Martin L. Bryant

SC-52151, a novel inhibitor of the human immunodeficiency virus protease.

SC-52151 is a potent, selective, tight-binding human immunodeficiency virus (HIV) protease inhibitor containing the novel (R)-(hydroxyethyl) urea isostere. The mean 50% effective concentration for lymphotropic, monocytotropic strains and field isolates of HIV type 1 (HIV-1), HIV-2, and simian immunodeficiency virus is 26 ng/ml (43 nM). The combination of SC-52151 and nucleoside reverse transcriptase inhibitors synergistically inhibited HIV-1 replication without additive toxicity. An extended postantiviral effect correlates with inhibition of gag and gag-pol polyprotein processing. SC-52151 is highly protein bound ( >90%) in human plasma, and the level of partitioning into erythrocytes is low. Physiological concentrations of alpha-1-acid glycoprotein, but not albumin, substantially affect the antiviral potency of SC-52151. The oral bioavailability of [14C]SC-52151 is 17% when it is administered as an elixir to the rat, dog, or monkey. Oxidation of the t-butyl moiety is the major route of biotransformation, and elimination is mainly by biliary excretion. No toxicologically significant effects have been observed in animals. Pharmacokinetic and metabolism studies in multiple animal species predict 20 to 30% systemic bioavailability, an elimination half-life of 1 to 2 h, and a volume of distribution of greater than 3 liters/kg in humans.

Iminosugar glycosylation inhibitors as anti-HIV agents

A novel class of compounds which are potent inhibitors of the posttranslational glycan trimming enzyme α-glucosidase I have been found to display anti-HIV activity. These compounds are iminosugar analogs ofd-glucose, with the oxygen in the ring replaced by a nitrogen, and were originally isolated from plants and microorganisms, although a considerable number of analogs have been synthesized during the past few years. One of these compounds,N-butyl-1-deoxynojirimycin (Bu-DNJ), is presently under evaluation in clinical trials for the control of HIV infections. Cumulative data, to date, suggest that compounds such asN-Bu-DNJ have a hierarchy of effects, with reduction in syncytia formation being the predominant feature, and are known to alter glycosylation of the HIV-1 envelope glycoproteins gp120 and gp41. Consequently, there are a number of different ways in which iminosugars may be exerting an antiviral effect. This paper discusses the basic properties of this class of compounds and the changes they effect in posttranslational processing of gp120 and gp41, as well as the synthesis and characterization of prodrug forms of Bu-DNJ (e.g.N-butyl-6-phospho-1-deoxynojirimycin), which do not inhibit intestinal disaccharidases and may be useful for eliminating the intestinal discomfort and diarrhea associated with administration of α-glucosidase inhibitors.

(Hydroxyethyl) sulfonamide HIV-1 Protease inhibitors: Identification of the 2-methylbenzoyl moiety at P-2

Abstract We have discovered a potent low molecular weight series of HIV-1 Protease inhibitors incorporating the (R)-(hydroxyethyl) sulfonamide isostere.

MyristolyCoA:protein N-myristoyltransferase as a therapeutic target for inhibiting replication of human immunodeficiency virus-1

Human myristoylCoA:protein N-myristoyltransferase (hNmt) is a 416-residue, monomeric enzyme that catalyzes the covalent attachment of myristate (C14:0), via an amide bond, to the amino-terminal glycine residue of several proteins encoded by the HIV-1 genome. These proteins include Pr160gag-pol, Pr55gag, the capsid protein p17 derived from proteolytic processing of gag, and negative factor (nef). N-myristoylation of Pr160gag-pol and Pr55gag is required for viral replication. Recent genetic and biochemical studies have provided insights about the hNmts structure-function relationships, acylCoA and peptide substrate specificities, as well as its kinetic mechanism. Based on the results of host-guest studies, myristic acid analogs have been designed that are substrates for cellular myristoylCoA synthetases and Nmt both in vitro and in vivo. These analogs are selectively incorporated into subsets of cellular and viral N-myristoylproteins. Incorporation can produce analog- and protein-specific alterations in function. In the case of HIV-1, certain oxatetradecanoic acids cause redistribution of Pr55gag from membrane to cytosolic fractions, a reduction in its proteolytic processing, and an inhibition of viral replication in acutely and chronically infected T-lymphocytes at doses that do not cause cellular toxicity. Members of this class of compounds also are fungicidal — producing a rapid and marked reduction in the viability ofC. neoformans. This raises the possibility that Nmt may be an attractive therapeutic target for inhibiting HIV-1 replication in AIDS patients and for treating certain of their opportunistic infections.

In vitro Sequential Selection and Characterization of Human Immunodeficiency Virus Type 1 Variants with Reduced Sensitivity to Hydroxyethylurea Protease Inhibitors

In vitro resistance to the human immunodeficiency virus (HIV) protease inhibitors SC-52151 and SC-55389A was evaluated in an in vitro sequential selection scheme. HIVRF variants were selected for reduced sensitivity to SC-52151 and subsequently passaged in both SC-52151 and a structurally different hydroxyethylurea protease inhibitor, SC-55389A, to select for dual-resistant virus. SC-52151 selection alone resulted in a 23-fold reduction in virus sensitivity whereas selection in both inhibitors resulted in 34- and eightfold reductions in virus sensitivity to SC-52151 and SC-55389A, respectively. Sequence analysis of the protease gene revealed that SC-52151 -resistant virus had a Gly to Val substitution at residue 48 (G48V) and, in 58% of subclones, an accompanying Val to Ala substitution at residue 82 (V82A). Dual-resistant virus had both G48V and V82A substitutions present and, in the majority of subclones, an lle to Thr and/or Leu to Pro substitution at residues 54 and 63, respectively. Drug susceptibility assays with limiting dilution-cloned HIVRFR (G48V/V82A) and HIVRFRR (G48V/154T/L63P/V82A) viruses demonstrated moderate to high-level cross-resistance to additional structurally non-related protease inhibitors. Recombinant HIVHXB2 proviral clones with G48V, L63P and V82A substitutions showed that one active site mutation was permissible, but the presence of both G48V and V82A substitutions together significantly reduced infectious virus production. Insight into the contributions of the observed substitutions to drug resistance is presented in molecular modelling studies.