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TMC-114, new protease inhibitor for PI resistance
Reported by Jules Levin
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TMC-114 is a new protease inhibitor in early stages of development that is intended to be used by patients who have resistance to the currently available protease inhibitors, and the drug appears to be promising for patients who are resistant to currently available protease inhibitors. New resistance information on this drug was presented at the Resistance Workshop in addition to results from studies that had already been presented at previous conferences.
Tibotec-Virco is the company developing this drug and TMC-125 which is a new NNRTI. Johnson & Johnson and Tibotec-Virco previously have announced an agreement between the two companies for development of Tibotec-Virco drugs. Researchers from Tibotec-Virco were present at this conference as 2 posters and 1 oral talk were presented on TMC-114. The plan appears to be that the new NNRTI (TMC-125) will initially be developed as a first-line NNRTI. New resistance information on the NNRTI presented on this drug at the Resistance Workshop was reported and emailed by me to you and is posted on the NATAP website where all reports from this Workshop are posted at: http://www.natap.org. After initially developing the new NNRTI for first-line use Tibotec-Virco appears to want to develop the drug for use in patients with resistance to the currently available NNRTIs (Sustiva, Viramune).
TMC-114 was previously given in a 14-day study to 50 patients who had experience with multiple protease inhibitors and PI-resistance. TMC-114 is boosted by 100 mg of ritonavir and was looked at in this study as a twice or once daily regimen. Results from this study were previously reported at a conference. The first abstract below reports new resistance information from this study. The 50 patients had an average of 6 protease mutations and had extensive phenotype resistance. 46% of the patients were phenotypically resistant to all currently available protease inhibitors. But patients had <2 fold resistance to TMC-114 before starting TMC-114 therapy in the study and after 14 days of receiving TMC-114 treatment. After 14 days the average viral load reduction for the patients in the study was -1.35 log. So, this study established the drug has antiviral activity in a 14-day study for patients with PI resistance.
The second study abstract below was an oral talk at the Workshop and presented new information about TMC-114. The study reports that after examining crystal structures of protease inhibitors TMC-114 binds into the pocket of the protease enzyme more tightly than currently available protease inhibitors. This unique binding may explain why TMC114 remains active against most multi-PI-resistant viruses. This explanation was a bit controversial amongst researchers at the Workshop. In the end all that matters is the effect of this drug on reducing viral load in patients with resistance to protease inhibitors.
In the third study presented at the Workshop TMC-114 was tested in vitro (test tube) against >4000 clinical isolates (patient samples with protease inhibitor resistance) submitted for phenotypic resistance testing. The antiviral activity of TMC114 on these isolates was compared to the currently approved PIs: indinavir, ritonavir, nelfinavir, saquinavir, amprenavir and lopinavir. Tibotec-Virco researchers tested over 4000 patient isolates and found that among patients with extensive phenotypic and genotypic PI resistance TMC-114 was effective in vitro. Again, the ultimate test for this drug and any other is how it performs by reducing viral load in studies in patients who have extensive PI resistance. In talking with Tibotec-Virco researchers at this conference they said new studies are being planned now. One of the questions that emerges is since tipranavir will be available for patients before TMC-114 will TMC-114 be effective against tipranavir resistance. This questions remains to be researched.
TMC114, a potent next-generation protease inhibitor: characterization of antiviral activity in multiple protease inhibitor-experienced patients participating in a Phase IIa study
S De Meyer 1 , M Peeters 1 , C Jordens 2 , P McKenna 2 , R van der Geest 1 , R Pauwels 1 and M-P de Bethune 1. 1 Tibotec, Mechelen, Belgium; and 2 Virco, Mechelen, Belgium
BACKGROUND: TMC114 is a potent next-generation protease inhibitor (PI), active against wild-type as well as PI-resistant HIV. The study TMC114-C207
was a placebo-controlled Phase IIa trial to evaluate the antiviral activity, safety and tolerability of TMC114 over 14 days treatment. Fifty multiple PI-experienced subjects (range 2-4 PIs) on a failing nucleoside reverse
transcriptase inhibitor (NRTI)- and PI-containing regimen (HIV-1 RNA >2000 copies/ml) were enrolled. They received TMC114 with low-dose ritonavir
(TMC114/RTV) at one of three doses (300/100 mg twice daily, 600/100 mg twice daily or 900/100 mg once daily) as a substitution for their current PI or remained on their current regimen (control group) for 14 days.
