post #2: my CROI Report

CROI 2007, Los Angeles - Selected topics from 14th Conference on Retroviruses and Opportunistic Infections, Rob Camp

At the 14th Conference on Retroviruses and Opportunistic Infections (CROI) held in Los Angeles USA from Feb 25-28, 2007, two drugs stood out above the crowd and may herald a new beginning in HIV treatment. As always, the world of investigation in HIV (from immunology and vaccines through research on clinical care and scale-up in developing countries) is varied and at times confusing if not contradictory. CROI offers plenaries and roundtable symposia, oral presentations, posters and poster discussions, late breakers, and now hands-on computer workshops and a workshop for new investigators and trainees.

More than half (57%) of the abstracts (oral, poster or late breakers) were university-driven, 22% of hospital/medical center origin, and 14% were government-driven. The other 10% was divvied up between industry and foundations/private practices (with some inter-sectoral collaborations). Geographically, North America led the way (54% of presentations) with Europe second (30%). Africa was third, with 9% of the total. Asia (4%), Australia (2%) and South America (1%) filled out the rest.

This year’s most annoying ‘screw you’ to the community was the offering of transparent plastic bags – similar to those sometimes used to pick up dog poop - to hold our abstract books, conference programs, etc (~5 lbs). Although in the line of insults it was fairly mild, there truly was no reason for it, except to underline the organizers’ sheer lack of interest in or respect for, the community (“you didn’t pay, do you really think you need a CROI backpack?”). It must have saved them so much money…

Many of the sessions are both webcast and podcast and can be seen at www.retroconference.org for free. To learn more about any drug mentioned here, please look it up by abstract number at the above web-site and you can read the whole abstract and in many cases, the full poster is also available. I will focus on drugs in the pipeline, from two that are just months away from approval to many that are just seeing the light of day for the first time here at the conference. This article gives a quick overview of what was presented in Los Angeles.

New ARV Agents

Recently approved

Darunavir is approved and available and is being slowly introduced throughout the global north. It is to be used in PI-resistant situations (heavily PI-treated populations), and 7 abstracts were presented at CROI on its value in various settings of resistance. For example, although DRV/r and APV in vitro susceptibility patterns are very similar, predicted incidence of cross-resistance is low, due to differences in clinical cut-offs, which are higher for DRV/r. The expected increased value of DRV/r compared to APV in PI-experienced patients is most probably a result of higher potency and higher free drug levels in plasma, rather than a unique cross-resistance profile, according to Monogram.

The manufacturer of the drug (Tibotec) had a similar study with similar outcomes, and reported results slightly more emphatically: high levels of resistance to APV at baseline had only a small effect on the response to DRV/r at 48 weeks in patients enrolled in POWER 1, 2, and 3. DRV/r works against viral isolates resistant to APV.

Investigators at Kumamoto University in Japan highlight that when a mixture of multiple PI-resistant HIV isolates is used, highly DRV-resistant variants are selected. Although DRV generally would not easily permit significant resistance, HIV-1 could develop high levels of DRV-resistance when superinfection with multi-PI-resistant HIV-1 variants and resulting recombinations happen. Theoretically, these data have significance at least in the understanding of emergence of DRV resistance.

The ANRS presented a study that said that amprenavir, atazanavir and tipranavir may all work less well in HIV-2, while darunavir and lopinavir might also be compromised in HIV-2 in the presence of mutations at codons 82, 84, and 90.

Phase III

Twenty years after the approval of the first anti-HIV drug, AZT, HIV research is on the brink of ushering in a series of new antiretroviral drug classes that just may revolutionize the paradigms for how ART regimens are constructed. In 2007 alone, regulatory authorities will be reviewing a CCR5 antagonist and an integrase inhibitor. Early in 2008, they will review the first NNRTI with a distinct resistance profile, and not far off are maturation inhibitors, monoclonal antibodies and X4-tropic antagonists.

Maraviroc (MVC) is a first-in-class CCR5 inhibitor that has been studied for use in treatment-experienced patients. The current New Drug Application (NDA), and this paper, deal only with the sponsor's current application for accelerated approval for maraviroc (formerly known as UK-427,857) among treatment-experienced individuals, based on 24 week data from the two pivotal studies, MOTIVATE-1 and –2, involving 949 patients with advanced disease (169 CD4s).

Development of MVC was not without its ups and downs. Due to a surprising series of adverse events in other drugs of the same class in the same (relatively early) stage of development, Pfizer was forced to persevere through what could have been the last days of the drug for much of the past year. Before data from phase IIb studies were presented publicly, the sponsor had to come to terms with cancers and malignancies seen with Schering’s drug, and fatal liver toxicities and final termination of Glaxo’s compound. They dealt with, at the same time, two near fatal liver toxicities in their studies and other development tribulations that could have generated enough grief in a less experienced company to call it a day. The 24-week phase III data recently presented at the 14th CROI in Los Angeles were generally greeted with a sigh of relief.

