m of Action
Carfilzomib is a tetrapeptide epoxyketone proteasome inhibitor that irreversibly binds to the N-terminal threonine-containing active sites of the 20S proteasome, the proteolytic core particle within the 26S proteasome. Carfilzomib had antiproliferative and proapoptotic activities in vitro in solid and hematologic tumor cells. In animals, carfilzomib inhibited proteasome activity in blood and tissue and delayed tumor growth in models of multiple myeloma, hematologic, and solid tumors.
12.2 Pharmacodynamics
Intravenous carfilzomib administration resulted in suppression of proteasome chymotrypsin-like (CT-L) activity when measured in blood 1 hour after the first dose. Doses of carfilzomib ≥ 15 mg/m2 with or without lenalidomide and dexamethasone induced a ≥ 80% inhibition of the CT-L activity of the proteasome. In addition, carfilzomib, 20 mg/m2 intravenously as a single agent, resulted in a mean inhibition of the low molecular mass polypeptide 2 (LMP2) and multicatalytic endopeptidase complex-like 1 (MECL1) subunits of the proteasome ranging from 26% to 32% and 41% to 49%, respectively. Proteasome inhibition was maintained for ≥ 48 hours following the first dose of carfilzomib for each week of dosing.
12.3 Pharmacokinetics
The mean (CV%) Cmax and AUC following a 2- to 10-minute intravenous infusion of 27 mg/m2 of carfilzomib were 4232 ng/mL (49%) and 379 ng∙hr/mL (25%), respectively. Following repeated doses of carfilzomib at 15 and 20 mg/m2, systemic exposure (AUC) and half-life were similar on Days 1 and 15 or 16 of Cycle 1, suggesting there was no systemic carfilzomib accumulation.
Following a 30-minute infusion of the 56 mg/m2 dose, the mean (CV%) AUC of 948 ng∙hr/mL (34%) was approximately twice that observed following a 2- to 10-minute infusion at the 27 mg/m2 dose with a mean (CV%) of 379 ng∙hr/mL (25%). The mean (CV%) Cmax of 2079 ng/mL (44%) following a 30-minute infusion of the 56 mg/m2 dose was lower compared to that of 27 mg/m2 over the 2- to 10-minute infusion with a mean (CV%) of 4232 ng/mL (49%).
At doses between 20 and 56 mg/m2, there was a dose-dependent increase in exposure at either infusion duration.
Distribution: The mean steady-state volume of distribution of a 20 mg/m2 dose of carfilzomib was 28 L. When tested in vitro, the binding of carfilzomib to human plasma proteins averaged 97% over the concentration range of 0.4 to 4 micromolar.
Metabolism: Carfilzomib was rapidly and extensively metabolized. The predominant metabolites measured in human plasma and urine, and generated in vitro by human hepatocytes, were peptide fragments and the diol of carfilzomib, suggesting that peptidase cleavage and epoxide hydrolysis were the principal pathways of metabolism. Cytochrome P450-mediated mechanisms played a minor role in overall carfilzomib metabolism. The metabolites have no known biologic activity.
Elimination: Following intravenous administration of doses ≥ 15 mg/m2, carfilzomib was rapidly cleared from the systemic circulation with a half-life of ≤ 1 hour on Day 1 of Cycle 1. The systemic clearance ranged from 151 to 263 L/hour, and exceeded hepatic blood flow, suggesting that carfilzomib was largely cleared extrahepatically. In 24 hours, approximately 25% of the administered dose of carfilzomib was excreted in urine as metabolites. Urinary and fecal excretion of the parent compound was negligible (0.3% of total dose).
Specific Populations: Clinically significant differences were |