Afterwards, all patients switched to an investigator-selected highly active antiretroviral therapy (HAART) regimen. Overall, the median change in plasma HIV-1 RNA for the three TMC114/RTV groups at day 14 was -1.35 log 10 compared to +0.02 log 10 for the control group. No significant difference was observed between the three TMC114/RTV treatment arms. In this study, phenotypic and genotypic resistance data from screening, baseline and end of therapy were analysed.
METHODS: Phenotypic analysis was conducted using the Antivirogram assay and genotypic analysis using the Virtual Phenotype. Both determinations were per-formed on plasma samples taken at screening (within 28 days prior to treatment start), baseline (day 1) and end of therapy (day 15) time-points.
RESULTS: Subjects in this study had a broad range of protease mutations at baseline. The median number of total protease gene mutations was 15 (range 8-26) and the median number of PI resistance-associated mutations was 6 (range 1-11), with a median number of primary PI mutations of 3 (range 0-5) (including D30N, M46I/L, G48V, I50V/L, V82A/F/T/S, I84V or L90M). More than 80% of subjects had more than one primary PI mutation. All primary PI mutations, except I50L and V82S, were present at baseline in at least one
sample. Phenotyping of the baseline samples showed that 46% of the subjects were resistant to all currently approved PIs and only 27% of the subjects were sensitive to two or more PIs (cut-offs as defined by the Antivirogram). In the treatment arms, the median fold change in EC 50 as compared to wild-type for
TMC114 was 1.8 (range 0.3 to >21) at baseline and 1.5 (range 0.3-13.1) at end of treatment. There was no correlation between TMC114 susceptibility at baseline and virological outcome at day 14. Many genotypic changes were observed between screening, baseline and end of treatment. No mutation pattern could be associated with virological response to TMC114.
CONCLUSIONS: This study demonstrates the potent antiviral activity of TMC114, a next-generation PI, in multiple PI-experienced patients over 14 days. No
mutation patterns influencing the response to treatment with TMC114 could be detected in this study.
TMC114 binds within the substrate envelope of HIV-1 protease, which could account for its efficacy against multi-protease inhibitor-resistant virus
N King 1 , M Prabu-Jeyabalan 1 , P Wigerinck 2 , M-P de Bethune 2 and CA Schiffer 1. 1 University of Massachusetts, Worcester, Mass., USA; and 2
Tibotec, Mechelen, Belgium
INTRODUCTION: HIV-1 protease is the target of very potent antiviral drugs for the treatment of HIV-1 infection. All current protease inhibitors (PIs) are the
successful result of structure-based drug design. Unfortunately, as the viral reverse transcriptase is highly error prone, and under the selective pressure of drug therapy, many viable drug-resistant variants of HIV-1 protease have emerged. These PI-resistance mutations occur mostly at positions in the protease that will compromise inhibitor binding whilst retaining substrate
specificity. We have determined from crystal structures of substrate complexes with HIV protease that the current PIs protrude beyond the substrate envelope, this may explain why resistance mutations constrain inhibitor binding. TMC114 is a next generation PI: recent virological and clinical results indicate that it is effective against known multi-PI-resistant variants of HIV-1. Furthermore, in vitro selection of TMC114-resistant variants from wild-type HIV-1 has proven difficult.
In the present study we determined and compared the high-resolution crystal structure and thermodynamics of TMC114 or substrate binding to wild
type HIV-1 protease.
METHODS: TMC114 was crystallized in complex with wild-type HIV-1 protease, and X-ray diffraction data was collected, processed and refined, using stan-dard crystallographic techniques. The structure of the inhibitor complex was compared graphically with sub-strate complexes previously determined in our laboratory. The thermodynamics of inhibitor binding was determined using isothermal titration calorimetry (ITC) at 25C and compared with other inhibitors binding.
