New Drugs

A number of new drugs are in development, and to one degree or another, all are expected to be effective for people with resistance to currently available drugs. However, problems can occur in drug development, such as unforeseen toxicities which can derail development. ABT-378 is the furthest along in development, so there is more information available on it. Abbott Labs, the manufacturer, has applied to the FDA for accelerated approval, and it should be available before the end of 2000.

ABT-378 (Kaletra) In Treatment NaÔve: 72 week Update. One hundred treatment naÔve individuals were randomized to receive one of three dose levels of ABT-378/r (200/100 mg BID), 400/100 mg BID or 400/200 BID), together with d4T and 3TC, given either from study entry (group 2) or after 3 weeks (group 1). Enrollment into group 2 began following an evaluation of preliminary efficacy and safety in group 1. After 48 weeks, all patients began conversion to open label ABT-378/r (Kaletra) 400/100 BID dosing. Plasma viral load was measured using Roche Amplicor Monitor 400copy/ml assay, and Abbott Labs quantitative 50 copy/ml assay.

At baseline, there were 32 individuals in group 1; 30 men, two women; 69% Caucasian, 28% Black, 3% Hispanic. Median viral load was 5 log (100,000 copies/ml) (range 3.7 log-6.0 log). Mean CD4 count was 421. In group 2 (n=68), two were women; 63% Caucasian, 29% Black, 7% Hispanic. Viral load was 4.9 log (79,000 copies/ml) (range 3.3 log to 6.7 log; 2000 copies/ml to 500,000 copies/ml). Median CD4 count was 301.

Viral Load Suppression.

ITT: 81% (26/32) in group 1, and 79% (54/68) in group 2 had <50 copies/ml

ABT-378 performed the same, using the 400 copy assay, whether a person's viral load was <100,000 copies/ml or >100,000 copies/ml. There was no data on performance regarding <50 when a person was less than or greater than 100,000 copies/ml.

Patients with baseline viral load >100,000 copies/ml generally took longer to reach <400 copies/ml than patients with <100,000 copies/ml, but response rates were the same by week 20 and subsequently. At week 72, those with <100,000 copies/ml 100% had <400 copies/ml at week 72 by on treatment analysis, and by ITT 78% had <400 copies/ml. For those with >100,000 copies/ml at baseline, 95% had <400 copies/ml at week 72 by on treatment analysis, and 87% had <400 copies/ml by ITT analysis.

Mean CD4 count increase was 304 in group 1 by week 72, and 240 in group 2.

Based on patient reported dose interruptions, adherence was reportedly 98% through week 72. The most common adverse events were diarrhea, nausea, and abnormal stools. Abbott reported that at week 72, only one patient discontinued due to an adverse event/lab abnormality related to study drug. (See Table 3)

..+  adverse events of at "least moderate severity, and probable, possible or unknown relationship" to ABT-378

..*   >3 stools/day

..**  ≤3 stools/day

..*** 4/8 patients with AST/ALT elevations were seropositive for HBV surface antigen (HbsAg) or HCV antibody at baseline  

PATIENT DISPOSITION- 13 patients discontinued at or before week 72: 1 due to AST/ALT; 4 for noncompliance, 3 lost to follow-up, 1 for personal reasons, 3 for adverse event; lymphoma, hyperglycemia in diabetic patient, alcohol detoxification.

Identification of Clinically Relevant Phenotypic and Genotypic Breakpoints for ABT-378/r in Multiple PI-experienced, NNRTI-naÔve Patients. Dale Kempf & Eugene Sun from Abbott delivered these talks at the Resistance Workshop. Abbott reports that at a dose of 400/100 ABT-378/r (higher doses are being explored for salvage), pre-dose mean plasma trough levels are ≥75-fold above its serum adjusted EC50. The high plasma levels of ABT-378 appear to have an important significance. Firstly, the effectiveness of ABT-378 in individuals with PI experience and resistance will likely be associated with the drug's high blood levels rather than a unique resistance profile, which it does not appear to have. Second, it appears that due to high blood levels ABT-378 will have higher phenotypic susceptibility cut-offs or breakpoints than other protease inhibitors. What does this mean in plain language? For example, assume for the sake of discussion that 12-fold reduced susceptibility may be enough for full resistance to a given PI. A similar situation applies to RTV-IDV and RTV-amprenavir combinations, as there are no defined cut-offs for efficacy. The amount of reduced susceptibility to ABT-378 may have to be significantly higher for resistance to develop, since ABT-378 achieves high blood levels. It is in this context that Abbott has designed and reported at this meeting their approach to analyzing the response to ABT-378 in PI experienced individuals.

