Clinical activity of carfilzomib correlates with inhibition of multiple proteasome subunits: application of a novel pharmacodynamic assay

Abstract

SummaryWhile proteasome inhibition is a validated therapeutic approach for multiple myeloma (MM), inhibition of individual constitutive proteasome (c20S) and immunoproteasome (i20S) subunits has not been fully explored owing to a lack of effective tools. We utilized the novel proteasome constitutive/immunoproteasome subunit enzyme‐linked immunosorbent (ProCISE) assay to quantify proteasome subunit occupancy in samples from five phase I/II and II trials before and after treatment with the proteasome inhibitor carfilzomib. Following the first carfilzomib dose (15–56 mg/m2), dose‐dependent inhibition of c20S and i20S chymotrypsin‐like active sites was observed [whole blood: ≥67%; peripheral blood mononuclear cells (PBMCs): ≥75%]. A similar inhibition profile was observed in bone marrow–derived CD138+ tumour cells. Carfilzomib‐induced proteasome inhibition was durable, with minimal recovery in PBMCs after 24 h but near‐complete recovery between cycles. Importantly, the ProCISE assay can be used to quantify occupancy of individual c20S and i20S subunits. We observed a relationship between MM patient response (n = 29), carfilzomib dose and occupancy of multiple i20S subunits, where greater occupancy was associated with an increased likelihood of achieving a clinical response at higher doses. ProCISE represents a new tool for measuring proteasome inhibitor activity in clinical trials and relating drug action to patient outcomes.

Polymer micelle formulation for the proteasome inhibitor drug carfilzomib: Anticancer efficacy and pharmacokinetic studies in mice

“…Similar results showing an effective and long-lasting inhibition of the proteasome in blood have been reported, especially in the samples collected from patients who received multiple doses of CFZ. In clinical studies that employed repeated dosing schedules with 14- or 28-day cycles (similar to the currently used clinical regimens and that used in our present study), the proteasome activities in whole blood were almost completely inhibited and remained low even in pre-dose samples obtained right before subsequent cycles [15,16]. These findings are also in line with the irreversible, covalent nature of proteasome inhibition by CFZ and the slow proteasome de novo biogenesis rates taking at least several days [17–21].…”

Amelioration of autoimmunity with an inhibitor selectively targeting all active centres of the immunoproteasome

“…In humans, carfilzomib is approved for treatment of multiple myeloma at a dose of 20 mg·m −2 . Since carfilzomib achieves, in humans, an 80% inhibition of ß5c and LMP7 activity in whole blood and PBMCs at this dose (Lee et al, ), therapeutically effective doses of LU‐005i should also be feasible in humans to treat autoimmunity. Apart from autoimmune diseases, the immunoproteasome has been shown to be involved in other processes.…”

Carfilzomib in relapsed or refractory multiple myeloma patients with early or late relapse following prior therapy: A subgroup analysis of the randomized phase 3 ASPIRE and ENDEAVOR trials

“…Furthermore, carfilzomib was administered at a higher dose (56 mg/ m 2 twice weekly), which may lead to inhibition of multiple subunits of the immunoproteasome. 11 Also, in ENDEAVOR, patients received a twice-weekly bortezomib regimen, which has been associated with a higher rate of peripheral neuropathy than once-weekly bortezomib. 12 Upon discontinuation of study drug, 8% of patients in the Vd arm of ENDEAVOR received carfilzomib as a subsequent therapy.…”