Drug-drug interactions and the pharmacotherapy of HIV infection

Knowledge of drug-drug interactions is crucial to HIV therapeutics. Recent reports in this area include reduced atazanavir exposure with coadministration of omeprazole or rifampin; increased hepatic toxicity with coadministration of saquinavir and rifampin; reduced buprenorphine exposure with concurrent efavirenz administration; absence of clinically significant interactions of depomedroxyprogesterone with nevirapine, efavirenz, or nelfinavir; increased atazanavir and saquinavir exposure with the double-boosted regimen of atazanavir/saquinavir/ritonavir; reduced amprenavir, lopinavir, and saquinavir exposure with the addition of tipranavir/ritonavir therapy; and reduced lopinavir and amprenavir exposure with the addition of fosamprenavir or fosamprenavir/ritonavir to lopinavir/ritonavir. This article summarizes a presentation on drug-drug interactions in HIV therapeutics by Angela D. M. Kashuba, PharmD, at the International AIDS Society-USA course in Los Angeles in April 2005.     

Measuring Adherence by Visual Inspection of Returned Empty Gel Applicators in the CAPRISA 004 Microbicide Trial

In the CAPRISA 004 trial, adherence was estimated as the proportion of reported sex acts covered by two gel doses, which was assessed by counting returned empty gel applicators. The returned empty applicators were inspected visually in a standardized manner for residue on the outside of the applicator, as an indicator of vaginal insertion. Over 15 months, spanning 11,839 study visits by 838 women, a total of 59,800 returned empty applicators were inspected. By visual assessment, 77.5 % of these applicators appeared to have been inserted. To test the accuracy of the assessment we fitted a Cox model and found that the risk for HIV infection was doubled when less than half of the returned empty applicators had been assessed as not inserted in the vagina. Visual inspection enhanced both the accuracy of the adherence measurement and aided identification of mechanical problems with applicator use experienced by women in the trial.     

Antiviral agents and HIV prevention: controversies, conflicts, and consensus

Antiviral agents can be used to prevent HIV transmission before exposure as preexposure prophylaxis (PrEP), after exposure as postexposure prophylaxis, and as treatment of infected people for secondary prevention. Considerable research has shed new light on antiviral agents for PrEP and for prevention of secondary HIV transmission. While promising results have emerged from several PrEP trials, the challenges of poor adherence among HIV-negative clients and possible increase in sexual risk behaviors remain a concern. In addition, a broader pipeline of antiviral agents for PrEP that focuses on genital tract pharmacology and safety and resistance issues must be developed. Antiretroviral drugs have also been used to prevent HIV transmission from HIV-infected patients to their HIV-discordant sexual partners. The HIV Prevention Trials Network 052 trial demonstrated nearly complete prevention of HIV transmission by early treatment of infection, but the generalizability of the results to other risk groups - including intravenous drug users and MSM - has not been determined. Most importantly, the best strategy for use of antiretroviral agents to reduce the spread of HIV at either the individual level or the population level has not been developed, and remains the ultimate goal of this area of investigation.     

Evaluation of dyskerin expression and the Cajal body protein WRAP53β as potential prognostic markers for patients with primary vaginal carcinoma

Primary vaginal cancer (PVC) is a rare gynaecological malignancy, which, at present, lacks appropriate biomarkers for prognosis. The proteins dyskerin and WD repeat containing antisense to TP53 (WRAP53β), both of which exert their functions in the telomerase holoenzyme complex, have been shown to be upregulated in different cancer types. These proteins have also been proposed as prognostic markers in some types of cancer. The aim of the present study was to examine the expression patterns of dyskerin and WRAP53β in patients with PVC. Moreover, as part of a search for effective biomarkers to evaluate prognosis in PVC, the expression of these two proteins and their potential association with clinical variables and survival were also evaluated. The expression of dyskerin and WRAP53β was assessed in PVC tumour samples from 68 patients using immunohistochemistry. The majority of tumour samples showed low and moderate expression levels of dyskerin. Upregulation of dyskerin in tumour samples was significantly associated with a shorter survival time and a poorer cancer-specific survival rate. WRAP53β was also expressed in most of the cells but was not significantly associated with clinical variables or survival. This study demonstrates that upregulation of dyskerin is significantly associated with poor prognosis. Thus, dyskerin may serve as a promising prognostic marker and a potential putative therapeutic target in PVC.     