The safety profile is unremarkable at 24 weeks. Because this compound was generally studied as an add-on to a triple regimen, side effects and tolerability were as good as one might expect. The most commonly reported adverse events across all clinical trials include diarrhea, nausea, headache, fatigue, cough, pyrexia, ISRs (probably due to co-administration withT-20), upper RTIs and nasopharyngitis, vomiting and dizziness, all in more than 10% of participants. The most common laboratory abnormalities were elevated liver enzymes and bilirubin (triglycerides and lipids are unreported). The longer-term adverse events need to be better described, as well as a better description of tropism shifts (see below).

There is still much to learn about these new compounds, including the significance of blocking host cell signalling, agents’ impact on HIV tropism switches (from the less rapidly pathogenic R5/non-syncytium inducing HIV to the more aggressive, rapidly destructive X4/syncytium inducing strains), side effects, and pharmacokinetic issues, like (need for) boosting with ritonavir. It is not clear that tropism switching has long-term clinical consequences, and this is one of a number of factors that the FDA is asking developers to maintain vigilance on over the next few years.

Given the existing tolerability problems of most salvage products, in particular the risk of hepatotoxicity associated with drugs like TPV/r, safety data need to be rigorously scrutinized. Side effects, severe side effects, AIDS-defining events and lab abnormalities occurred with similar frequency across all groups in MOTIVATE, including placebo.

Discontinuation due to adverse events were low: MOTIVATE-1 had 5% and 4% in the QD and BID arms versus 5% in OBT; MOTIVATE-2 showed 5% and 4% (QD and BID) versus 2% in OBT.

In a poster at CROI ’07 (Abstr 509), analyzing all nine phase I and IIa studies done in 600 patients in a comprehensive immune function monitoring program, no increased risk of infection or adverse effects on immune parameters were seen. But rather than concluding “it is safe”, the authors laudably point out the short term of therapy so far, and promise to “continue reviewing the data to identify the frequency and severity of infections”.

One of the two late breakers at this year’s CROI, LB104aLB, presented by H Mayer, showed that in the 90% male trial, grade 3 (moderate) and grade 4 (severe) adverse events occurred in 24% of the once a day (QD) arm and 30% of the twice a day (BID) arm. There were another 13% and 16% serious (life threatening) adverse events reported in the same two arms. Diarrhea, nausea, headache, fatigue, cough, pyrexia, ISR, upper respiratory tract infection and dizziness all occurred somewhere between 12% and 22%. T-20 use was 43% and 46% (of whom 40% were ‘recycling’ T-20, 60% using it for the first time). Inexplicably, herpes infections and esophageal candidiasis were seen in LB104bLB in the QD arms 4 and 3 times as frequently as in the BID arms.

When treatment failed (n = 145 at 24 weeks), the HIV remained R5-tropic virus 1/3 of the time (n = 35), while 2/3 of the quantified failures switched to X4 or dual/mixed virus (n = 63). The numbers do not add up because some people did not get a tropism test at failure. This may be a signal that tropism issues won’t be that smooth in real life, if they were not rigorously controlled in these registrational trials.

Hy’s law (ALT elevations combined with elevations in serum bilirubin) was noted in 0.7% in the QD arm and 1.0% in the BID arm, much less than with GSK’s aplaviroc (4%). ALT elevations occurred sporadically were not dose related and were not associated with bilirubin elevation.

MOTIVATE -1 (PF 1027) is being conducted at clinical investigational sites in the US and Canada and MOTIVATE -2 (PF 1028) in Europe, Australia and the US. MOTIVATE patients were randomized to receive OBT combined with either placebo or maraviroc, dosed once (QD) or twice (BID) daily.  OBT included 3-6 antiretrovirals, with or without low-dose ritonavir.

Results of MOTIVATE-1 and -2

One notable difference to previous ‘salvage’ trials is the much better result in the OBT + placebo arms. In the POWER, RESIST and TORO trials, patients achieved a –0.6 result in the placebo arm, here they had a –1.2 log drop.

In LB104bLB at CROI, it was seen that T-20 effectiveness was as additive as any other active agent, but was not synergistic. A long-held myth for extra-cellular agents is that they would work synergistically with each other. This was not seen here.

Maraviroc was equally effective in people with either more or less than 100,000 copies of viral RNA.

Integrase

Merck has been investigating integrase for over ten years. Persistent, high quality science has brought a new drug from a new class to approval in a relatively short time – first dose in humans to packet submission will be likely no more than 3.5 years!

Raltegravir, first in its class, presents no cross-resistance problems. It is a strand-transfer HIV integrase inhibitor with an in vitro IC95 of 33nM. The compound is metabolized by glucuronidation (UGT1A1). It requires BID dosing, regardless of food. To date, there are no significant drug interactions. In phase I trials, it showed a VL -1.7-2.2 log cps/ml in just10 days in a treatment-naïve population (Morales-Ramirez, EACS 2005).

The Phase III BENCHMRK trials were mirror trials in North, Central and South America and Europe and Oceania. Patients presented with resistance to 3 or more classes of ART. Efficacy endpoints included the percentage of patients with HIV RNA <400 and <50 copies/mL and change from baseline in CD4 cell counts. About 60% of patients completed week 24. RGV showed an adverse event profile similar to that of placebo. RGV 400 mg twice daily plus OBT demonstrated potent and superior antiretroviral effect compared to placebo plus OBT at weeks 16 and 24.

