/r-resistant virus and protease inhibitor-related major mutations without LPV/r resistance in 2 other children. Of the 18 children with VF, 15 received a 3TC-based HAART: 12 of 15 (80%) harbored a 3TC-resistant virus. No virus resistant to zidovudine or abacavir was found. In all, 70% of HAART-naive children had virologic success at month 12. The selection of LPV-resistant strains was a rare event. A high rate of selection of 3TC-mutations strengthens the recommendation to prefer a first-line 3TC-sparing regimen, particularly for children with risk factors of poor adherence.