High Effectiveness in Actions of Carfilzomib on Delayed-Rectifier K+ Current and on Spontaneous Action Potentials.

Edmund Cheung So,Sheng-Nan Wu,Ping-Yen Liu,Chien-Ching Lee

doi:10.3389/fphar.2019.01163

Abstract

Carfilzomib (CFZ, Kyprolis®) is widely recognized as an irreversible inhibitor of proteasome activity; however, its actions on ion currents in electrically excitable cells are largely unresolved. The possible actions of CFZ on ionic currents and membrane potential in pituitary GH3, A7r5 vascular smooth muscle, and heart-derived H9c2 cells were extensively investigated in this study. The presence of CFZ suppressed the amplitude of delayed-rectifier K+ current (I K(DR)) in a time-, state-, and concentration-dependent manner in pituitary GH3 cells. Based on minimal reaction scheme, the value of dissociation constant for CFZ-induced open-channel block of I K(DR) in these cells was 0.33 µM, which is similar to the IC50 value (0.32 µM) used for its efficacy on inhibition of I K(DR) amplitude. Recovery from I K(DR) block by CFZ (0.3 µM and 1 µM) could be well fitted by single exponential with 447 and 645 ms, respectively. The M-type K+ current, another type of K+ current elicited by low-threshold potential, was slightly suppressed by CFZ (1 µM). Under current-clamp condition, addition of CFZ depolarized GH3 cells, broadened the duration of action potentials as well as raised the firing frequency. In A7r5 vascular smooth muscle cells or H9c2 cardiac cells, the CFZ-induced inhibition of I K(DR) remained efficacious. Therefore, our study led us to reflect that CFZ or other structurally similar compounds should somehow act on the activity of membrane KV channels through which they influence the functional activities in different types of electrically excitable cells such as endocrine, neuroendocrine cells, smooth muscle cells, or heart cells, if similar in vivo findings occur.

Highlights

Carfilzomib (CFZ, Kyprolis®), an analog of epoxomicin, is a second-generation irreversible tetrapeptide epoxyketone class proteasome inhibitor which is recognized as an anti-cancer drug
The whole-cell configuration of the patch-clamp technique was employed to investigate any modifications of CFZ on ionic currents inherently in GH3 cells
B, when the examined cell was maintained at −50 mV and a series of voltage pulses ranging from −60 to +50 mV in 10-mV increments were thereafter delivered, a family of K+ outward currents with slight inactivation was readily elicited. These outward K+ currents in response to membrane depolarization were previously proofed as the delayed-rectifier K+ current (IK(DR)) (Wu et al, 2000; Wang et al, 2008b)

Summary

Introduction

Carfilzomib (CFZ, Kyprolis®), an analog of epoxomicin, is a second-generation irreversible tetrapeptide epoxyketone class proteasome inhibitor which is recognized as an anti-cancer drug. Acute administration of CFZ was shown to produce short-term modifications on vascular and myocardial properties such as myocardial ischemia, arterial hypertension, or acute renal dysfunction (Gavazzoni et al, 2018; Heckmann et al, 2018; Efentakis et al, 2019). They reported that cardiotoxicity of CFZ could have been linked to its action through inhibition of AMPKα phosphorylation and autophagy-related proteins (Efentakis et al, 2019). Previous studies have demonstrated that proteasome inhibitors (e.g., PSI [N-[(phenylmethoxy) carbonyl]-L-isoleucyl-L-α-glutamyl-tert-butyl ester-N-[(1S)1-formyl-3-methylbutyl]-L-alaninamide]) could induce apoptotic changes in pituitary tumor (GH3) cells, suggesting that these agents were thought to be potential novel agents for treating pituitary tumors not amenable to other treatments (Yu et al, 2002)

Methods

Results

Conclusion