Of the 16% of those on raltegravir who failed virologically, approximately 2/3 had mutations at codons N155H, Q148K/R/H, and some Y143R/C, similar to the mutations for GS-9137, the Gilead integrase agent.

NNRTI

The third drug in phase III reviewed at CROI is an NNRTI, TMC125 (etravirine). Etravirine is a diarylpyrimidine (DAPY) compound with a flexible chemical structure. Its in vitro EC50 is 1.4-4.8 nM (wild-type HIV-1); it has a 3.5 uM in HIV-2. In vitro, it showed activity against NNRTI-resistant virus. In vivo, it is showing better staying power against the K103N (-1.4 logs) mutation than the Y181C (-0.86 logs). It is metabolized mostly through the CYP 3A4 with some glucuronidation. It has some interaction activity with other ARVs that will need to be kept in mind. (Vingerhoets, J Virol 2005;79:12773, Kakuda, Glasgow 2006 PL5.2, Grossman, ICAAC 2005, abstract H-416c, Vingerhoets, Sitges 2006, abst 17). 24-week data from the registrational DUET studies is pending, therefore only PK study results were presented at CROI.

Phase II

The elvitegravir 24 week dose finding study was presented by Andrew Zolopa. Doses studied were: 20mg, 50mg and 125 mg. At first PI use was not allowed in the study, but at week 8, it was allowed (when PI interaction data became available) and by week 24 some 15% of people were using PIs. Elvitegravir was used as an add-on (to a triple drug regimen).

CD4 recuperation was better in both elvitegravir arms (+50) vs the CPI arm (+16). Other than that, this drug looks to be of limited use – cross-resistant to raltegravir (which hopefully will be approved this year) and the 125mg arm minimally better than placebo in terms of virologic activity at 16 or 24 weeks (-1.7 logs vs –1.2 logs).

Anton Pozniak presented the 48-week data from a dose ranging study of a potentially first line NNRTI, TMC278, also known as rilpivirine (RPV). He reminded us that it is also a diarylpyrimidine (DAPY) compound, like etravirine above; this is a very small molecule and there is potential for co-formulation – any interested parties should get in touch with them ASAP. Its in vitro EC50 is 0.5 nM and it has been shown to be active against NNRTI-resistant virus (N=3500 clinical isolates) with a high genetic barrier in vitro. Its T1/2 is between 38 and 45 hours, great for QD dosing. In Phase IIa, it acheived up to 1.3 log cps/ml reductions by day 8 (Janssen PA, J Med Chem 2005;48: 1901, de Bethune, CROI 2005 abstr #556, Goebel F, CROI 2005 Abstr 160).

The mutations seen at failure were at codons 138K, 101E and 230L. Because they will be seeking a naïve indication, all people in the studies were naive. People either took 25, 75 or 150 mg per day vs EFV either with TVD or CBV as backbone. Baseline indicators were more interesting than normal – 33% women, although with only 200 CD4s (a late-presenting naïve population). 80% of everyone was undetectable (<50 copies) at 48 weeks. There was 9% virologic failure (vs 6% on EFV). Those on EFV did seem to reach <50 faster (significance not clear). People on RPV got –2.6 logs at 12-16 weeks, and added some 140 CD4s. There was little rash reported (0.4%). Neurocognitive events were much less than in the EFV arms (no specifics as yet), and headache was seen in 18% of people. SAEs were the same (RPV vs EFV); there seemed to be more gr 3/4 events with RPV. There was much less of a rise in cholesterol with RPV (5% vs 31%). Triglycerides with RPV dropped by some 10 points, while they went up by 18 with EFV. The 75 mg dose will move forward now into Phase III.

Probably the most beautiful visual presentation was given by Joe Baumann from Rutgers on the crystal engineering of TMC278. His work was meant to describe the “wiggling and jiggling” (the seeming ability of the molecule to adjust itself according to the binding site offered to it) of the agent that allows it to be so much more flexible in binding to the site.

CCR5 antagonist

There was not much presented on vicriviroc, except for a basic look to see if blocking the CCR5 inhibitor might mean an upregulation of Epstein Barr replication. In this study, it was not associated. To recap what is known about this second CCR5 inhibitor: In vitro, its EC50 is <3nM, and its EC90 <19nM against diverse viral strains. It is >89% orally bioavailable and has a T1/2 of 27 hours, which allows once-daily dosing. It is a CYP 3A4 substrate and not a PGP substrate. Its PK concentrations are enhanced with RTV 2-5X, so it will always be used with ritonavir (Strizki, AAC 2005;49:4911, Schurmann, 11th CROI #140LB). It is advancing slowly due to two reasons: the failure to show maintained activity vs EFV at doses of up to 75 mg QD without ritonavir (Greaves, CROI 2006, abst. #161LB, Landovitz, Sitges 2006, abst. #18) and due to at least (5) malignancies and cancers seen in a lower dose study with ritonavir, a percentage much higher than what would be seen in the general HIV population (Gulick, JID 2007, in press).

