ABSTRACT
Farnesyl:protein transferase (FPTase) inhibitors were developed as anti-Ras drugs, but they fail to inhibit Ki-Ras activity because Ki-Ras can be modified by geranylgeranyl:protein transferase type-I (GGPTase-I). L-778,123, an inhibitor of FPTase and GGPTase-I, was developed in part because it can completely inhibit Ki-Ras prenylation. To support the clinical development of L-778,123, we developed pharmacodynamic assays using peripheral blood mononuclear cells (PBMCs) to measure the inhibition of prenylation of HDJ2 and Rap1A, proteins that are FPTase- and GGPTase-I substrates, respectively. We validated these assays in animal models and show that inhibition of HDJ2 prenylation in mouse PBMCs correlates with the concentration of FPTase inhibitors in blood. In dogs, continuous infusion of L-778,123 inhibited both HDJ2 and Rap1A prenylation in PBMCs, but we did not detect inhibition of Ki-Ras prenylation. We reported previously results from the first L-778,123 Phase I trial that showed a dose-dependent inhibition of HDJ2 farnesylation in PBMCs. In this report, we present additional analysis of patient samples from this trial and a second Phase I trial of L-778,123, and demonstrate the inhibition of both HDJ2 and Rap1A prenylation in PBMC samples. This study represents the first demonstration of GGPTase-I inhibition in humans. However, no inhibition of Ki-Ras prenylation by L-778,123 was detected in patient samples. These results confirm the pharmacologic profile of L-778,123 in humans as a dual inhibitor of FPTase and GGPTase-I, but indicate that the intended target of the drug, Ki-Ras, was not inhibited.
Subject(s)
Alkyl and Aryl Transferases/antagonists & inhibitors , Antineoplastic Agents/pharmacology , Enzyme Inhibitors/pharmacology , Imidazoles/pharmacology , Animals , Dogs , Dose-Response Relationship, Drug , Humans , Immunoblotting , Leukocytes/drug effects , Leukocytes, Mononuclear/drug effects , Mice , Models, Chemical , Proto-Oncogene Proteins p21(ras)/metabolism , Time Factors , rap1 GTP-Binding Proteins/metabolismABSTRACT
In vitro and in animals, I is a potent and specific peptidomimetic for the potential treatment of airway inflammation in the pathogenesis of asthma. Preclinical studies indicated extensive conversion of I to an active metabolite II, and thus, a very sensitive assay for I and II was needed to support an inhalation ascending-dose study in man. The LC/MS/MS plasma/urine assay method (1.0 ml of sample) involves the following: liquid-liquid extraction of acidified plasma into pentane-ethyl acetate (90:10 v/v); evaporation of the organic extract, reconstitution into methanol; addition of water to the methanolic extract and freezing. After thawing, the extract is centrifuged and the clear supernatant injected for chromatography. Extract is chromatographed on a YMC ODS-AM column (50 x 2.0 mm). For detection, a Sciex 365 LC/MS/MS with an electrospray inlet and used in the positive ion, multiple reaction monitoring mode was used to monitor precursor-->fragment ions of m/z 709-->594 for I and m/z 513-->380 for II. The plasma assay was linear over the concentration range of 0.1-100 ng/ml in plasma for I and II. Accuracy and precision for I ranged from 97.9 to 102.1% of nominal with a 0.84-10.65% CV; similarly for II, 98.0-101.7% and 1.39-9.28% CV, respectively. Extraction recovery averaged 63.7% for I and 64.9% for II. This general assay methodology may be applied to assay small acidic peptides and peptidomimetics from biological fluids by LC/MS/MS.
