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Virco Proposes Preliminary Biological Cutoffs for Integrase Inhibitors
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6th European HIV Drug Resistance Workshop
March 26-28, 2008
Budapest, Hungary
Mark Mascolini
Working with recombinant clones of virus from 49 subtype B-infected people, Virco proposed preliminary biological cutoffs for the integrase inhibitors raltegravir and elvitegravir [1]. Although the cutoffs will be fine-tuned as virologists analyze further samples, these kickoff cutoffs are a first step to studying decreased viral susceptibility ("phenotypic resistance") to these potent drugs.
With colleagues at the University of Rome "Tor Vergata," the Virco team used polymerase chain reaction (PCR) to amplify the reverse transcriptase, RNase H, and integrase regions of HIV RNA from 49 people who had never taken an integrase inhibitor. Twenty-one people had no antiretroviral experience, and 28 were taking a failing regimen. Technicians cloned this virus and randomly picked 970 clones to transfect MT4 cells. From the resulting 427 replication-competent recombinant viruses, they successfully tested 349 (82%) for susceptibility to raltegravir and elvitegravir.
The 50% inhibitory concentration (IC50) for a wild-type reference strain of HIV-1 measured 6.1 + 2.3 nM for raltegravir and 11.6 + 3.5 nM for elvitegravir. Fold-change in IC50 for recombinant viruses ranged from 0.11 to 2.48 and averaged 0.88 for raltegravir; fold changes ranged from 0.14 to 15.94 and averaged 0.92 for elvitegravir. Sequence analysis and phylogenetic studies indicated that PCR or resampling errors did not skew these estimates. The sequence analysis also found no big differences in sequence diversity between antiretroviral-naive and -experienced people.
Estimating biological cutoffs as the 97.5 percentile of all fold-change values for integrase inhibitor-naive recombinant viruses, the investigators proposed cutoffs of 1.97 for raltegravir and 2.21 for elvitegravir. In other words subtype B HIV-1 with about a 2-fold drop in susceptibility to either integrase inhibitor would be rated resistant.
Clones with a biological cutoff above these values for each integrase inhibitor harbored both known and novel substitutions in HIV integrase, as well as changes negatively associated with resistance to elvitegravir in cells studies:
· Known substitutions: I72V, L74I, T97A, S119G, G140S, M154I, M154L
· Novel substitutions: S17T, M50T, A91V, E92G, K111T, T124N, T125M, E138D, S155C, G193P
· Substitutions negatively associated with resistance to elvitegravir: L101I, V201I
The Virco team cautioned that "determination of a more established biological cutoff will require extensive clonal [reverse transcriptase-integrase] phenotypic analysis on a larger set of subjects."
Reference
1. Rondelez E, Van Baelen K, Ceccherini-Silberstein F, et al. Preliminary biologicalal cutoffs for GS-9137 and MK-0518 integrase inhibitors derived from clonal phenotypic analysis. 6th European HIV Drug Resistance Workshop. March 26-28, 2008. Budapest. Abstract 73.
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