Phase I and preclinical

The same investigators who developed Nikavir (an approved thymidine NRTI) in Russia evaluated other groups of novel NRTIs such as the acyclic nucleoside phosphonates that demonstrate a broad spectrum of activity. Derivatives of adenine (Z)- and (E)-9-[3-(phosphonomethoxy) prop-1-en-1yl] adenine were selected. Besides in vitro studies on activity and safety, pharmacokinetics was evaluated in dogs and rabbits. Both isomers inhibited HIV replication without apparent cellular toxicity up to 3300 µM, although the Z-isomer had about a 10-fold more effective inhibition of HIV replication than the E-isomer. Both possessed lower cytotoxicity compared to zidovudine (AZT) and the T1/2 of both was 3-10-fold greater than that of AZT. The investigators will move ahead with the (Z) compound as a potential therapeutic for HIV infection and potential microbicide.

4’-Ed4T is a novel thymidine analog, active against multi-drug-resistant HIV-1. Selection in vitro of HIV resistant to 4’-Ed4T revealed that the M184V mutation confers some resistance (3- to 10-fold) to 4’-Ed4T, yet additional mutations (P119S and T165A) were required to achieve significant resistance (40-fold). The 184V mutation acts as a primary mutation (increasing resistance to 4’-Ed4T), and the 119S as a secondary mutation (increasing viral fitness). Addition of the 165A mutation (at day 12) compromised viral fitness.

For a new NNRTI, efficacy against wild type and mutant strains, an increased barrier to the development of resistance, and favorable pharmacokinetics are essential attributes. Idenix identified two candidates, IDX-12899 and IDX-12989, novel phospho-heterocyclic NNRTI that may have the potential to fit such a profile. Oral absorption, metabolism, and pharmacokinetics were studied in the rat, rabbit, dog, and monkey. Potency is retained against panels of clinical isolates containing various single and double NNRTI mutations, including those associated with high-level resistance to efavirenz, with possibly a higher barrier. For both compounds, oral absorption in the monkey was around 60% and plasma drug levels significantly exceeded EC90 values 24 hours post-dose. No adverse effects were observed in acute toxicity studies in rats and monkeys administered up to 1000 mg/kg. Genotoxicity studies were negative. Both compounds are weak to moderate inducers of CYP450 3A4. Extrapolation from animal data supports the potential for once-daily dosing in humans.

A group from NCI and Rutgers investigated the target and mechanism of action of the cholesterol-binding compound amphotericin B methyl ester (AME), a water-soluble, relatively non-toxic derivative of the polyene fungal antibiotic amphotericin B. AME blocks the replication of diverse HIV-1 isolates, irrespective of their clade, target cell tropism, or resistance to RT or PR inhibitors. AME profoundly impairs virus entry and also induces a ~5-fold decrease in virus particle production. This study identifies a novel mechanism of resistance to an HIV-1 entry inhibitor and is the first instance in which HIV-1 Env is activated by PR-mediated Env cleavage.

GS-8374 is a novel bis-tetrahydrofuran-based peptidomimetic HIV protease inhibitor (PI) with a unique diethyl-phosphonate motif. GS-8374 inhibits HIV-1 in acutely and chronically infected T-cell lines, primary CD4+ lymphocytes and macrophages with a potency comparable to that of darunavir, atazanavir, and lopinavir in vitro. The results presented supports further evaluation of this novel PI.

The effects of CCR5 and CD4-receptor density levels were evaluated on primary CD4 T cells on the replication efficiency and T-20 susceptibility of R5 HIV-1. In addition, the effects of Rapamycin (RAPA), an immunomodulatory drug previously shown to reduce CCR5 expression, were evaluated on the antiviral activity of T-20. In vitro results indicate that CCR5 density levels on CD4 T cells determine the replicative efficiency and T-20 susceptibility of R5 strains of HIV-1. Furthermore, they demonstrate that reduction of CCR5 levels by the drug RAPA results in enhancement of T-20 antiviral activity against R5 HIV-1. These results suggest that therapeutic and preventive approaches to alter CCR5 density may have clinical consequences and warrant further investigation.

Phosphorodiamidate morpholino oligomers (PMO) are nuclease-resistant antisense oligonucleotide analogs that act by blocking complementary RNA sequences. PMO have recently been reported to be effective against several families of RNA viruses and therefore represent a prospective new class of anti-HIV compounds. To evaluate their potential, 2 targets were selected:  the highly conserved start codon region of the HIV-1 Vif gene (also important to viral infectivity), and the Tar stem-loop. Both may be candidates for further investigation in animal model systems.

One of the major reservoirs of HIV-1 is monocytes that remain generally immune to current drug treatments. Following previous findings that amiloride analogs block a Vpu ion channel activity and can inhibit HIV replication in monocyte-derived macrophages, Biotron Limited selected BIT-225 as their lead pre-clinical candidate based on its superior anti-HIV activity in vitro, and on its in vivo safety and pharmacology profile. BIT-225 demonstrated broad-spectrum activity against clinical isolates from different virus clades and selected drug resistant strains.