First Dale Kempf talked about genotypic and phenotypic correlates of reduced in vitro susceptibility to ABT-378. He discussed the 11 mutations identified to be associated with ABT-378 resistance development and their correlations to reduced phenotypic susceptibility. Then Eugene Sun delivered an oral presentation on how these geno/pheno correlations relate to virologic response to ABT-378.

Study Design. This analysis is of participants in study M98-957, which was for individuals with multiple PI experience, NNRTI-naÔve, and HIV-RNA >1000 copies/ml. The number of median prior protease inhibitors was 3, 4 NRTIs, and 7.5 total antiretroviral drugs. Individuals received ABT-378, efavirenz, and NRTIs as chosen by a treating physician. The mean HIV-RNA viral load was 4.5 log (31,600 copies/ml). All but two individualsí baseline clinical viral isolates were susceptible to efavirenz. Baseline genotypic and phenotypic resistance tests were performed, and PK profiles were performed on all participants at week 5. Additional week 24 data was presented at Durban and is reported below.

Baseline Susceptibility of Viruses to ABT-378. In study M97-765, in single PI experienced individuals, the mean reduced susceptibility was 2.8 fold, while in study M98-957 the mean reduced susceptibility was 16 fold.

Frequency of Mutations: ABT-378 Mutation Score of Baseline Clinical Isolates. Of the 11 mutations identified and reported to be associated with ABT-378 reduced susceptibility by Dale Kempf, here is a breakdown of the frequency of mutations. Nearly 80% of patients had at least 4 of the 11 mutations (10, 20, 24, 46, 53, 54, 63, 71, 82, 84, 90) in their clinical viral isolates (blood samples). There were 0 mutations in 2 isolates, 1 mutation in 6 isolates, 3 mutations in 1 isolate, 4 mutations in 7 isolates, 5 mutations in 9 isolates, 6 mutations in 11 isolates, 7 mutations in 10 isolates, 8 mutations in 3 isolates, 9 mutations in 3 isolates, and 10 mutations in 1 isolate.

Virologic Responses. At week 24, 52 of the 57 who enrolled in study M98-957 qualified for the analysis of week 24 response, with 42 (81%) of these patients having had HIV RNA ≤400 copies/ml at week 24. See below for more details on virologic response.

Disposition of Patients (Week 24).

Analysis of Response with Respect to Baseline Phenotypic Resistance:

…        Of individuals with <10-fold reduced baseline phenotypic susceptibility to ABT-378, 27/29 (93%) had ≤400 copies/ml

…        Of those individuals who had 10-20 fold reduced susceptibility (resistance to ABT-378) at baseline, 78% had ≤400 copies/ml (n=9)

…        67% with 20-40 fold reduced susceptibility had ≤400 copies/ml (n=6)

…        50% with >40 fold reduced susceptibility had ≤400 copies/ml (n=8)

Baseline Genotype and Week 24 Virologic Response:

Discussion. This early ABT-378 data preliminarily suggests a continuum of approximate phenotypic and genotypic breakpoints that may be useful in estimating the potential for a positive virologic response by a given person. By the time ABT-378 receives accelerated approval (expected near the end of 2000), both phenotypic resistance testing companies (Virco and Virologic) should be able to integrate this information on breakpoints into their reporting of test results. The information and research on these cut-offs is preliminary. Continued work by Abbott is required to confirm and validate this information clinically. The more data that is collected as the drug is tested and used, the more such validation attempts can be made. For example, it is possible that there are mutations associated with ABT-378 resistance that have not been identified yet. The influence or affect of one mutation may be greater than the others. For example, maybe the 82 mutation is more influential in causing virologic failure and reduced susceptibility. This has yet to be determined.  

