Background:  Adverse metabolic effects induced by HAART are becoming a major factor in limiting the clinical successes that have been initially achieved through HAART. Many of the first generation HIV protease inhibitors (PI) are known to contribute to the development of peripheral insulin resistance at least in part due to their direct effects on the intrinsic activity of the insulin-responsive facilitative glucose transporter GLUT4. GS-8374 is a novel PI with potent in vitro antiretroviral activity and favorable resistance profile. Here we report on the in vitro and in vivo characterization of the potential of GS-8374 to affect glucose disposal.

Methods:  Effect of atazanavir (ATV), lopinavir (LPV), ritonavir (RTV), or GS-8374 were assessed on insulin-stimulated uptake of 2-deoxyglucose in mouse OP-9 stromal cell-derived adipocytes. Euglycemic hyperinsulinemic clamp experiments in vivo were performed in chronically catheterized healthy lean male Wistar rats during acute intravenous infusion of the PI. Insulin sensitivity was assessed from the glucose infusion rate required to maintain blood sugars at ~105 mg/dL during continuous intravenous infusion of insulin (10 mU/kg/min). Serum drug levels were assessed by high performance liquid chromatography (HPLC) analysis during the steady-state phase of each clamp experiment.

Results:  Treatment of differentiated OP-9 cells with 10 µM GS-8374 or ATV showed no effect the insulin-stimulated deoxyglucose uptake, whereas RTV and LPV caused 50 and 33% reduction, respectively, under the same conditions. In rats, sustained serum GS-8374 levels of 8 µM had no effect on peripheral glucose disposal (R_d’ = 47.0±0.3 mg/kg/min) when compared to vehicle or atazanavir-treated animals (R_d’ = 49.1±5.4 and 47.7±0.6, respectively). Consistent with previous studies, comparable serum levels of ritonavir produced an acute 43% reduction in R_d’ (R_d’ = 26.9±0.4 mg/kg/min).

Conclusions:  Similar to ATV, but unlike RTV and LPV, GS-8374 neither affects insulin-stimulated glucose uptake in differentiated adipocytes in vitro nor acutely alters peripheral glucose disposal under hyperinsulinemic euglycemic clamp conditions in a healthy rodent model system. These results confirm that it is possible to dissociate the adverse effects of PI on insulin sensitivity from antiretroviral activity and provide further support for the use of these experimental systems in the pre-clinical evaluation of the safety of candidate PI.