Pharmacokinetics, pharmacodynamics and metabolism of Bcl-2 antisense phosphorothioate oligonucleotide G3139 (Genasense(R))

Overexpression of the anti-apoptotic protein Bcl-2 has been found in about half of human cancers. G3139 is an 18-mer phosphorothioate antisense oligonucleotide designed to bind to the first six codons of the open reading frame of the human Bcl-2 mRNA. In this project, the preclinical and clinical pharmacokinetics, pharmacodynamics and metabolism of this novel therapeutics were investigated.; A novel, ultrasensitive, nonradioactive hybridization ELISA method has been developed and validated for quantification of G3139. Plasma pharmacokinetics of G3139 in acute myeloid leukemia (AML) patients was characterized and found to fit a two-compartment open infusion model. The mean total body clearance was 7.1 L/hr and the t1/2alpha and t1/2beta were 0.4 hr and 4.3 hr, respectively. There was no major pharmacokinetic interaction between G3139 and concomitant chemotherapeutic agents. Robust intracellular concentrations (ICs) of G3139 in bone marrow (BM) and PBMC obtained from treated AML patients were achieved and a correlation between the Bcl-2 mRNA/protein down-regulation and disease response was found. A higher median ICs of G3139 was detected in the complete responders as compared with non-responders.; Cellular uptake and distribution of G3139 was studied in K562 cells. When exposed to free G3139, only low intracellular concentrations of G3139 were found in the cells with no significant suppression of Bcl-2 mRNA. In contrast, a 10 to 25-fold increase of the intracellular G3139 was observed when G3139 was delivered with cationic lipids. Dose-response curve shows that G3139 concentration that produces 50% down-regulation was 0.29 muM. Two in vitro PK/PD models were developed for AML cells NB4, which describe the relationship between drug exposure and target down-regulation reasonably well.; A novel ESI LC/MS/MS method has been developed. Using this method, several chain-shortened G3139 metabolites were identified in mice, rats and humans, implicating the involvement of 3'-exonuclease in G3139 metabolism. In the mouse, tissue distribution is extensive and the highest concentrations were found in kidneys, liver, spleen and BM. Metabolite kinetics were modeled and they appear to follow formation-limited kinetics.; The results from these studies have provided a better characterization and understanding of disposition and pharmacological roles of G3139 and other antisense therapeutics.