There was some discussion about the relative contribution of efavirenz and ABT-378 to the virologic response of individuals. I think it was generally agreed by many researchers that ABT-378 is making a substantial contribution, certainly to those individuals with possibly about 33% reduced susceptibility or less. How much contribution ABT-378 makes to virologic success for individuals with 40 fold or more reduced susceptibility appears questionable. It was also estimated by Sun that this triple combination was effective for individuals with up to 7 mutations. These questions need to be continued to be addressed as they cannot absolutely be answered yet.

Parameters Associated With Virologic Response.

Three stepwise regression models were performed to assess the effect of baseline phenotype and genotype in the context of other parameters that might impact virologic response. Baseline phenotype (p=0.016), genotype (p=0.024) and inhibitory quotient (trough/EC50, p=0.068) were associated independently to be predictive of virologic response.

In the first model, baseline phenotypic susceptibility and genotype at baseline were considered and phenotypic susceptibility remained the most closely associated with the virologic response at week 24. In model 2, in which the baseline phenotypic susceptibility was omitted, the ABT-378 mutation score remained a significant predictor of virologic response at week 24. In the third model, ABT-378 pharmacokinetic parameters were considered along with the other parameters considered in models 1 and 2. Baseline phenotype was incorporated as part of 4 exploratory inhibitory quotients (IQ), representing the ratio of Ctrough, Cmin, AUC and Cmax to the serum-adjusted EC50 for each baseline isolate (IQCtrough, IQCmin, IQAUC and IQCmax, respectively). Baseline genotype entered model 3 first but was ultimately displaced by the IQC trough, which remained associated with week 24 virologic response. The following parameters also appeared to indicate a trend towards association with being predictive of response: NRTI susceptibility, number of new NRTIs, years since HIV diagnosis, baseline patient weight. Sun concluded that these results provide a framework for the interpretation of HIV phenotypic and genotypic testing.

ABT-378 (Kaletra) and Efavirenz: 24-Week Safety/Efficacy Evaluation in Multiple PI-Experienced Patients. This study reports the percent <400 copies/ml for ABT-378 at week 24. In Sitges, at the Resistance Workshop, data was broken down by response according to baseline genotypic and phenotypic resistance. Individuals with 0-5 mutations responded best. Individuals with >7 mutations may not respond as well to ABT-378. Individuals with phenotypic resistance <20 fold responded best. Those with phenotypic resistance >40 fold may not respond well to ABT-378.

This is a study of 57 patients receiving ABT-378/r 400/100 mg (3 coformulated capsules) twice daily (BID) in place of their current PI, in combination with efavirenz (Sustiva) once daily (QD) and NRTIs chosen by the doctor/study investigator, for the first 13 days of the study. On day 14, some patients (n=28) randomly had their ABT-378/r dose increased to 533/133 (ABT/378/ritonavir); 4 co-formulated capsules. The remaining (n=29) continued on the 400/100 dose. ABT/378 trough levels were drawn at week 2l, full PK (drug levels) was performed at week 5; efavirenz levels were drawn at weeks 2 and 5. Viral load in plasma was measured with the Roche Amplicor Monitor assay, with a lower limit of quantification of 400 copies/ml. To qualify for this study patients had to be NNRTI-naÔve and had multiple PI-experience (history of sequential or concurrent treatment with at least 2 protease inhibitors for at least 3 months each.)

The baseline viral load was 4.6 log (39,000 copies/ml) in the group remaining on 400/100 dose; viral load was about 25,000 copies/ml (about the same) in the 533/133 arm. Cd4s in the 400/100 group were 230 and in the 533/133 arm they were 325.