Fosamprenavir. Vertex Pharmaceuticals/GlaxoSmithKline

Fosamprenavir, a Vertex Pharmaceuticals phosphate ester prodrug of the HIV protease inhibitor amprenavir, is under development by GlaxoSmithKline (GSK; formerly Glaxo Wellcome) for the potential treatment of HIV infection in adults and children. By November 2000, it was in phase III trials; a third phase III trial was initiated in April 2001. In October 2001, GSK expected filing in both the EU and US in 2002. In January 2002, Vertex anticipated an NDA filing during the second half of 2002. Fast-track status for fosamprenavir was received by Glaxo Wellcome in December 1999. As of January 2002, enrollment was complete for two of the three phase III trials, and an NDA was expected to be filed during 2002. Fosamprenavir was first synthesized at Vertex as part of a collaboration with Glaxo Wellcome and by 1999, it was being developed by Glaxo Wellcome as part of an ongoing agreement between the two companies. In September 2000 and January 2001, Merrill Lynch predicted a 2002 launch, with sales of pounds sterling 50 million in 2002, rising to pounds sterling 150 million in 2004.     

Epstein-Barr virus encoded nuclear protein EBNA-3 binds XAP-2, a protein associated with Hepatitis B virus X antigen

EBNA-3 (also called EBNA-3A) is one of the EBV encoded nuclear antigens that are necessary for B-cell transformation. EBNA-3 is known to target RBPs, nuclear proteins that also interacts with EBNA-2, EBNA-4 and EBNA-6. In order to identify additional EBNA-3 targets, an EBV-transformed human lymphocyte cDNA library was screened in the yeast two-hybrid system with N-terminus truncated EBNA-3 that cannot interact with RBP-Jkappa. A clone, encoding Xap-2 protein, a cellular partner of Hepatitis B virus X-antigen was isolated. This protein is also known as the p38 subunit of the aryl hydrocarbon receptor complex (ARA9). The specific binding to EBNA-3 was confirmed by showing that the GST-Xap-2 precipitated EBNA-3 from CV1 cells that were infected with recombinant vaccinia virus expressing EBNA-3. Deletion of the C-terminus of Xap-2 eliminated the binding. Fusion with green fluorescent protein showed that Xap-2 is preferentially cytoplasmic but translocates to the nucleus upon expression of EBNA-3.     

High frequency somatic mutations in RASSF1A in nasopharyngeal carcinoma

High frequency loss of 3p21.3 region is a common event in various kinds of tumors including nasopharyngeal carcinoma (NPC). RASSF1A has been identified as a putative tumor suppressor gene residing in this region. Chromosome alterations and epigenetic changes are commonly observed as mechanisms for inactivation of RASSF1A function. In this study, we applied the PCR-cloning-sequencing strategy to examine somatic mutations in RASSF1A in NPC tissues as compared with the sequences detected in the matched peripheral blood lymphocytes. Our results revealed a high incidence of RASSF1A mutation in primary tumor tissues of NPC. There are totally 35 mutations identified in 74% (17/23) of these NPC cases, including 30 transitions, three transversions and two deletions. Most of these mutations result in amino acid changes: three nonsense (stop codon) mutations, two-1 bp deletion (frameshift), 26 missense and the remaining four are synonymous (silent). No obvious 'hot-spot' mutations were observed in this study. A similarly high rate (74%) of promoter methylation of RASSF1A was also detected in the same group of NPC tissues, but no significant correlation between mutation and methylation was detected. Our results suggest various mechanisms involved in inactivation of RASSF1A function and indicate a critical role of RASSF1A in NPC development.     

The pharmacokinetics, safety, and initial virologic response of a triple-protease inhibitor salvage regimen containing amprenavir, saquinavir, and ritonavir

The aim of this study was to quantify the change in saquinavir and amprenavir exposure when combined and used with low-dose ritonavir; to evaluate 24-week safety and immunologic and virologic response. It was a randomized, nonblinded, prospective study. There were 11 HIV-1-infected, antiretroviral-experienced, male and female subjects > or = 18 years old, median HIV-1 RNA and CD4(+) T-cell count of 4.86 log copies/mL and 10(6) cells/mm(3), respectively. Subjects were randomly assigned to receive saquinavir 1000 mg/ritonavir 100 mg every 12 hours or amprenavir 600 mg/ritonavir 100 mg every 12 hours for 7 days. After 12-hour pharmacokinetic sampling, the third protease inhibitor (PI) was added, and pharmacokinetics sampling was repeated 14 days later. Subsequent PI dosage adjustments were based on real-time pharmacokinetic assessment. Saquinavir did not affect amprenavir or ritonavir pharmacokinetics. Amprenavir decreased area under the concentration-time curve (AUC(0-12h)) and C(12h) for saquinavir 82 and 61%, and 74 and 75% for ritonavir. An adjusted PI regimen of amprenavir 600 mg/saquinavir 1400 mg/ritonavir 200 mg every 12 hours returned saquinavir exposure to baseline. At 24 weeks, HIV RNA declined a median of 1.55 log copies/mL and CD4(+) T-cell counts increased a median of 52 cells/mm(3). Gastrointestinal events predominated and were mild to moderate. These data suggest that amprenavir/saquinavir/ritonavir may be a viable salvage regimen in heavily PI-experienced individuals. New formulations of amprenavir and saquinavir may simplify this regimen.