Synthesis and pharmacological evaluation of CGP 57813 and CGP 61755, HIV-1 protease inhibitors from the Phe-c-Phe peptidomimetic class

In this report we describe the enzyme inhibitory, antiviral and pharmacokinetic properties of CGP 57813 and CGP 61755, structural analogues of CGP 53437 that were synthesized in an attempt to obtain human immunodeficiency virus type 1 (HIV-1) protease inhibitors with improved selectivity and oral bioavailability. CGP 57813 inhibited HIV-1 protease with an IC50 of 11 nM (similar to CGP 53437). CGP 61755, on the other hand, was c.a. 10-fold more potent (IC50 = 1 nM; similar to saquinavir and indinavir). The selectivity profile of CGP 57813 was comparable to that of CGP 53437 while CGP 61755 clearly had improved selectivity for HIV-1 protease over human aspartic proteases. All three compounds had similar antiviral activity in HIV-1/MN infected MT-2 cells; ED50s were c.a. 5 nM and ED90s were 30 nM. Compared to CGP 53437, both CGP 57813 and CGP 61755 had markedly better bioavailability in mice after oral administration in a DMSO-hydroxypropyl-β-cyclodextrin formulation. However, when CGP 57813 was administered in a sesame oil-based formulation to either mice or dogs no useful plasma concentrations could be measured. In contrast, CGP 61755 was clearly bioavailable in dogs after oral administration of the compound in the same formulation; 1.2 g per dog resulted in a mean AUC0-8h = 21.06 ± 3.53 μM.h, a mean Cmax= 4.8 ± 0.52 μM and compound was detectable for at least 8 h after administration. The potent antiviral activity of CGP 61755 together with improved selectivity and oral bioavailability holds promise for efficacy in AIDS therapy.