ABL Tyrosine Kinase Inhibitors (TKIs) Are Associated with Increased Rho-Associated Kinase (ROCK) Activity That May Contribute to Vascular Toxicity in Patients with Chronic Myeloid Leukemia (CML)
Authors: Osman Afaf , Yu Brian , Glavin Nancy , Polonsky Tamar S. , Liao James K. , Larson Richard A. 
Published: October 2019

Abstract
Introduction
The use of 2nd or 3rd generation ABL TKIs in patients with CML is associated with vascular toxicity, including peripheral arterial occlusive disease and cardiovascular and cerebrovascular events. However, Imatinib, a 1st generation TKI, has not been shown to increase risk of cardiovascular events (Douxfils J et al. JAMA Oncol 2016;2:625). Therefore, there is a need to identify risk factors and predictors of vascular toxicity for patients receiving these TKIs. In mice, inhibition of the Abl kinases results in activation of Rho and its downstream target Rho kinase (ROCK) (Zandy et al. Proc Natl Acad Sci USA 2007;104:17686). Growing evidence suggests that elevated ROCK activity plays a central role in the pathogenesis of cardiovascular disease and stroke in both animal and clinical studies. TKIs used in CML are potent inhibitors of ABL1 and ABL2 kinases. We hypothesized that CML patients receiving 2nd or 3rd generation BCR/ABL1 TKIs have higher ROCK activity than patients not receiving these TKIs, providing a putative mechanism for the vascular toxicity observed in clinical studies.
Methods
We measured leukocyte ROCK activity in CML patients and analyzed results based on their last TKI dose. We isolated fresh peripheral blood leukocytes from 38 patients (17 females, 21 males) with a median age of 53 years (range, 24-90 years). 4 patients had newly diagnosed untreated CML at the start of the study. One male was receiving Dasatinib for Ph+ ALL and was also included. ROCK activity was assessed in leukocytes by measuring the ratio of phospho-myosin-binding subunit (p-MBS) on myosin light-chain phosphatase, a downstream target of ROCK, to total MBS using an automated Western blotting system (Wes, ProteinSimple, San Jose, CA) (Hata T et al. Atherosclerosis 2011; 214:117). Each patient had 1-6 measurements of leukocyte ROCK activity over 1 - 18 months (n=78 measurements). Information about cardiovascular risk factors, concomitant medications, CML status, and total duration of TKI therapy was collected. For patients with multiple samples over time, ROCK activity was calculated as the mean of all samples taken while receiving the same TKI. Patients in treatment-free remission (TFR) were considered off-TKI, but those in TFR < 1 month were excluded from the analysis to reduce potential confounding effects.
Results
We analyzed blood samples from 4 untreated CML patients, 8 while in TFR, and 31 who were actively receiving one of the 5 TKIs (7 Imatinib, 12 Dasatinib, 9 Nilotinib, 2 Ponatinib, 1 Bosutinib). 3 patients developed acute coronary syndrome during the study and required coronary revascularization for myocardial infarction. We found no significant difference in ROCK activity when comparing all patients receiving TKIs to those not receiving TKIs. However, we found higher leukocyte ROCK activity when comparing all patients receiving 2nd and 3rd generation TKIs to those not receiving any TKI (Welch's t test, mean leukocyte ROCK activity 1.00 ± 0.06 vs 0.80 ± 0.06; p=0.03). We also found higher leukocyte ROCK activity when comparing patients receiving Dasatinib to patients receiving Imatinib (mean leukocyte ROCK activity 1.05 ± 0.09 vs 0.75 ± 0.10; p=0.04). The comparison of Imatinib to all 2nd and 3rd generation TKIs was not significant (p=0.06).
Conclusions
We found that patients on 2nd and 3rd generation TKIs have higher leukocyte ROCK activity compared to those not receiving TKIs, and higher leukocyte ROCK activity in patients on Dasatinib compared with patients receiving Imatinib. These results are consistent with the known lower-risk of cardiovascular side-effects observed with Imatinib in comparison to the next generation ABL TKIs. Limitations include small sample size and heterogeneity in the patient population in terms of age, cardiovascular risk factors, specific TKI used, and total duration and sequencing of TKI agents. The study continues to accrue CML subjects in order to follow individual patients over time on TKI therapy.

Disclosures
Larson: Ariad/Takeda: Consultancy, Research Funding; BristolMyers Squibb: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding.