Protease Inhibitors for the Treatment of HIV/AIDS: Recent Advances and Future Challenges

Acquired Immunodeficiency Syndrome (AIDS) is a chronic disease characterized by multiple life-threatening illnesses caused by a retro-virus, Human Immunodeficiency Virus (HIV). HIV infection slowly destroys the immune system and increases the risk of various other infections and diseases. Although, there is no immediate cure for HIV infection/AIDS, several drugs targeting various cruxes of HIV infection are used to slow down the progress of the disease and to boost the immune system. One of the key therapeutic strategies is Highly Active Antiretroviral Therapy (HAART) or ' AIDS cocktail' in a general sense, which is a customized combination of anti-retroviral drugs designed to combat the HIV infection. Since HAART's inception in 1995, this treatment was found to be effective in improving the life expectancy of HIV patients over two decades. Among various classes of HAART treatment regimen, Protease Inhibitors (PIs) are known to be widely used as a major component and found to be effective in treating HIV infection/AIDS. For the past several years, a variety of protease inhibitors have been reported. This review outlines the drug design strategies of PIs, chemical and pharmacological characteristics of some mechanism-based inhibitors, summarizes the recent developments in small molecule based drug discovery with HIV protease as a drug target. Further discussed are the pharmacology, PI drug resistance on HIV PR, adverse effects of HIV PIs and challenges/impediments in the successful application of HIV PIs as an important class of drugs in HAART regimen for the effective treatment of AIDS.

Hepatic Safety of Rilpivirine/Emtricitabine/Tenofovir Disoproxil Fumarate Fixed-Dose Single-Tablet Regimen in HIV-Infected Patients with Active Hepatitis C Virus Infection: The hEPAtic Study

OBJECTIVES

The aim of this study was to evaluate the frequency of transaminase elevations (TE) and total bilirubin elevations (TBE) during the first year of therapy with a single tablet regimen including RPV/FTC/TDF (EPA) in HIV/hepatitis C virus (HCV)-coinfected subjects in clinical practice.

METHODS

In a retrospective analysis, HIV/HCV-coinfected subjects who started EPA at 17 centres throughout Spain were included as cases. Subjects who started an antiretroviral therapy (ART) other than EPA during the study period at the same hospitals were randomly selected as controls in a 1:2 ratio. Primary outcome variables were grade (G) 3-4 TE and G4 TBE.

RESULTS

Of the 519 subjects included, 173 individuals started EPA. Nine (5.2%) subjects of the EPA group and 49 (14.2%) controls were naïve to ART. The median (Q1-Q3) follow-up was 11.2 (9.7-13.9) months. TE was observed in 2 [1.2%; 95% confidence interval (CI): 0.14%-4.1%] subjects receiving EPA and 11 (3.2%; 95%CI: 1.6%-5.6%) controls (p = 0.136), all events were G3. No patient discontinued ART due to TE. One (0.6%; 95%CI: 0.01%-3.1%) subject on EPA and 8 (2.3%; 95%CI: 1%-4.5%) subjects in the control group developed TBE (p = 0.141), without developing any other hepatic event during follow-up. Three (2.3%) subjects with cirrhosis versus 10 (3.1%) without cirrhosis showed G3-4 TE (p = 0.451).

CONCLUSION

The frequency of severe liver toxicity in HIV/HCV-coinfected subjects receiving EPA under real-life conditions is very low, TE were generally mild and did not lead to drug discontinuation. All these data suggest that EPA can be safely used in this particular subpopulation.

Incidence and risk factors for liver enzymes elevations in highly treatment-experienced patients switching from enfuvirtide to raltegravir: a sub-study of the ANRS-138 EASIER trial

Background

In the ANRS EASIER trial where treatment-experienced patients switched from enfuvirtide (ENF) to raltegravir (RAL), a high incidence of transaminase elevation was reported in the RAL arm.

Methods

We compared the incidence of emergent liver enzyme elevations (LEE) of grade 2 or more among patients randomized to the maintenance ENF arm or the switch RAL arm up to W24. We also assessed the overall incidence of LEE over the 48-week duration of the trial and baseline risk factors for grade 2 or more alanine aminotransferase (ALT) elevation using univariate and multivariate analyses.

Results

During the first 24 weeks, 6/84 (7.1 %) and 2/85 patients (2.4 %) presented with ALT elevation of grade 2 or more in the RAL and ENF arms, respectively (p = 0.21). Grade 2 or more γGT and ALP elevations were seen in 18 and 11 % (p = 0.35), and 5 and 1 % (p = 0.14) of patients in the RAL and ENF arms, respectively. The 48-week incidence of grade 2 or more LEE was 11.6 per 100-pts-years for ALT, 24.5 per 100-pts-years for γ-GT and 4.5 per 100-pts-years for ALP, respectively. In the multivariate analysis, tipranavir/ritonavir use (OR 3.66; 95 % CI [1.20–11.1], p = 0.022) and elevated ALT at baseline (OR 10.3; 95 % CI [2.67–39.6], p < 10⁻³) were significantly associated with a grade 2 or more ALT elevation during follow-up.

Conclusion

The incidence of LEE was relatively high in these highly treatment-experienced patients switching to a RAL-based regimen. Both tipranavir/ritonavir use and high baseline ALT levels were associated with an increased risk of ALT.

Trial registration: ClinicalTrials.gov identifier: NCT00454337

Review article: prescribing medications in patients with cirrhosis - a practical guide

BACKGROUND

Most drugs have not been well studied in cirrhosis; recommendations on safe use are based largely on experience and/or expert opinion, with dosing recommendations often based on pharmacokinetic (PK) changes.

AIM

To provide a practical approach to prescribing medications for cirrhotic patients.

METHODS

An indexed MEDLINE search was conducted using keywords cirrhosis, drug-induced liver injury, pharmacodynamics (PDs), PKs, drug disposition and adverse drug reactions. Unpublished information from the Food and Drug Administration and industry was also reviewed.

RESULTS

Most medications have not been adequately studied in cirrhosis, and specific prescribing information is often lacking. Lower doses are generally recommended based on PK changes, but data are limited in terms of correlating PD effects with the degree of liver impairment. Very few drugs have been documented to have their hepatotoxicity potential enhanced by cirrhosis; most of these involve antituberculosis or antiretroviral agents used for HIV or viral hepatitis. Paracetamol can be used safely when prescribed in relatively small doses (2-3 g or less/day) for short durations, and is recommended as first-line treatment of pain. In contrast, NSAIDs should be used cautiously (or not at all) in advanced cirrhosis. Proton pump inhibitors have been linked to an increased risk of spontaneous bacterial peritonitis (SBP) in cirrhosis and should be used with care.

CONCLUSIONS

Most drugs can be used safely in cirrhosis, including those that are potentially hepatotoxic, but lower doses or reduced dosing frequency is often recommended, due to altered PKs. Drugs that can precipitate renal failure, gastrointestinal bleeding, SBP and encephalopathy should be identified and avoided.

Liver toxicity of antiretroviral combinations including fosamprenavir plus ritonavir 1400/100 mg once daily in HIV/hepatitis C virus-coinfected patients

Abstract Our objective was to evaluate the liver toxicity of antiretroviral regimens including fosamprenavir plus ritonavir (FPV/r) 1400/100 mg once daily (QD) in HIV/hepatitis C virus (HCV)-coinfected patients. This was a prospective cohort study that included 117 HIV/HCV-coinfected patients who started FPV/r 1400/100 mg QD-based antiretroviral therapy (ART) and who neither had received a previous antiretroviral regimen containing FPV nor had a past history of virologic failure while receiving protease inhibitors (PI). The primary end point of the study was the occurrence of grade 3-4 liver enzymes elevations (LEE) within 1 year after starting FPV/r QD. Factors potentially associated with grade 3-4 LEE, including baseline liver fibrosis, were analyzed. Eleven (9%) patients had a grade 3-4 LEE during the follow-up, resulting in an incidence of severe liver toxicity of 9% (95% confidence interval 4.1-14.6%). None of these cases led to FPV/r discontinuation. Baseline liver fibrosis could be assessed in 97 (83%) patients. Six of 71 patients (8%) with significant fibrosis had a grade 3-4 LEE versus 2 of 26 (8%) without significant fibrosis (p=1.0). Twenty (21%) patients had cirrhosis at baseline. There were no cases of LEE among cirrhotics. In conclusion, the incidence of severe liver toxicity after 1 year of therapy with FPV/r QD-based ART in HIV/HCV-coinfected patients is similar to what has been reported with other boosted PIs. In addition, the presence of significant fibrosis or cirrhosis was not associated with the emergence of liver toxicity. Thus, ART regimens containing FPV/r QD may be considered safe in HIV/HCV-coinfected patients, including those with cirrhosis.

Efficacy and safety of raltegravir in treatment-experienced HIV-1-infected patients switching from enfuvirtide-based regimens: 48 week results of the randomized EASIER ANRS 138 trial

OBJECTIVES

To assess the sustainable efficacy and safety of a switch from enfuvirtide to raltegravir in patients with multidrug-resistant HIV infection.

METHODS

One hundred and seventy patients with multidrug-resistant HIV infection and suppressed plasma HIV RNA levels < 400 copies/mL under an enfuvirtide-based regimen were randomized to maintain their regimen or to switch to a raltegravir-based regimen (immediate group) in a 48 week prospective, randomized, open-label trial. At week 24, patients in the maintenance arm also switched to raltegravir (deferred group). Baseline genotypic susceptibility scores (GSSs) were calculated using available historical resistance tests. Efficacy was assessed by the cumulative proportion of patients with virological failure, defined as a confirmed plasma HIV RNA ≥ 400 copies/mL up to week 48. The EASIER ANRS 138 trial is registered at ClinicalTrials.gov (NCT00454337).

RESULTS

At baseline, 86% of patients had plasma HIV RNA levels <50 copies/mL and 86% had a GSS ≥ 1. Through to week 48, in the on-treatment analysis, only one patient in the immediate group, with a GSS of 0, developed virological failure. At week 48, 90% of patients in both the immediate and deferred groups had plasma HIV-1 RNA levels <50 copies/mL. Median CD4 cell counts remained stable during follow-up. Of note, 12 of 66 (18.2%) patients receiving a regimen combining raltegravir and ritonavir-boosted tipranavir experienced alanine aminotransferase elevations, which led to a switch from tipranavir to darunavir in 8 cases, without discontinuation of raltegravir.

CONCLUSIONS

In well-suppressed patients with multidrug-resistant HIV infection, a switch from enfuvirtide to raltegravir is generally well tolerated and has sustained antiviral efficacy when combined with a potent background regimen.

Hypersensitivity reactions to HIV therapy

Many drugs used for the treatment of HIV disease (including the associated opportunistic infections) can cause drug hypersensitivity reactions, which vary in severity, clinical manifestations and frequency. These reactions are not only seen with the older compounds, but also with the newer more recently introduced drugs. The pathogenesis is unclear in most cases, but there is increasing evidence to support that many of these are mediated through a combination of immunologic and genetic factors through the major histocompatibility complex (MHC). Genetic predisposition to the occurrence of these allergic reactions has been shown for some of the drugs, notably abacavir hypersensitivity which is strongly associated with the class I MHC allele, HLA-B*5701. Testing before the prescription of abacavir has been shown to be of clinical utility, has resulted in a change in the drug label, is now recommended in clinical guidelines and is practiced in most Western countries. For most other drugs, however, there are no good methods of prevention, and clinical monitoring with appropriate (usually supportive and symptomatic) treatment is required. There is a need to undertake further research in this area to increase our understanding of the mechanisms, which may lead to better preventive strategies through the development of predictive genetic biomarkers or through guiding the design of drugs less likely to cause these types of adverse drug reactions.

Liver tolerance of raltegravir-containing antiretroviral therapy in HIV-infected patients with chronic hepatitis C

OBJECTIVES

To evaluate the liver safety of raltegravir-including combinations in HIV/hepatitis C virus (HCV) co-infected patients.

METHODS

Grade 3-4 transaminase elevations (TEs) and grade 4 total bilirubin elevations (TBEs) were assessed during 12 months in 108 HIV/HCV co-infected patients starting antiretroviral therapy including raltegravir in a retrospective cohort study. Furthermore, the relationship between baseline fibrosis and hepatotoxic events was determined.

RESULTS

Eight patients (7.4%) developed grade 3 TEs and two (1.9%) patients showed grade 4 TEs. TBE grade 4 was detected in two (1.9%) patients. No patient permanently discontinued raltegravir because of hepatotoxic events. Of the patients with and without significant fibrosis, six (9.4%) and two (11.8%), respectively, showed grade 3-4 TEs (P = 0.769). Grade 3-4 TEs was observed in four (9.8%) patients in whom cirrhosis was ruled out, while none of the patients diagnosed with cirrhosis developed grade 3-4 TEs (P = 0.303). During the follow-up, the median (Q1-Q3) CD4 cell count increased from 257 (145-421) cells/mm(3) to 407 (213-587) cells/mm(3) (P < 0.0001) and the number of patients with an undetectable HIV viral load augmented from 33 (30.6%) to 73 (81.1%) (P = 0.002).

CONCLUSIONS

Raltegravir-containing regimens are safe in HIV/HCV co-infected patients. The incidence of severe liver toxicity of raltegravir in these individuals is in the range of boosted protease inhibitors in clinical trials. The frequencies of grade 3-4 TEs and grade 4 TBEs were similar in patients receiving raltegravir with or without significant fibrosis or cirrhosis.

Current and Novel Inhibitors of HIV Protease

The design, development and clinical success of HIV protease inhibitors represent one of the most remarkable achievements of molecular medicine. This review describes all nine currently available FDA-approved protease inhibitors, discusses their pharmacokinetic properties, off-target activities, side-effects, and resistance profiles. The compounds in the various stages of clinical development are also introduced, as well as alternative approaches, aiming at other functional domains of HIV PR. The potential of these novel compounds to open new way to the rational drug design of human viruses is critically assessed.

Co-infections and co-therapies: treatment of HIV in the presence of hepatitis C and hepatitis B

An increasing number of people are chronically infected with HIV and HCV, and/or HBV owing to shared routes of transmission. With the advent of HAART, liver disease secondary to hepatitis co-infections has emerged as a leading cause of morbidity and mortality in HIV-infected persons. There is increasing need to manage dual infection, but treatment is complicated by co-morbidities, overlapping toxicities, drug activities and resistance. A model of treatment that builds on the lessons learned from the treatment of HIV has evolved to maximize success of treating dual infections. This review will address current strategies for the management of HIV in the setting of HCV and HBV co-infection and discuss future treatment directions and challenges.