Lack of pharmacokinetic interaction between the HIV-1 maturation inhibitor GSK3640254 and combination oral contraceptives in healthy women.

AIMS: GSK3640254 is a next-generation maturation inhibitor likely to be coadministered with combined oral contraceptives in HIV-positive women. METHODS: This phase I, open-label, 1-way study assessed pharmacokinetic and pharmacodynamic interactions of GSK3640254 200 mg and ethinyl oestradiol 0.03 mg/levonorgestrel 0.15 mg once daily in healthy female participants who received ethinyl oestradiol/levonorgestrel for 10 days with a moderate-fat meal after which GSK3640254 was added from Days 11 to 21. Primary endpoints were area under the plasma concentration-time curve to the end of the dosing interval (AUC0-t ), maximum observed concentration (Cmax ) and plasma concentration at the end of the dosing interval (Cτ ) for ethinyl oestradiol and levonorgestrel. Serum follicle-stimulating hormone, luteinizing hormone and progesterone concentrations were determined. Adverse events were monitored. RESULTS: Among 23 enrolled participants, 17 completed the study. Geometric least squares mean ratios (with vs. without GSK3640254) of AUC0-t , Cmax and Cτ were 0.974, 0.970 and 1.050 for ethinyl oestradiol and 1.069, 1.032 and 1.083 for levonorgestrel, respectively. Three participants had elevated progesterone levels, which occurred before GSK3640254 administration in 2 participants. No participants had elevated follicle-stimulating hormone or luteinizing hormone values. Fourteen participants (61%) reported adverse events. Four participants reported asymptomatic elevated transaminase levels meeting liver-stopping criteria; of these, 3 events occurred before GSK3640254 administration and led to study withdrawal. CONCLUSION: Ethinyl oestradiol/levonorgestrel plus GSK3640254 coadministration did not affect steady-state pharmacokinetics or pharmacodynamics of ethinyl oestradiol and levonorgestrel in healthy female participants. No major tolerability findings were reported. Elevated liver transaminase levels were probably due to ethinyl oestradiol/levonorgestrel.

Phase I Study of the Novel Enhancer of Zeste Homolog 2 (EZH2) Inhibitor GSK2816126 in Patients with Advanced Hematologic and Solid Tumors.

PURPOSE: Enhancer of zeste homolog 2 (EZH2) activity is dysregulated in many cancers. PATIENTS AND METHODS: This phase I study determined the safety, maximum-tolerated dose (MTD), pharmacokinetics, and pharmacodynamics of the intravenously administered, highly selective EZH2 inhibitor, GSK2816126, (NCT02082977). Doses of GSK2816126 ranged from 50 to 3,000 mg twice weekly, and GSK2816126 was given 3-weeks-on/1-week-off in 28-day cycles. Eligible patients had solid tumors or B-cell lymphomas with no available standard treatment regimen. RESULTS: Forty-one patients (21 solid tumors, 20 lymphoma) received treatment. All patients experienced ≥1 adverse event (AE). Fatigue [22 of 41 (53.7%)] and nausea [20 of 41 (48.8%)] were the most common toxicity. Twelve (32%) patients experienced a serious AE. Dose-limiting elevated liver transaminases occurred in 2 of 7 patients receiving 3,000 mg of GSK2816126; 2,400 mg was therefore established as the MTD. Following intravenous administration of 50 to 3,000 mg twice weekly, plasma GSK2816126 levels decreased biexponentially, with a mean terminal elimination half-life of approximately 27 hours. GSK2816126 exposure (maximum observed plasma concentration and area under the plasma-time curve) increased in a dose-proportional manner. No change from baseline in H3K27me3 was seen in peripheral blood mononuclear cells. Fourteen of 41 (34%) patients had radiological best response of stable disease, 1 patient with lymphoma achieved a partial response, 21 of 41 (51%) patients had progressive disease, and 5 patients were unevaluable for antitumor response. CONCLUSIONS: The MTD of GSK2816126 was established at 2,400 mg, but the dosing method and relatively short half-life limited effective exposure, and modest anticancer activity was observed at tolerable doses.

Expression of a Src family kinase in chronic myelogenous leukemia cells induces resistance to imatinib in a kinase-dependent manner.

The Bcr-Abl kinase inhibitor imatinib is remarkably effective in chronic myelogenous leukemia (CML), although drug resistance is an emerging problem. Myeloid Src family kinases such as Hck and Lyn are often overexpressed in imatinib-resistant CML cells that lack Bcr-Abl mutations. Here we tested whether Hck overexpression is sufficient to induce imatinib resistance using both wild-type Hck and a mutant (Hck-T338A) that is uniquely sensitive to the pyrazolo-pyrimidine inhibitor, NaPP1. Expression of either kinase in K562 CML cells caused resistance to imatinib-induced apoptosis and inhibition of soft-agar colony formation. Treatment with NaPP1 restored sensitivity to imatinib in cells expressing T338A but not wild-type Hck, demonstrating that resistance requires Hck kinase activity. NaPP1 also reduced Hck-mediated phosphorylation of Bcr-Abl at sites that may affect imatinib sensitivity exclusively in cells expressing Hck-T338A. These data show that elevated Src family kinase activity is sufficient to induce imatinib resistance through a mechanism that may involve phosphorylation of Bcr-Abl.

Conformational disturbance in Abl kinase upon mutation and deregulation.

Protein dynamics are inextricably linked to protein function but there are few techniques that allow protein dynamics to be conveniently interrogated. For example, mutations and translocations give rise to aberrant proteins such as Bcr-Abl where changes in protein conformation and dynamics are believed to result in deregulated kinase activity that provides the oncogenic signal in chronic myelogeous leukemia. Although crystal structures of the down-regulated c-Abl kinase core have been reported, the conformational impact of mutations that render Abl resistant to small-molecule kinase inhibitors are largely unknown as is the allosteric interplay of the various regulatory elements of the protein. Hydrogen exchange mass spectrometry (HX MS) was used to compare the conformations of wild-type Abl with a nonmyristoylated form and with 3 clinically relevant imatinib resistance mutants (T315I, Y253H and E255V). A HX-resistant core localized to the interface between the SH2 and kinase domains, a region known to be important for maintaining the down-regulated state. Conformational differences upon demyristoylation were consistent with the SH2 domain moving to the top of the small lobe of the kinase domain as a function of activation. There were conformational changes in the T315I mutant but, surprisingly, no major changes in conformation were detected in either the Y253H or the E255V mutants. Taken together, these results provide evidence that allosteric interactions and conformational changes play a major role in Abl kinase regulation in solution. Similar analyses could be performed on any protein to provide mechanistic details about conformational changes and protein function.