Abstr 607, Darunavir/Amprenavir Cross-resistance in Clinical Samples Submitted for Phenotype/Genotype Combination Resistance Testing, Neil Parkin*, E Stawiski, C Chappey, and E Coakley, Monogram Biosci, South San Francisco, CA, US

Abstr 602, An Investigation into the Influence of the Tipranavir-asssociated V82L/T Mutations on the Susceptibility to Darunavir and Brecanavir, R Elston1, Daniel Kuritzkes*2, and R Bethell1, 1Boehringer Ingelheim Ltd, Laval, Canada and 2Brigham and Women's Hosp, Boston, MA, US

Abstr 609, Prior Utilization or Resistance to Amprenavir at Screening Has Minimal Effect on the 48-Week Response to Darunavir/r in the POWER 1, 2, and 3 Studies, Gaston Picchio*1, T Vangeneugden2, B Van Baelen2, E Lefebvre1, D Miralles2, and M de Bethune2, 1Tibotec Inc, Yardley, PA, US and 2Tibotec BVBA, Mechelen, Belgium

Abstr 610, Defining the Upper and Lower Phenotypic Clinical Cut-offs for Darunavir/Ritonavir by the PhenoSense Assay, Eoin Coakley*1, C Chappey1, J Benhamida1, G Picchio2, and M P de Béthune3, 1Monogram Biosci, South San Francisco, CA, US; 2Tibotec Inc, Yardley, PA, US; and 3Tibotec BVBA, Mechelen, Belgium

Abstr 605, Binding Kinetics of PI to Wild Type and Multi-drug Resistant HIV-1 Proteases: A Mechanistic Study of the Genetic Barrier to Resistance of Darunavir, M De Wit, I Keuleers, E Gustin, Inge Dierynck*, S Hallenberger, and K Hertogs, Tibotec BVBA, Mechelen, Belgium

Abstr 606, Selection in vitro of HIV-1 Variants Highly Resistant to Darunavir Using a Mixture of HIV-1 Isolates Resistant to Multiple PI, Yasuhiro Koh*1, T Towata1, A Ghosh2, H Mitsuya1,3, and H Mitsuya1,3, 1Kumamoto Univ Sch of Med, Japan; 2Purdue Univ, West Lafayette, IN, US; and 3NCI, NIH, Bethesda, MD, US

Abstr 104aLB, Efficacy and Safety of Maraviroc plus Optimized Background Therapy in Viremic, ART-experienced Patients Infected with CCR5-tropic HIV-1 in Europe, Australia, and North America: 24-Week Results, M Nelson1, G Fätkenheuer2, I Konourina3, A Lazzarin4, N Clumeck5, A Horban6, M Tawadrous7, J Sullivan3, H Mayer7, and Elna van der Ryst*3, 1Chelsea and Westminster Hosp, London, UK; 2Universitaetsklinik Köln, Germany; 3Pfizer Global R&D, Sandwich, UK; 4Hosp San Raffaele, Milan, Italy; 5Ctr Hosp Univ St Pierre, Brussels, Belgium; 6Szpital Zakazny Centrum Diagnostyki i Terapii AIDS, Warsaw, Poland; and 7Pfizer Global R&D, New London, CT, US

Abstr 104bLB, Efficacy and Safety of Maraviroc plus Optimized Background Therapy in Viremic ART-experienced Patients Infected with CCR5-tropic HIV-1: 24-Week Results of a Phase 2b/3 Study in the US and Canada, J Lalezari1, J Goodrich2, E DeJesus3, H Lampiris4, R Gulick5, M Saag6, C Ridgway7, M McHale7, E van der Ryst7, and Howard Mayer*2, 1Quest Clin Res, Univ of California, San Francisco, US; 2Pfizer Global R&D, New London, CT, US; 3Orlando Immunology Ctr, FL, US; 4San Francisco VAMC, Univ of California, US; 5Weill Med Coll of Cornell Univ, New York, NY, US; 6Univ of Alabama at Birmingham, US; and 7Pfizer Global R&D, Sandwich, UK

Abstr 509, A Review of the Markers of Immune Function during the Maraviroc Phase I and IIa Studies, A Ayoub, E Van der Ryst, K Turner, and Mary McHale*, Pfizer Global R&D, Sandwich, UK

Abstr 105aLB, Results of BENCHMRK-1, a Phase III Study Evaluating the Efficacy and Safety of MK-0518, a Novel HIV-1 Integrase Inhibitor, in Patients with Triple-class Resistant Virus, David Cooper*1, J Gatell2, J Rockstroh3, C Katlama4, P Yeni5, A Lazzarin6, J Chen7, R Isaacs7, H Teppler7, B Nguyen7, and for the BENCHMRK-1 Study Group, 1Univ of New South Wales, Sydney, Australia; 2Univ of Barcelona, Spain; 3Univ of Bonn, Germany; 4Hosp Pitie Salpetriere, Paris, France; 5Hosp Bichat Claude Bernard, Paris, France; 6San Raffaele Sci Inst, Milan, Italy; and 7Merck Res Labs, West Point, PA, US

Abstr 105bLB, Results of BENCHMRK-2, a Phase III Study Evaluating the Efficacy and Safety of MK-0518, a Novel HIV-1 Integrase Inhibitor, in Patients with Triple-class Resistant Virus, Ron Steigbigel*1, P Kumar2, J Eron3, M Schechter4, M Markowitz5, M Loufty6, J Zhao7, R Isaacs7, B Nguyen7, H Teppler7, and for the BENCHMRK-2 Study Group, 1State Univ of New York at Stony Brook, US; 2Georgetown Univ Med Ctr, Washington, DC, US; 3Univ of North Carolina at Chapel Hill, US; 4Federal Univ of Rio de Janeiro, Brazil; 5Aaron Diamond AIDS Res Ctr, The Rockefeller Univ, New York, NY, US; 6Canadian Immunodeficiency Res Collaborative, Toronto; and 7Merck Res Labs, West Point, PA, US

