Carfilzomib

Overview

Carfilzomib (brand name Kyprolis) is a tetrapeptide epoxyketone proteasome inhibitor approved by the FDA in 2012 for relapsed and refractory multiple myeloma. Developed originally by Proteolix and marketed by Amgen, carfilzomib was designed to overcome limitations of the first-generation reversible inhibitor bortezomib, particularly treatment-limiting peripheral neuropathy. Its irreversible mechanism delivers deeper, more sustained proteasome inhibition and has produced notable gains in progression-free and overall survival when combined with lenalidomide or daratumumab.

Carfilzomib, along with bortezomib and oral ixazomib, is a mainstay of modern multiple myeloma therapy.

Structure / Sequence

Carfilzomib is a synthetic tetrapeptide (Phe-homoPhe-Leu-morpholino-acetyl cap) bearing an epoxyketone warhead. It is derived from the natural product epoxomicin and designed for selective chymotrypsin-like (beta-5) subunit inhibition.

Mechanism of Action

Carfilzomib's epoxyketone warhead forms an irreversible morpholino adduct with the N-terminal threonine of the chymotrypsin-like beta-5 proteasome subunit. Proteasome recovery requires new subunit synthesis, which takes about 24 hours. This irreversibility leads to more complete and sustained inhibition than reversible boronates, driving deeper apoptotic responses in myeloma cells via ER stress, unfolded protein response, and NF-kB pathway inhibition.

Because the epoxyketone is highly selective for the constitutive and immunoproteasome chymotrypsin-like subunit, off-target effects on other proteases are minimal, contributing to its improved neurotoxicity profile compared to bortezomib.

Research Summary

Pharmacokinetics

Carfilzomib is administered IV and has a very short plasma half-life of less than 1 hour. It is primarily cleared through peptidase cleavage and epoxide hydrolysis rather than CYP metabolism, producing few drug-drug interactions. Proteasome inhibition, however, is sustained despite rapid clearance because of the irreversible mechanism.

Dosing Protocols

• Twice-weekly (Kd or KRd): 20 mg/m2 on days 1-2 of cycle 1, then 27 or 56 mg/m2 on days 1, 2, 8, 9, 15, 16 of 28-day cycles
• Once-weekly (KdD): 20 mg/m2 day 1 of cycle 1, then 70 mg/m2 on days 1, 8, 15 of 28-day cycles
• Hydration: Oral and/or IV hydration is required, particularly at cycle 1, to mitigate tumor lysis and renal risk
• Infusion duration: 30-minute infusion at higher doses

Dose reductions apply for infusion reactions, cardiac events, renal impairment, and thrombocytopenia.

Common Discussion Topics

• Cardiovascular toxicity (heart failure, hypertension) requiring pre-treatment screening
• Reduced peripheral neuropathy versus bortezomib
• Role of KRd and KdD in modern relapsed/refractory MM sequencing
• Need for IV access versus preference for oral ixazomib in some patients
• Response rates after bortezomib refractoriness

Related Compounds

• Bortezomib — reversible proteasome inhibitor
• Enfuvirtide — peptide antiretroviral
• Daptomycin — cyclic lipopeptide antibiotic
• Bivalirudin — peptide anticoagulant