Prior to this study the mean number of HIV drugs were 7 (range 3-10); mean number of prior protease inhibitors was 3 (range 1-4); and the mean number of NRTIs was 2 (range 1-4). The types of drugs previously used in both arms were pretty evenly distributed, but all protease inhibitors and NRTIs were used. For example, 83% in the 400/100 arm had used indinavir, and 89% had used indinavir in the 533/133 arm. 68% (38/56) of patients had baseline viral isolates demonstrating ≥4 fold resistance (increased EC50 relative to wild-type) to at least 3 approved protease inhibitors. 43% of these viral isolates (24/56) showed ≥10-fold resistance (increased EC50 of ABT-378 relative to wild-type virus). (See Table 4)

Pharmacokinetic Data. ABT-378 levels achieved with 400/100 dose are reduced when taken with efavirenz (C-trough reduced -33%; AUC reduced -25%). Abbott reported that increasing ABT-378 dose produced similar levels as taking 400/100 without efavirenz. They also reported efavirenz levels are similar for both ABT-378/r dose levels studied, so ABT-378 doesn't appear to affect levels.  

Patient Discontinuation at Week 24. In the 400/100 group (n=29), 4 (13.8%) patients discontinued at or before week 24; 2 due to virologic failure, and 2 due to CNS side effects, GI/CNS side effects, lactic acidosis. In the 533/133 arm, there were 3 patients discontinued (10.7%); 1 due to virologic failure, and 2 due to drug related side effects described just above (both discontinuations occurred prior to study day 145 and initiation of the 533/133 dose).

Viral Load Suppression at 24 Weeks:

On Treatment Analysis

ITT Analysis

In both dose groups CD4s increased about 45 at week 24.

Safety and Tolerability. The most common study drug side effects of at least moderate severity were diarrhea and asthenia, while the most common lab abnormality was lipid elevations. Of the 7 patients who discontinued through week 24, 4 were due to adverse events/lab abnormalities related to study drug. (See Table 5)  

Total cholesterol/HDL cholesterol ratios were not significantly changed from baseline at week 24 at either dose level of ABT-378.

ABT-378 Resistance May Respond to Tipranavir, Amprenavir, and Saquinavir. This laboratory study reported at the Resistance Workshop in Spain suggests that individuals who develop resistance to ABT-378 may respond to tipranavir, amprenavir, and saquinavir. In a small study Abbott researchers looked at phenotypic resistance to ABT-378 for 3 individuals who had used ABT-378 and had detectable HIV viral. They had 4 to 112-fold resistance to ABT-378 and had pre-existing resistance to other protease inhibitors. Using lab (in vitro) testing, they found that all 3 had no resistance or demonstrated modest resistance to amprenavir (8.5 fold resistance), while they had 99-resistance to ABT-378. Two of the 3 individuals who had no prior saquinavir experience had no resistance to saquinavir. A virus that was created to be resistant to ABT-378 in the lab (34 fold resistant to ABT-378) had no resistance to tipranavir. Three isolates tested against tipranavir were fully sensitive.

DAPD. From preliminary studies in humans, it appears that DAPD should be effective for individuals with extensive NRTI experience and resistance. Viral load results were reported from two preliminary studies of DAPD at this Workshop. The results of a small study in 30+ individuals with NRTI experience was reported at Sitges. After receiving 15 days of DAPD monotherapy in several doses, the individuals receiving the highest dose of 500 mg twice a day achieved a viral load reduction of -1.1 log. In a study of treatment naÔve individuals receiving various doses, the individuals receiving the highest dose of 500 mg twice a day achieved a viral load reduction of -1.6 log. Laboratory resistance experiments were conducted and reported at this meeting. The researchers found in these experiments that DAPD can be effective against viruses with AZT or AZT/3TC resistance. However, DAPD was effective against some viruses with "multi-nucleoside" resistance mutations and was not effective against virus with different "multi-nucleoside" mutations. A virus with mutation associated with multi-NRTI resistance due to SS or SG insertions between codons 68/69 was sensitive to DAPD. The Q151M multi-nucleoside mutation in a background of AZT resistance mutations as well as the Q151M in combination with the 116Y showed moderate resistance (EC50 fold increase) to DAPD. Larger studies are needed to confirm this information and to explore how to use DAPD. The most common adverse events were headache, other pain, nausea and diarrhea. Adverse laboratory events that were moderate or worse (at least "grade 2") were decreased white cells (neutrophils), increased glucose, increased creatine kinase (muscle enzyme), increased triglycerides, increased amylase (pancreas gland enzyme), increased ALT (liver enzyme), increased bilirubin. No patient discontinued due to toxicity. DAPD is in phase I/II clinical trials for HIV but has not yet entered clinical trials for HBV.