Abstr 616, Phenotypic Susceptibility in vitro to Amprenavir, Atazanavir, Darunavir, Lopinavir, and Tipranavir of HIV-2 Clinical Isolates from the French ANRS HIV-2 Cohort, D Desbois1, G Peytavin1, S Matheron1, F Damond1, G Collin1, A Bénard2, P Campa3, G Chêne2, F Brun-Vézinet1, Diane Descamps*1, and The French ANRS HIV-2 Cohort (ANRS CO 05 VIH-2), 1Hosp Bichat-Claude Bernard, Paris, France; 2INSERM U593, Bordeaux, France; and 3Hosp St Antoine, Paris, France

Abstr 143LB, The HIV Integrase Inhibitor GS-9137 Demonstrates Potent Antiretroviral Activity in Treatment-experienced Patients, Andrew R. Zolopa*1, M Mullen2, D Berger3, P Ruane4, T Hawkins5, L Zhong6, S Chuck6, J Enejosa6, B Kearney6, and A Cheng6, 1Stanford Univ, CA, US; 2Mt Sinai Sch of Med, New York, NY, US; 3NorthStar Medical Center, Chicago, IL, USA; 4Light Source Med, Los Angeles, CA, US; 5Southwest CARE, Santa Fe, NM, US; and 6Gilead Sci, Foster City, CA, US

Abstr 627, Resistance Profile of HIV-1 Mutants in vitro Selected by the HIV-1 Integrase Inhibitor, GS-9137 (JTK-303), G Jones, R Ledford, F Yu, M Miller, M Tsiang, and Damian McColl*, Gilead Sci, Foster City, CA, US

Abstr 87, Next Generation of Inhibitors of HIV-1 Integrase Strand Transfer Inhibitor: Structural Diversity and Resistance Profiles, John Wai*, T Fisher, M Embrey, M Egbertson, J Vacca, D Hazuda, M Miller, M Witmer, L Gabryelski, and T Lyle, Merck Res Labs, West Point, PA, US

Abstr 144LB, 48-Week Primary Analysis of Trial TMC278-C204: TMC278 Demonstrates Potent and Sustained Efficacy in ART-naïve Patients, Anton Pozniak*1, J Morales-Ramirez2, L Mohapi3, M Santoscoy4, P Chetchotisakd5, M Hereygers6, S Vanveggel6, M Peeters6, B Woodfall6, and K Boven7, 1Chelsea and Westminster Hosp, London, UK; 2Clinical Res, San Juan, Puerto Rico; 3Univ of the Witwatersrand, Johannesburg, South Africa; 4Hosp Gabriel Mancera IMSS, Mexico City, Mexico; 5Srinagarind Hosp, Khon Kaen, Thailand; 6Tibotec BVBA, Mechelen, Belgium; and 7Tibotec Inc, Yardley, PA, US

Abstr 88, Structures of HIV-1 Reverse Transcriptase Complexed with NNRTI TMC278: Conformational and Positional Adaptability Overcomes Resistance Mutations, Joe D. Bauman*1, K Das1, M Baweja1, A Clark Jr1, P Boyer2, A Shatkin1, P Lewi3, S Hughes2, and E Arnold1, 1Ctr for Advanced Biotech and Med, Rutgers Univ, Piscataway, NJ, US; 2NCI-Frederick Cancer Res and Devt Ctr, MD, US; and 3Katholieke Univ, Leuven, Belgium

Abstr 844, Vicriviroc Therapy and EBV Plasma Viral Loads in HIV-1-infected Treatment-experienced Subjects, Athe M.N. Tsibris*1,2, Athe M.N. Tsibris*1,2, R Paredes3,4, R Paredes3,4, Z Su5, C Flexner6, P Skolnik7, C Godfrey8, W Greaves9, M Hughes5, R Gulick10, D Kuritzkes1,3, and D Kuritzkes1,3, 1Harvard Med Sch, Boston, MA, US; 2Massachusetts Gen Hosp, Boston, US; 3Brigham and Women's Hosp, Boston, MA, US; 4Fndn irsiCaixa, Badalona, Spain; 5Harvard Sch of Publ Hlth, Boston, MA, US; 6Johns Hopkins Univ, Baltimore, MD, US; 7Boston Med Ctr, MA, US; 8Div of AIDS, NIAID, NIH, Bethesda, MD, US; 9Schering Plough, Kenilworth, NJ, US; and 10Cornell Univ, New York, NY, US

Abstr 487, Antiviral Activity of Novel NRTI, Edward Karamov*1, M Kukhanova2, G Kornilaeva1, T Pavlova1, and M Jasko2, 1Ivanovsky Inst of Virology, Moscow, Russia and 2Engelhardt Inst of Molecular Bio, Moscow, Russia

