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Differing Integrase Dissociation Rates With S/GSK1349572 and Raltegravir
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International HIV and Hepatitis Drug Resistance Workshop, June 8-12, 2010, Dubrovnik. Croatia
Mark Mascolini
S/GSK1349572 (or 572), the experimental integrase inhibitor from Shinogi/GlaxoSmithKline, clung to wild-type (nonmutant) and raltegravir-resistant mutant integrase substantially longer than Merck's raltegravir in lab studies conducted by Shinogi/GSK [1]. Together with earlier work by Merck, the findings appear to illuminate mechanisms of resistance to these integrase inhibitors.
Merck investigators reported in 2009 that a 7.3-hour raltegravir dissociation half-life on viral integrase/DNA complexes could explain the robust activity of this antiretroviral [2]. Warping the integrase protein with the resistance mutation N155H sliced the dissociation half-life 10-fold to 0.7 hour. An experimental Merck integrase inhibitor, MK-2048, had a dissociation half-life of 32 hours on wild-type integrase and 4 hours with the N155H mutant.
S/GSK investigators measured raltegravir and 572 dissociation rates from wild-type and mutant integrase in a 7-day experiment* [1]. They analyzed the impact of five resistance mutations--N155H, Q148H, Q148R, Q148K, and G140S--and substitutions at position E92, as well as a position E92 substitution plus N155H and G140S plus Q148H.
The dissociation half-life of 572 from wild-type virus stretched to 100 hours, almost 10 times longer than the 10.1 hours with raltegravir. In the face of the first four major resistance mutations, dissociation half-lives fell sharply with both integrase inhibitors:
N155H: 11.6 hours with 572 versus 0.6 hour with raltegravir
Q148H: 7.7 hours with 572 versus under 0.3 hour with raltegravir
Q148R: 10.7 hours with 572 versus 0.4 hour with raltegravir
Q148K: 15.4 hours with 572 versus under 0.3 hour with raltegravir
By itself, a change at position E92 had a smaller impact on dissociation half-life with 572 (23.6 hours) and raltegravir (3.9 hours). But adding the N155H mutation to an E92 substitution cut the dissociation half-life to 5.8 hours with 572 and under 0.3 hour with raltegravir. The same trend held true for G140S alone (22.7 hours with 572 versus 3.7 with raltegravir) and G140S plus Q148H (4.2 hours with 572 and under 0.3 hour with raltegravir).
All told, dissociation rates were 6 to more than 51 times longer with 572 than with raltegravir. The Shinogi/GSK investigators proposed that "the long dissociation half-life of S/GSK1349572 may contribute to its resistance profile and highlight a potential for improved activity against wild-type HIV-1 and raltegravir-resistant viruses."
The study did not assess dissociation rates with substitutions T124A, S153Y, or L101I, which conferred resistance to 572 in an earlier S/GSK in vitro study [3]. Session cochair Raymond Schinazi (Emory University, Atlanta) cautioned that results seen in cell-free assays like the ones used in this study* may not reflect what happens in humans taking these drugs.
*Shinogi/GSK reports the method as follows: HIV-1 integrase BH10 wild-type and site-directed mutant proteins (N155H, E92Q, Q148H, Q148R and N155H/E92Q) were used for inhibitor binding studies. These studies were performed by pre-incubating 40 nM 3H-labelled S/GSK1349572 or raltegravir overnight at room temperature with an integrase-donor DNA complex that was bound to SPA imaging beads. Following incubation at 37°C for 1 h, 40 uM cold compound was added, and dissociation at 37 C was monitored over 7 days using a ViewLux(TM).
References
1. Hightower KE, Wang R, Underwood MR. S/GSK1349572 demonstrates significantly slower dissociation rates than raltegravir when comparing wild-type and raltegravir-resistant integrase protein. International HIV and Hepatitis Drug Resistance Workshop. June 8-12, 2010. Dubrovnik. Croatia. Abstract 8.
2. Grobler JA, McKenna PM, Ly S, et al. Functionally irreversible inhibition of integration by slowly dissociating strand transfer inhibitors. 10th International Workshop on Clinical Pharmacology of HIV Therapy. April 15-17, 2009. Amsterdam. Abstract O-10. http://www.natap.org/2009/PK/PK_10.htm
3. Sato A, Kobayashi M, Yoshinaga T, et al. S/GSK1349572 is a potent next generation HIV integrase inhibitor. 5th IAS Conference on HIV Pathogenesis, Treatment and Prevention. July 19-22, 2009. Cape Town, South Africa. Abstract WEPEA097. http://www.ias2009.org/pag/PDF/1181.pdf
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