[12] In vitro antiviral activity of T-1249 a second generation fusion inhibitor

XI International HIV Drug Resistance Workshop: Basic Principles and Clinical Implications

Seville, Spain, 2–5 July 2002

IN VITRO ANTIVIRAL ACTIVITY OF T-1249 A SECOND GENERATION FUSION INHIBITOR

Antivir Ther. 2002;7(Suppl 1):S10 (abstract no. 12)

ML Greenberg¹, D Davison¹, L Jin¹, S Mosier¹, T Melby¹, P Sista¹, R Demasi¹, D Miralles¹, N Cammack² and TJ Matthews¹
¹Trimeris Inc. Durham, NC, USA; and ²Roche Biosciences, Palo Alto, Calif., USA

BACKGROUND: T-1249 is a synthetic 39-amino acid peptide inhibitor of HIV-1 gp41 mediated viral fusion. T-1249 is the second fusion inhibitor (FI) to be evaluated clinically in a Phase I/II trial. Here we describe the in vitro antiviral activity of T-1249 and the effect of resistance to approved antiretrovirals and the influence of T-20 (enfuvirtide; ENF) resistance-associated mutations on this activity.

METHODS: T-1249 and enfuvirtide susceptibility of patient isolates and NL4-3 constructs was assessed in the MAGI/cMAGI assay. Resistance to 14 approved antiretrovirals was analysed in the Virco Virtual Phenotype assay for a subset of 35 of the baseline patient isolates. The gp41 ectodomain of virus isolates with decreased enfuvirtide susceptibility was sequenced. Amino acid substitutions were introduced into a modified pNL4-3 HIV-1 parental strain (harbouring D36G in gp41) by site-directed mutagenesis.

RESULTS: The geometric mean EC₅₀ for T-1249 in vitro was 0.008 µg/ml (SD=0.010, range 0.0004–0.052 µg/ml) against 117 baseline virus isolates from enfuvirtide-naïve patients enrolled in enfuvirtide clinical studies. Moreover, T-1249 was equally active against 35 of the baseline virus isolates grouped by predicted resistance to antiretrovirals from zero (n=5) to three (n=18) classes. The geometric mean T-1249 EC₅₀s ranged from 0.002–0.007 µg/ml across the groups. We evaluated the activity of T-1249 against virus from 19 patients with matched isolates at baseline and after 48 weeks of chronic enfuvirtide treatment. The geometric mean enfuvirtide EC₅₀ against the 48-week isolates was 0.228 µg/ml (range 0.003–10.78 µg/ml) in comparison with a geometric mean EC₅₀ of 0.012 µg/ml (range 0.0008–0.231 µg/ml) for baseline isolates. For T-1249, the geometric mean EC₅₀ was 0.012 µg/ml (range 0.002–0.109 µg/ml) against the 48-week isolates versus 0.004 µg/ml (range 0.0008–0.021 µg/ml) for the baseline isolates. Substitutions in gp41 amino acids 36–45 associated with enfuvirtide resistance were inserted into a pNL4-3 parental virus to examine their effects on T-1249 activity in vitro. For the panel of 21 mutant NL4-3 constructs, the enfuvirtide geometric mean EC₅₀ was 0.13 µg/ml (range 0.006–6.156 µg/ml), compared to an EC₅₀ of 0.012 µg/ml for the parental NL4-3 strain. In contrast, the geometric mean EC₅₀ for T-1249 against the mutant NL4-3 constructs was 0.004 µg/ml (range 0.001–0.019 µg/ml) compared to an EC₅₀ of 0.009 µg/ml for the parental virus.

CONCLUSION: T-1249 exhibited potent in vitro activity against enfuvirtide-naïve clinical isolates. The activity of T1249 was independent of resistance to existing classes of antiretrovirals. Clinical isolates and site-directed mutants of pNL4-3 bearing enfuvirtide resistance associated substitutions in gp41 amino acids 36-45 remained largely sensitive to T-1249. These findings suggest that the gp41 target and mechanism of action of T-1249 and enfuvirtide, though similar and perhaps overlapping, are not identical.

PRESENTING AUTHOR: ML Greenberg

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2002-07-02
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