Abstr 616, A Novel Mechanism of Resistance to an HIV-1 Entry Inhibitor: Cleavage of the gp41 Cytoplasmic Tail by the Viral Protease, Abdul Waheed*1, S Ablan1, M Mankowski2, J Cummins2, R Ptak2, C Schaffner3, and E Freed1, 1NCI-Frederick, MD, US; 2Southern Res Inst, Frederick, MD, US; and 3Rutgers Univ, New Brunswick, NJ, US

Abstr 582, The Fitness and Antiviral Susceptibility of Unique HIV-RT Resistance Mutations of a Novel Thymidine Analog, Elijah Paintsil*1, G Dutschman1, S Grill1, M Baba2, H Tanaka3, G Yang1, and Y C Cheng1, 1Yale Univ, New Haven, CT, US; 2Univ Sch of Med, Kagoshima, Japan; and 3Sch of Pharma Sci, Tokyo, Japan

Abstr 489, IDX12899 and IDX12989, Novel NNRTI with Potent Anti-HIV Activity, Enhanced Barrier to Resistance and Favorable Pharmacokinetic Profile, Douglas Richman*1, C Dousson2, R Storer3, A Moussa3, J Randall3, E Bridges3, M Liuzzi4, J Jakubik3, M Seifer3, and D Standring3, 1Univ of California, San Diego, US; 2Idenix Pharma, Montpellier, France; 3Idenix Pharma, Cambridge, MA, US; and 4Idenix Pharma, Cagliari, Italy

Abstr 499, Morpholino Antisense Oligonucleotides that Target the Lentiviral vif Gene and Tar Stem-loop Are Novel Antiretroviral Drug Candidates, Richard Bestwick*1, R Wu1, J Kellogg1, J Deere2, D Meadows2, E Sparger2, T North2, and P Iversen1, 1AVI BioPharma, Corvallis, OR, US and 2Univ of California, Davis, US

Abstr 502, A Novel Inhibitor of HIV-1 Release from Human Macrophage Reservoirs, Carolyn Luscombe*1, L Williams1, G Khoury1, D Hill2, R Ptak2, G Ewart1, and M Miller1, 1Biotron Ltd, Canberra, Australia and 2Southern Res Inst, Frederick, MD, US

Abstr 491, Profile of GS-8374, a Novel Phosphonate-containing HIV PI: in vitro Antiretroviral Activity, Toxicity, and Resistance, Christian Callebaut*1, K Stray1, L Tsai1, L Xu1, G X He1, A Mulato1, T Priskich2, N Parkin2, W Lee1, and T Cihlar1, 1Gilead Sci, Foster City, CA, US and 2Monogram Biosci, South San Francisco, CA, US

Abstr 498, CCR5 Density Levels on Primary CD4 T Cells Affect the Replication and Enfuvirtide Susceptibility of R5 HIV-1: Clinical Implications, Alonso Heredia*, B Gilliam, O Latinovic, N Le, D Bamba, A DeVico, G Melikyan, R Gallo, and R Redfield, Inst of Human Virology, Univ of Maryland Biotech Inst, Baltimore, US

Studies and protocols on existing agents

Ten years ago, John Mellors originally posited in 1996 (Mellors JW, Rinaldo CR Jr, Gupta P, White RM, Todd JA, Kingsley LA. Prognosis in HIV-1 infection predicted by the quantity of virus in plasma. Science. 1996 May 24;272(5265): 1167-70. Erratum in: Science 1997 Jan 3; 275(5296):14) that RNA, CD4 and CD8 cells were predictors of slope and progression of HIV. He recently updated them and made adjustments. He stated that the large variability in time to AIDS is explained by: baseline RNA - 46%, CD4 count – 29%, CD38 count – 40%, the HIV RNA - 53.4%, and the CD4 slope – 2.9%. Baseline RNA + CD4 explains slightly better - 54%, while baseline RNA + CD38 explains 58%.

Using data from two large cohorts, they investigated the same relationship and the predictive value of HIV RNA for clinical disease progression. The predictive value of a single HIV RNA measurement for CD4 slope over a median of 3.18 years in cohort 1 was minimal (<0.01) and for short-term CD4 slopes in cohort 2, data was <0.05. Initial CD4 explained a large proportion of CD4 slopes (p <0.001), especially over a short period of time even after adjusting for HIV RNA levels. The predictive value of a single HIV RNA measurement with time to clinical AIDS or death (n = 45; 23%) in cohort 1 was substantially higher. Using time-updated HIV RNA values, the predictive value of HIV RNA was even stronger (0.61, p <0.002). Results confirm that HIV RNA has poor predictive value for CD4 slope alone and that any explanation for rate of CD4 slope should account for initial CD4.

Another illustrative look into viral dynamics was presented by John Mellors, using data from Abbott: Initial treatment of HIV-1 infection results in a two-phase viral decay, representing rapid clearance of virus from productively infected cells and more gradual clearance from longer-lived cells. The dynamics of further phases of decline are not well-described. There was a third phase of decay with half-lives of 77 weeks and 69 weeks (16-18 months). The decline appeared to level off after the third phase, implying a fourth phase with no decay. Low-level persistent viremia appears to arise from at least 2 cell compartments, one with a half-life comparable to that previously described for latently infected CD4+ T cells (6 to 44 months), and one or more with a half-life longer than the 7-year treatment period.

