Ibrutinib impairs IGF-1-dependent activation of intracellular Ca handling in isolated mouse ventricular myocytes

Background: The Bruton tyrosine kinase (Btk) inhibitor Ibrutinib is associated with a higher incidence of cardiotoxic side effects including heart failure (HF).

Objectives: Ibrutinib is capable of inhibiting PI3K/Akt signaling in neonatal rat ventricular cardiomyocytes when stimulated with insulin-like growth factor 1 (IGF-1). We therefore hypothesized that Ibrutinib might disrupt IGF-1-mediated activation of intracellular CA handling in adult mouse cardiomyocytes by inhibiting PI3K/Akt signaling.

Methods: Isolated ventricular myocytes (C57BL6/J) were exposed to IGF-1 at 10 nmol/L in the presence or absence of Ibrutinib (1 µmol/L) or Acalabrutinib (10 µmol/L; Cell Culture for 24 ± 2 h). Intracellular CA handling was measured by epifluorescence (Fura-2 AM) and confocal microscopy (Fluo-4 AM). Ruptured-patch whole-cell voltage-clamp was used to measure I_CA. Levels of key cardiac CA handling proteins were investigated by immunoblots.

Results: IGF-1 significantly increased CA transient amplitudes by ∼83% as compared to vehicle treated control cells. This was associated with unaffected diastolic CA, enhanced SR CA loading and increased I_CA. Co-treatment with Ibrutinib attenuated both the IGF-1-mediated increase in SR CA content and in I_CA. IGF-1 treated cardiomyocytes had significantly increased levels of pS473Akt/Akt and SERCA2a expression as compared to cells concomitantly treated with IGF-1 and Ibrutinib. SR CA release (as assessed by CA spark frequency) was unaffected by either treatment. In order to test for potential off-target effects, second generation Btk Inhibitor Acalabrutinib with greater Btk selectivity and lower cardiovascular toxicity was tested for IGF1-mediated activation of intracellular CA handling. Acalabrutinib induced similar effects on CA handling in IGF-1 treated cultured myocytes as Ibrutinib in regard to decreased CA transient amplitude and slowed CA transient decay, hence implying a functional class effect of Btk inhibitors in cardiac myocytes.

Conclusions: Inhibition of Btk by Ibrutinib impairs IGF-1-dependent activation of intracellular CA handling in adult ventricular mouse myocytes in the face of disrupted Akt signaling and absent SERCA2a upregulation.

EC-coupling; IGF-1; Ibrutinib; SR Ca handling; heart failure.