Real-world efficacy and safety outcomes of imatinib treatment in patients with chronic myeloid leukemia: an Australian experience

Background: Tyrosine kinase inhibitors (TKI) have revolutionised the treatment of chronic myeloid leukaemia (CML), but patients still experience treatment-limiting toxicities or therapeutic failure. Aims: To investigate real-world use and outcomes of imatinib in patients with CML in Australia. Methods: A retrospective cohort study of patients with CML commencing imatinib (2001-2018) was conducted across two sites. Prescribing patterns, tolerability outcomes, survival and molecular response were evaluated. Results: 86 patients received 89 imatinib treatments. Dose modifications were frequently observed (12-month rate of 58%). At last follow-up, 62 patients (5-year rate of 55%) had permanently discontinued imatinib treatment, of which 44 switched to another TKI (5-year rate of 46%). Within 3 months of starting imatinib, 43% (95% CI, 32–53%) of patients experienced imatinib-related grade ≥3 adverse drug reactions (ADRs). Higher comorbidity score, lower body weight, higher imatinib starting dose, and Middle Eastern or North African ancestry were associated with a higher risk of grade ≥ 3 ADR occurrence on multivariable analysis (MVA). Estimated overall survival and event-free survival rates at 3 years were 97% (95% CI, 92–100%) and 81% (95% CI, 72–92%), respectively. Cumulative incidence of major molecular response (MMR) at 3 years was 63% (95% CI, 50–73%). On MVA, imatinib starting dose, ELTS score, BCR-ABL1 transcript type, pre-existing pulmonary disease, and potential drug-drug interactions were predictive of MMR. Conclusion: Imatinib induced deep molecular responses that translated to good survival outcomes in a real-world setting, but was associated with a higher incidence of ADRs, dose modifications and treatment discontinuations than in clinical trials.

Case Report: Long-Term Response to Radiotherapy Combined With Targeted Therapy in Histiocytic Sarcoma Harboring Mutations in MAPK and PI3K/AKT Pathways

BackgroundHistiocytic sarcoma (HS) is a rare hematopoietic malignancy with an aggressive clinical presentation associated with a poor overall survival. To date, surgical resection, radiation therapy, and chemotherapy were often utilized for HS, but curative effects are rather disappointing.Case PresentationA 19-year-old female was referred to our hospital with a pathologic diagnosis of HS in December 2017. The patient had a severe airway obstruction resulting from a large mass (6.0 cm × 4.4 cm) arising from the left parapharyngeal space. She did not respond to cyclophosphamide, doxorubicin, vincristine, prednisone, and etoposide (CHOEP) chemotherapy, then she was switched to radiotherapy and crizotinib according to next-generation sequencing (NGS) results (mutations in MET and MAP2K1). The patient got a partial response after radiotherapy and crizotinib, then she switched to imatinib combined with thalidomide treatment. The patient got a long-term complete response from the treatment and is alive 44 months after initial diagnosis without disease progression. Further KEGG pathway enrichment analysis of NGS results from patient’s tissue revealed that phosphatidylinositol 3′ kinase (PI3K)/AKT and mitogen-activated protein kinase (MAPK) pathways were activated in this HS patient. We further performed experiments in vitro in a canine histiocytic sarcoma cell line DH82, in order to explore the possible mechanism of imatinib plus thalidomide in HS. Results of cell counting kit-8 (CCK8) assays showed that the proliferation activity of DH82 was significantly inhibited by imatinib but not thalidomide. Combined thalidomide and imatinib treatment did not improve the inhibitory effects of imatinib to DH82. Results of Western blot confirmed the inhibitory effects of imatinib on DH82 by targeting activation of MAPK and PI3K/AKT pathways.ConclusionRadiotherapy combined with targeted therapy guided by NGS may be promising, and further perspective clinical trial is warranted for the localized HS.

Regulatory T Cell as a Biomarker of Treatment-Free Remission in Patients with Chronic Myeloid Leukemia

Treatment-free remission (TFR) has become a therapeutic goal in chronic myeloid leukemia (CML), and approximately half of the patients with chronic phase-CML (CML-CP) with deep molecular remission (DMR) by tyrosine-kinase inhibitors (TKIs) have achieved TFR. However, the mechanism of continuous TFR is still unclear, as there are “fluctuate” patients who have BCR–ABL-positive leukemia cells but do not observe obvious relapse. We focused on the immune response and conducted an immune analysis using clinical samples from the imatinib discontinuation study, JALSG-STIM213. The results showed that, in the group that maintained TFR for 3 years, changes in regulatory T (Treg) cells were observed early after stopping imatinib treatment. The effector Treg (eTreg) cells increased transiently at 1 month after stopping imatinib and then returned to baseline at 3 months after stopping imatinib treatment. There was no difference in the Treg phenotype, and CD8+ T cells in the TFR group were relatively activated. High concentrations of imatinib before stopping were negatively correlated with eTreg cells after stopping imatinib. These data suggest immunological involvement in the maintenance of the TFR, and that Treg cells after stopping imatinib might be a biomarker for TFR. Furthermore, high imatinib exposure may have a negative immunological impact on the continuous TFR.

