The Rate of Cellular Energy Production of Muscle Cells Is Attenuated By Carnitine Intracellular Deficiency Caused By Imatinib Treatment

Introduction: Previous works identified that imatinib intake through the carnitine-specific OCTN2 (SLC22A5) transporter resulted in a significant decrease of carnitine intracellular concentrations in chronic myeloid leukemia (CML) and muscle cell lines. On contrary, even high doses of carnitine in preincubation did not influence imatinib cell intake capacity. Specifically performed inhibition of OCTN2 activity by vinorelbine resulted in block of carnitine cell intake, while imatinib intake was only slightly reduced (13-30%). This observation is in line with the knowledge that imatinib is transported also through other known SLC transporters. OCTN2 transporter is the major transporter for carnitine, an essential compound in cell energy metabolism. Presented work follows a hypothesis that non-equal competition between imatinib and carnitine intake through OCTN2 can lead to the carnitine intracellular deficiency, which can be in CML patients manifested by a disruption of skeletal muscle mitochondrial density and cause side effects like fatigue, muscle pain and cramps reported up to 80% of patients treated with imatinib (Kekale et al., 2015).

Methods: Muscle cell HTB-153 (human rhabdomyosarcoma, ATCC HS 729), CML cell line KCL-22 (DSMZ ACC 519) were used for in vitro experiments. Intracellular concentration of imatinib, carnitine and metabolites were measured by chromatographic separation using XBridge Amide column (50x2.1mm, 3.5µm; Waters, Milford (MA), USA) and ZIC-pHILIC column (50x2.1mm, 5 µm; Merck, Darmstadt, Germany) coupled to tandem mass spectrometer (QTRAP 4000; Sciex, USA).

Results: Carnitine, resp. L-carnitine transports long-chain fatty acids to mitochondria and its high rate is required especially in energetically demanding tissues such as skeletal and cardiac muscles. The concentrations of citric acid cycle (CAC) metabolites (citrate, malate, alpha-ketoglutarate, succinate, fumarate, 2-hydroxyglutarate, cis-aconitate), glycolysis (phosphoenolpyruvate, 3- phosphoglycerate, lactate), production of ATP, ADP and AMP were measured in HTB-153 cells 3 and 24 hours after imatinib treatment in vitro. The significant decrease of malate (CAC), lactate (glycolysis) and ATP levels were found at both time points after imatinib treatment compared to baseline. The same observations were found in KCL-22, which was used for comparison as BCR-ABL1 positive cell line. Additionally, significant decrease of succinate and 2-hydroxyglutarate (CAC) was detected in KCL-22 after imatinib treatment. Next, HTB-153 was incubated with imatinib (1-8 µM) for 24 hours and carnitine (8 µM) was supplied for last 3 hours of incubation, i.e., after 21 hours of imatinib treatment start. No significant changes were found in any metabolites of CAC and glycolysis. Production of ATP, ADP and AMP was not changed as well.

Conclusions: Imatinib treatment of muscle (rhabdomyosarcoma) and CML cell lines caused a significant decrease of intracellular concentrations of carnitine. Significant decrease of ATP levels and of certain metabolites of CAC and glycolysis outlined that cells struggle from attenuated mitochondria energy production after imatinib treatment. This has not happened, if carnitine was supplied to the culture for final 3 hours of 24 hours incubation with imatinib. Observed data strongly support the hypothesis that decreased carnitine intake to the muscle cells due to competition with imatinib transport through OCTN2 attenuated mitochondria energy production. Interestingly, the clinical trial NCT03426722 (Chae H et al. 2019) showed that L-carnitine could effectively relieve imatinib-related muscle cramps and significantly increase QoL in patients with advanced gastrointestinal stromal tumor.

Supported by GACR18-18407S, MZCR00023736