Another intriguing viral decay measurement study was from ACTG. While initial viral clearance (PH1) has been useful to compare regimen potency, this study looked at the PH1 of 3 regimens to evaluate gender differences and to relate PH1 to longer-term virologic responses: lopinavir/ritonavir + efavirenz (L/E) vs lopinavir/ritonavir + 2 nucleoside reverse transcriptase inhibitor (NRTI) (LPV) vs efavirenz + 2 NRTI (EFV. Early viral clearance, as evaluated by phase-1 viral load decay and day 7 viral load change, was greater for EFV than LPV or L/E. Phase-1 decay was not different for subjects by gender and race/ethnicity. Day 7 viral load change may predict week-48 virologic outcome.

Tenofovir (TDF) plasma exposure is increased when co-administered with some ritonavir-boosted protease inhibitors (PI/r). TDF-treated patients taking a PI/r might thus have higher TDF plasma exposures and greater declines in renal function than TDF + non-nucleoside reverse transcriptase inhibitor (NNRTI)-treated patients. In the studie wanting to answer this question of clinical implication of this finding 147 subjects were evaluated:  51 received TDF+PI/r-, 29 TDF+NNRTI- and 67 non-TDF-containing regimens. TDF+PI/r-treated patients tended to have higher TDF plasma exposures, TDF pharmacokinetic parameters did not predict renal function over time. Combination therapy with TDF+PI/r was also associated with greater renal function decline over 48 weeks compared to TDF+NNRTI-based regimens.

One study analyzed use of lamivudine (3TC), tenofovir (TDF), and nevirapine (NVP) combination as  first-line ART. This trial compared twice daily vs. once daily use of this combination; 71 patients (36 in group 1 – QD, and 35 in group 2 - BID) were included. Although NVP plasma concentrations were above the expected levels in all the patients, once daily combination of these 3 drugs resulted in an unexpectedly high rate of failure and a high incidence of the K65R and M184V mutations. The trial steering committee decided to stop the trial and recommended that all group 1 patients be switched to another ART regimen. The reasons for such frequent failures are unclear.

The OK and OK 2004 studies are randomized, controlled, open-label, clinical trials comparing lopinavir/ritonavir (LPV/r) + 2 nucleoside reverse transcription inhibitors (NRTI) vs LPV/r monotherapy. 42 and 198 patients, respectively, were enrolled in both trials. They had no history of virological failure while receiving a protease inhibitor, were previously receiving 2 NRTI + LPV/r and had serum HIV-1 RNA <50 copies/mL for >6 months prior to randomization. In OK, 21 patients received monotherapy, and in OK04, 100 did so. In the univariate analysis, factors related with loss of virologic suppression were:  time with HIV-1 RNA <50 copies/mL before starting monotherapy <9 months, lower baseline hemoglobin, and low adherence as measured by self-reported total missed doses in the week prior to visits. In the multivariate analysis, independent factors associated with the endpoint were:  low adherence (p = 0.002), lower baseline hemoglobin (p = 0.013), and nadir CD4 cell count <100 cells/mm3 (p = 0.02). Short time with undetectable viral load before monotherapy (probably also a proxy for suboptimal adherence) is not an independent factor when adherence is taken into account.

OK 2004 is a still ongoing 144-week, randomized, open-label, non-inferiority trial comparing control of lopinavir/ritonavir (LPV/r) + 2 nucleosides with LPV/r monotherapy. Patients were eligible for OK04 if their HIV-1 RNA was suppressed to <50 for ≥6 months and had not had previous virologic failure. 198 patients were randomized, n = 100 to monotherapy and n = 98 to control. Through week 48, 15 subjects (26 episodes of viral load >500) qualified for genotypic testing, 11 in the monotherapy arm, 4 in the control arm. Protease inhibitor (PI) -associated mutations were detected in 3 subjects, 2 of them in monotherapy, 1 in the control arm. Three subjects exhibited >1 episode of viral load >500. Reverse transcriptase (RT) mutations were detected in 2 subjects, 1 in monotherapy and 1 in control. Most subjects who qualified for resistance testing were not found to have PI-associated resistance mutations. The 2 subjects who showed resistance mutations on LPV/r monotherapy were able to re-suppress after being switched to a SQV-based regimen. Archived RT mutations could be detected at rebound in 1 patient receiving LPV/r monotherapy. Further LPV/r monotherapy will now be studied in an even larger multicenter trial.

After successful induction treatment with LPV/r + AZT/3TC, LPV/r monotherapy maintained plasma viral load suppression <50 copies/mL in a majority of subjects treated with monotherapy for as long as 72 weeks in Study M03-613. However, subjects receiving LPV/r monotherapy experienced more confirmed plasma viral load rebound above 50 copies/mL than subjects receiving efavirenz (EFV) + AZT/3TC. The authors looked for predictors of loss of virologic response to LPV/r monotherapy. Of 104 subjects randomized to LPV/r+AZT/3TC, 92 achieved 3 consecutive plasma viral load <50 copies/mL, deintensified to LPV/r monotherapy, and were followed for a median of 68 weeks on monotherapy. Potential predictors of response (subject demographics, baseline plasma viral load and CD4 count, and adherence [4-day subject recall]) were assessed. People reporting at least