RESULTS: The structure of TMC114 in complex with wild-type protease was determined to 1.93 (P2 1 2 1 2 1 ; R=19.7; Rf=22.2). In addition, the binding constant determined by ITC showed that the interaction of the inhibitor with the enzyme is very tight (Kd=10 -12 M) and is extremely enthalpically driven. When the structure was compared with the substrate complexes of HIV-1 protease, it was found that TMC114 occupies a volume that is contained within the substrate envelope, unlike most of the currently approved PIs.
CONCLUSIONS: Many drug-resistant variants of HIV protease evolve to maintain substrate recognition while compromising inhibitor binding, especially when
the inhibitors extend beyond the substrate envelope. The fact that TMC114 fits well within the substrate envelope, associated with its tight binding to the
enzyme, therefore, could account for why TMC114 remains active against most multi-PI-resistant variants. Hence, a mutation that affects TMC114 binding will
likely cause a dramatic change in the ability of HIV-1 protease to recognize its substrates. This may also explain why selection of TMC114-resistant virus in
vitro has proven difficult, as this might require changes beyond the protease gene, most probably in the cleavage sites. These results support our previous hypothesis that inhibitors that fit within the substrate envelope of HIV-1 protease may be more effective and less susceptible to drug resistance mutations.
Antiviral activity of TMC114, a potent next-generation protease inhibitor, against >4000 recent recombinant clinical isolates exhibiting a wide range of (protease inhibitor) resistance profiles
S De Meyer 1 , H Van Marck 1 , J Veldeman 2 , McKenna 2 , R Pauwels 1 and M-P de Bethune 1. 1 Tibotec, Mechelen, Belgium; and 2 Virco, Mechelen, Belgium
INTRODUCTION: TMC114 is a potent, next-generation protease inhibitor (PI), active against wild-type as well as PI-resistant HIV. Recently, TMC114 showed in vivo antiviral efficacy in a 2-week Phase IIa trial in multiple PI-experienced patients. In order to assess the performance of TMC114 against currently circulating strains of HIV, the compound was tested against >4000 clinical isolates submitted for phenotypic resistance testing. The antiviral activity of TMC114 on these isolates was compared to the currently approved PIs: indinavir, ritonavir, nelfinavir, saquinavir, amprenavir and lopinavir.
METHODS: Recombinant clinical isolates were constructed according to the Antivirogram method. Phenotypic and genotypic analyses were performed by
the Antivirogram and VirtualPhenotypeassays, respectively. Data analysis was performed using SAS and Spotfire DecisionSite software.
RESULTS: From the 4024 tested recombinant clinical isolates, 1666 (41%) were resistant to at least one of the currently approved PIs, defined as a change in EC 50 >fourfold as compared to wild-type. The median fold change in EC 50 against these 1666 resistant isolates for TMC114 was 1.1, corresponding to an EC 50 of 3.5 nM. Eighty percent of these PI-resistant isolates were still
susceptible (defined as fold change in EC 50 <4) to TMC114. For the remaining 20% isolates, the median fold change in EC 50 for TMC114 was 10, thus show-ing that the compound can inhibit 90% of the 1666 PI-resistant isolates with a fold change 10.
A subgroup of 1501 isolates, for which data for all six approved PIs were available, was used to determine the influence of the number of PIs with a fold change >4 on the activity of TMC114. Among these PI-resistant isolates, 67% were resistant to 4 or more PIs, with 31% resistant to all 6 approved PIs, 23% to 5, and 13% to 4. The median fold change in EC 50 for TMC114 was <4 for each of these subgroups, which illustrates the activity of TMC114 against PI-resistant isolates. A genotype was available for 498 of the 1666 PI-resistant isolates. The number of primary mutations (D30N, M46I/L, G48V, I50V/L, V82A/F/T/S, I84V or L90M) was determined for each of these isolates. One percent had no primary mutation, 23% had 1, 41% had 2, 31% had 3 and 4% had 4 primary mutations. The median fold change in EC 50 for TMC114 was <4 for each of these subgroups.
CONCLUSIONS: TMC114 is a potent, next-generation PI with activity against a wide range of PI-resistant recombinant clinical isolates. This activity, defined
by a median fold change of <4, extended to isolates resistant to all currently-approved PIs and also to isolates carrying up to four primary PI mutations.
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