BMS-232632. This is a once daily PI which appears to have a favorable resistance profile in early in vitro testing with clinical isolates. At the Resistance Workshop, Richard Colonna from Bristol Myers Squibb reported sensitivity was often retained to BMS-232632 by clinical isolates with resistance to one or two of the approved protease inhibitors. Isolates (patientsí samples) with high resistance levels to 3 or more protease inhibitors tended to lose sensitivity to BMS-232632. Clinical studies are planned.

T-20: an entry inhibitor. T-20 is a fusion inhibitor, which is a type of entry inhibitor. Current drugs act to prevent HIV replication once HIV is in the CD4 cell. Entry inhibitors act to prevent HIV from entering the CD4 cell. There are several ports of entry for HIV into the CD4, and researchers are trying to develop many different types of entry inhibitors. At Durban, Joe Eron reported 48 weeks results from a study whose primary objective was to evaluate T-20's safety. The secondary objective was to evaluate the antiviral activity of T-20. The dose was 50 mg twice daily administered by subcutaneous injection. T-20 is a powder that is reconstituted with water. Patients with prior T-20 use were allowed to enter this study.

The study participants were highly treatment-experienced. 97% were PI experienced, 79% were experienced with all 3 classes of drugs; NRTIs, NNRTIs, and protease inhibitors. Participants received genotypic & phenotypic resistance testing to aid in selecting their regimen for this study. Participants received a median of 5 drugs in their study regimen. The initial indication for use of this drug is intended for people with resistance to drugs, who have limited treatment optionsóso-called "salvage therapy."

Baseline median CD4 count was 90, and viral load was 100,000 copies/ml. 71 patients were enrolled The Intent-To-Treat (ITT, non-completer=failure) analysis is based on 70 patients. At week 48, 41 of 71 patients remained on the study. Fourteen patients discontinued due to virologic failure, defined as plasma viral load <0.5 log from baseline. Study investigators reported that no one discontinued the study due to T-20 related toxicity.

There were 30 discontinuations: 14 virologic failure; 7 voluntary withdrawal; 4 lost to follow-up; 3 adverse events; 2 non-compliance. Twenty-three of 70 (ITT) individuals had decreased viral load of >1 log from baseline and/or <400 copies/ml. Sixteen patients (16/70, ITT) had viral load <400 copies/ml. 13% of 70 had <50 copies/ml (ITT). For the on-study group, the mean and median viral load decline was 1.4 log and 1 log, respectively. The study investigators concluded that T-20 is well tolerated with other HIV drugs. Patients have to be taught about storage (refrigeration) and reconstituting powder but investigators said this was able to be done. They also said that these study results suggest that T-20 contributes to the suppression of viral load in extensively treatment experienced patients.

71% had injection site reactions (mild to moderate). A new formulation in development and possibly available for upcoming studies may reduce this reaction. 21% had grade 3 event(s) possibly related to T-20 but these were not reported. 10% had serious adverse events possibly related to T-20: elevated GGT, altered mental state, anemia, elevated SGOT (LFT), elevated amylase, neutropenia, elevated SGPT (LFT). Two large pivotol studies are expected to start this autumn in anticipation of applying for FDA approval.

Tipranavir: In Vitro Resistance Data on a Protease Inhibitor for PI Resistance. Tipranavir is a non-peptidic dihydropyrone protease inhibitor that has antiviral activity against broadly PI resistant HIV. At last year's Resistance Workshop in San Diego, Brendan Larder reported that 96/107 highly PI cross-resistant clinical isolates were fully sensitive (< 4-fold resistance or a mean of 2-fold resistance) to tipranavir when tested in vitro. Eight of the 107 isolates had intermediate resistance (4-10 fold resistance), and only 3 clinical isolates had resistance (>10-fold). He suggested tipranavir's activity against PI resistant HIV could be due to a flexible mode of binding in the protease active site. Clinical development of tipranavir has been slow because the drug's rights were sold from Pharmacia & Upjohn to Boehringer Ingelheim this past winter/spring. At this year's meeting, Sharon Kemp of Virco reported on additional in vitro resistance testing of tipranavir.