Vitreous hemorrhage: A rare ophthalmic adverse effect due to imatinib treatment

Introduction Imatinib is generally well tolerated by patients. The most common ophthalmic side effects are eyelid edema and periorbital edema. Other side effects which occur at rates of <1% include blepharitis, blurred vision, conjunctival hemorrhage, conjunctivitis, retinal hemorrhage, etc. An uncommon case is here reported of a 51-year-old male with chronic myeloid leukemia who developed vitreous hemorrhage due to imatinib after 9 months of treatment. Case report A 51-year-old male with leukocytosis detected in the blood test examination was referred to the Hematology Department. The bone marrow biopsy result was compatible with chronic myeloid leukemia. Imatinib treatment (400 mg/day) was started. In the ninth month of imatinib treatment, the patient complained of a sudden decrease in vision. Vitreous hemorrhage was detected in the left eye and the patient underwent surgery. Vitreous hemorrhage recurred 1 month after the operation. On the fourth day after the discontinuation of imatinib treatment, the patient's ophthalmic complaints improved significantly. The Naranjo algorithm was applied and a score of 9 was detected. The vitreous hemorrhage of the patient was attributed to imatinib, and so the treatment of the patient was switched to bosutinib. Discussion Imatinib is an oral signal inhibitor that targets tyrosine kinase for BCR/ABL, platelet-derived growth factor, stem cell factor, and c-kit (CD117). The conjunctiva and sclera have a large amount of c-kit positive mast cells which are inhibited by imatinib. The inhibition of c-kit positive mast cells by imatinib may be responsible for further exposure of the conjunctival mucosa to injuries.

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 Disclosures No relevant conflicts of interest to declare.

Evaluating Real-World Effectiveness and Safety of Generic and Brand-Name Imatinib in Chronic Myeloid Leukemia

Introduction: Generic formulations of imatinib were approved and commercially available in the United States starting in 2016, introducing vast cost savings to the standard treatment of chronic myeloid leukemia (CML). While bioequivalence studies of generic formulations are required for Food and Drug Administration approval, the safety of generic drug supply chains have come into question. There is limited real-world data comparing the effectiveness and safety profiles of generic formulations to the original. This study aimed to evaluate the effectiveness and safety of generic imatinib compared to the branded product. Methods: This retrospective study included patients treated at UNC Medical Centers who were diagnosed with CML and treated with imatinib at any time during their course of treatment. Data was retrieved from the institution's electronic health record and collected over the first 6 months of imatinib treatment to include both safety and effectiveness outcomes. The primary endpoint was to compare generic versus branded product effectiveness, as defined by the European LeukemiaNet (ELN) guidelines (achieving BCR-ABL/ABL ratio of &lt;10% and &lt;1% at 3 and 6 months, respectively). The secondary endpoints included comparisons of generic vs branded product safety, measured via patient adverse drug events (ADEs), all-cause hospitalizations, and early treatment discontinuation. Patients were excluded from primary endpoint evaluation and only included for safety endpoint analysis if they were not treated with imatinib first-line and if duration of imatinib treatment was less than 6 months. Results: Fifty-one CML patients met criteria with no significant differences in age or gender between the generic (n = 23) and brand (n = 28) imatinib groups (Table 1). First-line therapy was composed of 83% of patients on generic imatinib and 29% of patients on brand imatinib. Of those receiving first-line imatinib therapy, there was no difference in molecular responses at 3 and 6 months between generic and brand imatinib (p = 0.71). Brand imatinib was associated with numerically lower CML-related emergency department visits and hospitalizations when compared to generic imatinib, although this difference was not statistically significant (p = 0.12). Rates of discontinuation were numerically lower for brand imatinib although overall time to discontinuation was shorter for generic imatinib (Table 1). Conclusions: This study demonstrates real-world treatment effectiveness and safety of generic and brand imatinib in clinical practice. Generic imatinib appears to be associated with higher rates of CML-related ED visits and hospitalizations although sample size was small and statistical significance was not reached. Further analyses of comparisons and continuation of data collection will provide a more robust assessment to compare the effectiveness and safety of generic and brand imatinib in the real-world setting. Figure 1 Figure 1. Disclosures Muluneh: Novartis: Other: Spouse works for Novartis.