Kemp reported that of 85 clinical isolates that had greater than 10-fold resistance to at least 4 of the current protease inhibitors in a recombinant phenotypic assay, and 74 (87%) remained completely susceptible to tipranavir. Limited phenotypic resistance to tipranavir has been seen. The purpose of Kemp's study was to define the patterns of PI resistance mutations associated with TPV resistance.

They constructed 11 site directed mutants containing 6-8 known protease mutations which were highly cross-resistant to other protease inhibitors, and >4 fold resistant to TPV. The most common genotypic mutations were at positions 10, 20, 36, 46, 54, 71, and 84, together with 82T and 90M. Twenty site-directed mutants were constructed, and upon phenotypic testing the site-directed mutant with only the backbone mutations had a 2 fold tipranavir resistance. When 82T or 90M or both were added to the secondary mutations a mean 2.4 fold tipranavir resistance resulted. They constructed a series of site-directed mutants with various mutations (up to 10 mutations in one mutant) selected from 4 viruses with >10 fold TPV resistance but were unable to create TPV resistance greater than 4 fold. Often TPV had no more than 2 fold increased IC50. One virus they created included 82A, 54V, and 90M with a background of 10/20/36/71/84. Although these viruses were resistant, and in a number of cases highly resistant, to other protease inhibitors, they were sensitive to TPV.

To further test for resistance they passaged a pre-existing PI resistant, but tipranavir sensitive clinical isolate in escalating doses of tipranavir (up to 30uM). This isolate had >10 mutations and was >40 fold resistant to IDV, RTV, NFV, and SQV but was sensitive to TPV. 13-33 fold tipranavir resistance developed in culture with the following mutations developed: I47V, V82L, I85V, and T91A in a background of 10I, 20I, 46I, 77I, 84V, and 90M. Thereupon, Kemp created a site-directed mutant with a 47V mutation added to 82L and 54V to the backbone of 10/20/36/71/84. The mean fold increase in IC50 for TPV was about 5-fold.

Kemp concluded that there does not appear to be an obvious combination of mutations associated with tipranavir resistance. Complex combinations of mutations were observed in PI cross-resistant samples with > 4 fold increase in IC50 to TPV (n=11). Unusual mutations at codon 82 (T/L) appear to play a role in TPV resistance. To date, re-constructed virus mutants have failed to show high level TPV resistance, although resistance development is possible by in vitro selection.

The in vitro resistance data so far generated suggests tipranavir will be helpful as a salvage drug for people with PI resistance. But as you know, along the way in drug development, obstacles can emerge. So enthusiasm should be reserved until safety and antiviral activity can be further tested in humans with PI resistance.

PMPA

Results from Clinical Studies. Tenofovir (PMPA) is a nucleotide RT inhibitor and is currently in phase III human studies. Study 902 looked at highly NRTI experienced individuals receiving 300 mg once daily PMPA. The 48-week double-blind, dose-ranging study enrolled 189 treatment-experienced patients who were on a stable antiretroviral regimen of no more than 4 antiretroviral drugs for at least 8 weeks prior to entering the study. Patients were randomized to receive one of three PMPA doses (300 mg, 150 mg or 75 mg) or placebo in addition to their existing treatment regimen. The mean change in HIV RNA from baseline for patients receiving the 300 mg dose was -0.68 log10 copies/mL after 48 weeks of treatment (n=41). In that study the mean baseline viral load was 3.7 log (5000 copies/ml). In study 901, a 1.06 log reduction was seen in treatment experienced individuals, and in a 28 day monotherapy study of treatment-naÔve individuals, a 1.5 log reduction in HIV RNA was reported. A full report on PMPA in study 902 is available on the NATAP web site.

Discontinuations and Adverse Events. In the 300 mg arm, 20% (11) patients discontinued through 48 weeks. While 24% (12), 26% (14), and 25% (7) discontinued in the 150 mg, 75 mg, and placebo arms, respectively. In the 300 mg arm 4% withdrew for adverse events and 11% "withdrew consent/lost to follow-up". The percentages were similar in the other arms. After a minimum of 32 weeks data (n=54), 9% (5) patients experienced a serious adverse event, compared to 4% (1) in the placebo arm. In the 300-mg arm, the serious adverse events included 1 depression and 1 pneumonia. In the 300 mg PMPA arm at week 48, 39% (21 of 54) experienced grade 3 or 4 lab abnormalities: 11% triglyceride elevation; 11% creatine kinase; 7% AST elevation; 7% neutropenia; 6% amylase elevation; 4% ALT elevation, 0% serum glucose elevation, and 2% each for serum lipase and bilirubin elevations. In the placebo arm, 29% reported experiencing lab abnormalities of grade 3 or 4.

Thompson reported that through 48 weeks, no patients randomized to tenofovir 300 mg had confirmed elevations (greater than or equal to 0.5 mg/dL) of serum creatinine (a marker of kidney function). There were two unconfirmed cases (4%) in the 300 mg dose arm by week 48, and one in the placebo (4%) arm by week 24. Gilead said that the pattern of phosphate declines <2.0 was different in this study than with adefovir. Gilead reported that 5 patients (10%) in the TDF 300-mg dose group and 1 patient (4%) in the placebo group (censored at 24 weeks when they crossed over to active therapy) had a serum phosphate <2.0 mg/dl through week 48 of the study. The decreases in serum phosphate occurred (by looking at Kaplan-Meier curves) between weeks 4 and 28. From week 28 to week 72 the rate remained stable in both arms. At week 76 there was one case of phosphate decline <2.0 mg/dL in the 300 mg PMPA arm. In the adefovir studies, 47% of patients treated with the 120 mg dose of adefovir experienced serum phosphate <2.0 mg/dL by week 48, but didn't occur until after 20 weeks on therapy. As well, phosphate <2.0 mg/dL was often associated with creatinine abnormalities.  

In pre-clinical animal studies (rat, dogs, monkeys), decreased bone mineral density (BMD) has been previously observed at PMPA drug levels 10-30 times the amount used in humans. Gilead said that in experimenting with giving a dose of 5 times the human dose (10 mk/kg) to young animals (who Gilead says may be more susceptible to bone loss), they did not see bone loss out to two years of dosing. So far (48 weeks) in the human study described here (#902), Gilead reported a 1-2% BMD loss which Gilead reported was within the assay variability. Gilead said that clinical significance, in terms of being at risk for bone fracture, occurs when there is a 10-20% bone loss. Gilead also said there is data on women for osteoporosis that says if there is 1-2% per year bone loss that accumulates to 20% over 10 years, there is increased risk for bone fracture. Gilead reported there were no changes in serum markers of bone disease (serum calcium, serum phosphate, alkaline phosphatase, parathyroid hormone), and no clinical reports of bony abnormalities (spontaneous fractures or pain requiring hospitalization) through 48 weeks. To evaluate the risk of bone loss associated with PMPA, longer-term studies appear to be required. Gilead will continue to evaluate bone density changes in their phase 3 program using standardized methodologies across study centers. Changes in bone mineral density have recently been preliminarily reported in HIV patients taking HAART therapy including protease inhibitors.

Due to the BMD observations associated with PMPA, the FDA may be requesting 48 week safety before granting commercial availability. Accelerated approval is granted with 24 weeks data. Gilead and the FDA will be meeting for further discussions. PMPA appears to have utility for salvage therapy, but requiring 48 weeks safety data will delay availability.

PMPA Resistance. Mike Miller, from Gilead Sciences, reported on this preliminary resistance research. Miller selected blood samples from the Virco library of resistant viruses. Seventy-two outpatient samples with the following genotypic resistance patterns were chosen according to pre-defined resistance genotypic patterns. Susceptibility to all approved NRTIs and PMPA were assessed using the Virco Antivirogram phenotypic test. The samples included patient sample viruses with either 3TC resistance containing the M184 mutation, high level AZT resistance with & without M184 3TC resistance, or multi-nucleoside resistance mutations Q151M, or T69S double insertions with and without the 3TC M184 mutation.

Results:

…        PMPA had a slight hypersensitivity (mean 0.7 EC50 fold change) to the set of viruses with M184V resistance alone.

…        PMPA had a mean 3.7 fold reduced susceptibility to the set of viruses with high level AZT resistance (3.5 AZT mutations), .....and 3/10 of these viruses had intermediate susceptibility to PMPA (between 4-10 fold reduced susceptibility). These viruses had a mean 47 fold increase in IC50 (47 fold resistance) to AZT.

…        All the viruses with the 3TC M184V mutation added to high level AZT resistance had less than 4 fold resistance to PMPA with a mean fold change in IC50 of 2.4.

…        PMPA appeared to retain almost full antiviral activity (mean 1.7 fold increase in IC50) to viruses with the Q151M complex (multi-nucleoside resistance) and with the Q151M+M184V.

ß         With or without the 3TC M184 mutation, PMPA appears resistant to viruses containing the rare T69S double insertion mutation.

…        This data suggests that PMPA should have antiviral activity for people with low level and high level AZT resistance accompanied by 3TC resistance. High level resistance was defined by a mean of 3.5 AZT mutations. The amount of antiviral activity may differ between individuals and may be related to how much AZT/3TC resistance a person has.

…        When treating a person with PMPA, you want to retain the presence of the M184V.

Second-Generation NNRTI: DPC 083. DuPont Pharma first reported on DPC 083, a new second generation NNRTI, at the Retrovirus Conference this past February. They reported that preliminary data shows a favorable PK profile in covering NNRTI double mutants. Meaning that they are hopeful that 083 will have adequate blood levels (above the IC90 for double mutants) to suppress HIV for individuals with key double NNRTI mutants. Of course, this remains to be confirmed in human studies.

Fiske reported DPC 083 is potent against the single mutant variants such as L100I and K103N, and against double substitution variants such as K103N + Y181C, K103N + V108I and K103N + P225H which are observed in nevirapine, delavirdine and efavirenz failures.

Fiske reported on a phase 1 human study in HIV uninfected individuals. Five groups of male subjects (6 active/2 placebo per cohort) received 50, 100, 200, 300 and 400 mg doses of DPC 083, and one group of female subjects received 100 mg doses of DPC 083. Two doses were administered on the first day, followed by single daily doses for the following 8 days, for a total of 10 doses. Plasma samples were collected during the dosing period and for 3 weeks thereafter. They have also experimented with up to 1600 mg single doses.

DPC 083 had a very long half-life (>140 hours). The half-life for efavirenz is about 50 hours, and for the other NNRTI DPC-961, 72 hours. But it appears dosing for 083 will be tested once daily. DPC 083 plasma concentrations increased during the dosing period, and steady-state had not been achieved after 10 doses. After 10 doses of ≥100 mg DPC 083, the average trough concentration (Cmin-24) exceeded the calculated protein-binding-adjusted concentration needed for 90% inhibition of wild type viruses by >172-fold, of K103N virus by >11-fold, of K103N + P225H by >1.9-fold, or K103N + V108I by >2.9-fold, and of K103N + Y181C by >1.6-fold. One double mutant, which appears difficult to cover, is K103N+L100I. It has been seen in 2% of efavirenz failures, mostly in people who failed efavirenz, switched to nevirapine and remained on the failing regimen for a while. DuPont reported in Durban that in vitro experiments may not always select for mutations that may occur in humans. Therefore human studies are required to see if 083 will suppress NNRTI resistant virus for individuals.

A phase 2 study in HIV-infected is planned for later this year. Dosing will be based on tolerability. The goal is to optimize tolerability.

Also in Durban, DuPont reported on two protease inhibitors in early development. Based on in vitro studies, DPC 681 and DPC 684 appear potent against wild-type and resistant viruses, suggesting less drug will go further. In vitro, viruses with 1-5 standard PI mutations appear to retain sensitivity to both 681 & 684. Further studies are planned.